Source code for strawberryfields.compilers.gbs

# Copyright 2019 Xanadu Quantum Technologies Inc.

# Licensed under the Apache License, Version 2.0 (the "License");
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"""Compiler for the general Gaussian Boson Sampling class of circuits."""

from strawberryfields.program_utils import CircuitError, Command, group_operations
import strawberryfields.ops as ops

from .gaussian import Gaussian

[docs]class GBS(Gaussian): """Compiler for the general GBS class of circuits.""" short_name = "gbs" primitives = { # meta operations "All", "_New_modes", "_Delete", # state preparations "Vacuum", "Coherent", "Squeezed", "DisplacedSqueezed", "Thermal", "Gaussian", # measurements "MeasureHomodyne", "MeasureHeterodyne", "MeasureFock", "MeasureThreshold", # channels "LossChannel", "ThermalLossChannel", # single mode gates "Dgate", "Sgate", "Rgate", "Fouriergate", "BSgate", } decompositions = {"Xgate": {}, "Zgate": {}, "Fouriergate": {}, "S2gate": {}}
[docs] def compile(self, seq, registers): """Try to arrange a quantum circuit into a form suitable for Gaussian boson sampling. This method checks whether the circuit can be implemented as a Gaussian boson sampling problem, i.e., if it is equivalent to a circuit A+B, where the sequence A only contains Gaussian operations, and B only contains Fock measurements. If the answer is yes, the circuit is arranged into the A+B order, and all the Fock measurements are combined into a single :class:`MeasureFock` operation. Args: seq (Sequence[Command]): quantum circuit to modify registers (Sequence[RegRefs]): quantum registers Returns: List[Command]: modified circuit Raises: CircuitError: the circuit does not correspond to GBS """ A, B, C = group_operations(seq, lambda x: isinstance(x, ops.MeasureFock)) # C should be empty if C: raise CircuitError("Operations following the Fock measurements.") # A should only contain Gaussian operations # (but this is already guaranteed by group_operations() and our primitive set) # without Fock measurements GBS is pointless if not B: raise CircuitError("GBS circuits must contain Fock measurements.") # there should be only Fock measurements in B measured = set() for cmd in B: if not isinstance(cmd.op, ops.MeasureFock): raise CircuitError("The Fock measurements are not consecutive.") # combine the Fock measurements temp = set(cmd.reg) if measured & temp: raise CircuitError("Measuring the same mode more than once.") measured |= temp # replace B with a single Fock measurement B = [Command(ops.MeasureFock(), sorted(list(measured), key=lambda x: x.ind))] return super().compile(A + B, registers)