arXiv subjects
Publications and source records attributed to D. L. Zhou.
We implement the normal ordering technique to study the quantum dissipation of a single mode harmonic oscillator system. The dynamic evolution of the system is investigated for a reasonable initial state by solving the Schrödinger equation directly through the normal ordering technique. The decoherence process of the system for the cases $T=0K$ and $T\neq0K$ is investigated as an application.
A practical method is developed to deal with the second quantization of the many-body system containing the composite particles. In our treatment, the modes associated with composite particles are regarded approximately as independent ones compared with those of unbound particles. The field operators of the composite particles thus arise naturally in the second quantization Hamiltonian. To be emphasized, the second quantization Hamiltonian has the regular structures which correspond clearly to different physical processes.
We show how to improve the efficiency for preparing Bell states in coupled two quantum dots system. A measurement to the state of driven quantum laser field leads to wave function collapse. This results in highly efficiency preparation of Bell states. The effect of decoherence on the efficiency of generating Bell states is also discussed in this paper. The results show that the decoherence does not affect the relative weight of $|00>$ and $|11>$ in the output state, but the efficiency of finding Bell states.
To account for the phenomenon of quantum decoherence of a macroscopic object, such as the localization and disappearance of interference, we invoke the adiabatic quantum entanglement between its collective states(such as that of the center-of-mass (C.M)) and its inner states based on our recent investigation. Under the adiabatic limit that motion of C.M dose not excite the transition of inner states, it is shown that the wave function of the macroscopic object can be written as an entangled state with correlation between adiabatic inner states and quasi-classical motion configurations of the C.M. Since the adiabatic inner states are factorized with respect to each parts composing the macroscopic object, this adiabatic separation can induce the quantum decoherence. This observation thus provides us with a possible solution to the Schroedinger cat paradox
The decoherence in trapped ion induced by coupling the ion to the engineered reservoir is studied in this paper. The engineered reservoir is simulated by random variations in the trap frequency, and the trapped ion is treated as a two-level system driven by a far off-resonant plane wave laser field. The dependence of the decoherence rate on the amplitude of the superposition state is given.
We propose a natural expansion of the atomic field operator in studying elementary excitations in trapped Bose-Einstein Condensation (BEC) system near T=0K. Based on this expansion, a system of coupled equations for elementary excitations, which is equivalent to the standard linearized GP equation, is given to describe the collective excitation of BEC in a natual way. Applications of the new formalism to the homogeneous case emphasize on the zero mode and its relevant ground state of BEC.
We derive and discuss the temperature dependance of the condensate and noncondensate density profile of a Bose-Einstein condensate gas with Feshbach resonance in a parabolic trap. These quantities are calculated self-consistently using the generalized Hartree-Fock-Bogoliubov (HFB) equations within the Bogoliubov approximation. At zero temperature, the HFB equation can be solved by means of a variation method that give the low excitation spectrum. Moreover, within the two-body collision theory, we estimate the relationship between the atom number and the external magnetic field $B$, it is in good agreement with the data in recent experiments.
In order to understand quantum decoherence of a quantum system due to its interaction with a large system behaving classically, we introduce the concept of adiabatic quantum entanglement based on the Born-Oppenhemeir approximation. In the adiabatic limit, it is shown that the wave function of the total system formed by the quantum system plus the large system can be factorized as an entangled state with correlation between adiabatic quantum states and quasi-classical motion configurations of the large system. In association with a novel viewpoint about quantum measurement, which has been directly verified by most recent experiments [e.g, S. Durr et.al, Nature 33, 359 (1998)], it is shown that the adiabatic entanglement is indeed responsible for the quantum decoherence and thus it can be regarded as a "clean" quantum measurement when the large system behaves as a classical object. The large system being taken respectively to be a macroscopically distinguishable spatial variable, a high spin system and a harmonic oscillator with a coherent initial state, three illustrations are present with their explicit solutions in this paper.
The high density Frenkel exciton which interacts with a single mode microcavity field is dealed with in the framework of the q-deformed boson. It is shown that the q-defomation of bosonic commutation relations is satisfied naturally by the exciton operators when the low density limit is deviated. An analytical expression of the physical spectrum for the exciton is given by using of the dressed states of the cavity field and the exciton. We also give the numerical study and compare the theoretical results with the experimental results
In the view of the quantum dynamic theory of measurement developed from the Hepp-Colemen (HC) model (K. Hepp, Hev.Phys.Acta, {\bf 45}, 237 (1972)), the quantum decoherence in neutrino flavor oscillation caused by an environment surrounding neutrinos is generally considered in this paper. The Ellis, Hagelin, Nanopoulos and Srednicki (EHNS) mechanism for solving the solar neutrino problem can be comprehended in a framework of the ordinary quantum mechanics. In the weak- coupling limit, a microscopic model is proposed to describe the transition of two neutrino system from a pure state to a mixed state. It gives the modified formula of survival probability of neutrino oscillation with two additional time-dependent parameters. For specified environments, this result shows that the oscillating phenomena of neutrino still exist even without a mass difference in free neutrino.