Interaction validator

This pass checks whether all interactions in the circuit, i.e. two-qubit gates, are executable given the backend connectivity. If certain interactions are not possible, the validator will throw a ValueError, specifying which interactions cannot be executed.

The interaction validator (InteractionValidator) can be used in the following manner.

Check the circuit builder on how to generate a circuit.

from opensquirrel import CircuitBuilder
from opensquirrel.passes.validator import InteractionValidator

connectivity = {
    "0": [1, 2],
    "1": [0, 2, 3],
    "2": [0, 1, 4],
    "3": [1, 4],
    "4": [2, 3]
}

builder = CircuitBuilder(5)
builder.H(0)
builder.CNOT(0, 1)
builder.H(2)
builder.CNOT(1, 2)
builder.CNOT(2, 4)
builder.CNOT(3, 4)
circuit = builder.to_circuit()

interaction_validator = InteractionValidator(connectivity=connectivity)
circuit.validate(validator=interaction_validator)

In the scenario above, there will be no output since all qubit interactions are executable given the connectivity. On the other hand, the circuit below will raise an error (ValueError) as certain interactions are not possible.

builder = CircuitBuilder(5)
builder.H(0)
builder.CNOT(0, 1)
builder.CNOT(0, 3)
builder.H(2)
builder.CNOT(1, 2)
builder.CNOT(1, 3)
builder.CNOT(2, 3)
builder.CNOT(3, 4)
builder.CNOT(0, 4)
circuit = builder.to_circuit()

circuit.validate(validator=interaction_validator)

ValueError: the following qubit interactions in the circuit prevent a 1-to-1 mapping:{(2, 3), (0, 3), (0, 4)}

Resolving the error

The circuit can be redefined to only contain interactions between connected qubits or a routing pass can be used to resolve the error.