Parity violation in hydrogen and longitudinal atomic beam spin echo I

We discuss the propagation of hydrogen atoms in static electric and magnetic fields in a longitudinal atomic beam spin echo (lABSE) apparatus. There the atoms acquire geometric (Berry) phases that exhibit a new manifestation of parity-(P-)violation in atomic physics. We provide analytical as well as numerical calculations of the behaviour of the metastable 2S states of hydrogen. The conditions for electromagnetic field configurations that allow for adiabatic evolution of the relevant atomic states are investigated. Our results provide the theoretical basis for the discussion of possible measurements of P-violating geometric phases in lABSE experiments.     

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.     

Large parity violating effects in atomic dysprosium with nearly degenerate Floquet eigenvalues

In this article we study effects of parity nonconservation in atomic dysprosium, where one has a pair of nearly degenerate levels of opposite parity. We consider the time evolution of this two-level system within oscillatory electric and magnetic fields. These are chosen to have a periodical structure with the same period, such that a Floquet matrix describes the time evolution of the quantum states. We show that, if the states are unstable, the eigenvalues of the Floquet matrix may have contributions proportional to the square root of the parity violating interaction matrix element while they are almost degenerate in their parity even part. This leads to beat frequencies proportional to which are expected to be larger by several orders of magnitude compared to ordinary P-violating contributions which are of order . However, for the simple field configurations we considered, it still seems to be difficult to observe these P-violating beat effects, since the states decay too fast. On the other hand, we found that, within only a few Floquet cycles, very large parity violating asymmetries with respect to experimental setups of opposite chirality may be obtained. The electric and magnetic fields as well as the time intervals necessary for this are in an experimentally accessible range. For statistically significant effects beyond one standard deviation a number of about 10⁷ atoms is required. Our ideas may be applied directly to other 2-level atomic systems and different field configurations. We hope that these ideas will stimulate experimental work in this direction. Received 16 September 1999 and Received in final form 10 March 2000     

Future directions in parity violation

I discuss the prospects for future studies of parity-violating (PV) interactions at low energies and the insights they might provide about open questions in the standard model as well as physics that lies beyond it. I cover four types of parity-violating observables: PV electron scattering; PV hadronic interactions; PV correlations in weak decays and searches for the permanent electric dipole moments of quantum systems.     

Implementation of single-qubit quantum gates by adiabatic passage and static laser phases

We propose and analyse experimentally feasible implementations of single-qubit quantum gates based on stimulated Raman adiabatic passage (STIRAP) between magnetic sublevels in atoms coupled by elliptically polarized pulsed laser fields, in part based on a proposal by Kis and Renzoni [Z. Kis, F. Renzoni, Phys. Rev. A 65 (2002) 032318]. These techniques require only the control of the relative phase of the driving fields but do not involve any dynamical or geometric phases, which makes it independent of the other interaction details: detuning, pulse shapes, pulse areas and pulse durations. The suggested techniques are immune to spontaneous emission since the qubit manipulation proceeds through non-absorbing dark states. We also propose an alternative technique using compensation of dynamical Stark shifts by two consecutive non-resonant fractional-STIRAP processes.     

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     

Disordering and annealing of a Si surface under low-energy Si bombardment

Abstract

We simulated the bombardment of Si(100)(2 × 1) by Si atoms using molecular dynamics. The kinetic energies of the projectiles were 100 and 50 eV. To model the Si–Si-interactions the empirical potential of Stillinger and Weber with the two body part of the potential splined to the universal potential was used. A geometric criterion based on the Lindemann radius was defined to study damage in the Si target. We observed clusters of disordered Si atoms in the target induced by the bombardment. Large clusters of about 50 atoms are formed in the beginning of the bombardment; they shrink and decay into smaller clusters until and equilibrium cluster size of about 10 atoms is reached. Upon annealing at elevated temperature the disordered zones dissolve into point defects.     

