Rapid exchange cooling with trapped ions

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 40Ca+ ions, executing the necessary transport in 107 μs, 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.

Spatial and Temporal Detection of Ions Ejected from Coulomb Crystals

“…, the movement of ions from where they are initially formed in the trap to their equilibrium position in the crystal). Understanding the efficiency of sympathetic cooling is critical in fields such as quantum information processing, where cooling the computational ions has been described as the “runtime bottleneck” . While sympathetic cooling has been experimentally measured in very small crystals (with <5 ions), ,, it is challenging to apply these techniques to more complex systems, and sympathetic cooling in larger crystals has been predominantly studied using detailed simulations. − The time-dependent kinetic energy distribution of laser-irradiated 113 Cd + ions was recently experimentally measured in large bicomponent Cd + –Ca + Coulomb crystals .…”

“…Understanding the efficiency of sympathetic cooling is critical in fields such as quantum information processing, where cooling the computational ions has been described as the “runtime bottleneck” . While sympathetic cooling has been experimentally measured in very small crystals (with <5 ions), ,, it is challenging to apply these techniques to more complex systems, and sympathetic cooling in larger crystals has been predominantly studied using detailed simulations. − The time-dependent kinetic energy distribution of laser-irradiated 113 Cd + ions was recently experimentally measured in large bicomponent Cd + –Ca + Coulomb crystals . However, as this approach was based on the Doppler broadening of the 113 Cd + fluorescence signal, it cannot be straightforwardly applied to the majority of (nonfluorescing) cotrapped species that are of interest in ion reactivity studies.…”