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Quantum logic gate

In quantum computing and specifically the quantum circuit model of computation, a quantum logic gate (or simply quantum gate) is a basic quantum circuit operating on a small number of qubits. Quantum logic gates are the building blocks of quantum circuits, like classical logic gates are for conventional digital circuits.

Unlike many classical logic gates, quantum logic gates are reversible. It is possible to perform classical computing using only reversible gates. For example, the reversible Toffoli gate can implement all Boolean functions, often at the cost of having to use ancilla bits. The Toffoli gate has a direct quantum equivalent, showing that quantum circuits can perform all operations performed by classical circuits.

Quantum gates are unitary operators, and are described as unitary matrices relative to some orthonormal basis. Usually the computational basis is used, which unless comparing it with something, just means that for a d-level quantum system (such as a qubit, a quantum register, or qutrits and qudits) the orthonormal basis vectors are labeled $ or use binary notation.

History
The current notation for quantum gates was developed by many of the founders of quantum information science including Adriano Barenco, Charles Bennett, Richard Cleve, David P. DiVincenzo, Norman Margolus, Peter Shor, Tycho Sleator, John A. Smolin, and Harald Weinfurter, building on notation introduced by Richard Feynman in 1986.

Representation
Quantum logic gates are represented by unitary matrices. A gate that acts on $$n$$ qubits is represented by a $$2^n \times 2^n$$ unitary matrix, and the set of all such gates with the group operation of matrix multiplication is the unitary group U(2n). The quantum states that the gates act upon are unit vectors in $$2^n$$ complex dimensions, with the complex Euclidean norm (the 2-norm). The basis vectors (sometimes called eigenstates) are the possible outcomes if the state of the qubits is measured, and a quantum state is a linear combination of these outcomes. The most common quantum gates operate on vector spaces of one or two qubits, just like the common classical logic gates operate on one or two bits.

Even though the quantum logic gates belong to continuous symmetry groups, real hardware is inexact and thus limited in precision. The application of gates typically introduces errors, and the quantum states' fidelities decrease over time. If error correction is used, the usable gates are further restricted to a finite set. Later in this article, this is ignored as the focus is on the ideal quantum gates' properties.

Quantum states are typically represented by "kets", from a notation known as bra–ket.

The vector representation of a single qubit is
 * $$|a\rangle = v_0 | 0 \rangle + v_1 | 1 \rangle \rightarrow \begin{bmatrix} v_0 \\ v_1 \end{bmatrix} .$$

Here, $$v_0$$ and $$v_1$$ are the complex probability amplitudes of the qubit. These values determine the probability of measuring a 0 or a 1, when measuring the state of the qubit. See measurement below for details.

The value zero is represented by the ket $ and the value one is represented by the ket $

The tensor product (or Kronecker product) is used to combine quantum states. The combined state for a qubit register is the tensor product of the constituent qubits. The tensor product is denoted by the symbol $\otimes$.

The vector representation of two qubits is:
 * $$| \psi \rangle = v_{00} | 00 \rangle + v_{01} | 0 1 \rangle + v_{10} | 1 0 \rangle + v_{11} | 1 1 \rangle \rightarrow \begin{bmatrix} v_{00} \\ v_{01} \\ v_{10} \\ v_{11} \end{bmatrix}.$$

The action of the gate on a specific quantum state is found by multiplying the vector $$|\psi_1\rangle$$, which represents the state by the matrix $$U$$ representing the gate. The result is a new quantum state $

 * $$U|\psi_1\rangle = |\psi_2\rangle.$$

Notable examples
There exists an uncountably infinite number of gates. Some of them have been named by various authors,   and below follow some of those most often used in the literature.

Identity gate
The identity gate is the identity matrix, usually written as I, and is defined for a single qubit as

 * $$ I = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} ,$$

where I is basis independent and does not modify the quantum state. The identity gate is most useful when describing mathematically the result of various gate operations or when discussing multi-qubit circuits.

Pauli gates (X,Y,Z)
The Pauli gates $$(X,Y,Z)$$ are the three Pauli matrices $$(\sigma_x,\sigma_y,\sigma_z)$$ and act on a single qubit. The Pauli X, Y and Z equate, respectively, to a rotation around the x, y and z axes of the Bloch sphere by $$\pi$$ radians.

The Pauli-X gate is the quantum equivalent of the NOT gate for classical computers with respect to the standard basis $ which distinguishes the z axis on the Bloch sphere. It is sometimes called a bit-flip as it maps $$|0\rangle$$ to $$|1\rangle$$ and $$|1\rangle$$ to $$|0\rangle$$. Similarly, the Pauli-Y maps $$|0\rangle$$ to $$i|1\rangle$$ and $$|1\rangle$$ to $-i. Pauli Z leaves the basis state $$|0\rangle$$ unchanged and maps $$|1\rangle$$ to $- Due to this nature, Pauli Z is sometimes called phase-flip.

These matrices are usually represented as
 * $$ X = \sigma_x =\operatorname{NOT} = \begin{bmatrix} 0 & 1 \\ 1 & 0 \end{bmatrix} ,$$
 * $$ Y = \sigma_y = \begin{bmatrix} 0 & -i \\ i & 0 \end{bmatrix}, $$
 * $$ Z = \sigma_z = \begin{bmatrix} 1 & 0 \\ 0 & -1 \end{bmatrix}.$$

The Pauli matrices are involutory, meaning that the square of a Pauli matrix is the identity matrix.

 * $$I^2 = X^2 = Y^2 = Z^2 = -iXYZ = I$$

The Pauli matrices also anti-commute, for example $$ZX=iY=-XZ.$$

The matrix exponential of a Pauli matrix $$\sigma_j$$ is a rotation operator, often written as $$e^{-i\sigma_j\theta/2}.$$

Controlled gates
Controlled gates act on 2 or more qubits, where one or more qubits act as a control for some operation. For example, the controlled NOT gate (or CNOT or CX) acts on 2 qubits, and performs the NOT operation on the second qubit only when the first qubit is $ and otherwise leaves it unchanged. With respect to the basis $ $ $ $ it is represented by the Hermitian unitary matrix:

 * $$ \mbox{CNOT} = \begin{bmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \end{bmatrix} . $$

The CNOT (or controlled Pauli-X) gate can be described as the gate that maps the basis states $$|a,b\rangle \mapsto |a,a \oplus b\rangle$$, where $$\oplus$$ is XOR.

The CNOT can be expressed in the Pauli basis as:

 * $$ \mbox{CNOT} = e^{i\frac{\pi}{4}(I-Z_1)(I-X_2)}=e^{-i\frac{\pi}{4}(I-Z_1)(I-X_2)}. $$

Being a Hermitian unitary operator, CNOT has the property that $$ e^{i\theta U}=(\cos \theta)I+(i\sin \theta) U$$ and $$ U =e^{i\frac{\pi}{2}(I-U)}=e^{-i\frac{\pi}{2}(I-U)}$$, and is involutory.

More generally if U is a gate that operates on a single qubit with matrix representation
 * $$ U = \begin{bmatrix} u_{00} & u_{01} \\ u_{10} & u_{11} \end{bmatrix}, $$

then the controlled-U gate is a gate that operates on two qubits in such a way that the first qubit serves as a control. It maps the basis states as follows.
 * $$ | 0 0 \rangle \mapsto | 0 0 \rangle $$
 * $$ | 0 1 \rangle \mapsto | 0 1 \rangle $$
 * $$ | 1 0 \rangle \mapsto | 1 \rangle \otimes U |0 \rangle = | 1 \rangle \otimes (u_{00} |0 \rangle + u_{10} |1 \rangle) $$
 * $$ | 1 1 \rangle \mapsto | 1 \rangle \otimes U |1 \rangle = | 1 \rangle \otimes (u_{01} |0 \rangle + u_{11} |1 \rangle) $$

The matrix representing the controlled U is

 * $$ \mbox{C}U = \begin{bmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & u_{00} & u_{01} \\ 0 & 0 & u_{10} & u_{11} \end{bmatrix}.$$

When U is one of the Pauli operators, X,Y, Z, the respective terms "controlled-X", "controlled-Y", or "controlled-Z" are sometimes used. Sometimes this is shortened to just CX, CY and CZ.

In general, any single qubit unitary gate can be expressed as $$ U = e^{iH} $$, where H is a Hermitian matrix, and then the controlled U is $$ CU =  e^{i\frac{1}{2}(I-Z_1)H_2}.$$

Control can be extended to gates with arbitrary number of qubits and functions in programming languages. Functions can be conditioned on superposition states.

Classical control
Gates can also be controlled by classical logic. A quantum computer is controlled by a classical computer, and behaves like a coprocessor that receives instructions from the classical computer about what gates to execute on which qubits. Classical control is simply the inclusion, or omission, of gates in the instruction sequence for the quantum computer.

Phase shift gates
The phase shift is a family of single-qubit gates that map the basis states $$|0\rangle \mapsto |0\rangle$$ and $$|1\rangle \mapsto e^{i\varphi}|1\rangle$$. The probability of measuring a $$|0\rangle$$ or $$|1\rangle$$ is unchanged after applying this gate, however it modifies the phase of the quantum state. This is equivalent to tracing a horizontal circle (a line of constant latitude), or a rotation about the z-axis on the Bloch sphere by $$\varphi$$ radians. The phase shift gate is represented by the matrix:

 * $$P(\varphi) = \begin{bmatrix} 1 & 0 \\ 0 & e^{i \varphi} \end{bmatrix}$$

where $$\varphi$$ is the phase shift with the period $x, y, z$. Some common examples are the T gate where $\varphi = \frac{\pi}{4}$ (historically known as the $$\pi /8$$ gate), the phase gate (also known as the S gate, written as S, though S is sometimes used for SWAP gates) where $\varphi= \frac{\pi}{2}$  and the Pauli-Z gate where $$\varphi = \pi.$$

The phase shift gates are related to each other as follows:

 * $$ Z = \begin{bmatrix} 1 & 0 \\ 0 & e^{i \pi} \end{bmatrix} = \begin{bmatrix} 1 & 0 \\ 0 & -1 \end{bmatrix} = P\left(\pi\right)$$

 * $$ S = \begin{bmatrix} 1 & 0 \\ 0 & e^{i \frac{\pi}{2}} \end{bmatrix} = \begin{bmatrix} 1 & 0 \\ 0 & i \end{bmatrix} = P\left(\frac{\pi}{2}\right)=\sqrt{Z}$$

 * $$ T = \begin{bmatrix} 1 & 0 \\ 0 & e^{i \frac{\pi}{4}} \end{bmatrix} =P\left(\frac{\pi}{4}\right) = \sqrt{S} = \sqrt[4]{Z}$$

Note that the phase gate $$P(\varphi)$$ is not Hermitian (except for all $$\varphi = n\pi, n \in \mathbb{Z}$$). These gates are different from their Hermitian conjugates: $$P^\dagger(\varphi)=P(-\varphi)$$. The two adjoint (or conjugate transpose) gates $$S^\dagger$$ and $$T^\dagger$$ are sometimes included in instruction sets.

