Zhi-Ming Bai

Effect of inhomogeneous magnetic flux on double-dot Aharonov-Bohm interferometer

The influence of the inhomogeneous distribution of the magnetic flux on quantum transport through coupled double quantum dots embedded in an Aharonov–Bohm interferometer are investigated. We show that the effective tunnelling coupling between two dots can be tuned by the magnetic flux imbalance threading two AB subrings. Thus the conductance and the local densities of states become periodic functions of the magnetic flux imbalance. Therefore, transport signals can be manipulated by adjusting the magnetic flux imbalance. Thus accurate control of the distribution of the magnetic flux is necessary for any practical application of such an Aharonov–Bohm interferometer.

Exact solutions for the time-dependent Hamiltonian in high-dimension and many-body problem

Abstract The method of Ray is used to solve the high-dimensional and many-body time-dependent problems. Exact solutions of the models including Calogero model in time-dependent harmonic potential are studied by using this method.

Nonclassical properties of photons and atoms in interaction of an atomic Bose–Einstein condensate with laser

Abstract We study nonclassical properties of photons and atoms in interaction of 7Li atomic Bose–Einstein condensate in the ground-state hyperfine sublevel with laser field. When the quantized laser field is initially in a coherent state whereas the atomic field is initially in a displaced Fock state, respectively, it is shown that there exists the energy exchange between atoms in the condensate and photons in the quantized laser field. We find that a proper choice of the pulse area can significantly modify the atom (and photon) statistics from sub to super-Poissonian distribution, and vice versa. But there does not exist quadrature squeezing both for the quantized laser field and the atomic field. The analysis for photon–atom correlation shows that under some circumstances nonclassical correlation can be built.

Non-adiabatic Berry's phase in many-body and high-dimensional system

Abstract A series of solvable time-dependent models about high-dimensional and many-body systems are given, which include the Calogero model trapped in a time-dependent harmonic well. If these models evolve periodically with time, a non-adiabatic Berrys phase in these models can be obtained.

THE NON-ADIABATIC BERRY PHASE IN TWO DIMENSIONS : THE CALOGERO MODEL TRAPPED IN A TIME-DEPENDENT EXTERNAL FIELD

The two-dimensional Calogero model in a time-independent external magnetic field is extended to the time-dependent case which can be solved exactly. Both the invariant operator and the eigenstate are obtained. For the periodical time-dependent case, the non-adiabatic Berry phase is also presented.

PERSISTENT CURRENT IN TWO SUB-RINGS COUPLED BY ONE EMBEDDED QUANTUM DOT

We investigate a two sub-rings mesoscopic system embedded with one quantum dot in common. Owing to the screening cloud of the two sub-rings, the change of the magnetic flux and the number of lattice sites in one sub-ring influence the persistent current not only in itself but also in another. Kondo-assisted (suppressed) tunneling appears in the two sub-rings system constructed by even (odd) number of lattice sites.

Free energy and Green function for the multi-coupled spin system

The free energy and Green function of the multi-coupled spin chain in low-energy theory are given by using the functional bosonization method. We deduce that 2m coupled spinless chains (m = 0,1,2,...), by using a series of unitary transformations, can be reduced to some uncoupled chains, but for other numbers of coupled spinless chains we need to solve a series of inverse matrices generally; for either case, the system can be formally separated into the charge and spin parts.

Electric current and conductance in a chain of quantum dots

By using the non-equilibrium Green function method, we give the current flowing in a chain of quantum dots exactly. The result coincides with the Landauer formula. Finally, the conductance of the system is given in the linear approximation.

Interaction of mesoscopic Josephson junction with superposition of even and odd coherent states

Abstract The interaction of a mesoscopic Josephson junction with superposition of even and odd coherent states is investigated. It is found that the expectation value and the fluctuation of a supercurrent can exhibit dc components. The number of current-voltage steps (CVSs) for the former are less than the latter. For the former the static supercurrent flows in a positive or negative direction, which depends on the phase of the light field. The correlation function and squeezing of the dc components of a supercurrent depend on the value of CVS. For some special value of a CVS, the squeezing disappears.

Interaction of a mesoscopic Josephson junction with the second-order excitation of the even coherent state

The interaction of a mesoscopic Josephson junction with the second-order excitation of the even coherent state is investigated. It is found that the expectation value and the fluctuation of supercurrent can exhibit dc components. The static supercurrent flows in the positive or negative direction, which depends on the phase of the light field. It is shown that the dc components of the supercurrent fluctuation are also related to the phase of the light field.