Quantum Router Research Articles

Highly scalable quantum router with frequency-independent scattering spectra

Abstract Optical quantum routers play a crucial role in quantum networks and have been extensively studied in both theory and experiment, leading to significant advancements in their performance. However, these routers impose stringent requirements for achieving desired routing results, as the incident photon frequency must be in strict resonance with one or several specific frequencies. To address this challenge, we propose an efficient quantum router scheme composed of semi-infinite coupled-resonator waveguide (CRW) and a giant atom. The single-channel router scheme enables stable output with 100% transfer rate over the entire energy band of the CRW. Leveraging this intriguing result, we further propose a multi-channel router scheme that possesses high stability and universality, while also being capable of performing various functionalities. The complete physical explanation of the underlying mechanism for this intriguing result is also presented. We hope that quantum router with output results unaffected by the frequency of the incoming information carriers presents a more reliable solution for the implementation of quantum networks.

Solving a real-world package delivery routing problem using quantum annealers.

Research focused on the conjunction between quantum computing and routing problems has been very prolific in recent years. Most of the works revolve around classical problems such as the Traveling Salesman Problem or the Vehicle Routing Problem. The real-world applicability of these problems is dependent on the objectives and constraints considered. Anyway, it is undeniable that it is often difficult to translate complex requirements into these classical formulations. The main objective of this research is to present a solving scheme for dealing with realistic instances while maintaining all the characteristics and restrictions of the original real-world problem. Thus, a quantum-classical strategy has been developed, coined Q4RPD, that considers a set of real constraints such as a heterogeneous fleet of vehicles, priority deliveries, and capacities characterized by two values: weight and dimensions of the packages. Q4RPD resorts to the Leap Constrained Quadratic Model Hybrid Solver of D-Wave. To demonstrate the application of Q4RPD, an experimentation composed of six different instances has been conducted, aiming to serve as illustrative examples.

Quantum routing with teleportation

We study the problem of implementing arbitrary permutations of qubits under interaction constraints in quantum systems that allow for arbitrarily fast local operations and classical communication (LOCC). In particular, we show examples of speedups over swap-based and more general unitary routing methods by distributing entanglement and using LOCC to perform quantum teleportation. We further describe an example of an interaction graph for which teleportation gives a logarithmic speedup in the worst-case routing time over swap-based routing. We also study limits on the speedup afforded by quantum teleportation—showing an O(NlogN) upper bound on the separation in routing time for any interaction graph—and give tighter bounds for some common classes of graphs. Published by the American Physical Society 2024

Tunable targeted single-photon routing in a waveguide-QED structure containing a time-modulated two-level atom

Single-photon routing between two one-dimensional waveguides mediated by a single-mode cavity embedded with a time-modulated two-level atom is investigated. Two configurations, where the single photon is incident from an infinite or semi-infinite waveguide, are considered. Using the analytical expressions of the single-photon scattering amplitudes, the transmission behaviors in the two waveguides are discussed. The results show that the time modulation of the atomic frequency enables a dynamically tunable quantum router. A single photon with different frequencies can be routed dynamically from the incident waveguide to the other by properly manipulating the amplitude-to-frequency ratio of the atom. The routing efficiency can be improved to approach 100% by terminating the incident waveguide. In the semi-waveguide configuration, the routing behaviors controlled by the quantum coherent feedback are also investigated. The influence of the phase shifts introduced by the terminated waveguide on the routing capability and the conditions for perfect single-photon routing are discussed in detail. A frequency tunable targeted single-photon router can even be realized with the help of chiral coupling. These results may be beneficial to the photon control in a quantum network based on time-modulated quantum nodes.

Quantum routing of single photons within a specified frequency range

Quantum routing of single photons within a specified frequency range

Chiral quantum router with Rydberg atoms

Chiral quantum router with Rydberg atoms

Phase-modulated single-photon router and chiral scattering between two waveguides coupled by a giant three-level atom

We investigate a T-shaped single-photon router constructed by two waveguides connected via a giant Λ-type three-level atom. Under a real-space approach, the analytical expressions of the single-photon transmission and reflection amplitudes are obtained. It is shown that a high transfer-rate routing between two waveguides can be effectively achieved by modulating the phase difference, the accumulated phase and the atom-waveguide coupling strengths, and its frequencies can be tuned with a classical driving field. Interestingly, chiral scattering and a single-photon targeted router with direction selectivity have been realized by the ideally equivalent atom-waveguide interaction. We believe that our results have potential applications in constructing optical quantum devices and designing the single-photon quantum routing using the giant-atom setup.

