Bose Einstein Condensation Condensed Matter II –Spring 2007 Davi Ortega In Diluted Gas

Summary From counting to a new state of matter –Indistinguishability of particles –Counting indistinguishable particles –Einstein’s conclusion = New State –Some properties BEC in Dilute Gases and Liquid Helium Experiments to achieve the BEC. News

Statistics of Idea Gas Two Particles Gas: A and B. Classical Bosons: Can occupy the same level Indistinguishable Particles Fermions: Cannot occupy the same level Distinguishable Particles Average number of occupation for each energy state (Boson Case)

Some Theory Particle in a 3D box: Calculating explicitly the total number:

More Theory But what happens now if I let at this temperature the density n V of the substance increase(e.g., by isothermal compression) to even higher values? I claim that in this case a number of molecules which always grows with the total density makes a transition to the 1. quantum state (state without kinetic energy)… … The claim thus asserts that something similar happens as when isothermally compressing a vapor beyond the volume of saturation. A separation occurs; a part “condenses”, the rest remains a “saturated ideal gas”. (Einstein, 1925).

Two more useful results The order of the de Broglie wavelenght is the same as the volume ocupied by the ensemble Number of the particles that falls to the “condensate” state

An Last statement This whole theory assume non interacting particles: Schrödinger Equation Interacting Particles: Gross-Pitaeviski Eq.

Achievements 1938 – Pyotr Kapitsa John Allen and Don Misener: Helium – Eric Cornell and Carl Wieman: Rb87: Pure BEC – Wolfgang Ketterle Na23. (4 months later)

Liquid He vs. Diluted Gas Strong Interactions in He qualitatively changes the nature of transition. Diluted Gas –Pure Condensate state Liquid Helium –Zero Viscosity –And other strange properties.

How to make a BEC ? Heat the atoms: 600 K (gas) Confine them in a beam Decelerate the beam Trap the atoms (Magneto Optical Trap) Magnetic Trapping (avoid atoms recoil by spontaneous emission and random absorption) Evaporative Cooling

Famous Picture

Any other way ?! YES Michael Chapman All Optical BEC

Current Research BEC achieved in several atoms. Strange Properties: –Superfluidity – Slowing of light Wave-like phenomena in atoms. –Interference between two condensates. Atom Laser –Coherent Matter Waves