Atomic parity non-conservation: Present status and future prospects

The general features of parity nonconservation (PNC) in atoms arising from neutral weak currents and the nuclear anapole moment are discussed. The theoretical approaches used to calculate PNC observables are briefly mentioned. A brief review of the present status of atomic PNC is presented and its potential as a probe of physics beyond the standard model is highlighted.     

Small-angle X-ray diffraction study of the thermotropic and lyotropic phases of five alkyl cyclic and acyclic disaccharides: Influence of the linkage between the hydrophilic and hydrophobic moieties

We present a comparative study of the thermotropic and lyotropic phases of 5 surfactants with an aliphatic chain of 12 carbon atoms and a cyclic or acyclic sugar head with different linkages between the two moieties. These linkages can concern different chemical groups or different orientations between the head and the chain. The compounds included the α- and β-N dodecyl-D-maltosides, N-dodecylamino-1-deoxylactitol, N-dodecyl lactobionamide and N-acetyl N-dodecyl lactosylamine. The influence of the polar head (with closed- and opened-type sugars) and the linkage with the hydrocarbon chain on the phases obtained by the heating of the anhydrous compounds and after addition of water was studied by X-ray diffraction and optical microscopy. In the anhydrous state, the surfactants were either crystalline or amorphous. On heating, they went through a liquid crystal smectic phase which, in some cases, was preceded by solid-to-solid transitions. On addition of water, the sequence of phases from the micellar phase to the lamellar phase was accounted for in terms of the geometric model of Sadoc and Charvolin. However, with certain surfactants this sequence was not complete, and the domains of existence of phases were altered. Received 31 March 2000     

The cold atom Hubbard toolbox

We review recent theoretical advances in cold atom physics concentrating on strongly correlated cold atoms in optical lattices. We discuss recently developed quantum optical tools for manipulating atoms and show how they can be used to realize a wide range of many body Hamiltonians. Then, we describe connections and differences to condensed matter physics and present applications in the fields of quantum computing and quantum simulations. Finally, we explain how defects and atomic quantum dots can be introduced in a controlled way in optical lattice systems.     

Trapped radioactive isotopes for fundamental symmetry investigations

Discrete symmetries tested in high precision atomic physics experiments provide guidance to model building beyond the Standard Model (SM). Here experimental opportunities arise for searches for permanent electric dipole moments (EDMs) and measurements of atomic parity violation (APV). Heavy atoms are favorable for such experiments since symmetry violating effects in atoms increase faster than the third power of the nuclear charge Z. Of special interest are isotopes of the heavy alkaline earth element radium (Z=88) since they offer large enhancement factors for EDMs and provide a new experimental road towards high precision measurements of atomic parity violation. These opportunities are exploited at the TRIμP facility at KVI, Groningen.     

Topological quantum matter with cold atoms

This is an introductory review of the physics of topological quantum matter with cold atoms. Topological quantum phases, originally discovered and investigated in condensed matter physics, have recently been explored in a range of different systems, which produced both fascinating physics findings and exciting opportunities for applications. Among the physical systems that have been considered to realize and probe these intriguing phases, ultracold atoms become promising platforms due to their high flexibility and controllability. Quantum simulation of topological phases with cold atomic gases is a rapidly evolving field, and recent theoretical and experimental developments reveal that some toy models originally proposed in condensed matter physics have been realized with this artificial quantum system. The purpose of this article is to introduce these developments. The article begins with a tutorial review of topological invariants and the methods to control parameters in the Hamiltonians of neutral atoms. Next, topological quantum phases in optical lattices are introduced in some detail, especially several celebrated models, such as the Su–Schrieffer–Heeger model, the Hofstadter–Harper model, the Haldane model and the Kane–Mele model. The theoretical proposals and experimental implementations of these models are discussed. Notably, many of these models cannot be directly realized in conventional solid-state experiments. The newly developed methods for probing the intrinsic properties of the topological phases in cold-atom systems are also reviewed. Finally, some topological phases with cold atoms in the continuum and in the presence of interactions are discussed, and an outlook on future work is given.     

