Quasi-Probability Decomposition (QPD)
qiskit_addon_cutting.qpd
Main quasiprobability decomposition functionality.
QPDBasis | Basis in which to decompose an operation. |
BaseQPDGate | Base class for a gate to be decomposed using quasiprobability decomposition. |
SingleQubitQPDGate | Single qubit gate to be decomposed using quasiprobability decomposition. |
TwoQubitQPDGate | Two qubit gate to be decomposed using quasiprobability decomposition. |
WeightType
class WeightType(value)
Bases: Enum
Type of weight associated with a QPD sample.
EXACT
Default value: 1
A weight given in proportion to its exact weight
SAMPLED
Default value: 2
A weight that was determined through some sampling procedure
generate_qpd_weights
generate_qpd_weights(qpd_bases, num_samples=1000)
Generate weights from the joint quasiprobability distribution.
Each weight whose absolute value is above a threshold of 1 / num_samples will be evaluated exactly. The remaining weights – those in the tail of the distribution – will then be sampled from, resulting in at most num_samples unique weights.
Parameters
- qpd_bases (
Sequence[QPDBasis]) – TheQPDBasisobjects from which to generate weights - num_samples (
float) – Controls the number of weights to generate
Return type
dict[tuple[int, ...], tuple[float, WeightType]]
Returns
A mapping from a given decomposition to its weight. Keys are tuples of indices – one index per input QPDBasis. The indices correspond to a specific decomposition mapping in the basis.
Values are tuples. The first element is a number corresponding to the weight of the contribution. The second element is the WeightType, either EXACT or SAMPLED.
decompose_qpd_instructions
decompose_qpd_instructions(circuit, instruction_ids, map_ids=None, *, inplace=False)
Replace all QPD instructions in the circuit with local Qiskit operations and measurements.
Parameters
- circuit (QuantumCircuit) – The circuit containing QPD instructions
- instruction_ids (Sequence[Sequence[int]]) – A 2D sequence, such that each inner sequence corresponds to indices of instructions comprising one decomposition in the circuit. The elements within a common sequence belong to a common decomposition and should be sampled together.
- map_ids (Sequence[int] | None) – Indices to a specific linear mapping to be applied to the decompositions in the circuit. If no map IDs are provided, the circuit will be decomposed randomly according to the decompositions’ joint probability distribution.
- inplace (bool) – If
True, thecircuitwill be modified in place.
Return type
QuantumCircuit
Returns
Circuit which has had all its BaseQPDGate instances decomposed into local operations.
The circuit will contain a new, final classical register to contain the QPD measurement outcomes (accessible at retval.cregs[-1]).
Raises
- ValueError – An index in
instruction_idscorresponds to a gate which is not aBaseQPDGateinstance. - ValueError – A list within instruction_ids is not length 1 or 2.
- ValueError – The total number of indices in
instruction_idsdoes not equal the number ofBaseQPDGateinstances in the circuit. - ValueError – Gates within the same decomposition hold different QPD bases.
- ValueError – Length of
map_idsdoes not equal the number of decompositions in the circuit.
qpdbasis_from_instruction
qpdbasis_from_instruction(gate, /)
Generate a QPDBasis object, given a supported operation.
All two-qubit gates which implement the to_matrix() method are supported. This should include the vast majority of gates with no unbound parameters, but there are some special cases (see, e.g., qiskit issue #10396).
The Move operation, which can be used to specify a wire cut, is also supported.
Return type
Returns
The newly-instantiated QPDBasis object
Raises
- ValueError – Instruction not supported.
- ValueError – Cannot decompose instruction with unbound parameters.
- ValueError –
to_matrixconversion of two-qubit gate failed.
Parameters
gate (Instruction)