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arXiv:2608.19333

Strongly coupled atom-cavity systems under boundary modulation: simulating gravitational-wave effects

Patryk Michalski, Jerzy Paczos, Navdeep Arya, Magdalena Zych

quant-phgr-qcSubmitted Aug 19, 2026• Announced Aug 21, 2026• 0 citations
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Abstract

One of the proposed platforms in which both quantum and general relativistic effects can become observable is an atom interacting with the electromagnetic field in a gravitational-wave background. The periodic modulation of field modes induced by variations of the spacetime metric modifies the atomic emission spectrum. Notably, the temporal modulation of the mode-frequency induced by a plane gravitational wave can be simulated through modulated boundary conditions, such as moving cavity mirrors. We analyze the impact of this modulation on atom-field interactions in the strong atom-cavity coupling regime, where Rabi oscillations occur. We show analytically that the modulation is resonantly enhanced, leading to measurable imprints in the atomic transition probability. This establishes a realistic and experimentally accessible platform for probing analogue general relativistic effects in quantum optical systems.

Comments
14 pages, 4 figures

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Physical Review A•Apr 1, 1996•49 citations
One of the proposed platforms in which both quantum and general relativistic effects can become observable is an atom interacting with the electromagnetic field in a gravitational-wave background. The periodic modulation of field modes induced by variations of the spacetime metric modifies the atomic emission spectrum. Notably, the temporal modulation of the mode-frequency induced by a plane gravitational wave can be simulated through modulated boundary conditions, such as moving cavity mirrors. We analyze the impact of this modulation on atom-field interactions in the strong atom-cavity coupling regime, where Rabi oscillations occur. We show analytically that the modulation is resonantly enhanced, leading to measurable imprints in the atomic transition probability. This establishes a realistic and experimentally accessible platform for probing analogue general relativistic effects in quantum optical systems.
This thesis examines how atomic quantum systems can be utilized to probe spacetime effects in regimes where quantum mechanics and general relativity intersect, and how gravitational phenomena imprint on experimentally accessible observables. The work is based on two complementary studies. In Article I, we propose an experimental scheme that combines trapped-atom interferometry with Ramsey interrogation to realize a clock held in a spatial superposition at two heights in Earth’s gravitational field. Using a path-integral treatment of interferometric phases and incorporating the internal-energy contribution to mass, we derive leading relativistic corrections and identify two signatures of proper-time superposition: (i) oscillations of interferometric visibility and (ii) an effective shift of the clock transition frequency. We argue that this frequency-shift signature may be within reach of current or near-term technology, even when visibility changes are too small to resolve. In Article II, we develop a general framework for spontaneous emission in curved spacetime and apply it to a gravitational-wave background. We demonstrate that gravitational waves can induce spectral sidebands and directional modulations in the emitted radiation, and formulate parameter estimation via Fisher-information-based sensitivity bounds, yielding order-of-magnitude requirements for detectability under idealized measurement conditions.
The Rabi Hamiltonian, describing the interaction between a two-level atomic system and a single-cavity mode of the electromagnetic field, is one of the fundamental models in quantum optics. The model becomes exactly solvable by considering an atom without permanent dipole moments, whose excitation energy is quasiresonant with the cavity photon energy, and by neglecting the nonresonant (counter-rotating) terms. In this case, after including the decay of either the atom or the cavity mode to a continuum, one can derive the well-known phenomenology of quasiresonant transitions, including the fluorescence triplets. In this work we consider the most general Rabi model, incorporating the effects of permanent atomic electric dipole moments. Based on a perturbative analysis, we compare the intensities of emission lines induced by rotating terms, counter-rotating terms, and parity-symmetry-breaking terms in order to identify the parameter regimes in which these different contributions play a significant role. The analysis reveals that the emission strength related to the existence of permanent dipoles may surpass the one due to the counter-rotating interaction terms but is usually much weaker than the emission due to the main, resonant coupling. This ratio can be modified in systems with a reduced dimensionality or by engineering the energy spectral density of the continuum.
