Quantum Computing by Quantum Walk on Quantum Slide

TL;DR

This paper demonstrates how quantum slide techniques can enable universal quantum computation using quantum walks on optical waveguides, overcoming initial state preparation challenges and achieving high gate fidelities.

Contribution

It introduces a method to implement universal quantum gates via quantum slide, bypassing the need for plane-wave initial states in quantum walk-based quantum computation.

Findings

Gate fidelities increase with slide length.

Universal gates can be realized with phase tuning.

Fidelities can reach unity asymptotically.

Abstract

Continuous-time quantum walk is one of the alternative approaches to quantum computation, where a universal set of quantum gates can be achieved by scattering a quantum walker on some specially-designed structures embedded in a sparse graph [Childs, Phys. Rev. Lett. 2009]. Recent advances in femtosecond laser-inscribed optical waveguides represent a promising physical platform for realizing this quantum-walk model of quantum computation. However, the major challenge is the problem of preparing a plane-wave initial state. Previously, the idea of quantum slide has been proposed and experimentally realized for demonstrating the working principle of NAND tree [Wang et al. Phy. Rev. Lett. 2020]. Here we show how quantum slide can be further applied to realize universal quantum computation, bypassing the plane-wave requirement. Specifically, we apply an external field to the perfect-state-transfer chain, which can generate a moving Gaussian wave packet with an arbitrary momentum. When the phase is properly tuned, the universal gate set in Childs' proposal can be realized in our scheme. Furthermore, we show that the gate fidelities increase with the length of the slide, and can reach unity asymptotically.