Joint
Atomic Physics Colloquium Series
Jointly
sponsored by Harvard Physics Department and ITAMP
The colloquia are held Wednesdays in
Jefferson Lab 356 at 4:30 p.m unless otherwise noted. Tea Is served
at 4 p.m.
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| Fall Semester 09 |
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September
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9/9/09 |
Prof. Ami Vardi , Ben
Gurion University
Dephasing and noise in weakly coupled Bose-Einstein
condensates
Bose-Einstein condensates have
been coherently split so as to prepare a coherent state with a well-defined
relative phase between their constituents. Due to interparticle interactions,
the coherence of this preparation is lost over time, a process known
as 'phase diffusion'. The
dynamics of phase-diffusion in weakly-coupled condensates (as opposed
to the more familiar case of fully-separated BECs) will be discussed,
focusing on its sensitivity to the initial phase [1]. Next, we consider
the interplay between phase-diffusion and decoherence, showing that dephasing
may be slowed down by noise, in a Bose-enhanced quantum Zeno scenario
[2,3]. Finally, the reverse process of dynamical phase-locking will be
discussed [4]. In this case interactions result in the emergence
of a definite relative phase between initially incoherent BECs. The many
realization fringe visibility is universal at 1/3 throughout the Josephson
regime as evident from the semiclassical picture. Time permitting, I
will also discuss the implications for the implementation of a sub-shot-noise
SU(1,1) atom interferometer using the coherent dissociation of a molecular
BEC [5].
[1] E. Boukobza, M. Chuchem, D. Cohen, and AV, Phys. Rev. Lett. 102,
180403 (2009).
[2] Y. Khodorkovsky, G. Kurizki, and AV, Phys. Rev. Lett. 100, 220403
(2008).
[3] Y. Khodorkovsky, G. Kurizki, and AV, Phys. Rev. A 80, 023609 (2009).
[4] E. Boukobza, D. Cohen, and AV, eprint arXiv:0909.0195.
[5] I. Tikhonenkov and AV, eprint arXiv:0904.2121.
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9/23/09 |
Prof.
Chris Greene, JILA and University of Colorado
Four-body collisions, universality, and the Efimov effect
Recent theoretical progress on the four-body problem has resulted in
a study of the bound and quasi-bound states of four interacting bosonic
atoms. New developments in this area will be described, including recent
theory and experiments on the surprisingly rapid process of four-body
recombination, including the relationship of these phenomena to Efimov
physics.
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10/7/09 |
Dr Charles
W. Clark, Joint Quantum Institute, National Institute of
Standards and
Technology and University of Maryland
"Relativity at a billionth of the speed of light"
Abstract: Ultracold atoms enable us to explore exotic physical phenomena
in conditions far removed from their original, inaccessible manifestations.
In particular, we can design optical lattice configurations which produce
strong "spin-orbit coupling" in the motion of cold atoms. I
describe several related themes of current research: cold-atom analogues
of Dirac-particle physics, which provide ways of observing the elusive "Zitterbewegung" phenomenon
first noted by Schroedinger in 1931; the design and consturction of non-Abelian
gauge potentials; atomic analogues of spintronic devices; and atomic
analogues of the topological insulators.
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10/21/09 |
Dr
Sebastiaan van de Meerakker, Fritz-Haber-Institut der Max-Planck-Gesellschaft
"Collision Experiments with Stark Decelerated
Beams"
Over the last years our group has been developing methods to get improved
control over the velocity of molecules in a molecular beam [1]. With
the Stark decelerator, a part of a molecular beam can be selected and
transferred to any arbitrary velocity, producing bunches of state-selected
molecules with a computer-controlled velocity and with longitudinal temperatures
as low as a few mK. So far, this new molecular beam technology has been
used mainly to decelerate packets of molecules to standstill, and to
subsequently confine these molecules in a trap. We will report on various
experiments that have been performed with these samples of trapped molecules.
