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Quantum Information/Bose-Einstein Condensation
QIBEC seminars
The Quantum Information/Bose-Einstein Condensation (QIBEC) seminars are
extended group meetings of NIST researchers in quantum information and
quantum gases. They are unscripted and informal. Here we provide
audio-visual transcripts primarily for the benefit of QIBEC's external
collaborators, but anyone is welcome to view them. These transcripts
are offered here in the form of MPEG-4 files (.m4a designator), which
contain an audio recording of the seminars, plus copies of the slides
used by the speakers, synchronized approximately with the audio track.
These files may be played with any MPEG-4 application, but they have
been designed in particular for podcast dissemination. -
[Get a free MPEG-4 player]
Feedback on these programs is always welcome:
charles.clark@nist.gov |
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Introduction
(867 kB) |
Welcome to the podcasts of the Quantum Information and Bose-Einstein
Condensation lecture series at the National Institute of Standards and
Technology, where we bring to you discussion-filled lectures on the hottest
topics in the ultracool. This is your portal to the exhilarating world of
ultracold atomic physics, where the pristine quantum behavior at the atomic
scale confronts the complexities of many-body physics to help unlock the
secrets of quantum mechanics at the macroscopic scale. Now sit back and enjoy
the show! |
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May 12, 2006
Ana Maria Rey |
Cold Atoms in optical lattices
- (Plenary talk presented at
the conference "Physics and Society - World Year of Physics 2005,"
Nogota, Columbia September 5-7, 2005.)
Spanish presentation, there is no English translation
Átomos fríos en redes ópticas
(parte 1 de 3)
(21 MB);
(parte 2 de 3)
(23 MB);
(parte 3 de 3)
(16 MB)
En esta conferencia presento bajo un contexto apropiado para el público
general algunas de las contribuciones de mi tesis de doctorado al campo de
átomos fríos en redes ópticas. Mi tesis se dedicó
particularmente a estudiar la transición cuántica de superfluido a
aislante de Mott. Esta transición tiene lugar debido a la competencia entre
la energía de movimiento y la energía de interacción. Aunque es
un trabajo teórico se realizo en el contexto de experimentos encaminados en
la implementación de un computador cuántico con átomos neutros.
En esta presentación comienzo con una introducción básica al tema
de átomos fríos, seguido de una visión general de los avances
experimentales y teóricos mas recientes en el campo. Después presento
brevemente un resumen de mi tesis concentrándome en dos puntos
específicos: la dinámica de átomos selectivamente cargados cada
tres pozos en una red unidimensional, y la inicialización de un registro
cuántico. El primero fue motivado por la realización experimental de
este sistema por el grupo del enfriamiento láser del NIST (Instituto
Nacional de Estándares y Medidas). Después de demostrar como las
teorías cinéticas estándares fallan en describir la dinámica
de los átomos en la red selectivamente cargada, presento nuevos
métodos capaces de describir adecuadamente la dinámica cuántica.
Respecto al segundo punto, discuto como es posible a través de la
transición de Mott generar una configuración en la red con exactamente
un átomo por pozo haciendo uso apropiado del campo magnético presente
en los experimentos. Presentado originalmente en la conferencia, Fisica y
Sociedad - Año Mundial de la Fisica 2005, Simposio del Programa
Nacional de Ciencias Basicas, Colciencias, Septiembre 5-7/2005, Bogotá,
Colombia.
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May 8, 2006
John Sidles |
Measurement operator methods for quantum model
order reduction in large-scale spin simulations
(49 MB)
This talk introduces a new technique for model order reduction in large-scale
quantum spin simulations. The technique has three stages: first the deliberate
introduction of noise into the simulation; then the conversion of that noise
into an equivalent continuous measurement process; and finally the projection
of the resulting quantum trajectory onto a product-sum manifold of
Beylkin-Mohlenkamp type. The application of this technique is illustrated by
numerical quantum trajectory simulations of single-spin detection by magnetic
resonance force microscopy (MRFM). Excellent agreement with experimental
results is obtained. It is shown that in the Markovian noise limit single-spin
data statistics can be predicted in closed form to all orders, despite the
nonlinearity of the underlying quantum model. A new closed-form positive
P-representation of the thermal density matrix is derived as an auxiliary
result. Large-scale quantum simulations of up to eighteen interacting spins are
then presented, in the context of a spin-dust model that has no symmetries, no
spatial ordering, and high temperature; the technique is found to work well
even within this deliberately challenging model. Classical and quantum model
order reduction (MOR) techniques are compared, and the invariance associated
with Choi's Theorem is shown to be essential to quantum model order reduction.
