Alexei Chizhov

Shape transitions in excited states of two-electron quantum dots in a magnetic field

We use entanglement to study shape transitions in two-electron axially symmetric parabolic quantum dots in a perpendicular magnetic field. At a specific magnetic field value the dot attains a spherical symmetry. The transition from the axial to the spherical symmetry manifests itself as a drastic change of the entanglement of the lowest state with zero angular momentum projection. While the electrons in such a state are always localized in the plane (x − y) before the transition point, after this point they become localized in the vertical direction.

Photon statistics and phase properties of two-mode squeezed number states

Abstract Two-mode squeezed number states are defined. These states can be treated as a natural generalization of a two-mode squeezed vacuum state. The photon number statistics and the phase properties of these states are investigated. It is shown that the photon number distribution and the Pegg-Barnett phase distribution for such states have a similar (N+1)-peak structure for a nonzero value of the difference in the numbers of photons between the modes. Exact analytical formulas for phase distributions based on different phase approaches are derived. The Pegg-Barnett phase distribution and the phase quasiprobability distribution associated with the Wigner function are close to each other, while the phase quasiprobability distribution associated with the Q function carries less phase information. Analytical expressions for the Q function and the Wigner function for the two-mode squeezed number states are obtained.

Phase space distributions from three-port couplers

Abstract A wide class of phase space distributions of a single mode radiation field is shown to be directly accessible to measurement by linear symmetric three-port optical couplers.

A TWO-STEP OPTIMIZED MEASUREMENT FOR THE PHASE SHIFT

Abstract A two-step detection strategy is suggested for the precise measurement of the optical phase shift. In the first step an unsharp, but unbiased, joint measurement of the phase and photon number is performed by heterodyning the signal field. Information coming from this step is then used for appropriate squeezing of the probe mode to obtain a sharp phase distribution. Application to squeezed states leads to a phase sensitivity scaling as Δϕ ⋍ N −1 relative to the total number of photons impinged onto the apparatus. Numerical simulations of the whole detection strategy are also presented.

A geometrical crossover in excited states of two-electron quantum dots in a magnetic field

We use the entanglement measure to study the evolution of quantum correlations in two-electron axially-symmetric parabolic quantum dots under a perpendicular magnetic field. We found that the entanglement indicates on the shape transition in the density distribution of two electrons in the lowest state with zero angular momentum projection at the specific value of the applied magnetic field.

Quantum statistics of vacuum in a cavity with a moving mirror

Abstract We consider the electromagnetic field in a cavity when one of its mirrors can move along a given trajectory. Within a path-integral approach we calculate the Q -function of the electromagnetic field for individual modes inside the cavity and study the fluctuation properties of the field for different resonant cases.

On the vibron nature in the system of two parallel macromolecular chains: The influence of interchain coupling

Abstract We studied the properties of the intramolecular vibrational excitation (vibron) at finite temperature in a system which consists of two parallel macromolecular chains. It was assumed that vibron interacts exclusively with dispersionless optical phonons and the whole system is considered to be in thermal equilibrium. Particular attention has been paid to the examination of the impact of the temperature and strength of the interchain coupling on the small polaron crossover. For that purpose we employed partial dressing method which enables the study of the degree of the phonon dressing of the vibron excitations in a wide area of system parameter space. We found that in the non-adiabatic regime the degree of dressing as a function of coupling constant continuously increases reflecting the smooth transition of the slightly dressed, practically free vibron, to a heavily dressed one: small polaron. As “adiabaticity” rises this transition becomes increasingly steeper, and finally, in the adiabatic limit, a discontinuous “jump” of the degree of dressing is observed. The interchain coupling manifests itself through the increase of the effective adiabatic parameter of the system.

Vibron transport in macromolecular chains

We study the hopping mechanism of the vibron excitation transport in the simple 1D model of biological macromolecular chains. We supposed that the vibron interaction with thermal oscillations of the macromolecular structural elements will result in vibron self-trapping, and the formation of the partial dressed vibron state. With use of the modified Holstein polaron model, we calculate vibron diffusivity in dependence of the basic system parameters and temperature. We obtain that the vibron diffusivity smoothly decreases in non adiabatic limit when the strength of the vibron-phonon coupling grows. However this dependence becomes by discontinuous one in case of growth of the adiabaticity of the system. The value of the critical point depends of the system temperature, and at room temperatures it belongs to the low or intermediate coupling regime. We discuss an application of these results to study of vibron transport to 3D bundles of such macromolecules chains considering it as polymer nanorods and to 2D polymer films organized from such macromolecules.

On the vibron-polaron damping in quasi 1D macromolecular chains

The properties of the intramolecular vibrational excitation (vibron) in a quasi 1D macromolecular structure are studied. It is supposed that due to the vibron interaction with optical phonon modes, a vibron might form partially dressed small polaron states. The properties of these states are investigated in dependence on the basic system parameters and temperature of a thermal bath. We also investigate the process of damping of the polaron amplitude as a function of temperature and vibron-phonon coupling strength. Two different regimes of the polaron damping are found and discussed.

Vibron properties in quasi 1D molecular structures: the case of two parallel unshifted macromolecuar chains

We study the hopping mechanism of the vibron excitation transport in the system of two parallel unshifted 1D macromolecuar chains in the framework of non-adiabatic polaron theory. We suppose that the vibron interaction with thermal oscillations of the macromolecular structural elements will result in vibron self-trapping and the formation of the partial dressed vibron state. We also suppose that quasiparticle motion takes place via a sequence of random sitejumps, in each of which the quasiparticle can migrate either to the first neighbor site of the macromolecular chain. With use of the modified Holstein polaron model, we calculate the vibron effective mass in dependence of the basic system parameters and temperature. Special attention is paid to the influence of interchain coupling on vibron dressing. We find that for certain values of the system parameters the quasiparticle mass abruptly changes.