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arXiv:2504.14581 · npj Quantum Information

Photonic qubit gates via 1D scattering from an array of two-level emitters

Evangelos Varvelis, Joachim Ankerhold

Published Jul 17, 2026• 0 citations
arXivHTMLPDF

Abstract

Abstract Photonic quantum computing offers a promising platform for quantum information processing, benefiting from the long coherence times of photons and their ease of manipulation. This paper presents a scheme for implementing a deterministic phase gate for dual-rail number encoded photonic qubits, leveraging a standard 1D waveguide coupled to an array of two-level emitters (TLE). Using a transfer matrix approach, we develop a protocol for deterministic phase gate operation, demonstrating its robustness against non-waveguide mode coupling and disorder. Finally, we relax the idealized assumption of monochromatic light, considering finite-bandwidth pulses. Despite these realistic considerations, our results indicate high fidelity for the proposed phase gate protocol. Finally we will discuss two qubit operations.

DOI
10.1038/s41534-026-01324-w

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Abstract Photonic quantum computing offers a promising platform for quantum information processing, benefiting from the long coherence times of photons and their ease of manipulation. This paper presents a scheme for implementing a deterministic phase gate for dual-rail number encoded photonic qubits, leveraging a standard 1D waveguide coupled to an array of two-level emitters (TLE). Using a transfer matrix approach, we develop a protocol for deterministic phase gate operation, demonstrating its robustness against non-waveguide mode coupling and disorder. Finally, we relax the idealized assumption of monochromatic light, considering finite-bandwidth pulses. Despite these realistic considerations, our results indicate high fidelity for the proposed phase gate protocol. Finally we will discuss two qubit operations.
Abstract We propose an architecture for achieving high-fidelity deterministic quantum logic gates on dual-rail encoded photonic qubits by letting photons interact with a two-level emitter (TLE) inside an optical cavity. The photon wave packets that define the qubit are preserved after the interaction due to a quantum control process that actively loads and unloads the photons from the cavity and dynamically alters their effective coupling to the TLE. The controls rely on nonlinear wave mixing between cavity modes enhanced by strong externally modulated electromagnetic fields or on AC Stark shifts of the TLE transition energy. We numerically investigate the effect of imperfections in terms of loss and dephasing of the TLE as well as control field miscalibration. Our results suggest that III-V quantum dots in GaAs membranes is a promising platform for photonic quantum information processing.
We present a scheme for implementing a high-fidelity non-linear phase shift on a photonic state. The scheme is based on repeated scattering off a two-level quantum emitter embedded in a chiral or one-sided waveguide. The waveguide is equipped with elements inducing second-order dispersion and temporal phase shifts, which effectively form a harmonic trap and confine the photon pulses to a Gaussian shape. The same quantum emitter can be used for each scattering, and thus, only one quantum emitter is needed in this scheme. To illustrate the application of our scheme for photonic quantum computing and quantum communication, we analyze the implementation of a control-Z gate and a deterministic Bell-state analyzer for photonic qubits. Through numerical optimization, we show that we can reach a control-Z gate fidelity of F∼99.2%\mathcal{F} \sim 99.2\%F∼99.2% (F∼96%\mathcal{F} \sim 96\%F∼96%) and a success probability of Ps∼99.6%P_s \sim 99.6 \%Ps​∼99.6% (Ps∼98%P_s\sim 98 \%Ps​∼98%) for a Bell-state measurement with N=17N=17N=17 (N=5N=5N=5) scatterings.
A central goal in photonic quantum information processing is the ability to perform high-fidelity logic gates between multiple optical qubits. Here, we present our recent theoretical work on using optical nonlinearities to implement controlled-phase gates between two optical qubits. Our approach is based on using dynamically coupled cavities to convert photons travelling in a waveguide into highly confined cavity modes. This conversion enables very strong interactions between photons in quasi-monochromatic modes, which enables high fidelity gates. We will discuss gate protocols based on second- and third order nonlinear materials as well as interactions with two-level emitters.
Engineering deterministic photonic gates with simple resources is one of the long-standing challenges in photonic quantum computing. Here, we design a passive conditional gate between copropagating photons using an array of only two-level emitters. The key resource is to harness the effective photon-photon interaction induced by the chiral coupling of the emitter array to two waveguide modes with different resonant momenta at the emitter’s transition frequency. By studying the system’s multiphoton scattering response, we demonstrate that, in certain limits, this configuration induces a nonlinear π -phase shift between the polariton eigenstates of the system without distorting spectrally the wave packets. Then, we show how to harness this nonlinear phase shift to engineer a conditional, deterministic photonic gate in different qubit encodings, with a fidelity arbitrarily close to 1 in the limit of large number of emitters and coupling efficiency. Our configuration can be implemented in topological photonic setups with multiple chiral-edge modes, opening their use for quantum information processing, or in other setups where such chiral light-matter couplings can be effectively obtained, such as optical fibers or photonic-crystal optical and microwave waveguides.
Photons are appealing as flying quantum bits due to their low-noise, long coherence times, light-speed transmission, and ease of manipulation at the single-qubit level using standard optical components such as beam splitters and waveguides. The challenge in optical quantum information processing has been the realization of two-qubit gates for photonic qubits due to the lack of highly efficient optical Kerr nonlinearities at the single-photon level. To date, only probabilistic two-qubit photonic controlled-phase gates based on linear optics and projective measurement using photon detectors have been demonstrated. Here we show that a high-fidelity frequency-encoded deterministic two-photon controlled-phase gate can be achieved by exploiting the strong photon-photon correlation enabled by photonic dimers, and the unique nonreciprocal photonic propagation in chiral quantum nanophotonic systems.
Abstract The single-photon quantum computing paradigm currently relies on the multi-port interference in linear optical devices, which is intrinsically based on probabilistic measurements outcome, and thus non-deterministic. Devising a fully deterministic, universal, and practically achievable quantum computing platform based on single-photon encoding and integrated photonic circuits is still an open challenge. Here we propose to exploit the interplay of distributed self-Kerr nonlinearity and localized hopping in quantum photonic interferometers to implement deterministic entangling quantum gates with dual rail photonic qubits. It is shown that a universal set of single- and two-qubit gates can be designed by a suitable concatenation of few optical interferometric elements, reaching optimal fidelities arbitrarily close to 100% that are theoretically demonstrated through a bound constrained optimization algorithm. The actual realization would require the concatenation of a few tens of elementary operations, as well as on-chip optical nonlinearities that are compatible with some of the existing quantum photonic platforms, as it is finally discussed.