The Mixed Simulator Device¶
You can instantiate the mixed-state simulator device in PennyLane as follows:
import pennylane as qml dev = qml.device('cirq.mixedsimulator', wires=2)
This device can then be used just like other devices for the definition and evaluation of QNodes within PennyLane.
cirq.simulator backend, this device also supports several of Cirq’s custom non-unitary channels,
from pennylane_cirq import ops @qml.qnode(dev) def circuit(x, p, q): qml.RX(x, wires=) ops.BitFlip(p, wires=) ops.Depolarize(q, wires=) qml.CNOT(wires=[0, 1]) return qml.expval(qml.PauliZ(wires=1)) circuit(0.2, 0.1, 0.3)
This device stores the internal state of the quantum simulation as a density matrix.
This has additional memory overhead compared to pure-state simulation, but allows for
additional channels to be performed. The density matrix can be accessed after a circuit
Cirq has different ways of defining qubits, e.g.,
GridQubit. The Cirq device therefore accepts
an additional argument
qubits=None that you can use to define your own
qubits and give them to the device as a list.
import cirq qubits = [ cirq.GridQubit(0, 0), cirq.GridQubit(0, 1), cirq.GridQubit(1, 0), cirq.GridQubit(1, 1), ] dev = qml.device("cirq.mixedsimulator", wires=4, qubits=qubits)
The wire of each qubit corresponds to its index in the
qubit list. In the above example,
the wire 2 corresponds to
If no qubits are given, the plugin will create an array of