Magnetic field induced transition in a quantum magnet described by the quantum dimer model

The effect of a magnetic field on a gapped quantum magnet is described within the framework of the quantum dimer model. A minimal model describing the proliferation of itinerant spinons above a critical field is proposed and investigated by Lanczos exact diagonalizations and quantum Monte Carlo simulations. For both square and triangular lattices, it is shown that spinons are fully polarized and Bose condense. This offers a novel scenario of a quantum critical point in the dimer-liquid phase (triangular lattice) characterized by the continuous appearance of a spinon superfluid density, contrasting with the usual triplet condensation picture. The possible role of other spinon kinetic terms neglected in the model are discussed.     

Binding of holons and spinons in the one-dimensional anisotropic t-J model

We study the binding of a holon and a spinon in the one-dimensional anisotropic t-J model using a Bethe-Salpeter equation approach, exact diagonalization, and density matrix renormalization group methods on chains of up to 128 sites. We find that holon-spinon binding changes dramatically as a function of anisotropy parameter alpha=J( perpendicular)/J(z): it evolves from an exactly deducible impuritylike result in the Ising limit to an exponentially shallow bound state near the isotropic case. A remarkable agreement between the theory and numerical results suggests that such a change is controlled by the corresponding evolution of the spinon energy spectrum.     

Resonating valence bond phase in the triangular lattice quantum dimer model

We study the quantum dimer model on the triangular lattice, which is expected to describe the singlet dynamics of frustrated Heisenberg models in phases where valence bond configurations dominate their physics. We find, in contrast to the square lattice, that there is a truly short ranged resonating valence bond phase with no gapless excitations and with deconfined, gapped, spinons for a finite range of parameters. We also establish the presence of crystalline dimer phases.     

Resonance effects in the nonadiabatic nonlinear quantum dimer

In the presence of 1/f ^β noise, we investigate the logical stochastic resonance (LSR) in an asymmetric bistable model driven by various cycling combinations of two logic inputs. The probability of correct logic outputs is calculated according to true table of logic relationships. Two major results are presented. Firstly, it is shown that the LSR effect can be obtained by changing noise strength. Over entire range of noise variance, white noise can be considered to be better than 1/f noise or 1/f ² noise to obtain clean logic operation. At a smaller noise level, 1/f noise can realize higher output probability than white noise or 1/f ² noise. In the sense, 1/f noise can be considered to be better than white noise or 1/f ². On the other hand, the correct probability can evolves nonmonotonically as noise exponent β increases, and a kind of SR-like effect can be obtained as a result of β. At certain intermediate noise variance, the output probability is able to attain its minimum at β = 1. It is also shown that actually some finite β sometime can be better than β = 0 at small range of noise variance. The study might provide some potential complement to LSR effect in the presence of 1/f ^β noise.     

Entanglement and decoherence in a quantum dimer

The dynamical properties of quantum entanglement in an integrable quantum dimer are studied in terms of the reduced-density linear entropy with various coupling parameters and total boson numbers. The characteristic time of decoherence process in the early-time evolution of the linear entropy is obtained, indicating that the characteristic time and the corresponding entropy exhibit a maximum near the position of the corresponding classical separatrix energy.     

Phase separation and flux quantization in the doped quantum dimer model on square and triangular lattices

The doped two-dimensional quantum dimer model is investigated by numerical techniques on the square and triangular lattices, with significantly different results. On the square lattice, at small enough doping, there is always a phase separation between an insulating valence-bond solid and a uniform superfluid phase, whereas on the triangular lattice, doping leads directly to a uniform superfluid in a large portion of the resonating-valence-bond (RVB) phase. Under an applied Aharonov-Bohm flux, the superfluid exhibits quantization in terms of half-flux quanta, consistent with Q=2e elementary charge quanta in transport properties.     

Coherent electron transport in a Si quantum dot dimer

We show that the coherence of charge transfer through a weakly coupled double-dot dimer can be determined by analyzing the statistics of the conductance pattern, and does not require a large phase coherence length in the host material. We present an experimental study of the charge transport through a small Si nanostructure, which contains two quantum dots. The transport through the dimer is shown to be coherent. At the same time, one of the dots is strongly coupled to the leads, and the overall transport is dominated by inelastic cotunneling processes.     

