Quantum Skip Gates: Coherently Conditioned Subroutines in Iterative Quantum Algorithms

TL;DR

This paper introduces Quantum Skip Gates, a unitary primitive enabling coherent conditional execution of subroutines in quantum algorithms, demonstrated experimentally to improve efficiency and reduce noise in near-term quantum hardware.

Contribution

The paper presents the Quantum Skip Gate, a novel unitary primitive for coherently controlling subroutine execution without measurement, enhancing resource management in quantum algorithms.

Findings

QSG reduces costly subroutine calls by 9-25%.

QSG achieves 31-61% higher success-per-oracle efficiency.

Simulations show up to 45% improvements with optimized design.

Abstract

The Quantum Skip Gate (QSG) is a unitary circuit primitive that coherently superposes the execution and omission of an expensive quantum subroutine based on the outcome of a cheaper preceding subroutine, without mid-circuit measurement or loss of coherence. By using a control qubit and an internal flag, QSG enables conditional quantum logic entirely within a unitary framework. We demonstrate QSG experimentally in a Grover-style search on IBM quantum hardware with four data qubits and three Grover iterations, where it reduces costly subroutine calls by 9 to 25 percent and achieves 31 to 61 percent higher success-per-oracle efficiency relative to a fixed-order baseline. Noise-model simulations further confirm and strengthen these gains, reaching improvements of up to 45 percent when using an optimized swap-out design. These results show that coherently conditioned subroutines provide practical resource management, significantly reducing runtime cost and noise accumulation in near-term quantum algorithms.