Unitary and efficient spin squeezing in cavity optomechanics

TL;DR

This paper introduces a method for producing highly efficient spin squeezed states in nitrogen-vacancy centers coupled to an optical cavity, overcoming previous limitations and achieving near-Heisenberg-limited squeezing.

Contribution

The authors propose a novel approach that completely erases spin-phonon entanglement, enabling unitary spin squeezing and transforming it into two-axis-twisting for enhanced precision.

Findings

Achieves spin squeezing scaling of J^{-2/3} with one-axis-twisting.

Transforms one-axis-twisting into two-axis-twisting for Heisenberg-limited scaling J^{-1}.

Method is robust against spin dephasing and relaxation effects.

Abstract

We propose an approach to produce spin squeezed states of a large number of nitrogen-vacancy centers in diamond nanostructures coupled to an optical cavity. Unlike the previous squeezing method proposed by Bennett et al. [Phys. Rev. Lett. 110, 156402 (2013)], which is limited by phonon number fluctuations due to the existence of phonon-spin entanglement, our proposal can completely erase the entanglement between spins and hybrid phonon-photon mode mediating the effective spin-spin interaction, and thus achieves unitary one-axis-twisting interactions between nitrogen-vacancy centres, yielding a squeezing scaling $J^{-2/3}$, where J is the total angular momentum. We found that, under certain conditions, our method has the potential to enhance the spin-spin nonlinear interactions. We also proposed a scheme utilizing repeatedly applying the one-axis-twisting evolution to two orthogonal spin directions, which enables the transformation of the one-axis-twisting interactions into two-axis-twisting type, and therefore leads to the spin squeezing with Heisenberg-limited scaling $J^{-1}$. Taking into account the noise effects of spin dephasing and relaxtion, we found that the proposed approaches are robust against imperfections.