Public Seminar of Physics PhD Candidate
posted by Department of Physics for HKU and Public
Event Type: Public Lecture/Forum/Seminar/Workshop/Conference/Symposium
Event Nature: Science & Technology
Public Seminar of Physics PhD Candidate =====================================
Investigations of Timedependent Quantum Transport Properties in Nanoscale Structures
Mr. Jiangtao YUAN
Abstract:
In this talk, certain aspects of timedependent quantum transport properties in nanoscale structures are introduced. First of all, for the transient behaviors of the electric current and heat current after a quantum quench, the exact analytical solution beyond the wide band limit (WBL) is obtained for the first time which paves a way to simulate realistic physical systems. Then, the timedependent thermoelectric effects are evaluated based on this general solution and it is shown that the timedependent thermopower is significantly enhanced in the transient regime. By taking initial correlation into account, the combined Caroli and Cini scheme in quantum transport is proposed and its exact solution beyond WBL is derived for the first time as well. Furthermore, besides the average electric current, a current conserving and gauge invariant formalism for the total electric current operator is established at equilibrium state with the help of the electric displacement current operator formulated by taking the Coulomb interaction into account at the operator level. By means of the nonequilibrium Green’s function (NEGF) as well as the scattering matrix theory (SMT), a current conserving theory for equilibrium noise power at finite frequencies is obtained which solves one of the fundamental problems in quantum transport. A generalized equilibrium fluctuationdissipation theorem is presented. Moreover, the entanglement entropy fluctuation and its distribution are investigated by introducing the entanglement entropy operator. The essential feature of the entanglement entropy generated by quantum transport is that it is a stochastic quantity whose fluctuation and distribution can be obtained from the generating function (GF). Combining the NEGF with the Grassmann algebras, it is found that the GF of entanglement entropy can be expressed in terms of the lesser Green’s function of the subsystem. The general relation connecting the full counting statistics (FCS) of charge transfer with the GF of entanglement entropy is found which indicates that, from the experimental point of view, the entanglement entropy fluctuation can be measured indirectly. As an illustration of the general theoretical framework of entanglement entropy fluctuation, the quantum point contact (QPC) system as well as the quantum dot (QD) system are studied. It is shown that for a QPC under dc bias, the entanglement entropy is maximized and fluctuationless when the transmission coefficient T is onehalf. For the quantum dot system, at short times, a universal scaling relation among transient peak values of cumulants of entanglement entropy is shown.
Anyone interested is welcome to attend.
 Date/Time  16/08/2017 14:3015:00  Venue  Rm 518, 5/F, Chong Yuet Ming Physics Building, HKU  Language  English 

Registration is not required.
Should you have any enquiries, please feel free to contact Ms Eva Wong by email at physdept@hku.hk or by phone at 2859 2360 or by fax at 2559 9152.
