arXiv subjects

A. del Campo

Publications and source records attributed to A. del Campo.

At least 55 records · Page 3Linked to original sources

arXiv2009

Preparation of atomic Fock states by trap reduction

We describe the preparation of atom-number states with strongly interacting bosons in one dimension, or spin-polarized fermions. The procedure is based on a combination of weakening and squeezing of the trapping potential. For the resulting state, the full atom number distribution is obtained. Starting with an unknown number of particles $N_i$, we optimize the sudden change in the trapping potential which leads to the Fock state of $N_f$ particles in the final trap. Non-zero temperature effects as well as different smooth trapping potentials are analyzed. A simple criterion is provided to ensure the robust preparation of the Fock state for physically realistic traps.

quant-ph↗

arXiv2009

Dwell-time distributions in quantum mechanics

Some fundamental and formal aspects of the quantum dwell time are reviewed, examples for free motion and scattering off a potential barrier are provided, as well as extensions of the concept. We also examine the connection between the dwell time of a quantum particle in a region of space and flux-flux correlations at the boundaries, as well as operational approaches and approximations to measure the flux-flux correlation function and thus the second moment of the dwell time, which is shown to be characteristically quantum, and larger than the corresponding classical moment even for freely moving particles.

quant-ph↗

arXiv2008

Momentum-space interferometry with trapped ultracold atoms

Quantum interferometers are generally set so that phase differences between paths in coordinate space combine constructive or destructively. Indeed, the interfering paths can also meet in momentum space leading to momentum-space fringes. We propose and analyze a method to produce interference in momentum space by phase-imprinting part of a trapped atomic cloud with a detuned laser. For one-particle wave functions analytical expressions are found for the fringe width and shift versus the phase imprinted. The effects of unsharpness or displacement of the phase jump are also studied, as well as many-body effects to determine the potential applicability of momentum-space interferometry.

quant-ph↗

arXiv2008

Symplectic tomography of ultracold gases in tight-waveguides

The phase space is the natural ground to smoothly extrapolate between local and non-local correlation functions. With this objective, we introduce the symplectic tomography of many-body quantum gases in tight-waveguides, and concentrate on the reduced single-particle symplectic tomogram (RSPST) whose marginals are the density profile and momentum distribution. We present an operational approach to measure the RSPST from the time evolution of the density profile after shutting off the interactions in a variety of relevant situations: free expansion, fall under gravity, and oscillations in a harmonic trap. From the RSPST, the one-body density matrix of the trapped state can be reconstructed.

quant-ph↗

arXiv2008

Atom Fock state preparation by trap reduction

We study the production of low atom number Fock states by reducing suddenly the potential trap in a 1D strongly interacting (Tonks-Girardeau) gas. The fidelity of the Fock state preparation is characterized by the average and variance of the number of trapped atoms. Two different methods are considered: making the trap shallower (atom culling [A. M. Dudarev {\it et al.}, Phys. Rev. Lett. {\bf 98}, 063001 (2007)], also termed ``trap weakening'' here) and making the trap narrower (trap squeezing). When used independently, the efficiency of both procedures is limited as a result of the truncation of the final state in momentum or position space with respect to the ideal atom number state. However, their combination provides a robust and efficient strategy to create ideal Fock states.

quant-ph↗

arXiv2008

Fermionization and bosonization of expanding 1D anyonic fluids

The momentum distribution of an expanding cloud of one-dimensional hard-core anyons is studied by an exact numerical approach, and shown to become indistinguishable from that of a non-interacting spin-polarized Fermi gas for large enough times (dynamical fermionization). We also consider the expansion of one-dimensional anyons with strongly attractive short-range interactions suddenly released from a parabolic external potential, and find that momentum distribution approaches that of its dual system, the ideal Bose gas (dynamical bosonization). For both processes the characteristic time scales are identified, and the effect of the initial confinement is analyzed comparing the dynamics associated with both harmonic and hard-wall traps.

cond-mat.stat-mech↗

arXiv2008

Generalized relation between pulsed and continuous measurements in the quantum Zeno effect

