Mapping

Mapping#

class iqm.qaoa.transpiler.routing.Mapping(qpu, problem_bqm, partial_initial_mapping=None)[source]#

Bases: object

Mapping between logical and hardware qubits.

It maintains two dictionaries: log2hard and hard2log which are mappings between logical and hardware qubits. They are always kept in sync. The names for the hardware and logical qubits are extracted from qpu and problem_bqm at initialization.

Parameters:

  • qpu (QPU) – a QPU object describing the topology of the QPU, used to get hardware qubits.

  • problem_bqm (BinaryQuadraticModel) – The BinaryQuadraticModel of the problem we’re trying to solve, used to get logical qubits.

  • partial_initial_mapping (dict[HardQubit, LogQubit] | None) – An optional dictionary that contains a partial mapping to use as a starting point. The keys should be HardQubit and the values LogQubit.

Raises:

ValueError – If partial_initial_mapping is provided, but it’s not bijective.

Attributes

hard2log

The dictionary containing the mapping from hardware qubits to logical qubits.

log2hard

The dictionary containing the mapping from logical qubits to hardware qubits.

Methods

move_hard(source_qubit, target_qubit)

Move a logical qubit from a one hardware qubit to a an unassigned hardware qubit on the QPU.

swap_hard(gate)

Swap association between a pair of hardware qubits.

swap_log(gate)

Swap association between a pair of logical qubits.

update(layer)

Update the mapping based on the swap gates found in a Layer object.
property hard2log: dict[HardQubit, LogQubit]#

The dictionary containing the mapping from hardware qubits to logical qubits.

property log2hard: dict[LogQubit, HardQubit]#

The dictionary containing the mapping from logical qubits to hardware qubits.

swap_log(gate)[source]#

Swap association between a pair of logical qubits.

Updates the dictionaries hard2log and log2hard.

Parameters:

gate (LogEdge) – The pair of logical qubits to swap.

Return type:

None

swap_hard(gate)[source]#

Swap association between a pair of hardware qubits.

Updates the dictionaries hard2log and log2hard.

Parameters:

gate (HardEdge) – The pair of hardware qubits to swap.

Return type:

None

move_hard(source_qubit, target_qubit)[source]#

Move a logical qubit from a one hardware qubit to a an unassigned hardware qubit on the QPU.

The target target_qubit must not be part of the Mapping. Updates the dictionaries hard2log and log2hard. The dictionaries are changed as follows:

  • If the dictionary hard2log has a key source_qubit (but not target_qubit), this method removes the key source_qubit, creates a new key target_qubit and gives it the value formerly associated to source_qubit

  • The dictionary log2hard is modified correspondingly. The value source_qubit is changed to target_qubit.

Parameters:
Raises:

ValueError – If the target_qubit is already assigned to a different logical qubit.

Return type:

None

update(layer)[source]#

Update the mapping based on the swap gates found in a Layer object.

A convenience function that iterates over the gates in a Layer object and swaps the hardware qubits corresponding to swap gates.

Parameters:

layer (Layer) – The layer whose swap gates are used.

Return type:

None

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