Quantum Optical Simulator Demonstrates Unruh-DeWitt Detector Dynamics with Entangled Nonlinear Biphoton Sources

The elusive nature of Unruh-DeWitt radiation, a predicted effect where accelerating observers experience vacuum as a thermal bath, has long presented a challenge to physicists, but new research offers a promising pathway towards its experimental observation. Tai Hyun Yoon from Korea University and colleagues demonstrate a quantum optical simulator capable of recreating the dynamics of an Unruh-DeWitt detector using entangled nonlinear biphoton sources. This innovative approach maps the behaviour of these light sources onto the theoretical detector model, effectively mimicking the influence of vacuum fluctuations and allowing scientists to explore phenomena like coherence harvesting and field-induced entanglement on a laboratory benchtop. The team’s results establish a photonic platform for investigating relativistic effects, offering a novel means to study fundamental questions about gravity, vacuum energy, and the interplay between quantum mechanics and spacetime.

Entangled Photons Simulate Relativistic Quantum Detectors

This research establishes entangled nonlinear biphoton sources as a versatile platform for simulating the dynamics of relativistic quantum field detectors, bringing phenomena traditionally considered experimentally inaccessible into a compact quantum optics setting. By mapping the excitation and coherence properties of these sources onto the Unruh-DeWitt detector model, scientists have demonstrated the emulation of key effects such as vacuum-induced excitation and entanglement harvesting. Analytical modelling and numerical simulations confirm that the signal-mode output of the source carries controllable quantum information, with fidelity, interference visibility, and entanglement entropy all tunable through coherent seeding. The team’s work reveals full phase-dependent control over coherence and entanglement generation, establishing the source not only as a simulator of detector-field dynamics but also as a programmable quantum light source with engineered coherence properties.

Researchers acknowledge that the current simulator employs a single effective idler mode and does not fully reproduce the continuum of relativistic quantum fields. However, the system successfully emulates the detector’s local response through engineered temporal correlations, capturing key observables of Unruh-DeWitt-like dynamics within a controllable quantum optical environment. Future developments, including the incorporation of multimode idler continua and spatially separated units, offer a promising route to emulate spacelike entanglement harvesting and further investigate relativistic quantum phenomena. Scientists have developed a fully photonic platform to simulate the dynamics of relativistic quantum field detectors, utilizing entangled nonlinear biphoton sources.

This simulator employs seeded single-photon frequency combs, enabling tabletop replication of interactions typically found in high-energy physics scenarios. The core of the system involves two frequency combs pumped by laser light at a specific wavelength, with coherent seed fields injected into the idler paths, generating signal photons. These signal photons exhibit quantum correlations analogous to detector excitations, controlled by a tunable relative phase difference between the seed fields. Experiments reveal that by manipulating the detection configuration, researchers can access complementary observables.

Removing a beam splitter allows measurement of the average number of signal photons, while coincidence detection at the beam splitter outputs provides information about the correlation between photons. Crucially, monitoring a single output after the beam splitter enables measurement of the single-photon detection rate, revealing the coherence of the signal field as a function of the seeding phase difference. This coherence directly corresponds to interference between excitation amplitudes of the two effective detectors, demonstrating vacuum-mediated correlations central to the Unruh-DeWitt analogy. The team demonstrated phase-resolved control over entangled single-photon states, achieving a system where the quantum correlations of the signal photons are directly influenced by the relative phase of the seed fields. This allows for precise probing of detector-detector entanglement and provides a platform for investigating phenomena like the Unruh effect and entanglement harvesting. Compared to previous analog experiments using Bose-Einstein condensates, this platform offers coherent control and scalability, enabling investigation of relativistic field theory through accessible nonlinear optics.