Control the relaxation properties of the diffuse bistable potential

The purpose of this work is to investigate procedures to control the population dynamics in a bistable potential. We use the solutions of the Fokker–Planck equation for the distribution function corresponding to a bistable potential under action of an external electric field. The control is performed with a piecewise protocol with time independent potentials. This protocol provides to be adequate for this problem, controlling the time necessary to balance of system probabilities. Some trajectories were controlled and the limits of procedure clarified. Nevertheless, with the application of the control protocol we clarify some simple phenomena of the system, associating the application of the external field with the system diffusion coefficient.     

Finite time thermodynamic analysis of quantum Otto heat engine with squeezed thermal bath

We investigate the finite time performance of reciprocating quantum Otto heat engine coupled to squeezed hot reservoir. We emphasize the converged limit cycle where each stroke is performed in finite time. To fully exploit the quantum availability provided by the squeezed bath, an optimal frequency protocol in the work extraction stroke is explicitly proposed. The power output is optimized with respect to the hot and cold isochore times. Thermodynamic analysis shows that for a wide range of squeezing parameters, efficiency at maximum power exceeds the generalized Curzon–Ahlborn efficiency defined by the effective temperature of the squeezed bath.     

Experimental study of the dynamic Newtonian field with a cryogenic gravitational wave antenna

We present an experiment performed to study the behaviour of the dynamic gravitational interaction at laboratory scale. We used as field generator a mass quadrupole rotating in the range of 460 Hz and we detected the acceleration field with the cryogenic gravitational wave antenna Explorer of the Rome group. We report the measurements of this interaction as a function of the distance between the field source and the detector. An upper limit on the parameters of a Yukawa-like potential, modeling an hypotetic deviation from the Newtonian law of gravity, is derived. Received: 14 June 1998 / Published online: 16 September 1998     

Comparison of discharge lamp and laser pumped cesium magnetometers

We have performed a comparison of laser (LsOPM) and lamp (LpOPM) pumped cesium vapor magnetometers. Although the LsOPM operated 50% above its shot-noise limit we found an intrinsic sensitivity of 15 fT/√Hz and 25 fT/√Hz for the LsOPM and the LpOPM, respectively. Two modes of operation, viz. the phase-stabilized and the self-oscillating modes, were investigated and found to yield a similar performance. We have compared the performance of the LsOPM and the LpOPM directly by simultaneous measurements of field fluctuations of a 2-μT magnetic field inside a multilayer magnetic shield and have used one of the magnetometers for an active field stabilization. In the stabilized mode we found a gradient instability of 25 fT within an integration time of 100 s, which represents an upper limit of the long-term stability of the magnetometers. Our research is motivated by the need for an improved control of magnetic fields and gradients in a planned neutron electric dipole experiment.This revised version was published online in August 2005 with a corrected cover date.     

Stress aging in the electron glass

A new protocol for an aging experiment is studied in the electron-glass phase of indium-oxide films. In this protocol, the sample is exposed to a non-Ohmic electric field F for a waiting time t(w) during which the system attempts to reach a steady state (rather than relax towards equilibrium). The relaxation of the excess conductance Delta G after Ohmic conditions are restored exhibits simple aging as long as F is not too large.     

Harmonic generation by an intense laser pulse in neutral andionized gases

Reported are the results of a harmonic generation experiment in a simple gas (hydrogen) using 1-ps, 1-μm laser pulses with a range of intensities extending from below to far above the laser ionization saturation threshold. The scaling with intensity above saturation of the third harmonic generated by a single laser-pulse in a filled gas cell is observed not to fit with a simple model that takes into consideration volume ionization effects alone. In another experiment, a pump-probe type, an upper limit on the conversion efficiency of third-harmonic generation in a preformed plasma is determined. It is found to be in agreement with the efficiency predicted by a relativistic harmonic generation theory     

Scheme to Implement Optimal Asymmetric Economical Phase-Covariant Quantum Cloning in Cavity QED

We propose an experimentally feasible scheme to implement the optimal asymmetric economical 1→2 phase-covariant quantum cloning in two dimensions based on the cavity QED technique. The protocol is very simple and only two atoms are required. Our scheme is insensitive to the cavity field states and cavity decay. During the processes, the cavity is only virtually excited and it thus greatly prolongs the efficient decoherent time. Therefore, it may be realized in experiment.     