Electro-weak interaction in muonic atoms

The parity non-conserving effective neutral current interaction between charged leptons and nucleons is studied in its implications for atomic physics. Present results on heavy electronic atoms are discussed within the standard electroweak theory and beyond. The new features provided by muonic atoms open the way to the nuclear-spin-dependent parity non-conserving effects. Different observables proposed to study these effects in muonic atoms are reviewed.     

Entanglement reciprocation using three level atoms in a lambda configuration

We propose a scheme in which entanglement can be transferred from atoms (discrete variables) to entangled states of cavity fields (continuous variables). The cavities play the role of a kind of quantum memory for entanglement, in such a way that it is possible to retrieve it back to the atoms. In our method, two three level atoms in a lambda configuration, previously entangled, are set to interact with single mode cavity fields prepared in coherent states. During the process, one e-bit of entanglement may be deposited in the cavities in an efficient way. We also show that the stored entanglement may be transferred back to flying atoms.     

Observation of geometric phases for mixed states using NMR interferometry

Examples of geometric phases abound in many areas of physics. They offer both fundamental insights into many physical phenomena and lead to interesting practical implementations. One of them, as indicated recently, might be an inherently fault-tolerant quantum computation. This, however, requires one to deal with geometric phases in the presence of noise and interactions between different physical subsystems. Despite the wealth of literature on the subject of geometric phases very little is known about this very important case. Here we report the first experimental study of geometric phases for mixed quantum states. We show how different they are from the well-understood, noiseless, pure-state case.     

One Step to Generate Cluster States Using Dipole-Induced Transparency in a Cavity-Waveguide System

We present a very simple scheme for generating four-qubit cluster states with one step using parity measurement based on dipole-induced transparency in a cavity-waveguide system. The scheme only uses the photon detectors to check the parity of the spatially separated dipole, which are the same (even parity) or different (odd parity) through measuring the light fields in the waveguide. The initial entangled states remain after nondetective identification and they can be used for successive tasks.     

Entanglement generation and protection for two atoms in the presence of two parallel mirrors

We study, in the framework of open quantum systems, the entanglement generation of two atoms in between two parallel mirrors in a thermal bath of quantum scalar fields. We find that the presence of mirrors plays an important role in entanglement generation and protection. The entanglement dynamics is crucially dependent on the geometric configurations of the two-atom system with respect to the mirrors, and the ranges of temperature and interatomic separation within which entanglement can be generated are significantly changed compared with those in a free space. In particular, when the atomic transition wavelength is larger than twice the distance between the two mirrors, the atoms behave as if they were isolated from the environment and the entanglement can persist in the steady state if the atoms are initially entangled and no entanglement can be created if they are initially separable, no matter how the atoms are placed with respect to the mirrors and to each other. This is in sharp contrast to the fact that in a free space, steady-state entanglement is possible only when the two atoms are placed extremely close to each other, while in the presence of one mirror, it is possible when the two atoms placed extremely close to the mirror.     

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     

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.     

通过圆孔衍射实现冷分子(或冷原子)囚禁的光学偶极阱

以单色标量波衍射理论为基础,研究单色平面波由圆孔衍射产生实现冷分子(或冷原子)光学囚禁的光阱。运用圆孔衍射理论分析讨论了光学偶极阱的光强分布、光学势及偶极力,并导出了有关光阱的几何参量、光强分布、强度梯度及其曲率与光学系统参量(如照明光波的波长、小孔的孔径)间的解析关系。研究表明,当激光功率与波长分别为P=500 W和λ=1.08μm,小孔半径a=20μm时,产生囚禁甲烷CH4分子的光阱光学势约为57.9μK。通过圆孔衍射可实现冷分子或冷原子囚禁,该方案不仅简单可行、操作方便,而且在冷分子物理、原子光学、分子光学和量子光学等领域中有着广阔的应用前景。