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arXiv:2511.16865

Quantum Optical Simulator for Unruh-DeWitt Detector Dynamics

Tai Hyun Yoon

quant-phgr-qcSubmitted Nov 21, 2025• Announced Nov 24, 2025• 0 citations
v1 · Nov 21, 2025v2 · Apr 20, 2026
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Abstract

We present a quantum-optical platform for simulating relativistic detector-field interactions using entangled nonlinear biphoton sources (ENBSs), realized through phase-controlled single-photon frequency-comb (SPFC) sources. By mapping the dynamical evolution of this system onto the Unruh-DeWitt (UDW) detector model, we show that signal-mode excitations emulate detector transitions driven by vacuum fluctuations, while coherently seeded idler modes act as an effective quantum field. This correspondence enables tabletop exploration of Unruh-like excitation, coherence harvesting, and field-induced entanglement. We derive the effective interaction Hamiltonian and Lindblad master equation for two coherently seeded ENBS units and obtain analytical solutions for the signal photon number \(N_{\rm sig}(t)\) and second-order correlation function \(g^{(2)}(0;t)\). Numerical simulations confirm that phase-dependent biphoton dynamics reproduce UDW-type behavior, including tunable excitation and quantum correlations. The output signal state exhibits controllable fidelity, interference visibility, and entanglement entropy as functions of the seeding phase and amplitude. These results establish ENBSs as experimentally accessible quantum simulators of relativistic field phenomena, providing a photonic testbed for analog gravitational effects, vacuum fluctuations, and spacetime-induced coherence-all within reach of current nonlinear-optics technology.

Comments
11 pages, 5 figures, submitted for publication

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We present a quantum-optical platform for simulating relativistic detector-field interactions using entangled nonlinear biphoton sources (ENBSs), realized through phase-controlled single-photon frequency-comb (SPFC) sources. By mapping the dynamical evolution of this system onto the Unruh-DeWitt (UDW) detector model, we show that signal-mode excitations emulate detector transitions driven by vacuum fluctuations, while coherently seeded idler modes act as an effective quantum field. This correspondence enables tabletop exploration of Unruh-like excitation, coherence harvesting, and field-induced entanglement. We derive the effective interaction Hamiltonian and Lindblad master equation for two coherently seeded ENBS units and obtain analytical solutions for the signal photon number (N_{\rm sig}(t)) and second-order correlation function (g^{(2)}(0;t)). Numerical simulations confirm that phase-dependent biphoton dynamics reproduce UDW-type behavior, including tunable excitation and quantum correlations. The output signal state exhibits controllable fidelity, interference visibility, and entanglement entropy as functions of the seeding phase and amplitude. These results establish ENBSs as experimentally accessible quantum simulators of relativistic field phenomena, providing a photonic testbed for analog gravitational effects, vacuum fluctuations, and spacetime-induced coherence-all within reach of current nonlinear-optics technology.
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A new theoretical framework to describe the experimental advances in electro-optic detection of broadband quantum states, specifically the quantum vacuum, is devised. Electro-optic sampling is a technique in ultrafast photonics which, when transferred into the quantum domain, can be utilized to resolve properties of a sampled quantum state via its interaction with a strong coherent probe pulse at ultrafast timescales. By making use of fundamental concepts from quantum field theory on spacetime metrics, the nonlinear interaction behind the electro-optic effect is shown to be equivalent to a stationary Unruh-DeWitt detector coupled to a conjugate field during a very short time interval. When the coupling lasts for a time interval comparable to the oscillation periods of the detected field mode (i.e., the subcycle regime), virtual particles inhabiting the field vacuum are transferred to the detector in the form of real excitation. We demonstrate that this behavior can be rigorously translated to the scenario of electro-optic sampling of the quantum vacuum, in which the (spectrally filtered) probe works as an Unruh-DeWitt detector, with its interaction-generated photons arising from virtual particles inhabiting the electromagnetic vacuum. Our analysis accurately encapsulates the quantum nature of the vacuum, and we propose the specific working regime in which we can experimentally verify the existence of virtual photons with quantum correlations in the electromagnetic ground state.
Abstract The Unruh effect predicts an astonishing phenomenon that an accelerated detector would detect counts despite being in a quantum field vacuum in the rest frame. Since the required detector acceleration for its direct observation is prohibitively large, recent analog studies in quantum simulation platforms help in revealing various properties of the Unruh effect and thus to explore the not-yet-understood physics of quantum gravity. To further reveal the quantum aspect of the Unruh effect, analogous experimental exploration of the correlation with respect to the detector and the field, and the consequences for coherent quantum trajectories of the detector that without classical counterparts, are essential steps but currently missing. Here, we utilize a laser-controlled trapped ion to experimentally simulate an oscillating detector coupled with a cavity field. We observe joint excitation of both the detector and the field in the detector’s frame, matching with the coordinated dynamics predicted by the Unruh effect. Particularly, we simulate the detector moving in single and superposed quantum trajectories, where the latter case shows coherent interference of excitation. Our demonstration reveals properties of quantum coherent superposition of accelerating trajectories associated with quantum gravity theories that have no classical counterparts, and may offer a new avenue to investigate phenomena in quantum field theory and quantum gravity. We also show how a generalization of the method and results in this work may be beneficial for direct observation of the Unruh effect.
It is a well-known fact that, in recent times, entanglement harvesting from the quantum field is being rigorously investigated further in flat and different curved backgrounds. The usually understood formulation studies the possibility of two uncorrelated Unruh-DeWitt detectors getting entangled over time due to the effects of quantum vacuum fluctuations. Our current work presents a thorough formulation to realize the entanglement harvesting from nonvacuum background fluctuations. In particular, we further consider single excitation field states and a pair of inertial detectors, respectively, in (1+11+11+1) and (1+31+31+3) dimensions for this investigation. Our main observation asserts that entanglement harvesting is suppressed compared to the vacuum fluctuations in this situation. Our other observations confirm a nonzero individual detector transition probability in this background and vanishing entanglement harvesting for parallel comoving detectors. We look into the characteristics of the harvested entanglement and discuss its dependence on different system parameters.
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Abstract We explore the quantum coherence between a pair of entangled Unruh–DeWitt detectors, interacting with a quantum field, using a nonperturbative approach in a (3+1)-dimensional Minkowski spacetime with instantaneous switching ( δ\delta δ δ -switching). It is intriguing to observe that for a maximally entangled state, increasing the coupling strength enhances the detectors’ initial quantum coherence while simultaneously causing a monotonic decrease in their initial entanglement. This reveals a remarkable phenomenon: through nonperturbative interactions, entangled Unruh–DeWitt detectors can exhibit a dual effect-amplifying quantum coherence while degrading quantum entanglement. This finding stands in stark contrast to previous studies based on perturbative methods or Gaussian switching functions, which generally concluded that interactions between detectors and the field lead to a simultaneous degradation of quantum coherence and entanglement due to environmental decoherence. Notably, while initially separable detectors successfully harvest quantum coherence from the vacuum, entanglement extraction remains fundamentally prohibited. These contrasting behaviors underscore the fundamental distinction between coherence and entanglement as quantum resources, and highlight their complementary roles in field-detector interactions.