高功率二极管端泵浦板条模块波前畸变实验研究

二极管激光器阵列端泵浦Nd:YAG板条具有热效应低、波前畸变小的特点,温度场和应力场的不均匀是引起板条增益介质波前畸变的主要原因。对端泵浦传导冷却Nd:YAG板条增益模块的泵浦和冷却均匀性进行了优化设计,获得了板条激光增益模块静态波前畸变最大偏差（PV）值为0.22 m。该模块用于双通放大器实验装置中,测试了板条增益模块有无注入功率条件下的波前畸变,测得无注入功率波前畸变PV值为3.49 m,能量提取后波前畸变PV值为3.41 m。在注入功率3120 W时,获得输出激光功率4660 W,光束质量为3.88倍衍射极限,该模块光光效率为27%。     

高功率二极管端泵浦板条模块波前畸变实验研究

二极管激光器阵列端泵浦Nd:YAG板条具有热效应低、波前畸变小的特点,温度场和应力场的不均匀是引起板条增益介质波前畸变的主要原因。对端泵浦传导冷却Nd:YAG板条增益模块的泵浦和冷却均匀性进行了优化设计,获得了板条激光增益模块静态波前畸变最大偏差（PV）值为0.22 m。该模块用于双通放大器实验装置中,测试了板条增益模块有无注入功率条件下的波前畸变,测得无注入功率波前畸变PV值为3.49 m,能量提取后波前畸变PV值为3.41 m。在注入功率3120 W时,获得输出激光功率4660 W,光束质量为3.88倍衍射极限,该模块光光效率为27%。     

Investigation of the Leggett-Garg inequality for precessing nuclear spins

We report experimental implementation of a protocol for testing the Leggett-Garg inequality (LGI) for nuclear spins precessing in an external magnetic field. The implementation involves certain controlled operations, performed in parallel on pairs of spin-1/2 nuclei (target and probe) from molecules of a nuclear magnetic resonance ensemble, which enable evaluation of temporal correlations from an LG string. Our experiment demonstrates violation of the LGI for time intervals between successive measurements, over which the effects of relaxation on the quantum state of target spin are negligible. Further, it is observed that the temporal correlations decay, and the same target spin appears to display macrorealistic behavior consistent with LGI.     

Shortcut-to-Adiabatic Controlled-Phase Gate in Rydberg Atoms

A shortcut-to-adiabatic protocol for the realization of a fast and high-fidelity controlled-phase gate in Rydberg atoms is developed. The adiabatic state transfer, driven in the high-blockade limit, is sped up by compensating nonadiabatic transitions via oscillating fields that mimic a counterdiabatic Hamiltonian. High fidelities are obtained in wide parameter regions. The implementation of the bare effective counterdiabatic field, without original adiabatic pulses, enables to bypass gate errors produced by the accumulation of blockade-dependent dynamical phases, making the protocol efficient also at low blockade values. As an application toward quantum algorithms, how the fidelity of the gate impacts the efficiency of a minimal quantum-error correction circuit is analyzed.     

Convection in a slowly diffusing,weakly stratified salt field

We examine thermohaline convection in the small Lewis number limit for a background salt field with a weak gradient. As a result of small diffusivity, the problem cannot be reduced to a simple amplitude equation in the usual manner, but the salt field is described by an advection-diffusion equation coupled to an equation for the amplitude of the convective pattern.     

Magnetic duplication and contact printing method

We present a simple and effective method of magnetic duplication. It is based on the printing of a patterned microstructure from a medium with low coercivity into a medium with high coercivity by subjecting both media to the external magnetic field. The prints obtained are studied by magnetic force microscopy and magnetooptic visualisation techniques. The images of duplicated prints show high efficiency of the method. Theoretical estimates of the external magnetic field range suitable for duplication are in good agreement with the magnetic field range obtained in experiment. Numerical calculations of the field distribution during duplication are also presented.     

New limit on Lorentz- and CPT-violating neutron spin interactions

We performed a search for neutron spin coupling to a Lorentz- and CPT-violating background field using a magnetometer with overlapping ensembles of K and 3He atoms. The comagnetometer is mounted on a rotary platform for frequent reversal of its orientation. We measure sidereal oscillations in the signal to search for anomalous spin coupling of extra-solar origin. We determine the equatorial components of the background field interacting with the neutron spin to be b?Xn=(0.1 ± 1.6) × 10?33 GeV and b?Yn=(2.5 ± 1.6) × 10?33 GeV, improving on the previous limit by a factor of 30. This measurement represents the highest energy resolution of any spin anisotropy experiment.     

