2004年度
2005/2/22 (Tue)
Lecturer 
Neil Mochan (M1)

Title 
Spin2 dynamics in BEC under varying interaction strength

Abstract 
Recently, Dr. Saito has studied Bose Einstein condensation trapped in
free space by manipulating the Feshbach resonance. I study, by
computer simulation, how a variation in the three interaction
parameters (which were previously constant) could affect the spin
dynamics of a spin2 condensate.

2005/2/8
(Tue) 13:30
Lecturer 
Keiji Murata

Title 
BoseEinstein condensation with internal degrees of freedom (II)

Abstract 
In last semester, I presented MFT of the spin1 BoseEinstein
Condensates and derived the ground state structures.
The phase of special interest is
the "Mixed phase" which shows the spontaneous symmetry breaking
in the case of ferromagnetic interaction.
Therefore it is expected that this system has gapless Goldstone
mode(s).
Obtaining such modes is one of our goals.
I'd like to present the Bogoliubov theory formalization of the spin1 system and examine it in ferromagnetic and polor phases.
If possible, I'll show the results in mixed phase and mention
about physical interpretation of such modes.

2005/2/4
(Fri) 13:30
Lecturer 
Hiroki Saito (Interactive Research Center of Science, Titech)

Title 
Selftrapped BoseEinstein condensates stabilized by
oscillating interactions

Abstract 
A matterwave bright soliton  a Bose Einstein condensate (BEC)
confined by itself without an external potential  is known to be
stable in 1D, in which quantum kinetic pressure counterbalances an
attractive interaction.
However, in 2D or higher dimensions, selftrapped BECs are always
unstable against collapse or expansion as long as the attractive
interaction is constant in time.
I will show that the selftrapped BEC in 2D can be stabilized
by rapid oscillations of the interaction between attractive and
repulsive through the Feshbach resonance.
The mechanism of the stabilization is similar to that of an inverted
pendulum, in which a bob is stabilized above the vertically oscillating
pivot.
In 3D space, the stabilization of the selftrapped BEC by oscillating
interactions has been elusive, since complex dynamical instabilities and
strong collapse arise in the 3D system.
I will show that if we take into account the effect of dissipation, the
selftrapped BEC can be stabilized in 3D.

2005/2/1(Tue)16:0017:00
Lecturer 
Hiromi ARAI(M1)

Title 
Observational study on protein expression system

Abstract 
Cellfree system is very simplified protein synthesis system which
produces pure, amount of protein. Because of its simplisity, we estimate
that we can extract characteristic behavior of the system, like expression dependence on codon or amino acid, etc. Moreover, because translation process might affects protein folding, I expect that the result of the analysation might become one of the clues of protein folding.
In this seminar, I'd like to introduce about what I am analyzing and results I have obtained so far.

2005/1/25 (Tue)
Lecturer 
Teppei Sekizawa (D1)

Title 
Superfluid density of weakly interacting spin1 bosons

Abstract 
Superfluid density of weakly interacting spin1 bosons is derived by
using
HohenbergMartin theory when a system is polar, ferromagnetic and super
fragmented phase. We show that the superfluid density which is different
in
these phases is
also the total density at absolute zero as the case of spinless bosons.

2005/1/18 (Tue)
13:00
Lecturer 
Hiroaki Terashima (PD)

Title 
Nonunitary Quantum Circuit

Abstract 
A quantum circuit is generalized to a nonunitary one whose constituents
are nonunitary gates operated by quantum measurement.
It is shown that a specific type of onequbit nonunitary gates,
the controlledNOT gate, as well as all onequbit unitary gates
constitute a universal set of gates for the nonunitary quantum circuit,
without the necessity of introducing ancilla qubits.
A reversing measurement scheme is used to improve
the probability of successful nonunitary gate operation.
A quantum NAND gate and AbramsLloyd's nonlinear gate are analyzed as
examples.
Our nonunitary circuit can be used to reduce the qubit overhead needed
to ensure faulttolerant quantum computation.

