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arXiv:2202.01873 · Physical Review A

Biphoton entanglement of topologically distinct modes

Cooper Doyle, Weiwei Zhang, Michelle Wang, Bryn A. Bell, Stephen D. Bartlett, Andrea Blanco‐Redondo

Published Feb 17, 2022• 32 citations
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Abstract

The robust generation and manipulation of entangled multiphoton states on chip has an essential role in quantum computation and communication. Lattice topology has emerged as a means of protecting photonic states from disorder, but entanglement across different topologies remains unexplored. We report biphoton entanglement between topologically distinct spatial modes in a bipartite array of silicon waveguides. The results highlight topology as an additional degree of freedom for entanglement and open avenues for investigating information teleportation between trivial and topological modes.

DOI
10.1103/physreva.105.023513

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The robust generation and manipulation of entangled multiphoton states on chip has an essential role in quantum computation and communication. Lattice topology has emerged as a means of protecting photonic states from disorder, but entanglement across different topologies remains unexplored. We report biphoton entanglement between topologically distinct spatial modes in a bipartite array of silicon waveguides. The results highlight topology as an additional degree of freedom for entanglement and open avenues for investigating information teleportation between trivial and topological modes.
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The robust generation and propagation of multiphoton quantum states are crucial for applications in quantum information, computing, and communications. Although photons are intrinsically well isolated from the thermal environment, scaling to large quantum optical devices is still limited by scattering loss and other errors arising from random fabrication imperfections. The recent discoveries regarding topological phases have introduced avenues to construct quantum systems that are protected against scattering and imperfections. We experimentally demonstrate topological protection of biphoton states, the building block for quantum information systems. We provide clear evidence of the robustness of the spatial features and the propagation constant of biphoton states generated within a nanophotonics lattice with nontrivial topology and propose a concrete path to build robust entangled states for quantum gates.
Biphoton states have shown promising applications in quantum information processing, including quantum communications, quantum metrology, and quantum imaging. The generation and manipulation of biphoton entanglement in topologically distinct modes paves the way in this direction. Here we present a comprehensive method for regulating the topological properties of the system by combining the nonlinearity in waveguides, i.e., nonlinearity in the waveguide coupling materials, and the waveguide lattice structure. Our method enables the generation of topological biphoton states with injected pump activation on the topologically trivial modes. This is realized through self-induced manipulation on pump-dependent nonlinear couplings on the defects, which is unable to be realized while there are no such nonlinear couplings. Specifically, by including the nonlinear gain/loss mechanism in the coupling between the nearest-neighbor waveguides and the third-order Kerr nonlinearity effect along the waveguides, the injected pump power will be the controllable parameter for the manipulation of the topology in the defect states and the generation of biphoton entanglement states. We also present an experimental proposal to realize our scheme and its generalization in the contemporaneous "active" topological photonics time-bin platforms. Our method can be used in other Su-Schrieffer-Heeger (SSH) models with various defect configurations. Our method enables the reusability and versatility of SSH lattice chips and their application for fault-tolerant quantum information processing, promoting the industrialization process of quantum technology.
The field of topological photonics leverages concepts from geometry and topology – the branch of mathematics that deals with global properties that cannot be changed under continuous deformation – to produce electromagnetic modes that propagate with immunity to certain types of disorder and imperfections. In the last few years, several experiments have achieved the generation and propagation of quantum states of light in these so-called topological modes, demonstrating enhanced robustness of such inherently fragile quantum states. In this talk we will focus on our recent results in this area including topological protection of spatial entanglement and the demonstration of topology as an additional degree of freedom for entanglement using CMOS-compatible silicon photonics platforms.