Hadamard gate
The Hadamard or Walsh-Hadamard gate, named after Jacques Hadamard and Joseph L. Walsh, acts on a single qubit. It maps the basis states $|0\rangle \mapsto \frac{|0\rangle + |1\rangle}{\sqrt{2}}$ and $|1\rangle \mapsto \frac{|0\rangle - |1\rangle}{\sqrt{2}}$  (it creates an equal superposition state if given a computational basis state). The two states $$(|0\rangle + |1\rangle)/\sqrt{2}$$ and $$(|0\rangle - |1\rangle)/\sqrt{2}$$ are sometimes written $$|+\rangle$$ and $$|-\rangle$$ respectively. The Hadamard gate performs a rotation of $$\pi$$ about the axis $$(\hat{x}+\hat{z})/\sqrt{2}$$ at the Bloch sphere, and is therefore involutory. It is represented by the Hadamard matrix:

 * $$ H = \frac{1}{\sqrt{2}} \begin{bmatrix} 1 & 1 \\ 1 & -1 \end{bmatrix} .$$

If the Hermitian (so $$H^{\dagger}=H^{-1}=H$$) Hadamard gate is used to perform a change of basis, it flips $$\hat{x}$$ and $$\hat{z}$$. For example, $$HZH=X$$ and $$H\sqrt{X}\;H=\sqrt{Z}=S.$$

Swap gate
The swap gate swaps two qubits. With respect to the basis $$|00\rangle$$, $$|01\rangle$$, $$|10\rangle$$, $$|11\rangle$$, it is represented by the matrix

 * $$ \mbox{SWAP} = \begin{bmatrix} 1&0&0&0\\0&0&1&0\\0&1&0&0\\0&0&0&1\end{bmatrix} . $$

The swap gate can be decomposed into summation form:

 * $$\mbox{SWAP}=\frac{I\otimes I +X\otimes X+Y\otimes Y+Z\otimes Z}{2}$$

Toffoli (CCNOT) gate
The Toffoli gate, named after Tommaso Toffoli and also called the CCNOT gate or Deutsch gate $$D(\pi/2)$$, is a 3-bit gate that is universal for classical computation but not for quantum computation. The quantum Toffoli gate is the same gate, defined for 3 qubits. If we limit ourselves to only accepting input qubits that are $$|0\rangle$$ and $ then if the first two bits are in the state $$|1\rangle$$ it applies a Pauli-X (or NOT) on the third bit, else it does nothing. It is an example of a CC-U (controlled-controlled Unitary) gate. Since it is the quantum analog of a classical gate, it is completely specified by its truth table. The Toffoli gate is universal when combined with the single qubit Hadamard gate.

The Toffoli gate is related to the classical AND ($$\land$$) and XOR ($$\oplus$$) operations as it performs the mapping $$|a, b, c\rangle \mapsto |a, b, c\oplus (a \land b)\rangle$$ on states in the computational basis.

The Toffoli gate can be expressed using Pauli matrices as

 * $$ \mbox{Toff} = e^{i\frac{\pi}{8}(I-Z_1)(I-Z_2)(I-X_3)}= e^{-i\frac{\pi}{8}(I-Z_1)(I-Z_2)(I-X_3)}. $$

Universal quantum gates
A set of universal quantum gates is any set of gates to which any operation possible on a quantum computer can be reduced, that is, any other unitary operation can be expressed as a finite sequence of gates from the set. Technically, this is impossible with anything less than an uncountable set of gates since the number of possible quantum gates is uncountable, whereas the number of finite sequences from a finite set is countable. To solve this problem, we only require that any quantum operation can be approximated by a sequence of gates from this finite set. Moreover, for unitaries on a constant number of qubits, the Solovay–Kitaev theorem guarantees that this can be done efficiently. Checking if a set of quantum gates is universal can be done using group theory methods and/or relation to (approximate) unitary t-designs

Some universal quantum gate sets include:

 * The rotation operators $2π$, $R_{x}(θ)$, $R_{y}(θ)$, the phase shift gate $R_{z}(θ)$ and CNOT are commonly used to form a universal quantum gate set.
 * The Clifford set {CNOT, H, S} + T gate. The Clifford set alone is not a universal quantum gate set, as it can be efficiently simulated classically according to the Gottesman–Knill theorem.
 * The Toffoli gate + Hadamard gate. The Toffoli gate alone forms a set of universal gates for reversible Boolean algebraic logic circuits, which encompasses all classical computation.

Deutsch gate
A single-gate set of universal quantum gates can also be formulated using the parametrized three-qubit Deutsch gate $$D(\theta)$$, named after physicist David Deutsch. It is a general case of CC-U, or controlled-controlled-unitary gate, and is defined as

 * $$|a, b, c\rangle \mapsto \begin{cases}

i \cos(\theta) |a, b, c\rangle + \sin(\theta) |a, b, 1 - c\rangle & \text{for}\ a = b = 1, \\ |a, b, c\rangle & \text{otherwise}. \end{cases}$$

Unfortunately, a working Deutsch gate has remained out of reach, due to lack of a protocol. There are some proposals to realize a Deutsch gate with dipole–dipole interaction in neutral atoms.

A universal logic gate for reversible classical computing, the Toffoli gate, is reducible to the Deutsch gate $$D(\pi/2)$$, thus showing that all reversible classical logic operations can be performed on a universal quantum computer.

There also exist single two-qubit gates sufficient for universality. In 1996, Adriano Barenco showed that the Deutsch gate can be decomposed using only a single two-qubit gate (Barenco gate), but it is hard to realize experimentally. This feature is exclusive to quantum circuits, as there is no classical two-bit gate that is both reversible and universal. Universal two-qubit gates could be implemented to improve classical reversible circuits in fast low-power microprocessors.

Serially wired gates
Assume that we have two gates A and B that both act on $$n$$ qubits. When B is put after A in a series circuit, then the effect of the two gates can be described as a single gate C.

 * $$C = B \cdot A$$

where $$\cdot$$ is matrix multiplication. The resulting gate C will have the same dimensions as A and B. The order in which the gates would appear in a circuit diagram is reversed when multiplying them together.

For example, putting the Pauli X gate after the Pauli Y gate, both of which act on a single qubit, can be described as a single combined gate C:

 * $$C = X \cdot Y = \begin{bmatrix} 0 & 1 \\ 1 & 0 \end{bmatrix} \cdot \begin{bmatrix} 0 & -i \\ i & 0 \end{bmatrix} = \begin{bmatrix} i & 0 \\ 0 & -i \end{bmatrix} = iZ$$

The product symbol ($$\cdot$$) is often omitted.

Exponents of quantum gates
All real exponents of unitary matrices are also unitary matrices, and all quantum gates are unitary matrices.

Positive integer exponents are equivalent to sequences of serially wired gates (e.g. $X^3 = X \cdot X \cdot X$), and the real exponents is a generalization of the series circuit. For example, $$X^\pi$$ and $$\sqrt{X}=X^{1/2}$$ are both valid quantum gates.

$$U^0=I$$ for any unitary matrix $$U$$. The identity matrix ($$I$$) behaves like a NOP and can be represented as bare wire in quantum circuits, or not shown at all.

All gates are unitary matrices, so that $$U^\dagger U = UU^\dagger = I$$ and $U^\dagger = U^{-1}$, where $$\dagger$$ is the conjugate transpose. This means that negative exponents of gates are unitary inverses of their positively exponentiated counterparts: $U^{-n} = (U^n)^{\dagger}$. For example, some negative exponents of the phase shift gates are $$T^{-1}=T^{\dagger}$$ and $T^{-2}=(T^2)^{\dagger}=S^{\dagger}$.

Note that for a Hermitian matrix $$H^\dagger=H,$$ and because of unitarity, $$HH^\dagger=I,$$ so $$H^2 = I$$ for all Hermitian gates. They are involutory. Examples of Hermitian gates are the Pauli gates, Hadamard, CNOT, SWAP and Toffoli. Each Hermitian unitary matrix $$H$$ has the property that $$e^{i\theta H}=(\cos \theta)I+(i\sin \theta) H$$ where $$H=e^{i\frac{\pi}{2}(I-H)}=e^{-i\frac{\pi}{2}(I-H)}.$$

Parallel gates
The tensor product (or Kronecker product) of two quantum gates is the gate that is equal to the two gates in parallel.

If we, as in the picture, combine the Pauli-Y gate with the Pauli-X gate in parallel, then this can be written as:

 * $$C = Y \otimes X = \begin{bmatrix} 0 & -i \\ i & 0 \end{bmatrix} \otimes \begin{bmatrix} 0 & 1 \\ 1 & 0 \end{bmatrix} = \begin{bmatrix} 0 \begin{bmatrix} 0 & 1 \\ 1 & 0 \end{bmatrix} & -i \begin{bmatrix} 0 & 1 \\ 1 & 0 \end{bmatrix} \\ i \begin{bmatrix} 0 & 1 \\ 1 & 0 \end{bmatrix} & 0 \begin{bmatrix} 0 & 1 \\ 1 & 0 \end{bmatrix}\end{bmatrix} = \begin{bmatrix} 0 & 0 & 0 & -i \\ 0 & 0 & -i & 0 \\ 0 & i & 0 & 0 \\ i & 0 & 0 & 0 \end{bmatrix}$$

Both the Pauli-X and the Pauli-Y gate act on a single qubit. The resulting gate $$C$$ act on two qubits.

Sometimes the tensor product symbol is omitted, and indexes are used for the operators instead.

Hadamard transform
The gate $$H_2 = H \otimes H$$ is the Hadamard gate ($H$) applied in parallel on 2 qubits. It can be written as:

 * $$H_2 = H \otimes H = \frac{1}{\sqrt{2}} \begin{bmatrix} 1 & 1 \\ 1 & -1 \end{bmatrix} \otimes \frac{1}{\sqrt{2}} \begin{bmatrix} 1 & 1 \\ 1 & -1 \end{bmatrix} = \frac{1}{2} \begin{bmatrix} 1 & 1 & 1 & 1 \\ 1 & -1 & 1 & -1 \\ 1 & 1 & -1 & -1 \\ 1 & -1 & -1 & 1 \end{bmatrix}$$

This "two-qubit parallel Hadamard gate" will, when applied to, for example, the two-qubit zero-vector ($ create a quantum state that has equal probability of being observed in any of its four possible outcomes; $ $ $ and $ We can write this operation as:

 * $$H_2 |00\rangle = \frac{1}{2} \begin{bmatrix} 1 & 1 & 1 & 1 \\ 1 & -1 & 1 & -1 \\ 1 & 1 & -1 & -1 \\ 1 & -1 & -1 & 1 \end{bmatrix} \begin{bmatrix} 1 \\ 0 \\ 0 \\ 0 \end{bmatrix} = \frac{1}{2} \begin{bmatrix} 1 \\ 1 \\ 1 \\ 1 \end{bmatrix} = \frac{1}{2} |00\rangle + \frac{1}{2} |01\rangle +\frac{1}{2} |10\rangle +\frac{1}{2} |11\rangle = \frac{|00\rangle + |01\rangle + |10\rangle + |11\rangle}{2}$$

Here the amplitude for each measurable state is $1/2$. The probability to observe any state is the square of the absolute value of the measurable states amplitude, which in the above example means that there is one in four that we observe any one of the individual four cases. See measurement for details.

$$H_2$$ performs the Hadamard transform on two qubits. Similarly the gate $$\underbrace{ H \otimes H \otimes \dots \otimes H }_{n\text{ times}} = \bigotimes_1^n H = H^{\otimes n} = H_n$$ performs a Hadamard transform on a register of $$n$$ qubits.

When applied to a register of $$n$$ qubits all initialized to $ the Hadamard transform puts the quantum register into a superposition with equal probability of being measured in any of its $$2^n$$ possible states:

 * $$\bigotimes_0^{n-1}(H|0\rangle) = \frac{1}{\sqrt{2^n}} \begin{bmatrix} 1 \\ 1 \\ \vdots \\ 1 \end{bmatrix} = \frac{1}{\sqrt{2^n}} \Big( |0\rangle + |1\rangle + \dots + |2^n-1\rangle \Big)= \frac{1}{\sqrt{2^n}}\sum_{i=0}^{2^{n}-1}|i\rangle$$

This state is a uniform superposition and it is generated as the first step in some search algorithms, for example in amplitude amplification and phase estimation.

