arXiv subjects

L. Sanz

Publications and source records attributed to L. Sanz.

26 records · Page 2Linked to original sources

arXiv2008

Phonon modulation of the spin-orbit interaction as a spin relaxation mechanism in quantum dots

We calculate the spin relaxation rates in a parabolic InSb quantum dots due to the spin interaction with acoustical phonons. We considered the deformation potential mechanism as the dominant electron-phonon coupling in the Pavlov-Firsov spin-phonon Hamiltonian. By studying suitable choices of magnetic field and lateral dot size, we determine regions where the spin relaxation rates can be practically suppressed. We analyze the behavior of the spin relaxation rates as a function of an external magnetic field and mean quantum dot radius. Effects of the spin admixture due to Dresselhaus contribution to spin-orbit interaction are also discussed.

cond-mat.mes-hall↗

arXiv2007

Order parameter for the dynamical phase transition in Bose-Einstein condensates with topological modes

In a trapped Bose-Einstein condensate, subject to the action of an alternating external field, coherent topological modes can be resonantly excited. Depending on the amplitude of the external field and detuning parameter, there are two principally different regimes of motion, with mode locking and without it. The change of the dynamic regime corresponds to a dynamic phase transition. This transition can be characterized by an effective order parameter defined as the difference between fractional mode populations averaged over the temporal period of oscillations. The behavior of this order parameter, as a function of detuning, pumping amplitude, and atomic interactions is carefully analyzed. A special attention is payed to numerical calculations for the realistic case of a quadrupole exciting field and the system parameters accessible in current experiments.

quant-ph↗

arXiv2007

Ramsey fringes formation during excitation of topological modes in a Bose-Einstein condensate

The Ramsey fringes formation during the excitation of topological coherent modes of a Bose-Einstein condensate by an external modulating field is considered. The Ramsey fringes appear when a series of pulses of the excitation field is applied. In both Rabi and Ramsey interrogations, there is a shift of the population maximum transfer due to the strong non-linearity present in the system. It is found that the Ramsey pattern itself retains information about the accumulated relative phase between both ground and excited coherent modes.

cond-mat.stat-mech↗

arXiv2006

Control of the geometric phase and pseudo-spin dynamics on coupled Bose-Einstein condensates

We describe the behavior of two coupled Bose-Einstein condensates in time-dependent (TD) trap potentials and TD Rabi (or tunneling) frequency, using the two-mode approach. Starting from Bloch states, we succeed to get analytical solutions for the TD Schroedinger equation and present a detailed analysis of the relative and geometric phases acquired by the wave function of the condensates, as well as their population imbalance. We also establish a connection between the geometric phases and constants of motion which characterize the dynamic of the system. Besides analyzing the affects of temporality on condensates that differs by hyperfine degrees of freedom (internal Josephson effect), we also do present a brief discussion of a one specie condensate in a double-well potential (external Josephson effect).

quant-ph↗

arXiv2005

Generation of generalized coherent states with two coupled Bose-Einstein condensates

We present a scheme to prepare generalized coherent states in a system with two species of Bose-Einstein condensates. First, within the two-mode approximation, we demonstrate that a Schrodinger cat-like can be dynamically generated and, by controlling the Josephson-like coupling strength, the number of coherent states in the superposition can be varied. Later, we analyze numerically the dynamics of the whole system when interspecies collisions are inhibited. Variables such as fractional population, Mandel parameter and variances of annihilation and number operators are used to show that the evolved state is entangled and exhibits sub-Poisson statistics.

quant-ph↗

arXiv2005

Entanglement, chaos and atomic Wigner function of the Dicke model

We calculate the atomic (spin) Wigner function for the single mode Dicke model in the regime of large number of two-level atoms. The dynamics of this quasi-probability function on the Bloch sphere allows us to visualize the consequences of the entanglement process between the boson and the spin subsystems. Such investigation shows a distinct localization behavior of the spin state with respect to the polar and azimuthal Bloch sphere angles. A complete {\em breakdown of reflection symmetry} in the azimuthal angle is shown in the non-integrable case, even at short evolution times. Also, in the classically chaotic situation, the appearance of {\em sub-planck structures} in the Wigner function is shown, and its evolution analyzed.

quant-ph↗

arXiv2005

Quantum Entanglement and fixed point Hopf bifurcation

We present the qualitative differences in the phase transitions of the mono-mode Dicke model in its integrable and chaotic versions. We show that a first order phase transition occurs in the integrable case whereas a second order in the chaotic one. This difference is also reflected in the classical limit: for the integrable case the stable fixed point in phase space suffers a bifurcation of Hopf type whereas for the second one a pitchfork type bifurcation has been reported.

quant-ph↗

arXiv2002

Reversible entanglement in a Kerr-like interaction Hamiltonian: an integrable model

An exactly soluble non-linear interaction Hamiltonian is proposed to study fundamental properties of the entanglement dynamics for a coupled non-linear oscillators. The time-evolved state is obtained analytically for initial products of two coherent and two number states and relevant informations are extracted from the dynamics of various quantities like subsystem linear and Von Neumann entropies, quadrature mean values, variances and Q-functions. We determined the re-coherence time scales and found among the interaction terms present in the Hamiltonian the one responsible for the entanglement in both cases. We identify the existence of two regimens for the entanglement dynamics in the case of initially coherent states: the short time, phase spread regimen where the entropy rises monotonically and the self-interference regimen where the entropy oscillates and re-coherence phenomenon can be observed. We also found that the break time from the first regimen to the second one becomes longer, as well as the re-coherence and reversibility times, as the Planck's constant becomes much smaller than a typical action in phase space.

quant-ph↗