Continuous Raman sideband cooling beyond the Lamb-Dicke Regime in a trapped ion chain

TL;DR

This paper demonstrates continuous Raman sideband cooling of a 24-ion chain to the motional ground state beyond the Lamb-Dicke regime, achieving robust, wide-bandwidth cooling suitable for large-scale quantum computing.

Contribution

It introduces a novel continuous Raman sideband cooling method that works beyond the Lamb-Dicke regime and is scalable to large ion chains.

Findings

Nearly all axial modes cooled to ground state in a 24-ion chain.

Cooling bandwidth of 4 MHz, independent of ion number.

Enhanced robustness compared to traditional cooling methods.

Abstract

We report continuous Raman sideband cooling (CRSC) of a long ion chain to the motional ground state beyond the Lamb-Dicke (LD) regime. By driving multiple sideband transitions simultaneously, we show that nearly all axial modes of a 24-ion chain are cooled to the ground state, with an LD parameter as large as $\eta = 1.3$, spanning a frequency bandwidth of 4 MHz. Compared to traditional ground-state cooling methods such as pulsed sideband cooling or electromagnetic-induced-transparency (EIT) cooling, our method offers two key advantages: robustness to timing errors; and an ultra-wide bandwidth unlimited by the number of ions. This technique contributes as a crucial step for large-scale quantum information processing with linear ion chains and higher dimensions alike, and can be readily generalized to other atomic and molecular systems.