Unruh Effect Research Articles

Effect of acceleration on information delocalization

We study the impact of acceleration on information delocalization under the Unruh (anti-Unruh) effect for two types of tripartite entangled states, namely the GHZ and W states. Our findings indicate that the anti-Unruh effect can result in stronger delocalization of quantum information, as measured by tripartite mutual information (TMI). Additionally, we show that the W state is more stable than the GHZ state under the influence of uniformly accelerated motion. Lastly, we extend our analysis to N-partite entangled states and product states.

Robustness of Wave-Particle Duality under Unruh Effect.

By considering a uniformly accelerated two-level system in an initial superposition state of a qubit, we investigate the loss of coherence induced by the acceleration. In addition, we investigate the impact of acceleration on the complementarity relation in a quantum interferometric circuit or quantum scattering circuit. We present an alternative approach to exploring acceleration effects through examination of quantum coherence decay and degradation in the interference pattern. Our investigations help to provide understanding of the consequences of decoherence induced by the Unruh effect on the wave-particle duality of a uniformly accelerated qubit.

The Horizons in Circular Accelerated Motions and Its Consequences

In this work, we study the existence of horizons in circular accelerated motions and its consequences. One particular case is the existence of two horizons in any uniform circular motion. The radiation of the Poincaré invariant vacuum is related to the spontaneous breakdown of the conformal symmetry in Quantum Field Theory The main consequence of the existence of these horizons is the Unruh radiation coming from such horizons. This consequence allows us to study the possible experimental detection of the Unruh radiation in such motions. The radiation of the Poincaré invariant vacuum is related to the spontaneous breakdown of the conformal symmetry in Quantum Field Theory. This radiation is associated with an effective temperature that can be detected using an Unruh–DeWitt detector. In fact, this effective temperature at the relativistic limit depends linearly with respect to the proper acceleration. However, in general, this dependence is not linear, contrary of what happens in the classical Unruh effect. In the relativistic limit and high density case, the uniform circular motion becomes a rotating black hole. This allows for future studies of pre-black hole configurations.

Entanglement and quantum teleportation in terms of Dirac modes observed by accelerated observers

In this paper, we have studied entanglement between two Dirac modes observed, respectively, by two independently accelerated observers. Due to Unruh effect, the entanglement degrades, but residual entanglement remains in the limit of infinite accelerations. We have also investigated quantum teleportation using entangled Dirac modes, and calculated the fidelities in various cases. In general, the fidelity depends on both the single-qubit state and the Bell state used in the teleportation.

Accelerated paths and Unruh effect: finite time detector response in (anti) de Sitter spacetime and Huygen’s principle

We study the finite time response of an Unruh–DeWitt particle detector described by a qubit (two-level system) moving with uniform constant acceleration in maximally symmetric spacetimes. The D dimensional massless fermionic response function in de Sitter (dS) background is found to be identical to that of a detector linearly coupled to a massless scalar field in 2D dimensional dS background. Furthermore, we visit the status of Huygen’s principle in the Unruh radiation observed by the detector.

GEMS Embeddings of Hayward Regular Black Holes in Massless and Massive Gravities

After finding a solution for the Hayward regular black hole (HRBH) in massive gravity, we embed the (3+1)-dimensional HRBHs both in massless and in massive gravities into (5+2)- and (6+3)-dimensional Minkowski spacetimes, respectively. Here, massive gravity denotes that a graviton acquires a mass holographically by broken momentum conservation in the HRBH. The original HRBH has no holographically added gravitons, which we call ‘massless’. Making use of newly found embedding coordinates, we obtain desired Unruh temperatures and compare them with the Hawking and local fiducial temperatures, showing that the Unruh effect for a uniformly accelerated observer in a higher-dimensional flat spacetime is equal to the Hawking effect for a fiducial observer in a black hole spacetime. We also obtain freely falling temperatures of the HRBHs in massless and massive gravities seen by freely falling observers, which remain finite even at the event horizons while becoming the Hawking temperatures in asymptotic infinity.

