556 research outputs found
Seeing spin dynamics in atomic gases
The dynamics of internal spin, electronic orbital, and nuclear motion states
of atoms and molecules have preoccupied the atomic and molecular physics
community for decades. Increasingly, such dynamics are being examined within
many-body systems composed of atomic and molecular gases. Our findings
sometimes bear close relation to phenomena observed in condensed-matter
systems, while on other occasions they represent truly new areas of
investigation. I discuss several examples of spin dynamics that occur within
spinor Bose-Einstein gases, highlighting the advantages of spin-sensitive
imaging for understanding and utilizing such dynamics.Comment: Chapter in upcoming Review Volume entitled "From Atomic to Mesoscale:
The Role of Quantum Coherence in Systems of Various Complexities" from World
Scientifi
Making, probing and understanding Bose-Einstein condensates
Contribution to the proceedings of the 1998 Enrico Fermi summer school on
Bose-Einstein condensation in Varenna, Italy.Comment: Long review paper with ~90 pages, ~20 figures. 2 GIF figures in
separate files (4/5/99 fixed figure
Generating Schr\"{o}dinger-cat states in momentum and internal-state space from Bose-Einstein condensates with repulsive interactions
Resonant Raman coupling between internal levels induced by continuous
illumination of non-collinear laser beams can create double-well momentum-space
potentials for multi-level ``periodically-dressed'' atoms. We develop an
approximate many-body formalism for a weakly interacting, trapped
periodically-dressed Bose gas which illustrates how a tunable exchange
interaction yields correlated many-body ground states. In contrast to the case
of a position-space double well, the ground state of stable
periodically-dressed Bose gases with repulsive interactions tends toward a
Schr\"{o}dinger cat state in the regime where interactions dominate the
momentum-space tunnelling induced by the external trapping potential. The
dependence of the momentum-space tunnelling and exchange interaction on
experimental parameters is derived. We discuss how real-time control of
experimental parameters can be used to create Schr\"{o}dinger cat states either
between momentum or internal states, and how these states could be dynamically
controlled towards highly sensitive interferometry and frequency metrology.Comment: 7 pages, 3 figures. Submitted to PR
Cavity-assisted measurement and coherent control of collective atomic spin oscillators
We demonstrate continuous measurement and coherent control of the collective
spin of an atomic ensemble undergoing Larmor precession in a high-finesse
optical cavity. The coupling of the precessing spin to the cavity field yields
phenomena similar to those observed in cavity optomechanics, including cavity
amplification, damping, and optical spring shifts. These effects arise from
autonomous optical feedback onto the atomic spin dynamics, conditioned by the
cavity spectrum. We use this feedback to stabilize the spin in either its high-
or low-energy state, where, in equilibrium with measurement back-action
heating, it achieves a steady-state temperature, indicated by an asymmetry
between the Stokes and anti-Stokes scattering rates. For sufficiently large
Larmor frequency, such feedback stabilizes the spin ensemble in a nearly pure
quantum state, in spite of continuous measurement by the cavity field.Comment: 5 pages, 4 figures, and supplemental materia
Kinetic theory and dynamic structure factor of a condensate in the random phase approximation
We present the microscopic kinetic theory of a homogeneous dilute Bose
condensed gas in the generalized random phase approximation (GRPA), which
satisfies the following requirements: 1) the mass, momentum and energy
conservation laws; 2) the H-theorem; 3) the superfluidity property and 4) the
recovery of the Bogoliubov theory at zero temperature \cite{condenson}. In this
approach, the condensate influences the binary collisional process between the
two normal atoms, in the sense that their interaction force results from the
mediation of a Bogoliubov collective excitation traveling throughout the
condensate. Furthermore, as long as the Bose gas is stable, no collision
happens between condensed and normal atoms. In this paper, we show how the
kinetic theory in the GRPA allows to calculate the dynamic structure factor at
finite temperature and when the normal and superfluid are in a relative motion.
The obtained spectrum for this factor provides a prediction which, compared to
the experimental results, allows to validate the GRPA.
PACS numbers:03.75.Hh, 03.75.Kk, 05.30.-dComment: 6 pages, 1 figures, QFS2004 conferenc
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