Passive photonic CZ gate with two-level emitters in chiral multi-mode waveguide QED

TL;DR

This paper proposes a passive, deterministic photonic controlled-Z gate using an array of two-level emitters coupled to chiral multi-mode waveguides, enabling high-fidelity quantum information processing.

Contribution

It introduces a novel passive photonic CZ gate design leveraging chiral emitter-waveguide interactions, achieving near-perfect fidelity with scalable emitter arrays.

Findings

Demonstrates a non-linear π-phase shift without spectral distortion.

Shows the gate fidelity approaches 1 with increasing emitters and efficiency.

Applicable to topological photonic platforms and other chiral waveguide systems.

Abstract

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 co-propagating 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 multi-photon scattering response, we demonstrate that, in certain limits, this configuration induces a non-linear $\pi$-phase shift between the polariton eigenstates of the system without distorting spectrally the wavepackets. Then, we show how to harness this non-linear 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 platforms with multiple chiral edge modes, opening their use for quantum information processing, or in other setups where such chiral multi-mode waveguide scenario can be obtained, e.g., in spin-orbit coupled optical fibers or photonic crystal waveguides.