16 results on '"Tilman Pfau"'
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2. Onset of a modulational instability in trapped dipolar Bose-Einstein condensates
- Author
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Fabian Böttcher, Tilman Pfau, M. H. Schmitt, Matthias Wenzel, and Igor Ferrier-Barbut
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Condensed Matter::Quantum Gases ,Physics ,Condensed matter physics ,Atomic Physics (physics.atom-ph) ,FOS: Physical sciences ,Scattering length ,Lambda ,01 natural sciences ,Physics - Atomic Physics ,010305 fluids & plasmas ,law.invention ,Modulational instability ,Dipole ,Quantum Gases (cond-mat.quant-gas) ,law ,0103 physical sciences ,Condensed Matter - Quantum Gases ,010306 general physics ,Adiabatic process ,Quantum ,Bose–Einstein condensate ,Phase diagram - Abstract
We explore the phase diagram of a finite-sized dysprosium dipolar Bose-Einstein condensate in a cylindrical harmonic trap. We monitor the final state after the scattering length is lowered from the repulsive BEC regime to the quantum droplet regime. Either an adiabatic transformation between a BEC and a quantum droplet is obtained or, above a critical trap aspect ratio ${\ensuremath{\lambda}}_{\mathrm{c}}=1.87(14)$, a modulational instability results in the formation of multiple droplets. This is in full agreement with the predicted structure of the phase diagram with a crossover region below ${\ensuremath{\lambda}}_{\mathrm{c}}$ and a multistable region above. Our results provide the missing piece connecting the previously explored regimes resulting in a single or multiple dipolar quantum droplets. more...
- Published
- 2018
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3. Rydberg polaritons in a thermal vapor
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Yi-Hsin Chen, Tilman Pfau, Robert Löw, and Fabian Ripka
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Physics ,Quantum Physics ,Atomic Physics (physics.atom-ph) ,Dephasing ,FOS: Physical sciences ,7. Clean energy ,01 natural sciences ,Physics - Atomic Physics ,010309 optics ,symbols.namesake ,0103 physical sciences ,Thermal ,symbols ,Polariton ,Rydberg formula ,Rydberg matter ,Physics::Atomic Physics ,Atomic physics ,Rydberg state ,Quantum Physics (quant-ph) ,010306 general physics ,Excitation - Abstract
We present a pulsed four-wave mixing (FWM) scheme via a Rydberg state to create, store and retrieve collective Rydberg polaritons. The storage medium consists of a gas of thermal Rb atoms confined in a 220 {\mu}m thick cell, which are heated above room temperature. The experimental sequence consists of a pulsed excitation of Rydberg polaritons via the D1 line, a variable delay or storage time, and a final retrieval pulse via the D2 line. The lifetime of the Rydberg polaritons is around 1.2 ns, almost entirely limited by the excitation bandwidth and the corresponding motional dephasing of the atoms. The presented scheme combined with a tightly confined atomic ensemble is a good candidate for a deterministic single-photon source, as soon as strong interactions in terms of a Rydberg blockade are added., Comment: 5 pages, 3 figures more...
- Published
- 2016
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4. Observation of mixed singlet-tripletRb2Rydberg molecules
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Kathrin S. Kleinbach, Karl M. Westphal, Fabian Böttcher, Michael Schlagmüller, Sebastian Hofferberth, Tilman Pfau, Anita Gaj, T. Cubel Liebisch, and Robert Löw
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Physics ,Zeeman effect ,Atomic Physics (physics.atom-ph) ,Scattering ,FOS: Physical sciences ,Scattering length ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Physics - Atomic Physics ,symbols.namesake ,0103 physical sciences ,Atom ,Rydberg formula ,symbols ,Physics::Atomic Physics ,Singlet state ,Atomic physics ,010306 general physics ,0210 nano-technology ,Spectroscopy ,Hyperfine structure - Abstract
We present high-resolution spectroscopy of ${\mathrm{Rb}}_{\text{2}}$ ultralong-range Rydberg molecules bound by mixed singlet-triplet electron-neutral atom scattering. The mixing of the scattering channels is a consequence of the hyperfine interaction in the ground-state atom, as predicted recently by Anderson et al. [Phys. Rev. A 90, 062518 (2014)]. Our experimental data enable the determination of the effective zero-energy singlet $s$-wave scattering length for Rb. We show that an external magnetic field can tune the contributions of the singlet and the triplet scattering channels and therefore the binding energies of the observed molecules. This mixing of molecular states via the magnetic field results in observed shifts of the molecular line which differ from the Zeeman shift of the asymptotic atomic states. Finally, we calculate molecular potentials using a full diagonalization approach including the $p$-wave contribution and all orders in the relative momentum $k$, and compare the obtained molecular binding energies to the experimental data. more...
