Source code for

# Copyright 2019 Xanadu Quantum Technologies Inc.

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at


# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
This module contains functions for loading and saving Strawberry
Fields :class:`~.Program` objects from/to Blackbird scripts.
# pylint: disable=protected-access,too-many-nested-blocks
import os

import blackbird

import strawberryfields.program as sfp
import strawberryfields.parameters as sfpar
from . import ops

# for automodapi, do not include the classes that should appear under the top-level strawberryfields namespace
__all__ = ["to_blackbird", "to_program", "loads"]

[docs]def to_blackbird(prog, version="1.0"): """Convert a Strawberry Fields Program to a Blackbird Program. Args: prog (Program): the Strawberry Fields program version (str): Blackbird script version number Returns: blackbird.BlackbirdProgram: """ bb = blackbird.BlackbirdProgram(, version=version) # TODO not sure if this makes sense: the program has *already been* compiled using this target if is not None: # set the target bb._target["name"] = # set the run options if prog.run_options: bb._target["options"].update(prog.run_options) if prog.backend_options: bb._target["options"].update(prog.backend_options) # fill in the quantum circuit for cmd in prog.circuit: op = {"kwargs": {}, "args": []} op["op"] = cmd.op.__class__.__name__ op["modes"] = [i.ind for i in cmd.reg] if "Measure" in op["op"]: # special case to take into account 'select' keyword argument if is not None: op["kwargs"]["select"] = if cmd.op.p: # argument is quadrature phase op["kwargs"]["phi"] = cmd.op.p[0] if op["op"] == "MeasureFock": # special case to take into account 'dark_counts' keyword argument if cmd.op.dark_counts is not None: op["kwargs"]["dark_counts"] = cmd.op.dark_counts else: for a in cmd.op.p: if sfpar.par_is_symbolic(a): # SymPy object, convert to string a = str(a) op["args"].append(a) bb._operations.append(op) return bb
[docs]def to_program(bb): """Convert a Blackbird Program to a Strawberry Fields Program. Args: bb (blackbird.BlackbirdProgram): the input Blackbird program object Returns: Program: corresponding SF program """ # create a SF program if not bb.modes: # we can't return an empty program, since we don't know how many modes # to initialize the Program object with. raise ValueError("Blackbird program contains no quantum operations!") prog = sfp.Program(max(bb.modes) + 1, # append the quantum operations with prog.context as q: for op in bb.operations: # check if operation name is in the list of # defined StrawberryFields operations. # This is used by checking against the __all__ # module attribute, which contains the names # of all defined quantum operations if op["op"] in ops.__all__: # get the quantum operation from the sf.ops module gate = getattr(ops, op["op"]) else: raise NameError("Quantum operation {} not defined!".format(op["op"])) # create the list of regrefs regrefs = [q[i] for i in op["modes"]] if "args" in op: # the gate has arguments args = op["args"] kwargs = op["kwargs"] # Convert symbolic expressions in args/kwargs containing measured and free parameters to # symbolic expressions containing the corresponding MeasuredParameter and FreeParameter instances. args = sfpar.par_convert(args, prog) vals = sfpar.par_convert(kwargs.values(), prog) kwargs = dict(zip(kwargs.keys(), vals)) gate(*args, **kwargs) | regrefs # pylint:disable=expression-not-assigned else: # the gate has no arguments gate | regrefs # pylint:disable=expression-not-assigned,pointless-statement prog._target =["name"] if "shots" in["options"]: prog.run_options["shots"] =["options"]["shots"] if "cutoff_dim" in["options"]: prog.backend_options["cutoff_dim"] =["options"]["cutoff_dim"] return prog
[docs]def save(f, prog): """Saves a quantum program to a Blackbird .xbb file. **Example:** .. code-block:: python3 prog = sf.Program(3) with prog.context as q: ops.Sgate(0.543) | q[1] ops.BSgate(0.6, 0.1) | (q[2], q[0]) ops.MeasureFock() | q"program1.xbb", prog) This will create the following Blackbird file: .. code-block:: pycon >>> f = open("program1.xbb").read() >>> print(f) name None version 1.0 Sgate(0.543, 0.0) | 1 BSgate(0.6, 0.1) | [2, 0] MeasureFock() | [0, 1, 2] Args: f (Union[file, str, pathlib.Path]): File or filename to which the data is saved. If file is a file-object, then the filename is unchanged. If file is a string or Path, a .xbb extension will be appended to the file name if it does not already have one. prog (Program): Strawberry Fields program """ own_file = False bb = to_blackbird(prog).serialize() if hasattr(f, "read"): # argument file is a file-object fid = f else: # argument file is a string or Path filename = os.fspath(f) if not filename.endswith(".xbb"): filename = filename + ".xbb" fid = open(filename, "w") # this function owns the open file, # must remember to safely close it. own_file = True try: fid.write(bb) finally: if own_file: # safely close the file fid.close()
[docs]def loads(s): """Load a quantum program from a string. Args: s (str): string containing the Blackbird circuit Returns: prog (Program): Strawberry Fields program """ bb = blackbird.loads(s) return to_program(bb)
[docs]def load(f): """Load a quantum program from a Blackbird .xbb file. **Example:** The following Blackbird file, ``program1.xbb``, .. code-block:: python3 name test_program version 1.0 Sgate(0.543, 0.0) | 1 BSgate(0.6, 0.1) | [2, 0] MeasureFock() | [0, 1, 2] can be imported into Strawberry Fields using the ``loads`` function: >>> sf.loads("program1.xbb") >>> 'test_program' >>> prog.num_subsystems 3 >>> prog.print() Sgate(0.543, 0) | (q[1]) BSgate(0.6, 0.1) | (q[2], q[0]) MeasureFock | (q[0], q[1], q[2]) Args: f (Union[file, str, pathlib.Path]): File or filename from which the data is loaded. If file is a string or Path, a value with the .xbb extension is expected. Returns: prog (Program): Strawberry Fields program """ own_file = False try: if hasattr(f, "read"): # argument file is a file-object fid = f else: # argument file is a Path or string filename = os.fspath(f) fid = open(filename, "r") own_file = True except TypeError: raise ValueError("file must be a string, pathlib.Path, or file-like object") try: bb_str = finally: if own_file: # safely close the file fid.close() # load blackbird program return loads(bb_str)