Stark decelerated molecular beams also hold great promise in molecular
beam scattering experiments. In a crossed-beam configuration, these beams
offer the revolutionary capability to study elastic or inelastic and
reactive scattering as a function of the continuously variable collision
energy with a high intrinsic energy resolution. We will report on the
first scattering experiment using a Stark decelerated beam of OH radicals
[2], and our progress on a new crossed beam machine containing two Stark
decelerators under 90 degrees crossing angle. The prospects of a molecular
synchrotron for scattering studies will be discussed.
[1] S.Y.T. van de Meerakker, H.L. Bethlem and G. Meijer,
Taming molecular beams,
Nature Physics 4, 595 (2008).
[2] J.J. Gilijamse, S. Hoekstra, S.Y.T. van de Meerakker, G.C. Groenenboom,
and G. Meijer,
Near-threshold inelastic collisions using molecular beams with a tunable velocity,
Science 313, 1617 (2006).
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Tuesday 11/3/09 |
Special Talk
Prof. Edward Gerjuoy,
University of Pittsburgh
Pratt Conference Room, ITAMP, 60
Garden Street, Cambridge MA
1-2pm
"Recollections of Oppenheimer and Schwinger"
The career of J. Robert Oppenheimer, who was born
on April 22, 1904, was celebrated in a June, 2004 Los Alamos Symposium,
wherein I recalled my experiences as a Ph.D. student of Oppenheimer's
in Berkeley, California during the period August 1938 to January 1942.
I shall recount some of these recollections, concentrating on conveying
a portrait of Oppenheimer as creator and inspiration of probably the
most important pre-war United States school of theoretical physics.
During a portion of this period (the 1940 academic year) Julian Schwinger,
who shared the 1965 Nobel Prize for the development of the modern formulation
of quantum electrodynamics and deservedly has been termed a genius,
was employed as what today would be termed Oppenheimer's post doc.
Therefore, especially because Schwinger now seems almost forgotten,
although he died only fifteen years ago (on July 16, 1994), I also
will recall some of Schwinger's interactions with Oppenheimer and Oppenheimer's
students including myself, in an attempt to convey some comprehension
of Schwinger's astonishing theoretical physics talents.
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11/4/09 |
Prof.
Thierry Giamarchi, DPMC-MaNEP, University of Geneva
"Disorder in cold atomic gases"
For quantum systems of fermionic and bosonic particles, disorder has
drastic effects. For free fermions, it leads to Anderson localization
where quantum interference due to scattering on disorder transform a
metal and an insulator. When interactions are present they can either
compete or help the disorder to localize the particles. Such a problem
has been one of the most challenging questions in condensed matter physics.
Cold atoms offer the unique possibility to realize very controlled disordered
systems and thus offer a unique laboratory to explore these issues. I
will thus review some of the most important issues on the interplay between
disorder and interactions, focusing on what happens in low dimensional
systems. I will discuss the various consequences for Bosons in either
a disordered or a biperiodic optical lattice potential, in the light
of recent experiments in cold atomic gases, and in particular whether
one can probe the existence of the Bose glass phase by expansion or by
shaking of the optical lattice.
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Thursday 11/12/09 |
Prof. Michael Fleischhauer,
Fachbereich Physik, Uni Kaiserslautern
"Single- and many-body
physics with stationary-light polaritons"
When light interacts with coherently driven three-level
atoms composite particles, called dark-state polaritons (DSP) are formed
which behave as massive objects. They are bosons and thus can undergo
a Bose-Einstein condensation, which due to the small effective mass
happens at a high critical temperature. When the characteristic length
of the light pulse becomes small, the dynamics of DSPs obeys a two-component
Dirac equation. Since the corresponding effective mass $m^*$ and ``speed
of light'' $c^*$ are rather small, relativistic effects such as Klein-tunneling
and Zitterbewegung can arise at laboratory length scales. Furthermore
anusual localization phenomena associated with the dynamics of Dirac
particles with random mass can be observed. Multi-component i.e. spinor
polaritons can be created with multi-chromatic drive fields. When confined
to 1D and in the presence of a strong elastic scattering heavy photons
can fermionize. Finally using a rotating medium one can generate effective
magnetic fields for DSPs with small magnetic length which provides
a new approach to study the fractional quantum-Hall effect.
