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The equality of electron’s and proton’s electric charges is the most impressive numerical coincidence in Nature. It has no generally accepted explanation. The Author presents arguments to the effect that this unusual degeneracy is of kinematical rather than dynamical origin.

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At the Kernfysisch Versneller Instituut (KVI) in Groningen, NL, a new facility (TRI\(\mu \)P) is under development. It aims for producing, slowing down and trapping of radioactive isotopes in order to perform accurate measurements on fundamental symmetries and interactions. A spectrum of radioactive nuclids will be produced in direct, inverse kinematics of fragmentation reactions using heavy ion beams from the superconducting AGOR cyclotron. The research programme pursued by the KVI group includes precision studies of nuclear \(\beta \)-decays through \(\beta \)–neutrino (recoil nucleus) momentum correlations in weak decays and searches for permanent electric dipole moments in heavy atomic systems. This offers a large potential for discovering new physics or to limit parameters in models beyond standard theory significantly. The scientific approach chosen in TRI\(\mu \)P can be regarded as complementary to such high energy physics. The facility in Groningen will be open for use by the worldwide community of scientists.

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A simple method of the description of optical pulses of finite dimensions and finite duration time is presented. The pulses are given by superpositions of the known analytical as well as numerical solutions of the Maxwell equations. The examples show optical properties of scattering in detail. In the general case the wide pulses split in the scattering processes. The description of these phenomena requires a full wave approach. The pulses (or their fragments) that do not split but move smoothly through the optical system (or its fragment) may be described with the help of the geometrical optics theory.

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We describe how quantum entanglement can be used in secure communication.

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Quantum entanglement remains invariant with respect to unitary transformations performed locally in each subsystem. Local orbits of a state of an \(N \times N\) bi-partite quantum system are analyzed. For a pure state their dimensions depend on the degeneracy of the vector of coefficients arising by the Schmidt decomposition. For instance, the generic orbit of a pure state has \(2N^2 -N-1\) dimensions, the set of separable states is \(4(N-1)\) dimensional, while the manifold of maximally entangled states has \(N^2-1\) dimensions.

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We show that combination of a linearly polarized resonant microwave field and a parallel static electric field may be used to create a non-dispersive electronic wavepacket in Rydberg atoms. The static electric field allows for manipulation of the shape of the elliptical trajectory the wavepacket is propagating on. Exact quantum numerical calculations for realistic experimental parameters show that the wavepacket evolving on a linear orbit can be very easily prepared in a laboratory either by a direct optical excitation or by preparing an atom in an extremal Stark state and then slowly switching on the microwave field. The latter scheme seems to be very resistant to experimental imperfections. Once the wavepacket on the linear orbit is excited, the static field may be used to manipulate the shape of the orbit.

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We study experimentally and numerically properties of quarter-stadium billiard’s eigenfunctions in the regime of quantum cantori. A quarter-stadium billiard was simulated experimentally by a thin quarter-stadium microwave cavity. Experimental eigenfunctions in the cantori regime \(N=7\)–63 of the quarter-stadium microwave billiard with the parameter \(\varepsilon =0.1\) were reconstructed using a field perturbation technique and a circular wave expansion method. The eigenfunctions \(N=76\)–499 lying in the cantori regime of the quarter-stadium billiard with \(\varepsilon =0.05\) were investigated numerically.

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We describe the use of permanent magnetic microstructures based on grooved, perpendicularly magnetised thin films fabricated by electron-beam lithography as optical elements for atom optics. Strong reflection signals and predominantly specular reflection have been realised for beams of cold caesium or rubidium atoms normally incident on grooved perpendicularly magnetised microstructures with periodicities of 1–4 \(\mu \)m. We discuss the use of perpendicularly magnetised microstructures to construct miniature integrated atom optical elements, including magnetic waveguides, microtraps and beamsplitters, for manipulating atomic de Broglie waves on the surface of a substrate.

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In the present paper, we analyze several factors which limit the fringe contrast in atom interferometers of the Mach–Zehnder type. We consider only the case of interferometers operating with thermal atoms, as there are very specific problems in this case. All the effects considered here are already known to reduce the fringe contrast but the quantitative analysis was not complete. In particular, vibrations play a very important role: a static description of the grating motions is not sufficient and dynamical effects must be taken into account. Such a description has been already made by Schmiedmayer et al. in their contribution to the book “Atom Interferometry” (1997). We recall this description and we discuss further some results of this calculation.

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In recent years, the application of laser cooling has led to significant advances in atomic frequency standards. In particular, the caesium fountain has advanced the accuracy of the realisation of the SI second by about an order of magnitude, to 1 in 10\(^{15}\). It is anticipated that optical frequency standards, either single trapped ions or cold neutral atoms, will provide advances in frequency stability. Highly stable optical frequencies will be translated to microwave frequencies by a revolutionary new technique. This paper gives a brief review of current techniques in frequency metrology. The atomic physics processes underlying the progress, as well as those responsible for the limitations to the performance of these new standards, are discussed.

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Van der Waals or Casimir interaction between neutral quantum objects in their ground state is known to be universally attractive. This is not necessarily so when these objects are embedded in a polarizable medium. We show that atomic impurities in liquid helium may indeed realize repulsive forces, and even Van der Waals and Casimir forces with different signs.