Measuring this state results in a random number between $$|0\rangle$$ and $ How random the number is depends on the fidelity of the logic gates. If not measured, it is a quantum state with equal probability amplitude $$\frac{1}{\sqrt{2^n}}$$ for each of its possible states.

The Hadamard transform acts on a register $$|\psi\rangle$$ with $$n$$ qubits such that $|\psi\rangle = \bigotimes_{i=0}^{n-1} |\psi_i\rangle$ as follows:
 * $$\bigotimes_0^{n-1}H|\psi\rangle = \bigotimes_{i=0}^{n-1}\frac{|0\rangle + (-1)^{\psi_i}|1\rangle}{\sqrt{2}} = \frac{1}{\sqrt{2^n}}\bigotimes_{i=0}^{n-1}\Big(|0\rangle + (-1)^{\psi_i}|1\rangle\Big) = H|\psi_0\rangle \otimes H|\psi_1\rangle \otimes \cdots \otimes H|\psi_{n-1}\rangle$$

Application on entangled states
If two or more qubits are viewed as a single quantum state, this combined state is equal to the tensor product of the constituent qubits. Any state that can be written as a tensor product from the constituent subsystems are called separable states. On the other hand, an entangled state is any state that cannot be tensor-factorized, or in other words: An entangled state can not be written as a tensor product of its constituent qubits states. Special care must be taken when applying gates to constituent qubits that make up entangled states.

If we have a set of N qubits that are entangled and wish to apply a quantum gate on M < N qubits in the set, we will have to extend the gate to take N qubits. This application can be done by combining the gate with an identity matrix such that their tensor product becomes a gate that act on N qubits. The identity matrix ($I$) is a representation of the gate that maps every state to itself (i.e., does nothing at all). In a circuit diagram the identity gate or matrix will often appear as just a bare wire.

For example, the Hadamard gate ($H$) acts on a single qubit, but if we feed it the first of the two qubits that constitute the entangled Bell state $\frac{ we cannot write that operation easily. We need to extend the Hadamard gate $$H$$ with the identity gate $$I$$ so that we can act on quantum states that span two qubits:

 * $$K = H \otimes I = \frac{1}{\sqrt{2}} \begin{bmatrix} 1 & 1 \\ 1 & -1 \end{bmatrix} \otimes \begin{bmatrix} 1 & 0 \\ 0 & 1\end{bmatrix} = \frac{1}{\sqrt{2}} \begin{bmatrix} 1 & 0 & 1 & 0 \\ 0 & 1 & 0 & 1 \\ 1 & 0 & -1 & 0 \\ 0 & 1 & 0 & -1\end{bmatrix}$$

The gate $$K$$ can now be applied to any two-qubit state, entangled or otherwise. The gate $$K$$ will leave the second qubit untouched and apply the Hadamard transform to the first qubit. If applied to the Bell state in our example, we may write that as:

 * $$K \frac{|00\rangle + |11\rangle}{\sqrt{2}} = \frac{1}{\sqrt{2}} \begin{bmatrix} 1 & 0 & 1 & 0 \\ 0 & 1 & 0 & 1 \\ 1 & 0 & -1 & 0 \\ 0 & 1 & 0 & -1\end{bmatrix} \frac{1}{\sqrt{2}} \begin{bmatrix}1 \\ 0 \\ 0 \\ 1\end{bmatrix} = \frac{1}{2} \begin{bmatrix} 1 \\ 1 \\ 1 \\ -1 \end{bmatrix} = \frac{|00\rangle + |01\rangle + |10\rangle - |11\rangle}{2}$$

Computational complexity and the tensor product
The time complexity for multiplying two $$n \times n$$-matrices is at least $\Omega(n^2 \log n)$, if using a classical machine. Because the size of a gate that operates on $$q$$ qubits is $$2^q \times 2^q$$ it means that the time for simulating a step in a quantum circuit (by means of multiplying the gates) that operates on generic entangled states is $\Omega({2^q}^2 \log({2^q}))$. For this reason it is believed to be intractable to simulate large entangled quantum systems using classical computers. Subsets of the gates, such as the Clifford gates, or the trivial case of circuits that only implement classical Boolean functions (e.g. combinations of X, CNOT, Toffoli), can however be efficiently simulated on classical computers.

The state vector of a quantum register with $$n$$ qubits is $$2^n$$ complex entries. Storing the probability amplitudes as a list of floating point values is not tractable for large $$n$$.

Unitary inversion of gates
Because all quantum logical gates are reversible, any composition of multiple gates is also reversible. All products and tensor products (i.e. series and parallel combinations) of unitary matrices are also unitary matrices. This means that it is possible to construct an inverse of all algorithms and functions, as long as they contain only gates.

Initialization, measurement, I/O and spontaneous decoherence are side effects in quantum computers. Gates however are purely functional and bijective.

If $$U$$ is a unitary matrix, then $$U^\dagger U = UU^\dagger = I$$ and $U^\dagger = U^{-1}$. The dagger ($$\dagger$$) denotes the conjugate transpose. It is also called the Hermitian adjoint.

If a function $$F$$ is a product of $$m$$ gates, $F = A_1 \cdot A_2 \cdot \dots \cdot A_m$, the unitary inverse of the function $$F^\dagger$$ can be constructed:

Because $$(UV)^\dagger = V^\dagger U^\dagger$$ we have, after repeated application on itself

 * $$F^\dagger = \left(\prod_{i=1}^{m} A_i\right)^\dagger = \prod_{i=m}^{1} A^\dagger_{i} = A_m^\dagger \cdot \dots \cdot A_2^\dagger \cdot A_1^\dagger$$

Similarly if the function $$G$$ consists of two gates $$A$$ and $$B$$ in parallel, then $$G=A\otimes B$$ and $G^\dagger = (A \otimes B)^\dagger = A^\dagger \otimes B^\dagger$.

Gates that are their own unitary inverses are called Hermitian or self-adjoint operators. Some elementary gates such as the Hadamard (H) and the Pauli gates (I, X, Y, Z) are Hermitian operators, while others like the phase shift (S, T, P, CPhase) gates generally are not.

For example, an algorithm for addition can be used for subtraction, if it is being "run in reverse", as its unitary inverse. The inverse quantum Fourier transform is the unitary inverse. Unitary inverses can also be used for uncomputation. Programming languages for quantum computers, such as Microsoft's Q#, Bernhard Ömer's QCL, and IBM's Qiskit, contain function inversion as programming concepts.

Measurement
Measurement (sometimes called observation) is irreversible and therefore not a quantum gate, because it assigns the observed quantum state to a single value. Measurement takes a quantum state and projects it to one of the basis vectors, with a likelihood equal to the square of the vector's length (in the 2-norm) along that basis vector. This is known as the Born rule and appears as a stochastic non-reversible operation as it probabilistically sets the quantum state equal to the basis vector that represents the measured state. At the instant of measurement, the state is said to "collapse" to the definite single value that was measured. Why and how, or even if the quantum state collapses at measurement, is called the measurement problem.

The probability of measuring a value with probability amplitude $$\phi$$ is $1 \ge where $$|\cdot|$$ is the modulus.

Measuring a single qubit, whose quantum state is represented by the vector $a will result in $$|0\rangle$$ with probability $ and in $

For example, measuring a qubit with the quantum state $$\frac{|0\rangle -i|1\rangle }{\sqrt{2}} = \frac{1}{\sqrt{2}}\begin{bmatrix} 1 \\ -i \end{bmatrix}$$ will yield with equal probability either $$|0\rangle$$ or $

A quantum state $$|\Psi\rangle$$ that spans $n$ qubits can be written as a vector in $$2^n$$ complex dimensions: $ This is because the tensor product of $n$ qubits is a vector in $$2^n$$ dimensions. This way, a register of $n$ qubits can be measured to $$2^n$$ distinct states, similar to how a register of $n$ classical bits can hold $$2^n$$ distinct states. Unlike with the bits of classical computers, quantum states can have non-zero probability amplitudes in multiple measurable values simultaneously. This is called superposition.

The sum of all probabilities for all outcomes must always be equal to $1$. Another way to say this is that the Pythagorean theorem generalized to $$\mathbb C^{2^n}$$ has that all quantum states $$|\Psi\rangle$$ with $n$ qubits must satisfy $1 = \sum_{x=0}^{2^n-1}|a_x|^2,$ where $$a_x$$ is the probability amplitude for measurable state $ A geometric interpretation of this is that the possible value-space of a quantum state $$|\Psi\rangle$$ with $n$ qubits is the surface of the unit sphere in $$\mathbb C^{2^n}$$ and that the unitary transforms (i.e. quantum logic gates) applied to it are rotations on the sphere. The rotations that the gates perform form the symmetry group U(2n). Measurement is then a probabilistic projection of the points at the surface of this complex sphere onto the basis vectors that span the space (and labels the outcomes).

In many cases the space is represented as a Hilbert space $$\mathcal{H}$$ rather than some specific $2^n$-dimensional complex space. The number of dimensions (defined by the basis vectors, and thus also the possible outcomes from measurement) is then often implied by the operands, for example as the required state space for solving a problem. In Grover's algorithm, Grover named this generic basis vector set "the database".

The selection of basis vectors against which to measure a quantum state will influence the outcome of the measurement. See change of basis and Von Neumann entropy for details. In this article, we always use the computational basis, which means that we have labeled the $$2^n$$ basis vectors of an $n$-qubit register $ or use the binary representation $

In quantum mechanics, the basis vectors constitute an orthonormal basis.

An example of usage of an alternative measurement basis is in the BB84 cipher.

The effect of measurement on entangled states

If two quantum states (i.e. qubits, or registers) are entangled (meaning that their combined state cannot be expressed as a tensor product), measurement of one register affects or reveals the state of the other register by partially or entirely collapsing its state too. This effect can be used for computation, and is used in many algorithms.

The Hadamard-CNOT combination acts on the zero-state as follows:
 * $$\operatorname{CNOT}(H \otimes I)|00\rangle

= \left(   \begin{bmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \end{bmatrix}    \left( \frac{1}{\sqrt{2}} \begin{bmatrix} 1 & 1 \\ 1 & -1 \end{bmatrix} \otimes \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} \right) \right) \begin{bmatrix} 1 \\ 0 \\ 0 \\ 0 \end{bmatrix} = \frac{1}{\sqrt{2}} \begin{bmatrix} 1 \\ 0 \\ 0 \\ 1 \end{bmatrix} = \frac{|00\rangle + |11\rangle}{\sqrt{2}}$$

This resulting state is the Bell state $\frac{ It cannot be described as a tensor product of two qubits. There is no solution for

 * $$\begin{bmatrix} x \\ y \end{bmatrix} \otimes \begin{bmatrix} w \\ z \end{bmatrix} = \begin{bmatrix} xw \\ xz \\ yw \\ yz \end{bmatrix} = \frac{1}{\sqrt{2}}\begin{bmatrix} 1 \\ 0 \\ 0 \\ 1 \end{bmatrix},$$

because for example $w$ needs to be both non-zero and zero in the case of $xw$ and $yw$.

The quantum state spans the two qubits. This is called entanglement. Measuring one of the two qubits that make up this Bell state will result in that the other qubit logically must have the same value, both must be the same: Either it will be found in the state $ or in the state $ If we measure one of the qubits to be for example $ then the other qubit must also be $ because their combined state became $ Measurement of one of the qubits collapses the entire quantum state, that span the two qubits.

