Geometric phase induced by a cyclically evolving squeezed vacuum reservoir

We propose a new way to generate an observable geometric phase by means of a completely incoherent phenomenon. We show how to imprint a geometric phase to a system by adiabatically manipulating the environment with which it interacts. As a specific scheme, we analyze a multilevel atom interacting with a broadband squeezed vacuum bosonic bath. As the squeezing parameters are smoothly changed in time along a closed loop, the ground state of the system acquires a geometric phase. We also propose a scheme to measure such a geometric phase by means of a suitable polarization detection.     

Attractive electron-electron interaction induced by geometric phase in a Bloch band

Attractive interaction between electrons(or neutral fermions)is responsible for superconductivity(or superfluidity).In condensed matter systems,attractive interaction is usually induced by the boson-exchange mechanism[1].Indeed,in the celebrated Bardeen-Cooper-Schreiffer(BCS)theory,electrons develop attractive interaction by exchanging phonons[2].Subsequent studies show that other collective excitations such as charge density waves[3]and spin fluctuations[4]can also induce attractive interaction.The bosonexchange mechanism,together with the concept of Cooperpair,is considered to be the cornerstone of the modern theory of superconductivity.     

双光子过程耗散耦合腔阵列中的量子相变

基于准玻色方法, 利用平均场理论解析求解了环境作用下双光子过程耦合腔阵列体系的哈密顿量, 得到了体系序参量的解析表达式, 并讨论了耗散对体系超流-Mott绝缘相变的影响. 研究结果表明: 双光子共振情况下系统重铸相干的腔间耦合率临界值为(ZJ/β)= (ZJ/β)_c'≈ 0.34;双光子相互作用过程比单光子过程具有更大的耗散率, 系统维持长程相干状态的时间更短, 而实现重铸相干的腔间耦合率的临界值更大.     

Dynamics of the geometric phase in the adiabatic limit of a quench induced quantum phase transition

The geometric phase associated with a many body ground state exhibits a signature of quantum phase transition. In this context, we have studied the behavior of the geometric phase during a linear quench caused by a gradual turning off of the magnetic field interacting with a spin chain.     

Nulling interferometry by use of geometric phase

Nulling interferometry is a method of detecting a faint source near a bright one, in which destructive interference is realized for the light from the bright source. A nulling interferometer that makes use of geometric phase (Pancharatnam phase) is proposed. An experimental setup is constructed to simulate a stellar interferometer with geometric-phase modulation. We attained extinction of 6 x 10(-5) in white light.     

Bipartite entanglement induced by classically-constrained quantum dissipative dynamics

The properties of some complex many body systems can be modeled by introducing in the dissipative dynamics of each single component a set of kinetic constraints that depend on the state of the neighbor systems. Here, we characterize this kind of dynamics for two quantum systems whose independent dissipative evolutions are defined by a Lindblad equation. The constraints are introduced through a set of projectors that restrict the action of each single dissipative Lindblad channel to the state of the other system. Conditions that guarantee a classical interpretation of the kinetic constraints are found. The generation and evolution of entanglement is studied for two optical qubits systems. Classically constrained dissipation leads to a stationary state whose degree of entanglement depends on the initial state. Nevertheless, independently of the initial conditions, a maximal entangled state is generated when both systems are subjected to the action of local Hamiltonian fields that do not commutate with the constraints. The underlying physical mechanism is analyzed in detail.     

Ferrotoroidic moment as a quantum geometric phase

We present a geometric characterization of the ferrotoroidic moment tau in terms of a set of Abelian Berry phases. We also introduce a fundamental complex quantity z munu, which provides an alternative way to calculate tau and its moments and is derived from the tensor T munu=2 under summation operator jrj muSj nu. This geometric framework defines a natural computational approach for density functional and many-body theories.     

Polychromatic vectorial vortex formed by geometric phase elements

We propose the use of a geometric phase, obtained by spatial polarization state manipulations, for the formation of polychromatic vectorial vortices. Experimental demonstration is obtained by using Pancharatnam-Berry phase optical elements formed by a space-variant subwavelength grating etched on a GaAs wafer. We further demonstrate formation of scalar and unpolarized polychromatic vortices.     

Quantum dissonance induced by a thermal field and its dynamics in dissipative systems

In this paper, we study quantum correlation in separable systems termed quantum dissonance [K. Modi, T. Paterek, W. Son, V. Vedral, M. Williamson, Phys. Rev. Lett. 104, 080501 (2010)]. Firstly, we study the emergence of quantum dissonance between two atoms prepared in uncorrelated states and coupled to a single-mode thermal field. We show that even for situations when the thermal field cannot entangle the two atoms, it can nevertheless induce quantum dissonance between them. Then, we investigate the dynamics including the transfer in both Markovian and non-Markovian regimes of quantum dissonance due to dissipation modeled by two independent subsystems each of which consists of a leaky cavity containing a two-level atom and surrounded by a reservoir. The two subsystems possess some amount of atomic quantum dissonance at the beginning but do not interact with each other by any means later on. We show that the quantum dissonance can be transferred among the composite subsystems, but the way it evolves and is transferred may be very different compared to that of entanglement. Finally, we present an efficient method to refrain the unwanted transfer of quantum dissonance from interested systems to reservoirs.     

