arXiv subjects

C. P. Sun

Publications and source records attributed to C. P. Sun.

288 records · Page 16Linked to original sources

arXiv2001

Second Quantization of Cini Model for High Order Quantum Decoherence in Quantum Measurement

By making the second quantization for the Cini Model of quantum measurement without wave function collapse [M. Cini, Nuovo Cimento, B73 27(1983)], the second order quantum decoherence (SOQD) is studied with a two mode boson system interacting with an idealized apparatus composed by two quantum oscillators. In the classical limit that the apparatus is prepared in a Fock state with a very large quantum number, or in a coherent state with average quantum numbers large enough, the SOQD phenomenon appears similar to the first order case of quantum decoherence.

quant-ph↗

arXiv2001

High order quantum decoherence via multi-particle amplitude for boson system

In this paper we depict the high order quantum coherence of a boson system by using the multi-particle wave amplitude, whose norm square is just the high order correlation function. This multi-time amplitude can be shown to be a superposition of several "multi-particle paths". When the environment or a apparatus entangles with them to form a generalized "which-way" measurement for many particle system, the quantum decoherence happens in the high order case dynamically. An explicit illustration is also given with an intracavity system of two modes interacting with a moving mirror.

quant-ph↗

arXiv2001

Second order quantum decoherence in the boson system

The second order quantum decoherence (SOQDC)is proposed as a novel description for the loss of quantum coherence only reflected by second order quantum correlations. By calculating the two-time correlation function, the phenomenon of SOQDC is studied in details for a simple model, a two boson system interacting with a reservoir composed of one or many bosons. The second order quantum decoherence effects can be observed in the sketched cavity QED experiment.

quant-ph↗

arXiv2001

Normal ordering solution to quantum dissipation and its induced decoherence

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.

quant-ph↗

arXiv2000

Idealization Second Quantization of Composite Particles

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.

quant-ph↗

arXiv2000

Localization of Macroscopic Object Induced by the Factorization of Internal Adiabatic Motion

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

quant-ph↗

arXiv2000

Consequences of 't Hooft's Equivalence Class Theory and Symmetry by Large Coarse Graining

According to 't Hooft (Class.Quantum.Grav. 16 (1999), 3263), quantum gravity can be postulated as a dissipative deterministic system, where quantum states at the ``atomic scale''can be understood as equivalence classes of primordial states governed by a dissipative deterministic dynamics law at the ``Planck scale''. In this paper, it is shown that for a quantum system to have an underlying deterministic dissipative dynamics, the time variable should be discrete if the continuity of its temporal evolution is required. Besides, the underlying deterministic theory also imposes restrictions on the energy spectrum of the quantum system. It is also found that quantum symmetry at the ``atomic scale'' can be induced from 't Hooft's Coarse Graining classification of primordial states at the "Planck scale".

hep-th↗

arXiv2000

Quantum decoherence of excitons in a leaky cavity with quasimode

For the excitons in the quantum well placed within a leaky cavity, the quantum decoherence of a mesoscopically superposed states is investigated based on the factorization theory for quantum dissipation. It is found that the coherence of the exciton superposition states will decrease in an oscillating form when the cavity field interacting with the exciton is of the form of quasimode. The effect of the thermal cavity fields on the quantum decoherence of the superposition states of the exciton is studied and it is observed that the higher the temperature of the environment is, the shorter the decoherence characteristic time is.

quant-ph↗

arXiv2000

Decoherence in a single trapped ion due to engineered reservoir

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.

quant-ph↗

arXiv2000

Elementary Excitations in Trapped BEC and Zero Mode Problem

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.

quant-ph↗

arXiv2000

Stability properties of trapped Bose-Fermi gases mixture

The stability of Bose-Fermi gases trapped in an isotropic potentials at ultracold temperature is strongly influenced by the interaction between the fermions and the bosons. At zero temperature, the stability criterion is given in this paper using variation method, the results show that whether a fermion-boson mixture is stable depends mainly on the interaction between the fermions and the bosons. For finite temperature, however, the stability is not only related to the coupling constants, but also to the temperature. The stability conditions for finite temperature are also derived and discuss in details in this paper.

quant-ph↗

arXiv2000

Factoring the unitary evolution operator and quantifying entanglement

The unitary evolution can be represented by a finite product of exponential operators. It leads to a perturbative expression of the density operator of a close system. Based on the perturbative expression scheme, we present a entanglement measure, this measure has the advantage that it is easy to compute for a general dynamical process.

quant-ph↗

arXiv2000

Finite temperature excitations of an inhomogneous trapped Bose gas with Feshbach resonances

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.

quant-ph↗

arXiv2000

Controlling Decoherence in Bose-Einstein Condensation by Light Scattering far off Resonance

It is shown that, through a super-radiant Rayleigh scattering, a strong far off-resonant pump laser applied to a Bose-Einstein condensates(BEC) can induce a non-demolition coupling of the many-mode quantized vacuum field to the BEC. This effective interaction will force the total system of the BEC plus the light field to evolve from a factorized initial state to an ideal entangled state and thus result in the quantum decoherence in the BEC. Since the effective coupling coefficients are mainly determined by the Rabi frequency of the pump laser, the quantum decoherence process can be controlled by adjusting the intensity of the pump laser. To study the physical influence of decoherence on the BEC, we investigate how the coherent tunneling of BEC in a well-separated tight double wall is suppressed by the effectively-entangled vacuum modes.

quant-ph↗

arXiv2000

Quantum Decoherence from Adiabatic Entanglement

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.

quant-ph↗

arXiv1999

Waves in Open Systems via Bi-orthogonal Basis

Dissipative quantum systems are sometimes phenomenologically described in terms of a non-hermitian hamiltonian $H$, with different left and right eigenvectors forming a bi-orthogonal basis. It is shown that the dynamics of waves in open systems can be cast exactly into this form, thus providing a well-founded realization of the phenomenological description and at the same time placing these open systems into a well-known framework. The formalism leads to a generalization of norms and inner products for open systems, which in contrast to earlier works is finite without the need for regularization. The inner product allows transcription of much of the formalism for conservative systems, including perturbation theory and second-quantization.

math-ph↗

arXiv1998

Gardiner's phonon for Bose-Einstein Condensation: A physical realization of the $q$-deformed Boson

The Gardiner's phonon presented for a particle-number conserving approximation method to describe the dynamics of Bose-Einstein Condesation (BEC) (C.W. Gardiner, Phys. Rev. A 56, 1414 (1997)) is shown to be a physical realization of the $q$-deformed boson, which was abstractly developed in quantum group theory. On this observation, the coherent output of BEC atoms driven by a radio frequency (r.f) field is analyzed in the viewpoint of a $q$-deformed Fock space. It is illustrated that the $q$-deformation of bosonic commutation relation corresponds to the non-ideal BEC with the finite particle number $N$ of condensated atoms. Up to order 1/N, the coherent output state of the untrapped atoms minimizes the uncertainty relation like a coherent state does in the ideal case of BEC that $N$ approaches infinity or $q=1-2/N$ approaches one.

quant-ph↗

arXiv1998

Quantum decoherence effect and neutrino oscillation

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.

hep-ph↗