arXiv subjects

Chao Hang

Publications and source records attributed to Chao Hang.

28 records · Page 2Linked to original sources

arXiv2012

PT-symmetry with a system of three-level atoms

We show that a vapor of multilevel atoms driven by far-off resonant laser beams, with possibility of interference of two Raman resonances, is highly efficient for creating parity-time (PT) symmetric profiles of the probe-field refractive index, whose real part is symmetric and imaginary part is anti-symmetric in space. The spatial modulation of the susceptibility is achieved by proper combination of standing-wave strong control fields and of Stark shifts induced by a far-off-resonance laser field. As particular examples we explore a mixture of isotopes of Rubidium atoms and design a PT-symmetric lattice and a parabolic refractive index with a linear imaginary part.

physics.optics↗

arXiv2012

Stern-Gerlach Effect of Weak-Light Ultraslow Vector Solitons

We propose a scheme to exhibit Stern-Gerlach (SG) deflection of high-dimensional vector optical soliton (VOS) at weak-light level in a cold atomic gas via electromagnetically induced transparency. We show that the propagating velocity and generation power of such VOS can be reduced to $10^{-6}\,\,c$ ($c$ is light speed in vacuum) and lowered to magnitude of nanowatt, respectively. The stabilization of the VOS may be realized by using an optical lattice formed by a far-detuned laser field, and its trajectory can be deflected significantly by using a SG magnetic field. Deflection angle of the VOS can be of magnitude of $10^{-3}$ rad when propagating several millimeters. Different from atomic SG deflection, deflection angle of the VOS can be distinct for different polarization components and can be manipulated in a controllable way. The results obtained can be described in terms of a SG effect for the VOS with quasispin and effective magnetic moment.

physics.optics↗

arXiv2011

Highly Entangled Photons and Rapidly Responding Polarization Qubit Phase Gates in a Room-Temperature Active Raman Gain Medium

We present a scheme for obtaining entangled photons and quantum phase gates in a room-temperature four-state tripod-type atomic system with two-mode active Raman gain (ARG). We analyze the linear and nonlinear optical response of this ARG system and show that the scheme is fundamentally different from those based on electromagnetically induced transparency and hence can avoid significant probe-field absorption as well as temperature-related Doppler effect. We demonstrate that highly entangled photon pairs can be produced and rapidly responding polarization qubit phase gates can be constructed based on the unique features of enhanced cross-phase modulation and superluminal probe-field propagation of the system.

physics.optics↗

arXiv2011

Linear and Nonlinear Pulse Propagations in Lifetime-Broadened Atomic Media with Spontaneously Generated Coherence

The linear and nonlinear pulse propagations in lifetime-broadened three-state media with spontaneously generated coherence (SGC) are investigated theoretically. Three generic systems of V-, $Λ$-, and $Ξ$-type level configurations are considered and compared. It is shown that in linear propagation regime the SGC in the V-type system can result in a significant change of dispersion and absorption and may be used to completely eliminate the absorption and largely reduce the group velocity of a probe field. However, the SGC has no effect on the dispersion and absorption of the $Λ$- and $Ξ$-type systems. In nonlinear propagation regime, the SGC displays different influences on Kerr nonlinearity for different systems. Specifically, it can enhance the Kerr nonlinearity of the V-type system whereas weaken the Kerr nonlinearity of the $Λ$-type system. Using the SGC, stable optical solitons with ultraslow propagating velocity and very low pump power can be produced in the V-type system by exploiting only one laser field in the system.

physics.optics↗

arXiv2011

Fourier mode dynamics for the nonlinear Schroedinger equation in one-dimensional bounded domains

We analyze the 1D focusing nonlinear Schrödinger equation in a finite interval with homogeneous Dirichlet or Neumann boundary conditions. There are two main dynamics, the collapse which is very fast and a slow cascade of Fourier modes. For the cubic nonlinearity the calculations show no long term energy exchange between Fourier modes as opposed to higher nonlinearities. This slow dynamics is explained by fairly simple amplitude equations for the resonant Fourier modes. Their solutions are well behaved so filtering high frequencies prevents collapse. Finally these equations elucidate the unique role of the zero mode for the Neumann boundary conditions.

nlin.PS↗

arXiv2010

Analytical three-dimensional bright solitons and soliton-pairs in Bose-Einstein condensates with time-space modulation

We provide analytical three-dimensional bright multi-soliton solutions to the (3+1)-dimensional Gross-Pitaevskii (GP) equation with time and space-dependent potential, time-dependent nonlinearity, and gain/loss. The zigzag propagation trace and the breathing behavior of solitons are observed. Different shapes of bright solitons and fascinating interactions between two solitons can be achieved with different parameters. The obtained results may raise the possibility of relative experiments and potential applications.

nlin.SI↗

arXiv2010

All-optical steering of light via spatial Bloch oscillations in a gas of three-level atoms

A standing-wave control field applied to a three-level atomic medium in a planar hollow-core photonic crystal waveguide creates periodic variations of linear and nonlinear refractive indexes of the medium. This property can be used for efficient steering of light. In this work we study, both analytically and numerically, the dynamics of probe optical beams in such structures. By properly designing the spatial dependence of the nonlinearity it is possible to induce long-living Bloch oscillations of spatial gap solitons, thus providing desirable change in direction of the beam propagation without inducing appreciable diffraction. Due to the significant enhancement of the nonlinearity, such self-focusing of the probe beam can be reached at extremely weak light intensities.

physics.optics↗

arXiv2007

Weak-Light Ultraslow Vector Optical Solitons via Electromagnetically Induced Transparency

We propose a scheme to generate temporal vector optical solitons in a lifetime broadened five-state atomic medium via electromagnetically induced transparency. We show that this scheme, which is fundamentally different from the passive one by using optical fibers, is capable of achieving distortion-free vector optical solitons with ultraslow propagating velocity under very weak drive conditions. We demonstrate both analytically and numerically that it is easy to realize Manakov temporal vector solitons by actively manipulating the dispersion and self- and cross-phase modulation effects of the system.

physics.optics↗

arXiv2006

Three-Way Entanglement and Three-Qubit Phase Gate Based on a Coherent Six-Level Atomic System

We analyze the nonlinear optical response of a six-level atomic system under a configuration of electromagnetically induced transparency. The giant fifth-order nonlinearity generated in such a system with a relatively large cross-phase modulation effect can produce efficient three-way entanglement and may be used for realizing a three-qubit quantum phase gate. We demonstrate that such phase gate can be transferred to a Toffoli gate, facilitating practical applications in quantum information and computation.

quant-ph↗

arXiv2005

Controllable Entanglement of Lights in a Five-Level System

We analyze the nonlinear optical response of a five-level system under a novel configuration of electro-magnetically induced transparency. We show that a giant Kerr nonlinearity with a relatively large cross-phase modulation coefficient that occurs in such system may be used to produce an efficient photon-photon entanglement. We demonstrate that such photon-photon entanglement is practically controllable and hence facilitates promising applications in quantum information and computation.

quant-ph↗