31 research outputs found
Condensation of N interacting bosons: Hybrid approach to condensate fluctuations
We present a new method of calculating the distribution function and
fluctuations for a Bose-Einstein condensate (BEC) of N interacting atoms. The
present formulation combines our previous master equation and canonical
ensemble quasiparticle techniques. It is applicable both for ideal and
interacting Bogoliubov BEC and yields remarkable accuracy at all temperatures.
For the interacting gas of 200 bosons in a box we plot the temperature
dependence of the first four central moments of the condensate particle number
and compare the results with the ideal gas. For the interacting mesoscopic BEC,
as with the ideal gas, we find a smooth transition for the condensate particle
number as we pass through the critical temperature.Comment: 6 pages, 4 figures, to appear in Phys. Rev. Let
Noise quenching in lasers and masers by strong coherent pumping
An intense single-mode correlated-spontaneous-emission laser or maser can be realized by driving the active atoms coherently with an injected external field. The scheme involves single-photon transitions unlike the two-photon or quantum-beat correlated-emission lasers that utilize correlations between successive photon-cascade emissions or between simultaneous emissions into modes of the field. Quenching of both the amplitude and phase noise and, in certain cases, squeezing of the amplitude fluctuations are found
Broadband optical gain via interference in the free electron laser: principles and proposed realizations
We propose experimentally simplified schemes of an optically dispersive
interface region between two coupled free electron lasers (FELs), aimed at
achieving a much broader gain bandwidth than in a conventional FEL or a
conventional optical klystron composed of two separated FELs. The proposed
schemes can {\it universally} enhance the gain of FELs, regardless of their
design when operated in the short pulsed regime
A simple and surprisingly accurate approach to the chemical bond obtained from dimensional scaling
We present a new dimensional scaling transformation of the Schrodinger
equation for the two electron bond. This yields, for the first time, a good
description of the two electron bond via D-scaling. There also emerges, in the
large-D limit, an intuitively appealing semiclassical picture, akin to a
molecular model proposed by Niels Bohr in 1913. In this limit, the electrons
are confined to specific orbits in the scaled space, yet the uncertainty
principle is maintained because the scaling leaves invariant the
position-momentum commutator. A first-order perturbation correction,
proportional to 1/D, substantially improves the agreement with the exact ground
state potential energy curve. The present treatment is very simple
mathematically, yet provides a strikingly accurate description of the potential
energy curves for the lowest singlet, triplet and excited states of H_2. We
find the modified D-scaling method also gives good results for other molecules.
It can be combined advantageously with Hartree-Fock and other conventional
methods.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Letter
Generation of coherent terahertz pulses in Ruby at room temperature
We have shown that a coherently driven solid state medium can potentially
produce strong controllable short pulses of THz radiation. The high efficiency
of the technique is based on excitation of maximal THz coherence by applying
resonant optical pulses to the medium. The excited coherence in the medium is
connected to macroscopic polarization coupled to THz radiation. We have
performed detailed simulations by solving the coupled density matrix and
Maxwell equations. By using a simple -type energy scheme for ruby, we have
demonstrated that the energy of generated THz pulses ranges from hundreds of
pico-Joules to nano-Joules at room temperature and micro-Joules at liquid
helium temperature, with pulse durations from picoseconds to tens of
nanoseconds. We have also suggested a coherent ruby source that lases on two
optical wavelengths and simultaneously generates THz radiation. We discussed
also possibilities of extension of the technique to different solid-state
materials
Ultralow-power local laser control of the dimer density in alkali-metal vapors through photodesorption
Ultralow-power diode-laser radiation is employed to induce photodesorption of
cesium from a partially transparent thin-film cesium adsorbate on a solid
surface. Using resonant Raman spectroscopy, we demonstrate that this
photodesorption process enables an accurate local optical control of the
density of dimer molecules in alkali-metal vapors.Comment: 4 pages, 4 figure
A Delayed Choice Quantum Eraser
This paper reports a "delayed choice quantum eraser" experiment proposed by
Scully and Dr\"{u}hl in 1982. The experimental results demonstrated the
possibility of simultaneously observing both particle-like and wave-like
behavior of a quantum via quantum entanglement. The which-path or both-path
information of a quantum can be erased or marked by its entangled twin even
after the registration of the quantum.Comment: twocolumn, 4pages, submitted to PR
Narrowing of EIT resonance in a Doppler Broadened Medium
We derive an analytic expression for the linewidth of EIT resonance in a
Doppler broadened system. It is shown here that for relatively low intensity of
the driving field the EIT linewidth is proportional to the square root of
intensity and is independent of the Doppler width, similar to the laser induced
line narrowing effect by Feld and Javan. In the limit of high intensity we
recover the usual power broadening case where EIT linewidth is proportional to
the intensity and inversely proportional to the Doppler width.Comment: 4 pages, 2 figure
Scheme for the implementation of a universal quantum cloning machine via cavity-assisted atomic collisions in cavity QED
We propose a scheme to implement the universal quantum cloning
machine of Buzek et.al [Phys. Rev.A 54, 1844(1996)] in the context of cavity
QED. The scheme requires cavity-assisted collision processes between atoms,
which cross through nonresonant cavity fields in the vacuum states. The cavity
fields are only virtually excited to face the decoherence problem. That's why
the requirements on the cavity quality factor can be loosened.Comment: to appear in PR