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SPIE Conference on Quantum and Nonlinear Optics

Non-Hermitian unidirectional routing of photonic qubits

Enze Li, Yi-Yang Liu, Ming‐Xin Dong, Dong-Sheng Ding, Bao‐Sen Shi

Published Oct 12, 2023• 0 citations
Publisher

Abstract

The efficient unidirectional routing of photonic qubits is significant in the fields of both classical and quantum information processing. However, the photonic qubit router is still elusive due to the simultaneous requirements for high fidelity, precise directionality, and high isolation ratio. Here, we introduce a method to achieve non-Hermitian unidirectional routing of photonic qubits. Our method leverages tunable incoherent dissipative channels connecting traveling photonic qubits with localized atomic systems. Through dynamic control of both coherent and incoherent channels via manipulation of the control field’s helicity, we clarify the transition from nondirectional to unidirectional routing. The experimental results showcase the qubit fidelity exceeding 97.49% and the isolation ratio surpassing 14dB. This method not only enables the establishment of extensive quantum networks but also serves as a pivotal component in chiral topological photonics, chiral networks, and unidirectional quantum information transfer.

DOI
10.1117/12.2687469

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The efficient unidirectional routing of photonic qubits is significant in the fields of both classical and quantum information processing. However, the photonic qubit router is still elusive due to the simultaneous requirements for high fidelity, precise directionality, and high isolation ratio. Here, we introduce a method to achieve non-Hermitian unidirectional routing of photonic qubits. Our method leverages tunable incoherent dissipative channels connecting traveling photonic qubits with localized atomic systems. Through dynamic control of both coherent and incoherent channels via manipulation of the control field’s helicity, we clarify the transition from nondirectional to unidirectional routing. The experimental results showcase the qubit fidelity exceeding 97.49% and the isolation ratio surpassing 14dB. This method not only enables the establishment of extensive quantum networks but also serves as a pivotal component in chiral topological photonics, chiral networks, and unidirectional quantum information transfer.
This study employs a non-Hermitian process that effectively balances coherent and dissipative channels, ensuring the unidirectional transfer of photonic qubits. The significance of this approach lies in its applicability to unidirectional routing in both the classical and quantum domains, which is currently challenging to achieve in the synthesis of qubit unidirectional routers and spin-wave diodes. Additionally, this system's fully optical tunable properties can reverse the direction of qubit transfer. This scheme is expected to greatly impact the design of unidirectional devices in quantum communication and information processing.
The chiral interaction between single photons in waveguides and quantum emitters has gained considerable attention. Here, we proposed a tunable quantum routing scheme with a chiral quantum system by coupling an emitter to two chiral waveguides. Conventional quantum routers can only be achieved with each port output probability no larger than 25%. But our scheme can transfer quantum information arbitrarily from an input port to another, and each port’s output probability is 100%. Besides, we investigated the influence of the Purcell factor in quantum routing properties. No matter how to change the size of the directionalities Sj or set a specific value to the dissipation of the emitter, we always found that the quantum routing has very high efficiency. Moreover, we also used a superconducting qubit coupled to two resonators to show the present scheme is pretty feasible for experimental implementation.
For several decades, scientists have been aware of significant benefits allowing quantum information processing technologies to surpass their classical counterparts. Recent technological development allows these benefits to be tested experimentally and in some cases also implemented in practical devices. So far the majority of experimental quantum networks was limited to peer-to-peer communications between two parties. Practical implementation of quantum communications networks, however, needs to address the problem of scalability to serve large numbers of users. Similarly to classical computer networks, their quantum counterparts would require routing protocols to direct the signal from its source to destination. Devices implementing these routing protocols are called quantum routers and have recently been subject of an intense research. In this paper, we report on experimental implementation of a linear-optical quantum router. Our device allows single-photon polarization-encoded qubits to be routed coherently into two spatial output modes depending on the state of two identical control qubits. The polarization qubit state of the routed photon is maintained during the routing operation. The success probability of our scheme can be increased up to 25% making it the most efficient linear-optical quantum router developed to this date.
Abstract We present a theoretical study of controlled single-photon routing in a cavity-quantum electrodynamics system coupled to dual waveguides, where each cavity embedding with a two-level atom mediates photon transport between two channels. The proposed system achieves enhanced routing performance through tailored phase-dependent cavity–waveguide couplings that generate optimized quantum interference patterns. Using a real-space formalism, we derive analytical expressions for single-photon scattering amplitudes and identify optimal conditions for maximum routing efficiency. Our analysis shows that targeted routing with near-unity efficiency can be realized by precisely manipulating both the accumulated phase and differential phase shift, while the atom–cavity coupling strength enables frequency-selective tunability. Furthermore, we demonstrate engineered nonreciprocal transmission and chiral scattering, enabling deterministic control over photonic propagation direction. This phase-tunable protocol establishes a scalable platform for quantum network implementation and enables novel functionalities in photonic quantum information processing.
The photonic router is a key device in optical quantum networks. Conventional routers, however, can only transfer a photon from the input port to the desired port probabilistically. Here, we propose to use chiral photon-atom interactions for targeted routing that can transfer a single photon from the input port to an arbitrarily selected output port deterministically, i.e., with 100100%100 probability. The configuration of the proposed router consists of a driven three-level atom which is chirally coupled to two photonic waveguides simultaneously. It is shown that, by properly adjusting the driving field on the atom, a single photon inputting from one port of the first waveguide can be deterministically transferred to one of the selected output ports of the second waveguide. Both resonant and nonresonant photons can be deterministically routed to the desired ports. We also examine how the routing fidelity is influenced by dissipations and imperfections, and investigate the transmission characters of two resonant photons.
A quantum router takes the central role in an optical quantum network. However, how to route the expected photons with different frequencies to the targeted output ports of the quantum network is still a basic challenge. Here, we propose an effective approach, by setting the proper cavity-atom and photon-cavity chiral interactions, to realize quantum filter routing of single photons with different frequencies in a multi-channel quantum network. With the frequency serving as the signpost, the photons can be effectively routed to the targeted output ports by modulating the detunings between the cavities and the auxiliary atoms. Hopefully, this technique can play an important role in the construction of a highly efficient optical quantum network.