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- 2016
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5. Photoassociation of spin-polarized chromium
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Tilman Pfau, Tobias Bäuerle, Eite Tiesinga, Paul S. Julienne, and Jahn Rührig
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Physics ,Quantum Physics ,Atomic Physics (physics.atom-ph) ,Spectrum (functional analysis) ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Potential energy ,Omega ,Homonuclear molecule ,Physics - Atomic Physics ,Dipole ,Excited state ,0103 physical sciences ,Physics::Atomic Physics ,Atomic physics ,Quantum Physics (quant-ph) ,010306 general physics ,0210 nano-technology ,Spin (physics) ,Circular polarization - Abstract
We report the homonuclear photoassociation (PA) of ultracold $^{52}\mathrm{Cr}$ atoms in an optical dipole trap. This constitutes the measurement of PA in an element with total electron spin $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{S}g1$. Although Cr, with its $^{7}S_{3}$ ground and $^{7}P_{4,3,2}$ excited states, is expected to have a complicated PA spectrum we show that a spin-polarized cloud exhibits a remarkably simple PA spectrum when circularly polarized light is applied. Over a scan range of 20 GHz below the $^{7}P_{3}$ asymptote we observe two distinct vibrational series each following a LeRoy-Bernstein law for a ${C}_{3}/{R}^{3}$ potential with excellent agreement. We determine the ${C}_{3}$ coefficients of the Hund's case (c) relativistic adiabatic potentials to be $\ensuremath{-}1.83\ifmmode\pm\else\textpm\fi{}0.02$ and $\ensuremath{-}1.46\ifmmode\pm\else\textpm\fi{}0.01$ a.u.. Theoretical nonrotating Movre-Pichler calculations enable a first assignment of the series to $\mathrm{\ensuremath{\Omega}}={6}_{u}$ and ${5}_{g}$ potential energy curves. In a different set of experiments we disturb the selection rules by a transverse magnetic field which leads to additional PA series. more...
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- 2016
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6. Quantum correlations and entanglement in far-from-equilibrium spin systems
- Author
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Tilman Pfau, Ana Maria Rey, Mauritz van den Worm, Kaden R. A. Hazzard, Salvatore R. Manmana, E. G. Dalla Torre, Michael Foss-Feig, and Michael Kastner
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Physics ,Quantum Physics ,Quantum discord ,Quantum decoherence ,Atomic Physics (physics.atom-ph) ,Time evolution ,FOS: Physical sciences ,Quantum entanglement ,Squashed entanglement ,Atomic and Molecular Physics, and Optics ,Physics - Atomic Physics ,3. Good health ,Singularity ,Quantum Gases (cond-mat.quant-gas) ,Quantum mechanics ,Rydberg atom ,Condensed Matter - Quantum Gases ,Quantum Physics (quant-ph) ,Quantum - Abstract
By applying complementary analytic and numerical methods, we investigate the dynamics of spin-$1/2$ XXZ models with variable-range interactions in arbitrary dimensions. The dynamics we consider is initiated from uncorrelated states that are easily prepared in experiments, and can be equivalently viewed as either Ramsey spectroscopy or a quantum quench. Our primary focus is the dynamical emergence of correlations and entanglement in these far-from-equilibrium interacting quantum systems: we characterize these correlations by the entanglement entropy, concurrence, and squeezing, which are inequivalent measures of entanglement corresponding to different quantum resources. In one spatial dimension, we show that the time evolution of correlation functions manifests a non-perturbative dynamic singularity. This singularity is characterized by a universal power-law exponent that is insensitive to small perturbations. Explicit realizations of these models in current experiments using polar molecules, trapped ions, Rydberg atoms, magnetic atoms, and alkaline-earth and alkali atoms in optical lattices, along with the relative merits and limitations of these different systems, are discussed., Comment: 22 pages, 8 figures, 1 table more...
