Jiaxiang Wang

Scaling of entanglement at a quantum phase transition for a two-dimensional array of quantum dots

Using the Hubbard model, the entanglement scaling behavior in a two-dimensional itinerant system is investigated. It has been found that, on the two sides of the critical point denoting an inherent quantum phase transition (QPT), the entanglement follows different scalings with the size, just as an order parameter does. This fact reveals the subtle role played by the entanglement in QPT as a fungible physical resource.

SCALING OF ENTANGLEMENT IN FINITE ARRAYS OF EXCHANGE-COUPLED QUANTUM DOTS

We present a nite-size scaling analysis of the entanglement in a two-dimensional arrays of quantum dots modeled by the Hubbard Hamiltonian on a triangular lattice. Using multistage block renormalization group approach, we have found that there is an abrupt jump of the entanglement when a rst-order quantum phase transition occurs. At the critical point, the entanglement is constant, independent of the block size.

The interference effect of laser-assisted bremsstrahlung emission in Coulomb fields of two nuclei

In this paper, the spontaneous bremsstrahlung emission from an electron scattered by two fixed nuclei in an intense laser field is investigated in details based upon the Volkov state and the Dirac-Volkov propagator. It has been found that the fundamental harmonic spectrum from the electron radiation exhibits distinctive fringes, which is dependent not only upon the internucleus distance and orientation, but also upon the initial energy of the electron and the laser intensity. By analyzing the differential cross section, we are able to explain these effects in terms of interference among the electron scattering by the nuclei. These results could have promising applications in probing the atomic or molecular dressed potentials in intense laser fields.

Harmonic generation from free electrons in intense laser fields: classical versus semi-classical theory

In this paper, a detailed numerical comparison of the high-harmonic generation (HHG) from free electrons in intense laser fields in both classical and semi-classical frameworks has been presented. These two frameworks have been widely used in the literature. It has been found that the HHG spectra display distinct quantitative differences for high-energy electrons. In some special situations, qualitative differences appear. Even if the radiation reaction is included in the electron classical dynamics, no consistent result can be obtained. Hence it should be of critical importance to submit the present HHG theory for high-precision experimental tests, which can help us not only to justify the present theories, but also to check the QED predictions in the high-intensity regime.

Quantum phase transition in one-dimensional commensurate Frenkel-Kontorova model

We have studied the one-dimensional commensurate quantum Frenkel–Kontorova model by using a density-matrix renormalization group (DMRG) algorithm. The focus has been on its properties of entanglement, coordinate correlation, ground-state energy and energy gap between the ground state and the first excited state. It is demonstrated that a quantum phase transition (QPT) between the pinned and the sliding phases takes place as the quantum fluctuation, measured on the basis of an effective Planck constant \(\tilde{\hbar }\), increases to a threshold value \(\tilde{\hbar }_{c}\).

A Density-Matrix Renormalization Group Study of a One-Dimensional Incommensurate Quantum Frenkel–Kontorova Model

In this work, the one-dimensional incommensurate quantum Frenkel–Kontorova model is investigated using a density-matrix renormalization group algorithm. Special attention is given to the entanglement and ground-state energy. The energy gap between ground state and the first excited state is also calculated. From all the numerical results, we have observed clear property changes from the pinned state to the sliding state as the amount of quantum fluctuation is increased. However, no expected quantum critical point can be justified by the present data.

Influence of the intensity gradient upon HHG from free electrons scattered by an intense laser beam

When an electron is scattered by a tightly focused laser beam in vacuum, the intensity gradient is a critical factor to influence the electron dynamics. In this paper, we have further investigated its influence upon the electron high-harmonic generation (HHG) by treating the spacial gradient of the laser intensity as a ponderomotive potential. Based upon perturbative quantum electrodynamics calculations, it has been found that the main effect of the intensity gradient is the broadening of the originally line HHG spectra. A one-to-one relationship can be built between the beam width and the corresponding line width. Hence, this finding may provide us a promising way to measure the beam width of intense lasers in experiments. In addition, for a laser pulse, we have also studied the different influences from transverse and longitudinal intensity gradients upon HHG.