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CrosstalkAdaptiveSchedule

class CrosstalkAdaptiveSchedule(*args, **kwargs)[source]

Bases: TransformationPass

Crosstalk mitigation through adaptive instruction scheduling.

CrosstalkAdaptiveSchedule initializer.

Parameters
  • backend_prop (BackendProperties) -- backend properties object

  • crosstalk_prop (dict) --

    crosstalk properties object crosstalk_prop[g1][g2] specifies the conditional error rate of g1 when g1 and g2 are executed simultaneously. g1 should be a two-qubit tuple of the form (x,y) where x and y are physical qubit ids. g2 can be either two-qubit tuple (x,y) or single-qubit tuple (x). We currently ignore crosstalk between pairs of single-qubit gates. Gate pairs which are not specified are assumed to be crosstalk free.

    Example:

    crosstalk_prop = {(0, 1) : {(2, 3) : 0.2, (2) : 0.15},
                                (4, 5) : {(2, 3) : 0.1},
                                (2, 3) : {(0, 1) : 0.05, (4, 5): 0.05}}
    

    The keys of the crosstalk_prop are tuples for ordered tuples for CX gates e.g., (0, 1) corresponding to CX 0, 1 in the hardware. Each key has an associated value dict which specifies the conditional error rates with nearby gates e.g., (0, 1) : {(2, 3) : 0.2, (2) : 0.15} means that CNOT 0, 1 has an error rate of 0.2 when it is executed in parallel with CNOT 2,3 and an error rate of 0.15 when it is executed in parallel with a single qubit gate on qubit 2.

  • weight_factor (float) -- weight of gate error/crosstalk terms in the objective \(weight_factor*fidelities + (1-weight_factor)*decoherence errors\). Weight can be varied from 0 to 1, with 0 meaning that only decoherence errors are optimized and 1 meaning that only crosstalk errors are optimized. weight_factor should be tuned per application to get the best results.

  • measured_qubits (list) -- a list of qubits that will be measured in a particular circuit. This arg need not be specified for circuits which already include measure gates. The arg is useful when a subsequent module such as state_tomography_circuits inserts the measure gates. If CrosstalkAdaptiveSchedule is made aware of those measurements, it is included in the optimization.

Raises

ImportError -- if unable to import z3 solver

Methods

assign_gate_id

ID for each gate

basic_bounds

Basic variable bounds for optimization

check_dag_dependency

gate2 is a DAG dependent of gate1 if it is a descendant of gate1

check_xtalk_dependency

Check if two gates have a crosstalk dependency.

coherence_constraints

Set decoherence errors based on qubit lifetimes

create_updated_dag

Given a set of layers and barriers, construct a new dag

create_z3_vars

Setup the variables required for Z3 optimization

cx_tuple

Representation for two-qubit gate Note: current implementation assumes that the CX error rates and crosstalk behavior are independent of gate direction

enforce_schedule_on_dag

Z3 outputs start times for each gate.

extract_crosstalk_relevant_sets

Extract the set of program gates which potentially have crosstalk noise

extract_dag_overlap_sets

Gate A, B are overlapping if A is neither a descendant nor an ancestor of B.

extract_solution

Extract gate start and finish times from Z3 solution

fidelity_constraints

Set gate fidelity based on gate overlap conditions

filter_candidates

For a gate G and layer L, L is a candidate layer for G if no gate in L has a DAG dependency with G, and if Z3 allows gates in L and G to overlap.

find_layer

Find the appropriate layer for a gate

gate_tuple

Representation for gate

generate_barriers

For each gate g, see if a barrier is required to serialize it with some previously processed gate

is_significant_xtalk

Given two conditional gate error rates check if there is high crosstalk by comparing with independent error rates.

name

Return the name of the pass.

objective_function

Objective function is a weighted combination of gate errors and decoherence errors

parse_backend_properties

This function assumes that gate durations and coherence times are in seconds in backend.properties() This function converts gate durations and coherence times to nanoseconds.

powerset

Finds the set of all subsets of the given iterable This function is used to generate constraints for the Z3 optimization

r2f

Convert Z3 Real to Python float

reset

Reset variables

run

Main scheduling function

scheduling_constraints

DAG scheduling constraints optimization Sets overlap indicator variables

singleq_tuple

Representation for single-qubit gate

solve_optimization

Setup and solve a Z3 optimization for finding the best schedule

Attributes

is_analysis_pass

Check if the pass is an analysis pass.

If the pass is an AnalysisPass, that means that the pass can analyze the DAG and write the results of that analysis in the property set. Modifications on the DAG are not allowed by this kind of pass.

is_transformation_pass

Check if the pass is a transformation pass.

If the pass is a TransformationPass, that means that the pass can manipulate the DAG, but cannot modify the property set (but it can be read).