Entangling ions with engineered light gradients

TL;DR

This paper presents a new geometric-phase entangling method using structured light gradients in trapped-ion systems, achieving high-fidelity two-qubit gates despite spectral crowding.

Contribution

Introduces a transverse structured-light force scheme that reduces spectral crowding effects while enabling high-fidelity entangling gates in multi-ion traps.

Findings

Achieved two-qubit gate errors below 0.5% in up to 12-ion crystals

Demonstrated compatibility with various qubit encodings

Established gradient-field light-shift gates as scalable for complex ion systems

Abstract

Spectral crowding of collective motional modes limits the fidelity of entangling interactions in trapped-ion quantum processors by inducing off-resonant coupling to spectator modes. We introduce a geometric-phase entangling interaction driven by a transverse, time-dependent structured-light force. By applying the force in a plane orthogonal to the optical propagation direction, we reduce the effects of spectral crowding while preserving single-ion addressing. The scheme is compatible with arbitrary qubit encodings, provided that the qubit states experience a differential AC Stark shift. We experimentally realise high-fidelity two-qubit gates with error rates below $5\times10^{-3}$ in ion crystals containing up to 12 ions confined within a single potential well. These results establish gradient-field light-shift gates as a scalable approach to high-fidelity entangling generation in spectrally crowded trapped-ion systems.