Chenzhi Yuan

Surface solitons of four-wave mixing in an electromagnetically induced lattice

By creating lattice states with two-dimensional spatial periodic atomic coherence, we report an experimental demonstration of generating two-dimensional surface solitons of a four-wave mixing signal in an electromagnetically induced lattice composed of two electromagnetically induced gratings with different orientations in an atomic medium, each of which can support a one-dimensional surface soliton. The surface solitons can be well controlled by different experimental parameters, such as probe frequency, pump power, and beam incident angles, and can be affected by coherent induced defect states.

Generalized criterion for a maximally multi-qubit entangled state

We first present a generalized criterion for maximally entangled states of 2–8 and in theory to arbitrary-number qubits. By this criterion, some known highly entangled multi-qubit states are examined and a new genuine eight-qubit maximally entangled state is obtained. For the four-, seven- and eight-qubit system in which no perfect maximally multi-qubit entangled state (MMES) was thought to exist before, we find that the proven four- and eight-qubit MMESs and the suspected seven-qubit MMES, are not completely mixed in subsystems with two, four and three qubits, respectively, but are completely mixed in subsystems with fewer qubits. The new criterion and MMES can play important roles in quantum information technology, such as teleportation and dense coding.

Controllable Multiwave Mixing Talbot Effect

We theoretically study the Talbot effects resulted from the four-wave mixing and six-wave mixing signals, which are periodically modulated due to the coherence control effect. Corresponding to different dressing states, the enhancement and suppression conditions that will affect the properties of the multiwave mixing signals are also discussed in detail. Such proposal can be useful in all-optical-controlled pattern formation and propagation of light.

Optical vortices induced in nonlinear multilevel atomic vapors

In a numerical investigation, we demonstrate the existence and curious evolution of vortices in a ladder-type three-level nonlinear atomic vapor with linear, cubic, and quintic susceptibilities considered simultaneously with the dressing effect. We find that the number of beads and topological charge of the incident beam, as well as its size, greatly affect the formation and evolution of vortices. To determine the number of induced vortices and the corresponding rotation direction, we give common rules associated with the initial conditions coming from various incident beams.

Multicharged optical vortices induced in a dissipative atomic vapor system

We investigate numerically the dynamics of optical vortex beams carrying different topological charges, launched in a dissipative three level ladder type nonlinear atomic vapor. We impose the electromagnetically induced transparency (EIT) condition on the medium. Linear, cubic, and quintic susceptibilities, considered simultaneously with the dressing effect, are included in the analysis. Generally, the beams slowly expand during propagation and new vortices are induced, commonly appearing in oppositely charged pairs. We demonstrate that not only the form and the topological charge of the incident beam, but also its growing size in the medium greatly affect the formation and evolution of vortices. We formulate common rules for finding the number of induced vortices and the corresponding rotation directions, stemming from the initial conditions of various incident beams, as well as from the dynamical aspects of their propagation. The net topological charge of the vortex is conserved during propagation, as it should be, but the total number of charges is not necessarily same as the initial number, because of the complex nature of the system. When the EIT condition is lifted, an enhancement region of beam dynamics if reached, in which the dynamics and the expansion of the beam greatly accelerate. In the end, we discuss the liquid like behavior of light evolution in this dissipative system and propose a potential experimental scheme for observing such a behavior.

Observation of multi-component spatial vector solitons of four-wave mixing

We report the observation of multi-component dipole and vortex vector solitons composed of eight coexisting four-wave mixing (FWM) signals in two-level atomic system. The formation and stability of the multi-component dipole and vortex vector solitons are observed via changing the experiment parameters, including the frequency detuning, powers, and spatial configuration of the involved beams and the temperature of the medium. The transformation between modulated vortex solitons and rotating dipole solitons is observed at different frequency detunings. The interaction forces between different components of vector solitons are also investigated.

Four-Photon Imaging with Thermal Light

In a near-field four-photon correlation measurement, ghost imaging with classical incoherent light is investigated. By applying the Klyshko advanced-wave picture, we consider the properties of four-photon spatial correlation and find that the fourth-order spatial correlation function can be decomposed into multiple lower-order correlation functions. On the basis of the spatial correlation properties, a proof-of-principle four-photon ghost imaging is proposed, and the effect of each part in a fourth-order correlation function on imaging is also analyzed. In addition, the similarities and differences among ghost imaging by fourth-, second-, and third-order correlations are also discussed. It is shown that the contrast and visibility of fourth-order correlated imaging are improved significantly, while the resolution is unchanged. Such studies can be very useful in better understanding multi photon interference and multi-channel correlation imaging.

Observation of eight-wave mixing via electromagnetically induced transparency

We successfully observed the nonlinear eight-wave mixing (EWM) signal via one electromagnetically induced transparency (EIT) window and double optical pumping channels in an open five-level atomic system of 87Rb. By carefully controlling the arrangement of the incident laser beams, the corresponding four-wave mixing (FWM), six-wave mixing (SWM) and EWM signals can be made to coexist with similar signal amplitudes and transmit through the same EIT window in such open five-level atomic system.

Third-Order Self-Imaging with Thermal Light

Two kinds of theoretical schemes of third-order self-effect are proposed and analyzed, in which self-images of the object can be observed nonlocally in the two reference detectors. Plentiful self-imaging effects is presented in scheme I, where diffraction pattern of the periodic structure can be enlarged or diminished. In the scheme II, Talbot length is doubled that of the scheme I and the resolution may be improved by a factor of 2, and even higher. In the last, we discuss the similarities and the differences between self-imaging by third- and second-order process.

Resolution and Contrast Enhancement of Correlated Imaging in Photon Counting Regime

We theoretically discuss the four-photon spatial correlation property under different detection schemes. Compared with the two- and three-photon spatial correlation of thermal light source, we found that the enhancement in the visibility and the contrast when the fourth-order spatial correlation function is measured with quadruple coincidence measurement in the single photon counting regime. The resolution, however, is not changed when we scan three of four detectors with identical speed and direction. But if we scan two of three detectors in opposite directions and same speed, simultaneously, other two in identical direction and speed of one detector is twice of that of the other, we can see that both the contrast and resolution are improved significantly. We also show that the conclusion can be applied to the Nth-order ghost imaging.