The GHZ state is a similar entangled quantum state that spans three or more qubits.

This type of value-assignment occurs instantaneously over any distance and this has as of 2018 been experimentally verified by QUESS for distances of up to 1200 kilometers. That the phenomena appears to happen instantaneously as opposed to the time it would take to traverse the distance separating the qubits at the speed of light is called the EPR paradox, and it is an open question in physics how to resolve this. Originally it was solved by giving up the assumption of local realism, but other interpretations have also emerged. For more information see the Bell test experiments. The no-communication theorem proves that this phenomenon cannot be used for faster-than-light communication of classical information.

Measurement on registers with pairwise entangled qubits
Take a register A with $n$ qubits all initialized to $ and feed it through a parallel Hadamard gate $H^{\otimes n}$. Register A will then enter the state $\frac{1}{\sqrt{2^n}} \sum_{k=0}^{2^{n}-1} |k\rangle$ that have equal probability of when measured to be in any of its $$2^n$$ possible states; $$|0\rangle$$ to $ Take a second register B, also with $n$ qubits initialized to $$|0\rangle$$ and pairwise CNOT its qubits with the qubits in register A, such that for each $n$ the qubits $$A_{p}$$ and $$B_{p}$$ forms the state $

If we now measure the qubits in register A, then register B will be found to contain the same value as A. If we however instead apply a quantum logic gate $p$ on A and then measure, then $ where $$F^\dagger$$ is the unitary inverse of $F$.

Because of how unitary inverses of gates act, $F^\dagger For example, say $$F(x)=x+3 \pmod{2^n}$$, then $

The equality will hold no matter in which order measurement is performed (on the registers A or B), assuming that $F$ has run to completion. Measurement can even be randomly and concurrently interleaved qubit by qubit, since the measurements assignment of one qubit will limit the possible value-space from the other entangled qubits.

Even though the equalities holds, the probabilities for measuring the possible outcomes may change as a result of applying $F$, as may be the intent in a quantum search algorithm.

This effect of value-sharing via entanglement is used in Shor's algorithm, phase estimation and in quantum counting. Using the Fourier transform to amplify the probability amplitudes of the solution states for some problem is a generic method known as "Fourier fishing".

Logic function synthesis
Functions and routines that only use gates can themselves be described as matrices, just like the smaller gates. The matrix that represents a quantum function acting on $$q$$ qubits has size $2^q \times 2^q$. For example, a function that acts on a "qubyte" (a register of 8 qubits) would be represented by a matrix with $$2^8 \times 2^8 = 256 \times 256$$ elements.

Unitary transformations that are not in the set of gates natively available at the quantum computer (the primitive gates) can be synthesised, or approximated, by combining the available primitive gates in a circuit. One way to do this is to factor the matrix that encodes the unitary transformation into a product of tensor products (i.e. series and parallel circuits) of the available primitive gates. The group U(2q) is the symmetry group for the gates that act on $$q$$ qubits. Factorization is then the problem of finding a path in U(2q) from the generating set of primitive gates. The Solovay–Kitaev theorem shows that given a sufficient set of primitive gates, there exist an efficient approximate for any gate. For the general case with a large number of qubits this direct approach to circuit synthesis is intractable. This puts a limit on how large functions can be brute-force factorized into primitive quantum gates. Typically quantum programs are instead built using relatively small and simple quantum functions, similar to normal classical programming.

Because of the gates unitary nature, all functions must be reversible and always be bijective mappings of input to output. There must always exist a function $$F^{-1}$$ such that $F^{-1}(F( Functions that are not invertible can be made invertible by adding ancilla qubits to the input or the output, or both. After the function has run to completion, the ancilla qubits can then either be uncomputed or left untouched. Measuring or otherwise collapsing the quantum state of an ancilla qubit (e.g. by re-initializing the value of it, or by its spontaneous decoherence) that have not been uncomputed may result in errors, as their state may be entangled with the qubits that are still being used in computations.

Logically irreversible operations, for example addition modulo $$2^n$$ of two $$n$$-qubit registers a and b, $F(a, b) = a+b \pmod{2^n}$, can be made logically reversible by adding information to the output, so that the input can be computed from the output (i.e. there exists a function $F^{-1}$). In our example, this can be done by passing on one of the input registers to the output: $F( The output can then be used to compute the input (i.e. given the output $$a+b$$ and $a$, we can easily find the input; $$a$$ is given and $(a+b) - a = b$) and the function is made bijective.

All Boolean algebraic expressions can be encoded as unitary transforms (quantum logic gates), for example by using combinations of the Pauli-X, CNOT and Toffoli gates. These gates are functionally complete in the Boolean logic domain.

There are many unitary transforms available in the libraries of Q#, QCL, Qiskit, and other quantum programming languages. It also appears in the literature.

For example, $$\mathrm{inc}(|x\rangle) = |x + 1 \pmod{2^{x_\text{length}}}\rangle$$, where $$x_\text{length}$$ is the number of qubits that constitutes the register $x$, is implemented as the following in QCL:

In QCL, decrement is done by "undoing" increment. The prefix  is used to instead run the unitary inverse of the function. is the inverse of  and instead performs the operation $\mathrm{inc}^\dagger The   keyword means that the function can be conditional.

In the model of computation used in this article (the quantum circuit model), a classic computer generates the gate composition for the quantum computer, and the quantum computer behaves as a coprocessor that receives instructions from the classical computer about which primitive gates to apply to which qubits. Measurement of quantum registers results in binary values that the classical computer can use in its computations. Quantum algorithms often contain both a classical and a quantum part. Unmeasured I/O (sending qubits to remote computers without collapsing their quantum states) can be used to create networks of quantum computers. Entanglement swapping can then be used to realize distributed algorithms with quantum computers that are not directly connected. Examples of distributed algorithms that only require the use of a handful of quantum logic gates are superdense coding, the quantum Byzantine agreement and the BB84 cipherkey exchange protocol.

title: Quantum logic gate


text:
User talk:Jaredway

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Wild Willy Barrett

Roger John Barrett (born 30 May 1950), known professionally as Wild Willy Barrett, is an English experimental musician and multi-instrumentalist, best known for his collaborations with John Otway. His musical style has included folk, blues, psychedelia, pop and punk rock and his live performances are punctuated with his dry humour and onstage wit. He is known for virtuoso fiddle playing, ability with a great number of stringed instruments, and playing slide guitar with a whole raw egg (known as egg-necking). During recent Otway/Barrett performances, he has also introduced the 'wah wah wheelie bin'.

Barrett is also a skilled wood worker and carver and has produced highly unusual furniture over many years.

Career
Barrett comes from Aylesbury. He started playing the ukulele at the age of 4 and soon moved on to other instruments. By the age of 15 he was gigging regularly. He worked with and recorded alongside and in collaboration with his emerging contemporaries. His first commercially available recordings can be found on Guitar Workshop, issued in 1973 by Transatlantic Records. He is also featured on The Contemporary Folk Guitar album with Bert Jansch, John Renbourn, Gordon Giltrap & Ralph McTell. He has worked with many well known artists and has toured with Squeeze, Madness and Steeleye Span and played fiddle, guitar and mandolin for George Hamilton IV. He also played pedal steel guitar on the influential Keith Hudson reggae album entitled Rasta Communication, along with Sly and Robbie.

During the early 1980s, he ran his own record labels; "Black Eye" and "Red Eye", which released music by artists Barrett knew and played with. Amongst them was Eddie Stanton whose songs have been covered extensively by Barrett both live and on record. Before it folded, Black Eye had a number of albums to be released most notably Please Don't Throw Me to the Christians by Stanton – most of the songs from Organic Bondage were derived from those on the album – and "Man of Many Fingers" which would have been Barrett's 3rd solo album.

In the mid-1980s, Barrett started experimenting and recording with a more electronic sound which had been explored in "DK 50/80" and "Birthday Boy" from "Way & Bar". Following his mostly single-based approach at that point he recorded two singles, "Old Joe Clarke" and "Rapping on a Mountain", in 1983, which were both released on Carrere Records. A single called "The Hitchhiker and the Punk" contained a much more textured and layered sound which was created from using in-studio effects and multi-tracking. This culminated, in Barrett's words "By far the most 'off the wall' musical project I have embarked on ", in Organic Bondage. He made a wooden record sleeve for the album since he did not have the finances to get a sleeve printed.

In the 1990s, Barrett recorded two albums both featuring his drummer Mark Freeman on cardboard box (an 'instrument' he had played live). Far from the electronic sound Barrett had been focussing on in the last decade, these two albums were more organic, specifically the second. Mound of Sound had been influenced and recorded on an old English burial mound and features much of the ambience and "feel" that those interring might have felt had they been born in the 21st century.

Barrett has been performing vocal and strings for Sleeping Dogz, a band that he formed with his partner, Mary Holland, and John Devine, and closed the Cambridge Folk Festival in 2003, 2004, 2005 and 2009. He toured autumn 2009 with John Otway and toured with Sleeping Dogz in April and May 2010.

In 2012, Barrett formed French Connection, using the Sleeping Dogz line-up, with the addition of French vocalist Aurora Colson. Their first live performance took place at The Flying Shack, Cheltenham on 9 November 2012. As of 2017, Barrett continues to tour.

In 2014, Barrett recorded and produced new songs for the "Krazy Kong 40th Anniversary" project.

title: Wild Willy Barrett


text:
Talk:Activision

Bobby Kotick
This article reads like an investor advertisement sheet. It really needs a criticism section, or at least a section on Bobby Kotick, especially in light of a large series of articles like this http://arstechnica.com/gaming/news/2009/09/actiblizzard-ceo-kotick-policy-rewards-profits-removes-fun.ars and http://www.escapistmagazine.com/news/view/94711-Bobby-Kotick-Wants-to-Take-the-Fun-Out-of-Making-Games —Preceding unsigned comment added by 72.77.100.90 (talk) 20:27, 15 September 2009 (UTC)

NOBs Review
So this user: 68.205.39.116 goes through pages and adds links to (presumeably) their own reviews. There's a link to one of his reviews on the Activision main page now. Are these links of significant importance that they should be added? Should this user really be adding things solely to build themself up? TheMaster42 19:15, 20 February 2006 (UTC)

Cornerstone
The paragraph from the article:
 * Activision changed its name to Mediagenic in 1988, in an attempt to capture the business software market. To this end, Mediagenic released Cornerstone (developed by Infocom). The effort was a commercial failure, and in 1992 Mediagenic filed for Chapter 11 bankruptcy protection. This resulted in a reorganization and merger with The Disc Company.

Can't be correct. Infocom released Cornerstone before being acquired (or merging with) Activision. Its failire is why Infocom had to merge with them. See History of Infocom for details. Any ideas on how to fix it? — Frecklefoot | Talk 20:37, Aug 9, 2004 (UTC)

 * How about removing the wrong information? :)  Pfalstad 18:01, 6 October 2005 (UTC)

Darn that Cornerstone game still gives me the chills.

