Rapid Exchange Cooling with Trapped Ions

TL;DR

This paper introduces exchange cooling for trapped-ion quantum computers, enabling rapid, efficient cooling of computational ions without multi-species traps, thus enhancing quantum processing speed and fidelity.

Contribution

The authors demonstrate a novel exchange cooling protocol that replaces sympathetic cooling, allowing faster cooling of ions within a single species for improved quantum computation.

Findings

Achieved cooling of ions in 107 μs, ten times faster than traditional methods.

Removed over 96% of motional energy, up to 102 quanta.

Verified no decoherence occurs during coolant ion re-cooling.

Abstract

The trapped-ion quantum charge-coupled device (QCCD) architecture is a leading candidate for advanced quantum information processing. In current QCCD implementations, imperfect ion transport and anomalous heating can excite ion motion during a calculation. To counteract this, intermediate cooling is necessary to maintain high-fidelity gate performance. Cooling the computational ions sympathetically with ions of another species, a commonly employed strategy, creates a significant runtime bottleneck. Here, we demonstrate a different approach we call exchange cooling. Unlike sympathetic cooling, exchange cooling does not require trapping two different atomic species. The protocol introduces a bank of "coolant" ions which are repeatedly laser cooled. A computational ion can then be cooled by transporting a coolant ion into its proximity. We test this concept experimentally with two $^{40}\mathrm{Ca}^{+}$ ions, executing the necessary transport in 107 $\mathrm{\mu s}$, an order of magnitude faster than typical sympathetic cooling durations. We remove over 96%, and as many as 102(5) quanta, of axial motional energy from the computational ion. We verify that re-cooling the coolant ion does not decohere the computational ion. This approach validates the feasibility of a single-species QCCD processor, capable of fast quantum simulation and computation.