Many Bodies Make One Coherent Burst of Light Rice University researchers first to see superfluorescence from solid-state materialIn a flash, the world changed for Tim Noe -and for physicists who study what they call many-body problems.The Rice University graduate student was the first to see, in the summer of 2010, proof of a theory that solid-state materials are capable of producing an effect known as superfluorescence.That can only happen when "many bodies" -in this case, electron-hole pairs created in a semiconductor -decide to cooperate.Noe, a student of Rice physicist Junichiro Kono, and their research team used highintensity laser pulses, a strong magnetic field and very cold temperatures to create the conditions for superfluorescence in a stack of 15 undoped quantum wells.The wells were made of indium, gallium and arsenic and separated by barriers of galliumarsenide (GaAs).The researchers' results were reported this week in the journal Nature Physics.Noe spent weeks at the only facility with the right combination of gear to carry out such an experiment, the National High Magnetic Field Laboratory at Florida State University.There, he placed the device in an ultracold (as low as 5 kelvins) chamber, pumped up the magnetic field (which effectively makes the "many body" particlesthe electron-hole pairs -more sensitive and controllable) and fired a strong laser pulse at the array."When you shine light on a semiconductor with a photon energy larger than the band gap, you can create electrons in the conduction band and holes in the valence band.They become conducting," said Kono, a Rice professor of electrical and computer engineering and in physics and astronomy."The electrons and holes recombine -which means they disappear -and emit light.One electron-hole pair disappears and one photon comes out.This process is called photoluminescence."The Rice experiment acted just that way, but pumping strong laser light into the layers created a cascade among the quantum wells."What Tim discovered is that in these extreme conditions, with an intense pulse of light on the order of 100 femtoseconds (quadrillionths of a second), you create many, many electron-hole pairs.Then you
A group at the University of Texas at Austin has recently created Rb\-2 moleculaes from a Rubidium\|87 Bose\|Einstein condensate with two\|photon stimulated Raman transitions.The molecules are in a single ro\|vibrational level and have a temperature on the order of 100nK.These might be the coldest molecules in the universe,as says Paul Julienne,a senior atomic physicist at NIST.This method provides an alternative route for formation of ultra\|cold molecules which are still not achievable with the traditional laser cooling and trapping techniques,and may lead to the first realization of molecular Bose\|Einstein condensate.