sf.TDMProgram¶

class TDMProgram(N, name=None)[source]¶

Bases: strawberryfields.program.Program

Represents a photonic quantum circuit in the time domain encoding.

The TDMProgram class provides a context manager for easily defining a single time-bin of the time domain algorithm. As with the standard Program, Strawberry Fields operations are appended to the time domain program using the Python-embedded Blackbird syntax.

Once created, time domain programs can be executed on Strawberry Fields’ Gaussian backend in an efficient manner, or submitted to be executed on compatible hardware.

Parameters

N (int or Sequence[int]) – If an integer, the number of concurrent (or ‘alive’) modes in each time bin. Alternatively, a sequence of integers may be provided, corresponding to the number of concurrent modes in the possibly multiple bands in the circuit.
name (str) – the program name (optional)

Example

Below, we create a time domain program with 2 concurrent modes:

>>> import strawberryfields as sf
>>> from strawberryfields import ops
>>> prog = sf.TDMProgram(N=2)

Once created, we can construct the program using the prog.context() context manager.

>>> with prog.context([1, 2], [3, 4]) as (p, q):
...     ops.Sgate(0.7, 0) | q[1]
...     ops.BSgate(p[0]) | (q[0], q[1])
...     ops.MeasureHomodyne(p[1]) | q[0]

Printing out this program:

>>> prog.print()
Sgate(0.7, 0) | (q[1])
BSgate({p0}, 0) | (q[0], q[1])
MeasureHomodyne({p1}) | (q[0])

Note that p0 and p1 are symbolic gate parameters; to access the numeric values, we must use the prog.parameters attribute:

>>> prog.parameters
{'p0': [1, 2], 'p1': [3, 4]}

When we simulate a time-domain program, it is first unrolled by the engine; unrolling involves explicitly repeating the single time-bin sequence constructed above, and shifting the simulated registers. This ‘unrolling’ procedure is performed automatically by the engine, however, we can visualize the unrolled program by calling the unroll() method.

>>> prog.unroll(shots=3).print()
Sgate(0.7, 0) | (q[1])
BSgate(1, 0) | (q[0], q[1])
MeasureHomodyne(3) | (q[0])
Sgate(0.7, 0) | (q[0])
BSgate(2, 0) | (q[1], q[0])
MeasureHomodyne(4) | (q[1])
Sgate(0.7, 0) | (q[1])
BSgate(1, 0) | (q[0], q[1])
MeasureHomodyne(3) | (q[0])
Sgate(0.7, 0) | (q[0])
BSgate(2, 0) | (q[1], q[0])
MeasureHomodyne(4) | (q[1])
Sgate(0.7, 0) | (q[1])
BSgate(1, 0) | (q[0], q[1])
MeasureHomodyne(3) | (q[0])
Sgate(0.7, 0) | (q[0])
BSgate(2, 0) | (q[1], q[0])
MeasureHomodyne(4) | (q[1])

Note the ‘shifting’ of the measured registers — this optimization allows for time domain algorithms to be simulated in memory much more efficiently:

>>> eng = sf.Engine("gaussian")
>>> results = eng.run(prog, shots=3)

The engine automatically takes this mode shifting into account; returned samples will always be transformed to match the modes specified during construction:

>>> print(results.samples_dict)
{0: [array([1.26208025]), array([1.53910032]), array([-1.29648336]),
array([0.75743215]), array([-0.17850101]), array([-1.44751996])]}

Note that, unlike the standard Program, the TDM context manager has both required and essential arguments:

Positional arguments are used to pass sequences of gate arguments to apply per time-bin. Within the context, these are accessible via the p context variable; p[i] corresponds to the i-th positional arguments.

All positional arguments corresponding to sequences of gate arguments must be the same length. This length determines how many time-bins are present in the TDM program.

If the p variable is not used, the gate argument is assumed to be constant across all time-bins.
shift="default" (str or int): Defines how the qumode register is shifted at the end of each time bin. If set to "default", the qumode register is shifted such that each measured qumode reappears as a fresh mode at the beginning of the subsequent time bin. This is equivalent to a measured qumode being removed from the representation (by measurement) and a new one being added (by a light source). If set to an integer value, the register will shift by a step size of this integer at the end of each time bin.

Attributes

`compile_info`	The device specification and the compiler that was used during compilation.
`concurr_modes`	The number of concurrent modes in the program.
`has_feed_forward`	Indicate if any operation in the program uses feed-forwarding or not.
`has_post_selection`	Indicate if any operation in the program uses post-selection or not.
`is_unrolled`	Whether the circuit is either unrolled or space-unrolled.
`measured_modes`	The number of measured modes in the program returned as a list.
`num_subsystems`	Return the current number of valid quantum modes.
`parameters`	Return the parameters of the `TDMProgram` as a dictionary with the parameter name as keys, and the parameter lists as values.
`register`	Return a tuple of all the currently valid quantum modes.
`spatial_modes`	The number of spatial modes in the program.
`target`	The target specification the program has been compiled against.
`timebins`	The number of timebins in the program.

compile_info¶

The device specification and the compiler that was used during compilation.

