combine_single_qubit_gates#

combine_single_qubit_gates(qc: QuantumCircuit) → QuantumCircuit[source]#

Combine adjacent single-qubit gates into unitary operations.

This pass scans the circuit instruction-by-instruction and accumulates consecutive single-qubit gates on each qubit. When an interruption is encountered (multi-qubit gate, allocation, measurement, …) the pending gates are flushed: their unitaries are multiplied together and emitted as a single operation, cancelling any sequences that reduce to the identity.

Recursive processing

Composite gates (gates with a definition) are processed recursively so that single-qubit gate sequences inside compound operations are also combined.

Controlled operations whose base_operation carries a definition are handled analogously: the base definition is combined in place and the controlled wrapper is preserved.

This pass is designed as a local optimisation that reduces gate count and depth without changing the overall circuit semantics. It is especially useful after transpilation passes that may introduce redundant single-qubit rotations.

Parameters:

qcQuantumCircuit: The input circuit.

Returns:

QuantumCircuit: A new circuit with adjacent single-qubit gates combined.

Examples

>>> from qrisp import PassManager, combine_single_qubit_gates
>>> from qrisp import QuantumCircuit
>>> qc = QuantumCircuit(1)
>>> qc.x(0)
>>> qc.z(0)
>>> qc.h(0)   # X, Z, Y on the same qubit
>>> pm = PassManager()
>>> pm += combine_single_qubit_gates
>>> optimized_qc = pm.run(qc)
>>> # X, Z, Y combined into a single U3 gate
>>> print(optimized_qc)
       ┌──────────────┐
qb_64: ┤ U3(π/2,3π,0) ├
       └──────────────┘