CorrelatedReadoutMitigator

class CorrelatedReadoutMitigator(assignment_matrix, qubits=None)

Bases: qiskit.result.mitigation.base_readout_mitigator.BaseReadoutMitigator

N-qubit readout error mitigator.

Mitigates expectation_value() and quasi_probabilities(). The mitigation_matrix should be calibrated using qiskit experiments. This mitigation method should be used in case the readout errors of the qubits are assumed to be correlated. The mitigation_matrix of N qubits is of size $2^N x 2^N$ so the mitigation complexity is $O(4^N)$ .

Initialize a CorrelatedReadoutMitigator

Parameters

assignment_matrix (ndarray) – readout error assignment matrix.
qubits (Optional[Iterable[int]]) – Optional, the measured physical qubits for mitigation.

Raises

QiskitError – matrix size does not agree with number of qubits

Methods

assignment_matrix

CorrelatedReadoutMitigator.assignment_matrix(qubits=None)

Return the readout assignment matrix for specified qubits.

The assignment matrix is the stochastic matrix $A$ which assigns a noisy readout probability distribution to an ideal input readout distribution: $P(i|j) = \langle i | A | j \rangle$ .

Parameters

qubits (Optional[List[int]]) – Optional, qubits being measured.

Returns

the assignment matrix A.

Return type

np.ndarray

expectation_value

CorrelatedReadoutMitigator.expectation_value(data, diagonal=None, qubits=None, clbits=None, shots=None)

Compute the mitigated expectation value of a diagonal observable.

This computes the mitigated estimator of $\langle O \rangle = \text{Tr}[\rho. O]$ of a diagonal observable $O = \sum_{x\in\{0, 1\}^n} O(x)|x\rangle\!\langle x|$ .

Parameters

data (Counts) – Counts object
diagonal (Union[Callable, dict, str, ndarray, None]) – Optional, the vector of diagonal values for summing the expectation value. If None the the default value is $[1, -1]^\otimes n$ .
qubits (Optional[Iterable[int]]) – Optional, the measured physical qubits the count bitstrings correspond to. If None qubits are assumed to be $[0, ..., n-1]$ .
clbits (Optional[List[int]]) – Optional, if not None marginalize counts to the specified bits.
shots (Optional[int]) – the number of shots.

Returns

the expectation value and an upper bound of the standard deviation.

Return type

(float, float)

Additional Information:

The diagonal observable $O$ is input using the diagonal kwarg as a list or Numpy array $[O(0), ..., O(2^n -1)]$ . If no diagonal is specified the diagonal of the Pauli operator :math`O = mbox{diag}(Z^{otimes n}) = [1, -1]^{otimes n}` is used. The clbits kwarg is used to marginalize the input counts dictionary over the specified bit-values, and the qubits kwarg is used to specify which physical qubits these bit-values correspond to as circuit.measure(qubits, clbits).

mitigation_matrix

CorrelatedReadoutMitigator.mitigation_matrix(qubits=None)

Return the readout mitigation matrix for the specified qubits.

The mitigation matrix $A^{-1}$ is defined as the inverse of the assignment_matrix() $A$ .

Parameters

qubits (Optional[List[int]]) – Optional, qubits being measured.

Returns

the measurement error mitigation matrix $A^{-1}$ .

Return type

np.ndarray

quasi_probabilities

CorrelatedReadoutMitigator.quasi_probabilities(data, qubits=None, clbits=None, shots=False)

Compute mitigated quasi probabilities value.

Parameters

data (Counts) – counts object
qubits (Optional[List[int]]) – qubits the count bitstrings correspond to.
clbits (Optional[List[int]]) – Optional, marginalize counts to just these bits.
shots (Optional[bool]) – the number of shots.

Returns

A dictionary containing pairs of [output, mean] where “output”

is the key in the dictionaries, which is the length-N bitstring of a measured standard basis state, and “mean” is the mean of non-zero quasi-probability estimates.

Return type

QuasiDistibution

stddev_upper_bound

CorrelatedReadoutMitigator.stddev_upper_bound(shots)

Return an upper bound on standard deviation of expval estimator.

Parameters

shots (int) – Number of shots used for expectation value measurement.

Returns

the standard deviation upper bound.

Return type

float

Attributes

qubits

The device qubits for this mitigator

Return type

Tuple[int]

settings

Return settings.

Return type

Dict

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