Are high-energy physicists about to give us yet another probe?

October 17, 2009

In some recent posts I have highlighted the fact that some of the cutting-edge research in high-energy physics (HEP) is providing us with novel form of condensed matter – in particular, the quark-gluon plasma. This type of interaction between (or merging of) condensed matter and high-energy physics is new, since in the past HEP looked at process involving a few particles at a time, i.e. it was not concerned with collective states of matter or with phase diagrams.

On the other hand, there is a different short of interaction between HEP and condensed matter physics that goes a long way back, namely we owe to high-energy physicists some of the most powerful probes available of condensed matter systems. For example, the most advanced X-ray and neutron sources are based on particle accelerators (e.g. the electron and proton synchrotrons employed by Diamond and ISIS, respectively, here on the Harwell campus). Such machines ride on the back of advances in technology that were spurred by research at the frontier of particle physics some decades ago.

Now Andreas Ipp and Christoph Keitel propose that a new probe of matter may be provided by the quark-gluon itself:

Ipp, A., Keitel, C.H. & Evers, J., 2009. Yoctosecond Photon Pulses from Quark-Gluon Plasmas. Physical Review Letters, 103(15), 152301-4.

For a short summary see

Physics – The shortest known photon pulses.

The article argues that ultra-short pulses of light are emitted by the quark-gluon plasma formed in heavy-ion collisions and propose it as a probe of ultra-fast processes, such as those taking place inside the nucleus. The pulses are ~ 1 Yoctosecond = 1E-24 seconds in duration (look it up on Wikipedia). This corresponds to approximately 4 GeV. The question I ask is: what about condensed matter? Could this be useful there, too?

While all condensed matter processes are much less energetic than that, the energy of the probe need not be the energy of the excitation being probed – the energy of the probe just limits the resolution (the energy of the excitation being probed is the energy change of the photons in the pulse as they go through the sample). In that sense these ultra-short, high-energy pulses could be useful to probe excitations at much lower energies (e.g. ~ 10 meV, which is relevant for example for magnetic excitations in superconductors) but with potentially much more resolution than can be currently achieved.

The question is: are our current probes limited by their resolution? After all, what could we possibly learn that would be relevant to understand, say, a superconductor, that happens on the yoctosecond timescale? I’d love to know what people think about this.

One final though: the Yoctosecond pulses are obtained because a ys is the typical lifetime of a quark-gluon plasma (QGP). This raises the following difficulty, from the point of view of regarding the QGP itself as a condensed system and an object of study: if it only lasts for a ys, we are going to need even faster pulses to study its dynamics. In other words, if we regard the QGP as a condensed matter system, it is going to be really hard to invent the equivalents of neutron and X-ray scattering for this system. Perhaps we could use photons created in one QGP to probe another one…?


Strong correlations in ultra-cold atom gases and at the RHIC – the string connection

September 17, 2009

You may remember a brief mention of Brookhaven’s Relativistic Heavy Ion Collider (RHIC) in our article on strong correlations of a couple of months ago. This month Physics World carries another article, by Barbara Jacak, that discusses that type of strongly-correlated quantum matter in a lot more detail. The new article explains how string theory can be used to connect the experiments at RHIC to others carried out on another type of strongly-correlated system: ultra-cold atomic gases. Well worth reading:

PS: there was also a much more technical article on strongly interacting matter (as the quark-gluon soup is now known) in Rev. Mods. Phys. a few months ago:

Colloquium: Phase diagram of strongly interacting matter
P. Braun-Munzinger and J. Wambach, Rev. Mod. Phys. 81, 1031 (2009)