Multiple Bifurcations
in atom optics
W. K. Hensinger, B. Upcroft,
C. A. Holmes, N.R. Heckenberg, G.J. Milburn, and H. Rubinsztein-Dunlop
Physical Review A Vol.64, 063408, 2001
Abstract:
We report the observation
of multiple bifurcations in a non-linear Hamiltonian system: laser cooled atoms
in a standing wave with single frequency intensity modulation. We provide clear
evidence of the occurrence of bifurcations by analyzing the atomic momentum
distributions.
Dynamical tunneling of
ultra-cold atoms
W. K. Hensinger, H. Häffner, A. Browaeys, N.R. Heckenberg, K. Helmerson,
C. McKenzie, G. J. Milburn, W. D. Phillips, S. L. Rolston, H. Rubinsztein-Dunlop,
and B. Upcroft
Nature Vol. 412, 5 July, 52-55, 2001
Abstract:
The divergence of quantum and classical descriptions of particle motion is clearly
apparent in quantum tunneling between two regions of classically stable motion.
An archetype of such non-classical motion is tunneling through an energy barrier.
In the 1980s, a new process, ‘dynamical’ tunneling, was predicted,
involving no potential energy barrier; however, a constant of the motion (other
than energy) still forbids classically the quantum-allowed motion. This process
should occur, for example, in periodically driven, nonlinear Hamiltonian systems
with with one degree of freedom. Such system may be chaotic, consisting of regions
in phase space of stable, regular motion embedded in a sea of chaos. Previous
studies predicted dynamical tunneling between these stable regions. Here we
observe dynamical tunneling of ultra-cold atoms from a Bose-Einstein condensate
in an amplitude-modulated optical standing wave. Atoms coherently tunnel back
and forth between their initial state of oscillatory motion (corresponding to
an island of regular motion) and the state oscillating 180° out of phase
with the initial state.
Experimental study of
the quantum driven pendulum and its classical analogue in atom optics
W.K. Hensinger, A.G. Truscott, B. Upcroft, M. Hug, H.M. Wiseman, N.R. Heckenberg,
H. Rubinsztein-Dunlop
Physical Review A Vol. 64, 033407, 2001
Abstract:
We present experimental results for the dynamics of cold atoms in a far detuned
amplitude modulated optical standing wave. Phase space resonances constitute
distinct peaks in the atomic momentum distribution containing up to 65 % of
all atoms resulting from a mixed quantum chaotic phase space. We characterize
the atomic behavior in classical and quantum regimes and present the applicable
quantum and classical theory, which we have developed and refined. We show experimental
proof that the size and the position of the resonances in phase space can be
controlled by varying several parameters such as the modulation frequency, the
scaled well depth, the modulation amplitude and the scaled Planck's constant
of the system. We have found a surprising stability against amplitude noise.
We present methods to accurately control the velocity of an ensemble of atoms
using these phase space resonances which could be used for efficient phase space
state preparation.
Atoms in an amplitude
modulated standing wave - dynamics and pathways to quantum chaos
W.K. Hensinger, A.G. Truscott, B. Upcroft, N.R. Heckenberg and H. Rubinsztein-Dunlop
Journal of Optics B: Quantum and Semiclassical optics, Vol. 2(5): 659-667, 2000
Abstract:
Cold rubidium atoms are subjected to an amplitude modulated far detuned standing
wave of light to form a quantum driven pendulum. Here we discuss the dynamics
of these atoms. Phase space resonances and chaotic transients of the system
exhibit dynamics which can be useful in many atom optics applications as they
can be utilized as means for phase space state preparation. We explain the occurence
of distinct peaks in the atomic momentum distribution, analyze them in detail
and give evidence for the importance of the system for quantum chaos and decoherence
studies.
Coherent atomic beam
splitter using transients of a chaotic system
A.G. Truscott, M.E.J. Friese, W.K. Hensinger, H.M. Wiseman, H. Rubinsztein-Dunlop
and N.R. Heckenberg
Physical Review Letters, Vol. 84(18): 4023-4026, 2000
Abstract:
A coherent atomic beam splitter can be realised using the transient dynamics
of a chaotic system. We have experimentally observed such an effect using ultra-cold
rubidium atoms. Our experimental results are in good agreement with numerical
simulations of the Schrodinger equation for the system.
Variations of relative
line intensity in saturation spectroscopy due to low magnetic fields
W.K. Hensinger, A.G. Truscott, H. Rubinsztein-Dunlop and N.R. Heckenberg
Optical and Quantum Electronics, Vol. 31(5/7): 391-403, 1999
Abstract:
We have observed dramatic line intensity variations in the saturation spectrum
of Rb85 and Rb87 due to magnetic fields of magnitude on the order of 100 nT.
These variations are detected by rotation of the plane of polarisation of the
pump beam and probe beam relative to the magnetic field axis. A modified rate
equation model is proposed which accounts for all experimentally observed features.
Our results may explain some discrepancies between theory and experiment observed
by other authors. Furthermore, our study should lead to a better understanding
of the processes involved in saturation spectroscopy.
Popular Science Articles:
Nature, News and Views, 5th of July, 2001
Nature, Physics Portal, Research Highlights, 5th of July, 2001
Science, ScienceNow 6th of July, 2001
University of Queensland News, 3rd of August, 2001
IOP PhysicsWeb, 5th of July, 2001
Proceedings and invited articles:
Coherent dynamical tunneling
and quantum chaos with Bose-Einstein condensates
W. K. Hensinger
Invited article for the Australia & New Zealand Physicist, January/February
2002
Cold atoms in an amplitude
modulated optical lattice – dynamical tunneling
W. K. Hensinger, H. Häffner, A. Browaeys, N. R. Heckenberg, K. Helmerson,
C. McKenzie, G. J. Milburn, W. D. Phillips, S. L. Rolston, H. Rubinsztein-Dunlop,
and B. Upcroft
Laser Spectroscopy, Proceedings of the 15th International conference on Laser
Spectroscopy in Snowbird, Utah, USA, June 10-15, 2001
Theses:
Experimental
tests of quantum nonlinear dynamics in atom optics
W. K. Hensinger
PhD thesis, The University of Queensland 2002
Studies
on the atomic alignment in saturation spectroscopy of rubidium
W. K. Hensinger
Masters thesis, The University of Queensland 1999
Quantum
Chaos in Atom Optics
S. Dyrting
PhD thesis, The University of Queensland 1995