# Ultrafast coherent excitation of a Ca$^+$ ion

## TL;DR

This paper demonstrates a high-repetition-rate pulsed laser system for ultrafast coherent excitation of a Ca$^+$ ion, enabling faster quantum gate operations in trapped ion quantum computing.

## Contribution

Introduction of a 5 GHz pulsed laser system derived from a stabilized frequency comb for coherent control of Ca$^+$ ions.

## Key findings

- Achieved coherent population transfer with picosecond pulses
- Measured ion-laser coupling strength using three techniques
- Showed feasibility for implementing fast phase gates

## Abstract

Trapped ions are a well-studied and promising system for the realization of a scalable quantum computer. Faster quantum gates would greatly improve the applicability of such a system and allow for greater flexibility in the number of calculation steps. In this paper we present a pulsed laser system, delivering picosecond pulses at a repetition rate of 5 GHz and resonant to the S$_{1/2}$ to P$_{3/2}$ transition in Ca$^+$ for coherent population transfer to implement fast phase gate operations. The optical pulse train is derived from a mode-locked, stabilized optical frequency comb and inherits its frequency stability. Using a single trapped ion, we implement three different techniques for measuring the ion-laser coupling strength and characterizing the pulse train emitted by the laser, and show how all requirements can be met for an implementation of a fast phase gate operation.