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Spring/Summer 2017
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January 30, 2017
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Andrew
Koller
JILA/University
of Colorado,
Boulder
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| Collective
spin dynamics
in a weakly
interacting
Fermi gas
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(Host:
Hal Metcalf)
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Magnetic
correlations
in materials
are generated
by a variety
of complex
mechanisms,
including spin
exchange and
electronic
motion,
occurring both
in combination
and in
competition.
The interplay
of spin and
motional
mechanisms is
believed to be
at the heart
of rich
phenomena
including high
temperature
superconductivity.
Ultracold
atomic Fermi
gases, with
precisely
controllable
parameters,
represent a
versatile
platform with
which to
investigate
the interplay
of spin and
motion in
out-of-equilibrium
settings. In
this talk we
will discuss
the spin
dynamics of a
weakly
interacting
two-component
Fermi gas
subjected to a
magnetic field
gradient. In
contrast to
prior
investigations
done in the
unitary limit
where the
magnetization
relaxes very
quickly, in
this regime
large
oscillations
of the
magnetization
are driven by
single
particle
dynamics, and
spin and
motional
effects must
be treated at
the same
level. We
treat the
problem using
a spin model
formalism in
energy space
which predicts
a number of
interesting
effects such
as the global
spreading of
spin
correlations.
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February 13, 2017
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Prof.
Nathan Gemelke
Pennsylvania
State
University
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Analog
Models of
Gauge and
Gauge-Gravity
Dynamics in
Cold-Atom
Systems
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(Host:
Dominik
Schneble)
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The
quantum
mechanics of
gauge fields
in dynamical
systems is
often
plaguedby
subtleties
related to
quantization.
For example,
the existence
of a mass for
the gauge
bosons at long
length and
time scales in
quantum
chromodynamics
and
electroweak
physics is
complicated by
questions
relating to
confinement.
Similar
questions
arise in
gauge-field
formulations
of quantum
gravity, in
which the
dynamics of
spacetime are
treated as
gauge
excitations on
a disordered
network or
graph. It is
helpful in
understanding
these problems
to develop
laboratory
methods to
explore the
dynamical
evolution of
systems with
quantum
degrees of
freedom which
may be
described by
gauge
fields.
Cold atoms
offer one such
possibility,
in which
weakly
dissipative
couplings
between atom
and light can
be described
by dynamical
gauge fields,
and
investigated
over large
dynamic ranges
of length and
time.I will
describe one
such system,
which through
combined
effects of
relativistic
dynamics of
slow light and
disorder,
leads to
Higgs-like
transitions
and simple
models for
quantum
gravity.
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February 20, 2017
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Prof.
Jeffrey Moses
Cornell
University
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| New optical sources for
physics and
spectroscopy
based on an
old trick of
atomic physics
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(Host:
Tom Allison)
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From
strong-field
optical
physics to
nonlinear
phononics and
femtosecond-resolved
optical
spectroscopy,
developing
fields of
optical
physics are
making demands
for coherent
light sources
of greater
bandwidth,
greater
intensity, and
in new ranges
of the
electromagnetic
spectrum. Yet,
lasers and
nonlinear
optical
sources of
coherent light
have been
limited by the
same old
problems of
narrow gain
bandwidth and
a trade-off
between
bandwidth and
gain. Here we
show how an
old trick of
atomic
physics, rapid
adiabatic
passage, can
get around
these old
limitations.
Here the
Landau-Zener
adiabatic
transition is
between
photons, and
the physical
platform is
nonlinear
optical
frequency
conversion,
with
conversion
dynamics in
direct analogy
and
mathematically
isomorphic to
those of the
linear
Schrödinger
equation for a
coupled
two-level
system. We’ll
review the
physics of the
process and
our latest
experimental
results, which
include the
production of
arbitrarily
shapeable and
intense
mid-infrared
light pulses
covering more
than an octave
of optical
bandwidth. We
intend to use
these pulses
for a wide
range of
time-resolved
spectroscopy
and
strong-field
light-matter
interaction
experiments.
