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arXiv:2410.21555 · Physical Review A

Entanglement generation using single-photon pulse reflection in realistic networks

Ferdinand Omlor, Benedikt Tissot, Guido Burkard

Published Jan 10, 2025• 7 citations
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Abstract

A general entanglement generation protocol between remote stationary qubits using single-photon reflection in a photonic network is explored theoretically. The nodes of the network consist of single qubits that are typically represented by the spin of a color center, each localized in a separate optical cavity and linked to other nodes via photonic links such as optical fibers. We derive a model applicable to a wide range of parameters and scenarios to describe the nodes and the local spin-photon interaction accounting for the pulsed (finite-bandwidth) nature of flying single photons while optimizing the rate and fidelity. We investigate entanglement generation between remote qubits and tailor protocols to a variety of physical implementations with different properties. Of particular interest is the regime of weak coupling and low cooperativity between the spin and cavity, which is relevant in the cases of the nitrogen- and silicon-vacancy centers in diamond. We also take into account the variability of the properties between realistic (stationary) nodes.

DOI
10.1103/physreva.111.012612

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A general entanglement generation protocol between remote stationary qubits using single-photon reflection in a photonic network is explored theoretically. The nodes of the network consist of single qubits that are typically represented by the spin of a color center, each localized in a separate optical cavity and linked to other nodes via photonic links such as optical fibers. We derive a model applicable to a wide range of parameters and scenarios to describe the nodes and the local spin-photon interaction accounting for the pulsed (finite-bandwidth) nature of flying single photons while optimizing the rate and fidelity. We investigate entanglement generation between remote qubits and tailor protocols to a variety of physical implementations with different properties. Of particular interest is the regime of weak coupling and low cooperativity between the spin and cavity, which is relevant in the cases of the nitrogen- and silicon-vacancy centers in diamond. We also take into account the variability of the properties between realistic (stationary) nodes.
Abstract The generation of entanglement between remote matter qubits has developed into a key capability for fundamental investigations as well as for emerging quantum technologies. In the single-photon, protocol entanglement is heralded by generation of qubit-photon entangled states and subsequent detection of a single photon behind a beam splitter. In this work we perform a detailed theoretical and experimental investigation of this protocol and its various sources of infidelity. We develop an extensive theoretical model and subsequently tailor it to our experimental setting, based on nitrogen-vacancy centers in diamond. Experimentally, we verify the model by generating remote states for varying phase and amplitudes of the initial qubit superposition states and varying optical phase difference of the photons arriving at the beam splitter. We show that a static frequency offset between the optical transitions of the qubits leads to an entangled state phase that depends on the photon detection time. We find that the implementation of a Charge-Resonance check on the nitrogen-vacancy center yields transform-limited linewidths. Moreover, we measure the probability of double optical excitation, a significant source of infidelity, as a function of the power of the excitation pulse. Finally, we find that imperfect optical excitation can lead to a detection-arm-dependent entangled state fidelity and rate. The conclusion presented here are not specific to the nitrogen-vacancy centers used to carry out the experiments, and are therefore readily applicable to other qubit platforms.
Quantum networks involving multiqubit entanglement allow exciting applications in quantum communication, quantum sensing, and distributed quantum computation. The efficiency of nonlocal entanglement generation through optical channels drops exponentially with the distance between network nodes. We present a parallel and heralded protocol for generating distributed multiqubit entanglement across multiple nodes. This is achieved by using a high-dimensional single photon that works as a common-data bus connecting all stationary qubits (i.e., silicon-vacancy electron spins), each of which is coupled to a single-sided optical cavity. Parallel multiqubit entangled states are heralded by the detection of the single photon after it interacts with each stationary qubit and passes through each photonic modulation circuit. This parallel protocol can significantly improve the efficiency of distributed entanglement generation and provides a viable route towards distributed multinode quantum networks.
Nonlocal entanglement generation among multiple remote quantum nodes provides a critical foundation for a variety of counterintuitive quantum applications. The exponential loss of photons transmitting over optical fibers sets an upper limit for entangling these quantum nodes. Here, we propose a resource-efficient and parallel protocol for entangling multiple remote quantum nodes via time-bin multiplexing. The transmission of a single photon with qudit-encoding in the time-bin mode enables entangling multiple stationary qubits in parallel, when single photons and individual stationary qubits interfaces are used and photon-state modulations are properly introduced before subsequently impinging the photon into each interface. Our protocol can generate parallel multipartite entanglement among (N≥3N\geq3N≥3) quantum nodes with the dimension of the photonic time bins independent of NNN, exponentially reducing the requirements for the coherence time of the stationary qubits and for the complexity of the photonic modulations. These distinct features make our protocol particularly advantageous for the development of multinode quantum networks.
Nonlocal entanglement generation among multiple remote quantum nodes provides a critical foundation for a variety of counterintuitive quantum applications. The exponential loss of photons transmitting over optical fibers sets an upper limit for entangling these quantum nodes. Here, we propose a resource-efficient and parallel protocol for entangling multiple remote quantum nodes via time-bin multiplexing. The transmission of a single photon with qudit-encoding in the time-bin mode enables entangling multiple stationary qubits in parallel when single photons and individual stationary qubit interfaces are used and photon-state modulations are properly introduced before subsequently impinging the photon into each interface. Our protocol can generate parallel multipartite entanglement among (N≥3) quantum nodes with the dimension of the photonic time bins independent of N, exponentially reducing the requirements for the coherence time of the stationary qubits and for the complexity of the photonic modulations. These distinct features make our protocol particularly advantageous for the development of multinode quantum networks.
Remote state preparation is a fundamental quantum-information protocol that exploits prior knowledge of a target state to reduce the communication resources required for quantum-state distribution. Here, we propose a remote-state-preparation protocol for a stationary electron-spin qubit using hybrid entanglement between the electron spin and a coherent-state light pulse, generated by spin-dependent reflection from a spin-cavity system. Unlike single-photon encodings, the coherent-state encoding is naturally tolerant of photon loss: a loss channel attenuates the coherent-state amplitude, leading to a gradual reduction in preparation fidelity rather than probabilistic protocol failure. The central difficulty---implementing the projection onto superpositions of nonorthogonal coherent states required in the conventional protocol---is circumvented by coupling the transmitted pulse to an auxiliary spin, followed by homodyne detection and a spin projective measurement. The protocol therefore avoids direct coherent-state-superposition measurements and photon-number-resolving detection. In the ideal limit, deterministic preparation of a particular class of target states can be achieved using only one bit of classical communication. We analytically quantify the effects of coherent-state nonorthogonality, fiber loss, and spin dephasing on the preparation fidelity. Increasing the coherent-state amplitude improves state distinguishability and hence the preparation fidelity, but also enhances which-branch information leakage caused by photon loss, resulting in an optimal amplitude at each transmission distance. For experimentally relevant parameters, the optimized average fidelity remains well above the classical benchmark over distances of tens of kilometers. We also discuss a possible implementation using diamond nitrogen-vacancy centers.
Distributed quantum computing requires a quantum network with robust links between physically separated quantum nodes [1]. Hybrid networks where nodes from different types of stationary qubits (such as neutral atoms or solid state defects) are linked, can be used to take advantage of the strengths of various systems. An efficient interface for fast and reliable exchange of quantum information between stationary qubits at nodes with photons, or traveling qubits, is needed for distributing entanglement between nodes. A high rate of generating and distributing light-matter entangled states will scale up the speed of computation distributed between the nodes of a network.