Longitudinal atomic beam spin echo experiments: a possible way to study parity violation in hydrogen

We discuss the propagation of hydrogen atoms in static electric and magnetic fields in a longitudinal atomic beam spin echo (lABSE) apparatus. Depending on the choice of the external fields the atoms may acquire both dynamical and geometrical quantum mechanical phases. As an example of the former, we show first in-beam spin rotation measurements on atomic hydrogen, which are in excellent agreement with theory. Additional calculations of the behaviour of the metastable 2S states of hydrogen reveal that the geometrical phases may exhibit the signature of parity-(P-)violation. This invites for possible future lABSE experiments, focusing on P-violating geometrical phases in the lightest of all atoms.     

Metastable states,the adiabatic theorem and parity violating geometric phases II

We discuss and calculate parity conserving (PC) and parity violating (PV) geometric phases for the metastable 2S states of hydrogen and deuterium. The atoms are supposed to be subjected to slowly varying electric and magnetic fields which act as external parameters for the atoms. Geometric flux density fields are introduced which allow for an easy overview how to choose the paths in parameter space in order to obtain only PC or only PV geometric phases. The PV phases are calculated in the Standard Model of particle physics. Even if numerically they come out small they have interest of principle as a new manifestation of parity violation in atomic physics. Electronic supplementary material Supplementary Online Material     

Metastable states of hydrogen: their geometric phases and flux densities

We discuss the geometric phases and flux densities for the metastable states of hydrogen with principal quantum number n = 2 being subjected to adiabatically varying external electric and magnetic fields. Convenient representations of the flux densities as complex integrals are derived. Both, parity conserving (PC) and parity violating (PV) flux densities and phases are identified. General expressions for the flux densities following from rotational invariance are derived. Specific cases of external fields are discussed. In a pure magnetic field the phases are given by the geometry of the path in magnetic field space. But for electric fields in presence of a constant magnetic field and for electric plus magnetic fields the geometric phases carry information on the atomic parameters, in particular, on the PV atomic interaction. We show that for our metastable states also the decay rates can be influenced by the geometric phases and we give a concrete example for this effect. Finally we emphasise that the general relations derived here for geometric phases and flux densities are also valid for other atomic systems having stable or metastable states, for instance, for He with n = 2. Thus, a measurement of geometric phases may give important experimental information on the mass matrix and the electric and magnetic dipole matrices for such systems. This could be used as a check of corresponding theoretical calculations of wave functions and matrix elements.     

A collision-induced satellite in the Lyman profile due to H-H collisions

We present a theoretical profile of the Lyman line of atomic hydrogen perturbed by collisions with neutral hydrogen atoms and protons. We use a general unified theory in which the electric dipole moment varies during a collision. A collision-induced satellite appears on Lyman , correlated to the asymptotically forbidden transition of H₂. As a consequence, the appearance of the line wing between Lyman and Lyman is shown to be sensitive to the relative abundance of hydrogen ions and neutral atoms, and thereby to provide a temperature diagnostic for stellar atmospheres and laboratory plasmas. Received 15 January 2000 and Received in final form 17 May 2000     

Scattering of light exotic atoms in excited states

The differential and total cross-sections for the scattering of muonic, pionic, kaonic and antiprotonic hydrogen in excited states from atomic hydrogen have been calculated for the purpose of atomic cascade calculations. The scattering problem is treated in a fully quantum mechanical framework which takes the energy shifts and, in the case of the hadronic atoms, the widths of the ns states into account. The validity of semiclassical approximations is critically examined. Received 4 December 2001 and Received in final form 4 February 2002     

Multilevel atomic entanglement induced by spontaneous emission in free space

We investigate two identical Λ-type atoms in free space, and focus on the entanglement between the two atoms. We derive a master equation for the atomic subspace and solve it analytically to show how the spontaneous emission from the two atoms system induces entanglement. The magnitude of the entanglement and the steady state entanglement are found to be strongly dependent on the initial states and the orientation of the dipoles of the two atoms.     