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February
21, 2017 (4pm)
P&A
colloquium
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Prof.
Jack Harris
Yale
University
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| Topological physics with
a pair of
oscillators:
beyond Berry's
phase via
exceptional
points
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(Host:
Eden Figueroa/Dominik
Schneble)
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Topological
phenomena
appear in a
number of
physical
systems, from
exotic quantum
states to
carefully
engineered
waveguides.
These
phenomena
offer new
forms of
control, and
are also
intriguing in
their own
right. I will
describe a
topological
feature that
is generically
present in one
of nature's
simplest
systems: a
pair of
coupled
oscillators. I
will describe
experiments in
which we
demonstrate
this feature
and use it to
achieve
topological
control over
the
vibrational
modes of a
mechanical
oscillator.
Although these
effects are
classical, our
experiments
are carried
out using an
optomechanical
device that is
also capable
of detecting
the membrane's
quantum
fluctuations.
I will
describe some
prospects for
studying the
interplay of
topological
and quantum
effects in
such a
systemba
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February 27, 2017
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Dr.
Daniel Greif
Harvard
University
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| Exploring Quantum
Antiferromagnets
with
Single-Site
Resolution
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(Host:
Dominik
Schneble)
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Strongly
correlated
electron
systems such
as
high-temperature
superconductors
and pseudo-gap
states are a
cornerstone of
modern
condensed
matter
research. A
complementary
approach to
studying
solid-state
systems is to
build an
experimentally
tunable
quantum system
governed by
the Hubbard
model, which
is thought to
qualitatively
describe these
systems but is
difficult to
understand
theoretically.
Ultracold
fermionic
quantum gases
in optical
lattices
provide a
clean and
tunable
implementation
of the Hubbard
model. At the
same time,
optical
microscopy in
these systems
gives access
to single-site
observables
and
correlation
functions, and
provides
dynamic
control of the
potential
landscape at
the
single-site
level. So far,
ultracold atom
experiments
have not been
able to reach
the
low-temperature
regime of the
Hubbard model,
which becomes
particularly
interesting
when doped.
Here we report
on the
observation of
antiferromagnetic
long-range
order in a
repulsively
interacting
Fermi gas of
Li-6 atoms on
a 2D square
lattice
containing
about 80
sites. The
ordered state
is directly
detected from
a peak in the
spin structure
factor and a
diverging
correlation
length of the
spin
correlation
function. When
doping away
from
half-filling
into a
numerically
intractable
regime, we
find that
long-range
order extends
to doping
concentrations
of about 15%.
Our results
open the path
for a
controlled
study of the
low-temperature
phase diagram
of the Hubbard
model.
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March 6, 2017
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Prof.
Irina Novikova
College of
William &
Mary
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| Spatial Mode Structure of
Atom-Generated
Squeezed
Vacuum
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(Host:
Eden Figueroa)
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We
study the
spatial mode
structure in
the squeezed
vacuum
produced via
polarization
self-rotation
interaction of
an ensemble of
Rb atoms and a
strong
linearly
polarized
laser field.
In particular,
we show that
to accurately
predict the
measured
quadrature
noise of the
output
squeezed
vacuum field,
the analysis
must include
several
higher-order
spatial modes.
The quantum
fluctuations
for each such
mode may be
independently
modified by
the
interaction
with atoms,
thus affecting
the overall
detected
quadrature
noise and
potentially
limiting the
available
amount of
squeezing. We
also
investigate
the role of
the optical
depth of the
atomic medium.
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March
7, 2017 (4pm)
P&A
Colloquium
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Prof.
Irina Novikova
College of
William &
Mary
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| Cool Quantum Optics with
Hot Atoms
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(Host:
Eden Figueroa)
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Efficient
and reliable
quantum
communication
will require
the control of
the quantum
state of both
photons and
atoms. In this
talk I will
discuss a
possible
realization of
strong
coupling
between
quantum
optical field
and collective
spin
excitation in
atomic vapor
via
electromagnetically
induced
transparency,
as well as
possible
applications
of the effect
for precision
metrology,
quantum memory
and generation
of
non-classical
light.
