The coolest place in Serbia
In the experiment run by Dr. Senka Ćuk at the Photonics Center of the Institute of Physics Belgrade, a magneto-optical trapping of rubidium atoms has been realized in April 2015 for the first time in this part of Europe. Laser cooling of atoms to ultra-cold temperature of just 150 millionth of a degree above the absolute zero (150 μK) was realized by three pairs of counter-propagating laser beams, forming standing waves with the proper circular polarization. Trapping of the atoms happens in the intersection region of all laser beams due to the magnetic field gradient, and the atomic cloud forms in the center of hermetically sealed vacuum chamber. The fluorescence from the cloud, carrying information about its parameters, is observed by a CMOS camera, and under certain experimental conditions the reddish atomic cloud is visible even to the naked eye.
Research experience of Dr. Senka Ćuk gained at the Massachusetts Institute of Technology (MIT) in the group of Prof. Dr. Vladan Vuletić, while working on development of new techniques for entangling many atoms via light, contributed significantly to this new result in our lab. The MIT experiment also relies on ultra-cold rubidium atoms, this time trapped in an optical resonator. A weak vertically polarized light enters the resonator, and interacts with atoms multiple times before exiting the cavity towards detector. In most cases, the photon polarization remains the same, but from time to time a single photon of orthogonal polarization gets detected. Rotation of photon polarization results from its interaction with quantum noise associated with the atomic ensemble. The detection of a single output photon of polarization orthogonal to the input one generates strongly entangled states of almost all of the atoms in ensemble – nearly 3000 of them. Dr. Senka Ćuk significantly contributed to these results, which were published in Nature magazine on 25 March 2015 and present the largest number of mutually entangled particles ever realized in a laboratory.
IPB's Photonics Center is one of accredited national centers of excellence. It is headed by Dr. Branislav Jelenković, research professor at the Institute of Physics Belgrade and corresponding member of the Serbian Academy of Sciences and Arts.