Analytical study of four-wave mixing with large atomic coherence

Four-wave mixing in resonant atomic vapors based on maximum coherence induced by Stark-chirped rapid adiabatic passage (SCRAP) is investigated theoretically. We show the advantages of a coupling scheme involving maximum coherence and demonstrate how a large atomic coherence between a ground and an highly excited state can be prepared by SCRAP. Full analytic solutions of the field propagation problem taking into account pump field depletion are derived. The solutions are obtained with the help of an Hamiltonian approach which in the adiabatic limit permits to reduce the full set of Maxwell-Bloch equations to simple canonical equations of Hamiltonian mechanics for the field variables. It is found that the conversion efficiency reached is largely enhanced if the phase mismatch induced by linear refraction is compensated. A detailed analysis of the phase matching conditions shows, however, that the phase mismatch contribution from the Kerr effect cannot be compensated simultaneously with linear refraction contribution. Therefore, the conversion efficiency in a coupling scheme involving maximum coherence prepared by SCRAP is high, but not equal to unity. Received 16 August 2002 Published online 4 February 2003 RID="a" ID="a"e-mail: korsunsky@physik.uni-kl.de     

Protocol for multi-party superdense coding by using multi-atom in cavity QED

We present a protocol for multi-party superdense coding by using multi-atom in cavity quantum electrodynamics (QED). It is shown that, with a highly detuned cavity mode and a strong driving field, the protocol is insensitive to both cavity decay and thermal field. It is even certain to identify GHZ states via detecting the atomic states. Therefore we can realize the quantum dense coding in a simple way in the multiparty system.     

Quantum teleportation with a three-Bell-state analyzer

We present a novel Bell-state analyzer (BSA) for time-bin qubits allowing the detection of three out of four Bell states with linear optics, two detectors, and no auxiliary photons. The theoretical success rate of this scheme is 50%. Our new BSA demonstrates the power of generalized quantum measurements, known as positive operator valued measurements. A teleportation experiment was performed to demonstrate its functionality. We also present a teleportation experiment with a fidelity larger than the cloning limit.     

NMR of residual protons in partly deuterated anisotropic materials with phase-alternated decoupling of deuterium spins

A new method is presented for decoupling spins with S = 1 like deuterium in anisotropic media while observing other spins such as residual protons in partly deuterated samples. The carrier frequency of a weak radiofrequency (RF) field is applied near the center of the doublet arising from the quadrupolar interaction of the S = 1 spins. The phase of the RF field is periodically reversed with intervals matching the reciprocal of the magnitude of the quadrupolar splitting. It is shown by theory and experiment that, even when the irradiating field is quite weak, the efficiency of this phase-alternated decoupling scheme is much better than for simple continuous-wave irradiation at the center of the doublet, an established technique which is usually referred to as double quantum decoupling. The phase-alternated experiment makes it possible to decouple large quadrupolar interactions with a weak RF field. A theoretical analysis and numerical simulations are presented to demonstrate the decoupling performance. Proton spectra of partly deuterated dibromobutane in a liquid crystalline solvent have been recorded to illustrate the efficiency of phase-alternated deuterium decoupling.     

Upper limit on additional neutrino mass eigenstate in 2 to 100 eV region from “Troitsk nu-Mass” data

We performed a search for any sign of an additional neutrino mass state in β-electron spectrum based on data reanalysis of direct electron antineutrino mass measurements in Tritium beta-decay in the Troitsk nu-mass experiment. The existing data set allows us to search for such a state in the mass range up to 100 eV. The lowest value at a 95% C.L. upper limit for the contribution of a heavy eigenstate into electron neutrino is around or less than 1% for masses above 20 eV.     

基于量子远程通信的连续变量量子确定性密钥分配协议

基于量子远程通信的原理, 本文借助双模压缩真空态和相干态, 提出一种连续变量量子确定性密钥分配协议. 在利用零差探测法的情况下协议的传输效率达到了100%. 从信息论的角度分析了协议的安全性, 结果表明该协议可以安全传送预先确定的密钥. 在密钥管理中, 量子确定性密钥分配协议具有量子随机性密钥分配协议不可替代的重要地位和作用. 与离散变量量子确定性密钥分配协议相比, 该协议分发密钥的速率和效率更高, 又协议中用到的连续变量量子态易于产生和操控、适于远距离传输, 因此该协议更具有实际意义.