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.
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 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.
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.
The quantum router is an elementary building block in quantum information processing and quantum communication. This work constitutes a step forward in this direction, i.e., an efficient scheme is proposed for the implementation of a nonreciprocal single-photon quantum router, allowing the routing of a single photon from one side but blocking it from the other side. Our model consists of two directly coupled coplanar-waveguide resonators and a superconducting ring resonator, which are connected together through a transmission line. The nonreciprocity is realized by unidirectionally interacting the rotating microwave modes of the ring resonator with a dissipative magnon mode in an yttrium iron garnet disk. We find that a single-photon signal can be delivered from a given input port to either of the two output ports, but is fully absorbed from the opposite one. The proposed scheme not only enriches the family of nonreciprocal quantum devices, but also finds useful applications in chiral quantum technologies.
Abstract High-efficiency single-photon routing of photon signals between different quantum channels is of great importance for the quantum networks with the ability to coherently transfer quantum states between the desired sender and receiver nodes. We proposed an efficient scheme for realizing quantum routers via multiple semi-infinite coupled-resonator waveguides ( CRWs ) coupled to cavities nonreciprocally. Numerical results show that with the change of the phase difference value, the quantum routing function of multiple output ports can be realized, in the meantime, the information conversion rate can almost reach 100%. The optimal conditions for these phenomena are obtained by the time-reversal symmetry breaking the nonreciprocal of the single-photon transport. Moreover, we have also described a scalable scheme that can extend the router to an arbitrary number of outputs. Our results pave the way to design high-quality quantum devices based on breaking time-reversal symmetry waveguide-cavity systems.
Abstract Motivated by the need for quantum computers to communicate between multiple, well separated qubits, we introduce the task of routing the quantum state from one input mode to a superposition of several output modes coherently. We report an experimental demonstration of a deterministic photonic routing protocol applied to an entangled state. We show in a quantum walk architecture, quantum networks perfectly route entangled states from an initial input mode to an arbitrary output mode coherently and deterministically. Our results demonstrate the key principle of a perfect router, opening a route toward data routing and transferring for quantum computing systems. The routing algorithm in our work can be applied to a wide range of physical systems, which provides a way for effective design of efficient routing protocols on practical quantum networks.
The ability to manipulate the speed of light has recently become one of the most exciting emergent topics in optics. There are several experimental demonstrations showing the capability to slow down light more than six orders of magnitude in a variety of media, ranging from atomic vapor, solid state crystal, to semiconductors. These results have led to intensive research into new materials, devices, and system studies that examine their impact to new applications. It is believed that we are on the verge of a dramatic change in the way we envision and construct communication, processing and control systems. One direct application of slow and fast light devices is in the area of communications. One grand challenge remaining in information technology today is to store and buffer optical signals directly in optical format. As such, optical signals must be converted to electronic signals to route, switch, or be processed. This resulted in significant latencies and traffic congestions in current networks. In addition, keeping the data in optical domain during the routing process can greatly reduce the power, complexity and size of the routers. To this end, a controllable optical delay line can effectively function as an optical buffer, and the storage is proportional to the variability of the group velocity. In addition to optical buffers, slow and fast light devices can be used as tunable true-time delay elements in microwave photonics, which are important for remotely controlling phased array antenna. Other novel applications include nonlinear optics, optical signal processing, and quantum information processing. There are various approaches that can be used to vary the optical group velocity. Ultraslow or fast group velocity may result from a large material dispersion, waveguide dispersion, or both. In this paper, the authors provide a review of recent progress of slow and fast light using semiconductor devices. Specifically, they will discuss results obtained using semiconductor quantum-well/quantum-dot absorber and optical amplifiers. Slow and fast light are controllable electrically by changing the bias current or voltage as well as optically by changing the pump laser intensity and wavelength. Delay-bandwidth tradeoff and other figures of merits are analyzed