Bose-Einstein condensates & tests of quantum mechanics Poul Lindholm Pedersen Ultracold Quantum Gases Group PhD day, 31 10 12
Bose-Einstein condensation T high Classical particles T = 0 Pure condensate T low Quantum gas T = T c Condensation After Ketterle et al.: Making, probing and understanding Bose Einstein Condensates. 2
Statistical physics Bose distribution function: Density of states (3D harm. osc.): Number of atoms: Not normalised as temperature decreases! Problem: ground state is not accounted for. 3
Statistical physics Correct: Finite population in ground state at T c Coherent atomic ensemble! Atoms act in unison. 4
BEC: Ideal quantum system Clean quantum system Easy to confine Wave like behaviour Matter interference Test of quantum mechanics 5
Optical lattice Standing light wave Off resonant light AC Stark effect, two level atom: Attractive for red detuning Atoms seek high intensity 6
Optical lattice Periodic potential for atoms Leads to energy bands Effective solid state system Simulation of condensed matter physics! High tunability 7
Our experiment Laser cooling MOT cell Science chamber Evaporative cooling 8
Laser cooling Magneto optical trap (MOT) Kick from photon absorption Quadrupole B field When atom moves away from center, it is kicked back towards the center Cooling and confinement! Limit: Not cold enough! Pictures: C.J. Foot, Atomic physics, OUP 2005 9
Evaporative cooling Throw away the hottest particles Confine atoms in magnetic trap Hot atoms move furthest out E Transfer atoms to untrapped state with RF radiation Decrease frequency Hot atoms are removed x Picture: http://www.flixya.com/photo/2086450/steaming Coffee 10
Condensation: step by step Decreasing RF frequency 11
Condensation: step by step Decreasing RF frequency 12
Spinor condensates Condensate with spin degree of freedom Magnetic interaction The sign of J determines the interaction type J <0: Ferromagnetic J > 0: Antiferromagnetic 13
Spinor dynamics Investigation of spin changing collisions Rubidium 87, F=2 Quadratic Zeeman effect Excess energy in collision 14
Spatially excited states Excess energy: spatial excitation Visible with Stern Gerlach separation of m F. Experiment Theory Higher modes of cylindrical trap (Bessel func.) M. Scherer, B. Lücke,1 G. Gebreyesus, O. Topic, F. Deuretzbacher, W. Ertmer, L. Santos, J. J. Arlt, and C. Klempt, PRL 105, 135302 (2010). 15
Non-classical states The ±1 states are entangled. We don t know which particle? is +1 and which is 1. Measuring the spin of the two particles breaks entanglement. Spin orientations of the atoms are correlated. Bell inequality: Correlation measure (Valid in locally realistic universe ) 16
Bell inequality for atoms Violation of Bell inequality for photons. Our experiment: Produce correlated atoms in optical lattice Excess energy: band excitation Tunneling = outcoupling Measure spin correlation Alain Aspect, Philippe Grangier, and Gérard Roger, PRL 49 (2) p. 91, 1982. 17
People Multispecies experiment Poul Lindholm Pedersen Miroslav Gajdacz Nils Winter Lars Wacker Ridha Horchani Jan Arlt Andrew Hilliard Troels Mørch Romain Müller Mark Bason Julija Knokneryte Jacob Sherson Ultracold bosons in optical High resolution experiment 31 10 2012 latticespoul Lindholm Pedersen 18