def compile_tomo_expts(self, pauli_list=None):
"""
This method compiles the tomography experiment circuits
and prepares them for simulation.
Every time the circuits are adjusted,
re-compiling the tomography experiments
is required to affect the outcome.
"""
self.offset = 0
# use Forest's sorting algo from the Tomography suite
# to group Pauli measurements together
experiments = []
if pauli_list is None:
pauli_list = self.pauli_list
for term in pauli_list:
# if the Pauli term is an identity operator,
# add the term's coefficient directly to the VQE class' offset
if len(term.operations_as_set()) == 0:
self.offset += term.coefficient.real
else:
# initial state and term pair.
experiments.append(ExperimentSetting(
TensorProductState(),
term))
suite = Experiment(experiments, program=Program())
gsuite = group_experiments(suite)
grouped_list = []
for setting in gsuite:
group = []
for term in setting:
group.append(term.out_operator)
grouped_list.append(group)
if self.verbose:
print('Number of tomography experiments: ', len(grouped_list))
self.experiment_list = []
for group in grouped_list:
self.experiment_list.append(
GroupedPauliSetting(group,
qc=self.qc,
ref_state=self.ref_state,
ansatz=self.ansatz,
shotN=self.shotN,
parametric_way=self.parametric_way,
n_qubits=self.n_qubits,
method=self.method,
verbose=self.verbose,
cq=self.custom_qubits,
))
def expval(self, observable):
wires = observable.wires
# Single-qubit observable
if len(wires) == 1:
# identify Experiment Settings for each of the possible single-qubit observables
wire = wires[0]
qubit = self.wiring[wire]
d_expt_settings = {
"Identity":
[ExperimentSetting(TensorProductState(), sI(qubit))],
"PauliX": [ExperimentSetting(TensorProductState(), sX(qubit))],
"PauliY": [ExperimentSetting(TensorProductState(), sY(qubit))],
"PauliZ": [ExperimentSetting(TensorProductState(), sZ(qubit))],
"Hadamard": [
ExperimentSetting(TensorProductState(),
float(np.sqrt(1 / 2)) * sX(qubit)),
ExperimentSetting(TensorProductState(),
float(np.sqrt(1 / 2)) * sZ(qubit))
]
}
# expectation values for single-qubit observables
if observable.name in [
"PauliX", "PauliY", "PauliZ", "Identity", "Hadamard"
]:
prep_prog = Program()
for instr in self.program.instructions:
if isinstance(instr, Gate):
# split gate and wires -- assumes 1q and 2q gates
tup_gate_wires = instr.out().split(' ')
gate = tup_gate_wires[0]
str_instr = str(gate)
# map wires to qubits
for w in tup_gate_wires[1:]:
str_instr += f' {int(w)}'
prep_prog += Program(str_instr)
if self.readout_error is not None:
prep_prog.define_noisy_readout(qubit,
p00=self.readout_error[0],
p11=self.readout_error[1])
# All observables are rotated and can be measured in the PauliZ basis
tomo_expt = Experiment(settings=d_expt_settings["PauliZ"],
program=prep_prog)
grouped_tomo_expt = group_experiments(tomo_expt)
meas_obs = list(
measure_observables(
self.qc,
grouped_tomo_expt,
active_reset=self.active_reset,
symmetrize_readout=self.symmetrize_readout,
calibrate_readout=self.calibrate_readout))
return np.sum(
[expt_result.expectation for expt_result in meas_obs])
elif observable.name == 'Hermitian':
# <H> = \sum_i w_i p_i
Hkey = tuple(par[0].flatten().tolist())
w = self._eigs[Hkey]['eigval']
return w[0] * p0 + w[1] * p1
return super().expval(observable)
def expval(self, observable, wires, par):
# Single-qubit observable
if len(wires) == 1:
# identify Experiment Settings for each of the possible single-qubit observables
wire = wires[0]
qubit = self.wiring[wire]
d_expt_settings = {
"Identity":
[ExperimentSetting(TensorProductState(), sI(qubit))],
"PauliX": [ExperimentSetting(TensorProductState(), sX(qubit))],
"PauliY": [ExperimentSetting(TensorProductState(), sY(qubit))],
"PauliZ": [ExperimentSetting(TensorProductState(), sZ(qubit))],
"Hadamard": [
