Vacuum spin squeezing

TL;DR

This paper demonstrates that vacuum electromagnetic fields, enhanced by an optical cavity, can generate entanglement and spin squeezing in atomic ensembles, offering a simple, robust method for quantum manipulation without external light.

Contribution

It introduces a novel scheme for vacuum-induced spin squeezing in atomic clocks, eliminating the need for external light or precise cavity frequency control.

Findings

Vacuum fields can entangle atoms and produce spin squeezing.

The scheme is simple, robust, and does not require external light.

Two-axis twisting can be implemented for stronger squeezing.

Abstract

We investigate the generation of entanglement (spin squeezing) in an optical-transition atomic clock through the coupling to a vacuum electromagnetic field that is enhanced by an optical cavity. We show that if each atom is prepared in a superposition of the ground state and a long-lived electronic excited state, and viewed as a spin-1/2 system, then the collective vacuum light shift entangles the atoms, resulting in a squeezed distribution of the ensemble collective spin. This scheme reveals that even a vacuum field can be a useful resource for entanglement and quantum manipulation. The method is simple and robust since it requires neither the application of light nor precise frequency control of the ultra-high-finesse cavity. Furthermore, the scheme can be used to implement two-axis twisting by rotating the spin direction while coupling to the vacuum, resulting in stronger squeezing.