Yang Xiao-Xue

Laser-polarization-dependent spontaneous emission of the zero phonon line from single nitrogen–vacancy center in diamond

We investigate spontaneous emission properties and control of the zero phonon line (ZPL) from a diamond nitrogen–vacancy (NV) center coherently driven by a single elliptically polarized control field. We use the Schrodinger equation to calculate the probability amplitudes of the wave function of the coupled system and derive analytical expressions of the spontaneous emission spectra. The numerical results show that a few interesting phenomena such as enhancement, narrowing, suppression, and quenching of the ZPL spontaneous emission can be realized by modulating the polarization-dependent phase, the Zeeman shift, and the intensity of the control field in our system. In the dressed-state picture of the control field, we find that multiple spontaneously generated coherence arises due to three close-lying states decaying to the same state. These results are useful in real experiments.

SU(2) Coherent State Description of Two-Mode Bose–Einstein Condensates*

We show that the evolution equations for mean quantities such as atom numbers and the inter-mode correlation for two-mode Bose-Einstein condensates form a closed set of equations in the SU(2) coherent state description, and they are identical in form to the two-mode mean-field model with only a slightly reduced two-body interaction strength. The exact analytical solutions to the evolution equations are also presented.

Exact analytical solutions to the two-mode mean-field model describing dynamics of a split Bose-Einstein condensate

We present the analytical solutions to the two-mode mean-field model for a split Bose-Einstein condensate. These explicit solutions completely determine the systems dynamics under the two-mode mean-field approximation for all possible initial conditions.

Ultra-slow Bright and Dark Optical Solitons in Cold Media

We present a systematic study on the formation of ultra-slow bright and dark optical solitons in highly resonant media. By investigating four life-time broadened atomic systems, i.e., three-state Λ-type and cascade-type schemes, and four-state N-type and cascade-type schemes, we show that the formation of such ultra-slow solitons in cold atomic systems is a fairly universal phenomenon.

Multiphoton Squeezed States

We present analytical results for the multiphoton squeezed states defined through nonlinear quadrature-dependent Bogoliubov transformations. These analytical results turn a nonlinear problem into an essentially linear one and they can. be utilized to express explicitly the mean values and deviations of the quadrature operators and the photon variables under the multiphoton states in terms of those quantities averaged over the standard squeezed states which only involves the quadrature-independent Bogoliubov transformation.

Effective Raman Theory for a Three-Level Atom in the V-Configuration*

It is shown that the system of a three-level atom coupled with two modes of quantized cavity fields in the V-configuration with arbitrary detunings can be exactly reduced to a two-level system with a nonsingular effective coupling which depends nonlinearly on the intensity of the two cavity fields. By performing a unitary transformation, we obtain an exact transformed Hamiltonian in which one of the three levels is decoupled for all values of the detunings including the zero-detuning. We also present the analytical expressions of energy eigenvdues and eigenvectors, evolution operator, time-varying atomic inversion operator and photon number operators of the two modes for the effective two-level model.

Effective Two-State Model and NOON States for Double-Well Bose-Einstein Condensates in Strong-Interaction Regime

The model of double-well Bose–Einstein condensates in the strong-interaction regime is shown to reduce adiabatically to an effective two-state model describing the Rabi oscillations between the two atomic Fock states |N, 0〉 and |0, N〉, and the NOON states of arbitrary ultracold atoms can therefore be generated periodically from the initial state of either one of the Fock states.

Bare-state time-evolving operator solution to Raman model in a configuration

We derive exact analytical expressions of time-evolving bare-state operators of level occupation numbers and the photon numbers for a composite system consisting of a three-level atom interacting with two modes of a quantized electromagnetic held in A configuration. These results demonstrate the oscillations with three-family frequencies for a nonzero detuning, which dramatically differ from the previous results showing only single-family Rabi oscillations.

Novel formalism for energy eigenvalue problem with Hamiltonian expressible as function of angular momentum

We present a novel formalism for energy eigenvalue problems when the corresponding Hamiltonians can be expressed as a function of an angular momentum. The problems are turned into finding operator polynomials by solving a c-number differential equation. Simple and efficient computer-aided analytical and numerical methods may be developed based on the formalism.

A Simple Method to Obtain Exact Soliton Solutions for a Nonlinear Equation in a Loss Fibre System

We show that the nonlinear equation governing wave propagation in a loss fibre system considered by Nakkeeran in J. Phys. A34 (2001) 5111 can be brought into the standard nonlinear Schrodinger equation by a simple transformation.