Using nanokelvin quantum thermometry to detect timelike Unruh effect in a Bose–Einstein condensate

It is found that the Unruh effect can not only arise out of the entanglement between two sets of modes spanning the left and right Rindler wedges, but also between modes spanning the future and past light cones. Furthermore, an inertial Unruh–DeWitt detector along a spacetime trajectory in one of these cones may exhibit the same thermal response to the vacuum as that of an accelerated detector confined in the Rindler wedge. This feature thus could be an alternative candidate to verify the “Unruh effect”, termed as the timelike Unruh effect correspondingly. In this paper we propose to detect the timelike Unruh effect by using an impurity immersed in a Bose–Einstein condensate (BEC). The impurity acts as the detector which interacts with the density fluctuations in the condensate, working as an effective quantum field. Following the paradigm of the emerging field of quantum thermometry, we combine quantum parameter estimation theory with the theory of open quantum systems to realize a nondemolition Unruh temperature measurement in the nanokelvin (nK\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{nK}$$\\end{document}) regime. Our results demonstrate that the timelike Unruh effect can be probed using a stationary two-level impurity with time-dependent energy gap immersed in a BEC within current technologies.

An observer's perspective of the Unruh and Hawking effects—Using coherent signals to extract information from a black hole

The Unruh effect is one of the first calculations that explain what one would see when transiting between an inertial reference frame in its quantum field vacuum state and a non-inertial (specifically, uniformly accelerating) reference frame. The inertial reference frame's vacuum state would not correspond to the vacuum state of the non-inertial frame. The observer in the non-inertial frame would see radiation, with a corresponding Bose distribution and a temperature proportional to the acceleration. In this paper, I compute the response of this non-inertial observer to a single frequency mode in the inertial frame and deduce that, indeed, the cumulative distribution (over the observer's proper time) of frequencies observed by the accelerating observer would be the Bose distribution with a temperature proportional to the acceleration. The conclusion is that the Unruh effect (and the related Hawking effect) is generic, in that it would appear with any incoming incoherent state and the Bose distribution is obtained as a consequence of the non-inertial frame's motion, rather than some special property of the quantum vacuum. As a consequence of the analysis of a coherent set of signals, I show how to extract information from the spectrum that an accelerated observer would see (as well as from the radiation from a black hole).

Particle radiation produced by accelerated systems and their analogy with damped oscillators

The Unruh effect predicts how uniformly accelerated observers will perceive a change in the vacuum state. This shows that the concept of particle number depends on the acceleration of the reference frame. Although this is a result of quantum field theory, its experimental verification is still questioned, mainly due to the high accelerations required. In this work we study a quantum oscillator with only one complex coordinate and a damping term acting as perturbation, which has all the characteristics of the Unruh effect in second quantization for an accelerated observer. The Bogoliubov transformation connecting the two different vacuum states is obtained. This leads to an explicit formula for the particle occupation number as a function of energy and acceleration. Furthermore, it is shown that our analogue system contains an effective temperature that depends on the observer's sudden acceleration, seen as a friction force. The purpose of this work is to demonstrate that quanta production (particles or energy packets) is inevitable under the premises of quantum field theory.

Landauer’s Princple for Fermionic Fields in One-Dimensional Bags

In recent years, growing interest has been paid to the exploration of the concepts of entropy, heat and information, which are closely related to the symmetry properties of the physical systems in quantum theory. In this paper, we follow this line of research on the the validity of the concepts in quantum field theory by studying Landauer’s principle for a Dirac field interacting perturbatively with an Unruh–DeWitt detector in a 1+1-dimensional MIT bag cavity. When the field is initially prepared in the vacuum state, we find that the field always absorbs heat, while the Unruh–DeWitt detector can either gain or lose entropy, depending on its motion status, as a result of the Unruh effect. When the field is initially prepared in the thermal state and the detector remains still, the heat transfer and entropy change can be obtained under two additional but reasonable approximations: (i) one is where the duration of the interaction is turned on for a sufficiently long period, and (ii) the other is where the Unruh–DeWitt detector is in resonance with one of the field modes. Landauer’s principle is verified for both considered cases. Compared to the results of a real scalar field, we find that the formulas of the vacuum initial state differ solely in the internal degree of freedom of the Dirac field, and the distinguishability of the fermion and anti-fermion comes into play when the initial state of the Dirac field is thermal. We also point out that the results for a massless fermionic field can be obtained by taking the particle mass m→0 straightforwardly.