Notable published titles
Is it just me, or is the list in "Notable published titles" getting too long? How about we create a "List of Activision games" (or something similar—what is the precedent on this?) and just link to it in a "See also" section? We could slap all the games in there and then trim this section to just very prominent titles, such as Quake. What say ye? — Frecklefoot | Talk 22:12, September 10, 2005 (UTC)

 * Agreed. Apparently every game we do (I work there) is "notable." There are already lists for some of these series in template form, though, which would at least make it less unwieldy for the time being.  --Stellmach 21:21, 11 July 2006 (UTC)

 * For example, I see X-Men Legends and X-Men Legends II recently added back to this list. I like these games. I wish them success. They put bread and butter on my table and everything. But why are they notable in the context of Activision's entire existence across all of time and space? I couldn't really tell you. I think this section really needs a synopsis, for each listed item, of what makes that item notable, and "got pretty darn good reviews" shouldn't make the cut. I would suggest criterea might include:
 * Outstanding critical success (e.g. Metacritic aggregate score in the "Universal acclaim" range).
 * Industry awards (e.g. Game Developers Choice Awards).
 * Identifiable innovations or historical significance (e.g. Dragster, Fishing Derby, Checkers, and Boxing ... Activision's first games, I believe)
 * Newsworthy cultural impact (hard to set a critereon, as many games bother somebody somewhere).
 * That said, I recuse myself from making the actual changes, being as I say an employee of the company. --Stellmach 16:56, 3 August 2006 (UTC)

 * I agree they should be removed. I saw that they were added, but didn't know anything about the games, so I didn't feel qualified to remove them.  So please remove.  As for the synopsis, I think it's a good idea. — Frecklefoot | Talk 17:39, 3 August 2006 (UTC)
 * Well, if someone can provide some reasoning that's even better than removing items. My not knowing why a game is notable doesn't mean it isn't. But the list certainly doesn't seem very useful in its current form without some kind of context provided. --Stellmach 18:48, 3 August 2006 (UTC)

 * Here's my first pass at the synopsis. My personal comments are in red.  Some I don't know enough about.  Looks like just a couple of games would survive if I had my way.  Like them or not, Electronic Arts really published way more influential titles.  Please add synopsis or change mine so we can come up with something to put in the article:

 * Barnstorming (for the Atari 2600) First published game. Of course it's notable for that very reason
 * I'm seeing several sources citing Dragster, Fishing Derby, Checkers and Boxing (maybe released simultaneously?) as the first Activision games. --Stellmach 23:12, 6 August 2006 (UTC)
 * Battlezone: Not very notable. Nothing like the original  Battlezone
 * Call of Duty I don't know why this is here except that the series is very successful. Did it redefine WW2 games in some way?
 * Civilization: Call to Power Civilization rip-off, but otherwise not very notable
 * Doom 3 Notable because it was the re-emergence of one of the most successful computer game franchises of all time
 * GUN (2005) Don't think this belongs here. From what I hear, it's a good game, but not anything genre-defining.
 * Hacker Don't think this belongs here. It got some press and did pretty well, but not genre-defining or a hallmark of game design
 * MechWarrior 2: 31st Century Combat Don't know this game--there are tons of MechWarrior games. Don't know why this one in particular should be on the list.
 * The Movies Good game, from what I hear. Kind of a Sims rip-off.  Got some good press, but not a hallmark game.
 * Pitfall! (for the Atari 2600) Considered a hallmark game in terms of game design. Very popular, one of Activision's most successful franchises Per synopsis
 * Quake One of the most successful computer game franchsises. Considered a hallmark of FPS games.  Followed by Quake II, Quake III Arena and Quake 4
 * Return to Castle Wolfenstein Fine game, but not really genre defining. Not really even part of the  Wolfenstein 3D  cannon.
 * Rome: Total War Same as most of above. Fine game, probably pretty popular, but not incredibly notable,
 * Star Trek: Armada Same as above
 * Tony Hawk's Pro Skater Don't know enough about this franchise to comment
 * Vampire: The Masquerade - Bloodlines Another not incredibly notable games
 * Don't know offhand if there are arguments for the others, but Call of Duty, Rome: Total War, and Tony Hawk's Pro Skater all would meet my hypothetical "Outstanding" critical success mark. For context, that seems to be the ... let's see ... about the 98th percentile of Metacritic's database at the moment.
 * Award-winning games would include Call of Duty (a pair of Game Developers Choice awards) and MechWarrior 2 (and 3) with Origins Awards. --Stellmach 20:17, 3 August 2006 (UTC)

Stellmach, according to AtariAge.com, Dragster has the model # as AG-001, which would be       the first game in my book. Rricci428 (talk) 16:30, 27 June 2015 (UTC)

 * Tony Hawk's is very notable, I'd say, because it basically started the entire "extreme sports" genre. It was so successful, Activision started an entire brand of "O2 Games" that were all extreme sports games.  Although the brand ultimately failed, Tony Hawk continues to sell multi-million units per title.  Nowadays, games like SSX Tricky and a ton of budget titles continue the genre, along with Tony Hawk.

 * The Call of Duty franchise is currently Activision's highest selling title each year. Although Medal of Honor really started the resurgence of World War II games, Call of Duty is currently the genre leader.  Not sure that makes it survive the cut, but this info's there for you guys to use.

 * I remember MechWarrior 2 being a "huge, hallmark" game when I was playing it back in the day. From what I understand its success kept the struggling "old" Activision alive for a while.  I don't have anything really concrete to back that up; I'll try doing some research later on.  I agree with your appraisals of all the other titles. TheMaster42 02:08, 5 August 2006 (UTC)

 * This list really needs more Atari 2600 games. Activision was the top of the market during those days and released some of the best games for that system. Some suggestions would be
 * Enduro
 * H.E.R.O.
 * Kaboom!
 * River Raid
 * Andrzejbanas 08:51, 17 August 2006 (UTC)

 * What made those games significant? --Frodet 21:41, 17 August 2006 (UTC)

 * Hard to be sure what good examples from the Atari 2600 catalog would be (aside from Dragster, as their first game). It'd be good to have a source on sales numbers. I'd have thought Pitfall was bigger than any of those. Stellmach 13:16, 18 August 2006 (UTC)

 * I thought Laser Blast was their first game. I was thinking that we might want to add Spider-Man as a notable game.  To me, it was the first superhero video game that didn't suck.  It actually got everything right, for the first time.  It was the first superhero videogame where I actually felt like a superhero, instead of some lame wannabe. — Frecklefoot | Talk 14:41, 18 August 2006 (UTC)

 * Your argument for Spider-Man being notable, while valid for you, are very much subjective. For instance, have you played every superhero game ever?  And there will be plenty of other games who will disagree with any reasoning based on adverbs like suck and feel.  Personally, I have a hard time finding any notable games from any publisher the last ten years, but that might just be me. :)
 * The titles in the notable list must have some objective arguments for being there. I like the criteria as given by Stellmach above.  Maybe it's time for a separate List of Activision games?
 * BTW: Activision's first games were Dragster, Fishing Derby, Checkers and Boxing, all released in July 1980.
 * --Frodet 23:20, 18 August 2006 (UTC)
 * I did some more digging on that. Those four games had catalog numbers AG-001 through AG-004, of which Dragster was AG-001. So if one has to pick one to be first, it's in some sense technically that one. Laser Blast, by the way, wasn't released until the next calendar year, and was AG-008. -Stellmach 00:27, 19 August 2006 (UTC)

So, basically, this is what we currently have that can so far be substantiated in some authoritative way, plus Pitfall, whose claims (both here and on its own page) seem well-founded but still look shakily sourced. Note the shower of citations in the hopes of preventing future list bloat that would distract from the truly notable titles. Yes, the Tony Hawk list is huge, and I admit I'm biased, but then I can't guess another series to sustain 90+ Metacritics through four sequels. -Stellmach 23:23, 19 August 2006 (UTC)
 * Call of Duty (2004). Critically acclaimed. Game Developers Choice Awards: Excellence In Audio and Rookie Studio of the Year (Infinity Ward); Game of the Year nominee.
 * Doom (1993), Quake (1996) and related series. (needs description of cultural impact, citations).
 * Dragster (1980). First videogame by a third party publisher.
 * MechWarrior 2: 31st Century Combat (1995). Origins Award: Best Fantasy or Science Fiction Computer Game.
 * Pitfall! (1982). (needs description of cultural impact, citations).
 * Rome: Total War (2004). Critically acclaimed.
 * Tony Hawk's Pro Skater (1999) and related series. Repeatedly critically acclaimed series.

 * I'd like to propose some "first" and "last" titles (in addition to Dragster):
 * Pitfall! (1982). First Activision title for home computers/non-Atari consoles (May or June 1984 I think).
 * Activision Decathlon (1983). First joystick bashing game.
 * Ghostbusters (1984). First lisencing deal (?).  At the time outselling anything else before (?).
 * Ghostbusters II (1989). Last Activision title for the Atari consoles.

 * (From memory - need to dig out some references). Thoughts? --Frodet 00:21, 20 August 2006 (UTC)

 * Doom was first published as shareware and that's where it got most of it's exposure. Activision only took over as publisher when they started publishing Doom 2 (which was never shareware).  I don't think it should be on the list unless it is changed to Doom 2. — Frecklefoot | Talk 20:27, 7 September 2006 (UTC)

SelectSoft
The the line, "In 2005, the company was bought by and later merged into SelectSoft Publishing." seems really suspect. I couldn't find any 2005 press announcement from ATVI having anything to do with SelectSoft or MPS (http://investor.activision.com/releases.cfm?year=2005&startpage=all). Additionally SelectSoft's website doesn't mention anything about owning Activision (although they do publish some of Activision's older titles). Did they really buy them? I'm going to delete this in a few days unless someone posts better information than I have about this topic. - TheMaster42 03:50, 17 December 2005 (UTC)

 * Talked with some ATVI employees - they said the above information was not correct and I can find no other sources to say that it is correct. I have removed it. - TheMaster42 08:08, 17 December 2005 (UTC)

Expert Software?
why does "expert software" redirect to this page ?? wikipedia at domn dot net

 * I have no idea. Perhaps an enthuisiastic fan? — Frecklefoot | Talk 23:20, 17 April 2006 (UTC)

 * "Activision to Pay for Expert Software Acquisition With Stock" (April 2, 1999) --Mrwojo 02:05, 18 April 2006 (UTC)

 * We should put that in the article then. I was wondering the same thing. 69.236.83.191 16:51, 23 June 2006 (UTC)

 * Head Games Publishing also redirects to this page. These two redirects should redirect to Activision Value or become separate articles in themselves. WinterSpw 17:35, 19 July 2007 (UTC)

Activision the first independent game publisher?
According to the article, "Prior to the formation of Activision, video games were published exclusively by the makers of the systems for which the games were designed." What about Softape and Programma International? I'm pretty sure they were publishing games for the Apple II before Activision was formed in October 1979. Applegamer 19:25, 30 August 2006 (UTC)

 * Well, personally, I've never heard of Softape nor Programma International, and I was in the thick of the home computer boom of the late '70s and early '80s. But they are widely recognized as the first independent game publisher, though that claim could use a source.  They most certainly are the first independant game publisher for game consoles, but may have been beaten to the punch for home computers, since anyone could produce programs for those systems (not true for consoles).  I suppose this could use some clarification in the article. — Frecklefoot | Talk 19:33, 30 August 2006 (UTC)

 * Yes, "video game" is clearly meant in its sense as distinct from "computer game" here, i.e. software for dedicated game consoles specifically. -Stellmach 21:12, 30 August 2006 (UTC)

 * Yeah, specifying "video game" addresses the issue I raised. Never heard of Softape or Programma International, eh?  Well, that prompted me to create an article on Programma International.  I'll do one on Softape next.

Activision always claimed to be the first independent third party cartridge developer, but Gamevision (MB) released cartridges for the TI-99/4 (not 4a) in 1979 (http://www.ti994.com/), so this makes Activisions claim invalid.

