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arXiv:2001.04987 · Physical Review A

Quantum simulation of Unruh-DeWitt detectors with nonlinear optics

Eugene Adjei, Kevin J. Resch, Agata M. Brańczyk

Published Sep 10, 2020• 10 citations
arXivHTMLPDF

Abstract

We propose a method for simulating an Unruh-DeWitt detector, coupled to a $1+1$-dimensional massless scalar field, with a suitably engineered ${\ensuremath{\chi}}^{(2)}$ nonlinear interaction. In this simulation, the parameter playing the role of the detector acceleration is played by the relative inverse-group-velocity gradient inside the nonlinear material. We identify experimental parameters that tune the detector energy gap, acceleration, and switching function. This system can simulate time-dependent acceleration, time-dependent detector energy gaps, and nonvacuum initial detector-field states. Furthermore, for very short materials, the system can simulate the weak anti-Unruh effect, in which the response of the detector decreases with acceleration.

DOI
10.1103/physreva.102.033506

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We propose a method for simulating an Unruh-DeWitt detector, coupled to a 1+11+11+1-dimensional massless scalar field, with a suitably engineered \ensuremathχ(2){\ensuremath{\chi}}^{(2)}\ensuremathχ(2) nonlinear interaction. In this simulation, the parameter playing the role of the detector acceleration is played by the relative inverse-group-velocity gradient inside the nonlinear material. We identify experimental parameters that tune the detector energy gap, acceleration, and switching function. This system can simulate time-dependent acceleration, time-dependent detector energy gaps, and nonvacuum initial detector-field states. Furthermore, for very short materials, the system can simulate the weak anti-Unruh effect, in which the response of the detector decreases with acceleration.
Abstract We study, in the framework of open quantum systems, the entanglement dynamics for a quantum system composed of two uniformly accelerated Unruh-Dewitt detectors interacting with a bath of massive scalar fields in the Minkowski vacuum. We find that the entanglement evolution for the quantum system coupled with massive fields is always slower compared with that of the one coupled with massless fields, and this time-delay effect brought about by the field being massive can however be counteracted by a large enough acceleration, in contrast to the case of a static quantum system in a thermal bath, where this time delay is not affected by the temperature. Remarkably, the maximal concurrence of the quantum system generated during evolution may increase with acceleration for any inter-detector separation while that for static ones in a thermal bath decreases monotonically with temperature, and this can be considered as an anti-Unruh effect in terms of the entanglement generated.
We study the quantum metrology for a pair of entangled Unruh-Dewitt detectors when one of them is accelerated and coupled to a massless scalar field. Comparing with previous schemes, our model requires only local interaction and avoids the use of cavities in the probe state preparation process. We show that the probe state preparation and the interaction between the accelerated detector and the external field have significant effects on the value of quantum Fisher information, correspondingly pose variable ultimate limit of precision in the estimation of Unruh effect. We find that the precision of the estimation can be improved by a larger effective coupling strength and a longer interaction time. Alternatively, the energy gap of the detector has a range that can provide us a better precision. Thus we may adjust those parameters and attain a higher precision in the estimation. We also find that an extremely high acceleration is not required in the quantum metrology process.
Abstract The behavior of accelerating Unruh-DeWitt detectors coupled with a spinor field in (3+1)-dimensional spacetime is investigated. For a single point-like detector with Gaussian switching function, the transition probability increases with the acceleration and thus the antiUnruh effect effect cannot occur. Due to the spinor structure of the Dirac field, UV divergences are encountered in the calculation of the entanglement between the detectors. After introducing some UV cutoff Λ, the negativity of detectors is shown to behave nonmonotonically with respect to the acceleration. Besides, the negativity increases with the cutoff Λ and decreases with the distance between the detectors. The mutual information between the two detectors is also discussed.
We investigate the transition of a two-level atom as the Unruh-Dewitt detector accelerated in the electromagnetic field in this paper. The enhancement of the transition probability is found for different field states under the conditions that the anti-Unruh effect appears. In particular, the enhancement is the most prominent when the field state takes the squeezed state. We also construct a new atomic trajectory to realize the effect of acceleration-induced transparency. Based on this, we show that the anti-Unruh effect still exists even at the specific atomic energy difference where acceleration-induced transparency happens.
The Unruh-DeWitt model of particle detector is widely used to probe quantum effects in noninertial frames and curved spacetimes. In this paper, we investigate the entanglement dynamics of a quantum system composed of two rotating Unruh-DeWitt detectors in interaction with a fluctuating massless scalar field in vacuum. We obtain the necessary and sufficient condition for the detectors to achieve steady-state entanglement, and systematically investigate the steady-state entanglement of two Unruh-DeWitt detectors rotating in coaxial orbits with the same orbital radius and angular velocity. When the separation between the detectors is vanishing, the detectors can obtain steady-state entanglement dependent on the initial state, as the detectors in uniform acceleration and static detectors in a thermal bath do. Remarkably, however, when the separation between the detectors is nonvanishing but small compared with the transition wavelength of detectors, the detectors can obtain steady-state entanglement irrespectively of what the initial state is. This is the unique phenomenon caused by the centripetal acceleration and is not present in the uniform acceleration case and the case of static detectors in a thermal bath.
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 Nsig(t)N_{\rm sig}(t)Nsig​(t) and second-order correlation function g(2)(0;t)g^{(2)}(0;t)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.