Fast multi-qubit global-entangling gates without individual addressing of trapped ions

TL;DR

This paper introduces methods to significantly accelerate multi-qubit entangling gates in trapped ion systems without individual addressing, achieving high fidelity and robustness against motional phase fluctuations.

Contribution

It presents a novel scheme to speed up two-qubit and multi-qubit gates beyond traditional limits, using multiple frequency components and phase-insensitive techniques.

Findings

Increased gate speed independent of trap frequency.

Successful entanglement of more than two qubits simultaneously.

Gates are robust against motional phase fluctuations.

Abstract

We propose and study ways speeding up of the entangling operations in the trapped ions system with high fidelity. First, we find a scheme to increase the speed of a two-qubit gate without the limitation of trap frequency, which was considered as the fundamental limit. Second, we study the fast gate scheme for entangling more than two qubits simultaneously. We apply the method of applying multiple frequency components on laser beams for the gate operations. In particular, in order to avoid infinite terms from the coupling to carrier transition, we focus on the phase-insensitive gate scheme here. We carefully study the effect of large excitation of motional mode beyond the limit of Lamb-Dicke approximation by including up to second order terms of the Lamb-Dicke parameter. We study the speed limit of multi-qubit global entangling gates without individual addressing requirements. Furthermore, our gates can be made insensitive to the fluctuation of initial motional phases which are difficult to stabilise in the phase-insensitive gate scheme.