Cavity optomechanics deals with the radiation pressure induced interaction between photons and mechanical motion in a cavity. It has promising applications in quantum information science. In this review, the authors discuss quantum entanglement in this emerging area of research. After giving a brief historical background on the topic of entanglement and cavity optomechanics, measures of continuous variable entanglement are discussed somewhat in great details. This is followed by a short discussion on cavity quantum optomechanics, relevant to the topic on entanglement. Then the authors discuss most of the prominent ideas and proposals pertaining to entanglement research in cavity optomechanics up until now. The authors have emphasized the key theoretical concepts without too much rigor and provided relevant experimental details whenever deemed appropriate. Finally, the authors conclude by giving a perspective on other quantum correlations such as quantum discord and quantum synchronization.
Multipartite quantum entanglement in PT-symmetric molecular optomechanics: Nonreciprocal enhancement and thermal resilience to \SI{500}{\kelvin}
We present a theoretical framework for a PT-symmetric double-cavity molecular optomechanical system demonstrating nonreciprocal enhancement of multipartite quantum entanglement at elevated temperatures. All bipartite entanglement channels (Eac, EaB1, EcB2, EB1B2) simultaneously maximize at optimal nonreciprocal asymmetry J1/J2≈5, with entanglement persisting to $T \sim \SIrange{400}{500}{\kelvin}$ (material-limited ceiling) two orders of magnitude beyond conventional optomechanical systems. This thermal resilience and balanced enhancement across all channels arise from synergistic combination of ultra-high-frequency molecular vibrations ($ω_m/2π= \SI{30}{\tera\hertz}$), collective N coupling enhancement with $N=\num{e6}$ molecules, and directional nonreciprocal coupling shielding entanglement-generating interactions from backaction noise. Unlike optical parametric amplifier schemes where vibration-vibration enhancement suppresses optical-vibration correlations, our PT-symmetric architecture circumvents this fundamental trade-off, validated through rigorous stability analysis via Routh-Hurwitz criterion.