A surprising equivalence between compressed wave functions and cryptographic
keys is noted, and as a proof-of-principle, the numerical spin-dust
trajectories are used to implement a public key exchange protocol. A large
class of quantum systems can be simulated in polynomial space and time by this
method, with the main restriction that the noise level be large enough that the
system being simulated is not running a quantum computation. |
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April 5, 2006
Joseph Traub |
Qubit complexity of continuous
problems
(35 MB)
For the foreseeable future the number of qubits will be a crucial
computational resource. We show how to lower bound the qubit complexity using
the classical query complexity. We use this result to present a simple problem
which cannot be solved on a quantum computer in the standard quantum setting
with deterministic queries but can be solved on a classical computer using
randomized queries (Monte Carlo). This suggests introducing a quantum setting
with randomized queries. We apply this setting to high dimensional integration
and to path integration. In particular, there is an exponential improvement in
the qubit complexity of path integration using the quantum setting with
randomized queries. We end by discussing future directions and where to learn
more. |
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March 29, 2006
Richard Packard |
Superfluid weak links: physics and
applications
(50 MB)
During the past few years arrays of nanometer sized apertures connecting
reservoirs of superfluid helium have been found to exhibit properties described
by the two Josephson equations. This talk will describe some of the experiments,
in 3He below 1 mK, and in 4He near 2 K, which
reveal the quantum nature of these weak links. Both of these superfluids
exhibit Josephson oscillations, the so called “quantum whistle”. As temperature
rises, 4He weak link arrays morph continuously from a phase slip
regime into a Josephson sine-like current-phase relation. It is still a mystery
why these arrays exhibit quantum coherence over thousands of apertures.
Sensitive rotation sensors, analogous to the superconducting dc-squid, have
been demonstrated in both 3He and 4He. These matter-wave
quantum interferometers may find multiple applications such as examining some
fundamental interactions in nature, monitoring small changes in the Earth’s
motion, and navigating submarines. |
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March 8, 2006
Gerard Milburn |
Quantum entanglement, dynamical bifurcations
and quantum phase transitions
(53 MB)
Few-body interacting systems are generically nonlinear dynamical systems and
exhibit a rich structure of fixed point bifurcations. In a quantum description
fixed points correspond to stationary states, usually the ground state. How
does the associated stationary state reflect the loss of stability of the
corresponding fixed point in the classical description? Using a number of
examples I will show that ground state entanglement is large for those
parameter values at which a bifurcation occurs in the stability of the
corresponding fixed point. Various examples will be used to illustrate this
‘correspondence principle’ including: two component BECs, coupled magnetic
molecules, Jahn-Teller models and nano mechanical systems. I will also describe
a similar class of phenomenon based on quantum versions of area preserving maps.
These are more easily implemented on quantum computer systems, especially ion
traps. Finally I will conclude with a discussion of the relation between
entanglement at semiclassical bifurcations and quantum phase transitions.
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March 1, 2006
Carlos Sa de Melo |
Evolution from BCS to BEC Superfluidity in
Dilute Fermi Gases
(48 MB)
I will review briefly some old results of the evolution from BCS to BEC
superfluidity in dilute Fermi gases, including critical temperature, order
parameter amplitude, chemical potential, collective modes, and time dependent
Ginzburg-Landau theory for the s-wave channel in three dimensions. Following
this discussion, I will present new results for the BCS to BEC evolution of
Fermi gases in the p-wave channel. I will make comparisons between s-wave and
p-wave superfluidity and point out the main differences between the two cases.