Energetics and electronic properties of BN nanocones with pentagonal rings at their apexes

The geometric structures, energetics and electronic properties of the recently discovered BN nanocones are investigated using first-principles calculations based on the density-functional theory. We have proposed one particular structure for BN nanocones associated with the 240^° disclination, derived by the extraction of four 60^° segments, presenting as characteristic four pentagons at the apex and termination in two atoms. The cones are simulated by three clusters containing 58 B plus N atoms and additional 12 H atoms to saturate the dangling bonds at the edge. The most stable configuration is obtained when the two terminating atoms are one B and one N. For the cases where the two terminating atoms are of the same kind, the tip with B atoms is determined to have lower binding energy than with N atoms. The local densities of states of these BN nanocones are investigated and sharp states are found in the regions close (below and above) to the Fermi energy. Received 14 October 2002 / Received in final form 6 December 2002 Published online 11 February 2003 RID="a" ID="a"e-mail: ppiquini@smail.ufsm.br     

Generation of maximally entangled atom pairs in driven dissipative cavity QED systems

We investigate the entanglement of an open tripartite system where a cavity field mode in thermal equilibrium is off-resonantly coupled with two atoms that are simultaneously driven by a resonant coherent field. For moderately detuned atom-field coupling and strong atomic driving we show the generation, at given interaction times and for low enough cavity decay rates, of atomic Bell states and of Bell state superpositions relevant for quantum gates implementation. The system can oscillate between bi-separable and fully separable states. Also we describe the distribution of quantum correlations between the atom-atom and the two atom-field subsystems. In the dispersive coupling regime with strongly driven atoms we show the generation of nearly stationary Bell states which remain protected from cavity dissipation.     

Kaon absorption from kaonic atoms and formation spectra of kaonic nuclei

We considered the kaon absorption from atomic states into the nucleus. We found that the nuclear density probed by the atomic kaon significantly depends on the kaon orbit. Then, we re-examined the meanings of the observed strengths of one-body and two-body kaon absorption, and investigated the effects to the formation spectra of kaon bound states by in-flight (K ^-, p) reactions. As a natural consequence, if the atomic kaon probes a smaller nuclear density, the ratio of the two-body absorption at nuclear center is larger than the observed value in kaonic atoms, and the depth of the imaginary potential is deeper even at smaller kaon energies as in kaonic nuclear states because of the large phase space for the two-body processes. This deeper imaginary potential makes the signals of kaonic nucleus formation more unclear in the (K ^-, p) spectra.     

Nonclassical properties and algebraic characteristics of negative binomial states in quantized radiation fields

We study the nonclassical properties and algebraic characteristics of the negative binomial states introduced by Barnett recently. The ladder operator formalism and displacement operator formalism of the negative binomial states are found and the algebra involved turns out to be the SU(1,1) Lie algebra via the generalized Holstein-Primarkoff realization. These states are essentially Perelomov's SU(1,1) coherent states. We reveal their connection with the geometric states and find that they are excited geometric states. As intermediate states, they interpolate between the number states and geometric states. We also point out that they can be recognized as the nonlinear coherent states. Their nonclassical properties, such as sub-Poissonian distribution and squeezing effect are discussed. The quasiprobability distributions in phase space, namely the Q and Wigner functions, are studied in detail. We also propose two methods of generation of the negative binomial states. d 32.80.Pj Optical cooling of atoms; trapping Received 8 May 1999 and Received in final form 8 November 1999     

Exact results on decoherence and entanglement in a system of N driven atoms and a dissipative cavity mode