If the program has not been compiled, this will return None.

Returns: device specification and the short name of the Compiler that was used if compiled, otherwise None
Return type: tuple or None

concurr_modes¶: The number of concurrent modes in the program.

has_feed_forward¶

Indicate if any operation in the program uses feed-forwarding or not.

Returns: whether feed-forwarding is used anywhere in the circuit
Return type: bool

has_post_selection¶

Indicate if any operation in the program uses post-selection or not.

Returns: whether post-selection is used anywhere in the circuit
Return type: bool

is_unrolled¶: Whether the circuit is either unrolled or space-unrolled.

measured_modes¶: The number of measured modes in the program returned as a list.

num_subsystems¶

Return the current number of valid quantum modes.

Returns: number of currently valid register subsystems
Return type: int

parameters¶: Return the parameters of the TDMProgram as a dictionary with the parameter name as keys, and the parameter lists as values.

register¶

Return a tuple of all the currently valid quantum modes.

Returns: valid subsystem references
Return type: tuple[RegRef]

spatial_modes¶: The number of spatial modes in the program.

target¶

The target specification the program has been compiled against.

If the program has not been compiled, this will return None.

Returns: the short name of the target Compiler template if compiled, otherwise None
Return type: str or None

timebins¶: The number of timebins in the program.

Methods

`append`(op, reg)	Append a command to the program.
`apply_op`(cmd, modes, t)	Apply a particular operation on register q at timestep t.
`assert_modes`(device)	Check that the number of modes in the program is valid.
`bind_params`(binding)	Binds the free parameters of the program to the given values.
`can_follow`(prev)	Check whether this program can follow the given program.
`compile`(*[, device, compiler])	Compile the program given a Strawberry Fields photonic compiler, or hardware device specification.
`context`(*args[, shift])	Syntactic sugar for defining a Program using the `with` statement.
`draw_circuit`([tex_dir, write_to_file])	Draw the circuit using the Qcircuit \(\LaTeX\) package.
`equivalence`(prog, **kwargs)	Checks if two programs are equivalent.
`get_crop_value`()	Calculates and returns the value for where to crop the gate parameters.
`get_delays`()	Calculates and returns the loop delays.
`lock`()	Finalize the program.
`optimize`()	Simplify and optimize the program.
`params`(*args)	Create and access free circuit parameters.
`print`([print_fn])	Print the program contents using Blackbird syntax.
`roll`()	Represent the program in a compressed way without unrolling the for loops.
`space_unroll`([shots])	Construct the space-unrolled program and set it to `self.circuit`.
`unroll`([shots])	Construct program with the register shift and store it in `self.circuit`.

append(op, reg)¶

Append a command to the program.

Parameters

op (Operation) – quantum operation
reg (list[int, RegRef]) – register subsystem(s) to apply it to

Returns

subsystem list as RegRefs

Return type

list[RegRef]

apply_op(cmd, modes, t)[source]¶: Apply a particular operation on register q at timestep t.

assert_modes(device)[source]¶

Check that the number of modes in the program is valid.

Note

device.modes must be a dictionary containing the maximum number of allowed measurements for the specified target.

Parameters: device (strawberryfields.DeviceSpec) – device specification object to use

bind_params(binding)¶

Binds the free parameters of the program to the given values.

Parameters: binding (dict[Union[str, FreeParameter], Any]) – mapping from parameter names (or the parameters themselves) to parameter values
Raises: ParameterError – tried to bind an unknown parameter

can_follow(prev)¶

Check whether this program can follow the given program.

This requires that the final RegRef state of the first program matches the initial RegRef state of the second program, i.e., they have the same number number of RegRefs, all with identical indices and activity states.

Parameters: prev (Program) – preceding program fragment
Returns: True if the Program can follow prev
Return type: bool

compile(*, device=None, compiler=None, **kwargs)¶

Compile the program given a Strawberry Fields photonic compiler, or hardware device specification.

The compilation process can involve up to three stages:

Validation: Validates properties of the program, including number of modes and allowed operations, making sure all the Operations used are accepted by the compiler.
Decomposition: Once the program has been validated, decomposition are performed, transforming certain gates into sequences of simpler gates.
General compilation: Finally, the compiler might specify bespoke compilation logic for transforming the quantum circuit into an equivalent circuit which can be executed by the target device.

Example:

The gbs compile target will compile a circuit consisting of Gaussian operations and Fock measurements into canonical Gaussian boson sampling form.

>>> prog2 = prog.compile(compiler="gbs")

For a hardware device a Device object, and optionally a specified compile strategy, must be supplied. If no compile strategy is supplied the default compiler from the device specification is used.

>>> eng = sf.RemoteEngine("X8")
>>> device = eng.device_spec
>>> prog2 = prog.compile(device=device, compiler="Xcov")

Parameters

device (Device) – device specification object to use for program compilation
compiler (str, Compiler) – Compiler name or compile strategy to use. If a device is specified, this overrides the compile strategy specified by the hardware Device.