Lastly, I will discuss superfluidity of s-wave and p-wave Fermi gases in a
restricted two-dimensional geometry (one dimensional optical lattice), where a
Berezinskii-Kosterlitz-Thouless-type transition is proposed as the system
evolves from the weak to the strong attraction limit. I will show that
spontaneous vortex-antivortex pairs form and that they can condense into a
vortex-antivortex lattice at lower temperatures. |
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February 8, 2006
Rudolf Grimm |
New phenomena in ultracold
gases
(45 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC)
seminar of February 8, 2006. |
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January 25, 2006
Sandro Stringari |
Test of the Casimir-Polder force with
ultracold atomic gases
(50 MB)
The problem of the Casimir-Polder-Lifshitz force between an atom and the
surface of a substrate is discussed. When the temperatures of the substrate and
the environment are different, new physical phenomena arise, including the new
decay law 1/z3 of the force at large distances, which is slower than
at thermal equilibrium. New experimental possibilities of measurement of the
forces are discussed: the oscillations of a Bose-Einstein condensate near the
surface, Bloch oscillations of fermions in an optical lattice and the phase
evolution of a Bose-Einstein condensate in a double well trap. |
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January 18, 2006
Mikkel Andersen |
Transfer of orbital angular momentum from
photons to atoms
(38 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC)
seminar of January 18, 2006. |
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January 11, 2006
Steven Anlage |
Experimental investigation of universal
fluctuations in quantum wave chaotic scattering systems
(49 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC)
seminar of January 11, 2006. |
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December 14, 2005
NIST Quantum Communication Testbed Team |
Broadband quantum key distribution
(48 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC)
seminar of December 14, 2005. |
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December 7, 2005
Ennio Arimondo |
Collisions between Rb and Cs ultracold
atoms
(44 MB)
Collisional properties of a mixture of Cs and Rb atoms in a magnetic trap
at microK temperatures were studied. By selectively evaporating the Rb atoms
using a radio-frequency field, sympathetic cooling of Cs down to a few microK
was achieved. Microwave radiation was also applied selectively evaporate Rb or
Cs atoms in different Zeeman states. The interspecies collisional cross section
was determined through rethermalization measurements, leading to good agreement
with a theoretical prediction of 595 a0 for the triplet s-wave scattering
length for Rb in the F=2,mF=2 and Cs in the F=4,mF=4 magnetic states. The
experimental results were analysed through a model for collisional properties
of the mixture. By supposing that each atomic cloud was in thermal equilibrium
the rethermalization process was modeled through differential equations for the
two atomic temperatures. An alternative approach was based on the Monte Carlo
simulations of the individual collisional processes. |
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November 30, 2005
Jacob Taylor |
Solid state quantum computation: from physical
gates to architectures
(60 MB)
Solid state approaches to quantum computation offer intriguing prospects for
large scale integration and long term stability. However, achieving fault
tolerant quantum computation entails significant mitigation of environmental
couplings, which is particularly challenging in the solid-state. We will
discuss the theoretical and experimental development of a scalable architecture
for solid-state quantum computation based on actively protected two electron
spin states in quantum dots. Specifically, we find a universal set of gates for
two-spin states that can be implemented using only local electrical control,
with explicit suppression of hyperfine interactions, the dominant source of
error. The architecture allows for a modular, hierarchical design, and includes
autonomous control and non-local coupling using controlled electron transport.
Fault tolerance properties of the architecture will be considered. |
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November 16, 2005
Jennifer Sebby-Strabley and Marco Anderlini |
The double-well lattice
(82 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC)
seminar of November 16, 2005. |
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November 9, 2005
Andrew Skinner |
Damping and diffusion in a Heisenberg
chain-boson model: ohmic spin-flips, induced entanglement, and coherence
flow
(64 MB)
I develop a Born-Markov master equation for a chain of coupled spin-boson
models. Each subsystem is treated as an effectively unbiased two-level system,
or qubit, dissipating independently into an ohmic bath of oscillators. For a
few qubits, I show how the low-temperature bath causes the chain to dissipate
and decohere at selection-ruled rates that thermalize the chain. The
independent dissipation of each qubit can induce entanglement and, in resonant
transitions, can cause coherence to flow, along with the populations, into a
less decoherent subspace. |
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October 26, 2005
Frederick Strauch |
Theories versus experiments in superconducting
circuits
(67 MB)
Many experimental groups have studied superconducting circuits specially
designed to observe and manipulate the quantum mechanical states of (a
macroscopic number of) Cooper pairs oscillating across Josephson tunnel
junctions. Evidence observed so far includes quantum tunneling, energy level
quantization (spectroscopy), and coherent oscillations (Larmor, Rabi, and
Ramsey), in devices with multiple degrees of freedom (i.e., entanglement) and
extended electromagnetic geometries (i.e., cavities). Alongside this
significant progress remain many fundamental questions. Some recent experiments,
for example, suggest significant new physics for Josephson junctions, while
certain theories have developed classical analogies to multi-photon excitations
and Rabi oscillations. This talk will critically survey these issues, including
the question of what constitutes true evidence (i.e., proof) for quantum
mechanical behavior. |
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October 19, 2005
Lincoln Turner |
Holographic imaging of cold atoms
(30 MB)
Almost all measurements of cold atoms are made optically with near-resonant
light, with most being made with absorption imaging. A single photon has enough
momentum to knock many thousands of atoms out of a condensate, and so
absorption imaging destroys the cold atom sample. Off-resonant phase imaging
greatly reduces absorption, allowing many sequential images of the same cloud.
