Cavity-aided quantum parameter estimation in a bosonic double-well Josephson junction

We describe an apparatus designed to make non-demolition measurements on a Bose-Einstein condensate (BEC) trapped in a double-well optical cavity. This apparatus contains, as well as the bosonic gas and the trap, an optical cavity. We show how the interaction between the light and the atoms, under appropriate conditions, can allow for a weakly disturbing yet highly precise measurement of the population imbalance between the two wells and its variance. We show that the setting is well suited for the implementation of quantum-limited estimation strategies for the inference of the key parameters defining the evolution of the atomic system and based on measurements performed on the cavity field. This would enable {\it de facto} Hamiltonian diagnosis via a highly controllable quantum probe.Comment: 8 pages, 5 figures, RevTeX4; Accepted for publication in Phys. Rev.

Relativistic quantum mechanics with trapped ions

We consider the quantum simulation of relativistic quantum mechanics, as described by the Dirac equation and classical potentials, in trapped-ion systems. We concentrate on three problems of growing complexity. First, we study the bidimensional relativistic scattering of single Dirac particles by a linear potential. Furthermore, we explore the case of a Dirac particle in a magnetic field and its topological properties. Finally, we analyze the problem of two Dirac particles that are coupled by a controllable and confining potential. The latter interaction may be useful to study important phenomena as the confinement and asymptotic freedom of quarks.Comment: 17 pages, 4 figure

Generating coherence and entanglement with a finite-size atomic ensemble in a ring cavity

We propose a model to study the coherence and entanglement resulting from the interaction of a finite-size atomic ensemble with degenerate counter-propagating field modes of a high-Q ring cavity. Our approach applies to an arbitrary number of atoms N and includes the spatial variation of the field throughout the ensemble. We report several new interesting aspects of coherence and entangled behavior that emerge when the size of the atomic ensemble is not taken to the thermodynamic limit of N>>1. Under such conditions, it is found that the counter-propagating cavity modes, although in the thermodynamic limit are mutually incoherent and exhibit no one-photon interference, the modes can, however, be made mutually coherent and exhibit interference after interacting with a finite-size atomic ensemble. It is also found that the spatial redistribution of the atoms over a finite size results in nonorthogonality of the collective bosonic modes. This nonorthogonality leads to the super-bunching effect that the correlations of photons of the individual cavity modes and of different modes are stronger than those of a thermal field. However, we find that the correlations are not strong enough to violate the Cauchy-Schwarz inequality and to produce squeezing and entanglement between the modes. Therefore, we investigate the spectral distributions of the logarithmic negativity and the variances of the output fields. These functions determine squeezing and entanglement properties of the output cavity fields and can be measured by a homodyne technique. We find that the entanglement is redistributed over several components of the spectrum and the finite-size effect is to concentrate the entanglement at the zero-frequency component of the spectrum.Comment: Published versio

Freizeit im Wertewandel die neue Einstellung zu Arbeit und Freizeit

UuStB Koeln(38)-4L8053 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Assessment of weak-coupling approximations on a driven two-level system under dissipation

| openaire: EC/H2020/681311/EU//QUESS | openaire: EC/H2020/957440/EU//SCARThe standard weak-coupling approximations associated to open quantum systems have been extensively used in the description of a two-level quantum system, qubit, subjected to relatively weak dissipation compared with the qubit frequency. However, recent progress in the experimental implementations of controlled quantum systems with increased levels of on-demand engineered dissipation has motivated precision studies in parameter regimes that question the validity of the approximations, especially in the presence of time-dependent drive fields. In this paper, we address the precision of weak-coupling approximations by studying a driven qubit through the numerically exact and non-perturbative method known as the stochastic Liouville-von Neumann equation with dissipation. By considering weak drive fields and a cold Ohmic environment with a high cutoff frequency, we use the Markovian Lindblad master equation as a point of comparison for the SLED method and study the influence of the bath-induced energy shift on thequbit dynamics. We also propose a metric that may be used in experiments to map the regime of validity of the Lindblad equation in predicting the steady state of the driven qubit. In addition, we study signatures of the well-known Mollow triplet and observe its meltdown owing to dissipation in an experimentally feasible parameter regime of circuit electrodynamics. Besides shedding light on the practical limitations of the Lindblad equation, we expect our results to inspire future experimental research on engineered open quantum systems, the accurate modeling of which may benefit from non-perturbative methods.Peer reviewe

Out of equilibrium thermodynamics of quantum harmonic chains

The thermodynamic implications for the out-of-equilibrium dynamics of quantum systems are to date largely unexplored, especially for quantum many-body systems. In this paper we investigate the paradigmatic case of an array of nearest-neighbor coupled quantum harmonic oscillators interacting with a thermal bath and subjected to a quench of the inter-oscillator coupling strength. We study the work done on the system and its irreversible counterpart, and characterize analytically the fluctuation relations of the ensuing out-of-equilibrium dynamics. Finally, we showcase an interesting functional link between the dissipated work produced across a two-element chain and their degree of general quantum correlations. Our results suggest that, for the specific model at hand, the non-classical features of a harmonic system can influence significantly its thermodynamics