Off-diagonal geometric phase in a neutron interferometer experiment

Off-diagonal geometric phases acquired by an evolution of a 1/2-spin system have been observed by means of a polarized neutron interferometer. We have successfully measured the off-diagonal phase for noncyclic evolutions even when the diagonal geometric phase is undefined. Our data confirm theoretical predictions and the results illustrate the significance of the off-diagonal phase.     

绝热演化中一般量子态的几何相位

在绝热演化中的几何相位（即Berry相位）被推广到包括非本征态的一般量子态.这个新的几何相位同时适用于线性量子系统和非线性量子系统.它对于后者尤其重要因为非线性量子系统的绝热演化不能通过本征态的线性叠加来描述.在线性量子系统中,新定义的几何相位是各个本征态Berry相位的权重平均.     

Pancharatnam phase of two Cooper-pair boxes in a dissipative cavity

The time evolution of a single Cooper pair in the presence of another Cooper pair interacting with an electromagnetic field in a dissipative cavity is presented. The strong dependence of the dynamics of two superconducting charge qubits interacting with the microcavity field on the instantaneous phase shift experienced by the second qubit is demonstrated. The Pancharatnam phase is found to be more sensitive than the population dynamics to the phase shift. This leads us to suggest a new technique for controlling the system dynamics. Furthermore, although the atom is not directly coupled to the cavity modes, its coherent properties are found to be strongly influenced by dissipation, both qualitatively and quantitatively.     

The quantum geometric phase as a transformation invariant

The kinematic approach to the theory of the geometric phase is outlined. This phase is shown to be the simplest invariant under natural groups of transformations on curves in Hilbert space. The connection to the Bargmann invariant is brought out, and the case of group representations described.     

Entangling power of a two-qudit geometric phase gate

We construct a geometric quantum phase shift gate for qudits in NMR systems. We study the operator entanglement and entangling power of the geometric gate for quantum computations.     

Transverse diffusion induced phase transition in asymmetric exclusion process on a surface

We extend one-dimensional asymmetric simple exclusion process (ASEP) to a surface and show that the effect of transverse diffusion is to induce a continuous phase transition from a constant density phase to a maximal current phase as the forward transition probability p is tuned. The signature of the non-equilibrium transition is evident in the finite size effects near the transition. The results are compared with similar couplings operative only at the boundary. It is argued that the nature of the phases can be interpreted in terms of the modifications of boundary layers.     

Inverted regions induced by geometric constraints on a classical encounter-controlled binary reaction

A two-dimensional Cellular Automata model is proposed to simulate the exit dynamics of occupant evacuation. Concerning the exit width and the door separation, we put forward some useful standpoints: (1) exit width should be bigger than a critical value, and the door separation should be neither too small nor too big; (2) for single-exit door, with the increase of exit width, the flux per unit width will decrease but the total flux will always increase; (3) the total flux of the exit is an increasing nonlinear function of the exit width; (4) the optimal value of the door separation does not vary with the value of exit width; (5) the layout of exits should be symmetry. Those results are helpful in performance-based design of building.     

Observable acceleration of jets by a Kerr black hole

In the framework of a model based on the gravitational field of the Kerr black hole, we turn to investigate the kinematic behavior of extragalactic jets. We analytically calculate the observable velocities and accelerations along any geodesic. Then, by numerical calculations, we apply our results to a geodesic, typical of the M87 jet, and probe our results by confrontation to recent observations. A transition from non-relativistic to ultrarelativistic speeds at subparsec scale is highlighted. This transition comes sooner and more abruptly than in models based on magnetic paradigm, which indicates that we need a weaker magnetic field to explain observed synchrotron radiation. We attribute the ejection phenomenon to the repulsive effect of the gravitomagnetic Kerr field.     

Achromatic nulling interferometer based on a geometric spin-redirection phase

Nulling interferometry aims to perform destructive interference achromatically. It is used to detect a faint source near a bright one and to provide dark field, an annular pupil, and rotational shear. A nulling out-of-plane interferometer that utilizes the geometric phase of spin redirection is proposed. The degree of nulling is determined by beam collimation and angular orientation of mirrors. Simulations and experiments are in reasonable agreement.     

Electric polarization of heteropolar nanotubes as a geometric phase

The threefold symmetry of planar boron nitride (BN), the III-V analog to graphene, prohibits an electric polarization in its ground state, but this symmetry is broken when the sheet is wrapped to form a BN nanotube. We show that this leads to an electric polarization along the nanotube axis which is controlled by the quantum mechanical boundary conditions on its electronic states around the tube circumference. Thus the macroscopic dipole moment has an intrinsically nonlocal quantum mechanical origin from the wrapped dimension. We formulate this novel phenomenon using the Berry's phase approach and discuss its experimental consequences.     

Observation of a non-adiabatic geometric phase for elastic waves

We report the experimental observation of a geometric phase for elastic waves in a waveguide with helical shape. The setup reproduces the experiment by Tomita and Chiao [A. Tomita, R.Y. Chiao, Phys. Rev. Lett. 57 (1986) 937–940, 2471] that showed first evidence of a Berry phase, a geometric phase for adiabatic time evolution, in optics. Experimental evidence of a non-adiabatic geometric phase has been reported in quantum mechanics. We have performed an experiment to observe the polarization transport of classical elastic waves. In a waveguide, these waves are polarized and dispersive. Whereas the wavelength is of the same order of magnitude as the helix’s radius, no frequency dependent correction is necessary to account for the theoretical prediction. This shows that in this regime, the geometric phase results directly from geometry and not from a correction to an adiabatic phase.