The Wavefunction device¶
rigetti.wavefunction device provides an interface between PennyLane and
the Forest SDK wavefunction simulator. Because
the wavefunction simulator allows access and manipulation of the underlying quantum state vector,
rigetti.wavefunction is able to support the full suite of PennyLane and Quil quantum operations and observables.
In addition, it is generally faster than running equivalent simulations on the QVM, as the final state can be inspected and the expectation value calculated analytically, rather than by sampling measurements.
rigetti.wavefunction is initialized with
that the exact analytic expectation value is to be returned.
If the number of trials or shots provided to the
instead non-zero, a spectral decomposition is performed and a Bernoulli distribution
is constructed and sampled. This allows the
rigetti.wavefunction device to
‘approximate’ the effect of sampling the expectation value.
You can instantiate the device in PennyLane as follows:
import pennylane as qml dev_wfun = qml.device('rigetti.wavefunction', wires=2)
This device can then be used just like other devices for the definition and evaluation of QNodes within PennyLane.
A simple quantum function that returns the expectation value and variance of a measurement and depends on three classical input parameters would look like:
@qml.qnode(dev_wfun) def circuit(x, y, z): qml.RZ(z, wires=) qml.RY(y, wires=) qml.RX(x, wires=) qml.CNOT(wires=[0, 1]) return qml.expval(qml.PauliZ(0)), var(qml.PauliZ(1))
You can then execute the circuit like any other function to get the quantum mechanical expectation value and variance:
>>> circuit(0.2, 0.1, 0.3) array([0.97517033, 0.04904283])
All devices support all PennyLane operations and observables, with the exception of the PennyLane
QubitStateVector state preparation operation.
QVM and quilc server configuration¶
If using the downloadable Rigetti SDK with the default server configurations
for the QVM and the Quil compiler (i.e., you launch them with the commands
qvm -S and
quilc -R), then no special configuration is needed.
If using a non-default port or host for either of the servers, see the
pyQuil configuration documentation
for details on how to override the default values.