We solve the dynamics of an open quantum system where N strongly driven two-level atoms are equally coupled on resonance to a dissipative cavity mode. Analytical results are derived on decoherence, entanglement, purity, atomic correlations and cavity field mean photon number. We predict decoherencefree subspaces for the whole system and the N-qubit subsystem, the monitoring of quantum coherence and purity decay by atomic populations measurements, the conditional generation of atomic multi-partite entangled states and of cavity cat-like states. We show that the dynamics of atoms prepared in states invariant under permutation of any two components remains restricted within the subspace spanned by the completely symmetric Dicke states. We discuss examples and applications in the cases N = 3, 4. An erratum to this article can be found at     

Interaction of atomic hydrogen with the Si(100)2×1 surface

The interaction of atomic hydrogen with the Si(100)2×1 surface has been investigated in detail by a field ion-scanning tunneling microscope (FI-STM). At low exposure, hydrogen atoms reside singly on top of the dimerised Si atoms, and are imaged brightly. The hydrogen chemisorption induces the buckling of dimers, indicating the strong bonding between Si and hydrogen atoms. The adsorption geometry changed from the (2×1) monohydride phase to the (1×1) dihydride phase with increasing exposure of hydrogen. The former is imaged dark compared with the unreacted Si dimers due to the reduction of the density of electronic states near the Fermi level. Surface etching was also observed during the formation of the dihydride phase. The behavior of hydrogen desorption from the H-saturated Si(100) surface was investigated as a function of annealing temperatures. Our STM results suggest that the desorbing H₂ molecules are formed by two hydrogen atoms on the same dihydride species.     

Geometric phase in entangled bipartite systems

The geometric phase (GP) for bipartite systems in transverse external magnetic fields is investigated in this paper. Two different situations have been studied. We first consider two non-interacting particles. The results show that because of entanglement, the geometric phase is very different from that of the non-entangled case. When the initial state is a Werner state, the geometric phase is, in general, zero and moreover the singularity of the geometric phase may appear with a proper evolution time. We next study the geometric phase when intra-couplings appear and choose Werner states as the initial states to entail this discussion. The results show that unlike our first case, the absolute value of the GP is not zero, and attains its maximum when the rescaled coupling constant J is less than 1. The effect of inhomogeneity of the magnetic field is also discussed.     

Polarization correlation in the two-photon decay of atomic hydrogen: nonlocality versus entanglement

From the work by Perrie et al. [Phys. Rev. Lett. 54, 1790 (1985)], photon pairs from the 2s _1/2 → 1s _1/2 (two-photon) decay of atomic hydrogen are known to be quantum mechanically correlated. In these experiments, the polarization states of the photons emitted in back-to-back geometry were shown to violate the Bell inequality as a qualitative sign of nonlocality and entanglement. In the present contribution, we analyze how these nonlocal quantum correlations, as given by the violation of the Bell inequality, differ from the concurrence as a true entanglement measure. Results are shown for both quantifiers in dependence of the decay geometry and the initial polarization of the atoms for the 2s _1/2 → 1s _1/2 and 3d _5/2 → 1s _1/2 two-photon decay of atomic hydrogen. These results display the difference between nonlocality and entanglement and, hence, may stimulate further experiments on nonlocal quantum correlations in atomic systems.     

Generation of Greenberger-Horne-Zeilinger states for multiple atoms trapped in separated cavities

We propose a scheme for generating maximally entangled states for multiple atoms trapped in distant cavities connected by fibers. During the operation neither the atomic system nor the fibers are excited, which is important in view of decoherence. Under certain conditions, the probability that the cavities are excited is negligible. The scheme does not include projective measurement and the GHZ state is generated deterministically. Taking advantage of adiabatic passage, the entanglement fidelity is insensitive to fluctuation of experimental parameters.     

