Temperature Effects on the Self-trapping Energy of a Polaron in a GaAs Parabolic Quantum Dot

The temperature and the size dependences of the self-trapping energy of a polaron in a GaAs parabolic quantum dot are investigated by the second order Rayleigh-Schrodinger perturbation method using the framework of the effective mass approximation. The numerical results show that the self-trapping energies of polaron in GaAs parabolic quantum dots shrink with the enhancement of temperature and the size of the quantum dot. The results also indicate that the temperature effect becomes obvious in small quantum dots

Macroscopic Quantum Coherence in an Antiferromagnetic Spin Chain with Biaxial Anisotropy

Instanton configurations of (1+1)-dimensions in an antiferromagnetic biaxial-anisotropy-spin-ehain areobtained explicitly in the strong anisotropy limit,which interpolate between degenerate equilibrium orientations of theNeel vector along easy axis and are seen to be responsible for quantum tunneling.Macroscopic quantum coherence ofthe domain walls is demonstrated in terms of the instantons.

Emergence of the Macroscopic Quantum Superposition State in Microtubules

Many researchers conceive communication in Microtubules (MTs), and established theoretical models to show both classical and quantum information processing. In this paper, we studied the usually neglected interactions between the electronic dipole of water molecules in microtubules and the quantized electromagnetic radiation field. We find that the emergence collective coherent radiation, and it can turn into macroscopic quantum superposition state when passing through MTs. This could have a fundamental role in the quantum information processing.

Macroscopic Quantum System, Highly Correlated Electron State, and High-Temperature Superconductivity in Iron Pnictides

The qualitative model of the high-temperature superconductivity suggested earlier for cuprates and based on the idea that the superconductivity is associated with delocalized π bonding between ions is not only confirmed by experimental data on iron pnictides but is also improved. It is shown that the FeAs layer state is similar to that of a macroscopic quantum system characterized by a sandwich-type charge distribution in which negatively charged planes are two-dimensional electron crystals of pairs and positively charged planes are formed by positively charged ions. Superconductivity in such a system is accomplished by a two-dimensional Wigner crystal of bosons condensed into one and the same state. The crystal occupies a middle position with respect to charged planes in the sandwich structure, which leads to mutual compensation of all its interactions with all charged planes. The model can prove useful for development of the theory of superconductivity taking into consideration the highly correlated state of all valence electrons that manifests itself in formation of electron crystals with strong Coulomb interactions between them.

Quantum Decoherence of Macroscopic Object Induced by Inner Environments： an Exactly Solvable Model

我们重游一个宏观的目标的集体运动的中心的量 decoherence 问题，它作为一个维的原子链被建模。与自由的内部度由联合质量(C.M ) 的中心导致了运动，这 inner-environment-induceddecoherence 被 C.M 波浪包的本地化反映。我们显示出那，仅仅当链与外部潜力有相互作用时， C.M 运动被联合到内部状态。Thisresult 为一个宏观的目标的 inner-environment-induced 本地化的分析提供现实主义的机制。

Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets

The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80 (1998) 169), but also have great influence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.

Laser-Manipulating Macroscopic Quantum States of a Bose-Einstein Condensate Held in a Kronig-Penny Potential

We investigate the boundary value problem (BVP) of a quasi-one-dimensional Gross-Pitaevskii equationwith the Kronig-Penney potential (KPP) of period d,which governs a repulsive Bose-Einstein condensate.Under thezero and periodic boundary conditions,we show how to determine n exact stationary eigenstates {R_n} correspondingto different chemical potentials {μ_n} from the known solutions of the system.The n-th eigenstate R_n is the Jacobianelliptic function with period 2d/n for n=1,2,…,and with zero points containing the potential barrier positions.So R_nis differentiable at any spatial point and R_n^2 describes n complete wave-packets in each period of the KPP.It is revealedthat one can use a laser pulse modeled by a δ potential at site x_i to manipulate the transitions from the states of {R_n}with zero point x ≠x_i to the states of {R_n′} with zero point x=x_i.The results suggest an experimental scheme forapplying BEC to test the BVP and to observe the macroscopic quantum transitions.

Macroscopic resonant tunneling in an rf-SQUID flux qubit

We have observed the macroscopic resonant tunneling of magnetic flux between macroscopically distinct quantum states in a superconducting flux qubit. The dependences of the macroscopic resonant tunneling on the barrier height of the potential well, the flux bias and the initial state are investigated. Detailed measurements of the tunneling rate as a function of the flux bias reveal the feature of the quantum noise in the superconducting flux qubit.

