Nuclear-spin states of gaseous-state Cs atoms in the ground state are optically manipulated using a Ti: sapphire laser in a magnetic field of 1.516T, in which optical coupling of the nuclear-spin states is achieved through hyperfine interactions between electrons and nuclei. The steady-state population distribution in the hyperfine Zeeman sublevels of the ground state is detected by using a tunable diode laser. Furthermore, the state population transfer among the hyperfine Zeeman sublevels, which results from the collision-induced modification delta a( S . I) of the hyperfine interaction of Cs in the ground state due to stochastic collisions between Cs atoms and buffer-gas molecules, is studied at different buffer-gas pressures. The experimental results show that high-field optical pumping and the small change delta a( S . I) of the hyperfine interaction can strongly cause the state population transfer and spin-state interchange among the hyperfine Zeeman sublevels. The calculated results maybe explain the steady-state population in hyperfine Zeeman sublevels in terms of rates of optical-pumping, electron-spin flip, nuclear spin flip, and electron-nuclear spin flip-flop transitions among the hyperfine Zeeman sublevels of the ground state of Cs atoms. This method may be applied to the nuclear-spin-based solid-state quantum computation.

Variable-temperature hyperpolarized (HP) 129Xe NMR spectroscopy has been employed to characterize surface properties of mesoporous MCM-41 modified by silylation treatment. The characteristic chemical shifts responsible for Xe-surface interactions exhibit strong correlations with both the surface coverage and chain length of the grafted alkylsilanes. Consequently, the deshielding medium contribution due to individual alkyl ligand can be deduced based on the group contribution analysis revealing the potential use of HP 129Xe NMR for probing the surface properties of organic-functionalized porous materials.

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.

A summing algorithm is to evaluate and sum up a set of function samples. The paper [J. Phys. A. 35, L597(2001)] presented a new summing algorithm using ensemble computing which results in an exponential speedup. Here, we experimentally implemented the new algorithm on a four-qubit liquid state nuclear magnetic resonance ensemble system.

We have first successfully transferred the 129Xe polarization of natural isotopic composition to the proton of solid-state 1HCl via Spin Polarization-Induced Nuclear Overhauser Effect (SPINOE), by mixing the hyperpolarized 129Xe gas and the 1HCl gas and then cooling them to their condensated state in a flow system. The solid-state enhanced factor of the NMR signal of 6 for 1H was observed, and the equation of solid-state polarization enhancement via cross relaxation has also been theoretically deduced. Using this equation, the theoretically calculated enhancement is in agreement with the measured value within error. Also, this technique is maybe useful to establish a solid state NMR quantum computer.

We have successfully transferred the spin polarization of laser-polarized Xe-129 to the proton spins of solid-state (HCl)-H-1 via spin polarization-induced nuclear Overhauser effect (SPINOE). The key steps include mixing the laser-polarized Xe-129 gas with the (HCl)-H-1 gas and cooling them to their condensed state in a flow system. The solid-state nuclear magnetic resonance (NMR) signal enhancement factor of 6 for H-1 was observed, compared with the Boltzmann polarization signal at 1.879 T and 142 K. This method may be valuable for applications in both NMR spectroscopy and chemical physics.

We report production of hyperpolarized 129^Xe gas via spin-exchange with optically pumped Cs atoms at the D2 line, achieved at low magnetic field in a flow system and in the absence of nitrogen gas. The nuclear spin polarization of hyperpolarized 129^Xe gas is enhanced by a factor of 10000 compared to that without optical pumping under the same condition, which corresponds to polarization of about 2.66%. Due to the high spin polarization, the radiation damping of hyperpolarized 129^Xe gas has also been observed in the flow system.

In this study, we report an experiment realization of quantum superdense coding (QSDC) between three parties using nuclear magnetic resonance (NMR). The experimental results have shown that in terms of the QSDC schemes between multiparties proposed by Liu et al. and Crudka et al., three-qubit QSDC can transmit three bits of classical information by sending two qubits only. Our results experimentally show that quantum superdense coding, as one of the quantum information processing protocols, is superior to classical ones.

This paper presents a simple scheme for information transmission between two non-directly interactive qubits in an n-qubit system. An example has been realized on a three-qubit nuclear magnetic resonance (NMR) spectrometer quantum computer. The experimental result successfully demonstrates that the feasible measure can also be extended to other quantum logical gates, or other quantum algorithms, where some qubits have no direct interactions in a multi-qubit system.