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11/18/09 |
Prof. Hanns-Christoph Nägerl, Institut für
Experimentalphysik Universität Innsbruck
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12/02/09 |
Prof.
V. Sandoghdar, Laboratory
of Physical Chemistry,
ETH Zurich
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12/16/09 |
Dr. Liang Jiang, CalTech
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| Spring Semester 09 |
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January
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1/28/09 |
Tilman
Pfau, University
of Stuttgart
Rydberg atoms
in a Bose-Einstein Condensate
Rydberg atoms provide
a wide range of possibilities to tailor interactions in a quantum gas.
Here we report on Rydberg excitation of Bose-Einstein condensed 87
Rb atoms [1]. We observe coherent collective behavior for ensembles
of up to several thousand atoms [2]. Despite the strong interactions
between Rydberg atoms the evolution can still be reversed by a simple
phase shift in the excitation laser field. We experimentally proof
the coherence of the excitation in the strong blockade regime by applying
an optical ro- tary echo technique to a sample of magnetically trapped
ultracold atoms, analogous to a method known from nuclear magnetic
resonance. Using this echo technique we measured the dephasing time
due to the interaction between the Rydberg atoms [3]. We also show
that the ground state of the Pseudo-Spin Hamiltonian describing the
driven system exhibits a second order quantum phase transition. We
present the results of a critical theory for the quantum phase transition
and show that it describes the properties of the driven Rydberg system
in the saturated regime. We find that the suppression of Rydberg excitations
known as blockade phenomena exhibits an algebraic scaling law with
a universal exponent [4]. Very recently we successfully excited ultra–long–range
Rydberg molecules (dimers and trimers) [5,6]. The underlying novel mechanism
for the bond is low-energy electron scat- tering of Rydberg electrons from
polarizable ground state atoms. We determine the low energy scattering
length for electron– Rb(5S) scattering and the lifetimes and
polarizabil- ities of these exotic molecules.
References
[1] R. Heidemann, U. Raitzsch, V. Bendkowsky, B. Butscher, R. L?ow, T. Pfau ”Rydberg
excitation of Bose-Einstein condensates” Phys. Rev. Lett. 100 , 033601
(2008).
[2] R. Heidemann, U. Raitzsch, V. Bendkowsky, B. Butscher, R. L?ow, L.
Santos, T. Pfau ”Evidence for coherent collective Rydberg excitation in the strong
blockade regime” Phys. Rev. Lett. 99, 163601 (2007).
[3] U. Raitzsch, V. Bendkowsky, R. Heidemann, B. Butscher, R. L?ow, T.
Pfau ”An
echo experiment in a strongly interacting Rydberg gas” Phys. Rev.
Lett. 100 , 013002 (2008).
[4] H. Weimer, R. L?ow, T. Pfau, H.P. B?uchler ”Quantum critical behavior
in strongly interacting Rydberg gases” Phys. Rev. Lett. 101 250601
(2008).
[5] C. H. Greene, A. S. Dickinson, and H. R. Sadeghpour ”Creation of
Polar and Nonpolar Ultra-Long-Range Rydberg Molecules ” Phys. Rev.
Lett. 85, 2458 (2000).
[6] V. Bendkowsky, B. Butscher, J. Nipper, J.P. Shaffer, R. L?ow, T. Pfau ”Observation
of ultra-long range Rydberg molecules” accepted for publication in
Nature.
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February
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March
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3/4/09 |
John
Bohn,
JILA
Which way
is up? Or, How a BEC lives with dipolar interactions
Ultracold, quantum degenerate
gases consisting of dipolar particles bring a new richness to the phenomenon
of Bose-Einstein condensation (BEC). The dipolar interaction cares about
the direction the dipoles are pointing, which leads to novel structure
and properties in such a gas. Thanks to the efforts of the Pfau group in
Stuttgart in Bose-condensing chromium, dipolar BEC is now a reality, and
its properties are steadily emerging in the lab as well as in computer
simulations. In this talk I will report on our recent theoretical work
on dipolar BEC. I will show how the dipolar interaction leads to novel
ground state density profiles in the condensate, as well as to certain
collective excitations that bear a qualitative resemblance to rotons in
superfluid helium. These roton-like modes play a decisive role in the dynamical
stability of the condensate, for both non-rotating and vortex states. We
find that the stability diagram computed within mean field theory is in
excellent agreement with the experiment of Pfau and collaborators.
