Chun-Hua Yuan

Voltage-controlled slow light in asymmetry double quantum dots

The authors demonstrate theoretically that there exists electromagnetically induced transparency in an asymmetric double quantum dot system using tunneling instead of pump laser. The group velocity slowdown factor is theoretically analyzed as a function of electron tunneling at different broadened linewidths. With feasible parameters for applications to a 100Gbits∕s optical network, numerical calculation infers group velocity as low as 300m∕s. The scheme is expected to be useful in constructing a variable semiconductor optical buffer based on electromagnetically induced transparency in an asymmetric double quantum dot controlled by voltage.

The phase sensitivity of an SU(1,1) interferometer with coherent and squeezed-vacuum light

We theoretically study the phase sensitivity of an SU(1,1) interferometer with a coherent state in one input port and a squeezed-vacuum state in the other input port using the method of homodyne detection. In this interferometer, beam splitting and recombination are generated by the parametric amplifiers instead of the beam splitters. Compared with the traditional Mach–Zehnder interferometer, the phase sensitivity of this interferometer can be improved due to the amplification process of the parametric amplifiers. Combined with the squeezed state input, the sensitivity can be improved further due to the noise reduction. The phase sensitivity of our scheme can approach the Heisenberg limit and the associated optimal condition is analyzed. The scheme can be implemented with current experimental technology.

Slow light control with electric fields in vertically coupled InGaAs/GaAs quantum dots

Tunneling-induced transparency in vertically coupled InGaAs/GaAs quantum dots using tunneling instead of pump laser, analogous to electromagnetically induced transparency in atomic systems, is studied. The interdot quantum coupling strength is tuned by static electric fields. The group velocity slow-down factor is theoretically analyzed as a function of electron tunneling at different broadened linewidths. For parameters appropriate to a 100 Gbits/s optical network, group velocities as low as 850 m/s are calculated. The scheme is expected to be useful to construct a variable semiconductor optical buffer based on electromagnetically induced transparency in vertically coupled InGaAs/GaAs quantum dots controlled by electric fields.

Enhanced Raman scattering by spatially distributed atomic coherence

We demonstrate experimentally an enhancement in Raman scattering in Rb atomic vapor due to the atomic coherence initially prepared by a weak write laser. We find that the enhanced Raman scattering depends on the spatial distribution of the atomic spin coherence and can be explained with a simple picture of three-wave mixing. This effect can in principle be used to have a light conversion efficiency near unity in Raman process. Such an enhanced Raman scattering may have practical applications in quantum information, nonlinear optics, and laser spectroscopy.

Observation of the Rabi oscillation of light driven by an atomic spin wave.

Coherent conversion between a Raman pump field and its Stokes field is observed in a Raman process with a strong atomic spin wave initially prepared by another Raman process operated in the stimulated emission regime. The oscillatory behavior resembles the Rabi oscillation in atomic population in a two-level atomic system driven by a strong light field. The Rabi-like oscillation frequency is found to be related to the strength of the prebuilt atomic spin wave. High conversion efficiency of 40% from the Raman pump field to the Stokes field is recorded and it is independent of the input Raman pump field. This process can act as a photon frequency multiplexer and may find wide applications in quantum information science.

Coherently enhanced Raman scattering in atomic vapor

We present a scheme to obtain the coherently enhanced Raman scattering in atomic vapor which is induced by a spin wave initially written by a weak write laser. The enhancement of Raman scattering is dependent on the number and the spatial distribution of the flipped atoms generated by the weak write laser. Such an enhanced Raman scattering may have practical applications in quantum information, nonlinear optics, and laser spectroscopy because of its simplicity.

Correlation-enhanced phase-sensitive Raman scattering in atomic vapors

We theoretically propose a method to enhance Raman scattering by injecting a seeded light field which is correlated with the initially prepared atomic spin wave. Such a light-atom correlation leads to an interference in the Raman scattering. The interference is sensitive to the relative phase between the seeded light field and initially prepared atomic spin wave. For constructive interference, the Raman scattering is greatly enhanced. Such an enhanced Raman scattering may find applications in quantum information, nonlinear optics and optical metrology due to its simplicity.

Efficient Raman frequency conversion by coherent feedback at low light intensity

We experimentally demonstrate efficient Raman conversion to respective Stokes and anti-Stokes fields in both pulsed and continuous modes with a Rb-87 atomic vapor cell. The conversion efficiency is about 40-50% for the Stokes field and 20-30% for the anti-Stokes field, respectively. This efficient conversion process is realized with coherent feedback of both the Raman pump and the frequency-converted fields (Stokes or anti-Stokes). The experimental setup is simple and can be applied easily to produce light sources with larger frequency shifts using other Raman media with long coherence time. They may have potential applications in nonlinear optics, Raman spectroscopy and precision measurement.

Generation of a single-photon source via a four-wave mixing process in a cavity

It is shown that an efficient, well-directional single-photon source can be realized via a four-wave mixing process in a cavity. The probability of producing a single-photon state nearly approaches 50%. The bandwidth of single-photons generated in this way is controllable, which is determined by that of the input pulse. Furthermore, we propose a scheme to generate a coherent multichannel single-photon source, which might have significant applications in wavelength division multiplexing quantum key distribution.

SU(1,1)-type light-atom-correlated interferometer

The quantum correlation of light and atomic collective excitation can be used to compose an SU(1,1)-type hybrid light-atom interferometer, where one arm in the optical SU(1,1) interferometer is replaced by the atomic collective excitation. The phase-sensing probes include not only the photon field but also the atomic collective excitation inside the interferometer. For a coherent squeezed state as the phase-sensing field, the phase sensitivity can approach the Heisenberg limit under the optimal conditions. We also study the effects of the loss of light field and the dephasing of atomic excitation on the phase sensitivity. This kind of active SU(1,1) interferometer can also be realized in other systems, such as circuit quantum electrodynamics in microwave systems, which provides a different method for basic measurement using the hybrid interferometers.