Xizhi Zeng

Experimental NMR realization of a generalized quantum search algorithm

A generalized quantum search algorithm, where phase inversions for the marked state and the prepared state are replaced by pi /2 phase rotations, is realized in a 2-qubit NMR heteronuclear system. The quantum algorithm searches a marked state with a smaller step compared to standard Grover algorithm. Phase matching requirement in quantum searching is demonstrated by comparing it with another generalized algorithm where the two phase rotations are pi /2 and 3 pi /2, respectively. Pulse sequences which include non-90 degrees pulses are given

Laser-enhanced low-pressure gas NMR signal from 129Xe

Abstract We have greatly enhanced the nuclear magnetic resonance signal of low-pressure gas ( 15 Torr of 129 Xe) on an NMR spectrometer with linearly polarized laser radiation. An amplification factor of the nuclear polarization is of the order of magnitude of 10 4 as compared with the Boltzmann polarization in the same magnetic field.

Temperature properties of Na dispersive Faraday optical filter at D1 and D2 line

In this paper, investigations of a Na-atom dispersive Faraday optical filter that has been used in a narrow-band lidar of daytime operation are reported. We have constructed a Na Faraday optical filter and measured its transmission characteristics under the conditions of two different probe light beams from a CW laser and pulse Na fluorescent light, respectively. The analyses of temperature characteristics of the Na Faraday optical filter are given

Experimental realization of discrete fourier transformation on NMR quantum computers

We report the experimental implementation of discrete Fourier transformation (DFT) on a nuclear magnetic resonance (NMR) quantum computer. Experimental results agree well with the theoretical ones. With the pulse sequences that we propose and the refocusing pulse sequences that one uses to suppress unwanted one-spin and two-spin interactions, the DFT can, in principle, be realized on anyL-bit quantum number.

NMR study of low-pressure 129Xe gas

Abstract The enhanced 129 Xe gas (15 Torr) NMR signal has been observed on a Varian XL-200 NMR spectrometer with spin-exchange optical pumping. An amplification factor of the nuclear spin polarization of gaseous 129 Xe is of the order 10 3 times the Boltzmann polarization at 60°C. The binary spin-exchange cross section for Cs 129 Xe has been measured by observing the nuclear spin relaxation of 129 Xe in the presence of Cs vapor. The measured cross section is (1.7 ± 0.2) × 10 −20 cm 2 . The effect of diffusion of 129 Xe atoms on NMR signals is also discussed.

NMR experimental realization of seven-qubit D-J algorithm and controlled phase-shift gates with improved precision

In this study, we report the experimental realization of seven-qubit Deutsch-Jozsa (D-J) algorithm and controlled phase-shift gates with improved precision using liquid state nuclear magnetic resonance (NMR). The experimental results have shown that transformationsUf in the seven-qubit D-J algorithm have been implemented with different pulse sequences, and whetherf is constant or balanced is determined by using only a single function call (Uf). Furthermore, we propose an experimental method to measure and correct the error in the controlled phase-shift gate that is simple and feasible in experiments, and can have precise phase shifts. These may offer the possibility of surmounting the difficulties of low signal-to-noise ratio (SNR) in multi-qubit NMR quantum computers, more complicated experimental techniques, and the increase of gate errors due to using a large number of imperfect selective pulses. These are also applied to more complicated quantum algorithms with more qubits, such as quantum Fourier transformation and Shor’s algorithm.

A fast efficient passive cesium ARF

Abstract The properties of a passive cesium ARF (atomic resonance filter) are determined predominantly by the physical processes of absorption, emission and internal energy conversion in the cesium vapor. A fast efficient passive cesium ARF at 455 nm and 459 nm is demonstrated by the method of mixing molecular gas in the cesium vapor. The nominal maximum information rate of the passive cesium ARF, which is an important parameter for laser communication applications, is estimated by the fwhm (full width at half maximum) of the time-resolved fluorescence spectrum of its output emission at 852 nm.

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.

Frequency-selective laser optical pumping and spin exchange of cesium with Xe-129 and Xe-131 in a high magnetic field

We report the experimental results of frequency-selective laser optical pumping and spin exchange of Cs with129Xe and131Xe in a high magnetic field of 11.74 T. Our results show that hyperpolarized129Xe and131Xe nuclear magnetic resonance (NMR) signals exhibit alternating phases when the laser frequency for pumping the cesium atoms is changed, which is explained on the basis of the high-field optical pumping of Cs. We obtain about 3% polarization of the129Xe. The electron-spin polarization of the Cs atoms has been measured to be about 22% with a simple NMR method.