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P. Lambropoulos

Publications and source records attributed to P. Lambropoulos.

At least 37 records · Page 2Linked to original sources
arXiv2011

Passage-time statistics of superradiant light pulses from Bose-Einstein condensates

We discuss the passage-time statistics of superradiant light pulses generated during the scattering of laser light from an elongated atomic Bose-Einstein condensate. Focusing on the early-stage of the phenomenon, we analyze the corresponding probability distributions and their scaling behaviour with respect to the threshold photon number and the coupling strength. With respect to these parameters, we find quantities which only vary significantly during the transition between the Kapitza Dirac and the Bragg regimes. A possible connection of the present observations to Brownian motion is also discussed.

quant-ph↗
arXiv2011

Route to Direct Multiphoton Multiple Ionization

We address the concept of direct multiphoton multiple ionization in atoms exposed to intense, short wavelength radiation and explore the conditions under which such processes dominate over the sequential. Their contribution is shown to be quite robust, even under intensity fluctuations and interaction volume integration, and reasonable agreement with experimental data is also found.

quant-ph↗
arXiv2010

Early Stage of Superradiance from Bose-Einstein Condensates

We investigate the dynamics of matter and optical waves at the early stage of superradiant Rayleigh scattering from Bose-Einstein Condensates. Our analysis is within a spatially dependent quantum model which is capable of providing analytic solutions for the operators of interest. The predictions of the present model are compared to the predictions of a closely related mean field model, and we provide a procedure that allows one to calculate quantum expectation values by averaging over semiclassical solutions. The coherence properties of the outgoing scattered light are also analyzed, and it is shown that the corresponding correlation functions may provide detailed information about the internal dynamics of the system.

cond-mat.quant-gas↗
arXiv2010

Correlated directional atomic clouds via four-heterowave mixing

We investigate the coherence properties of pairs of counter-propagating atomic clouds, produced in superradiant Rayleigh scattering off atomic condensates. It is shown that these clouds exhibit long-range spatial coherence and strong nonclassical density cross-correlations, which make this scheme a promising candidate for the production of highly directional nonclassically correlated atomic pulses.

quant-ph↗
arXiv2010

State transfer in static and dynamic spin chains with disorder

We examine the speed and fidelity of several protocols for state or single excitation transfer in finite spin chains subject to diagonal and off-diagonal disorder. We find that, for a given chain length and maximal achievable inter-spin exchange (XY) coupling strength, the optimal static spin-coupling protocol, implementing the fastest state transfer between the two ends of the chain, is more susceptible to off-diagonal (XY coupling) disorder, as compared to a much slower but robust adiabatic transfer protocol with time-dependent coupling strengths.

quant-ph↗
arXiv2007

Effects of relative phase and interactions on atom-laser outcoupling from a double-well Bose-Einstein condensate: Markovian and non-Markovian dynamics

We investigate aspects of the dynamics of a continuous atom-laser scheme based on the merging of independently formed atomic condensates. Our theoretical analysis covers the Markovian as well as the non-Markovian operational regimes, and is based on a semiclassical (mean-field) two-mode model. The role of the relative phase between the two condensates and the effect of interatomic interactions on the evolution of the trapped populations and the distribution of outcoupled atoms are discussed.

quant-ph↗
arXiv2007

Coherent population transfer in a chain of tunnel coupled quantum dots

We consider the dynamics of a single electron in a chain of tunnel coupled quantum dots, exploring the formal analogies of this system with some of the laser-driven multilevel atomic or molecular systems studied by Bruce W. Shore and collaborators over the last 30 years. In particular, we describe two regimes for achieving complete coherent transfer of population in such a multistate system. In the first regime, by carefully arranging the coupling strengths, the flow of population between the states of the system can be made periodic in time. In the second regime, by employing a "counterintuitive" sequence of couplings, the coherent population trapping eigenstate of the system can be rotated from the initial to the final desired state, which is an equivalent of the STIRAP technique for atoms or molecules. Our results may be useful in future quantum computation schemes.

quant-ph↗
arXiv2007

Non-Markovian dynamics in atom-laser outcoupling from a double-well Bose-Einstein condensate

We investigate the dynamics of a continuous atom laser based on the merging of independently formed atomic condensates. In a first attempt to understand the dynamics of the system, we consider two independent elongated Bose-Einstein condensates which approach each other and focus on intermediate inter-trap distances so that a two-mode model is well justified. In the framework of a mean-field theory, we discuss the quasi steady-state population of the traps as well as the energy distribution of the outcoupled atoms.

