Universality in constrained thin sheets

Suppose you hang a curtain down before your window. Set the x-axis and y-axis in the vertical and horizontal direction, respectively. The upper edge (at x=0) of the curtain is somewhat constrained by the reel bar. Certain kind of creases develop that can be described by the out-of-plane deformation, a function z(x,y). Very generally, this function is largely sinusoidal along y given x, with a wavelength lambda(x). More interestingly, such crumpling pattern is also seen in much smaller thin sheets, such as graphene. Is there any universal manner to all thin sheets with constrained boundaries ? The answer is yes. The work has just been done to demonstrate it [PRL 106, 224301 (2011)]. A key result is that, lambda follows a simple power law, namely, lambda~x^m, where m for light sheet (2/3) is different from that for heavy sheet (1/2), thus showing a hierarchy. The amazing thing is the universality.

We show that thin sheets under boundary confinement spontaneously generate a universal self-similar hierarchy of wrinkles. From simple geometry arguments and energy scalings, we develop a formalism based on wrinklons, the localized transition zone in the merging of two wrinkles, as building blocks of the global pattern. Contrary to the case of crumpled paper where elastic energy is focused, this transition is
described as smooth in agreement with a recent numerical work [R. D. Schroll, E. Katifori, and B. Davidovitch, Phys. Rev. Lett. 106, 074301 (2011)]. This formalism is validated from hundreds of nanometers for graphene sheets to meters for ordinary curtains, which shows the universality of our description. We finally describe the effect of an external tension to the distribution of the wrinkles.

Cohen in a lecture

He gave a lecture on his recent work, in which he has listed a handful of his work on graphene, on photovoltaics, nano structures and superconductors. It might be worthy to put the link here: http://videochannel.ust.hk/Watch.aspx?Section=Channels&Channel=2&SubType=All&View=Icon&Sort=Date&Page=3&Current=30&Mode=Play

Delocalization of Cooper pairs by doping ?

This is definitely a very wonderful step forward. Have not read it yet, but eager to tomorrow.
http://www.nature.com/nature/journal/v472/n7344/pdf/nature09998.pdf

Trapped ions realize coupled harmonic oscillators

I highlight this work just because it was done at nearly the same time by two distant groups, one in US and the other in Austria. Both published their work in Nature. They demonstrated the potential of trapped ions in quantum computing.

[doi:10.1038/nature09800] More than 100 years ago, Hertz succeeded in transmitting signals over a few metres to a receiving antenna using an electromagnetic oscillator, thus proving the electromagnetic theory¹ developed by Maxwell. Since this seminal work, technology has developed, and various oscillators are now available at the quantum mechanical level. For quantized electromagnetic oscillations, atoms in cavities can be used to couple electric fields^{2, 3}. However, a quantum mechanical link between two mechanical oscillators (such as cantilevers^{4, 5} or the vibrational modes of trapped atoms⁶ or ions^{7, 8}) has been rarely demonstrated and has been achieved only indirectly. Examples include the mechanical transport of atoms carrying quantum information⁹ or the use of spontaneously emitted photons¹⁰. Here we achieve direct coupling between the motional dipoles of separately trapped ions over a distance of 54 micrometres, using the dipole–dipole interaction as a quantum mechanical transmission line¹¹. This interaction is small between single trapped ions, but the coupling is amplified by using additional trapped ions as antennae. With three ions in each well, the interaction is increased by a factor of seven compared to the single-ion case. This enhancement facilitates bridging of larger distances and relaxes the constraints on the miniaturization of trap electrodes. The system provides a building block for quantum computers and opportunities for coupling different types of quantum systems.

[doi:10.1038/nature09721] The harmonic oscillator is one of the simplest physical systems but also one of the most fundamental. It is ubiquitous in nature, often serving as an approximation for a more complicated system or as a building block in larger models. Realizations of harmonic oscillators in the quantum regime include electromagnetic fields in a cavity^{1, 2, 3} and the mechanical modes of a trapped atom⁴ or macroscopic solid⁵. Quantized interaction between two motional modes of an individual trapped ion has been achieved by coupling through optical fields⁶, and entangled motion of two ions in separate locations has been accomplished indirectly through their internal states⁷. However, direct controllable coupling between quantized mechanical oscillators held in separate locations has not been realized previously. Here we implement such coupling through the mutual Coulomb interaction of two ions held in trapping potentials separated by 40 μm (similar work is reported in a related paper⁸). By tuning the confining wells into resonance, energy is exchanged between the ions at the quantum level, establishing that direct coherent motional coupling is possible for separately trapped ions. The system demonstrates a building block for quantum information processing and quantum simulation. More broadly, this work is a natural precursor to experiments in hybrid quantum systems, such as coupling a trapped ion to a quantized macroscopic mechanical or electrical oscillator.

A circuit that beats Jaynes–Cummings model

In circuit quantum electrodynamics1–10 (QED), where superconducting
artificial atoms are coupled to on-chip cavities, the exploration of fundamental quantum physics in the strongcoupling regime has greatly evolved. In this regime, an
atom and a cavity can exchange a photon frequently before coherence is lost. Nevertheless, all experiments so far are well described by the renowned Jaynes–Cummings model11. Here, we report on the first experimental realization of a circuit QED system operating in the ultrastrong-coupling limit12,13, where the atom–cavity coupling rate g reaches a considerable fraction of the cavity transition frequency !r. Furthermore, we present direct evidence for the breakdown of the Jaynes–Cummings model.We reach remarkable normalized coupling rates g=!r of up to 12% by enhancing the inductive coupling14 of a flux qubit to a transmission line resonator. Our circuit extends the toolbox of quantum optics on a chip towards exciting explorations of ultrastrong light–matter interaction. [DOI: 10.1038/NPHYS1730]

Molecular superfluidity ?

Bosons could become superfluid at low temperatures: it flows without feeling the friction. This is so due to the opening of an energy gap as bosons condense into a so-called macro-molecule in the presence of interactions. It is expected that such condensation happens at a number of bosons. Now it was demonstrated that, this number can be down to 9 pH2 molecules.

Clusters of para-hydrogen (pH2) have been predicted to exhibit superfluid behavior, but direct observation of this phenomenon has been elusive. Combining experiments and theoretical simulations, we have determined the size evolution of the superfluid response of pH2 clusters doped with carbon dioxide (CO2). Reduction of the effective inertia is observed when the dopant is surrounded by the pH2 solvent. This marks the onset of molecular superfluidity in pH2. The fractional occupation of solvation
rings around CO2 correlates with enhanced superfluid response for certain cluster sizes. [PRL 105, 133401 (2010)]