Topological protection of two-photon quantum correlation on a photonic chip

Abstract

Low-decoherence regime plays a key role in constructing multi-particle quantum systems and has therefore been constantly pursued in order to build quantum simulators and quantum computers in a scalable fashion. Quantum error correction and quantum topological computing have been proved being able to protect quantumness but haven't been experimentally realized yet.Recently, topological boundary states are found inherently stable and are capable of protecting physical fields from dissipation and disorder, which inspires the application of such a topological protection on quantum correlation. Here, we present an experimental demonstration of topological protection of two-photon quantum states on a photonic chip. By analyzing the quantum correlation of photons out from the topologically nontrivial boundary state, we obtain a high cross-correlation and a strong violation of Cauchy-Schwarz inequality up to 30 standard deviations. Our results, together with our integrated implementation, provide an alternative way of protecting quantumness, and may inspire many more explorations in 'quantum topological photonics', a crossover between topological photonics and quantum information.Single photons inherently hold the features of single qubit in quantum computing, and has been widely used in various quantum simulation protocols, such as quantum walk [1,2], boson sampling [3-6] and quantum fast hitting [7]. The single-particle quantum walks have a precise mapping to classical wave phenomena. However, the advantage of uniquely quantum mechanical behavior is limited due to the single walker.In contrast, multiple indistinguishable particles can provide distinctly non-classical correlations, and this quantum behavior becomes a computational advantage. For example, two-particle quantum walk can be an algorithmic tool for the graph isomorphism problem [8], and the universal computation can be achieved by multiparticle quantum walk efficiently [9]. Thus, it is crucial to preserve the non-classical features when constructing a multi-particle quantum computers. * xianmin.jin@sjtu.edu.cn Quantum error correction is proposed to preserve logical quantum states in a subspace and rectify errors according to the measurement outcomes of ancillary particles [10,11]. Quantum topological computing, meanwhile, strives to store and manipulate quantum information with topological protection in a nonlocal manner using non-Abelian anyons [12]. Both of them are promising candidates in theoretical predictions but are still in their initial stage for experimental implementations [10][11][12][13].Topological photonics, derived from the discovery of topological phases in condensed-matter physics, aims to topologically protect photons from the inevitable fabrication-induced dissipation and disorder [14,15]. Many types of topological phases have been observed, for instance, Hall effect [16,17], edge states [18][19][20][21], topological insulators [22,23] and Weyl points [24,25], implying the capability of protecting physical fields. Inspired by these, we m...

Higher-order quantum spin Hall effect in a photonic crystal

“…It would then be possible to explore the quantum behavior of single or multiple photons which are related to the pseudospin degree of freedom, such as the spinful quantum walk, spinful quantum correlation, and entanglement. 46 – 49 . When coupled to quantum emitters, the spinful corner states may support chiral emission of photons with potential applications in quantum simulations 47 .…”

Topological protection versus degree of entanglement of two-photon light in photonic topological insulators

“…The prospect of generating topologically protected entangled states of several photons is a highly intriguing proposition 1 – 3 . Specifically, topological protection can enable robust transport of quantum information across disordered photonic structures without degradation 4 , 5 , just as efficiently as for single-particle wavepackets 6 – 10 .…”

Topology and Interactions in the Photonic Creutz and Creutz‐Hubbard Ladders

“…Photonic quantum simulators use the properties of quantum or classical states of light to analyze the behavior of different quantum systems. In the last few years, an increasing collection of topological materials have been studied in photonic setups, both using quantum and classical light . The latter type of simulators are easier to implement but can only simulate first‐quantized dynamics, and thus the realization of systems of interacting particles has been traditionally challenging.…”