Ancilla mediated qubit readout and heralded entanglement between rare-earth dopant ions in crystals

TL;DR

This paper proposes a method for optical readout and heralded entanglement of rare-earth dopant ions in crystals using an ancilla ion with Bayesian analysis, addressing incoherent effects and extending to remote ions.

Contribution

It introduces a novel ancilla-based architecture for qubit readout and entanglement in rare-earth ions, including strategies to mitigate incoherent processes.

Findings

Bayesian analysis effectively extracts qubit state information from ancilla fluorescence.

Proposed methods reduce the impact of incoherent processes on readout fidelity.

Continuous monitoring enables entanglement between remote ions.

Abstract

Owing to their long excited state lifetimes, rare-earth ions in crystals are widely used in quantum applications. To allow optical readout of the qubit state of individual ions, we propose to dope the crystal with an additional nearby ancilla ion with a shorter radiative lifetime. We show how a Bayesian analysis exhausts the information about the state of the qubit from the optical signal of the ancilla ion. We study the effects of incoherent processes and propose ways to reduce their effect on the readout. Finally, we extend the architecture to ions residing in two remote cavities, and we show how continuous monitoring of fluorescence signals from the two ancilla ions leads to entanglement of the qubit ions.