O n t h e T r a c k o f M o d e r n P h y s i c s

current

magnetic field

trapped atoms

Cooling ,by collisions: a ruby “atom” in "melassa" of photons

(here polystyrene balls).

Cooling with evaporation, even using a hot air stream,is very effective

laser beam

This picture is a wonderful example of the Unity of Physics. The free falling condensate covers distances rising in time according to Galileo’s law s=gt2 (and showing a parabolic trajectory here).

This picture is also a tribute to Werner Heisenberg. Initially, the atomic cloud is more squeezed in the vertical direction than in the horizontal one. But, the better determination of the position in space requires A worse determination of velocity. In fact, the velocity distribution is wider in the vertical direction, so the cloud diffuses more.

So called Gross-Pitaevskii equation is the basis for the practical description of Bose-Einstein condensate in diluted gases. It resembles much the “ordinary" Schrödinger equation, apart from an interaction term.

And this term makes thedifference: only including the interaction between separated particles (attracting, repulsing) one gets a real, experimental situation.

Three steps of Bose – Einstein condensation

1. Atoms are trapped in special configurationsof strong magnetic

fields

2. The atomic cloud is cooled (atoms slow down)by absorbing and emitting photon quanta from counter- propagating laser beams.

http://www.physik.uni-mainz.de/quantum/bec/introduction/evaporativecooling.html

3. The hottest atoms are removed, by flippingthem with radio-frequency to a non-trapped (anotherZeeman sublevel) state.

http://www.physik.uni-mainz.de/quantum/bec/

Concise and exemplary description of BEChttp://physicsweb.org/articles/world/10/3/3/1

Trapped atoms are like top-spins in the center of a quite shallow plate.

The experimental set-up for Bose-Einstein condensationThe tower in front is the magneto-optical trap and the magnetic trap, into which atoms pre-cooled in MOT are transferred.(Prof. Ennio Arimondo, University of Pisa)

The research team at the MPQ and University of Munich was the second group outside the USA to report BEC. The evidence for condensation emerged from time of flight measurements. A sharp peak in the velocity distribution was observed below a critical temperature. (© Immanuel Bloch, Quantum, Mainz)

Atoms are individuals. Sometimes, they loose their individuality and move together. This happens at low

temperatures (nK), when their de Broglie waves overlap. The whole atomic cloud becomes a single quantum object.

Each of the atoms in the condensate (in blue) has the same quantum mechanical wave function, and so they all move as one. Atoms outside the

condensate move faster and in all directions. (Science 22/12/2005, Illustration: Steve Keller, reproduced with permission)

A magnetic trap, below a cubic glass cell for cooling atoms(Dr Leonardo Ricci, Trento University

Cortesy Prof. Massimo Inguscio, LENS, Firenze

- Lev, the wavepacket describing an electron diverges in time. Does it result from a special, Gaussian form of the packet?- No! Any packet diverges in time – this is a superposition of waves with different lengths. Only a plane wave does not diverge in time.

- So, quantum mechanics does notdescribe electron as a stable object?-Wrong! Electron is stable and point-like! Schrödinger’s equation does NOT describe the electron itself but the probability of finding the electron in a given point!

- Lev, tell me what ideawas behind Your famousequation?

- In 1956 H. Hall and W. Vined in UK discovered a very interesting phenomenon - quantum vortexes in superfluidHelium. They were predicted by L. Onsagerand R. Feynman, but we had no good theory. I thought on the subject for several years and finally, in 1961, being on vacations, I understood that the theory can be developedfor the Bose-condensed gases, which were in fact created in 1975 only. I remember thatLandau agreed with my theory not immediately, but after several discussions.

Photos are from professor Pitaevskii’s 70th birthday dinner. Thanks! Asking questions: GK

Antezza, Mauro; Pitaevskii, Lev P; Stringari, Sandro We calculate the effect of the interaction between an optically active material and a Bose-Einstein condensate on the collective oscillations of the condensate. We provide explicit expressions for the frequency shift of the center of mass oscillation in terms of the potential generated by the substrate and of the density profile of the gas. The form of the potential is discussed in details and various regimes (van der Waals-London, Casimir-Polder and thermal regimes) are identified as a function of the distance of atoms from the surface.Submitted to PRA

Studies of this new, exotic, supercool form of matter allow to understand numerous other phenomena, from high temperature super-conductors, to neutron stars or the quark-gluon plasma of the early Universe.

Possible applications range from atomic lasers to precise measu-rements of the Casimir-Polder force.