2005/1/11 (Tue)
Lecturer 
Takahiro Ohkuma (B4)

Title 
Statistical Mechanics of Attractive System

Abstract 
The recent experiments show us the atomsMolecles crossover by arranging
the scatterring length with magnetic field (Feshbach resonance). In this
seminar,I will discuss the general way we calculate the grand partition
function by means of LEE & YANG cluster expansion method.(T.D.Lee,C.N.Yang
Phys.Rev.113,1165(1959))
My motivation is to apply this method to the attractively interacting
system which has some bound states.

2004/12/7(Tue)
Lecturer 
Dr. Kenichi Kasamatsu (Osaka City Univ.)

Title 
Pattern formation and quantized vortices in twocomponent
BoseEinstein condensates

Abstract 
In the seminor, we talk about pattern formation in twocomponent
BoseEinstein condensates (BECs), focusing on the dynamics of
multipledomain formation and the structure of quantized vortices in
rotating BECs. Crossphase modulation instability gives rise to the
formation of multiple domains that alternate two components, which are
consistent with the experimental observation by the Ketterle's group.
Multicomponent order parameter allows the excitation of various exotic
topological defects, e.g., skyrmions or merons, which have no analogue
in a system with a singlecomponent order parameter. We discuss their
structure
in twocomponent BECs based on the nonlinear sigma model by introduing
the
"pseudospin". Rapidly rotating twocomponent BECs exhibit a rich variety
of vortex states such as square lattices and vortex sheets of the
skyrmions, which depend on the strength of intercomponent interaction and the
rotation frequency.

2004/11/30(Tue)
Lecturer 
Yasuaki Suzuki (B4)

Title 
Path Integral Approach to a RotatingBoseSystem

Abstract 
In first semester, I introduce to the paper, gAtomic Theory of the
Transition in Helium h by R.Feynman in 1953.In this paper, Feynman
showed that liquid He exhibit a transition, using path integral
approach. I apply this approach to noninteraction system. In addition,
applying to a rotatingtrappedsystem, I get critical point, which
depends on angularvelocity.

2004/11/9 POSTPONED UNTIL 11/16!!!
Lecturer 
Neil Mochan (M1)

Title 
Spin Dynamics in Spatially Uniform BoseCondensed Rb87

Abstract 
T. Kuwamoto et al at Gakushuin university recently studied the
spindependent collision dynamics of Rb87 spin2 Bose Einstein
Condensates confined in an optical trap and came up with some very
interesting results. I make preliminary attempts
to simulate their results theoretically, taking for now, the case
where the condensate is uniform. I derive the equations of motion for
each component and study the time evolution, with a view to eventually
being able to fully simulate their observations.

2004/11/2(Tue)
Lecturer 
Keiji Murata (M1)

Title 
BoseEinstein condensation with internal degrees of freedom

Abstract 
In MIT, Stenger group realized linear form 'spinor BEC' in
magnetic field (1998).
Linear and quadratic Zeeman terms which are changed arbitrarily play
essential role in this system and give us a number of ground state
structures by balancing them and interaction energy.
Concerning with this, we can draw the phase diagrams of this system
and also verify them experimentally.
I'd like to show how to obtain them and mention the Bogoliubov
spectrums especially the Goldstone modes followed by the spontaneous
symmetry breaking in the 'mixed state' in antiferromagnetic case.

2004/10/26(Tue)14:00
Lecturer 
Hiromi ARAI (M1)

Title 
Introduction of bioinformatics

Abstract 
Bioinformatics is a marriage of computer science with molecular biology. Recently data of molecular biology, DNA or protain sequence data etc., have been increasing exponentially. In order to shift out the core information, it is necessary to use informatical method. Moreover, information skill can be used to manage complex science data. In this seminar, i'd like to introduce
basis of molecular biology and topics of bioinformatics.