Simulation of the Unruh signals of decoherence with quantum circuits

Detecting the Unruh effect is currently an important experimental goal, but it is difficult to realize under laboratory conditions because of the extreme acceleration required for observable signals. Therefore, various schemes for indirect detection have been proposed. Recently, Nesterov and his collaborators discovered that the exponential phase decay in the decoherence of a uniformly accelerated particle detector can significantly improve the conditions for measuring the Unruh effect, and the acceleration required for observable signals can be considerably reduced to ∼1013m/s2. We notice that this exponential phase decay is consistent with its counterpart of the dephasing channel in quantum information theory. In this paper, we use the IBM quantum cloud platform to construct a quantum circuit that can realize the dephasing channel, successfully simulate the Unruh signal, and test the correctness of the method.

Circular motion analogue Unruh effect in a thermal bath: robbing from the rich and giving to the poor

The Unruh effect states that a uniformly linearly accelerated observer with proper acceleration experiences the Minkowski vacuum as a thermal state at temperature . An observer in uniform circular motion experiences a similar effective temperature, operationally defined in terms of excitation and de-excitation rates, and physically interpretable in terms of synchrotron radiation, but this effective temperature depends not just on the acceleration but also on the orbital speed and the excitation energy. In this paper we consider an observer in uniform circular motion when the Minkowski vacuum is replaced by an ambient thermal bath, and we address the interplay of ambient temperature, Doppler effect, acceleration, and excitation energy. Specifically, we consider a massless scalar field in spacetime dimensions, probed by an Unruh–DeWitt detector, in a Minkowski (rather than proper) time formulation: this setting describes proposed analogue spacetime systems in which the effect may become experimentally testable, and in which an ambient temperature will necessarily be present. We establish analytic results for the observer’s effective temperature in several asymptotic regions of the parameter space and provide numerical results in the interpolating regions, finding that an acceleration effect can be identified even when the Doppler effect dominates the overall magnitude of the response. We also identify parameter regimes where the observer sees a temperature lower than the ambient temperature, experiencing a cooling Unruh effect.

Equivalence principle, de-Sitter space, and cosmological twistors

In this paper, I discuss the impact of the positive cosmological constant on the interplay between the equivalence principle in general relativity, and the rules of quantum mechanics. At the nonrelativistic level, there is an ambiguity in the definition of a phase of a wave function measured by inertial and accelerating observes. This is the cosmological analogue of the Penrose effect, which can also be seen as a nonrelativistic limit of the Unruh effect. The symmetries of the associated Schrödinger equation are generated by the Newton–Hooke algebra, which arises from a nonrelativistic limit of a cosmological twistor space.

Unruh effect and Takagi's statistics inversion in strained graphene

We present a theoretical study of how a spatially varying quasiparticle velocity in honeycomb lattices, achievable using strained graphene or in engineered cold-atom optical lattices that have a spatial dependence to the local tunneling amplitude, can yield the Rindler Hamiltonian embodying an observer accelerating in Minkowski space-time. Within this setup, a sudden switch on of the spatially varying tunneling (or strain) yields a spontaneous production of electron-hole pairs, an analog version of the Unruh effect characterized by the Unruh temperature. We discuss how this thermal behavior, along with Takagi's statistics inversion, can manifest themselves in photoemission and scanning tunneling microscopy experiments. We also calculate the average electronic conductivity and find that it grows linearly with frequency $\ensuremath{\omega}$. Finally, we find that the total system energy at zero environment temperature looks like Planck's blackbody result for photons due to the aforementioned statistics inversion, whereas for an initial thermally excited state of fermions, the total internal energy undergoes stimulated particle reduction.

Reparameterization invariance in accelerated proton decay

The inverse β-decay of uniformly accelerated protons has proved to be a useful playground to investigate the asymptotic nature of mixed neutrino states - either flavor or mass. Based on recent results, here we explore in more depth the role of neutrino mixing in the inverse β-decay and the consistency with CP-violation in flavor oscillations. We compute the proton decay rate Γ both in the laboratory and in the comoving frame, taking into account the emergence of Unruh effect in the latter. We show that, while the flavor representation correctly leads to a CP-quantifier proportional to Jarlskog invariant, mass states give instead a vanishing value for such parameter. This implies that the mass basis cannot account for CP-asymmetry in neutrino oscillations, making its usage meaningless.

