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In computing science, the controlled NOT gate (also C-NOT or CNOT) is a quantum gate that is an essential component in the construction of a quantum computer. It can be used to entangle and disentangle EPR states. Any quantum circuit can be simulated to an arbitrary degree of accuracy using a combination of CNOT gates and single qubit rotations. The CNOT gate is the "quantization" of a classical gate. ==Operation== The CNOT gate operates on a quantum register consisting of 2 qubits. The CNOT gate flips the second qubit (the target qubit) if and only if the first qubit (the control qubit) is . If one allows only as input values for both qubits, the TARGET output of the CNOT gate corresponds to the result of a classical XOR gate. Fixing CONTROL as , the TARGET output of the CNOT gate yields the result of a classical NOT gate. More generally, the inputs are allowed to be a linear superposition of . The CNOT gate transforms the quantum state: into: The CNOT gate can be represented by the matrix (permutation matrix form): : The first experimental realization of a CNOT gate was accomplished in 1995. Here, a single Beryllium ion in a trap was used. The two qubits were encoded into an optical state and into the vibrational state of the ion within the trap. At the time of the experiment, the reliability of the CNOT-operation was measured to be on the order of 90%. In addition to a regular controlled NOT gate, one could construct a function-controlled NOT gate, which accepts an arbitrary number ''n''+1 of qubits as input, where ''n''+1 is greater than or equal to 2 (a quantum register). This gate flips the last qubit of the register if and only if a built-in function, with the first ''n'' qubits as input, returns a 1. The function-controlled NOT gate is an essential element of the Deutsch-Jozsa algorithm. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Controlled NOT gate」の詳細全文を読む スポンサード リンク
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