Fig. 9: Circuit implementation of the depolarising channel.
From: IBM Q Experience as a versatile experimental testbed for simulating open quantum systems
The circuit was run on ibmqx2. Qubit \({q}_{2}\) is used as the system qubit, as it is the only one that can be targeted with three CNOTs. The ancillae \({a}_{1},{a}_{2}\) and \({a}_{3}\) are initially in the state \(\left|0\right\rangle\) and rotated around the \(y\) direction by an angle \(\theta (p)=\frac{1}{2}\arccos (1-2p)\). They then act as controls for controlled-\(X\), -\(Y\) and -\(Z\) gates, respectively.
