Bose-Einstein condensation (BEC) was first predicted by Bose and Einstein, and originally defined as a macroscopic occupation of bosonic particles in the ground state. After first demonstration of a nearly ideal Bose-Einstein condensate in 1995 with ultra cold atoms, a great amount of research has been done, such as Bose-Einstein condensates in two-dimensional system, and the observation of a quantised vortex. Exciton polaritons (EPs) are quasi-particles resulting from the strong coupling between (cavity) photons and (quantum well) excitons, and have been considered as a candidate for BEC in solids. Because of their photonic component, their mass is much lighter than that of atoms or excitons, which leads to a much higher critical temperature for BEC in EP systems. The observation of BEC in EP systems has been reported by several groups. Because EPs have a short lifetime of the order of ～ps they may decay from the system before reaching the thermal equilibrium. Continuous pumping replenishes EPs in the system, and as aresult phase coherence for a time longer than their lifetime. Therefore the system has been considered to undergo dynamic condensation of EPs. In atomic systems, another research direction that has attracted a large amount of attention in recent years is quantum simulation. The aim of quantum simulation is to give another way to investigating difficult quantum many-body problems by simulating quantum models experimentally on other quantum devices. This is advantageous because it is often easier to control the model parameters in the artificially fabricated device, rather than the original system being examined. Currently, most researchers working on quantum simulation have been working with cold atom systems and ion trap systems. To perform the quantum simulation, how to implement the desired model is an important question. In cold atom systems, optical lattices provide a suitable way to create periodic lattice potentials. On the other hand, in EP systems, several ways to create potentials have been suggested and demonstrated. Currently weak one dimensional lattice potentials have been demonstrated experimentally. In this thesis, we implemented several two dimensional lattice potentials in EP systems. The dynamic nature of EPs gives us rich physics, especially due to metastable condensation. The EP systems have the advantage over atomic system in that it is easier for excited state condensations to be formed. The periodic lattice potentials are implemented by depositing patterned thin metals. The metal changes the boundary condition of photons and make the cavity resonance higher in energy, which leads to the potential barriers for EPs of the order of ～200μeV. In two dimensional square lattice potentials, we have observed d-orbital wave condensates at M-points. The order parameter of this meta-stable condensation has 2D atomic d-orbital symmetry, and two-fold rotational symmetry against the trap center. We detect this d-orbital wave through the momentum space distribution, and the real field distribution. In two dimensional triangular lattice potentials, we observed several results indicating the formation of vortex-antivortex lattices, which originates from the single particle wave function of the meta-stable state at M-points.

発行年

2011-03-24

日本十進分類法

549

学位名

博士(情報理工学)

学位

doctoral

学位分野

Information Science and Technology (情報理工学)

学位授与機関

University of Tokyo (東京大学)

研究科・専攻

Department of Information and Communication Engineering, Graduate School of Information Science and Technology (情報理工学系研究科電子情報学専攻)

学位授与年月日

2011-03-24

学位授与番号

甲第27285号

学位記番号

博情第323号

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