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April 10, 2017
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Prof.
Navid
Vafaei-Najafabadi
Stony Brook
University
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| Laser Acceleration of
Electrons in a
Laser
Wakefield
Accelerator
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(Host:
Tom Weinacht)
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A
plasma wave
driven by a
high intensity
laser can
accelerate
electrons at a
rate that is a
thousand times
higher than
that of a
conventional
accelerator.
This laser
wakefield
accelerator
(LWFA)
technology has
the potential
for
revolutionizing
the particle
acceleration
field by
creating
table-top
electron
accelerators
as well as
particle
colliders that
are orders of
magnitude
shorter than
the currently
operating
machines.
Additionally,
because of the
linear
focusing force
in the plasma
wave, the
electrons
undergo
transverse
oscillations,
which creates
x-ray photons
with energies
of tens of
MeV. In the
ideal regime
of the laser
wakefield
accelerator,
the laser
pulse occupies
less than half
of the plasma
wave, and
therefore will
not overlap
with the
accelerating
electrons,
which reside
in the back
half of this
wave. In this
talk, I will
explore how
the
acceleration
mechanism is
modified if
the laser
field overlaps
these
electrons. In
particular, I
will show that
in the
presence of
the ion
column, the
transverse
field of the
laser can
couple to the
longitudinal
momentum of
electrons in a
process that
is similar to
inverse free
electron laser
(IFEL).
Through this
process,
called direct
laser
acceleration
(DLA), the
transverse
laser field
can provide a
significant
boost to the
energy of the
accelerating
electrons. The
significant
role that DLA
can play in
increasing the
energy of the
electrons in
an LWFA was
recently
demonstrated
experimentally
and confirmed
through 3D
simulations. I
will discuss
these results
as well as the
implications
of DLA for
increasing the
yield and
energy of the
x-ray
radiation that
may be
obtained from
a table top
machine based
on an LWFA.
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April 24, 2017
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Prof.
Bryce Gadway
University of
Illinois,
Urbana-Champaign
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| Engineering topological
quantum fluids
with flying
matter waves
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(Host:
Dominik
Schneble)
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Since
their
realization
over two
decades ago,
quantum gases
of dilute
atomic vapors
have provided
a unique
playground for
the
exploration of
many-body
quantum
physics. In
particular,
precisely
controlled
systems of
ultracold
atoms in
optical
lattices
naturally
mimic the
behavior of
electrons in
crystal
lattices, and
have been used
for the
quantum
simulation of
complex
electronic
matter. To
expand the
types of
systems that
can be quantum
simulated, and
to enable the
exploration of
entirely new
forms of
matter, many
groups are
working to
expand the
quantum
simulation
toolbox
through the
engineering of
novel lattice
structures,
designer
artificial
gauge fields,
and novel
interactions.
In this talk,
I will discuss
a new approach
developed in
our group for
the
realization of
effective
gauge fields
and nontrivial
topological
order in
neutral atomic
gases. Our
technique is
based on a
mapping
between atomic
momentum
states and
sites of a
synthetic
lattice.
Compared to
real-space
lattices, the
high degree of
control over
individual
laser-driven
transitions
between
momentum
states permits
an essentially
universal
engineering of
designer
tight-binding
lattices. I’ll
discuss some
recent studies
of topological
and disordered
lattices, the
first
observation of
a
disorder-driven
topological
phase
transition
with cold
atoms, and
some first
studies of
interaction-driven
effects in our
synthetic
momentum-space
lattices.
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May 8, 2017
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Dr.
Mary Lyon,
University of
Maryland
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| Modeling
Fusion Physics
with Ultracold
Neutral
Plasmas
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(Host:
Hal Metcalf)
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Plasmas comprise the vast
majority of
the known
universe and
exist over a
wide range of
temperatures
and densities.