A relation is found between pulsed measurements of the excited state probability of a two-level atom illuminated by a driving laser, and a continuous measurement by a second laser coupling the excited state to a third state which decays rapidly and irreversibly. We find the time between pulses to achieve the same average detection time than a given continuous measurement in strong, weak, or intermediate coupling regimes, generalizing the results in L. S. Schulman, Phys. Rev. A 57, 1509 (1998).

quant-ph↗

arXiv2008

Disclosing hidden information in the quantum Zeno effect: Pulsed measurement of the quantum time of arrival

Repeated measurements of a quantum particle to check its presence in a region of space was proposed long ago [G. R. Allcock, Ann. Phys. {\bf 53}, 286 (1969)] as a natural way to determine the distribution of times of arrival at the orthogonal subspace, but the method was discarded because of the quantum Zeno effect: in the limit of very frequent measurements the wave function is reflected and remains in the original subspace. We show that by normalizing the small bits of arriving (removed) norm, an ideal time distribution emerges in correspondence with a classical local-kinetic-energy distribution.

quant-ph↗

arXiv2008

Seeking better times: atomic clocks in the generalized Tonks-Girardeau regime

This article is based on the talk with the same title at the Blaubeuren meeting. First we discuss briefly the importance of time and time keeping, explaining the basic functioning of clocks in general and atomic clocks in particular, which rely on Ramsey interferometry. The usefulness of cold atoms is discussed as well as their limits in Bose-Einstein condensates. An alternative that we study is a different cold-atom regime: the Tonks-Girardeau (TG) gas of tightly confined and strongly interacting bosons. The TG gas is reviewed and then generalized for two-level atoms. Finally, we explore the combination of Ramsey interferometry and TG gases.

quant-ph↗

arXiv2008

Atom laser dynamics in a tight-waveguide

We study the transient dynamics that arise during the formation of an atom laser beam in a tight waveguide. During the time evolution the density profile develops a series of wiggles which are related to the diffraction in time phenomenon. The apodization of matter waves, which relies on the use of smooth aperture functions, allows to suppress such oscillations in a time interval, after which there is a revival of the diffraction in time. The revival time scale is directly related to the inverse of the harmonic trap frequency for the atom reservoir.

cond-mat.other↗

arXiv2007

Quantum matter wave dynamics with moving mirrors

When a stationary reflecting wall acting as a perfect mirror for an atomic beam with well defined incident velocity is suddenly removed, the density profile develops during the time evolution an oscillatory pattern known as diffraction in time. The interference fringes are suppressed or their visibility is diminished by several effects such as averaging over a distribution of incident velocities, apodization of the aperture function, atom-atom interactions, imperfect reflection or environmental noise. However, when the mirror moves with finite velocity along the direction of propagation of the beam, the visibility of the fringes is enhanced. For mirror velocities below beam velocity, as used for slowing down the beam, the matter wave splits into three regions separated by space-time points with classical analogues. For mirror velocities above beam velocity a visibility enhancement occurs without a classical counterpart. When the velocity of the beam approaches that of the mirror the density oscillations rise by a factor 1.8 over the stationary value.

quant-ph↗

arXiv2007

Ramsey interferometry with a two-level Tonks-Girardeau gas

We propose a generalization of the Tonks-Girardeau model that describes a coherent gas of cold two-level Bosons which interact with two external fields in a Ramsey interferometer. They also interact among themselves by contact collisions with interchange of momentum and internal state. We study the corresponding Ramsey fringes and the quantum projection noise which, essentially unaffected by the interactions, remains that for ideal Bosons. The dual system of this gas, an ideal gas of two-level Fermions coupled by the interaction with the separated fields, produces the same fringes and noise fluctuations. The cases of time-separated and spatially-separated fields are studied. For spatially separated fields the fringes may be broadened slightly by increasing the number of particles, but only for large particle numbers far from present experiments with Tonks-Girardeau gases. The uncertainty in the determination of the atomic transition frequency diminishes, essentially with the inverse root of the particle number.