2004/10/19(Tue)
Lecturer 
Dr. Takashi Mukaiyama (Univ. of Tokyo)

Title 
Creation of the optically trapped ultracold sodium molecules
via a Feshbach resonance

Abstract 
Recently it has become possible to create ultracold molecular gases
from precooled atomic condensates.
Feshbach resonance, which originates from the degeneracy of free atomic
state and molecular bound state,
has been utilized to form molecules in an atomic condensate by
adiabatic magneticfield sweep.
Because of the high conversion efficiency and the tunability of the
intermolecular interaction, this method is
one of the most promising way to realize momentumcorrelated pair of
atoms (BCS pair), and to study BECBCS
cross over of paired atoms.
Here we present the experimental result on the formation of sodium
molecules in an atomic bose condensate.
We have produced 10^5 molecules, which corresponds to the phase space
density of more than 20 in our trap
conditions. We have measured the typical evidence of the condensation
of "falling cloud like a rock." We
have also studied the dissociation and decay of those molecules in the
negative scatteringlength side of
resonance, where BCS paired state exists for molecules composed of
fermions. Understanding the
dissociation mechanism is crucial for the discussion of what the
smoking gun of BCS pairing is.

2004/10/12(Tue)
Lecturer 
Dr. Yuki Kawaguchi (Kyoto Univ.)

Title 
Vortex state in a superfluid Fermi gas near a Feshbach
resonance

Abstract 
I discuss the vortex state in the BCSBEC crossover region. Using a
Feshbach resonance, it is possible to study the crossover between a
BCS superfluid of Fermi atoms and a Bose Einstein condensate (BEC) of
molecules. In a pure molecular condensate at zero temperature, there
is no normalfluid in a vortex core. On the other hand, far from the
resonance in BCS side, a vortex core is filled with atoms. The microscopic
properties of a single vortex in the crossover region are studied by using
selfconsistent Bogoliubovde Gennes theory. Crossing a Feshbach resonance
from BCS to BEC side, the number of atoms decreases and, moreover, the
fraction of atoms in the vortex core decreases because of the existence of
the molecular BEC.

2004/10/5(Tue)
Lecturer 
Teppei Sekizawa (D1)

Title 
Superfluid Density of Weakly Interacting Bosons on a Surface
of a Rotating Torus

Abstract 
We use linear response theory generalized to fit a rotating system to show
that the superfluid density of interacting bosons on the surface of
a rotating torus becomes less than the total density even at 0 K. This
reduction of the superfluid density is shown to originate
from the correlation of noncondensate
bosons. Our prediction can be tested by measuring the superfluid density
of liquid $^4$He in a rotating porous media with torsional pendulum.
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2004/9/28(Tue)
Lecturer 
Dr. Tetsufumi Tanamoto (Toshiba R&D Center)

Title 
Charged qubit based on coupled quantum dots and measurement
process

Abstract 
I theoretically discuss charged qubits. The outline is following:
(1) Charged qubit Hamiltonian and its similarity to NMR Hamiltonian
 I derive charged qubit Hamiltonian from capacitance network of
quantum dots.
(2) Charged qubit in SiMOSFET (MetalOxideSemiconductor Field Effect
Transistor)
 By using conventional MOSFET current formula, I consider the possible
number of qubits that can be readout.
(3) Measurement process by single electron transistor(SET) and quantum
point contact(QPC)
 By using density matrix equations, I describe the timedependent
behavior of detector current of SET and QPC.

2004/4/1(Thu)
Lecturer 
Prof.Anthony J. Leggett(University of Illinois)

Title 
BEC (BoseEinstein Condensation): a "tapas" of topic

Abstract 
I discuss the following topics related to BoseEinstein condensation in the alkali gases:
(1) What is BEC?
(2) The relation between the GrossPitaevskii and Bogoliubov descriptions.
(3) What is superfluidity?
(4) Limits on the condensate fraction.
(5) Detecting the normal component in Ramseyfringe type experiments.
