Ying-Yen Liao

Spin relaxation in a GaAs quantum dot embedded inside a suspended phonon cavity

The phonon-induced spin relaxation in a two-dimensional quantum dot embedded inside a semiconductor slab is investigated theoretically. An enhanced relaxation rate is found due to the phonon van Hove singularities. Oppositely, a vanishing deformation potential may also result in a suppression of the spin relaxation rate. For larger quantum dots, the interplay between the spin orbit interaction and Zeeman levels causes the suppression of the relaxation at several points. Furthermore, a crossover from confined to bulklike systems is obtained by varying the width of the slab.

Rotational entangled states between two coupled molecules

A method is proposed to create entanglement between two coupled identical polar molecules separated at a distance of tens of nanometres. Entangled states of two coupled polar molecules controlled by half-cycle pulses are studied theoretically. The von Neumann entropy is calculated to characterize the degree of entanglement. By varying the pulse shape of the applied laser, transition from regular to irregular behaviour occurs. Moreover, the entanglement is also found to be enhanced by applying multiple laser pulses. The behaviour from quantum to classical limit is also discussed.

Alignment and orientation of absorbed dipole molecules

Half-cycle laser pulse is applied on an absorbed molecule to investigate its alignment and orientation behavior. Crossover from field-free to hindered rotation motion is observed by varying the angel of hindrance of potential well. At small hindered angle, both alignment and orientation show sinusoidal-like behavior because of the suppression of higher excited states. However, mean alignment decreases monotonically as the hindered angle is increased, while mean orientation displays a minimum point at certain hindered angle. The reason is attributed to the symmetry of wavefunction and can be explained well by analyzing the coefficients of eigenstates.

Bell states and entanglement of two-dimensional polar molecules in electric fields

Abstract Entanglement generated from polar molecules of two-dimensional rotation is investigated in a static electric field. The electric field modulates the rotational properties of molecules, leading to distinctive entanglement. The concurrence is used to estimate the degree of entanglement. When the electric field is applied parallel or perpendicular to the intermolecular direction, the concurrences reveal two overlapping features. Such a pronounced signature corresponds to the coexistence of all Bell-like states. The characteristics of Bell-like states and overlapping concurrences are kept independent of the modulation of dipole–field and dipole–dipole interactions. On the contrary, the Bell-like states fail to coexist in other field directions, reflecting nonoverlapping concurrences. Furthermore, the thermal effect on the entanglement is analyzed for the Bell-like states. Dissimilar suppressed concurrences occur due to different energy structures for the two specific field directions. Graphical abstract

Orientation of adsorbed molecules under the influence of electric fields

ABSTRACT The dynamic orientation of vertically adsorbed polar molecules is investigated by switching on electric fields. The rotational properties of molecules are modulated by the electric field and the conical well. The orientation reveals multiple pronounced oscillations, depending on the specific field parameters. The range of oscillation is enhanced even in the presence of conical-well confinement. Furthermore, population concentration and inversion cyclically occur in the system, corresponding to distinctive molecular orientations. Specific field-free orientation is also obtained by turning off the field. The population can be concentrated or reversed for a long time. The thermal effect on the properties of orientation is analysed in detail.

Electric-field-controlled electron relaxation in lateral double quantum dots embedded in a suspended slab

This study investigates phonon-induced electron relaxation in a lateral double quantum dot that is embedded in a suspended slab. Exact calculations are made in electric fields. The dependence of the relaxation rate on the parameters of the dots and the slabs is analyzed. Numerical results indicate that the relaxation rate depends strongly on the phonon character of the slab. Unlike in the bulk environment, phonon-subband quantization clearly influences the behavior. In particular, the relaxation rate can be greatly suppressed or enhanced by tuning the electric fields. This fact may be useful in manipulating the relaxation rate in lateral double quantum dots.