arXiv subjects

Bruno Juliá-Díaz

Publications and source records attributed to Bruno Juliá-Díaz.

65 records · Page 4Linked to original sources

arXiv2015

Hybrid synchronization in coupled ultracold atomic gases

We study the time evolution of two coupled many-body quantum systems one of which is assumed to be Bose condensed. Specifically, we consider two ultracold atomic clouds populating each two localized single-particle states, i.e. a two-component Bosonic Josephson junction. The cold atoms cloud can retain its coherence when coupled to the condensate and displays synchronization with the latter, differing from usual entrainment. We term this effect among the ultracold and the condensed clouds as {\it hybrid synchronization}. The onset of synchronization, which we observe in the evolution of average properties of both gases when increasing their coupling, is found to be related to the many-body properties of the quantum gas, e.g. condensed fraction, quantum fluctuations of the particle number differences. We discuss the effects of different initial preparations, the influence of unequal particle numbers for the two clouds, and explore the dependence on the initial quantum state, e.g. coherent state, squeezed state and Fock state, finding essentially the same phenomenology in all cases.

cond-mat.quant-gas↗

arXiv2015

Topological phases of lattice bosons with a dynamical gauge field

Optical lattices with a complex-valued tunnelling term have become a standard way of studying gauge-field physics with cold atoms. If the complex phase of the tunnelling is made density-dependent, such system features even a self-interacting or dynamical magnetic field. In this paper we study the scenario of a few bosons in either a static or a dynamical gauge field by means of exact diagonalization. The topological structures are identified computing their Chern number. Upon decreasing the atom-atom contact interaction, the effect of the dynamical gauge field is enhanced, giving rise to a phase transition between two topologically non-trivial phases.

cond-mat.quant-gas↗

arXiv2013

Quantum Hall phases of two-component bosons

The recent production of synthetic magnetic fields acting on electroneutral particles, like atoms or photons, has boosted the interest in the quantum Hall physics of bosons. Adding pseudospin-1/2 to the bosons greatly enriches the scenario, as it allows them to form an interacting integer quantum Hall (IQH) phase with no fermionic counterpart. Here we show that, for a small two-component Bose gas on a disk, the complete strongly correlated regime, extending from the integer phase at filling factor $ν=2$ to the Halperin phase at filling factor $ν=2/3$, is well described by composite fermionization of the bosons. Moreover we study the edge excitations of the IQH state, which, in agreement with expectations from topological field theory, are found to consist of forward-moving charge excitations and backward-moving spin excitations. Finally, we demonstrate how pair-correlation functions allow one to experimentally distinguish the IQH state from competing states, like non-Abelian spin singlet (NASS) states.

cond-mat.quant-gas↗

arXiv2013

Topological phases in small quantum Hall samples

Topological order has proven a useful concept to describe quantum phase transitions which are not captured by the Ginzburg-Landau type of symmetry-breaking order. However, lacking a local order parameter, topological order is hard to detect. One way to detect is via direct observation of anyonic properties of excitations which are usually discussed in the thermodynamic limit, but so far has not been realized in macroscopic quantum Hall samples. Here we consider a system of few interacting bosons subjected to the lowest Landau level by a gauge potential, and theoretically investigate vortex excitations in order to identify topological properties of different ground states. Our investigation demonstrates that even in surprisingly small systems anyonic properties are able to characterize the topological order. In addition, focusing on a system in the Laughlin state, we study the robustness of its anyonic behavior in the presence of tunable finite-range interactions acting as a perturbation. A clear signal of a transition to a different state is reflected by the system's anyonic properties.

cond-mat.quant-gas↗

arXiv2013

One-loop contributions in the EFT for the $ΛN \to NN$ transition

We consider the $ΛN\to NN$ weak transition, responsible for a large fraction of the non-mesonic weak decay of hypernuclei. We follow on the previously derived effective field theory and compute the next-to-leading one-loop corrections. Explicit expressions for all diagrams are provided, which result in contributions to all relevant partial waves.