quant-ph↗
arXiv2005

Signatures of direct double ionization under XUV radiation

In anticipation of upcoming two-photon double ionization of atoms and particularly Helium, under strong short wavelength radiation sources (45 eV), we present quantitative signatures of direct two-photon double ejection, in the photoelectron spectrum (PES) and the peak power dependence, that can be employed in the interpretation of related data. We show that the PES provides the cleanest signature of the process. An inflection (knee) in the laser power dependence of double ionization is also discernible, within a window of intensities which depends on the pulse duration and cross sections

physics.atom-ph↗
arXiv2004

Quantum Zeno effect by indirect measurement: The effect of the detector

We study the quantum Zeno effect in the case of indirect measurement, where the detector does not interact directly with the unstable system. Expanding on the model of Koshino and Shimizu [Phys. Rev. Lett., 92, 030401, (2004)] we consider a realistic Hamiltonian for the detector with a finite bandwidth. We also take explicitly into account the position, the dimensions and the uncertainty in the measurement of the detector. Our results show that the quantum Zeno effect is not expected to occur, except for the unphysical case where the detector and the unstable system overlap.

quant-ph↗
arXiv2003

Electron wavepacket propagation and entanglement in a chain of coupled quantum dots

We study the coherent dynamics of one- and two-electron transport in a linear array of tunnel-coupled quantum dots. We find that this system exhibits a rich variety of coherent phenomena, ranging from electron wavepacket propagation and interference to two-particle bonding and entanglement. Our studies, apart from their relevance to the exploration of quantum dynamics and transport in periodic structures, are also aimed at possible applications in future quantum computation schemes.

quant-ph↗
arXiv2003

Effects of interatomic collisions on atom laser outcoupling

We present a computational approach to the outcoupling in a simple one-dimensional atom laser model, the objective being to circumvent mathematical difficulties arising from the breakdown of the Born and Markov approximations. The approach relies on the discretization of the continuum representing the reservoir of output modes, which allows the treatment of arbitrary forms of outcoupling as well as the incorporation of non-linear terms in the Hamiltonian, associated with interatomic collisions. By considering a single-mode trapped condensate, we study the influence of elastic collisions between trapped and free atoms on the quasi steady-state population of the trap, as well as the energy distribution and the coherence of the outcoupled atoms.

cond-mat↗
arXiv2002

Basis-dependent dynamics of trapped Bose-Einstein condensates and analogies with semi-classical laser theory

We present a consistent second order perturbation theory for the lowest-lying condensed modes of very small, weakly-interacting Bose-Einstein condensates in terms of bare particle eigenstates in a harmonic trap. After presenting our general approach, we focus on explicit expressions for a simple three-level system, mainly in order to discuss the analogy of a single condensate occupying two modes of a trap with the semi-classical theory for two-mode photon lasers. A subsequent renormalization of the single-particle energies to include the dressing imposed by mean fields demonstrates clearly the consistency of our treatment with other kinetic approaches.

cond-mat↗
arXiv2000

Phase-Control of Photoabsorption in Optically Dense Media

We present a self-consistent theory, as well as an illustrative application to a realistic system, of phase control of photoabsorption in an optically dense medium. We demonstrate that, when propagation effects are taken into consideration, the impact on phase control is significant. Independently of the value of the initial phase difference between the two fields, over a short scaled distance of propagation, the medium tends to settle the relative phase so that it cancels the atomic excitation. In addition, we find some rather unusual behavior for an optically thin layer.

quant-ph↗
arXiv2000

Beyond single-photon localization at the edge of a Photonic Band Gap

We study spontaneous emission in an atomic ladder system, with both transitions coupled near-resonantly to the edge of a photonic band gap continuum. The problem is solved through a recently developed technique and leads to the formation of a ``two-photon+atom'' bound state with fractional population trapping in both upper states. In the long-time limit, the atom can be found excited in a superposition of the upper states and a ``direct'' two-photon process coexists with the stepwise one. The sensitivity of the effect to the particular form of the density of states is also explored.

quant-ph↗
arXiv1999

Quantum systems coupled to a structured reservoir with multiple excitations

We present a method for dealing with quantum systems coupled to a structured reservoir with any density of modes and with more than one excitation. We apply the method to a two-level atom coupled to the edge of a photonic band gap and a defect mode. Results pertaining to this system, provide the solution to the problem of two photons in the reservoir and possible generalization is discussed.

quant-ph↗
arXiv1999

Time-dependent calculation of ionization in Potassium at mid-infrared wavelengths

We study the dynamics of the Potassium atom in the mid-infrared, high intensity, short laser pulse regime. We ascertain numerical convergence by comparing the results obtained by the direct expansion of the time-dependent Schroedinger equation onto B-Splines, to those obtained by the eigenbasis expansion method. We present ionization curves in the 12-, 13-, and 14-photon ionization range for Potassium. The ionization curve of a scaled system, namely Hydrogen starting from the 2s, is compared to the 12-photon results. In the 13-photon regime, a dynamic resonance is found and analyzed in some detail. The results for all wavelengths and intensities, including Hydrogen, display a clear plateau in the peak-heights of the low energy part of the Above Threshold Ionization (ATI) spectrum, which scales with the ponderomotive energy Up, and extends to 2.8 +- 0.5 Up.

physics.atom-ph↗