Probing the spacetime structure of vacuum entanglement

We introduce a framework for probing the spacetime structure of vacuum entanglement that exhibits infinite range correlations between the future and the past, as well as spatially separated regions. Our results are non-perturbative and analytical.Comment: I.F. previously published as Fuentes-Guridi and Fuentes-Schulle

On relativistic particle creation in Bose-Einstein condensates

We show that particle creation of Bogoliubov modes in a Bose-Einstein condensate due to the accelerated motion of the trap is a genuinely relativistic effect. To this end we show that Bogoliubov modes can be described by a time rescaling of the Minkowski metric. A consequence of this is that Rindler transformations are perceived by the phonons as generalised Rindler transformations where the speed of light is replaced by the speed of sound, enhancing particle creation at small velocities. Since the non-relativistic limit of a Rindler transformation is just a Galilean transformation entailing no length contraction or time dilation, we show that the effect vanishes in the non-relativistic limit.Comment: This work provides further theoretical support to the results in Sci. Rep. 4, 4996 (2014), http://www.nature.com/srep/2014/140521/srep04996/full/srep04996.htm

Active Interferometry with Gaussian Channels

We consider an interferometer that contains active elements, such as a parametric amplifier, with general two-mode Gaussian unitary channels rather than the usually considered phase-shift channel. We concentrate on a scheme based on the recently proposed pumped-up SU(1,1) active interferometer where all input particles participate in the parameter estimation, and from which a conventional SU(1,1) interferometer is a limiting case. Using the covariance matrix formalism, we derive the quantum Fisher information of this active interferometer with a general two-mode Gaussian unitary channel, as well as the sensitivity for a number-sum measurement scheme, finding simple expressions for the latter. As an example application, we apply our results to Bose-Einstein condensates (BECs), and in particular a BEC gravitational-wave detector based on resonance, finding that the sensitivity of the detector can be improved by several orders of magnitude with this new interferometry scheme.Comment: 17 pages, 1 figur

Observer dependent entanglement

Understanding the observer-dependent nature of quantum entanglement has been a central question in relativistic quantum information. In this paper we will review key results on relativistic entanglement in flat and curved spacetime and discuss recent work which shows that motion and gravity have observable effects on entanglement between localized systems.Comment: Ivette Fuentes previously published as Ivette Fuentes-Guridi and Ivette Fuentes-Schulle

Spatially extended Unruh-DeWitt detectors for relativistic quantum information

Unruh-DeWitt detectors interacting locally with a quantum field are systems under consideration for relativistic quantum information processing. In most works, the detectors are assumed to be point-like and, therefore, couple with the same strength to all modes of the field spectrum. We propose the use of a more realistic detector model where the detector has a finite size conveniently tailored by a spatial profile. We design a spatial profile such that the detector, when inertial, naturally couples to a peaked distribution of Minkowski modes. In the uniformly accelerated case, the detector couples to a peaked distribution of Rindler modes. Such distributions are of special interest in the analysis of entanglement in non-inetial frames. We use our detector model to show the noise detected in the Minkowski vacuum and in single particle states is a function of the detector's acceleration.Comment: Revised for publication, 9 pages (+1 references page), 7 figure

Analog quantum simulation of gravitational waves in a Bose-Einstein condensate

We show how to vary the physical properties of a Bose-Einstein condensate (BEC) in order to mimic an effective gravitational-wave spacetime. In particular, we focus in the simulation of the recently discovered creation of particles by real spacetime distortion in box-type traps. We show that, by modulating the speed of sound in the BEC, the phonons experience the effects of a simulated spacetime ripple with experimentally amenable parameters. These results will inform the experimental programme of gravitational wave astronomy with cold atoms.Comment: 9 pages. I. F. previously published as I. Fuentes-Guridi and I.Fuentes-Schuller. v2: minor changes, references adde

Dynamical Casimir effect in curved spacetime

A boundary undergoing relativistic motion can create particles from quantum vacuum fluctuations in a phenomenon known as the dynamical Casimir effect. We examine the creation of particles, and more generally the transformation of quantum field states, due to boundary motion in curved spacetime. We provide a novel method enabling the calculation of the effect for a wide range of trajectories and spacetimes. We apply this to the experimental scenario used to detect the dynamical Casimir effect, now adopting the Schwarzschild metric, and find novel resonances in particle creation as a result of the spacetime curvature. Finally, we discuss a potential enhancement of the effect for the phonon field of a Bose-Einstein condensate.Comment: 17 pages, 0 figures, 2 appendice

Optimal quantum estimation of the Unruh-Hawking effect

We address on general quantum-statistical grounds the problem of optimal detection of the Unruh-Hawking effect. We show that the effect signatures are magnified up to potentially observable levels if the scalar field to be probed has high mean energy from an inertial perspective: The Unruh-Hawking effect acts like an amplification channel. We prove that a field in a Fock inertial state, probed via photon counting by a non-inertial detector, realizes the optimal strategy attaining the ultimate sensitivity allowed by quantum mechanics for the observation of the effect. We define the parameter regime in which the effect can be reliably revealed in laboratory experiments, regardless of the specific implementation.Comment: 4 pages, 2 figures. Close to published version. (I.F. previously published as Fuentes-Guridi and Fuentes-Schuller

Ruling out stray thermal radiation in analogue black holes

Experimental searches for the thermal radiation from analogue black holes require the measurement of very low temperatures in regimes where other thermal noises may interfere or even mimic the sought-after effect. In this letter, we parameterize the family of bosonic thermal channels which give rise to such thermal effects and show that by use of coherent states and homodyne detection one can rule out the non-Hawking contributions and identify those candidate sources which arise from Hawking-like processes.Comment: 5 pages, 2 figure

Quantum discord in the Dynamical Casimir Effect

We analyse the generation of quantum discord by means of the dynamical Casimir effect in superconducting waveguides modulated by superconducting quantum interferometric devices. We show that for realistic experimental parameters, the conditions for the existence of quantum discord are less demanding than the previously considered for quantum entanglement or non-classicality. The states with non-zero discord and zero entanglement generated by the dynamical Casimir effect are a useful resource for quantum cryptography.Comment: 4 pages, 2 figures. v2: minor changes, published versio