Reset instruction

A reset instruction resets the state of the qubit to \(|0\rangle\). It does this by first measuring the qubit and then, conditioned on the outcome being 1, applying a Pauli X gate.

Note

Even though the reset instruction internally measures the qubit state, it does not store the measurement outcome in the measurement register, i.e., the measurement register is unaffected by the reset instruction. The measurement outcome is only used to determine whether or not a Pauli X gate needs to be performed, in order to bring the qubit into the state \(|0\rangle\).

The general form of a reset instruction is as follows:

 reset qubit-argument

Grammar for reset instruction

reset-instruction:
  reset
  reset qubit-argument

qubit-argument:
  qubit-variable
  qubit-index

qubit-variable:
  identifier

qubit-index:
  index

Example

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qubit q
qubit[5] qq
reset

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qubit q
reset q

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qubit[5] q
reset q[2, 4]

Note

The reset instruction accepts SGMQ notation, similar to gates.

The following code snippet shows how the reset instruction might be used in context.

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version 3.0

qubit[2] q
bit[2] b

H q[0]
CNOT q[0], q[1]

reset q[0]  // Resets the state of qubit q[0] to |0>

b = measure q

The reset instruction is performed by measuring q[0] along the computational basis. Based on the measurement outcome, either no operation is performed (in case the outcome is 0) or a Pauli X gate is applied (in case the outcome is 1). The result of the subsequent measure instruction will be 00 in roughly half of the cases and 10 in the remaining cases, with the qubit register indices decreasing from left to right, i.e., q[n]...q[0].

Info

Qubits that are part of an entangled state, are disentangled from that state, when the reset instruction is applied to them.