 * Well, someone better tell the IGDA: "David Crane, Larry Kaplan, Jim Levy, Alan Miller and Bob Whitehead were honored for establishing the first third-party developer of video game software." Unlike the other companies mentioned, Activision is still in business. — Frecklefσσt | Talk 16:29, 24 September 2007 (UTC)

 * Once again, the claim in the article is that they were the first third-party game publisher on a game console. The TI-99/4 was not a game console, but a home computer. - -Stellmach 18:01, 24 September 2007 (UTC)

 * Best to change your second sentence though, as it says COMPUTER and Video Games. Also, Pitfall! (1982) is not considered by many to be the first platform game, many think Donkey Kong (1981) is. In truth, Space Panic (1980) was the first ever platformer >>Me 0000<<

 * You know, you don't actually have to tell other people what to change. You can just do it. That's kind of the idea. -Stellmach 03:19, 26 September 2007 (UTC)

Notable games revisted
Where are we with this list? We were making some good progress, but we seemed to lose steam somewhere. What's the current list? I don't think what's in the article is current, as it includes a lot of titles we already said were non-notable. — Frecklefoot | Talk 15:58, 12 September 2006 (UTC)

 * I started the List of Electronic Arts games and still am not done with it. I propose we go ahead and start a List of Activision games so we can start removing non-notable stuff from the "Notable" list (plus, a full list like this is always desirable).  I don't want to start another project, however, before finishing the EA list.  Anyone else want to start it?  An easy way is to get a listing from MobyGames or another favorite website, copy & paste and format it for Wikipedia.  Lists can't be copyrighted, so it's not violating anyone's rights. — Frecklefoot | Talk 17:42, 5 January 2007 (UTC)

I Would add THPS 2,3,4 Tony Hawk's UNDERGROUND 1,2 Tony Hawks AMERICAN WASTELAND. SPIDERMAN 2,3 Kelly Slaters pro surfer,Shaun Palmers pro snowboarder,the pro wakeboarder game Matt Hoffmanns pro BMX 1,2 DOOM ,DOOM 2

Location
Some anon user keeps changing the company's location. Their website says they are in Santa Monica, CA (from their website: "Activision's headquarters is located at 3100 Ocean Park Boulevard, Santa Monica, California 90405"). The anon user keeps changing it to Los Angeles, CA. Santa Monica is adjacent to LA, so I can see how it's mistaken for being there (and it is in LA county), but one quick hop over to their website shows they are headquartered in Santa Monica. While they do have at least one satellite office in LA, what we should list is their headquarter's location. I'd change it again, but I'm afraid another user would just revert it back. Can we please resolve this? — Frecklefσσt | Talk 16:19, 25 July 2007 (UTC)

 * We must resolve this. WinterSpw 17:45, 25 July 2007 (UTC)

 * It seems to me that Frecklefoot did just resolve it, with a citation. Their HQ is in fact in Santa Monica, and repeatedly changing it without grounds to do so is vandalism. -Stellmach 21:02, 25 July 2007 (UTC)

 * I note, by the way, that the same user made a similar change on the Stop & Shop page which is equally easily debunked by checking their corporate web page (e.g. the press release here. -Stellmach 21:08, 25 July 2007 (UTC)

 * Thanks for changing it back. I added the cite as a ref to remove any question. — Frecklefσσt | Talk 14:03, 26 July 2007 (UTC)

 * ARGH! Mark Redekas did it again!  He didn't provide any rational or a ref or anything, he just changed it back to LA (and screwed up the template in the process).  He just said "Changed correct company location because Activision, Inc. is in Los Angeles, CA not Santa Monica, CA. That true." as if somehow that is proof that they're really in LA.  The ref clearly states that they are HQ'ed in Santa Monica.  Can't he be banned or something?  I'm not changing it because of the three revert rule.  Please, this is getting ridiculous. — Frecklefσσt | Talk 19:06, 26 July 2007 (UTC)
 * There's a process for these things. I've added a second notice about the right way to go about these things to his talk page. If he keeps it up without citations or dicussing his changes here, then yes, he can be blocked. -Stellmach 20:59, 26 July 2007 (UTC)

Opening Paragraph
Though the quote about Mr. Moore may or may not be true, it does not belong in the first paragraph -- it is a text of opinion, and looks unprofessional in an encyclopedia. User:MsgrCloche 23:47, 31 July 2007 (UTC)
 * Nor is it the case that the statement "may or may not be true," because it's patent nonsense. Moore's move from Microsoft to EA was only announced a few days ago, so unless he affected both EA and Activision's profits retroactively with his magic bad luck powers, I don't see what he could have had to do with it. -Stellmach 02:27, 1 August 2007 (UTC)

The List
I created the List of Activision games. Please visit it if you're bored and disambiguate/fix some of the wikilinks. Hopefully this list will help cut down on some of the spam in the in-article list. — Frecklefσσt | Talk 15:26, 14 August 2007 (UTC)

Activision to merge with Vivendi Games.
If anyone would care to update this, the link is here. · AndonicO Talk 03:12, 3 December 2007 (UTC)

 * It should be noted that an acquisition is not really a "merger", as is continuous throughout this article. The French bought the company as nearly all large companies do. A merger is technically the combination of 2 or more companies with equal standing. This was a combination of a smaller company with a larger company, of which only the larger entity survives and is by all technical definitions an acquisition, regardless of the publicity (see Public Relations) that may have accompanied the consolidation. Yes, if I buy your company in its entirety, that would be an acquisition - but you may call it a merger if you would like to not offend and alienate the fans of your company.... 10:53, 21 December 2008 (UTC)

No cite/NPOV?
"Davis was against the merger from the start and was heavy-handed in management of them. He also forced marketing changes on Infocom which caused sales of their games to plummet." This phrase seems very 'point of view' and is unsubstantiated? (for all I know, could be true but I would think a statement this negative needs some support/reference?) 124.191.2.144 (talk) 11:40, 6 December 2007 (UTC)
 * Agreed. The videogame business is notoriously bad at predicting what will sell, so making uncited claims about why Infocom sales plummeted seems very dubious. -Stellmach 18:58, 6 December 2007 (UTC)

 * I wrote that. Sorry, that was back in my "I don't know how to ref, so I'm not going to do it" days.  I just added the ref for that.  The "opinion" is that of the paper's author. — Frecklefσσt | Talk 21:32, 7 December 2007 (UTC)

3 things im tired of:infinity ward and activision saying they were the only companies making the call of duty series (treyarch and activision for 2 big red one) activision and neversoft saying they made the entire guitar hero series (no just 3 and upcoming 4) and how annoying typing is on PsP Dude867 (talk) 07:49, 6 January 2008 (UTC)

Notable titles - Final stage ;)
Well, I've put into the section. It strictly breaks WP:POV and WP:VER. Section should be cited somehow (refs. to game portals, 80s, 90s computer magazines etc.). Until then, it's still our individual judgment and POV-ed, Lothar25 (talk) 19:31, 28 February 2008 (UTC)

 * It sure is. Some research is in order, as you mention. — Frecklefσσt | Talk 14:12, 14 May 2008 (UTC)

Activision 02
Activision 02 should be added into the article. They made Tony Hawk's Pro Skater 2 for some proof of existance —Preceding unsigned comment added by DragonX83 (talk • contribs) 14:48, 3 May 2008 (UTC)

 * The Tony Hawk's Pro Skater 2 article says that Neversoft developed it. MobyGames says the same thing. But MobyGames does have this list, which makes it look like a label. Assuming "O2" stands for Oxygen, it would actually be O2. It should be mentioned in a labels section.  Do they have any other publishing labels? — Frecklefσσt | Talk 17:42, 18 June 2008 (UTC)

Editing needed
The first paragraphs are an absolute mess. I am not informed as to this subject so I am not a good person to edit, but how can Activision "so far be the leading publisher in 2007" ? Just little things like that need to be changed throughout to make the article read better. 75.143.109.72 (talk) 06:17, 17 September 2008 (UTC)

Development teams
I'm a little unhappy with the new section called "Development teams". It only talks about one division, Software Conversions Ltd, that doesn't even exist anymore, and hasn't for like, what, 23 years? Do we really need this section? It's ref'ed, but doesn't really seem all that important. And, as it is, is really just one development team. — Frecklefσσt | Talk 17:56, 23 January 2009 (UTC)

Tony Hawk Games Wiki
Help is needed at the Tony Hawk Games Wiki, which can be found here. It is very lonely. There are only about 3 users on there. If anyone of you join, and have questions, please see this user page. --98.148.171.15 (talk) 00:24, 10 February 2009 (UTC)

Changed the word sans
I changed the word sans because 80% of the population has no idea what that word means... using technical out-dated words in a wikipedia article that is to be understood by 50% of the population is stupid, if you do use such a stupid term, at least link to a page explaining its meaning, damnit. /endrant (Yes I know what sans means, but I hate being messaged at 3am to be asked what it means)

Gabliaven (talk) 11:42, 21 June 2009 (UTC)Gabliaven

What the fuck. Aardark (talk) 21:19, 10 November 2009 (UTC)

Criticism section?
EA has quite a lengthly criticism section, and with recent events Activision has been copping alot of flack. Some possible points; Kotick's refusal to release new IP's that don't have $100M dollar potential, Calling for a PS3 price cut then a couple of months later be calling for game prices to be raised etc etc. Could something like this be done for Activision? —Preceding unsigned comment added by 125.238.254.18 (talk) 13:28, 10 August 2009 (UTC)

I second this, give me an hour to pull some stuff together.--125.236.135.149 (talk) 06:29, 21 September 2009 (UTC)

Actually after looking over most of my material, it isn't as such criticism of Activision, more criticism of Kotick. All of which are detailed on his page. Not sure whether or not it needs to be practically copied from there.--125.236.135.149 (talk) 06:46, 21 September 2009 (UTC)

There's people who make jokes about how bad activision is and i went to this page to find out why some people think this company is so bad. Why do people use this company as a derogatory thing? —Preceding unsigned comment added by 71.231.28.185 (talk) 05:32, 23 January 2010 (UTC)

Add the Criticism section right now Lopey273 (talk) 15:54, 29 April 2018 (UTC)

No Info On Sierra Entertainment
Can someone supplement this article with information on Sierra Entertainment which were currently in control of Naughty Dog's Crash Bandicoot & Insomniac's Spyro The Dragon Series?  Gaogier How can I help? 11:05, 15 August 2009 (UTC)

Sledgehammer Games
Why does Sledgehammer Games have a lengthy discussion in this article while none of their other studios do? They all have their own articles. Why doesn't Sledgehammer have its own article as well, instead of cluttering up this article? It has more than enough refs to justify its own page. — Frεcklεfσσt | Talk 22:45, 26 December 2009 (UTC)
 * See this AfD in which consensus was to merge to this page. It was decided that notability was not established as of yet. When it is (a month or two, I'd guess), then the article can be recreated and the section here can be shortened. -- Thejadefalcon Sing your song The bird's seeds 22:59, 26 December 2009 (UTC)

Without a doubt the most hated gaming company in the world...
Does anyone else find it strange that a corporation that is such a magnet for bad press doesn't have a criticisms/controversy section? It seems like any time Activision is brought up on any video game message board an endless flurry of hate and calls for a boycott ensue. Xizer (talk) 23:54, 4 March 2010 (UTC)