The Deutsch-like algorithm [Phys. Rev. A. 63 (2001) 034101] distinguishes between even and odd query functions using fewer function calls than its possible classical counterpart in a two-qubit system. But the similar method cannot be applied to a multi-qubit system. We propose a new approach for solving Deutsch-like problem using ensemble computing. The proposed algorithm needs an ancillary qubit and can be easily extended to multi-qubit system with one query. Our ensemble algorithm beginning with a easily-prepared initial state has three main steps. The classifications of the functions can be obtained directly from the spectra of the ancilla qubit. We also demonstrate the new algorithm in a four-qubit molecular system using nuclear magnetic resonance (NMR). One hydrogen and three carbons are selected as the four qubits, and one of carbons is ancilla qubit. We choice two unitary transformations, corresponding to two functions (one odd function and one even function), to validate the ensemble algorithm. The results show that our experiment is successfully and our ensemble algorithm for solving the Deutsch-like problem is virtual.

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 transformationsU f 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 (U f ). 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.

We propose a scalable method on the basis of nth-order coupling operators to construct f-dependent phase transformations in the n-qubit modified Deutsch-Jozsa (D-J) quantum algorithm. The novel n-qubit entangling transformations are easily implemented via J-couplings between neighboring spins. The seven-qubit modified D-J quantum algorithm and seventh-order coupling transformations are then experimentally demonstrated with liquid state nuclear magnetic resonance (NMR) techniques. The method may offer the possibility of creating generally entangled states of n qubits and simulating n-body interactions on n-qubit NMR quantum computers.

We propose a simple scheme to create entangled states and realize information transmission between qubits with non-direct interactions on the basis of quantum superdense coding and swap operations. This may offer the possibility of applications in scalable quantum computers.

Laser-polarized Xe-129 gas was produced by spin-exchange with Cs atom optically pumped with diode laser array in a low field under flow. The nuclear spin polarizations of the solid and liquid Xe-129 frozen from the laser-polarized Xe-129 gas were 2.16% and 1.45% respectively in the SY-80M NMR spectrometer, which corresponded to the enhancements of 6000 and 5000 compared to those without optical pumping under the same conditions. It could provide the base and possibility for quantum computers using laser-enhanced solid and liquid 129Xe. Polarization loss of transport and state change also was discussed in this paper.

A generalized quantum search algorithm, where phase inversions for the marked state and the prepared state are replaced by π/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 π/2 and 3π/2, respectively. Pulse sequences which include non-90° pulses are given.

The NMR signal from the laser polarized 129 Xe in low pressure natural xenon gas has been observed with a Bruker WP 80SY NMR spectrometer. The laser polarized 129 Xe was produced by the method of laser pumping and spin exchange in a magnetic field of 1.87 Tesla. It is obtained experimentally that the nuclear spin relaxation rate 1/T 1 of laser polarized 129 Xe are (4.03±1.97)×10 -3 /sec～(2.21±0.78)×10 -3 /sec in the range of the 3.33×10 3 Pa～8.29×10 4 Pa Xe gas pressures, the apparent wall relaxation rate 1/T W *=(1.98±0.18)×10 -3 /sec, and the relaxation rate coefficient C of 133 Cs 129 Xe spin exchange is (2.81±0.74)×10 -16 cm 3/sec.

The controlled-NOT gate and controlled square-root NOT gate play an important role in quantum algorithm. This article reports the experimental results of these two universal quantum logic gates (controlled square-root NOT gate and controlled-NOT gate) on a 7-qubit NMR quantum computer. Further, we propose a simple experimental method to measure and correct the error in the controlled phase-shift gate, which is helpful to construct a more perfect phase-shift gate experimentally and can also be used in more qubits discrete Fourier transformation.

Cs atoms were optically pumped with a Ti:sapphire laser in a magnetic field of 1.516 T. Steady absorption spectra and populations of Zeeman sublevels of the ground state of Cs in N2 gas at various pressures (5, 40, and 80 Torr) were obtained. The results show that in a high magnetic field, the combined electron-nuclear spin transition (flip-flop transition), which is mainly induced by the collision modification δa(J · I) of hyperfine interaction, is an important relaxation mechanism at high buffer-gas pressures.

We report the experimental results of frequency-selective laser optical pumping and spin exchange of Cs with Xe-129 and Xe-131 in a high magnetic field of 11.74 T. Our results show that hyperpolarized Xe-129 and Xe-131 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 the Xe-129. The electron spin polarization of the Cs atoms has been measured to be about 22% with a simple NMR method.

Nuclear-magnetic-resonance (NMR) measurement of laser-polarized gaseous 129 Xe produced by spin-exchange optical pumping with a narrow-linewidth laser at a high magnetic field of 4.7 T is reported. The samples are contained in the glass tubes. The nuclear spin polarization of the laserpolarized 129 Xe is 3.9%, and this corresponds to an enhancement of 9· 10 3 compared to the equilibrium value at 311 K and at the same magnetic field. The laser-enhanced 129 Xe NMR signals can be used in MR imaging.