What does it mean for half of an empty cavity to be full?

Abstract

It is well known that the vacuum state of a quantum field is spatially entangled. This is true both in free and confined spaces, for example in an optical cavity. The obvious consequence of this, however, is surprising and intuitively challenging; namely, that in a mathematical sense half of an empty cavity is not empty. Formally this is clear, but what does this physically mean in terms of, say, measurements that can actually be made? In this paper we utilize the tools of Gaussian quantum mechanics to easily characterize the reduced state of a subregion in a cavity and expose the spatial profile of its entanglement with the opposite region. We then go on to discuss a thought experiment in which a mirror is introduced between the regions. In so doing we expose a simple and physically concrete answer to the above question: the vacuum excitations resulting from entanglement are mathematically equivalent to the real excitations generated by suddenly introducing a mirror. Performing such an experiment in the laboratory may be an excellent method of verifying vacuum entanglement, and we conclude by discussing different possibilities of achieving this aim.

arXiv comment21 pages, 8 figures

References in corpus (30)

• Circuit Quantum Electrodynamics: Coherent Coupling of a Single Photon to a Cooper Pair Box
• Cavity quantum electrodynamics for superconducting electrical circuits: an architecture for quantum computation
• Peres-Horodecki separability criterion for continuous variable systems
• Entropy and Area
• The logarithmic negativity: A full entanglement monotone that is not convex
• Atomic physics and quantum optics using superconducting circuits
• Observation of the Dynamical Casimir Effect in a Superconducting Circuit
• Entanglement in continuous variable systems: Recent advances and current perspectives
• Entanglement entropy in free quantum field theory
• Photon-mediated interactions between distant artificial atoms
• The Single-Photon Router
• Better Late than Never: Information Retrieval from Black Holes
• Violating Bell's inequalities in the vacuum
• Entangling Power of an Expanding Universe
• An entanglement-area law for general bosonic harmonic lattice systems
• Generation of nonclassical microwave states using an artificial atom in 1D open space
• Spatial structures and localization of vacuum entanglement in the linear harmonic chain
• Detectors for probing relativistic quantum physics beyond perturbation theory
• Detection of vacuum entanglement in a linear ion trap
• Sustainable entanglement production from a quantum field
• Time evolution techniques for detectors in relativistic quantum information
• Entanglement and discord: accelerated observations of local and global modes
• Localised projective measurement of a relativistic quantum field in non-inertial frames
• Entanglement from thermal black body radiation
• Thermal amplification of field-correlation harvesting
• Entanglement between smeared field operators in the Klein-Gordon vacuum
• Generation of atom-atom correlations inside and outside the mutual light cone
• Ultrafast Optical Response of a High-Reflectivity GaAs/AlAs Bragg Mirror
• Local quanta, unitary inequivalence, and vacuum entanglement
• Short-time quantum detection: probing quantum fluctuations

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