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Physical Review A

Dark-state entanglement of two atomic ensembles via cavity superradiance

Kang Shen, Xiangming Hu, Fei Wang

Published Sep 15, 2025• 1 citation
Publisher

Abstract

We propose an effective model leveraging cavity superradiance to achieve entanglement between two spatially separated two-level atomic ensembles trapped in a standing-wave optical cavity. This model is based on permutational symmetry breaking, which leads to the emergence of entangled quantum dark states with nonzero excitations but vanishing decay rate. This steady-state entanglement is created by purely dissipative dynamics, unlike the superradiance of permutationally symmetric two-level atoms, whose steady state is the ground state. Furthermore, we show that the entanglement is significantly enhanced near critical points in the superradiance potential because of the extremely high two-mode squeezing factor between two atomic ensembles. We also discuss spin squeezing in each atomic ensemble in the vicinity of specific critical points in the potential. These findings may play an important role in the generation of correlations immune to dissipation in separated atomic modes.

DOI
10.1103/8jcs-g21s

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We propose an effective model leveraging cavity superradiance to achieve entanglement between two spatially separated two-level atomic ensembles trapped in a standing-wave optical cavity. This model is based on permutational symmetry breaking, which leads to the emergence of entangled quantum dark states with nonzero excitations but vanishing decay rate. This steady-state entanglement is created by purely dissipative dynamics, unlike the superradiance of permutationally symmetric two-level atoms, whose steady state is the ground state. Furthermore, we show that the entanglement is significantly enhanced near critical points in the superradiance potential because of the extremely high two-mode squeezing factor between two atomic ensembles. We also discuss spin squeezing in each atomic ensemble in the vicinity of specific critical points in the potential. These findings may play an important role in the generation of correlations immune to dissipation in separated atomic modes.
We present and analyze a new approach for the generation of atomic spin-squeezed states. Our method involves the collective coupling of an atomic ensemble to a decaying mode of an open optical cavity. We demonstrate the existence of a collective atomic dark state, decoupled from the radiation field. By explicitly constructing this state we find that it can feature spin squeezing bounded only by the Heisenberg limit. We show that such dark states can be deterministically prepared via dissipative means, thus turning dissipation into a resource for entanglement. The scaling of the phase sensitivity taking realistic imperfections into account is discussed.
We investigate the collective decay dynamics of atoms with a generic multilevel structure (angular momenta F ↔ F 0 ) coupled to two light modes of different polarization inside a cavity.In contrast to twolevel atoms, we find that multilevel atoms can harbor eigenstates that are perfectly dark to cavity decay even within the subspace of permutationally symmetric states (collective Dicke manifold).The dark states arise from destructive interference between different internal transitions and are shown to be entangled.Remarkably, the superradiant decay of multilevel atoms can end up stuck in one of these dark states, where a macroscopic fraction of the atoms remains excited.This opens the door to the preparation of entangled dark states of matter through collective dissipation that are useful for quantum sensing and quantum simulation.Our predictions should be readily observable in current optical cavity experiments with alkaline-earth atoms or Raman-dressed transitions.
We present a cross-cavity system in which steady-state superradiance is achieved using solely collective dissipative dynamics. Two cavities symmetrically couple an ensemble of four-level atoms by driving transitions between two electronic states and two motional states along perpendicular cavity axes. Both cavities operate in the bad-cavity regime: one cavity mediates collective atomic decay, while the other cavity, together with a coherent drive, mediates collective pumping via an off-resonant Raman transition. With this, we find steady-state superradiant states that possess nonclassical properties, such as super-Poissonian photon statistics. The system thus requires a beyond mean-field description, and so we develop an exact master equation simulation technique utilizing strong symmetries of the system's jump operators. Because superradiant decay is accompanied by a momentum impulse along the corresponding cavity axis, the system exhibits substantial hybrid entanglement between the atoms' spin and motional degrees of freedom at steady state. We also demonstrate that heralded measurements of the two cavity outputs prepare a state with significant particle-particle entanglement with prospects for quantum-enhanced acceleration sensing.
We describe a method to create and store scalable and long-lived entangled spin-squeezed states within a manifold of many-body cavity dark states using collective emission of light from multilevel atoms inside an optical cavity. We show that the system can be tuned to generate squeezing in a dark state where it will be immune to superradiance. We also show more generically that squeezing can be generated using a combination of superradiance and coherent driving in a bright state, and subsequently be transferred via single-particle rotations to a dark state where squeezing can be stored. Our findings, readily testable in current optical cavity experiments with alkaline-earth-like atoms, can open a path for dissipative generation and storage of metrologically useful states in optical transitions.
We utilize multilevel atoms trapped in a driven resonant optical cavity to produce scalable multimode squeezed states for quantum sensing and metrology. While superradiance or collective dissipative emission by itself has been typically a detrimental effect for entanglement generation in optical cavities, in the presence of additional drives it can also be used as an entanglement resource. In a recent work [B. Sundar, D. Barberena, A. M. Rey, and A. Pi\~neiro Orioli, companion paper, Phys. Rev. Lett. 132, 033601 (2024)], we described a protocol for the dissipative generation of two-mode squeezing in the dark state of a six-level system with only one relevant polarization. There we showed that up to two quadratures can be squeezed. Here, we develop a generalized analytic treatment to calculate the squeezing in any multilevel system where atoms can collectively decay by emitting light into two polarization modes in a cavity. We show that in this more general system up to four spin squeezed quadratures can be obtained. We study how finite-size effects constrain the reachable squeezing, and analytically compute the scaling with NNN. Our findings are readily testable in current optical cavity experiments with alkaline-earth-like atoms.