- Published
- 2014
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7. Motion-induced signal revival in pulsed Rydberg four-wave mixing beyond the frozen-gas limit
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A. Kölle, B. Huber, and Tilman Pfau
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Physics ,Atomic Physics (physics.atom-ph) ,FOS: Physical sciences ,chemistry.chemical_element ,Nanosecond ,01 natural sciences ,Signal ,Atomic and Molecular Physics, and Optics ,Physics - Atomic Physics ,Rubidium ,010309 optics ,symbols.namesake ,Four-wave mixing ,chemistry ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,symbols ,Rydberg formula ,Physics::Atomic Physics ,Atomic physics ,Rydberg state ,010306 general physics ,Doppler effect ,Mixing (physics) - Abstract
We present measurements on pulsed four-wave mixing involving a Rydberg state in an atomic vapor cell. The excitation to the Rydberg state is conducted by a pulsed two-photon excitation on the nanosecond timescale that is combined with a third CW laser in phase-matched geometry yielding light emission on the same timescale. An additional signal peak is observed shortly after the pulse that can be attributed to a revival of constructive interference between different velocity classes of the radiating atomic dipoles. Furthermore we investigate the density dependence of the four-wave mixing signal. From the shape of the respective curve we are able to confirm energy and momentum conservation in the photonic part of the system., Comment: 7 pages, 5 figures more...
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- 2014
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8. Publisher's Note: Ground state of a two-component dipolar Fermi gas in a harmonic potential [Phys. Rev. A88, 043604 (2013)]
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Krzysztof Pawłowski, Kazimierz Rzazewski, Przemyslaw Bienias, and Tilman Pfau
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Physics ,Dipole ,Component (thermodynamics) ,Quantum electrodynamics ,Quantum mechanics ,Harmonic potential ,Density functional theory ,Ground state ,Fermi gas ,Atomic and Molecular Physics, and Optics - Published
- 2014
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9. Ground state of a two-component dipolar Fermi gas in a harmonic potential
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Tilman Pfau, Krzysztof Pawłowski, Przemyslaw Bienias, and Kazimierz Rzążewski
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Condensed Matter::Quantum Gases ,Physics ,Phase transition ,Magnetic moment ,Condensed matter physics ,FOS: Physical sciences ,Macroscopic quantum phenomena ,Quantum phases ,Atomic and Molecular Physics, and Optics ,Paramagnetism ,Magnetization ,Quantum Gases (cond-mat.quant-gas) ,Condensed Matter - Quantum Gases ,Ground state ,Fermi gas - Abstract
Interacting two component Fermi gases are at the heart of our understanding of macroscopic quantum phenomena like superconductivity. Changing nature of the interaction is expected to head to novel quantum phases. Here we study the ground state of a two component fermionic gas in a harmonic potential with dipolar and contact interactions. Using a variational Wigner function we present the phase diagram of the system with equal but opposite values of the magnetic moment. We identify the second order phase transition from paramagnetic to ferronematic phase. Moreover, we show the impact of the experimentally relevant magnetic field on the stability and the magnetization of the system. We also investigate a two component Fermi gas with large but almost equal values of the magnetic moment to study how the interplay between contact and dipolar interactions affects the stability properties of the mixture. To be specific we discuss experimentally relevant parameters for ultracold $^{161}$Dy. more...
