BoseEinstein condensation of chromium Ashok Mohapatra NISER Bhubaneswar

Bose-Einstein condensation of chromium Ashok Mohapatra NISER, Bhubaneswar 1

SFB/TRR 21 The team Cr BEC team Axel Tilman Jonas Yong Wan (diploma student) Stefan Ashok 2

Chromium BEC, 2004 by Pfau’s group 3

Chromium Large magnetic moment 6μB 36 times more dipolar interaction compared to alkali atoms 4

Relevant energy levels of chromium 7 P 4 7 P 3 MOT 425 nm Repumper 663 nm 5 D 7 S Optical Pumping 427 nm 3 4 Ti: Sa 851 nm 2 W doubled (LBO) (600 m. W) 5

Experimental set up 6

Steps to get the BEC Step 1: CLIP load Step 2: RF evapolarion to 15 μK and load to a dipole trap Step 3: Switch off the MT and optically pump the atoms to the energetically lowest Zeeman state to prevent the dipolar relaxation (large μB helps to flip the atoms to wrong Zeeman states) 7

Steps to get the BEC Step 4: Forced evaporation in a crossed dipole trap A. Griesmaier, Phys. Rev. Lett. 94, 160401 (2005) Condensate of 50, 000 atoms 8

Feshbach resonances in Chromium J. Werner et al. , Phys. Rev. Lett. 94, 183201 (2005) Braodest resonance @ 590 G, Δ ~ 1. 4 G Control of magnetic field to 10 -5 is needed to have a noise of ± 1 a 0 at 0 scattering length Active stabilization of the current in the Feshbach coils was used 9

Feshbach resonances in Chromium B 0 ~ 590 G ΔB ~ 1. 4 G 10

Broad feshabch resonance Fit: B 0 ~ 590 G ΔB ~ 1. 4 G 11

Strong dipolar effects T. Lahaye, T. Koch, B. Fröhlich, M. Fattori, J. Metz, A. Griesmaier, S. Giovanazzi, T. Pfau; Nature 448, 672 (2007) 12

Roton like excitation spectrum in a dipolar quantum gas L. Santos et al. , PRL 90 250403 (2003) D-W. Wang et al. , ar. Xiv: 0812. 1838 13

Dipolar coupling in classical ferrofluids Rosensweig instability M. D. Cowley and R. E. Rosensweig, J. Fluid Mech. 30, 671 (1967) 14

Roton like excitation spectrum in classical ferrofluid Dispersion relation of surface wave in ferrofluid J. Browaeys et al. , Braz. J. Phys. 31, 447 (2001) R. E. Rosensweig, Ferrohydrodynamics, Dover Publications, Inc (1997), page 191 15

Roton like excitation spectrum in classical ferrofluid Spontaneous static deformation around critical magnetic field J. Browaeys et al. , Braz. J. Phys. 31, 447 (2001) The rotonization mechanism in quantum dipolar gas a quantum could be a classical phenomenon………… Do we really need a superfluidity to have roton in quantum dipolar gas? ? ? 16

Roton and Supersolid phase in Rydberg dressed BEC Henkel et al. , Phys. Rev. Lett. 104, 195302 (2010)

Collective interaction using coherent Rydberg dressed BEC Honer et al, PRL 105, 160404 (2010)

Thank you 19

Rosensweig instability in classical ferrofluid Competition between the magnetic interaction with Gravity and surface free energy Surface wave C. Gollwitzer et al. , , J. Fluid Mech. (2006) Similar pattern in a quantum gas would lead to a supersolid state 20

dipolar interaction in a BEC Field in y-direction Field in Z-direction J. Stuhler et al. , Phys. Rev. Lett. 95 , 150406 (2005) 21