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Introduction to linkers

This guide provides a few examples that show how to initialize linkers in QCS, as well as to use a linker pass inside an executor to modify quantum programs.

In this example, Mapping from circuit to hardware, we will show how to map circuit-level instructions to pulses that can be executed on hardware.

Mapping from circuit to hardware

Consider the following program, which applies a Pauli-X gate to a qubit labelled 0 and subsequently measures the qubit in the computational basis.

import keysight.qcs as qcs

# initialize a qubit and an array to hold results
qubit = qcs.Qudits([0])

# define a program
program_in = qcs.Program()
program_in.add_gate(qcs.GATES.x, qubit)
program_in.add_measurement(qubit)

program_in.draw()

		Program Program Duration undefined Layers 1 Targets 1 Repetitions
		Layer #0 Layer #0 Duration undefined
qudits	0	X Gate X on ('qudits', 0) Matrix: 0 1 1 0	Measure on ('qudits', 0) Parameters Dim 2

We now define two linkers. The first linker maps the Pauli-X gate to a pulse executed on an AWG.

# define the replacement in terms of a pulse and channel
pulse = qcs.RFWaveform(
    duration=8e-8, envelope=qcs.GaussianEnvelope(), amplitude=1, rf_frequency=5e9
)

channel = qcs.Channels(range(1), "control_channel")

replacement_gt = qcs.Program()
replacement_gt.add_waveform(pulse, channel)

# specify the instruction to be replaced and create the Linker
linker_gt = qcs.Linker(qcs.GATES.x, qubit, replacement_gt)

The second linker maps the measurement instruction to an acquisition.

replacement_meas = qcs.Program()
integration_filter = qcs.IntegrationFilter(pulse)
classifier = qcs.Classifier([0.0, 1.0])
replacement_meas.add_acquisition(integration_filter, channel, classifier)

linker_meas = qcs.ParameterizedLinker(qcs.Measure(), qubit, replacement_meas)

Finally, we use the Executor to replace the circuit-level instructions with the new instructions.

program_out = qcs.Executor(qcs.LinkerPass(linker_gt, linker_meas)).execute(program_in)

By plotting program_out, we can see that the circuit-level instructions have been correctly replaced.

program_out.draw()

		Program Program Duration 160 ns Layers 1 Targets 1 Repetitions
		Layer #0 Layer #0 Duration 160 ns
control_channel	0	RFWaveform on ('control_channel', 0) Parameters Duration 80 ns Amplitude 1 Frequency 5 GHz Envelope GaussianEnvelope(2.0) Instantaneous Phase 0 rad Post-phase 0 rad	Acquisition on ('control_channel', 0) Parameters Duration 80 ns Integration Filter RFWaveform Parameters Duration 80 ns Amplitude 1 Frequency 5 GHz Envelope GaussianEnvelope(2.0) Instantaneous Phase 0 rad Post-phase 0 rad Classifier Classifier(Array(name=_implicit, shape=(2,), dtype=complex, unit=none))

Linking conditional operations

Rather than linking from a conditional operation to another conditional operation, we instead iterate through the possibile operations and link them all individually. Consider the case of active qubit reset.

program = qcs.Program()
program.add_measurement(qubit, reset=True, repeat_reset=2)
program.draw()

		Program Program Duration undefined Layers 5 Targets 1 Repetitions
		Layer #0 Layer #0 Duration undefined	Layer #1 Layer #1 (Data Transactions) Duration 0 s Transaction Source Measure on ('qudits', 0) Transaction Destinations ('qudits', 0)	Layer #2 Layer #2 Duration undefined		Layer #3 Layer #3 (Data Transactions) Duration 0 s Transaction Source Measure on ('qudits', 0) Transaction Destinations ('qudits', 0)	Layer #4 Layer #4 Duration undefined
qudits	0	Measure on ('qudits', 0) Parameters Dim 2 Register Register(name=qudits_results, num_bits=1, dim=2)		ConditionalOperation on ('qudits', 0) Operations Outcome 0 Gate ID Matrix: 1 0 0 1 Outcome 1 Gate X Matrix: 0 1 1 0 Register Name qudits_results Num Bits 1 Dim 2	Measure on ('qudits', 0) Parameters Dim 2 Register Register(name=qudits_results, num_bits=1, dim=2)		ConditionalOperation on ('qudits', 0) Operations Outcome 0 Gate ID Matrix: 1 0 0 1 Outcome 1 Gate X Matrix: 0 1 1 0 Register Name qudits_results Num Bits 1 Dim 2

Here, a conditional operation has been added after the measurement that will either perform a Pauli-X gate or the identity gate. To link this object properly, we add a linker for the identity gate in addition to the linker we already have.

replacement_id = qcs.Program()
replacement_id.add_waveform(qcs.Delay(0), channel)

linker_id = qcs.Linker(qcs.GATES.id, qubit, replacement_id)

Applying the linkers, we see we get a new conditional operation except with a waveform and delay:

program_out = qcs.LinkerPass(linker_gt, linker_id, linker_meas).apply(program)
program_out.draw()

		Program Program Duration 320 ns Layers 7 Targets 1 Repetitions
		Layer #0 Layer #0 Duration 80 ns	Layer #1 Layer #1 Duration 0 s	Layer #2 Layer #2 (Data Transactions) Duration 0 s Transaction Source Acquisition on ('control_channel', 0) Transaction Destinations ('control_channel', 0)	Layer #3 Layer #3 Duration 160 ns		Layer #4 Layer #4 Duration 0 s	Layer #5 Layer #5 (Data Transactions) Duration 0 s Transaction Source Acquisition on ('control_channel', 0) Transaction Destinations ('control_channel', 0)	Layer #6 Layer #6 Duration 80 ns
control_channel	0	Acquisition on ('control_channel', 0) Parameters Duration 80 ns Integration Filter RFWaveform Parameters Duration 80 ns Amplitude 1 Frequency 5 GHz Envelope GaussianEnvelope(2.0) Instantaneous Phase 0 rad Post-phase 0 rad Classifier Classifier(Array(name=_implicit, shape=(2,), dtype=complex, unit=none))			ConditionalOperation on ('control_channel', 0) Operations Outcome 0 Delay on None Parameters Duration 0 s Outcome 1 RFWaveform Parameters Duration 80 ns Amplitude 1 Frequency 5 GHz Envelope GaussianEnvelope(2.0) Instantaneous Phase 0 rad Post-phase 0 rad Register Name qudits_results Num Bits 1 Dim 2	Acquisition on ('control_channel', 0) Parameters Duration 80 ns Integration Filter RFWaveform Parameters Duration 80 ns Amplitude 1 Frequency 5 GHz Envelope GaussianEnvelope(2.0) Instantaneous Phase 0 rad Post-phase 0 rad Classifier Classifier(Array(name=_implicit, shape=(2,), dtype=complex, unit=none))			ConditionalOperation on ('control_channel', 0) Operations Outcome 0 Delay on None Parameters Duration 0 s Outcome 1 RFWaveform Parameters Duration 80 ns Amplitude 1 Frequency 5 GHz Envelope GaussianEnvelope(2.0) Instantaneous Phase 0 rad Post-phase 0 rad Register Name qudits_results Num Bits 1 Dim 2

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