Macroscopic resonant tunneling in an rf-SQUID flux qubit under a single-cycle sinusoidal driving

We experimentally demonstrate the observation of macroscopic resonant tunneling（MRT） phenomenon of the macroscopic distinct flux states in a radio frequency superconducting quantum interference device（rf-SQUID） under a singlecycle sinusoidal driving.The population of the qubit exhibits interference patterns corresponding to resonant tunneling peaks between states in the adjacent potential wells.The dynamics of the qubit depends significantly on the amplitude,frequency,and initial phase of the driving signal.We do the numerical simulations considering the intra-well and interwell relaxation mechanism,which agree well with the experimental results.This approach provides an effective way to manipulate the qubit population by adjusting the parameters of the external driving field.

Controllable cross-Kerr interaction between microwave photons in circuit quantum electrodynamics

We propose a scheme to enable a controllable cross-Kerr interaction between microwave photons in a circuit quantum electrodynamics （QED） system. In this scheme we use two transmission-line resonators （TLRs） and one superconducting quantum interference device （SQUID） type charge qubit, which acts as an artificial atom. It is shown that in the dispersive regime of the eircuit-QED system, a controllable cross-Kerr interaction can be obtained by properly preparing the initial state of the qubit, and a large cross-phase shift between two microwave fields in the two TLRs can then be reached. Based on this cross-Kerr interaction, we show how to create a macroscopic entangled state between the two TLRs.

Quantum Nucleation of Antiferromagnetic Bubbles with Tetragonal and Hexagonal Symmetries

We study the quantum nucleation in a nanomcter-seale antiferromagnet placed in a magnetic field at an arbitrary angle. We consider the magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal symmetry, respectively. Different structures of the tunneling barriers can be generated by the magnitude and the orientation of the magnetic field. We use the instanton method in the spin-coherent-state path-integral representation to calculate the dependence of the rate of qnantum nucleation and the crossover temperature on the orientation and strength of the field for bulk solids and two-dimensional films of antiferromagnets, respectively. We find that the rate of quantum nucleation and the crossover temperature from thermal-to-quantum transitions depend on the orientation and strength of the external magnetic field distinctly, which can bc tested by use of existing experimental techniques.

Effective Mass of Acoustic Polaron in Quantum Dots

The variational effective mass with respect to the e-p coupling constant for different values of cutoff wave vector is performed in quantum dot. The self-trapping transition of acoustic polaron in quantum dot is reconsidered by character of the effective mass curve varying with the e-p coupling. The holes are determined to be self-trapped in AlN quantum dot systems.

Conservation of Energy in Classical Mechanics and Its Lack from the Point of View of Quantum Theory

It is pointed out that the property of a constant energy characteristic for the circular motions of macroscopic bodies in classical mechanics does not hold when the quantum conditions for the motion are applied. This is so because any macroscopic body—lo-cated in a high-energy quantum state—is in practice forced to change this state to a state having a lower energy. The rate of the energy decrease is usually extremely small which makes its effect uneasy to detect in course of the observations, or experiments. The energy of the harmonic oscillator is thoroughly examined as an example. Here our point is that not only the energy, but also the oscillator amplitude which depends on energy, are changing with time. In result, no constant positions of the turning points of the oscillator can be specified;consequently the well-known variational procedure concerning the calculation of the action function and its properties cannot be applied.

Radiative loss of coherence in free electrons:a long-range quantum phenomenon

Quantum physics rules the dynamics of small objects as they interact over microscopic length scales.Nevertheless,quantum correlations involving macroscopic distances can be observed between entangled photons as well as in atomic gases and matter waves at low temperatures.The long-range nature of the electromagnetic coupling between charged particles and extended objects could also trigger quantum phenomena over large distances.Here,we reveal a manifestation of quantum mechanics that involves macroscopic distances and results in a nearly complete depletion of coherence associated with which-way free-electron interference produced by electron-radiation coupling in the presence of distant extended objects.This is a ubiquitous effect that we illustrate through a rigorous theoretical analysis of a two-path electron beam interacting with a semi-infinite metallic plate and find the inter-path coherence to vanish proportionally to the path separation at zero temperature and exponentially at finite temperature.The investigated regime of large distances originates in the coupling of the electron to radiative modes assisted by diffraction at material structures but without any involvement of material excitations.Besides the fundamental interest of this macroscopic quantum phenomenon,our results suggest an approach to measuring the vacuum temperature and nondestructively sensing the presence of distant objects.

