Local quanta, unitary inequivalence, and vacuum entanglement

In this work we develop a formalism for describing localised quanta for a real-valued Klein-Gordon field in a one-dimensional box $[0, R]$. We quantise the field using non-stationary local modes which, at some arbitrarily chosen initial time, are completely localised within the left or the right side of the box. In this concrete set-up we directly face the problems inherent to a notion of local field excitations, usually thought of as elementary particles. Specifically, by computing the Bogoliubov coefficients relating local and standard (global) quantizations, we show that the local quantisation yields a Fock space $\mathfrak F^L$ which is unitarily inequivalent to the standard one $\mathfrak F^G$. In spite of this, we find that the local creators and annihilators remain well defined in the global Fock space $\mathfrak F^G$, and so do the local number operators associated to the left and right partitions of the box. We end up with a useful mathematical toolbox to analyse and characterise local features of quantum states in $\mathfrak F^G$. Specifically, an analysis of the global vacuum state $|0_G\rangle\in\mathfrak F^G$ in terms of local number operators shows, as expected, the existence of entanglement between the left and right regions of the box. The local vacuum $|0_L\rangle\in\mathfrak F^L$, on the contrary, has a very different character. It is neither cyclic nor separating and displays no entanglement. Further analysis shows that the global vacuum also exhibits a distribution of local excitations reminiscent, in some respects, of a thermal bath. We discuss how the mathematical tools developed herein may open new ways for the analysis of fundamental problems in local quantum field theory.Comment: 28 pages, 8 figure

Non-monotonic entanglement of physical EM field states in non-inertial frames

We develop a general technique to analyse the quantum effects of acceleration on realistic spatially-localised electromagnetic field states entangled in the polarization degree of freedom. We show that for this setting, quantum entanglement may build up as the acceleration increases, providing a clear signature of the quantum effects of relativistic acceleration.Comment: 5 pages, 3 figure

Extracting past-future vacuum correlations using circuit QED

We propose a realistic circuit QED experiment to test the extraction of past-future vacuum entanglement to a pair of superconducting qubits. The qubit P interacts with the quantum field along an open transmission line for an interval T_on and then, after a time-lapse T_off, the qubit F starts interacting for a time T_on in a symmetric fashion. After that, past-future quantum correlations will have transferred to the qubits, even if the qubits do not coexist at the same time. We show that this experiment can be realized with current technology and discuss its utility as a possible implementation of a quantum memory.Comment: 5 pages, 2 figures. v2: version accepted to Physical Review Letters. Title changed by editor

The Fermi problem with artificial atoms in circuit QED

We propose a feasible experimental test of a 1-D version of the Fermi problem using superconducting qubits. We give an explicit non-perturbative proof of strict causality in this model, showing that the probability of excitation of a two-level artificial atom with a dipolar coupling to a quantum field is completely independent of the other qubit until signals from it may arrive. We explain why this is in perfect agreement with the existence of nonlocal correlations and previous results which were used to claim apparent causality problems for Fermi's two-atom system.Comment: 4 pages, 2 figures; typos corrected, introduction revised and experimental discussion extended, results unchange

Detectores cuánticos y correlaciones de vacío en espacio y tiempo: resultados teóricos y propuestas de simulación

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Teórica I, leída el 27/11/2014Depto. de Física TeóricaFac. de Ciencias FísicasTRUEunpu

Elementos de Matemáticas y aplicaciones

Material elaborado por profesores de la UCM para la asignatura de este nombre del grado en Ingeniería Matemáticas, el grado en Matemáticas y el grado en Matemáticas y Estadística. Contenidos: - Números enteros. Dígitos de control y criptografía. - Grupos de simetrías. Mosaicos. - Trigonometría plana y esférica. Aplicaciones (Navegación, Astronomía de posición, GPS). - Dinámica discreta. Aplicaciones (Finanzas, introducción al caos). - Teoría de grafos. Algoritmo de ordenación de Google

Short-time quantum detection: probing quantum fluctuations

In this work we study the information provided by a detector click on the state of an initially excited two level system. By computing the time evolution of the corresponding conditioned probability beyond the rotating wave approximation, as needed for short time analysis, we show that a click in the detector is related with the decay of the source only for long times of interaction. For short times, non-rotating wave approximation effects, like self-excitations of the detector, forbid a na\"{i}ve interpretation of the detector readings. These effects might appear in circuit QED experiments.Comment: 5 pages, 5 figure

Self-Organizing and Scalable Shape Formation for a Swarm of Pico Satellites

info:eu-repo/semantics/publishe

Wavepacket detection with the Unruh-DeWitt model

In this paper we deal with several issues regarding the localization properties of the Unruh-DeWitt (UdW) detector model. Since its original formulation as a pointlike detector, the UdW model has been used to study extensively the physics of quantum fields in presence of accelerations or curved backgrounds. Natural extensions of it have tried to take into account the spatial profile of such detectors, but all of them have met a series of problems in their spectral response which render them useless to study some of the most interesting physical scenarios. In this paper we provide a derivation of the smeared UdW interaction from QED first principles, then we analyze the spectral response of spatially smeared UdW detectors, and discuss the kind of spatial profiles which are useful for the study of relevant cases.Comment: 7 pages, 3 figure