2004/2/16(Mon) 16:00から

Lecturer	大橋 洋士 氏 （筑波大）
Title	トラップされたフェルミ原子ガス超流動の物理： Feshbach共鳴の役割と BCS-BECクロスオーバー領域での準粒子、集団励起スペクトル
Abstract	近年、理論／実験共に注目を集めている、Feshbach共鳴を利用したフェルミ原子ガスの超流動化について議論する。 この系は、磁場によりFeshbach共鳴を制御することで原子間の相互作用の強さを変えることができ、それにより、所謂「BCS-BECクロスオーバー」（超流動の性質が通常のBCS理論的なものから転移温度以上で形成された分子ボソンが凝縮するBEC的なものへと変化）の実現が期待されている。 特に、最近、BEC極限でフェルミ原子２個からなる分子の超流動化に成功、現在はその可変な相互作用を利用したBCS領域への到達が大きな目標になっている。 本講演では、Feshbach共鳴による分子ボソンを陽に取り入れた強結合超流動理論を用い、特に、転移温度以下の超流動状態において、準粒子（１粒子）励起スペクトル、集団励起、density profileといった、原子ガス系での重要な観測量がBCS-BECクロスオーバーの中でどのように変化するかを明らかにする。 その結果を踏まえ、実験手段が限られるこの系の超流動状態の観測方法についても議論する。

2003/12/16(Tue) 14:00から

Lecturer	Yoshitaka FUJII
Title	Muller-Lyer illusion and seeing by brain
Abstract	Which is the longer? <--> or >--< You must know this illusion. The answer is famous. But why happen this strangeness? I want to introduce seeing from this simple question.

2003/12/9(Tue) 14:00から

Lecturer	Neil Mochan
Title	Spin Dynamics of a spinor condensate
Abstract	I look at experimental results of time evolution of the mf spin states in a spinor condensate, in the case of F=1 and F=2. The mode development is analysed under varying initial conditions and the effects of atom-atom interactions are observed.

2003/12/2(Tue) 14:00から

Lecturer	荒井　ひろみ（B4)
Title	Creation of molecules from a fermi gas
Abstract	Recently there have been some reports in making a quasi-bound molecules in a fermi gas. In this seminor I'd like to present how 2 fermions are bound and introduce sereveral experiments about degenerate fermionic atoms and production molecules from it.

2003/11/25(Tue) 14:00から

Lecturer	谷村　孝介（B4)
Title	A Rigorous solutions of many-boson problems
Abstract	Some of many-boson problem in one-dimension becomes exactly soluble. In this seminar,I review some of works on the exact ground state of one-dimension Tonks gases.

2003/11/11(Tue) 14:00から

Lecturer	家田 淳一 氏　(東大理)
Title	Matter-Wave solitons of a F=1 Spinor Condensate
Abstract	The soliton properties of a multi-component Bose-Einstein condensate in an infinite homogeneous quasi-1D regime are discussed. We consider specifically an atomic condensate in the F=1 hyperfine state with the three internal degrees of freedom confined by an optical dipole trap. When the mean field interaction is attractive (c_0 < 0), bright solitons have been observed in single-component systems. In addition, the spin exchange interaction of a multi-component spinor condensate is ferromagnetic (c_2 < 0), then the system possesses a completely integrable point. By applying the inverse scattering method (ISM) to this system, we show the exact soliton solutions and the characteristic 2-soliton collision like a spin switching on/off.

2003/11/4(Tue) 14:00から

Lecturer	金本 理奈 (D3)
Title	Symptom of Symmetry Breaking in One-dimensional Bose-Einstein Condensates with Attractive Interactions
Abstract	In terms of low-lying excitation spectra of the many-body Hamiltonian, we show that the exact ground state above the critical strength of interaction breaks the translational symmetry by an infinitesimal asymmetric perturbation. The existence of a number of quasi-degenerate levels immediate vicinity of the ground state, are the symptom of the symmetry breaking of the ground state. These levels play essential roles in the localization of the bright soliton and in the increase of the condensate fraction.