Macroscopic Quantum Tunneling and Coherence of the Néel Vector in Small Antiferromagnets

The tunneling behavior of the Néel vector out of metastable easy directions or between degenerate easy directions is studied for a small single\|domain antiferromagnetic particle at low temperature. The quantum tunneling rates for these processes are evaluated for two examples of macroscopic quantum tunneling and one example of macroscopic quantum coherence. The calculations are performed by using the two sublattice model and the instanton method in the spin coherent state path integral. Quantum interference or the spin parity effect is also discussed for each case.

Macroscopic Quantum Phenomena and Topological Phase Interference Effects in Single-Domain Magnets

The tunneling of macroscopic object is one of the most fascinating phenomena in condensed matter physics. During the last decade, the problem of quantum tunneling of magnetization in nanometer-scale magnets has attracted a great deal of theoretical and experimental interest. A review of recent theoretical research of the macroscopic quantum phenomena in nanometer-scale single-domain magnets is presented in this paper. It includes macroscopic quantum tunneling (MQT) and coherence (MQC) in single-domain magnetic particles, the topological phase interference or spin-parity effects, and tunneling of magnetization in an arbitrarily directed magnetic field. The general formulas are shown to evaluate the tunneling rate and the tunneling level splitting for single-domain AFM particles. A nontrivial generalization of Kramers degeneracy for double-well system is provided to coherently spin tunneling for spin systems with m-fold rotational symmetry. The effects induced by the external magnetic field have been studied, where the field is along the easy, medium, hard axis, or arbitrary direction.

Enhancement of feasibility of macroscopic quantum superposition state with the quantum Rabi-Stark model

We propose an efficient scheme to generate a macroscopical quantum superposition state with a cavity optomechanical system,which is composed of a quantum Rabi-Stark model coupling to a mechanical oscillator.In a low-energy subspace of the Rabi-Stark model,the dressed states and then the effective Hamiltonian of the system are given.Due to the coupling of the mechanical oscillator and the atom-cavity system,if the initial state of the atom-cavity system is one of the dressed states,the mechanical oscillator will evolve into a corresponding coherent state.Thus,if the initial state of the atom-cavity system is a superposition of two dressed states,a coherent state superposition of the mechanical oscillator can be generated.The quantum coherence and their distinguishable properties of the two coherent states are exhibited by Wigner distribution.We show that the Stark term can enhance significantly the feasibility and quantum coherence of the generated macroscopic quantum superposition state of the oscillator.

量子计算与超导量子计算机

量子计算是一种基于量子力学相干叠加原理的新型计算体系,具有超越传统计算体系的优越性能。超导量子计算因为其在规模可扩展性方面的潜力而得到广泛的重视。超导约瑟夫森结是超导量子计算机方案中的关键器件,可用来控制超导体中的宏观波函数。阐述了量子计算的发展和优势,介绍了约瑟夫森结的原理以及三种超导量子比特的特性,并分析了面临的挑战。

一种新型的两态叠加多模Schrdinger猫态光场的等阶N次方Y压缩

本文根据量子力学的线性叠加原理，构造了由多模（即q模时目平态的相反态|｛｛－Zj｝〉q及多模虚相干态|｛｛－Zj｝〉q这两者的线性叠加所组成的一种新型的多模Schrodinger猫态光场利用新近建立的多模压缩态理论，研究了态的N次方Y压缩效应,结果发现：①当压缩阶数N＝Zp且p＝2m（m＝1，2，3，…，…）时，态。总是恒处于N－Y最小测不准态；②当压缩阶数N＝2p且p＝2m＋1（m＝0，1，2，3，…，…）时，如果各模的初始相位，态间的初始相位差以及各单模相干态光场的平均光子数之总和等满足一定的量子化条件，则态可呈现出周期性变化的、任意阶的N次方Y压缩效应；③当压缩阶数N＝2P＇＋1时，无论p＇＝2m（m＝0，1，2，…，…）还是p＇＝2m＋1（m＝0，1，2，3，…，……），只要各模的初始相位满足一定的量子条件，则当两态叠加几率幅满足时，态就恒处于N－Y测不准态，始终不呈现N－Y最小测不准态和N次方Y压缩；而当时，态始终不呈现N－Y测不准态、N－Y最小测不准态和N次方Y压缩效应．