- Published
- 2013
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10. Correlations of a quasi-two-dimensional dipolar ultracold gas at finite temperatures
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Tilman Pfau, Krzysztof Pawłowski, Kazimierz Rzążewski, and Przemyslaw Bienias
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Physics ,Correlation function (statistical mechanics) ,Dipole ,Current (mathematics) ,Field (physics) ,Condensed matter physics ,Particle ,Interatomic potential ,Atomic physics ,Quantum statistical mechanics ,Magnetic dipole ,Atomic and Molecular Physics, and Optics - Abstract
We study a quasi-two-dimensional dipolar gas at finite, but ultralow, temperatures using the classical field approximation. The method, already used for a contact interacting gas, is extended here to samples with a weakly interacting long-range interatomic potential. We present statistical properties of the system for the current experiment with chromium [M\"uller, Billy, Henn, Kadau, Griesmaier, Jona-Lasinio, Santos, and Pfau, Phys. Rev. A 84, 053601 (2011)] and compare them with statistics for atoms with larger magnetic dipole moments. Significant enhancement of the third-order correlation function, relevant for the particle losses, is found. more...
- Published
- 2013
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11. Deconfinement-induced collapse of a coherent array of dipolar Bose-Einstein condensates
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Axel Griesmaier, Thomas Maier, J. Billy, Tilman Pfau, Holger Kadau, Emanuel Alves de Lima Henn, Stefan Müller, Luis Santos, and M. Jona-Lasinio
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Condensed Matter::Quantum Gases ,Physics ,Optical lattice ,Condensed matter physics ,Deconfinement ,Atomic and Molecular Physics, and Optics ,law.invention ,Dipole ,law ,Lattice (order) ,Matter wave ,Anisotropy ,Bose–Einstein condensate ,Coherence (physics) - Abstract
We report on the observation of the collapse of a dipolar Bose-Einstein condensate (BEC) upon release from a one-dimensional optical lattice. In strong contrast with the typical behavior of quantum gases under time of flight (TOF), we show here that a strongly dipolar BEC, stabilized in the lattice, may become unstable during the TOF dynamics due to the combined effect of the anisotropy of the dipolar interaction and intersite coherence. Such TOF-triggered collapse is a peculiar case of a collapse induced by the deconfinement of a dipolar many-body system at a fixed two-body interaction strength. more...
- Published
- 2012
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12. Four-wave mixing involving Rydberg states in thermal vapor
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Harald Kübler, Tilman Pfau, Robert Löw, Georg Epple, and A. Kölle
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Physics ,chemistry.chemical_element ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Rubidium ,010309 optics ,symbols.namesake ,Four-wave mixing ,chemistry ,Electric field ,Excited state ,0103 physical sciences ,Rydberg atom ,Rydberg formula ,symbols ,Physics::Atomic Physics ,Atomic physics ,Rydberg state ,010306 general physics ,Mixing (physics) - Abstract
We present experimental results on nondegenerate four-wave mixing in a thermal vapor cell of rubidium atoms via highly excited Rydberg states. We observe sub-Doppler spectral features and a large sensitivity of the mixed light mode to small electric fields due to the large polarizabilities of the involved Rydberg state. We observe a saturation of the optical response due to the nonlinear four-level physics. The strong interaction between Rydberg atoms and the associated Rydberg blockade could potentially increase the nonlinearity dramatically. more...
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- 2012
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13. Stability of a dipolar Bose-Einstein condensate in a one-dimensional lattice
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Emanuel Alves de Lima Henn, Tilman Pfau, Stefan Müller, J. Billy, Holger Kadau, Axel Griesmaier, M. Jona-Lasinio, and Luis Santos
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Condensed Matter::Quantum Gases ,Physics ,Optical lattice ,Condensed matter physics ,Scattering ,Atomic and Molecular Physics, and Optics ,Bohr model ,law.invention ,symbols.namesake ,Mean field theory ,Residual dipolar coupling ,law ,Lattice (order) ,symbols ,Matter wave ,Bose–Einstein condensate - Abstract
We show that in contrast with contact interacting gases, an optical lattice changes drastically the stability properties of a dipolar condensate, inducing a crossover from dipolar destabilization to dipolar stabilization for increasing lattice depths. Performing stability measurements on a 52 Cr Bose-Einstein condensate in an interactiondominated regime, repulsive dipolar interaction balances negative scattering lengths down to −17 Bohr radii. Our findings are in excellent agreement with mean-field calculations, revealing the important destabilizing role played by intersite dipolar interactions in deep lattices. more...
