Quantum Measurements API

Quantum Measurements

class graphcalc.quantum.measurements.QuantumMeasurement(operators: Iterable[Sequence[Sequence[complex]] | ndarray], *, dim: int | None = None, validate: bool = True, tol: float = 1e-09)[source]

Bases: object

Finite quantum measurement represented by measurement operators.

The measurement is stored as a family (M_a) of operators on a fixed finite-dimensional Hilbert space. The corresponding effects are E_a = M_a^dagger M_a.

Conventions

  • all measurement operators act on the same Hilbert space

  • the measurement is complete when sum_a E_a = I

  • projective measurements are included as a special case

  • post-measurement states are normalized conditional states

param operators:

Measurement operators.

type operators:

iterable of array-like

param dim:

Hilbert-space dimension. If omitted, inferred from the operators.

type dim:

int | None, default=None

param validate:

Whether to validate the measurement as complete.

type validate:

bool, default=True

param tol:

Numerical tolerance used in validation.

type tol:

float, default=1e-9

classmethod computational_basis(*, dim: int = 2, tol: float = 1e-09) → QuantumMeasurement[source]

Return the computational-basis projective measurement in dimension dim.

effects() → tuple[ndarray, ...][source]

Return the POVM effects M_a^dagger M_a.

classmethod from_projectors(projectors: Iterable[Sequence[Sequence[complex]] | ndarray], *, dim: int | None = None, validate: bool = True, tol: float = 1e-09) → QuantumMeasurement[source]

Construct a projective measurement from projectors.

Notes

For projective measurements, the measurement operators and effects coincide.

property num_outcomes: int

Return the number of outcomes.

property operators: tuple[ndarray, ...]

Return copies of the measurement operators.

outcome_probabilities(state: QuantumState) → ndarray[source]

Return the vector of outcome probabilities.

outcome_probability(state: QuantumState, outcome: int) → float[source]

Return the probability of a specified outcome.

post_measurement_state(state: QuantumState, outcome: int) → QuantumState[source]

Return the normalized post-measurement state conditioned on an outcome.

Notes

If the outcome probability is zero, this function raises ValueError.

validate() → None[source]

Validate that the measurement is complete.

Notes

Completeness means that the effects satisfy sum_a E_a = I.