Physics Bits and Bites

Here are three interesting and intriguing physics items I came across recently:

• Last year, the American Association for the Advancement of Science (AAAS) had organized a symposium called "Quest for the Perfect Liquid: Connecting Heavy Ions, String Theory, and Cold Atoms". Perfect, low-viscosity liquids can be observed when there is a very strong interaction between the constituents of the fluid, as is the case for the quarks and gluons created in heavy ion collisions at RHIC, or clouds of ultracold lithium atoms in optical traps. The strongly coupled quark gluon plasma can be described using the AdS/CFT correspondence, which brings sting theory into play (see also this earlier post). At the AAAS symposium, physicist-blogger Clifford Johnson (from Asymptotia) and Peter Steinberg (from Entropy Bound) discussed this connection, and a write-up of their presentation has now come out as a feature article in the May 2010 issue of Physics Today, "What black holes teach about strongly coupled particles" (free access).


• You may be aware of the ongoing quest for the densest possible packing of tetrahedra? The NYT wrote about this in January, and the articles mentions that a paper on the subject "prompted Paul M. Chaikin, a professor of physics at New York University, to buy tetrahedral dice by the hundreds and have a high school student stuff them into fish bowls and other containers." This project now resulted in a Physical Review Letter, with an experimentally determined volume fraction of 0.76±0.02 (The current theoretical "record" is at 0.856). Analysis of the experiment was done using Magnetic Resonance Imaging to look "into" the container crammed with tetrahedra, which shows that the packing is highly disordered. More background can be found in an article at "Physics", which also contains a free link to the PRL paper.


• Also via Physics, I've learned about what is the fastest (and possibly smallest) analogue computer to perform Fourier transforms: a single iodine molecule. A iodine molecule consists of two iodine atoms, which can vibrate, realizing a tiny harmonic oscillator. During one period, a harmonic oscillator follows a circular trajectory in phase space, which means that the Wigner function describing the quantum state of the oscillator "switches" space and momentum coordinates every quarter period. Going from real space to momentum space corresponds to a Fourier transform, so when the wave function of the iodine molecule is prepared in real space, after quarter of a period, the wave function encodes the Fourier transform of the initial configuration. Using laser, it is possible to prepare the molecule in definite state, and to probe the state again later. This allows discrete Fourier transforms for four and eight elements, and all this within 145 femtoseconds, "which is shorter than the typical clock period of the current fastest Si-based computers by 3 orders of magnitudes." (Ultrafast Fourier Transform with a Femtosecond-Laser-Driven Molecule", PRL).