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Université de Fribourg

Atomic and molecular defects in solid ⁴He

Moroshkin, Peter ; Hofer, Adrian ; Weis, Antoine

In: Physics Reports, 2008, vol. 469, no. 1, p. 1-57

The studies of defects formed by impurity particles (atoms, molecules, exciplexes, clusters, free electrons, and positive ions) embedded in liquid and solid ⁴He are reviewed. The properties of free electrons and neutral particles in condensed helium are described by the electron (atomic) bubble model, whereas for the positive ions a snowball structure is considered. We compare the properties of...

Université de Fribourg

Lifetime studies of Cs*HeN exciplexes in solid ⁴He

Moroshkin, Peter ; Hofer, Adrian ; Lebedev, Victor ; Weis, Antoine

In: Physical Review A, 2008, vol. 78, p. 032501

We present time-resolved measurements of the laser-induced fluorescence from Cs atoms and Cs*HeN exciplexes in a solid ⁴He matrix. The linear Cs*He₌₂ exciplex is strongly quenched by a radiationless transformation into a ring-shaped Cs*HeN=6,7 exciplex, which decays radiatively with a lifetime of 88±2 ns. The analysis...

Université de Fribourg

Calculation of the forbidden electric tensor polarizabilities of free Cs atoms and of Cs atoms trapped in a solid ⁴He matrix

Hofer, Adrian ; Moroshkin, Peter ; Ulzega, Simone ; Weis, Antoine

In: Physical Review A, 2008, vol. 77, no. 12, p. 012502

We give a detailed account on our semiempirical calculations of the forbidden electric tensor polarizability α₂⁽³⁾ of the ground state of free Cs atoms and of Cs atoms implanted in a solid 4He matrix. The results are compared with measurements of α₂⁽³⁾ in the free atoms [Europhys. Lett. 76, 1074 (2006)] and in He-trapped atoms [Phys. Rev. A 75, 042505 (2007)]. Features with...

Université de Fribourg

Impurity-stabilized solid ⁴He below the solidification pressure of pure helium

Moroshkin, Peter ; Hofer, Adrian ; Ulzega, Simone ; Weis, Antoine

In: Nature Physics, 2007, vol. 3, no. <, p. 786 - 789

The modification of melting temperatures and pressures by dissolved impurities is well known in classical fluids. However, to our knowledge such effects have never been studied in quantum solids because of the difficulties in introducing impurities into such crystals that exist only at cryogenic temperatures, and, in the case of ⁴He, at pressures exceeding 25 bar. Here, we present an effect...

Université de Fribourg

6S1/2-6P1/2 transition of Cs atoms in cubic and hexagonal solid ⁴He

Hofer, Adrian ; Moroshkin, Peter ; Ulzega, Simone ; Nettels, Daniel ; Müller-Siebert, Reinhard ; Weis, Antoine

In: Physical Review A, 2007, vol. 76, no. 2, p. 022502

We present a systematic experimental study of the absorption and fluorescence spectra of the 6S1/2-6P1/2 transition in Cs atoms isolated in solid ⁴He matrices. The bubble model developed earlier for alkali-metal atoms in liquid He is revised and applied to the present system. The analysis of the dependencies of absorption and fluorescence wavelengths on He...

Université de Fribourg

Measurement of the forbidden electric tensor polarizability of Cs atoms trapped in solid ⁴He

Ulzega, Simone ; Hofer, Adrian ; Moroshkin, Peter ; Müller-Siebert, Reinhard ; Nettels, Daniel ; Weis, Antoine

In: Physical Review A, 2007, p. 042505

We have measured the electric tensor polarizabilities of the hyperfine levels of Cs atoms embedded in a body-centered cubic ⁴He crystal. The polarizabilities are inferred from the shift of optically detected magnetic resonance lines in each hyperfine level induced by static electric fields up to 50 kV/cm. We recorded the magnetic resonances both by scanning the rf frequency and in a...

Université de Fribourg

Reconciliation of experimental and theoretical electric tensor polarizabilities of the cesium ground state

Ulzega, Simone ; Hofer, Adrian ; Moroshkin, Peter ; Weis, Antoine

In: Europhysics Letters, 2006, vol. 76, no. 6, p. 1074-1080

We present a new theoretical analysis of the strongly suppressed F- and M-dependent Stark shifts of the Cs ground-state hyperfine structure. Our treatment uses third-order perturbation theory including off-diagonal hyperfine interactions not considered in earlier treatments. A numerical evaluation of the perturbation sum using bound states up to n = 200 yields ground-state...

Université de Fribourg

Theory of double resonance magnetometers based on atomic alignment

Weis, Antoine ; Bison, Georg ; Pazgalev, Anatoly S.

In: Physical Review A, 2006, p. 033401

We present a theoretical study of the spectra produced by optical–radio-frequency double resonance devices, in which resonant linearly polarized light is used in the optical pumping and detection processes. We extend previous work by presenting algebraic results which are valid for atomic states with arbitrary angular momenta, arbitrary rf intensities, and arbitrary geometries. The only...

Université de Fribourg

Spectroscopy of Rb₂ dimers in solid ⁴He

Moroshkin, Peter ; Hofer, Adrian ; Ulzega, Simone ; Weis, Antoine

In: Physical Review A, 2006, vol. 74, p. 032504

We present experimental and theoretical studies of the absorption, emission, and photodissociation spectra of Rb₂ molecules in solid helium. We have identified 11 absorption bands of Rb₂. All laser-excited molecular states are quenched by the interaction with the He matrix. The quenching results in efficient population of a metastable (1) ³πu state, which emits...

Université de Fribourg

Rb*Hen exciplexes in solid ⁴He

Hofer, Adrian ; Moroshkin, Peter ; Nettels, Daniel ; Ulzega, Simone ; Weis, Antoine

In: Physical Review A, 2006, vol. 74, p. 032509

We report the observation of emission spectra from Rb*Hen exciplexes in solid ⁴He. Two different excitation channels were experimentally identified, viz., exciplex formation via laser excitation to the atomic 5P3/2 and to the 5P1/2 levels. While the former channel was observed before in liquid helium, on helium nanodroplets, and...