Atom-ion quantum gate

TL;DR

This paper develops a theoretical model for spin-dependent atom-ion collisions, enabling the simulation and optimization of a high-fidelity two-qubit quantum gate using ultracold systems.

Contribution

It introduces a simplified single-channel model for spin-dependent atom-ion interactions and demonstrates a high-fidelity quantum gate simulation with optimal control.

Findings

Achieved a gate fidelity of 0.999

Simulated a two-qubit phase gate between Ba135+ ion and Rb87 atom

Optimized gate process with optimal control techniques

Abstract

We study ultracold collisions of ions with neutral atoms in traps. Recently, ultracold atom-ion systems are becoming available in experimental setups, where their quantum states can be coherently controlled. This allows for an implementation of quantum information processing combining the advantages of charged and neutral particles. The state-dependent dynamics that is a necessary ingredient for quantum computation schemes is provided in this case by the short-range interaction forces depending on hyperfine states of both particles. In this work we develop a theoretical description of spin-state-dependent trapped atom-ion collisions in the framework of a Multichannel Quantum Defect Theory (MQDT) and formulate an effective single channel model that reduces the complexity of the problem. Based on this description we simulate a two-qubit phase gate between a Ba135+ ion and a Rb87 atom using a realistic combination of the singlet and triplet scattering lengths. We optimize and accelerate the gate process with the help of optimal control techniques. Our result is a gate fidelity 0.999 within 350 microseconds.