Transpiler

The generate_boxing_pass_manager() function is a flexible and convenient tool to build a qiskit.transpiler.PassManager able to group the circuit instructions into annotated boxes. Whether you want to automate your workflow, you are interested in trying different boxing strategies for your circuits, or you simply want a quick and easy alternative to grouping and annotating by hand, generate_boxing_pass_manager() can help you achieve your goals.

This guide illustrates how to use generate_boxing_pass_manager() and its arguments. To highlight the effects of each of the function’s arguments, in the sections that follow we will mainly target the circuit below.

from qiskit.circuit import Parameter, QuantumCircuit

circuit = QuantumCircuit(4, 7)
circuit.h(1)
circuit.h(2)
circuit.cz(1, 2)
circuit.h(1)
circuit.cx(1, 0)
circuit.cx(2, 3)
circuit.measure(range(1, 4), range(3))
circuit.cx(0, 1)
circuit.cx(1, 2)
circuit.cx(2, 3)
for qubit in range(4):
    circuit.rz(Parameter(f"th_{qubit}"), qubit)
    circuit.rx(Parameter(f"phi_{qubit}"), qubit)
    circuit.rz(Parameter(f"lam_{qubit}"), qubit)
circuit.measure(range(4), range(3, 7))

circuit.draw("mpl", scale=0.8)

Group operations into boxes

The argument enable_gates can be set to True or False to specify whether the two-qubit gates should be grouped into boxes. Similarly, enable_measures allows specifying whether or not measurements should be grouped. The following snippet shows an example where both gates and measurements are grouped.

from samplomatic.transpiler import generate_boxing_pass_manager

boxing_pass_manager = generate_boxing_pass_manager(
    enable_gates=True,
    enable_measures=True,
)
transpiled_circuit = boxing_pass_manager.run(circuit)
transpiled_circuit.draw("mpl", scale=0.8)

As can be seen in the figure, the pass manager creates boxes of two types: those that contain a single layer of two-qubit gates, and those that contain a single layer of measurements. This separation reflects standard practices in noise learning and mitigation protocols, which usually target layers of homogeneous operations. The two-qubit gates and measurements are placed in the leftmost box that can accommodate them, and every single-qubit gates is placed in the same box as the two-qubit gate or measurement they preceed.

The following snippet shows another example where enable_gates is set to False. As can be seen, the two-qubit gates are not grouped into boxes, nor are the single-qubit gates that preceed them.

boxing_pass_manager = generate_boxing_pass_manager(
    enable_gates=False,
    enable_measures=True,
)
transpiled_circuit = boxing_pass_manager.run(circuit)
transpiled_circuit.draw("mpl", scale=0.8)

Choose how to dress your boxes

All the two-qubit gates and measurement boxes in the returned circuit own left-dressed annotations. In particular, all the boxes that contain two-qubit gates are annotated with a Twirl, while for measurement boxes, users can choose between Twirl, BasisTranform (with mode aset to "measure"), or both. The following code generates a circuit where the all the boxes are twirled, and the measurement boxes are additionally annotated with BasisTranform.

boxing_pass_manager = generate_boxing_pass_manager(
    enable_gates=True,
    enable_measures=True,
    measure_annotations="all",
)
transpiled_circuit = boxing_pass_manager.run(circuit)

Prepare your circuit for noise injection

The inject_noise_targets allows specifying what boxes should receive an InjectNoise annotation. As an example, the following snippet generates a circuit where the two-qubit gates boxes own an InjectNoise annotation but the measurement boxes do not.

boxing_pass_manager = generate_boxing_pass_manager(
    enable_gates=True,
    enable_measures=True,
    inject_noise_targets="gates",
)
transpiled_circuit = boxing_pass_manager.run(circuit)

If a circuit contains two or more boxes that are equivalent up to single-qubit gates, all of them are annotated with an InjectNoise annotation with the same ref. Thus, the number of unique refs in the returned circuit is equal to the number of unique boxes, with uniqueness defined up to single-qubit gates.

By selecting the appropriate value for inject_noise_strategy, users can decide whether the InjectNoise annotations should have:

• modifier_ref='', recommended when modifying the noise maps prior to sampling from them is not required,

• modifier_ref=ref, recommended when all the noise maps need to be scaled uniformly by the same factor, or

• a unique value of modifier_ref, recommended when every noise map needs to be scaled by a different factor.

