arXiv subjects

Carlos Sabín

Publications and source records attributed to Carlos Sabín.

At least 55 records · Page 3Linked to original sources

arXiv2016

Towards universal quantum computation through relativistic motion

We show how to use relativistic motion and local phase shifts to generate continuous variable Gaussian cluster states within cavity modes. Our results can be demonstrated experimentally using superconducting circuits where tuneable boundary conditions correspond to mirrors moving with velocities close to the speed of light. In particular, we propose the generation of a quadripartite square cluster state as a first example that can be readily implemented in the laboratory. Since cluster states are universal resources for universal one-way quantum computation, our results pave the way for relativistic quantum computation schemes.

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arXiv2016

Motion and gravity effects in the precision of quantum clocks

We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions.

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arXiv2015

Quantum estimation via parametric amplification in circuit QED arrays

We propose a scheme for quantum estimation by means of parametric amplification in circuit Quantum Electrodynamics. The modulation of a SQUID interrupting a superconducting waveguide transforms an initial thermal two-mode squeezed state in such a way that the new state is sensitive to the features of the parametric amplifier. We find the optimal initial parameters which maximize the Quantum Fisher Information. In order to achieve a large number of independent measurements we propose to use an array of non-interacting resonators. We show that the combination of both large QFI and large number of measurements enables -in principle- the use of this setup for Quantum Metrology applications.

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arXiv2015

Effects of three-body collisions in a two-mode Bose-Einstein condenstate

We study the effects of three-body collisions in the basic physical properties of a two-mode Bose-Einstein condensate. By finding the exact analytical solution of a model which includes two-body and three-body elastic and mode-exchange collisions, we show analytically that three-body interactions produce observable effects in the probability distribution of the ground state and the dynamics of the relative population. In particular, we find that three-body interactions under certain circumstances inhibit collapse of the relative population.

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arXiv2015

Generation of quantum steering and interferometric power in the Dynamical Casimir Effect

We analyse the role of the dynamical Casimir effect as a resource for quantum technologies, such as quantum cryptography and quantum metrology. In particular, we consider the generation of Einstein-Podolsky-Rosen steering and Gaussian interferometric power, two useful forms of asymmetric quantum correlations, in superconducting waveguides modulated by superconducting quantum interferometric devices. We show that, while a certain value of squeezing is required to overcome thermal noise and give rise to steering, any non-zero squeezing produces interferometric power which in fact increases with thermal noise.

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arXiv2015

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.

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arXiv2015

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.

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arXiv2014

Twin paradox with macroscopic clocks in superconducting circuits

We propose an implementation of a twin paradox scenario in superconducting circuits, with velocities as large as a few percent of the speed of light. Ultrafast modulation of the boundary conditions for the electromagnetic field in a microwave cavity simulates a clock moving at relativistic speeds. Since our cavity has a finite length, the setup allows us to investigate the role of clock size as well as interesting quantum effects on time dilation. In particular, our theoretical results show that the time dilation increases for larger cavity lengths and is shifted due to quantum particle creation.

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arXiv2014

Impurities as a quantum thermometer for a Bose-Einstein condensate

We introduce a primary thermometer which measures the temperature of a Bose-Einstein Condensate in the sub-nK regime. We show, using quantum Fisher information, that the precision of our technique improves the state-of-the-art in thermometry in the sub-nK regime. The temperature of the condensate is mapped onto the quantum phase of an atomic dot that interacts with the system for short times. We show that the highest precision is achieved when the phase is dynamical rather than geometric and when it is detected through Ramsey interferometry. Standard techniques to determine the temperature of a condensate involve an indirect estimation through mean particle velocities made after releasing the condensate. In contrast to these destructive measurements, our method involves a negligible disturbance of the system.

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arXiv2014

Phonon creation by gravitational waves

We show that gravitational waves create phonons in a Bose-Einstein condensate (BEC). A traveling spacetime distortion produces particle creation resonances that correspond to the dynamical Casimir effect in a BEC phononic field contained in a cavity-type trap. We propose to use this effect to detect gravitational waves. The amplitude of the wave can be estimated applying recently developed relativistic quantum metrology techniques. We provide the optimal precision bound on the estimation of the wave's amplitude. Finally, we show that the parameter regime required to detect gravitational waves with this technique could be, in principle, within experimental reach in a medium-term timescale.

