Mingsheng Zhan

Multi-output programmable quantum processor

By combining telecloning and the programmable quantum gate array presented by Nielsen and Chuang [Phys. Rev. Lett. 79, 321 (1997)], we propose a programmable quantum processor which can be programmed to implement a restricted set of operations with several identical data outputs. The outputs are approximately transformed versions of input data. The processor successes with certain probability.

Experiment and dynamic simulations of radiation damping of laser-polarized liquid129Xe at low magnetic field in a flow system

Radiation damping is generally observed when a sample with high spin concentration and high gyromagnetic ratio is placed in a high magnetic field. However, we firstly observed liquid-state129Xe radiation damping with laser-enhanced nuclear polarization at low magnetic field in a flow system in which the polarization enhancement factor for the liquid-state129Xe was estimated to be 5000, and, furthermore, theoretically simulated the envelopes of the129Xe free induction decay and spectral lineshape in the presence of both relaxation and radiation damping with different pulse flip angles and ratios ofT2*/Trd. The radiation damping time constantTrd of 5 ms was derived on the basis of the simulations. The reasons of depolarization and the further possible improvements were also discussed.

Realization of a decoherence-free subspace using multiple quantum coherences

This Letter presents a two-dimensional nuclear magnetic resonance (NMR) approach for constructing a two-logical-qubit decoherence-free subspace (DFS) by using four multiple-quantum coherences of a CH3 spin system as logical qubits. The three protons in this spin system are magnetically equivalent and can only be used as a single qubit in one-dimensional NMR. We have experimentally demonstrated that our DFS can protect against more types of decoherences than those of the one composed of four noisy physical qubits all with different chemical shifts. This idea may provide new insights into extending qubit systems in the sense that it effectively utilizes the magnetically equivalent nuclei.

Entangling Two Individual Atoms of Different Isotopes via Rydberg Blockade.

We report on the first experimental realization of the controlled-not (cnot) quantum gate and entanglement for two individual atoms of different isotopes and demonstrate a negligible cross talk between two atom qubits. The experiment is based on a strong Rydberg blockade for ^{87}Rb and ^{85}Rb atoms confined in two single-atom optical traps separated by 3.8u2009u2009μm. The raw fidelities of the cnot gate and entanglement are 0.73±0.01 and 0.59±0.03, respectively, without any corrections for atom loss or trace loss. Our work has applications for simulations of many-body systems with multispecies interactions, for quantum computing, and for quantum metrology.

Laser frequency stabilization based on Sagnac interferometric spectroscopy

A simple method based oil Saguac interferometric spectroscopy (SIS) is applied for frequency stabilization of diode lasers. Saguac interferometric spectra of rubidium vapor are investigated both theoretically and experimentally. The interference signal at, the output of the Saguac interferometer displays a sharp dispersion feature near the atomic resonance. This dispersion curve is used as the feedback error signal to stabilize the laser frequency. Linewidth of a diode laser is stabilized down to 1 MHz by this modulation-free method.

Control of optical bistability in the nonlinear regime of two-sided cavity quantum electrodynamics

We investigate the optical bistability behavior of a two-sided cavity quantum electrodynamics system. The non-linear input - output relation of the atom - cavity system coupled by two input light fields from two ends of the cavity can be controlled by a control light from the free space. Different from the common optical bistability phenomenon in the atom - cavity system, two separate bistability regions are observed. The bistability threshold and hysteresis loop can be well controlled by the control light. Because of field interference, the output light intensity becomes different with varying the relative phase of two incident fields. The output field intensity at the threshold of the first bistability region approaches zero with either increasing the detuning or lowering the intensity of the control light; thus, the perfect photon absorption condition is extended and a broadband near-perfect photon absorber is realized. Furthermore, we show an asymmetrical transmission feature due to field interference

Narrowband switchable dual-passband atomic filter with four-wave mixing optical amplification

By using Faraday optical filter combined with four-wave mixing (FWM) amplifier, a narrow bandwidth optical amplifying atomic filter with switchable dual-passband is demonstrated experimentally. The two transmission peaks of the filter correspond to the Stokes and anti-Stokes frequencies, exhibiting a Raman gain in 13- and 17-fold, respectively, with bandwidth of ?120 MHz. By properly setting pump laser detuning, switching between filter passbands is realized. We also investigate the dependence of peak transmission on both pump laser intensity and Rb cell temperature. This atomic filter can find practical applications in long-distance laser communications and laser remote-sensing systems.

Experimental demonstration of controllable double magneto-optical traps on an atom chip

We demonstrate controllable double magneto-optical traps (DMOTs) on an atom chip: At first, DMOTs, which trap atoms directly from the background rubidium vapor in an ultrahigh-vacuum environment, are realized on an atom chip simultaneously. The double quadrupole magnetic fields are produced by two separate U-shaped microwires on the atom chip, combined with a bias magnetic field. Then, we determine the best parameters for a U-shaped magneto-optical trap (UMOT) through a detailed comparison of the capture ability at different currents and the bias magnetic field between two different geometric sizes of UMOT. Finally, we demonstrate the mixing and splitting of the DMOTs on the atom chip with the help of an extra pair of anti-Helmholtz coils

Note: A compact low-vibration high-performance optical shutter for precision measurement experiments

The optical shutter is an important component for atom-interferometry-based precision measurements. To decrease its vibration noise and improve its performance, we present a compact design with a direct current motor and a photodetector inserted in a compact aluminum structure. The photodetector in the blade is driven by the motor to move either in or out of the way of the laser beam. This design can suppress laser intensity fluctuation down to 0.26% over 6 h in the method of sample and hold proportional-integral-derivative feedback. It is also quiet via an electrical braking process which not only reduces its vibration noise by an order of magnitude but also quickens and stabilizes its switching performance. The shutter has a switching time of 0.8 ms and an activation delay of 8 ms with low jitters. Besides, the shutter can work for over ten million cycles normally and reliably.

Realization of a compact one-seed laser system for atom interferometer-based gravimeters

A simple and compact design of the laser system is important for realization of compact atom interferometers (AIs). We design and realize a simple fiber bench-based 780-nm laser system used for 85Rb AI-based gravimeters. The laser system contains only one 780 nm seed laser, and the traditional frequency-doubling-module is not used. The Raman beams are shared with one pair of the cooling beams by using a liquid crystal variable retarder based polarization control technique. This laser system is applied to a compact AI-based gravimeter, and a best gravity measurement sensitivity of 230 μGal/Hz1/2 is achieved. The gravity measurements for more than one day are also performed, and the long-term stability of the gravimeter is 5.5 μGal.