PrepareSingleQubitIdentity operation


This documentation refers to the Classic QDK, which has been replaced by the Modern QDK.

Please see for the API documentation for the Modern QDK.

Namespace: Microsoft.Quantum.Preparation

Package: Microsoft.Quantum.Standard

Prepares a qubit in the maximally mixed state.

operation PrepareSingleQubitIdentity (qubit : Qubit) : Unit


Prepares the given qubit in the $\boldone / 2$ state by applying the depolarizing channel $$ \begin{align} \Omega(\rho) \mathrel{:=} \frac{1}{4} \sum_{\mu \in {0, 1, 2, 3}} \sigma_{\mu} \rho \sigma_{\mu}^{\dagger}, \end{align} $$ where $\sigma_i$ is the $i$th Pauli operator, and where $\rho$ is a density operator representing a mixed state.


qubit : Qubit

A qubit whose state is to be depolarized in the manner described above.

Output : Unit


The mixed state $\boldone / 2$ describing the result of applying this operation to a state implicitly describes an expectation value over random choices made in this operation. Thus, for any single application, this operation maps pure states to pure states, but it acts as described in expectation. In particular, this operation can be used in process tomography to measure the non-unital components of a channel.