Trapped ion scaling with pulsed fast gates

TL;DR

This paper introduces pulsed fast entangling gates for trapped ions that significantly improve speed and scalability, reducing infidelity and enabling entanglement across large ion crystals with manageable laser requirements.

Contribution

It proposes a new pulsed fast gate scheme with less stringent laser repetition rate requirements and analyzes its scalability to large ion crystals.

Findings

Fast gates restore motional modes at high speeds.

Reduced laser repetition rate improves fidelity.

Scaling to large crystals requires increased laser power.

Abstract

Fast entangling gates for trapped ions offer vastly improved gate operation times relative to implemented gates, as well as approaches to trap scaling. Gates on neighbouring ions only involve local ions when performed sufficiently fast, and we find that even a fast gate between distant ions with few degrees of freedom restores all the motional modes given more stringent gate speed conditions. We compare pulsed fast gate schemes, defined by a timescale faster than the trap period, and find that our proposed scheme has less stringent requirements on laser repetition rate for achieving arbitrary gate time targets and infidelities well below $10^{-4}$. By extending gate schemes to ion crystals, we explore the effect of ion number on gate fidelity for coupling neighbouring pairs of ions in large crystals. Inter-ion distance determines the gate time, and a factor of five increase in repetition rate, or correspondingly the laser power, reduces the infidelity by almost two orders of magnitude. We also apply our fast gate scheme to entangle the first and last ions in a crystal. As the number of ions in the crystal increases, significant increases in the laser power are required to provide the short gate times corresponding to fidelity above 0.99.