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arXiv2014

Analytical solution of a double-well Bose-Einstein Condensate

We introduce a microscopic computation which shows that the Hamiltonian of a Bose-Einstein Condensate can be analytically solved in the two-mode approximation, in particular, in the case of an asymmetric double-well condensate in the dilute regime. Our model is exactly diagonalisable when the overlap of the quasilocalized modes in each well is small enough with respect to the trap asymmetry. For larger overlaps or highly symmetric traps, our diagonalisable Hamiltonian acquires extra terms that we treat within perturbation theory.

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arXiv2014

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.

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arXiv2014

Testing the effects of gravity and motion on quantum entanglement in space-based experiments

We propose an experiment to test the effects of gravity and acceleration on quantum entanglement in space-based setups. We show that the entanglement between excitations of two Bose-Einstein condensates is degraded after one of them undergoes a change in the gravitational field strength. This prediction can be tested if the condensates are initially entangled in two separate satellites while being in the same orbit and then one of them moves to a different orbit. We show that the effect is observable in a typical orbital manoeuvre of nanosatellites like CanX4 and CanX5.

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arXiv2014

Relativistic Quantum Metrology: Exploiting relativity to improve quantum measurement technologies

We present a framework for relativistic quantum metrology that is useful for both Earth-based and space-based technologies. Quantum metrology has been so far successfully applied to design precision instruments such as clocks and sensors which outperform classical devices by exploiting quantum properties. There are advanced plans to implement these and other quantum technologies in space, for instance Space-QUEST and Space Optical Clock projects intend to implement quantum communications and quantum clocks at regimes where relativity starts to kick in. However, typical setups do not take into account the effects of relativity on quantum properties. To include and exploit these effects, we introduce techniques for the application of metrology to quantum field theory. Quantum field theory properly incorporates quantum theory and relativity, in particular, at regimes where space-based experiments take place. This framework allows for high precision estimation of parameters that appear in quantum field theory including proper times and accelerations. Indeed, the techniques can be applied to develop a novel generation of relativistic quantum technologies for gravimeters, clocks and sensors. As an example, we present a high precision device which in principle improves the state-of-the-art in quantum accelerometers by exploiting relativistic effects.

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arXiv2013

Relativistic Quantum Teleportation with Superconducting Circuits

We study the effects of relativistic motion on quantum teleportation and propose a realizable experiment where our results can be tested. We compute bounds on the optimal fidelity of teleportation when one of the observers undergoes non-uniform motion for a finite time. The upper bound to the optimal fidelity is degraded due to the observer's motion however, we discuss how this degradation can be corrected. These effects are observable for experimental parameters that are within reach of cutting-edge superconducting technology. Our setup will further provide guidance for future space-based experiments.

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arXiv2012

Dynamics of Atom-Atom Correlations in the Fermi problem

We present a detailed perturbative study of the dynamics of several types of atom-atom correlations in the famous Fermi problem. This is an archetypal model to study micro-causality in the quantum domain where two atoms, the first initially excited and the second prepared in its ground state, interact with the vacuum electromagnetic field. The excitation can be transferred to the second atom via a flying photon and various kinds of quantum correlations between the two are generated during this process. Among these, prominent examples are given by entanglement, quantum discord and nonlocal correlations. It is the aim of this paper to analyze the role of the light cone in the emergence of such correlations.

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arXiv2011

Bipartite entanglement of localized separated systems

The main part of this Thesis is devoted to the dynamics of entanglement in matter-radiation interaction and circuit QED systems, and its relationship with the notion of causality. Results on non-RWA effects in circuit QED and quantum simulations of relativistic dynamics are also included.

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arXiv2008

Generation of atom-atom correlations inside and outside the mutual light cone

We analyze whether a pair of neutral two level atoms can become entangled in a finite time while they remain causally disconnected. The interaction with the e. m. field is treated perturbatively in the electric dipole approximation. We start from an initial vacuum state and obtain the final atomic correlations for the cases where n = 0, 1, or 2 photons are produced in a time t, and also when the final field state is unknown. Our results show that correlations are sizable inside and outside the mutual light cone for n= 1 and 2, and also that quantum correlations become classical by tracing over the field state. For n = 0 we obtain entanglement generation by photon propagation between the atoms, the correlations come from the indistinguishability of the source for n = 1, and may give rise to entanglement swapping for n = 2.

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