量子环中量子比特的性质

通过精确求解能量本征方程获得量子环的电子能态,并利用电子的基态和第一激发态构造一个量子比特.对InAs/GaAs量子环的数值计算表明：当环尺寸给定时,量子比特内电子的概率密度分布与坐标位置及时间有关,在环内中心位置处电子出现的概率最大,电子的概率密度随柱坐标内的转角作周期性变化,并且各个空间点处的概率密度均随时间做周期性振荡. 关键词： 量子环 能量本征方程 电子能态 量子比特     

Criticality-enhanced quantum sensing in the anisotropic quantum Rabi model

Quantum systems that undergo quantum phase transitions exhibit divergent susceptibility and can be exploited as probes to estimate physical parameters. We generalize the dynamic framework for criticality-enhanced quantum sensing by the quantum Rabi model(QRM) to its anisotropic counterpart and derive the correspondingly analytical expressions for the quantum Fisher information(QFI). We fnd that the contributions of the rotating-wave and counterrotating-wave interaction terms are symmetric at the...     

Spectral and transport properties of the PT-symmetric dimer model

We study the scattering properties of the PT-symmetric tight-binding model with balanced gain and loss parameters. Our main interest is to establish the link between the spectral properties of scattering states and transport characteristics for the case of non-equal couplings between gain/loss sites. The analytical approach we have used allows one to reveal a quite unexpected role of this set-up in comparison with that of equal couplings. In particular, we demonstrate that for the exceptional points characterized by equal eigenvalues of the transfer matrix, the transmission coefficient can be different from one in contrast with the model with equal couplings. The analytical results are complemented by the numerical data.     

Properties of field quantum entropy evolution in the Jaynes--Cummings model with initial squeezed coherent states field

The properties of the field quantum entropy evolution in a system of a single-mode squeezed coherent state field interacting with a two-level atom is studied by utilizing the complete quantum theory, and we focus our attention on the discussion of the influences of field squeezing parameter $\gamma $, atomic distribution angle $\theta $ and coupling strength $g$ between the field and the atom on the properties of the evolution of field quantum entropy. The results obtained from numerical calculation indicate that the amplitude of oscillation of field quantum entropy evolution decreases with the increasing of squeezing parameter $\gamma $, and that both atomic distribution angle $\theta $ and coupling strength $g$ between the field and the atom can influence the periodicity of field quantum entropy evolution.     

HF dimer in small helium clusters: interchange-tunneling dynamics in a quantum environment

We present diffusion quantum Monte Carlo calculations of the interchange tunneling splitting of (4)He(n)(HF)(2) clusters, n = 1-10. The tunneling splitting decreases rapidly for n = 1-4 clusters, and much more slowly for n>4. The decrease calculated for (4)He(n)(HF)(2) represents 74% of the reduction in the tunneling splitting measured recently for HF dimer in nanodroplets of more than 2000 He atoms. The first four He atoms quench the interchange tunneling very efficiently by virtue of occupying the equatorial ring which encircles the C(2h) transition state of the tunneling pathway.     

Critical behavior of a three-dimensional dimer model

The phase transition behavior of a dimer model on a three-dimensional lattice is studied. This model is of biological interest because of its relevance to the lipid bilayer main phase transition. The model has the same kind of inactive low-temperature behavior as the exactly solvable Kasteleyn dimer model on a two-dimensional honeycomb lattice. Because of low-temperature inactivity, determination of the lowest-lying excited states allows one to locate the critical temperature. In this paper the second-lowest-lying excited states are studied and exact asymptotic results are obtained in the limit of large lattices. These results together with a finite-size scaling ansatz suggest a logarithmic divergence of the specific heat aboveT _c for the three-dimensional model. Use of the same ansatz recovers the exact divergence (α=1/2) for the two-dimensional model.     

Spin quantum tunneling via entangled states in a dimer of exchange-coupled single-molecule magnets

A new family of supramolecular, antiferromagnetically exchange-coupled dimers of single-molecule magnets (SMMs) has recently been reported. Each SMM acts as a bias on its neighbor, shifting the quantum tunneling resonances of the individual SMMs. Hysteresis loop measurements on a single crystal of SMM dimers have now established quantum tunneling of the magnetization via entangled states of the dimer. This shows that the dimer really does behave as a quantum mechanically coupled dimer, and also allows the measurement of the longitudinal and transverse superexchange coupling constants.