We develop a quantum description of the resonant interaction between electromagnetic (EM) and gravitational waves (GW). We first show that Lorentz invariance together with polarization selection rules forbids any photon-graviton mixing in free space. We demonstrate that confining the EM field within a cavity quantum electrodynamics (cavity-QED) environment breaks translational symmetry and isotropy, leading to non-vanishing mode coupling between EM and gravitational degrees of freedom. Within this framework, we identify multiple photon-graviton scattering channels, including photon up- and down-conversion and photon creation. In the semiclassical limit of the trilinear interaction where GW acts as a classical pump and the EM field is in a vacuum, spontaneous parametric photon amplification and two-mode squeezing occur. When the gravitational field is quantized, however, the back-action and energy exchange between photons and gravitons result in saturation of amplification, in contrast to exponential growth, and the loss of purity in the photonic subsystem. The characteristic timescale scales as tsp∼(gng)−1t_{\text{sp}}\sim (g\sqrt{n_g})^{-1}tsp​∼(gng​​)−1, where ggg and ngn_gng​ refer to the coupling strength and the mean graviton number, demonstrating collective enhancement of the interaction with the graviton occupation number. In the stimulated regime, where one EM mode is initially populated, the effective coupling is further enhanced, analogous to Dicke-type superradiant emission. This work introduces a cavity-based graviton transducer for probing quantum aspects of GWs.
The effects of spacetime geometry on quantum systems are typically very small. Here, we demonstrate a coherent many-body mechanism that can enhance these effects. We show that, in an ordered array, a gravitational wave induces long-range all-to-all dissipative coupling among atoms within half the gravitational wavelength. This coupling is mediated by the electromagnetic vacuum and leads to cooperative photon emission that we term gravitational wave-induced photon superradiance--delayed and intense emission of photons at frequencies shifted from the atomic transition by the gravitational wave frequency. The phenomenon arises in a regime distinct from flat-spacetime superradiance, allowing gravitational effects to dominate the collective photon emission from atoms. It persists despite common experimental challenges in atom arrays such as position disorder and partial filling. We thus identify a new class of effects arising from the interplay of general relativity and collective quantum optics that individual atoms do not exhibit, and demonstrate that engineered quantum many-body systems provide a new window into the interface of general relativity and quantum mechanics.
When an atom is strongly coupled to a cavity, the two systems can exchange a single photon through a coherent Rabi oscillation. This process enables precise quantum-state engineering and manipulation of atoms and photons in a cavity, which play a central role in quantum information and measurement. Recently, a new regime of cavity QED was reached experimentally where the strength of the interaction between light and artificial atoms (qubits) becomes comparable to the atomic transition frequency or the resonance frequency of the cavity mode. Here we show that this regime can strongly modify the concept of vacuum Rabi oscillations, enabling multiphoton exchanges between the qubit and the resonator. We find that experimental state-of-the-art circuit-QED systems can undergo two- and three-photon vacuum Rabi oscillations. These anomalous Rabi oscillations can be exploited for the realization of efficient Fock-state sources of light and complex entangled states of qubits.
We revisit the problem of spontaneous emission by a two-level system in a cavity, concentrating in particular on those aspects associated with the finite propagation time of light between the atom and the cavity boundaries. We find that spontaneous emission always occurs first at the free space rate and there is then an abrupt change in these dynamics when light reflected by the cavity mirrors returns to the atom, leading to interference effects that result either in an enhancement or a reduction of this rate or in a periodic exchange of excitation between the atom and the cavity field. From this point of view, reversible spontaneous emission in terms of single-mode ``vacuum Rabi oscillations'' can be interpreted as resulting from the interference between the multimode partial waves reflected at the cavity mirrors and the instantaneously radiated light. \textcopyright{} 1996 The American Physical Society.