Trapped-ion laser cooling in structured light fields

TL;DR

This paper explores structured light fields for laser cooling of trapped ions, aiming to improve efficiency and scalability by reducing unwanted carrier excitation through innovative optical configurations.

Contribution

It introduces simple waveguide-based structured light profiles, such as standing waves and Hermite-Gauss modes, for carrier-free cooling in trapped ions, enhancing cooling performance.

Findings

Carrier-free EIT cooling improves rate and final phonon number.

Structured light profiles enable selective sideband excitation.

Performance limitations due to polarization and modal impurities are quantified.

Abstract

Laser cooling is fundamental to quantum computation and metrology with trapped ions, and can occupy a majority of runtime in current systems. A key limitation to cooling arises from unwanted carrier excitation, which in typically used running wave (RW) fields invariably accompanies the sideband transitions effecting cooling. We consider laser cooling in structured light profiles enabling selective sideband excitation with nulled carrier drive; motivated by integrated photonic approaches' passive phase and amplitude stability, we propose simple configurations realizable with waveguide addressing using either standing wave (SW) or first-order Hermite-Gauss (HG) modes. We quantify performance of Doppler cooling from beyond the Lamb-Dicke regime (LDR), and ground-state (GS) cooling using electromagnetically induced transparency (EIT) leveraging these field profiles. Carrier-free EIT offers significant benefits simultaneously in cooling rate, motional frequency bandwidth, and final phonon number. Carrier-free Doppler cooling's advantage is significantly compromised beyond the LDR but continues to hold, indicating such configurations are applicable for highly excited ions. Our simulations focus on level structure relevant to $^{40}$Ca$^+$, though the carrier-free configurations can be generally applied to other species. We also quantify performance limitations due to polarization and modal impurities relevant to experimental implementation. Our results indicate potential for simple structured light profiles to alleviate bottlenecks in laser cooling, and for scalable photonic devices to improve basic operation quality in trapped-ion systems.