arXiv subjects

Da-Wei Wang

Publications and source records attributed to Da-Wei Wang.

60 records · Page 4Linked to original sources

arXiv2015

High-frequency Light Reflector via Low-frequency Light Control

We show that the momentum of light can be reversed via the atomic coherence created by another light with one or two orders of magnitude lower frequency. Both the backward retrieval of single photons from a timed Dicke state and the reflection of continuous waves by high-order photonic band gaps are analysed. The required control field strength scales linearly with the nonlinearity order, which is explained by the dynamics of superradiance lattices. Experiments are proposed with $^{85}$Rb atoms and Be$^{2+}$ ions. This holds promise for light-controllable X-ray reflectors.

physics.optics↗

arXiv2015

Superradiance Lattice

We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on electromagnetically induced transparency (EIT). For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective uniform force in momentum space. The quantum lattice dynamics, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing and dynamic localization can be observed in the SL. The two-dimensional SL provides a flexible platform for Dirac physics in graphene. The SL can be extended to three and higher dimensions where no analogous real space lattices exist with new physics waiting to be explored.

physics.atom-ph↗

arXiv2014

Heisenberg Limit Superradiant Superresolving Metrology

We propose a superradiant metrology technique to achieve the Heisenberg limit super-resolving displacement measurement by encoding multiple light momenta into a three-level atomic ensemble. We use $2N$ coherent pulses to prepare a single excitation superradiant state in a superposition of two timed Dicke states that are $4N$ light momenta apart in momentum space. The phase difference between these two states induced by a uniform displacement of the atomic ensemble has $1/4N$ sensitivity. Experiments are proposed in crystals and in ultracold atoms.

quant-ph↗

arXiv2014

Sideband generation of transient lasing without population inversion

We suggest a method to generate coherent short pulses by generating a frequency comb using lasing without inversion in the transient regime. We use a universal method to study the propagation of a pulse in various spectral regions through an active medium that is strongly driven on a low-frequency transition on a time scale shorter than the decoherence time. The results show gain on the sidebands at different modes can be produced even if there is no initial population inversion prepared. Besides the production of ultra-short pulse this frequency comb may have applications towards making short-wavelength or Tera-hertz lasers.

physics.optics↗

arXiv2012

An optical diode made from a `flying' photonic crystal

Optical diodes controlling the flow of light are of principal significance for optical information processing 1. They transmit light from an input to an output, but not in reverse direction. This breaking of time reversal symmetry is typically achieved via non-linear 2,3 or magnetic effects 4, which imposes limits to all-optical control 5-7, on-chip integration 7-11, or single-photon operation 12. Here, we propose an optical diode which requires neither magnetic fields nor strong input fields. It is based on a flying photonic crystal. Due to the Doppler effect, the crystal has a band gap with frequency depending on the light propagation direction relative to the crystal motion. Counter-intuitively, our setup does not involve the movement of any material parts. Rather, the flying photonic crystal is realized by optically inducing a spatially periodic but moving modulation of the optical properties of a near-resonant medium. The flying crystal not only opens perspectives for optical diodes operating at low light levels or integrated in small solid state devices, but also enables novel photonic devices such as optically tunable mirrors and cavities.

physics.optics↗

arXiv2011

High reflection emission assisted by phase compensation via anomalous dispersion

The reflection spectrum of a probe light in a -type three-level atomic system coupled by an off-resonant standing-wave is investigated experimentally and theoretically. We show that the maximum value of reflection coefficient occurs when both of the coupling and probe lights are tuned off resonances from the atomic transitions. The nature of enhanced reflection is attributed to the phase compensation caused by the anomalous dispersion, which leads to a significant reduction of nonlinear phase mismatch in atomic four-wave mixing. At certain detuning of coupling and probe frequencies near two-photon resonance, there exits a best compensation, so the reflection efficiency reaches its maximum. The dependences of efficiency on the intensity of coupling fields and the density of atoms are also studied.

quant-ph↗