Computational multiqubit tunnelling in programmable quantum annealers.

Sergio Boixo,Mohammad H. Amin,Masoud Mohseni,Sergei V. Isakov,Hartmut Neven,Alireza Shabani,Vadim N. Smelyanskiy,Vasil S. Denchev,Anatoly Yu Smirnov,Mark Dykman

doi:10.1038/ncomms10327

Abstract

Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive.

Highlights

Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself
We introduce a 16-qubit probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum
We present a nonperturbative theory of multiqubit tunnelling, which takes into account both high- and low-frequency noises

Summary

Introduction

Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. We experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive. The temperature is gradually lowered to distinguish between local minima with small energy differences This causes the stochastic process to freeze once the thermal energy is lower than the height of the barriers surrounding the state. Given a quantum annealer operating at finite temperature, noise and dissipation strengths, does it utilize tunnelling or thermal activation for computation?. We introduce a 16-qubit probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. Quantum tunnelling outperforms thermal hoping for these problems under similar parameters

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