Quantum aspects of spacetime: A quantum optics view of acceleration radiation and black holes

TL;DR

This paper surveys the intersection of quantum information, quantum optics, and curved-spacetime physics to illuminate horizon-related quantum effects. By recasting atom–field interactions in black-hole backgrounds within a multimode quantum Rabi framework and employing open quantum systems techniques, it derives horizon-brightened acceleration radiation (HBAR) and shows its thermal character at the Hawking temperature $T_H$. A central thread is the near-horizon conformal quantum mechanics (CQM), which underpins both the emergence of thermal spectra and a deep HBAR–black-hole thermodynamic correspondence, including entropy- and area-related relations. The work also emphasizes quantum-information measures, such as the von Neumann entropy, and discusses experimental analogs and future directions for probing these fundamental links between quantum theory and gravity. Overall, the article highlights a network of connections among quantum field theory in curved spacetime, quantum thermodynamics, and quantum-optics tools, offering a roadmap for exploring quantum gravity phenomena through laboratory analogs and theoretical constructs like CQM near horizons.

Abstract

For the centennial of quantum mechanics, we offer an overview of the central role played by quantum information and thermalization in problems involving fundamental properties of spacetime and gravitational physics. This is an open area of research still a century after the initial development of formal quantum mechanics, highlighting the effectiveness of quantum physics in the description of all natural phenomena. These remarkable connections can be highlighted with the tools of modern quantum optics, which effectively addresses the three-fold interplay of interacting atoms, fields, and spacetime backgrounds describing gravitational fields and noninertial systems. In this review article, we select aspects of these phenomena centered on quantum features of the acceleration radiation of particles in the presence of black holes. The ensuing horizon-brightened radiation (HBAR) provides a case study of the role played by quantum physics in nontrivial spacetime behavior, and also shows a fundamental correspondence with black hole thermodynamics.

Figures (11)

• Figure 1: A quantum information representation of the event horizon as a quantum computer, in units proportional to the Planck area $\ell_{P}^2 = \hbar G/(k_{B}c^3)$.
• Figure 2: The thought experiment for the HBAR model, where atoms freely fall into a black hole in a Boulware vacuum, simulating an analog quantum-optics system with boundary mirrors. This "optical cavity model" is only a conceptual device to represent the vacuum setup. The dashed lines show the direction of the free-fall motion of the atoms, which radiate in all directions (but only the outgoing radiation, to be measured far away, is shown for clarity). As the radiation goes up the gravity well, gravitational redshift makes its wavelength increase.
• Figure 3: In the thought experiment for the HBAR model, a mirror is an operational quantum-optics type device that enforces a boundary condition to guarantee the presence of a Boulware vacuum.
• Figure 4: Schematics of the emission and absorption processes corresponding to the four terms in the interaction Hamiltonian of Eq. (\ref{['eq:multimode-interaction-QO']}). Here, $\sigma_{\pm}$ are the atomic raising and lowering operators defined in Eq. (\ref{['eq:sigma-operators']}). The specific couplings of I and II give the rotating terms, while those of III and IV give the counter-rotating terms. The latter can be neglected as the rotating-wave approximation (RWA) under a broad range of ordinary lab conditions (near resonance and in the weak-coupling regime), but they are critically important in relativistic setups with accelerated particles and/or horizons.
• Figure 5: Schematic representation of the exchange of physical information of the system ($S$) with the environment ($E$). The corresponding mathematical procedure is that of the partial trace, Eq. (\ref{['eq:reduction-of-density-matrix']}).