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3/18/09 |
Andrei
Derevianko, Univ
of Nevada - Reno
Improved
test of the standard model of elementary particles with atomic parity violation
Atomic
parity violation places powerful constraints on new physic beyond the
Standard Model of elementary particles. The measurements are interpreted
in terms of the nuclear weak charge, quantifying the strength of the
electroweak coupling between atomic electrons and quarks of the nucleus.
We report the most accurate to-date determination of this coupling strength
by combining previous measurements by the Boulder group with our high-precision
calculations in cesium atom. Our result is in a perfect agreement with
the prediction of the Standard Model. In combination with the results
of high-energy collider experiments, our work confirms the predicted
energy dependence (or ``running'') of the electroweak interaction over
an energy range spanning four orders of magnitude (from ~10 MeV to ~100
GeV) and places new limits on the masses of extra Z bosons (Z'). Our
raised bound on the Z' masses carves out a lower-energy part of the discovery
reach of the Large Hadron Collider. At the same time, a major goal of
the LHC is to find evidence for supersymmetry (SUSY), one of the basic,
yet experimentally unproven, concepts of particle physics. Our result
is consistent with the R-parity conserving SUSY with relatively light
(sub-TeV) superpartners. This raises additional hopes of discovering
SUSY at the LHC.
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April
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4/1/09 |
Paul
Julienne, NIST
Ultracold
Polar Molecules: A Case Study with KRb
It is now
possible to make ultracold gases of ultracold polar molecules. This
process can be made very efficient by first associating two ultracold
atoms into a weakly bound "Feshbach molecule" and subsequently
coherently transferring such a molecule to the vibrational ground state.
Whether one considers the collision of two atoms or two molecules,
an ultracold collision prepares the system in a very precise and narrow
energy range from which one can probe the bound and quasi-bound states
of the "collision complex" made from the colliding species.
It is especially helpful to understand the properties of the bound
and scattering states of the long range potential in order to understand
near-threshold properties of the "collision complex." Coupled
channels and approximate model calculations for K + Rb collisions
and the bound states of the KRb molecule from threshold to the
vibrational ground state will be used to illustrate key principles
needed to understand the formation and applications of polar molecules.
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4/22/09 |
Alexey
Gorshkov,
Harvard University
Quantum Information
and Quantum Simulation with Ultracold Alkaline-Earth Atoms in Optical
Lattices
We describe a method
for quantum information processing and quantum simulation with ultracold
alkaline-earth atoms in optical lattices. First, we propose and analyze
a novel approach to quantum information processing, in which multiple
qubits can be encoded and manipulated using electronic and nuclear
degrees of freedom associated with individual alkaline-earth atoms
trapped in an optical lattice [1]. We discuss potential applications
of this approach to fault-tolerant quantum computation and precision
measurements. Second, we propose to use alkaline-earth atoms in optical
lattices to realize the two-orbital SU(N)-symmetric Hubbard Hamiltonian
(with N as large as 10), which relies on the interplay between nuclear
spin and electronic degrees of freedom. The unprecedented degree of
symmetry and the spin-orbital physics associated with this readily
accessible experimental system make it rich in its own right and capable
of providing valuable insights into strongly correlated physics of
transition metal oxides, heavy fermion materials, and spin liquid phases.
[1] A.V.G. et al., Phys. Rev. Lett. 102, 110503 (2009).
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4/29/09 |
Mark
Raizen,
UT-Austin
Towards
Trapping and Cooling of Atomic Tritium for Precision Measurement
of Beta Decay
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May
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5/13/09 |
Andreas
Buchleitner, Univ. of Freiburg
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June
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6/23/09
Special
Event held
in Pratt Conference Room. |
Dmitry
Fursa,
Curtin University, Australia
Relativistic
Convergent Close-Coupling method for excitation and ionization processes
in electron collisions with atoms and ions
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