Collective Spin-Light and Light-Mediated Spin-Spin Interactions in an Optical Cavity

Abstract

The interaction between an atomic ensemble and a light mode in a high-finesse optical cavity can easily reach the strong-coupling regime, where quantum effects dominate. In this regime, the interaction can be used to generate both atom-light and atom-atom entanglement. We analyze the dominant effects on the collective atomic state and the light field, and derive a unified approach that can account for atomic entanglement induced both by measurements on the light field, and by ignoring the state of the light field altogether. We present analytical expressions for the entanglement induced by the interaction, and determine the conditions that maximize the entanglement-induced gain over the standard quantum limit in quantum sensors and atomic clocks.

Efficient Generation of Spin Cat States

“…It does not require large modification to the existing experimental setups. Our scheme can be realized with state-ofthe-art techniques in a Bose-Einstein condensate (BEC) system [47,48] or an optical cavity system with lightmediated interactions [34,49,50]. It points out an alternative way for generating various entangled states, which has a broad interest for quantum technologies such as quantum metrology and quantum computing.…”

Generating Extreme Spin Squeezing

“…Our proposed scheme relies only on experimentally demonstrated OAT interactions in an alternating sequence with standard spin rotations. Thus, the advantage of our approach is that it can be realized in current experimental setups that employ OAT, specifically optical lattice clock atom experiments [14,[20][21][22][23]. We find that only two applications of the OAT Hamiltonian are sufficient to generate Heisenberg scaling.…”

“…Optical methods to generate collective entanglement rely on the interaction of the atomic ensemble with a cavity light field. Cavity feedback squeezing [20,23] is a deterministic technique to generate a control Hamiltonian χ Ŝ2…”

“…Moreover, any photon scattered in the free space projects one atom into either spin-up or spin-down, thus reducing the spin coherence. However, as it has been recently demonstrated [22,23] and modeled [31,32], decoherence can be minimized to reach a near-unitary evolution by tuning the entanglinglight frequency. The sign of the χ Ŝ2 z Hamiltonian can be reversed simply by switching the sign of the detuning between the atom-cavity resonance and the light [23,31].…”

“…One way to produce an effective OAT is by the interaction of the atomic ensemble with a single-mode cavity field [14,[20][21][22]33]. In this system, Ĥ = − ωn c Ŝz + S , (7) where ω represents the light shift per photon on the spin levels induced by the coupling to the cavity mode and n c is the number of photons [23]. If Ŝz = 0 one can expand the photon number n ( Ŝz ) in terms of the powers of Ŝz and approximate…”