2003/10/28(Tue) 16:00から ; S1-102にて (細谷研との合同セミナー ; 時間、場所 注意)

Lecturer	上田 正仁
Title	Goldstone Modes and Rotational Bands in the Yrast Spectrum of a Bose-Einstein Condensate
Abstract	One of the unique features of a gaseous Bose-Einstein condensate (BEC) is an unprecedented degree of controllability in the strength and sign of interaction.　We may exploit this degree of freedom to explore many-body effects of the system by making the strength of interaction very large or, surprisingly, close to (but, of course, not equal to) zero when the system is subject to rotation.　A rotating BEC in the long coherence-length limit has direct relevance to atomic and low-temperature physics as well as to other strongly correlated systems such as nuclear and fractional quantum Hall　systems, 　and has recently attracted widespread attention in several subfields of physics. The aim of this talk is to develop many-body theories and use them to unravel a remarkable crossover in the many-body spectrum of a rotating BEC that reflects the symmetry breaking of the system as the angular momentum of the system increases. This feature is genuinely many-body and cannot be captured by mean-field theory.

2003/10/21(Tue) 14:00から

Lecturer	関澤 鉄兵 (M2)
Title	Superfluid density of rotating bosons on a surface of a torus
Abstract	In this seminar, I talk about superfluid density of rotating bosons on a surface of a torus. As it is well known, superfluid density in a bulk system is total density at 0 K. In short, this system is 100% superfluid at 0 K. However, as we will see, superfluid density of interacting bosons in rotation is not total density even at 0 K. I obtain this result by using Bogoliubov transformation and Linear response theory in a rotating system. I hope that this study shed light on the concept of superfluid.

2003/10/14(Tue) 14:00から

Lecturer	梅澤 岳央 (M2)
Title	Steady Squeezed Spin State in the far-off resonant regime
Abstract	Much resarch has been don on atomic squeezed state with interaction between atomes and electromagnetic wave on the resonant, but not in the far-off resonant regime. In this seminar, I'd like to talk about the squeezed spin state of two collective atomes, in the case of total spin S=1 useing a J-C model in a far-off resonant regime. In this manner, we can see a steady spin state if the light is coherent.

2003/9/29(Mon) 16:30から (上妻研との合同セミナー)

Lecturer	宇佐見康二 氏（東工大総合理工学・ＮＥＣ基礎研）
Title	Observation of Antinormally-ordered Hanbury Brown and Twiss-type Correlation
Abstract	We have measured antinormally-ordered Hanbury Brown and Twiss-type correlations for vacuum and coherent states of electromagnetic field utilizing stimulated parametric down-conversion. Since the observable of this measurement was no longer the annihilation operator, but rather the creation operator, even the coherent states, i.e., the eigenstates of the annihilation operator, exhibited the photon bunching effects. The results are well explained by a continuous-mode treatment of the detection process and manifest that the measurement have the sensitivity to zero-point fluctuations.

2003/9/16(Tue) 10:15から

Lecturer	J. Rogel-Salazar 氏 (Imperial College London)
Title	Squeezing quiasiparticle excitations of a trapped Bose-Einstein condensate.
Abstract	We describe a Beliaev coupling process in a trapped Bose-Einstein condensate, analogous to degenerate parametric down conversion in light. It is shown that the down converted quisiparticles are squeezed.　We also probe the existence of correlations between the created pairs by means of an external coupling that competes with the Beliaev process.

2003/9/2(Tue) 13:30から

Lecturer	寺嶋容明(PD)
Title	Einstein-Podolsky-Rosen Correlation in General Relativity
Abstract	We study the Einstein-Podolsky-Rosen (EPR) correlation in the regime of general relativity. We show that both acceleration and gravity deteriorate the perfect anti-correlation of an EPR pair of spins in the same direction. To maintain the perfect EPR correlation, observers must measure the spins in the appropriately chosen different directions that depend on the velocity of the particles, the curvature of the spacetime, and the positions of the observers.