Frequency-tunable single-photon router based on a microresonator containing a driven three-level emitter

We propose a frequency-tunable router of single photons with high routing efficiency, which is constructed by two waveguides mediately linked by a single-mode whispering gallery resonator with a driven three-level emitter. Quantum routing probability in the output port is obtained via the real-space Hamiltonian. By adjusting the resonator–emitter coupling and the drive, the desired continuous central frequencies for the resonance peaks of routing photons can be manipulated nearly linearly, with the assistance of Rabi splitting effect and optical Stark shift. The proposed routing system may provide potential applications in designing other frequency-modulation quantum optical devices, such as multiplexers, filters, and so on.

Quantum filter routing of single 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.

A new quantum key distribution resource allocation and routing optimization scheme

Quantum key distribution (QKD) is a technology that can resist the threat of quantum computers to existing conventional cryptographic protocols. However, due to the stringent requirements of the quantum key generation environment, the generated quantum keys are considered valuable, and the slow key generation rate conflicts with the high-speed data transmission in traditional optical networks. In this paper, for the QKD network with a trusted relay, which is mainly based on point-to-point quantum keys and has complex changes in network resources, we aim to allocate resources reasonably for data packet distribution. Firstly, we formulate a linear programming constraint model for the key resource allocation (KRA) problem based on the time-slot scheduling. Secondly, we propose a new scheduling scheme based on the graded key security requirements (GKSR) and a new micro-log key storage algorithm for effective storage and management of key resources. Finally, we propose a key resource consumption (KRC) routing optimization algorithm to properly allocate time slots, routes, and key resources. Simulation results show that the proposed scheme significantly improves the key distribution success rate and key resource utilization rate, among others.

Quantum Routing for Emerging Quantum Networks

Quantum Routing for Emerging Quantum Networks

Directional router and controllable non-reciprocity transmission based on phase and pathway coherence

A multi-channel quantum router with four nodal cavities is constructed by two coupled-resonator waveguides and four single cavities. We can achieve directional routing by adjusting the probability of photon exiting from the specified port to close to 100% based on multiple pathways between the photon from the incident port to the outgoing port in this hybrid system. Under the effect of phase difference between two classical light fields, the mutual interference between different pathways can be adjusted to destructive interference or constructive interference, which lays the foundation for the increase and decrease of the routing probability. The influence of different parameter values on single photon routing probability is also studied. By studying the analytic formula of probability amplitude, we get the physical mechanism of exiting ports being closed under certain parameter conditions and the phase relationship between the backward transmission and the original direction transmission of photons. Furthermore the non-reciprocal transmission and directional routing beyond chiral coupling can also be realized, which provides new possibilities for the study of quantum routers and new insights for the study of photon transmission characteristics.

Planar and tunable quantum state transfer in a splicing Y-junction Su–Schrieffer–Heeger chain

We present a feasible scheme to implement a planar and tunable quantum state transfer (QST) via topologically protected zero-energy mode in a splicing Y-junction Su–Schrieffer–Heeger (SSH) chain. The introduction of the elaborate nearest-neighbor (NN) hopping enables one to generate a topological interface at the central site of the Y-junction. By modulating the NN hopping adiabatically in the chain, the quantum state initially prepared at the central site can be simultaneously transferred to the three endpoints of the Y-junction with the equal/unequal probabilities. The planar distribution of QST is expected to realize a quantum router, whose function is to make the quantum information on the central site (input port) appear equally/unequally at the three endpoints (output ports) with different directions. Moreover, the numerical simulations demonstrate that the scheme possesses the robustness on the fluctuations of the NN hopping and the on-site potential in the system. Furthermore, we show that the number of the output ports with different directions can be flexibly increased in an extended X-junction SSH chain, and the experimental feasibility for implementing special QST in a superconducting qubit-resonator system is briefly discussed. Our work extends the space distribution of QST from linear distribution to planar distribution and promotes the construction of large-scale quantum networks.

Quantum routing in planar graph using perfect state transfer

Quantum routing in planar graph using perfect state transfer

Single photon routing based on the selective coupling of the side-branch in the Plasmonic hybrid nanosystem with dipole–dipole interaction

We propose a theoretical model for the single photon quantum router that consists of two plasmonic waveguides, one of which is infinite and the other is semi-infinite, coupled to two two-level quantum dots (QDs) with dipole–dipole interaction (DDI). The infinite waveguide, the main branch, couples with both QDs, and the semi-infinite, the side branch, couples with the main branch at the position of one of the QDs. In such a system the incident single photon can also be transferred to the side branch, not only be transmitted or reflected. The results show that the transfer rate mainly depends on the coupling strength between the QDs and the two waveguides, but there exists a certain limit in the increase of the transfer rate. The DDI between the QDs gives a remarkable change to the routing spectra and the routing properties are different according to the position of the side branch. The proposed system is indeed multi-channel single photon quantum router, which has more practical significance than the one-dimensional router and can be employed in multi-user quantum networking.

