We use the Unruh effect to investigate how the teleportation of quantum states is affected when one of the entangled qubits used in the process is under the influence of some external force. In order to reach a comprehensive understanding, a detailed analysis of the acceleration effect on such entangled qubit system is performed. In particular, we calculate the mutual information and concurrence between the two qubits and show that the latter has a "sudden death" at a finite acceleration, whose value will depend on the time interval along which the detector is accelerated.

We use the Unruh effect to analyze the dynamics of classical and quantum correlations for a two-qubit system when one of them is uniformly accelerated for a finite amount of proper time. We show that the quantum correlation is completely destroyed in the limit of infinite acceleration, while the classical one remains nonzero. In particular, we show that such correlations exhibit the so-called sudden-change behavior as a function of acceleration. Eventually, we discuss how our results can be interpreted when the system lies in the vicinity of the event horizon of a Schwarzschild black hole.

We investigate the transmission of both classical and quantum information between two arbitrary observers in globally hyperbolic spacetimes using a quantum field as a communication channel. The field is supposed to be in some arbitrary quasifree state and no choice of representation of its canonical commutation relations is made. Both sender and receiver possess some localized two-level quantum system with which they can interact with the quantum field to prepare the input and receive the output of the channel, respectively. The interaction between the two-level systems and the quantum field is such that one can trace out the field degrees of freedom exactly and thus obtain the quantum channel in a nonperturbative way. We end the paper determining the unassisted as well as the entanglement-assisted classical and quantum channel capacities.Comment: 12 pages, Reference added, typos corrected. Minor changes to match the published versio

Recently, the inverse β-decay rate calculated with respect to uniformly accelerated observers (experiencing the Unruh thermal bath) was revisited. Concerns have been raised regarding the compatibility of inertial and accelerated observers' results when neutrino mixing is taken into account. Here, we show that these concerns are unfounded by discussing the properties of the Unruh thermal bath with mixing neutrinos and explicitly calculating the decay rates according to both sets of observers, confirming thus that they are in agreement. The Unruh effect is perfectly valid for mixing neutrinos.

Although the Unruh effect can be rigorously considered as well tested as free quantum field theory itself, it would be nice to provide an experimental evidence of its existence. This is not easy because the linear acceleration needed to reach a temperature 1 K is of order 10 20 m/s 2 . Here, we propose a simple experiment reachable under present technology whose result may be directly interpreted in terms of the Unruh thermal bath. Instead of waiting for experimentalists to perform it, we use standard classical electrodynamics to anticipate its output and fulfill our goal.Introduction: In 1976 Unruh unveiled one of the most interesting effects of quantum field theory according to which linearly accelerated observers with proper acceleration a = constant in the Minkowski vacuum (i.e., no-particle state for inertial observers) detect a thermal bath of particles at a temperature [1] (see also note [2])

No abstract

Dense enough compact objects were recently shown to lead to an exponentially fast increase of the vacuum energy density for some free scalar fields properly coupled to the spacetime curvature as a consequence of a tachyonic-like instability. Once the effect is triggered, the star energy density would be overwhelmed by the vacuum energy density in a few milliseconds. This demands that eventually geometry and field evolve to a new configuration to bring the vacuum back to a stationary regime. Here, we show that the vacuum fluctuations built up during the unstable epoch lead to particle creation in the final stationary state when the tachyonic instability ceases. The amount of created particles depends mostly on the duration of the unstable epoch and final stationary configuration, which are open issues at this point. We emphasize that the particle creation coming from the tachyonic instability will occur even in the adiabatic limit, where the spacetime geometry changes arbitrarily slowly, and therefore is quite distinct from the usual particle creation due to the change in the background geometry.

We investigate how relativity influences the spin correlation of entangled fermions described by wave packets and measured by moving detectors. In particular, we show that the Clauser-Horne-Shimony-Holt ͑CHSH͒ Bell inequality is not violated by quantum mechanics when the left and right spin detectors move fast enough. We also show that the violation of the Bell-CHSH inequality measured by the moving detectors decreases with increasing width of the initial wave packet. The discovery of the Bell inequalities can be considered one of the most important physics landmarks of the 20th century ͓1͔. It allows us to probe the essence of quantum theory by distinguishing it from local hidden variable theories. The genesis of this achievement can be traced back to the Einstein-Podolsky-Rosen discussion about the completeness of quantum mechanics ͓2͔. Presently the Clauser-HorneShimony-Holt ͑CHSH͒ Bell inequality ͓3͔ has been shown to be violated by 30 standard deviations ͓4͔, which strongly supports quantum mechanics. In order to contribute to the intense present debate on the interplay between relativity and quantum mechanics ͑see, e.g., Refs. ͓5-10͔͒, we investigate here how the former influences the spin correlation of entangled fermions measured by moving detectors. In particular we show that the CHSH Bell inequality can be satisfied rather than violated by quantum mechanics if the left and right spin detectors are set in fast enough relativistic motion. We adopt natural units ប = c =1.Let us assume a system composed of two spin-1/2 particles A and B with mass m and zero total spin angular momentum. Each particle spin is measured along some arbitrary direction defined on the y Ќ z plane. The distance between the planes along the x axis is large enough to make both measurements causally disconnected. This is well known that local hidden variable theories satisfy the CHSH Bell inequalitywhere a i ͑i =1,2͒ are two arbitrary unit vectors contained in the y Ќ z plane along which the spin s A of particle A is measured, and analogously for the two arbitrary unit vectors b j ͑j =1,2͒ and spin s B of particle B. Hereis the spin correlation function obtained after an arbitrarily large number N of experiments is performed, and a i · s A and b j · s B assume Ϯ1 / 2 values. Let us now test inequality ͑1͒ in the context of quantum mechanics, where we allow the left and right detectors to move along the x axis. For this purpose let us begin considering a quantum system composed of two spin-1/2 particles. The corresponding normalized state can be written as ͓6,11͔ ͑see also Ref.where ͚ s A ,s B ͵ dp A dp B ͉ s A s B ͑p A ,p B ͉͒ 2 = 1,and X = A , B distinguishes between both particles. Taking P X and S X ϵ s X I as the four-momentum and Wigner spin operators, respectively, where s X is half of the Pauli matrices, we havewith p X = ͑ ͱ p X 2 + m 2 , p X ͒ and s X = Ϯ 1 / 2. Let us now assume that the two-particle system is prepared in a singlet state ͑see, e.g., Refs. ͓9,13͔ for the two-spinor notation used below͒from which we read ͑7͒W...