全光学冷却与囚禁133Cs原子玻色-爱因斯坦凝聚的可能性

综述了近年来有关蒸发冷却¹³³Cs原子样品的实验进展,分析了磁囚禁¹³³Cs原子玻色爱因斯坦凝聚(BEC)的困难,并在此基础上提出了一个全光型冷却与囚禁¹³³Cs原子BEC的新方案.该方案主要由一个来自半导体激光(λ=0852μm)的倒金字塔形中空光束重力光学囚禁(pyramidal-hollow-beam gravito-optical trap,缩写为PHB GOT)和一个来自Ar⁺激光(λ=05013μm)的圆锥形中空光束重力光学囚禁(conical-hollow-beam gravito-optical trap,缩写为CHB GOT)组成.在PHB GOT中,冷原子经历了一个有效的中空光束感应的Sisyphus冷却(也即强度梯度冷却)和抽运光感应的几何冷却,原子温度将被从磁光囚禁(MOT)温度(约为60μK)冷却至几个光子反冲极限(约为2μK);而在Ar⁺中空光束囚禁(CHB GOT)中,冷原子将被Raman冷却或速度选择相干粒子数囚禁技术(velocity-selection coherent population trap,缩写为VSCPT)进一步冷却至光子反冲极限以下,并被激光频率高于原子共振频率的(也即蓝失谐的)covering光束压缩.我们就PHB冷却的动力学过程进行了Monte-Carlo模拟,并计算了Ar⁺中空光束囚禁¹³³Cs原子的光学势.研究结果表明,实现一个全光学冷却与囚禁的¹³³Cs原子BEC是可能的 关键词： 倒金字塔型中空光束重力光学囚禁 强度梯度冷却 氩离子中空光束囚禁 喇曼冷却 铯原子BEC     

Manipulating the phase of a single-mode micromaser by polarized three-level atoms

We investigate the phase probability distribution (PPD) of a single-mode micromaser pumped by atoms injected in the most general case, i.e. in the superposition of the upper, intermediate and lower states by the Monte Carlo wave function approach. The phase properties of the cavity mode are greatly influenced by the relative phases and the amplitudes of the polarized atoms, and the detunings between the atom and cavity. The cavity field has a single preferred phase if the cavity is pumped by the atoms in the superposition of the upper and intermediate states or of the intermediate and lower states. However, a double-peak feature appears in the PPD of the cavity field when the cavity is pumped by the atoms in the superposition of the upper and lower states. With appropriate detunings, the double peaks become narrower and more remarkable, which shows the better defined phase of the cavity field, as compared to the resonant case. The PPD displays complicated characteristics when the cavity is pumped by the atoms in the superposition of the upper, intermediate and lower states. The phase distribution changes from a single peak to double peaks and to another single peak when we modulate the phase of the intermediate state, which has been explained in the semi-classical radiation theory.     

Giant lamb shift in photonic crystals

We obtain a general result for the Lamb shift of excited states of multilevel atoms in inhomogeneous electromagnetic structures and apply it to study atomic hydrogen in inverse-opal photonic crystals. We find that the photonic-crystal environment can lead to very large values of the Lamb shift, as compared to the case of vacuum. We also suggest that the position-dependent Lamb shift should extend from a single level to a miniband for an assembly of atoms with random distribution in space, similar to the velocity-dependent Doppler effect in atomic/molecular gases.     

Photonic band gap of three dimensional magnetized photonic crystal with Voigt configuration

We study Bessel beams of two-level atoms that are driven by a linearly polarized laser field. Starting from the Schrödinger equation, we determine the states of two-level atoms in a plane-wave field respecting propagation directions both of the atom and the field. For such laser-driven two-level atoms, we construct Bessel beams beyond the typical paraxial approximation. We show that the probability density of these atomic beams obtains a non-trivial, Bessel-squared-type behavior and can be tuned under the special choice of the atom and laser parameters, such as the nuclear charge, atom velocity, laser frequency, and propagation geometry of the atom and laser beams. Moreover, we spatially and temporally characterize the beam of hydrogen and selected (neutral) alkali-metal atoms that carry non-zero orbital angular momentum (OAM). The proposed spatiotemporal Bessel states (i) are able to describe, in principle, twisted states of any two-level system which is driven by the radiation field and (ii) have potential applications in atomic and nuclear processes as well as in quantum communication.