nucl-th↗

arXiv2013

Thermal spin fluctuations in spinor Bose-Einstein condensates

We study the thermal activation of spin fluctuations in dynamically-stable spinor Bose-Einstein condensates. We analyze the specific cases of a non-dipolar spin-1 condensate in m = 0, where thermal activation results from spin-changing collisions, and of a Chromium condensate in the maximally stretched state m = -3, where thermal spin fluctuations are due to dipole-induced spin- relaxation. In both cases, we show that the low energy associated to the spinor physics may be employed for thermometry purposes down to extremely low temperatures, typically impossible to measure in BECs with usual thermometric techniques. Moreover, the peculiar dependence of the system's entropy with the applied Zeeman energy opens a possible route for adiabatic cooling.

cond-mat.quant-gas↗

arXiv2012

Quasihole dynamics as a detection tool for quantum Hall phases

Existing techniques for synthesizing gauge fields are able to bring a two-dimensional cloud of harmonically trapped bosonic atoms into a regime where the occupied single-particle states are restricted to the lowest Landau level (LLL). Repulsive short-range interactions drive various transitions from fully condensed into strongly correlated states. In these different phases we study the response of the system to quasihole excitations induced by a laser beam. We find that in the Laughlin state the quasihole performs a coherent constant rotation around the center, ensuring conservation of angular momentum. This is distinct to any other regime with higher density, where the quasihole is found to decay. At a characteristic time, the decay process is reversed, and revivals of the quasihole can be observed in the density. Measuring the period and position of the revival can be used as a spectroscopic tool to identify the strongly correlated phases in systems with a finite number of atoms.

cond-mat.quant-gas↗

arXiv2012

Spin-driven spatial symmetry breaking of spinor condensates in a double-well

The properties of an F=1 spinor Bose-Einstein condensate trapped in a double-well potential are discussed using both a mean-field two-mode approach and a simplified two-site Bose-Hubbard Hamiltonian. We focus in the region of phase space in which spin effects lead to a symmetry breaking of the system, favoring the spatial localization of the condensate in one well. To model this transition we derive, using perturbation theory, an effective Hamiltonian that describes N/2 spin singlets confined in a double-well potential.

cond-mat.quant-gas↗

arXiv2012

Non-Abelian spin singlet states of two-component Bose gases in artificial gauge fields

We study strongly correlated phases of a pseudo-spin-1/2 Bose gas in an artificial gauge field using the exact diagonalization method. The atoms are confined in two dimensions and interact via a two-body contact potential. In Abelian gauge fields, pseudo-spin singlets are favored by pseudo-spin independent interactions. We find a series of incompressible phases at fillings ν=2k/3. By comparison with the non-Abelian spin singlet (NASS) states, constructed as zero-energy eigenstates of a (k+1)-body contact interaction, we classify the non-trivial topology of the states. An additional spin-orbit coupling is shown to switch between NASS-like states and spin-polarized phases from the Read-Rezayi series.

cond-mat.quant-gas↗

arXiv2011

Improved variational approach to the two-site Bose-Hubbard model

An improved variational ansatz is proposed to capture the most striking properties of the ground state of a slightly biased attractive two-site Bose-Hubbard Hamiltonian. Our ansatz, albeit its simplicity, is found to capture well the exact properties of the ground state for a wide variety of model parameters, in particular the fragmentation occurring before the formation of cat-like states and also the formation of strongly correlated cat-like states.

cond-mat.quant-gas↗

arXiv2011

Current constraints on the EFT for the ΛN --> N N transition

The relation between the low energy constants appearing in the effective field theory description of the ΛN --> N N transition potential and the parameters of the one-meson-exchange model previously developed are obtained. We extract the relative importance of the different exchange mechanisms included in the meson picture by means of a comparison to the corresponding operational structures appearing in the effective approach. The ability of this procedure to obtain the weak baryon-baryon-meson couplings for a possible scalar exchange is also discussed.

nucl-th↗