A Wavelength-Insensitive, Multispecies Entangling Gate for Group-2 Atomic Ions

TL;DR

This paper introduces a wavelength-insensitive geometric phase gate for Group-2 atomic ions, enabling high-fidelity entanglement across a broad optical spectrum, with potential for multispecies ion quantum computing.

Contribution

The authors propose a novel, wavelength-insensitive entangling gate scheme for Group-2 ions using a geometric phase approach, applicable to multiple ion species and spanning ultraviolet to infrared wavelengths.

Findings

Error rates below 10^{-4} demonstrated

Gate durations analyzed across 300 nm to 2 μm spectrum

Applicable to both identical and dissimilar ion pairs

Abstract

We propose an optical scheme for generating entanglement between co-trapped identical or dissimilar alkaline earth atomic ions ($^{40}\text{Ca}^+$, $^{88}\text{Sr}^+$, $^{138}\text{Ba}^+$, $^{226}\text{Ra}^+$) which exhibits fundamental error rates below $10^{-4}$ and can be implemented with a broad range of laser wavelengths spanning from ultraviolet to infrared. We also discuss straightforward extensions of this technique to include the two lightest Group-2 ions ($\text{Be}^+$, $\text{Mg}^+$) for multispecies entanglement. The key elements of this wavelength-insensitive geometric phase gate are the use of a ground ($S_{1/2}$) and a metastable ($D_{5/2}$) electronic state as the qubit levels within a $\sigma^z \sigma^z$ light-shift entangling gate. We present a detailed analysis of the principles and fundamental error sources for this gate scheme which includes photon scattering and spontaneous emission decoherence, calculating two-qubit-gate error rates and durations at fixed laser beam intensity over a large portion of the optical spectrum (300 nm to 2 $\mu \text{m}$) for an assortment of ion pairs. We contrast the advantages and disadvantages of this technique against previous trapped-ion entangling gates and discuss its applications to quantum information processing and simulation with like and multispecies ion crystals.