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- 2011
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14. Interaction of atoms with a magneto-optical potential
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Tilman Pfau, Jürgen Mlynek, Christian Kurtsiefer, and Charles S. Adams
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Quantum optics ,Physics ,Diffraction ,Zeeman effect ,Linear polarization ,Polarization (waves) ,Atomic and Molecular Physics, and Optics ,law.invention ,symbols.namesake ,law ,symbols ,Physics::Atomic Physics ,Atomic physics ,Circular polarization ,Beam splitter ,Light field - Abstract
A theoretical study of the coherent interaction of multilevel atoms with a magneto-optical potential is presented. The potential is formed by counterpropagating linearly polarized laser beams whose polarization vectors intersect at an angle cphi and a static magnetic field applied parallel to the laser propagation direction. For a particular ratio of the light and magnetic field amplitudes, the light shift at positions of purely circularly polarized light is equal to the Zeeman splitting. In this case, for a three-level atom, one of the eigenvalues has a triangular spatial form. The diffraction of atoms from this triangular phase grating is an efficient beam splitter. The splitting is symmetric for cphi=90° and asymmetric for cphi more...
- Published
- 1993
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15. Intense source of cold Rb atoms from a pure two-dimensional magneto-optical trap
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A. Batär, Tilman Pfau, Volker Schweikhard, Yu. B. Ovchinnikov, Axel Grabowski, Robert Löw, and J. Schoser
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Condensed Matter::Quantum Gases ,Physics ,Full width at half maximum ,Magneto-optical trap ,Flux ,Production (computer science) ,Physics::Atomic Physics ,Trapping ,Rate equation ,Atomic physics ,Atomic and Molecular Physics, and Optics ,Beam (structure) ,Collimated light - Abstract
We present a two-dimensional (2D) magneto-optical trap (MOT) setup for the production of a continuous collimated beam of cold ${}^{87}\mathrm{Rb}$ atoms out of a vapor cell. The underlying physics is purely two-dimensional cooling and trapping, which allows for a high flux of up to $6\ifmmode\times\else\texttimes\fi{}{10}^{10}$ atoms/s and a small divergence of the resulting beam. We analyze the velocity distribution of the 2D MOT. The longitudinal velocity distribution of the atomic beam shows a broad feature (full width at half maximum $\ensuremath{\simeq}75 \mathrm{m}/\mathrm{s}),$ centered around 50 m/s. The dependence of the flux on laser intensity, on geometry of the trapping volume, and on pressure in the vapor cell was investigated in detail. The influence of the geometry of the 2D MOT on the mean velocity of the cold beam has been studied. We present a simple model for the velocity distribution of the flux based on rate equations describing the general features of our source. more...
- Published
- 2002
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16. Striped states in a many-body system of tilted dipoles
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Matthias Wenzel, Tilman Pfau, Fabian Böttcher, Tim Langen, and Igor Ferrier-Barbut
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Physics ,Condensed Matter::Quantum Gases ,Range (particle radiation) ,Condensed matter physics ,Atomic Physics (physics.atom-ph) ,FOS: Physical sciences ,Interference (wave propagation) ,01 natural sciences ,Many body ,010305 fluids & plasmas ,Physics - Atomic Physics ,Supersolid ,Dipole ,Phase coherence ,Quantum Gases (cond-mat.quant-gas) ,Metastability ,0103 physical sciences ,010306 general physics ,Condensed Matter - Quantum Gases ,Magnetic dipole - Abstract
We study theoretically and experimentally the behaviour of a strongly confined dipolar Bose-Einstein condensate, in the regime of quantum-mechanical stabilization by beyond-mean-field effects. Theoretically, we demonstrate that self-organized striped ground states are predicted in the framework of the extended Gross-Pitaevskii theory. Experimentally, by tilting the magnetic dipoles we show that self-organized striped states can be generated, likely in their metastable state. Matter-wave interference experiments with multiple stripes show that there is no long-range off-diagonal order (global phase coherence). We outline a parameter range where global phase coherence could be established, thus paving the way towards the observation of supersolid states in this system., Comment: 9 pages, 7 figures more...
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