Keyword Arguments

optimize (bool) – If True, try to optimize the program by merging and canceling gates. The default is False.
warn_connected (bool) – If True, the user is warned if the quantum circuit is not weakly connected. The default is True.
shots (int) – Number of times the program measurement evaluation is repeated. Passed along to the compiled program’s run_options.

Returns

compiled program

Return type

Program

context(*args, shift='default')[source]¶

Syntactic sugar for defining a Program using the with statement.

The Program object itself acts as the context manager.

draw_circuit(tex_dir='./circuit_tex', write_to_file=True)¶

Draw the circuit using the Qcircuit \(\LaTeX\) package.

This will generate the LaTeX code required to draw the quantum circuit diagram corresponding to the Program.

The drawing of the following Xanadu supported operations are currently supported:

Gate type	Supported gates
Single mode gates	`Dgate`, `Xgate`, `Zgate`, `Sgate`, `Rgate`, `Pgate`, `Vgate`, `Kgate`, `Fouriergate`
Two mode gates	`BSgate`, `S2gate`, `CXgate`, `CZgate`, `CKgate`

Note

Measurement operations MeasureHomodyne, MeasureHeterodyne, and MeasureFock are not currently supported.

Parameters

tex_dir (str) – relative directory for latex document output
write_to_file (bool) – if False, no output file is created

Returns

filename of the written tex document and the written tex content

Return type

list[str]

equivalence(prog, **kwargs)¶

Checks if two programs are equivalent.

This function converts the program lists into directed acyclic graphs, and runs the NetworkX is_isomorphic graph function in order to determine if the two programs are equivalent.

Note

This method is a convenience method, wrapping the program_equivalence() function in the program utils module.

Parameters

prog (strawberryfields.program.Program) – quantum program to check equivalence with

Keyword Arguments

compare_params (bool) – Set to False to turn of comparing program parameters; equivalency will only take into account the operation order.
atol (float) – the absolute tolerance parameter for checking quantum operation parameter equality
rtol (float) – the relative tolerance parameter for checking quantum operation parameter equality

Returns

returns True if two quantum programs are equivalent

Return type

bool

get_crop_value()[source]¶

Calculates and returns the value for where to crop the gate parameters.

This method returns the number of vacuum modes arriving at the detector before the first computational mode for any job run on a single spatial mode TDM program.

Returns: crop parameter
Return type: int

get_delays()[source]¶

Calculates and returns the loop delays.

This method calculates the delays present in the circuit by using the modes in which beamsplitters are acting on: on TMDPrograms with a single spatial mode, loop crossings always correspond to beamsplitters; if no beamsplitters are presents this method returns an empty list.

Returns: A list where the length represent the number of loops present in the circuit and every entry corresponds to the number of modes that will fit at the same time in each loop.
Return type: List[int]

lock()¶

Finalize the program.

When a Program is locked, no more Commands can be appended to it. The locking happens when the program is run, compiled, or a successor Program is constructed, in order to ensure that the RegRef state of the Program does not change anymore.

optimize()¶

Simplify and optimize the program.

The simplifications are based on the algebraic properties of the gates, e.g., combining two consecutive gates of the same gate family.

Returns a copy of the program, sharing RegRefs with the original.

See optimize_circuit().

Returns: optimized copy of the program
Return type: Program

params(*args)¶

Create and access free circuit parameters.

Returns the named free parameters. If a parameter does not exist yet, it is created and returned.

Parameters: *args (tuple[str]) – name(s) of the free parameters to access
Returns: requested parameter(s)
Return type: FreeParameter, list[FreeParameter]

print(print_fn=<built-in function print>)¶

Print the program contents using Blackbird syntax.

Example:

# create a 3 mode quantum program
prog = sf.Program(3)

with prog.context as q:
    ops.Sgate(0.54) | q[0]
    ops.Sgate(0.54) | q[1]
    ops.Sgate(0.54) | q[2]
    ops.BSgate(0.43, 0.1) | (q[0], q[2])
    ops.BSgate(0.43, 0.1) | (q[1], q[2])
    ops.MeasureFock() | q

>>> prog.print()
Sgate(0.54, 0) | (q[0])
Sgate(0.54, 0) | (q[1])
Sgate(0.54, 0) | (q[2])
BSgate(0.43, 0.1) | (q[0], q[2])
BSgate(0.43, 0.1) | (q[1], q[2])
MeasureFock | (q[0], q[1], q[2])

Parameters: print_fn (function) – optional custom function to use for string printing

roll()[source]¶: Represent the program in a compressed way without unrolling the for loops.

space_unroll(shots=1)[source]¶

Construct the space-unrolled program and set it to self.circuit.

Calls the _unroll_program method which constructs the space-unrolled single-shot program, storing it in self.space_unrolled_circuit when run for the first time, and returns the space-unrolled program.

Parameters: shots (int) – the number of times the circuit should be repeated

unroll(shots=1)[source]¶

Construct program with the register shift and store it in self.circuit.

Calls the _unroll_program method which constructs the unrolled single-shot program, storing it in self.unrolled_circuit when run for the first time, and returns the unrolled program.

Parameters: shots (int) – the number of times the circuit should be repeated

code/api/strawberryfields.TDMProgram

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sf.TDMProgram¶

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