It has not been widely used as traditional phase imaging techniques require
elaborate optics. I will describe how off-resonant images can be made with only
a point-source of light and a CCD detector. Lenses (and their aberrations) are
not needed, mis-focus is impossible and resolution down to 2-3 wavelengths
should be practical. |
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October 12, 2005
Zachary Dutton |
Electromagnetically induced transparency in
superconducting quantum circuits
(54 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC)
seminar of October 12, 2005. |
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September 28, 2005
Jabez McClelland |
Laser cooling of erbium
(39 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC)
seminar of September 28, 2005. |
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September 21, 2005
Yehuda Band |
Conversion of ultracold fermionic atoms to
bosonic molecules via Feshbach resonance sweeps
(65 MB)
We consider the conversion of ultracold Fermi gases into diatomic molecule Bose
gases using Feshbach resonance sweep experiments upon preparation of an
incoherent mixture of equal populations of two internal states of the fermionic
atoms. The preparation process produces a mixture of even and odd parity
pair-states, where only even parity can produce molecules. Analysis of the
dynamical equations of motion for the gas, supported by mean-field and
many-body numerical results, shows that the dependence of the remaining atomic
fraction on the sweep rate varies from exponential Landau-Zener behavior for a
single pair of particles to a power-law dependence for large particle
number. |
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September 14, 2005
Chui-ping Yang |
A method for realizing an n-qubit controlled
phase gate with SQUIDs coupled to a resonator
(42 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC) seminar of September 14, 2005. |
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September 7, 2005
Lin Tian |
Mesoscopic and nanoscale quantum information
processing with quantum optics
(61 MB)
I present my recent work on the control of low frequency noise in solid-state
devices with continuous measurement, and quantum teleportation with
nanomechanical systems without photons.
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August 31, 2005
Indu Satija |
Hanbury Brown-Twiss effect, glassy phase, and
mixed statistics in quasiperiodic lattices
(57 MB)
Transcript of the Quantum information/Bose-Einstein condensation (QIBEC)
seminar of August 31, 2005. |
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August 17, 2005
Hadley Lawler |
The theory of a phononic cavity
polariton
(58 MB)
Polaritons were originally considered within the context of the dielectric
response of bulk systems, and its relation to the dispersion of fundamental
solid-state excitations, such as excitons and optical phonons. More recently,
excitonic cavity polaritons have been
theoretically described and observed.
These excitonic cavity polaritons represent a tunable Rabi coupling between a
condensed matter excitation within a microstructure and a cavity-resonant
electromagnetic mode. Like excitons, optical phonons possess well-characterized
cross-sections with the electromagnetic field, but at lower energies and larger
length and time scales. We present theory relevant to a phononic cavity
polariton, discuss the prospects for the observation of such a system, and
detail our progress toward the prediction of the Rabi coupling's variation with
tunable parameters. While susceptibility-type measurements are a possible route
for the detection of such a system, we emphasize the possibility of measuring
the Rabi oscillation directly in the time domain using ultrafast lasers.
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August 10, 2005
Rainer Dumke |
Sub-Natural-Linewidth Quantum Interference
Features Observed in Photoassociation of a Thermal Gas (51 MB)
By driving photoassociation transitions we form electronically excited
molecules (Na2) from ultracold (50 µK-300 µK) Na atoms.
Using a second laser to drive transitions from the excited state to a level in
the molecular ground state, we are able to split the photoassociation line and
observe features with a width smaller than the natural linewidth of the excited
molecular state. The quantum interference which gives rise to this effect is
analogous to that which leads to electromagnetically induced transparency in
three level atomic systems, but here one of the ground states is a pair of free
atoms while the other is a bound molecule. The linewidth is limited primarily
by the finite temperature of the atoms. To generate even lower temperatures we
have setup an all optical BEC experiment. |
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August 3, 2005
Paul Julienne |
What you really want to know about Feshbach
resonances
or - A Tale of Two Resonances (62 MB)
Transcript of the Quantum Information/Bose-Einstein Condensation (QIBEC)
seminar |
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July 27, 2005
Xiao-Gang Wen |
New states of quantum matter and a unified
origin of photons and electrons (67 MB)
Recent advances in condensed matter theory have revealed that spin models can
realize new and exotic phases of matter via a simple physical mechanism, known
as "string-net condensation." These new phases of matter have the unusual
property that their collective excitations are gauge bosons and fermions. In
some cases, the collective excitations can behave just like the photons,
electrons, gluons, and quarks in our vacuum. This suggests that photons,
electrons, and other elementary particles may originate from string-net
condensation in our vacuum. In addition, the string-net picture indicates how
to make artificial photons, artificial electrons, and artificial quarks and
gluons in condensed matter systems. |
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