Perfect quantum state transfer in a dispersion-engineered waveguide

TL;DR

This paper demonstrates that by engineering the dispersion relation of a waveguide, one can passively achieve near-perfect quantum state transfer between qubits without active elements, advancing on-chip quantum networking.

Contribution

It introduces a passive dispersion engineering method for perfect quantum state transfer, avoiding the need for active components and enhancing robustness to qubit separation variations.

Findings

Achieves >= 98% transfer fidelity with dispersion engineering.

Derives optimal dispersion relations analytically and numerically.

Proposes a robust, inhomogeneous waveguide design.

Abstract

High-fidelity state transfer is fundamentally limited by time-reversal symmetry: one qubit emits a photon with a certain temporal pulse shape, whereas a second qubit requires the time-reversed pulse shape to efficiently absorb this photon. This limit is often overcome by introducing active elements. Here, we propose an alternative solution: by tailoring the dispersion relation of a waveguide, the photon pulse emitted by one qubit is passively reshaped into its time-reversed counterpart, thus enabling perfect absorption. We analytically derive the optimal dispersion relations in the limit of small and large qubit-qubit separations, and numerically extend our results to arbitrary separations via multiparameter optimization. We further propose a spatially inhomogeneous waveguide that renders the state transfer robust to variations in qubit separations. In all cases, we obtain near-unity transfer fidelity (>= 98%). Our dispersion-engineered waveguide provides a compact and passive route toward on-chip quantum networks, highlighting engineered dispersion as a powerful resource in waveguide quantum electrodynamics.