Measurement — measure, MeasureNode, QResult, StabilizerResult

API reference for quantum measurement operations in pyqpanda3.

measure

Creates a measurement operation that maps a quantum qubit to a classical bit.

Signature

measure(qubit: int, cbit: int) -> MeasureNode
measure(qubits: list[int], cbits: list[int]) -> list[MeasureNode]

Parameter	Type	Description
qubit	int	Qubit index to measure
cbit	int	Classical bit index to store result
qubits	list[int]	Multiple qubit indices to measure
cbits	list[int]	Multiple classical bit indices for results

Returns

MeasureNode or list[MeasureNode] — measurement node(s) to append to a QProg.

Examples

from pyqpanda3.core import H, CNOT, CPUQVM, QProg, measure

qvm = CPUQVM()
prog = QProg()

# Single-qubit measurement
prog << H(0) << measure(0, 0)

# Multi-qubit measurement
prog << CNOT(0, 1) << measure([0, 1], [0, 1])

qvm.run(prog, 1000)
result = qvm.result()
print(result.get_counts())

Output:

{'00': 514, '11': 486}

MeasureNode

Represents a measurement operation binding a qubit to a classical bit.

Signature

class MeasureNode

MeasureNode objects are created by the measure() function and appended to QProg instances via the << operator.

from pyqpanda3.core import QProg, measure

m = measure(0, 0)
prog = QProg()
prog << m

QResult

Stores the results of quantum simulation, including measurement counts, state vectors, and probability distributions.

Signature

class QResult:
    def __init__() -> None

Methods

QResult.get_state_vector

get_state_vector() -> list[complex]

Returns the state vector of the quantum system after simulation.

QResult.get_counts

get_counts() -> dict[str, int]

Returns a dictionary mapping measurement outcome bitstrings to their counts.

# Example output: {'00': 487, '11': 513}
result.get_counts()

QResult.get_prob_list

get_prob_list(qubits: list[int] = []) -> list[float]

Parameter	Type	Description
qubits	list[int]	Qubit indices (default all qubits)

Returns probability list for specified qubits.

QResult.get_prob_dict

get_prob_dict(qubits: list[int] = []) -> dict[str, float]

Parameter	Type	Description
qubits	list[int]	Qubit indices (default all qubits)

Returns probability dictionary mapping bitstrings to probabilities.

QResult.shots

shots() -> int

Returns the number of measurement shots.

QResult.print_results

print_results() -> None

Prints the measurement results to standard output.

StabilizerResult

Result class for the Stabilizer simulator. Inherits from QResult.

Signature

class StabilizerResult(QResult):
    def __init__() -> None

Methods

StabilizerResult.get_state_vector

get_state_vector() -> list[complex]

Returns the state vector of the stabilizer state.

Note: The Stabilizer simulator does not support state vector retrieval. Since 0.5.0 this method raises a descriptive RuntimeError (state vector unavailable for stabilizer) instead of silently returning an empty list.

Examples

from pyqpanda3.core import H, CNOT, Stabilizer, QProg, measure, NoiseModel

qvm = Stabilizer()
prog = QProg()
prog << H(0) << CNOT(0, 1)
prog << measure(0, 0) << measure(1, 1)

qvm.run(prog, 1000, NoiseModel())
result = qvm.result()  # StabilizerResult
print(result.get_counts())

Output:

{'11': 496, '00': 504}

QProg.get_measure_qubits_cbits

QProg.get_measure_qubits_cbits() -> list[tuple[Qubit, CBit]]

Return the (qubit, cbit) pair of each measurement operation in program order, recursing into nested subprograms. Repeated qubits or cbits are preserved.

Useful for checking which physical qubits a program measures before submitting to the cloud, or for confirming the measurement mapping before instruction export (to_instruction).

Return	Type	Description
measurement-pair list	list[tuple[Qubit, CBit]]	Each element is the qubit and classical bit involved in a measurement operation.

Example

from pyqpanda3.core import QProg, measure

prog = QProg()
prog << measure(0, 2) << measure(2, 4) << measure(1, 3) << measure(0, 5)

pairs = [(int(q), int(c)) for q, c in prog.get_measure_qubits_cbits()]
print(pairs)

Output:

[(0, 2), (2, 4), (1, 3), (0, 5)]

See Also

• Simulator — CPUQVM, Stabilizer, and other simulators
• Circuit — QProg for constructing quantum programs
• Noise — NoiseModel for noisy simulations