NPOV?
The NPOV tag was added recently. It's not appropriate in this circumstance. What people seem to want is the restoration of the Criticism section, most of which is now in the article on Robert Kotick, where it belongs, since the criticism is mostly of his business decisions since the formation of Activision Blizzard. --Jtalledo (talk) 21:52, 22 April 2010 (UTC)
 * How is this not appropriate, considering the coverage with the Infinity Ward / Activision fight, multiple news sources criticizing the exploitation of franchises such as Guitar Hero, the removal of Marvel: Ultimate Alliance DLC and along with it's sequel from Xbox Live/PSN...  Just because a criticism section has not been started does not mean the article is neutral. --Teancum (talk) 01:02, 26 April 2010 (UTC)
 * I do think the article needs to mention the lawsuits former and present Infinity Ward employees have filed against Activision. Whether or not these lawsuits should go in a Criticism section right now is something that should be discussed until a court ruling on the lawsuits is presented. A small criticism section is probably warranted given the immense amount of attention Activision's decisions receive, but as Jtalledo pointed out, much of that is a result of Robert Kotick, so perhaps briefly mentioning those criticisms and then linking this article to his would be a good idea. If we add a criticism section, it should be built upon criticism of Activision that comes primarily from sources within the gaming industry, the EA Games criticism section seems like a good example of the content we should try to find. Most of the content is derived from comments made by people inside the gaming industry, from lawsuits, or metacritic data. I'll see if there are any good sources we can use to build a criticism section later today or tomorrow sometime. -- Yo Soy Dan Halen (talk) 23:20, 27 April 2010 (UTC)

Lawsuits
As I'm not terribly interested in this article, I won't be writing the controversy section. However here are some things to consider regarding what can go in:

West And Zampella v. Activision
 * http://gameinformer.com/b/news/archive/2010/03/01/news-what-s-going-down-at-infinity-ward.aspx
 * http://www.xbox360achievements.org/news/news-4556-Future-Modern-Warfare-Releases-Could-Be-Vetoed-By-West-and-Zampella.html
 * http://xbox360.ign.com/articles/107/1074211p1.html

Infinity Ward Employee Group v. Activision
 * http://ps3.ign.com/articles/108/1086448p1.html

Guitar Hero 5 - Controversy over Kurt Cobain
 * http://www.eurogamer.net/articles/love-to-sue-the-s-out-of-activision
 * http://www.nme.com/news/nirvana/47369
 * http://www.google.com/hostednews/ap/article/ALeqM5ipFhOuBuSMv3z7cr0LgPJT4dWALAD9AKQQL80
 * http://news.bbc.co.uk/2/hi/entertainment/8259846.stm
 * http://kotaku.com/5357425/cobain-attorney-calls-for-activision-to-limit-musicians-use-in-gh5
 * http://www.joystiq.com/2009/09/15/lgj-come-as-your-avatar-smells-like-lawsuit-nevermind/

Band Hero - No Doubt v. Activision
 * http://kotaku.com/5397223/no-doubt-sues-activision-over-band-hero-likeness-%5Bupdate%5D
 * http://kotaku.com/5518649/no-doubt-vs-guitar-hero-publisher-hella-good-hella-bad
 * http://www.shacknews.com/onearticle.x/61544
 * http://latimesblogs.latimes.com/entertainmentnewsbuzz/2010/04/no-doubt-wins-round-in-activision-lawsuit.html

Marvel: Ultimate Alliance & Marvel: Ultimate Alliance 2 DLC removed without prior notice (angered gamers)
 * http://ps3.kombo.com/article.php?artid=11724
 * http://www.joystiq.com/2010/01/06/activision-marvel-ultimate-alliance-2-dlc-on-psn-was-a-limite/

Those five separate instances constitute enough for a Criticism section, although there are probably other, less publicized controversies as well. As far as whether this goes in Activision or Activision Blizzard I can't exactly say, however since they are both plausible in searches the one that doesn't receive the full section should have a wikilink to the other. --Teancum (talk) 11:57, 29 April 2010 (UTC)
 * The criticism about individual games belongs in the articles about those individual games. Recent criticism of Activison deserves a mention, but doesn't warrant an entire section. Just because articles on other companies have Criticism sections doesn't mean that this article needs one too. Criticism should really be integrated into the appropriate sections. I think that most of criticism of the company should be mentioned in the articles on Robert Kotick and Activision Blizzard, since the combined company and Kotick himself are at the center of this criticism.

 * As for the NPOV tag, this is not a neutral point of view issue. If the article said something like "Activision is a horrible company..." or "Activision is just making smart business decisions", that would be a POV issue. The issue is about whether or not to include an entire section dedicate to recent criticism of Activision. I don't think so - Activision had a long history before Kotick came into the picture, and even after he was hired, so adding one would be biased towards recent events. --Jtalledo (talk) 22:25, 30 April 2010 (UTC)

 * I respectfully disagree: adding the lawsuits to a criticism section (though perhaps a Lawsuits section is a better fit) would improve this page's accurate depiction of Activision. There is no bias towards recent events here: Activision has a lot of lawsuits, and while it may be true that Kotick is at the center of it all it's lawsuits with Activision.  Lawsuits involving Kotick personally can go on his page, lawsuits involving Activision belong on this page.

 * Lawsuits with Activision are included in the articles of the other parties (Infinity Ward and Valve both have their respective Activision lawsuits), making this page inconsistent with linked pages.

 * Not only that, but it is misleading by omission. Maybe some of these lawsuits aren't notable, maybe they are and maybe they aren't, but look at the number of them!  Activision and lawsuits go hand-in-hand.

 * Now can someone who cares please update this article? — Preceding unsigned comment added by 75.140.14.4 (talk) 01:44, 11 June 2011 (UTC)

discography
The discography thing should distinguish between games that they actually developed, and games that they just acquired the rights to / published. Activision doesn't actually make good games, they just buy smaller studios with existing franchises and run those franchises into the ground.

Iron Man 2
Small complaint, but if I recall the demo right, isn't the Iron Man 2 game being done by Sega, not Activision? ProjectPlatinum 23:45, 3 June 2010 (UTC) —Preceding unsigned comment added by ProjectPlatinum (talk • contribs)

When is Marvel Ultimate Alliance 2 DLC coming back to playstion network and xbox live? —Preceding unsigned comment added by BlackVenomHulk (talk • contribs) 16:24, 6 July 2010 (UTC)

Crash Bandicoot Overhaul
What is Crash Bandicoot Overhaul?--Gianchio (talk) 17:34, 12 December 2010 (UTC)

Semi-protection proposal
This article has been a recent target of a large amount of vandalism... it should probably become semi-protected. --114.241.31.176 (talk) 10:33, 9 February 2011 (UTC)

I like to to support this proposal, as despite my reasoning that can be viewed on the history page, several (or the same one, I can't tell) unregistered users keep re-adding Call of Duty Black Ops to the notable games list. KP-TheSpectre (talk) 18:49, 23 February 2011 (UTC)

Misleading Crash bandicoot Title in 2011 section
Please delete that title anyone because its not even rumored or official yet "Crash Bandicoot title (PS3, Xbox 360, Wii)" -Motwera 174.91.74.208 (talk) 23:03, 13 March 2011 (UTC)

Details on patent suit?
The article indicates they were majorly harmed by losing a patent infringement lawsuit during their time as Mediagenic, but does not say who sued them over what products. This is a glaring omission as it seems an important part of their company history. —Preceding unsigned comment added by 68.94.88.174 (talk) 06:02, 4 April 2011 (UTC)
 * Phillips sued Activision over Ralph Baer's videogame patents filed during the creation of the system that became the Magnavox Odyssey (Phillips bought Magnavox in the mid-1970s). Activision was one of many companies sued over those patents. Indrian (talk) 08:42, 4 April 2011 (UTC)

Activision Blizzard and Activision Publishing
I would assume that this article now refers to Activision Publishing, which is a subsidiary of Activision Blizzard. Bobby Kotick is 'not' the CEO of Activision Publishing; currently, Eric Hrishberg is (http://www.joystiq.com/2010/07/13/activision-publishing-names-eric-hirshberg-as-new-ceo/), so that and probably a lot of other parts of the article need to be changed. Velociostrich (talk) 23:40, 10 June 2011 (UTC)

Where is the proof for the upcoming Crash Bandicoot game?
No really where the fuck is the proof?

Vivendi
It should be added that French multi-national media conglomerate Vivendi is 80% owned by American multi-national conglomerate General Electric. A single line which adds a lot more context as to who holds purse strings. — Preceding unsigned comment added by 82.40.41.34 (talk) 10:32, 2 May 2012 (UTC)

Lulzsec?
"On May 2, 2012, hacktivist group LulzSec shared CEO Eric Hirshberg's private data through facebook after the release of the Call of Duty Black Ops II trailer. The Trailer included subliminal flashes of Guy Fawkes masks allegedly portrayed as the enemy. [12]"

What the hell is that about? Delete it post-haste. — Preceding unsigned comment added by 2.223.103.24 (talk) 10:27, 7 May 2012 (UTC)

Generator Rex Metacritic scores
The end of the Post-merger developments section mentions Activision's release of that Generator Rex game and how there are no Metacritic scores as of February 2012. Since it's semi-protected, I can't update that to June 2012. Nazumu (talk) 08:23, 30 June 2012 (UTC)

Proposal: merge Activision Publishing Minneapolis, Inc. into this article
I stand to be corrected, but isn't Activision Publishing Minneapolis, Inc. and Activision about the same company? If so, then I suggest Activision Publishing Minneapolis, Inc. be merged into this article. Singularity42 (talk) 23:01, 2 July 2012 (UTC)

According to the company, the two are distinct with Santa Montica, California being Activision Publishing Inc, and Eden Prairie/Bloomington, Minnesota being Activision Publishing Minneapolis, Inc. --Jundis (talk) 23:18, 2 July 2012 (UTC)

Different Incorporation. If your idea is what should be enforced, then I'd propose NBCUniversal merging with Comcast. Both entities have their own histories and identity and that is why I say you should not merge these two articles --De132Wiki (talk) 04:13, 12 September 2012 (UTC)

Activision Publishing used to be Expert Software and Head Games Publishing, it's not an interally created division. Normally when a company has it's own history, it's kept separate here. Disagree with the merger. --Marty Goldberg (talk) 04:46, 12 September 2012 (UTC)

Incorrect word usage!
The "Post-merger developments" section reads "On February 9, 2011, Activision announced that it was shuttering its once profitable Guitar Hero franchise....", which is incorrect usage of the word "shuttering". It should read "ON February 9, 2011, Activision announced that it was ending its once profitable Guitar Hero franchise...".

Please change "shuttering", which means to close the shutters on a building, to "ending" or "closing".

Also, I believe they have confirmed the Guiter Hero series will return sometime in the future.