Most plasmas
form from
energetic
collisions
between
particles in a
hot gas which
result in the
liberation of
one or more
electrons.
However, using
tools from
experimental
atomic
physics,
researchers
are able to
create
"ultracold
plasmas,"
which exist at
temperatures
close to
absolute zero.
Due to their
large
electrical
potential
energies and
comparatively
small kinetic
energies,
ultracold
plasmas fall
into a regime
of plasma
systems which
are called
“strongly
coupled,”
giving them
properties
similar to
certain
astrophysical
systems and
fusion-class
plasmas. In
this talk I
will give an
overview of
the field of
ultracold
plasmas,
provide
details about
some of our
recent work,
and show how
some of this
work relates
to fusion
physics.
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July 17, 2017
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Prof.
Jin-Tae Kim,
Chosun
University,
Korea,
Yale
University and
University of
Connecticut
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| Hyperfine
analysis on
the excited
states of
ultracold
85Rb-133Cs
molecules via
short-range
photoassociation
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(Host:
Tom Bergeman)
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Short-range
photoassociation
(PA), which
produces
continuously
ultracold
^{85}Rb
^{133}Cs
molecules in
the lowest
rovibronic
ground level X
^1\Sigma^+(v=0,
J=0), has
opened up to
investigate
various
hyperfine
structures of
deeply bound
rovibrational
levels in the
strongly
perturbed
regions.
Electronic
states with
strong
singlet-triplet
mixing can be
useful for
efficient
direct
molecule
production in
the rovibronic
ground state
via
short-range
PA. ^{85}Rb
and ^{133}Cs
atoms trapped
in their
|F_{Rb}=2>
and
|F_{Cs}=3>
hyperfine
states in dark
SPOT MOTs were
photoassociated
into excited
molecular
states, which
decay into the
electronic
ground state
by spontaneous
emission.
We have
investigated
deeply bound
short-range PA
lines of
the
B^1\Pi(\Omega=1),
c^3\Sigma^+(\Omega=0^-
and 1), and b
^3|pi(\Omega=0^-,0^+,
and 1) states
and the 2
^1\Pi(\Omega=1),
3
^3\Sigma^+(\Omega=1),
and 2
^3\Pi(\Omega=1)
states [1]
of 85 Rb
133 Cs
dissociating
into the
5s(Rb) +
6p(Cs) and
6s(Cs) +
5p(Rb) limits,
respectively.
Rich hyperfine
structures of
those
electronic
states with
the low J
which were not
observed in
molecular beam
[2] and the
FTS [3],
respectively
have been
explained
mainly
considering
nuclear
spin-electron
orbital
angular
momentum,
Fermi-contact,
and dipolar
electron
spin-nuclear
spin
interactions.
Through
triplet-singlet
spin-orbit
electronic
mixings, the
singlet state
often has
larger HFS
splittings and
shows HFS
structure like
a triplet
state
unexpectedly
although there
is no
electronic
spin. Analysis
of the
hyperfine
structures
makes it
possible to
assign
vibrational
levels of
singlet and
triplet states
which were not
assigned due
to strong
spin-orbit
interaction.
For selected
PA levels,
vibrational
branching and
rotational
branching in
the X
^1\Sigma^+
(v=0) state
have been
investigated
using
resonance-enhanced
multiphoton
ionization and
depletion
spectroscopy[4],
respectively.
Efficient
production
of the
rovibronic
ground level X
^1\Sigma+
(v=0, J=0) has
been observed
for some of
the PA levels.
Molecule
production
rate up to
~1×10^4
molecules/s
into the
lowest
rovibronic
ground level
has been
achieved.
[1] T.
Shimasaki et
al.,
ChemPhysChem
17, 3677
(2016).
[2] Y. Lee et
al., J. Phys.
Chem. A 112,
7214 (2008)
[3] I.
Birzniece et
al., J. Chem.
Phys. 138,
154304 (2013).
[4] T.
Shimasaki et
al., Phys.
Rev. A 91,
21401 (2015).
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