ExperimentSetting(TensorProductState(),
float(np.sqrt(1 / 2)) * sX(qubit)),
ExperimentSetting(TensorProductState(),
float(np.sqrt(1 / 2)) * sZ(qubit))
]
}
# expectation values for single-qubit observables
if observable in [
"PauliX", "PauliY", "PauliZ", "Identity", "Hadamard"
]:
prep_prog = Program()
for instr in self.program.instructions:
if isinstance(instr, Gate):
# split gate and wires -- assumes 1q and 2q gates
tup_gate_wires = instr.out().split(' ')
gate = tup_gate_wires[0]
str_instr = str(gate)
# map wires to qubits
for w in tup_gate_wires[1:]:
str_instr += f' {int(w)}'
prep_prog += Program(str_instr)
if self.readout_error is not None:
prep_prog.define_noisy_readout(qubit,
p00=self.readout_error[0],
p11=self.readout_error[1])
tomo_expt = Experiment(settings=d_expt_settings[observable],
program=prep_prog)
grouped_tomo_expt = group_experiments(tomo_expt)
meas_obs = list(
measure_observables(
self.qc,
grouped_tomo_expt,
active_reset=self.active_reset,
symmetrize_readout=self.symmetrize_readout,
calibrate_readout=self.calibrate_readout))
return np.sum(
[expt_result.expectation for expt_result in meas_obs])
elif observable == 'Hermitian':
# <H> = \sum_i w_i p_i
Hkey = tuple(par[0].flatten().tolist())
w = self._eigs[Hkey]['eigval']
return w[0] * p0 + w[1] * p1
# Multi-qubit observable
# ----------------------
# Currently, we only support qml.expval.Hermitian(A, wires),
# where A is a 2^N x 2^N matrix acting on N wires.
#
# Eventually, we will also support tensor products of Pauli
# matrices in the PennyLane UI.
probs = self.probabilities(wires)
if observable == 'Hermitian':
Hkey = tuple(par[0].flatten().tolist())
w = self._eigs[Hkey]['eigval']
# <A> = \sum_i w_i p_i
return w @ probs
def expval(self, observable):
wires = observable.wires
# `measure_observables` called only when parametric compilation is turned off
if not self.parametric_compilation:
# Single-qubit observable
if len(wires) == 1:
# Ensure sensible observable
assert observable.name in [
"PauliX", "PauliY", "PauliZ", "Identity", "Hadamard"
], "Unknown observable"
# Create appropriate PauliZ operator
wire = wires[0]
qubit = self.wiring[wire]
pauli_obs = sZ(qubit)
# Multi-qubit observable
elif len(wires) > 1 and isinstance(
observable, Tensor) and not self.parametric_compilation:
# All observables are rotated to be measured in the Z-basis, so we just need to
# check which wires exist in the observable, map them to physical qubits, and measure
# the product of PauliZ operators on those qubits
pauli_obs = sI()
for wire in observable.wires:
qubit = wire
pauli_obs *= sZ(self.wiring[qubit])
# Program preparing the state in which to measure observable
prep_prog = Program()
for instr in self.program.instructions:
if isinstance(instr, Gate):
# split gate and wires -- assumes 1q and 2q gates
tup_gate_wires = instr.out().split(" ")
gate = tup_gate_wires[0]
str_instr = str(gate)
# map wires to qubits
for w in tup_gate_wires[1:]:
str_instr += f" {int(w)}"
prep_prog += Program(str_instr)
if self.readout_error is not None:
for wire in observable.wires:
qubit = wire
prep_prog.define_noisy_readout(self.wiring[qubit],
p00=self.readout_error[0],
p11=self.readout_error[1])
# Measure out multi-qubit observable
tomo_expt = Experiment(
settings=[ExperimentSetting(TensorProductState(), pauli_obs)],
program=prep_prog)
grouped_tomo_expt = group_experiments(tomo_expt)
meas_obs = list(
measure_observables(
self.qc,
grouped_tomo_expt,
active_reset=self.active_reset,
symmetrize_readout=self.symmetrize_readout,
calibrate_readout=self.calibrate_readout,
))
# Return the estimated expectation value
return np.sum(
[expt_result.expectation for expt_result in meas_obs])
# Calculation of expectation value without using `measure_observables`
return super().expval(observable)