PMierdaP (talk) 08:14, 12 December 2012 (UTC)
 * Yes check.svg Done. No reason to oppose. — KuyaBriBri Talk 16:01, 12 December 2012 (UTC)

Edit request on 28 December 2012- correct link to proper page for video game "Enduro"

 * Enduro (Video Game) (1982)

Jamrhein71 (talk) 16:01, 28 December 2012 (UTC)

 * Yes check.svg Done Link corrected to Enduro (video game). —C.Fred (talk) 16:06, 28 December 2012 (UTC)

PS3 Breakages
Activsions also Broke 1000 upon 1000s off PS3's with there badly ported version of Black ops 2 and still denies it. Grow a pair and admit blame for all these Breakage — Preceding unsigned comment added by 89.126.39.181 (talk) 21:12, 17 July 2013 (UTC)

Edit request on 18 July 2013
Activision will be bringing Angry Birds Star Wars to the PS3, Vita, 360, Wii, Wii U and 3DS. Here's the link: http://www.cultofmac.com/236175/angry-birds-star-wars-flies-away-from-mobile-and-into-gaming-consoles-october-29th/

76.69.126.133 (talk) 23:01, 18 July 2013 (UTC)
 * Red information icon with gradient background.svg Not done for now: The source you provided looks like a promotional press release, not a reliable source. If you can find an independent, third-party source describing the release, I'd be happy to add it to the article. -- SamX‧☎‧✎‧ S  15:38, 28 July 2013 (UTC)

Edit request: the CEO is Eric Hirshberg
The article says the CEO is Bobby Kotick but he is the CEO of Activision's parent company Activision Blizzard. The Activision CEO is Eric Hirshberg. See Activision's own site: http://www.activisionblizzard.com/senior-corporate-management I don't know how to do references or I would do it myself — Preceding unsigned comment added by Camerajohn (talk • contribs) 15:13, 13 June 2015 (UTC)

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Holding company category
This would probably be the category for Activision Blizzard and not Publishing since the Infobox has it listed as subsidiary. --CharlesDeMint (talk) 19:05, 12 July 2017 (UTC)
 * You are correct. Activision is not a holding company, Activision Blizzard is. -- ferret (talk) 19:19, 12 July 2017 (UTC)

Matchmaking patent
Is it worth mentioning their matchmaking patent? Axl ¤ [Talk] 14:37, 18 October 2017 (UTC)
 * I have added a statement. Axl ¤ [Talk] 13:20, 19 October 2017 (UTC)

The Lost Treasures of Infocom had 20, not 50 games
This edit from an IP changed the quantity of games in The Lost Treasures of Infocom from 20 to 50, which is incorrect. Samboy (talk) 11:57, 17 March 2018 (UTC)

Criticism and Greed
Activision have been purchasing over 10 companies for the past 18 years time, The criticism is that people say that Activision are very greedy and they are the king of franchise milking, in 2007 they annocuned that they will merge with Vivdeni Games and they were a lot of Eyebrows shown at the annocument, after the merging Activision gained the rights to Crash Bandicoot and Spyro the Dragon and they been hated ever since. Lopey273 (talk) 15:58, 29 April 2018 (UTC)

Activision Publishing, Inc.
I think this edit not factually correct. Already prior the Activision–Vivendi Games merger, Activision Publishing had formally been in charge of publishing activities as a subsidiary of Activision, Inc., which was in turn publicly listed. Their California registration history (per SOS CA) paints the following picture:

The 'original' Activision, Inc. (registered in California on 1979-10-01; Cal entity number C0962542; legal name "Mediagenic" held from 1988-08-17 to 1992-08-03) was merged with an entity of the same name, though incorporated in Delaware (C1867531), on 1993-08-04; this Delaware corporation was renamed "Activision Publishing, Inc." on 2000-06-19. On the same day as the renaming, a company under the name "Activision Holdings, Inc." (incorporated 2000-05-25; C2235977) changed its name to "Activision, Inc." This third Activision, Inc. is also the one that merged with Vivendi Games as is now renamed as "Activision Blizzard, Inc."

The body already mentions the creation of the holding company in June 2000, but I'll have to see whether there is a source on the renaming part somewhere. However, the mentioned sentence, as it stands, is most likely incorrect. Lordtobi ( ✉ ) 17:44, 13 February 2019 (UTC)
 * Yeah, there's fuzziness here. I'll still trying to work through sources. --M asem (t) 18:16, 13 February 2019 (UTC)

 * I haven't started digging but it sounds like at the point of merge, all the subisidaries of "Activision Holdings" fell into "Activision Publishing"? Is that your take? --M asem (t) 19:07, 13 February 2019 (UTC)
 * , which subsidiaries do you mean? There are no corporate mergers on file for either Activision Holdings or Activision Publishing. What I can see that several mergers were filed for the original Activision/Mediagenic, though: Infocom on 1988-09-03, ten corporations for regional operations on 1989-01-13, two further on 1989-04-27, and Disc Company, Inc. on 1992-03-31. If there were asset mergers we'd need to check with their corporate entries. Lordtobi  ( ✉ ) 19:40, 13 February 2019 (UTC)
 * I guess the question is, taking Infinity Ward as an example: was it acquired as a Holdings or Publishing company? If it was a Holdings company, then at the point of the Vivendi merger, it technically would be handing off the merged orgs, but it seems that it now falls under Publishing. It's fully possible to do that of course, but just trying to make sure that we should be covering the studios in this article, rather than A-B. --M asem (t) 19:52, 13 February 2019 (UTC)
 * Asset deals usually go thrpugh the top company (cf. the Warhorse Studios situation from tomorrow morning), so the acquisition itself went through Atvi Holdings. For Infinity Ward specifically, in the press release, Atvi Publishing's CEO gets to have a word, suggesting that, by management, Infinity Ward became part of Atvi Publishing. If you find a source saying "X will now report to Y", you can take that as statement of managerial organization. Lordtobi  ( ✉ ) 20:02, 13 February 2019 (UTC)

 * Also, trying to confirm the initial headquarters when the four founded it. I'm getting Mountain View from sites that aren't best for confirming, but can't find anything else earlier. --M asem (t) 19:39, 13 February 2019 (UTC)
 * Their 1980 box arts list Sunnyvale (same loc as Atari at the time), Mountain View started appearing in 1981. This mag (p19) from Sep 1980 backs up the Sunnyvale location. I cannot tell whether this was the very first, but it might well be the first known (less than a year after founding). Lordtobi  ( ✉ ) 20:02, 13 February 2019 (UTC)

Lay-off of 800 employees
Hi. Looking through the article I'm surprised to find that there's been zero mention of Activision, despite having record profits, laying off 800 employees this month. The event has been one of the most notable in the company's history and one that has been widely criticized across the board. I presume this information can be included in the article? I'm just wondering why no one has done so already. -- Wikibenboy94 (talk) 13:17, 21 February 2019 (UTC)
 * Has been working on a large rewrite of these articles. But however note that it's Activision Blizzard, the parent, who made the layoffs, and that article DOES mention the layoffs already. This article is for Activision, the subsidiary publisher (sister to Blizzard, not parent of). -- ferret (talk) 14:03, 21 February 2019 (UTC)
 * Ah sorry, my mistake. I should have looked there instead. -- Wikibenboy94 (talk) 16:56, 21 February 2019 (UTC)
 * Yeah, and at this point, I haven't seen anything that says any Activision Publishing companies are affected (in contrast to the 2010 layoffs which did force A. Publishing to close studios). --M asem (t) 14:20, 21 February 2019 (UTC)
 * We know of some redundancies to Activision Publishing, High Moon and Vicarious Visions for jobs related to the Destiny series, but there are no precise numbers we could use. Lordtobi  ( ✉ ) 15:46, 21 February 2019 (UTC)
 * Barring outright closure or a massive rescaling, I wouldn't think that necessary here. I know I added the layoffs on the A-B page. --M asem (t) 15:50, 21 February 2019 (UTC)

Profit shifting and tax
Hello fellow Wikipedians. Full disclosure, I work for TaxWatch UK.

In August 2019, we published a report explaining how activision shifted €5bn to companies in Bermuda and Barbados between 2013-2017. This shifting of profits using royalty payments to tax haven companies is the same scheme used by Google, which has been heavily criticised by MPs.

This report was picked up by multiple outlets, including GamesIndustry and The Sunday Times,

I would like for a small section to be included on the Activision Wikipedia page. However, given the conflict of interest, I believe that someone else should make that edit.

Happy to answer any questions on the report.

Thanks,

Alex Alex0190 (talk) 12:09, 14 November 2019 (UTC)
 * This probably belongs on Activision Blizzard, this company's parent. Representative GamesIndustry.biz source: . Lordtobi  ( ✉ ) 12:16, 14 November 2019 (UTC)

A Commons file used on this page or its Wikidata item has been nominated for deletion
The following Wikimedia Commons file used on this page or its Wikidata item has been nominated for deletion: Participate in the deletion discussion at the. —Community Tech bot (talk) 20:34, 20 December 2020 (UTC)
 * Bobby Kotick in NYC photographed by Jordan Matter.jpg

The dot eaters allegedly not reliable
My edit was reverted for not using a reliable source. The Dot Eaters has been cited in several published books. cc User:IceWelder

https://scholar.google.com/scholar?hl=en&as_sdt=0%2C36&q=%22the+dot+eaters%22&btnG=

Anonymous-232 (talk) 21:01, 2 April 2021 (UTC)

 * First, I found a clear reliable source to establish the same info (as well as work out a few more things) from Game Informer.
 * But as for those other sources that use the Dot Eaters, those mostly look like student thesises, which we cannot use as evidence of reliability. If they were peer-reviewed published papers, that may be different. --M asem (t) 21:53, 2 April 2021 (UTC)

A Commons file used on this page or its Wikidata item has been nominated for deletion
The following Wikimedia Commons file used on this page or its Wikidata item has been nominated for deletion: Participate in the deletion discussion at the. —Community Tech bot (talk) 04:09, 18 August 2021 (UTC)
 * Bobby Kotick in NYC photographed by Jordan Matter.jpg

Microsoft is buying Activision.
Cheers. https://www.theverge.com/2022/1/18/22889258/microsoft-activision-blizzard-xbox-acquisition-call-of-duty-overwatch — Preceding unsigned comment added by 117.192.148.117 (talk) 13:42, 18 January 2022 (UTC)
 * To be more specific, they are buying the parent company Activision Blizzard. -- ferret (talk) 14:12, 18 January 2022 (UTC)
 * For those coming to change this page to reflect this, When the deal does go through, yes technically Microsoft will own Activision, however, they won't directly own Activision, and instead will own it through the parent company Activision Blizzard which, at this point in time will continue to be the parent company of Activision unless something changes. ― Blaze WolfTalkBlaze Wolf#6545 14:43, 19 January 2022 (UTC)

Semi-protected edit request on 19 January 2022
Add informatiom about Microsoft acquisition of Activision, announced yesterday. 179.181.83.108 (talk) 18:58, 19 January 2022 (UTC)
 * Red question icon with gradient background.svg Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format and provide a reliable source if appropriate. ScottishFinnishRadish (talk) 19:04, 19 January 2022 (UTC)

Wiki Education assignment: College Composition II
— Assignment last updated by Lindseybean28 (talk) 21:24, 9 May 2024 (UTC)

title: Talk:Activision


text:
Talk:Wild Willy Barrett

Untitled
why the lowercase letters? should this be moved?-R. fiend 20:37, 9 Aug 2004 (UTC)

Folk Singer?
Folk singer... it's like calling Leonardo da Vinci a 'painter'. I saw WWB on the Old Grey Whistle Test playing a guitar through a large Marshall stack for five minutes with no trace of tune or accompaniment. Made Jimi Hendrix look understated. Didn't sound like folk singing to me...

Perhaps describe Wild Willy as an "Experimental musician and multi-instrumentalist whose interests range from a modern folk idiom through psychadelia to pop." Can anyone do better?

Sounds about right to me, although modern technology reduces the need for large Marshall stacks now.. Wildbeest (talk) 21:15, 5 January 2012 (UTC)

16:50, 3 January 2012 (UTC) — Preceding unsigned comment added by The Yowser (talk • contribs)

External links modified
Hello fellow Wikipedians,

I have just added archive links to 2 one external links on Wild Willy Barrett. Please take a moment to review my edit. If necessary, add after the link to keep me from modifying it. Alternatively, you can add to keep me off the page altogether. I made the following changes:
 * Added archive https://web.archive.org/20080820062912/http://www.marshwoodvale.com/past%20articles/Wild%20Willy%20Barrett.htm to http://www.marshwoodvale.com/past%20articles/Wild%20Willy%20Barrett.htm
 * Added archive https://web.archive.org/20080509163317/http://www.musiczoo.co.uk/ to http://www.musiczoo.co.uk

When you have finished reviewing my changes, please set the checked parameter below to true to let others know.

Cheers. —cyberbot II  Talk to my owner :Online 03:08, 9 September 2015 (UTC)

title: Talk:Wild Willy Barrett