 |
Solid state physics, comprising broad research areas, deals with manifold of materials and investigates their properties from the viewpoint of 'universality'. In our normal procedures, we first perform experimental measurements of target systems, and then consider its theoretical model in order to understand the experimental results. The recent developments in solids state physics, however, have encouraged the precise control of quantum systems in mesoscale devices and formed new research ares of so-called mesoscopic physics.
The main topic of mesoscopic physics was the measurement of conductance in the region where quantum interference effects were important. Many experimental results have been understood by non-interacting electron models. However, recent experiments on Kondo effect and Tomonaga-Luttinger liquid added new examples, which require essential account of electron-electron interactions. Further, theory of the current-voltage characteristics and shot-noise essentially involve the consideration of nonequilibrium phenomena.
In our group, the main subject is theoretical study of the systems in which electron-electron interactions and nontrivial nonequilibrium properties play an important role. Particularly, we are trying to construct numerical methods to simulate these systems. From this point of view, we attempt to understand quantum transport properties of quantum dots, anti-dot lattices, quantum wires and quantum Hall systems in collaboration with experimentalists. We are also trying to evaluate performance of quantum computation by studying decoherence sources in realistic physical systems.
|
 |
Electron-electron interactions become important in several systems such as quantum wires, quantum dots and quantum point contact. Although many researches have studied these systems theoretically, it remains unsettled how many-body effects appears in these systems. For example, there remains problems to be solved in study of one-dimensional electron systems in carbon nanotubes and 0.7 anomaly in quantum point contact. We are making efforts to analyze these problems with help of numerical simulation based on quantum Monte Carlo and density-matrix renormalization group (DMRG).
|
 |
Mesoscopic systems can be characterized by nonequilibrium states in small regions between macroscipic leads. Although a number of theoretical approach based on approximations have been developed, general theory for characterization of nonequilibrium states including electron-electron interactions is not known. We are trying to construct general theory which is also applicable to numerical calculations of Kondo effect in quantum dots and molecular devices.
|
 |
For realization of quantum computer, we have to control quantum two- state systems (qubits). Because in realistic systems noise from environments make it difficult to keep coherence of qubits, it is important to evaluate character of noise and to propose new schemes for control of qubit to decrease noise effects. We are challenging to these problems by focusing mainly on superconducting qubits
.
|
 |
Generally, it is difficult to perform analytical calculation when we consider nonequilibrium states and electron-electron interactions. In such cases, it becomes important to use numerical methods. We are interested in applying recently developed numerical methods such as time-dependent DMRG to problems of mesoscopic systems. We are also interested in developing novel algorithms of quantum Monte Carlo methods.
|
|
|