Tripartite Uncertainty, Quantum, and Classical Correlations Dynamics under Unruh Effect

AbstractHow the dynamics of classical and quantum correlations due to the Unruh effect are reflected in the properties of tripartite entropic uncertainty is investigated. It is found that, despite the quantum correlations disappearing at the limit of infinite acceleration, the uncertainty about the measurement outcome is at its minimum. This is due to the three‐qubit system still containing classic correlations at that stage of acceleration. Additionally, the decrease in the entropic uncertainty when the measured qubit interacts strongly with the scalar field can be attributed to the increase in classical correlations. Furthermore, it is found that the entropic uncertainty is fully anti‐correlated to classical correlations, and minimal uncertainty can be obtained even in the absence of quantum correlations. A tremendously tight constraint that effectively defined the properties of tripartite entropic uncertainty based on the difference between the total correlation and the Holevo quantities is achieved.

Frame dependence of the nonrelativistic limit of quantum fields

We study the nonrelativistic limit of quantum fields for an inertial and a noninertial observer. We show that nonrelativistic particle states appear as a superposition of relativistic and nonrelativistic particles in different frames. Hence, the nonrelativistic limit is frame dependent. We detail this result when the noninertial observer has uniform constant acceleration. Only for low accelerations, the accelerated observer agrees with the inertial frame about the nonrelativistic nature of particles locally. In such a quasi-inertial regime, both observers agree about the number of particles describing quantum field states. The same does not occur when the acceleration is arbitrarily large (e.g., the Unruh effect). We furthermore prove that wave functions of particles in the inertial and the quasi-inertial frame are identical up to the coordinate transformation relating the two frames.

Generalized Unruh effect: A potential resolution to the black hole information paradox

We generalize the vacuum-Unruh effect to arbitrary excited states in the Fock space and find that the Unruh mode at the horizon induces coherent excitation on the canonical background ensemble measured by an accelerated observer. When there is only one type of Unruh mode in the system, for example, the ones outgoing from a black hole horizon, the mapping from an arbitrary density matrix on the maximal foliation to a vector space spanned by the pseudo-thermal density matrix on the partitioned spacetime wedge is one-to-one. Hence we propose that the information of the particles that are inside a collapsing shell, thus inside the asymptotic black hole horizon is at least partially retrievable by measuring the deviation of the Hawking radiation from the black body radiation spectrum. This work shows that the long-standing black hole information confusion might come from overlooking the possibility that the information could be preserved much better than we have expected in a seemingly non-unitary process when the partitions of the system are strongly entangled.

Orbital angular momentum entanglement in noninertial reference frame

The orbital angular momentum (OAM) of photons has shown the ability to generate high-dimensional entanglement. Here, we examine a novel kind of entanglement degradation caused by the Unruh effect. By paraxially quantizing the light field, we derive the mode functions in both inertial and noninertial reference frames and demonstrate that, from the perspective of an accelerating observer, empty inertial space may seem to be full of OAM particles. They may inundate the high-dimensional entangled OAM photons and cause them to decay. Additionally, we investigate high-dimensional entanglement in the vicinity of a Schwarzschild black hole. Our results suggest that higher-dimensional entanglement will suffer from greater adverse impacts in both instances.

Toward quantization of inhomogeneous field theory

We explore the quantization of a $$(1+1)$$ -dimensional inhomogeneous scalar field theory in which Poincaré symmetry is explicitly broken. We show the ‘classical equivalence’ between a scalar field theory on curved spacetime background and its corresponding inhomogeneous scalar field theory. This implies that a hidden connection may exist among some inhomogeneous field theories, which corresponds to general covariance in field theory on curved spacetime. Based on the classical equivalence, we propose how to quantize a specific field theory with broken Poincaré symmetry inspired by standard field theoretic approaches, canonical and algebraic methods, on curved spacetime. Consequently, we show that the Unruh effect can be realized in inhomogeneous field theory and propose that it may be tested by a condensed matter experiment. We suggest that an algebraic approach is appropriate for the quantization of a generic inhomogeneous field theory.