cond-mat.other↗

arXiv2007

Stability of spinor Fermi gases in tight waveguides

The two and three-body correlation functions of the ground state of an optically trapped ultracold spin-1/2 Fermi gas (SFG) in a tight waveguide (1D regime) are calculated in the plane of even and odd-wave coupling constants, assuming a 1D attractive zero-range odd-wave interaction induced by a 3D p-wave Feshbach resonance, as well as the usual repulsive zero-range even-wave interaction stemming from 3D s-wave scattering. The calculations are based on the exact mapping from the SFG to a ``Lieb-Liniger-Heisenberg'' model with delta-function repulsions depending on isotropic Heisenberg spin-spin interactions, and indicate that the SFG should be stable against three-body recombination in a large region of the coupling constant plane encompassing parts of both the ferromagnetic and antiferromagnetic phases. However, the limiting case of the fermionic Tonks-Girardeau gas (FTG), a spin-aligned 1D Fermi gas with infinitely attractive p-wave interactions, is unstable in this sense. Effects due to the dipolar interaction and a Zeeman term due to a resonance-generating magnetic field do not lead to shrinkage of the region of stability of the SFG.

cond-mat.other↗

arXiv2007

Time modulation of atom sources

Sudden turn-on of a matter-wave source leads to characteristic oscillations of the probability density which are the hallmark feature of diffraction in time. The apodization of matter waves relies on the use of smooth aperture functions which suppress such oscillations. The analytical dynamics arising with different aperture functions are discussed systematically for switching-on processes, and for single and many-pulse formation procedures. The possibility and time scale of a revival of the diffraction-in-time pattern is also analysed. Similar modulations in time of the pulsed output coupling in atom-lasers are responsible for the dynamical evolution and characteristics of the beam profile. For multiple pulses, different phase schemes and regimes are described and compared. Strongly overlapping pulses lead to a saturated, constant beam profile in time and space, up to the revival phenomenon.

cond-mat.other↗

arXiv2006

Exact propagators for atom-laser interactions

A class of exact propagators describing the interaction of an $N$-level atom with a set of on-resonance $δ$-lasers is obtained by means of the Laplace transform method. State-selective mirrors are described in the limit of strong lasers. The ladder, V and $Λ$ configurations for a three-level atom are discussed. For the two level case, the transient effects arising as result of the interaction between both a semi-infinite beam and a wavepacket with the on-resonance laser are examined.

quant-ph↗

arXiv2006

Decay by tunneling of Bosonic and Fermionic Tonks-Girardeau Gases

We study the tunneling dynamics of bosonic and fermionic Tonks-Girardeau gases from a hard wall trap, in which one of the walls is substituted by a delta potential. Using the Fermi-Bose map, the decay of the probability to remain in the trap is studied as a function of both the number of particles and the intensity of the end-cap delta laser. The fermionic gas is shown to be a good candidate to study deviations of the non-exponential decay of the single-particle type, whereas for the bosonic case a novel regime of non-exponential decay appears due to the contributions of different resonances of the trap.

quant-ph↗

arXiv2006

Matter-wave diffraction in time with a linear potential

Diffraction in time of matter waves incident on a shutter which is removed at time $t=0$ is studied in the presence of a linear potential. The solution is also discussed in phase space in terms of the Wigner function. An alternative configuration relevant to current experiments where particles are released from a hard wall trap is also analyzed for single-particle states and for a Tonks-Girardeau gas.

quant-ph↗

arXiv2006

Momentum interferences of a freely expanding Bose-Einstein condensate in 1D due to interatomic interaction change

A Bose-Einstein condensate may be prepared in a highly elongated harmonic trap with negligible interatomic interactions using a Feshbach resonance. If a strong repulsive interatomic interaction is switched on and the axial trap is removed to let the condensate evolve freely in the axial direction, a time dependent quantum interference pattern takes place in the short time (Thomas-Fermi) regime, in which the number of peaks of the momentum distribution increases one by one, whereas the spatial density barely changes.

cond-mat.other↗