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EPJ D - Speed-control zone for polar molecules

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Published on 17 June 2010

Stark deceleration has emerged over the last decade as a leading technique for obtaining packets of quantum-state-selected molecules whose velocity can be tuned all the way down to zero. Here, a new compact, ultrahigh-vacuum-compatible Stark decelerator is described and demonstrated. The deceleration stages are fashioned out of tantalum wires, reducing the total length to about a tenth of that of a conventional Stark decelerator with the same number of electrode pairs.

The significantly lower cost of assembling and operating the wire decelerator makes it an attractive source of cold molecules, for use in applications ranging from trapping experiments to cold collisions to sympathetic cooling.

Structural, optical and nanomechanical properties of (111) oriented nanocrystalline ZnTe thin films

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Published on 17 June 2010

Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported. X-ray diffraction patterns reveal that the films were preferentially oriented along the (1 1 1) direction. The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap showed strong thickness dependence. The average film hardness and Young's modulus obtained from load-displacement curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of (1 1 1) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from the nanoscratch test was ~0.4.

EPJ B - Superfluidity of a perfect quantum crystal

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Published on 11 June 2010

Only one liquid exhibits Bose-Einstein condensation in nature: Helium II, . At such temperatures, all other substances are solid. In these two papers, Vitaly Golovko demonstrates that Bose-Einstein condensation can also occur in the solid state. Moreover, it is shown that at 0 K, a condensate crystal is energetically preferable with respect to the same quantum crystal without condensate. Therefore, on lowering the temperature of the crystal there must somewhere happen Bose-Einstein condensation, as in liquid helium. This opens a huge field for experimental investigations of Bose-Einstein condensation and of its influence on properties of solids.

EPJ B - What atomistic methods tell us about the mechanical response of amorphous solids

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Published on 17 May 2010

Our understanding of elasticity, plasticity and failure in non-crystalline solids has greatly enhanced through atomic scale simulation. A new Colloquium paper In EPJ B reviews a variety of computational approaches that have been successful in elucidating the atomic scale phenomena that control the mechanics of amorphous solids. The constitutive theories that have been developed for describing mechanical response are briefly illustrated, as well as the prospects for testing the assumptions of these theories using simulation. The authors, M.L. Falk and C.E. Maloney, pose the most pressing open questions for substantiating these theoretical approaches, and ultimately for understanding and predicting the mechanical behaviour of amorphous solids.

EPJ B - sp3 domains in graphite induced by visible light

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Published on 03 May 2010

Keiichiro Nasu reviews models of photo-induced structural phase transitions in relation to recent experimental results on unconventionally photoactive solids, where the relaxation of optical states results in macroscopic excited domains with new structural and electronic orders. Two key concepts, the hidden multi-stability of the ground state and proliferations of optically excited states are discussed. Taking the ionic to neutral phase transition in an organic charge-transfer crystal as example, the author documents the fundamental nature of photo-induced structural phase transitions. Further, Nasu recounts the details of the discovery of a new photo-induced phase of carbon, named "diaphite", located in between graphite and diamond. The mechanism of this photo-induced structural phase transition is discussed in terms of the proliferation of photo-generated inter-layer charge-transfer excitations in the visible regime.

Schrödinger Medal awarded to EPJ D Editor in Chief

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Published on 26 April 2010

Kurt Becker, Associate Provost at the Polytechnic Institute of NYU and Editor in Chief of EPJ D, was awarded the 2010 SASP Erwin Schrödinger Medal. The announcement was made in January 2010 during the Symposium of Atomic, Cluster, and Surface Physics (SASP) held in Obergurgl, Austria. Dr. Becker was cited for his “outstanding scientific achievements and contributions to research in molecular physics – specifically, the interaction of electrons with molecules and clusters – as well as in the properties and applications of plasmas”. The medal is named after the Austrian theoretical physicist Schrödinger, who won the Nobel Prize in 1933 for his work on the development and formulation of quantum mechanics. The entire journal team is delighted for Kurt Becker and congratulates him on this prestigious achievement.

EPJ D - Electrons go unperturbed in a matter-wave interferometer

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Published on 19 April 2010

Photodetachment microscopy provides the best electron affinity measurements on atoms and molecules. Photodetachment of a negative ion produces a nearly free electron, hardly perturbed by the residual atomic core. Applying an external electric field does not only concentrate the photoelectron current in a round spot, but also gives rise to an electron interference pattern, due to the existence of a pair of possible trajectories bound to every point of the spot. This very fundamental matter-wave interferometer produces extraordinarily robust interferograms. Although magnetic fields, even in the sub-microT range, causes fluxes between the interfering trajectories that can be huge compared to the quantum unit of magnetic flux, a magnetic perturbation of the system appears to only produce a global deviation of the spot, without any modification of the interference pattern. The main result of the recent paper published in EPJ D by Chaibi et al. is that even in higher magnetic fields (typically 100 microT) the electron interference phase, or number of interference rings, remain unperturbed. This comfirms photodetachment as a highly accurate method for electron spectrometry and electron affinity measurements.

Quantum memories set to go a long way

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Published on 14 April 2010

Quantum memories are essential elements for many potential applications of quantum technology. Research on the development of such memories is currently very lively, with a particular emphasis on memories that can interface with photons, which are the best carriers of quantum information over long distances. A Colloquium paper in the May issue on EPJ D reviews a number of different approaches to this challenge, with a focus on the approaches that were represented in the large European Union Integrated Project "Qubit Applications". This Colloquium covers solid-state atomic ensembles, nitrogen-vacancy centres, quantum dots, single atoms and atomic gases. Since the considered approaches are very diverse, an important part of the work was to establish criteria that allow a meaningful comparison. The authors discuss both the current experimental state of the art and the potential long-term performance of the various systems.

Liquid crystals straighten up

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Published on 06 April 2010

Grazing incidence X-ray diffraction, performed by Grelet and colleagues, reveals that thin films of discotic liquid crystals typically prefer to lie flat in columns oriented along the surface of their substrate. These materials are potentially useful for organic solar cells, but to achieve good performance from such devices, the column axis should rather be oriented vertical to the conducting substrate. However, the authors of this EPJ E paper have discovered a specific thermal process that makes it possible to change the column alignment from planar to vertical and achieve the best conditions for charge transport in photovoltaic devices.

Giving light a good squeeze

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Published on 01 March 2010

Multi-mode optical systems can improve precision measurements in the domain of quantum imaging and metrology. In this context, mastering quantum fluctuations and correlations in complex optical systems is crucial. In a recent EPJ D paper, the authors G. Patera, N. Treps, C. Fabre and G.J. de Valcárcel present the quantum model for an optical parametric oscillator synchronously pumped by a mode locked laser. To cope with the complexity of a system that usually involves about 100 000 modes, the authors introduce new physical objects that they call supermodes, which are proper combinations of standard modes. Their dynamics is studied from both a classical and a quantum point of view with respect to the experimental condition considered. This study shows that a synchronously pumped optical parametric oscillator is a suitable and malleable source of highly multimode non-classical light in the temporal domain.