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This article describes experiments performed with an ultra-cold gas of metastable helium above the Bose–Einstein transition. The gas is trapped in an harmonic magnetic potential and collective excitations are induced. Both the frequency and the damping rate of the lowest monopole–quadrupole \(m=0\) mode of excitation are studied at different temperatures and compared to theoretical predictions. Results indicate that the gas goes from a collisionless regime towards a hydrodynamic regime as the elastic collision rate increases, when one goes down along the evaporative cooling ramp. However, we find a discrepancy for the collisional parameters in comparison with predictions relying on the value of the scattering length previously estimated. Possible explanations are put forward in the final discussion.

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At low magnetic field, the efficiency of metastability-exchange optical pumping of helium-3 is known to be optimal for pressures around 1 mbar. We demonstrate on several examples (up to 32 mbar) that operating in a higher magnetic field (here 0.12 T) can significantly increase the nuclear polarisations achieved at higher pressures. Since polarisation measurements cannot be made with the standard technique, we use a general optical method based on absorption measurements at 1083 nm to measure the polarisation of the atoms in the ground state.

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We report on RbI crystal decomposition due to electronic excitations in a vicinity of the top of the crystal band gap by UV photon irradiation. Dynamic force microscopy (DFM) studies reveal that randomly spread rectangular pits of monolayer depth in the topmost layer of the crystal are formed during irradiation. Growth and coalescence of the pits lead to almost ‘layer-by-layer’ desorption mode. Similarly to electron stimulated desorption, periodic changes of surface topography were found to have a profound effect on the desorption process. Since excited F-centre recombination with alkali atom emission was possible exclusively at low-coordinated sites the desorption yields were found to go hand in hand with the number of low-coordinated sites on the surface. Furthermore, simultaneous irradiation of the crystal by UV photons and visible light within the F-centre absorption band increases average F-centre mobility which has a profound effect on process efficiency. Such processes could be applied in controlled surface nanostructuring.

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Laser perturbation of an atom with fine or hyperfine structure is analyzed. The use of sufficiently powerful, or spectrally broad light produces effects, which form an optical analogue to the Back–Goudsmit effect. Such laser decoupling of hyperfine interaction is easily understood in terms of an analogy of the level-crossing effect and the double-slit experiment. The consequences of the optical Back–Goudsmit effect for efficiency of optical pumping in \(^3\)He are discussed.

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Cavity Ring-Down Spectroscopy (CRDS) is a novel technique of measurement of the absorption coefficient based on determination of the \(Q\)-factor of an optical resonator which contains the investigated absorber. We present a modified CRDS method (so called CRD-Spectrography) in which the signal is simultaneously analysed within a broad spectral range. This technique was used for monitoring of trace gases (nitrogen oxides) in the atmosphere. Another modification of CRDS technique allows to determine the transient absorption coefficient. This method was applied for studies of kinetics of CH radical produced by pulsed electric discharge in methane.

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Results of a series of experiments on collisional and speed-dependent effects caused by various foreign gases on the 326.1 nm Cd intercombination line are discussed in detail. Using a laser-induced fluorescence method precise measurements of pressure-broadened profiles of this line perturbed by all rare gases and some molecular gases (H\(_2\), D\(_2\), N\(_2\) and CH\(_4\)) were performed in our laboratory at pressures up to 400 Torr. The line shapes were analyzed in terms of a Speed-Dependent Asymmetric Voigt Profile (SDAVP) and the role of the correlation between pressure broadening rate and emitter velocity as well as of the finite duration of collisions were thoroughly investigated. These effects were found to be particularly important in the cases of perturbation by heavy, i.e. high-polarizability rare-gas atoms (Ar, Kr, Xe). Pressure-broadening and shift rates and the collision-time asymmetry factors as well as effective cross sections for the broadening and shifting of the 326.1 nm Cd line were determined and compared with those calculated on the basis of the van der Waals, Morse and Czuchaj–Stoll potentials.

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An excitation spectrum of the \(B1\leftarrow X0^+\) transition in CdXe has been recorded in a supersonic beam crossed with a pulsed dye laser beam. A thorough analysis of the data yielded the bond strength \(D_e'=(227.9\pm 5.0)\) cm\(^{-1}\), fundamental frequency \(\omega _e'=(18.3\pm 0.3)\) cm\(^{-1}\), anharmonicity \(\omega _e' x_e'=0.37\) cm\(^{-1}\), and internuclear equilibrium separation \(R_{e}'=(4.26\pm 0.05)\) Å in the excited \(B1(5^{3} P_{1})\) state of the molecule. Molecular spectroscopic constants of the \(X0^+(5^1S_0)\) ground state were also determined from the experimental data: \(D_e''=(276.0 \pm 5.0)\,{\rm cm}^{-1}\), \(\omega _e''=(33.1\pm 0.6)\,{\rm cm}^{-1}\), \(\omega _e''x_{e}''=(0.99\pm 0.02)\,{\rm cm}^{-1}\), and \(R_{e}''=(4.21 \pm 0.05)\) Å. The ground-state results were obtained from a direct observation of various “hot” bands in the \(B1\!\leftarrow \!X0^{+}\) transition. A repeat of earlier work of Funk and Breckenridge J. Chem. Phys. 90, 2927 (1989), and Helmi et al., Chem. Phys. 209, 53 (1996), relating to the \(A0^+\leftarrow X0^+\) transition yielded improved results which were essential for the correct spectroscopic characterisation of the \(A0^{+}(5^{3}P_{1})\) state of the molecule.