Compact Design for Bi-Polarization Quantum Routers on SOI Platform

An ultra-compact optical quantum router (QR) consisting of a Mach–Zehnder interferometer (MZI) and waveguide tapers is proposed and numerically simulated, using silicon-on-insulator (SOI). The interferometer is designed to work at the center wavelength of 1550 nm with visibilities of 99.65% and 98.80% for TE and TM polarizations, respectively. Using the principle of phase compensation and self-image, the length of the waveguide tapers is shortened by an order of magnitude with the transmission above 95% for both TE and TM polarizations. Furthermore, polarization beam splitters (PBS) with an ultra-compact footprint of 1.4 × 10.4 μm2 with transmissions of 98% for bi-polarizations are achieved by introducing anisotropic metamaterials. The simulated results indicate that the interferometer facilitates low loss, a broad operating spectral range, and a large tolerance to size variation in fabrications. The optical switch possesses the routing function while maintaining the polarization states, which promises to pave the point-to-point BB84 protocol into applications of network-based quantum communication.

Hybrid routing protocol for quantum network based on classical and quantum routing metrics

A quantum repeater is the heart of a quantum internet that enables end-to-end communication over long distances using the quantum entanglement feature. Although this characteristic gives quantum networks tremendous power in terms of speed and security, it puts quantum networks, especially the quantum internet, in front of challenges, like transforming a short-distance quantum link into a long-distance link, in addition to entanglement routing for finding the best path within a quantum network. So, this research aims to propose a hybrid quantum routing protocol (HQRP) based on routing metrics of the classical networks like hops count, as well as metrics of the quantum network represented by the possibility of entanglement between end nodes in the network. As a result, a mathematical model was built to determine the optimal path among many paths within the quantum network, and it was implemented on our quantum network simulator. Finally, we concluded that the proposed algorithm gives the optimal path based on the highest entanglement probability and lowest number of hop count.

Nonreciprocal photonic quantum router via synthetic magnetism

Nonreciprocal photon transmissions at the single-quantum level play crucial roles in optical information processing. Here, we propose to develop a nonreciprocal photonic quantum router via synthetic magnetism, which can route photons of an input quantum state in one direction but block them in the other direction. Our model is based on a superconducting circuit of linearly coupled microwave cavities, and the Lorentz reciprocity is broken by synthesizing an effective magnetic field for photons. As a result, an input quantum signal from a given direction can be delivered on-demand to either of the two output ports, but it from the opposite direction is completely absorbed. Our scheme does not involve strong static magnetic fields and optical nonlinearity for generating the desired optical nonreciprocity. It is, therefore, expected to be a key ingredient for the construction of on-chip quantum networks.

Quantum routing of information using chiral quantum walks

We address routing of classical and quantum information over quantum network and show how to exploit chirality (directionality) to achieve nearly optimal and robust transport. In particular, we prove how continuous-time chiral quantum walks over a minimal graph are able to model directional transfer of information over a network. At first, we show how classical information, encoded onto an excitation localized at one vertex of a simple graph, may be sent to any other chosen location with nearly unit fidelity by tuning a single phase. Then, we prove that high-fidelity transport is also possible for coherent superpositions of states, i.e., for routing of quantum information. Furthermore, we show that by tuning the phase parameter, one obtains universal quantum routing, i.e., independent on the input state. In our scheme, chirality is governed by a single phase, and the routing probability is robust against fluctuations of this parameter. Finally, we address characterization of quantum routers and show how to exploit the self-energies of the graph to achieve high precision in estimating the phase parameter.

Tunable multi-outlet single photon quantum router in an optomechanical system

An experimentally accessible tunable single-photon multi-channel quantum router is investigated in a system consisting of an optomechanics cavity coulomb coupling to a nano-mechanical resonator. The router can extract a single-photon from the coherent input signal directly modulate into three different output channels, and the output probability is all close to 1. More important, the two output signal frequencies can be selected by adjusting Coulomb coupling strength. We also demonstrate the vacuum and thermal noise will be insignificant for the optical performance of the single-photon router at temperature of the order of 20 mK. Our proposal may have paved a new avenue towards multi-channel router and quantum network.