The following code generates a circuit where the two-qubit gates boxes own an InjectNoise annotation with unique values of modifier_ref.

boxing_pass_manager = generate_boxing_pass_manager(
    enable_gates=True,
    enable_measures=True,
    inject_noise_targets="gates",
    inject_noise_strategy="individual_modification",
)
transpiled_circuit = boxing_pass_manager.run(circuit)

Specify how to treat barriers

By default, barriers are removed from the circuit prior to grouping the operations, as shown in the following snippet.

circuit_with_barrier = QuantumCircuit(4)
circuit_with_barrier.cz(0, 1)
circuit_with_barrier.barrier()
circuit_with_barrier.cz(2, 3)
circuit_with_barrier.measure_all()

boxing_pass_manager = generate_boxing_pass_manager()
transpiled_circuit = boxing_pass_manager.run(circuit_with_barrier)
transpiled_circuit.draw("mpl", scale=0.8)

Setting remove_barriers to False allows preserving the barriers.

boxing_pass_manager = generate_boxing_pass_manager(
    remove_barriers=False,
)

transpiled_circuit = boxing_pass_manager.run(circuit_with_barrier)
transpiled_circuit.draw("mpl", scale=0.8)

Notice that when two gates are separated by a barrier, setting remove_barriers to True potentially allows them to be placed into the same box. However, if remove_barriers is set to False, they are sure to be placed into different boxes. Thus, choosing to preserve the barriers guarantees that the alignment and schedule of gates in the input circuit are respected, but it generally results in circuits with larger depths.

Incorporate Samplomatic’s pass manager into Qiskit’s preset pass managers

The code below shows how to incorporate generate_boxing_pass_manager() into one of Qiskit’s preset pass managers. The transpiled circuit is ISA and contains boxes.

from qiskit.transpiler import generate_preset_pass_manager

preset_pass_manager = generate_preset_pass_manager(
    basis_gates=["rz", "sx", "cx"],
    coupling_map=[[0, 1], [1, 2]],
    optimization_level=0,
)
boxing_pass_manager = generate_boxing_pass_manager()

# Run the boxing pass manager after the scheduling stage
preset_pass_manager.post_scheduling = boxing_pass_manager

circuit = QuantumCircuit(3)
circuit.h(0)
circuit.cx(0, 1)
circuit.cx(0, 2)
circuit.measure_all()

transpiled_circuit = preset_pass_manager.run(circuit)
transpiled_circuit.draw("mpl", scale=0.8)

Build your circuit

Every pass manager produced by generate_boxing_pass_manager() returns circuits that can be successfully turned into a template/samplex pair by build(). As an example, the following code calls the build() function on a circuit produced by a boxing pass manager.

from samplomatic import build

boxing_pass_manager = generate_boxing_pass_manager(
    enable_gates=True,
    enable_measures=True,
)
transpiled_circuit = boxing_pass_manager.run(circuit)

template, samplex = build(transpiled_circuit)

In order to ensure that any transpiled circuit can be successfully built, the pass managers know how to include additional boxes when they are needed. As an example, consider the circuit below, which ends with an unmeasured qubit 0.

circuit_with_unmeasured_qubit = QuantumCircuit(4, 3)
circuit_with_unmeasured_qubit.cz(0, 1)
circuit_with_unmeasured_qubit.cz(2, 3)
for qubit in range(4):
    circuit_with_unmeasured_qubit.rz(Parameter(f"th_{qubit}"), qubit)
    circuit_with_unmeasured_qubit.rx(Parameter(f"phi_{qubit}"), qubit)
    circuit_with_unmeasured_qubit.rz(Parameter(f"lam_{qubit}"), qubit)
circuit_with_unmeasured_qubit.measure(range(1, 4), range(3))

circuit_with_unmeasured_qubit.draw("mpl", scale=0.8)

Drawing left-dressed boxes around the gates and the measurements would result in a circuit that has uncollected virtual gates on qubit 0, and calling build() on this circuit would result in an error. To avoid this, the pass managers returned by generate_boxing_pass_manager() are allowed to add right-dressed boxes to act as collectors. As an example, in the following snippet qubit 0 is terminated by a right-dressed box that picks up the uncollected virtual gate. The single-qubit gates acting on qubit 0 are also placed inside the box, in order to minimise the depth of the resulting circuit.

boxing_pass_manager = generate_boxing_pass_manager(
    enable_gates=True,
    enable_measures=True,
)
transpiled_circuit = boxing_pass_manager.run(circuit_with_unmeasured_qubit)
transpiled_circuit.draw("mpl", scale=0.8)

In another example, a right-dressed box is added to collect the virtual gates that would otherwise remain uncollected due to the unboxed measurements.

boxing_pass_manager = generate_boxing_pass_manager(
    enable_gates=True,
    enable_measures=False,
)
transpiled_circuit = boxing_pass_manager.run(circuit_with_unmeasured_qubit)
transpiled_circuit.draw("mpl", scale=0.8)