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Bose-Einstein condensation of Bose-Einstein condensation of chromiumchromium

Ashok MohapatraAshok Mohapatra

NISER, BhubaneswarNISER, Bhubaneswar

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Cr BEC team

Ashok

Axel

Stefan

Jonas

The teamThe teamSFB/TRR 21SFB/TRR21

TilmanTilman

Yong Wan (diploma student)Yong Wan (diploma student)

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ChromiumChromium

BEC, 2004BEC, 2004by Pfau’s groupby Pfau’s group

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ChromiumChromium

Large magnetic moment 6μB

36 times more dipolar interaction compared to alkali atoms

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Relevant energy levels of chromium Relevant energy levels of chromium

7S3

7P4

7P3

5D4

MOT425 nm

Optical Pumping427 nm

Repumper663 nm

Ti:SaTi:Sa 851 nm 2 W851 nm 2 W doubled (LBO) (600 mW)doubled (LBO) (600 mW)

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Experimental set upExperimental set up

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Steps to get the BECSteps to get the BEC Step 1: CLIP load Step 1: CLIP load

Step 2: RF evapolarion to 15 Step 2: RF evapolarion to 15 μμK and K and load to a dipole trap load to a dipole trap

Step 3: Switch off the MT and optically pump the atoms to the energetically lowest Step 3: Switch off the MT and optically pump the atoms to the energetically lowest Zeeman state to prevent the dipolar relaxation (large Zeeman state to prevent the dipolar relaxation (large μμB B helps to flip the atomshelps to flip the atoms

to wrong Zeeman states)to wrong Zeeman states)

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Steps to get the BECSteps to get the BEC

Step 4: Forced evaporation in a crossed dipole trapStep 4: Forced evaporation in a crossed dipole trap

Condensate ofCondensate of50,000 atoms50,000 atoms

A. Griesmaier, A. Griesmaier, Phys. Rev. Lett. Phys. Rev. Lett. 9494, 160401 (2005) , 160401 (2005)

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Feshbach resonances in Feshbach resonances in ChromiumChromium

J. Werner et al., Phys. Rev. Lett. 94, 183201 (2005)

Braodest Braodest resonanceresonance@ 590 G,@ 590 G,ΔΔ ~ 1.4 G ~ 1.4 G

Control of magnetic field to 10Control of magnetic field to 10-5-5 is needed to have a noise of ±1a is needed to have a noise of ±1a0 0 at 0 scattering lengthat 0 scattering length

Active stabilization of the current in the Feshbach coils was usedActive stabilization of the current in the Feshbach coils was used

Feshbach resonances in ChromiumFeshbach resonances in Chromium

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BB00 ~ 590 G ~ 590 G

ΔΔB ~ 1.4 GB ~ 1.4 G

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Broad feshabch resonanceBroad feshabch resonance

0

0

1bg

bg

Ba a

B B

a a

Fit:Fit:

BB00 ~ 590 G ~ 590 G

ΔΔB ~ 1.4 GB ~ 1.4 G

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

Strong dipolar effectsStrong dipolar effects

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Roton like excitation spectrum in a Roton like excitation spectrum in a dipolar quantum gasdipolar quantum gas

L. Santos et al., PRL 90 250403 (2003)L. Santos et al., PRL 90 250403 (2003)D-W. Wang et al., arXiv:0812.1838D-W. Wang et al., arXiv:0812.1838

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Rosensweig instabilityM. D. Cowley and R. E. Rosensweig, J. Fluid Mech. 30, 671 (1967)

Dipolar coupling in classical ferrofluidsDipolar coupling in classical ferrofluids

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Roton like excitation spectrum in Roton like excitation spectrum in classical ferrofluidclassical ferrofluid

Dispersion relation of surface wave in ferrofluidDispersion relation of surface wave in ferrofluid

J. Browaeys et al., Braz. J. Phys. J. Browaeys et al., Braz. J. Phys. 31,31, 447 (2001) 447 (2001)R. E. Rosensweig, Ferrohydrodynamics,R. E. Rosensweig, Ferrohydrodynamics,Dover Publications, Inc (1997), page 191Dover Publications, Inc (1997), page 191

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Roton like excitation spectrum in Roton like excitation spectrum in classical ferrofluidclassical ferrofluid

Spontaneous static deformation around critical magnetic fieldSpontaneous static deformation around critical magnetic fieldJ. Browaeys et al., Braz. J. Phys. J. Browaeys et al., Braz. J. Phys. 31,31, 447 (2001) 447 (2001)

The rotonization mechanism in quantum dipolar gas a quantum could be a The rotonization mechanism in quantum dipolar gas a quantum could be a classical phenomenon…………classical phenomenon…………

Do we really need a superfluidity to have roton in quantum dipolar gas?????Do we really need a superfluidity to have roton in quantum dipolar gas?????

Roton and Supersolid phase in Roton and Supersolid phase in Rydberg dressed BECRydberg dressed BEC

Henkel et al., Phys. Rev. Henkel et al., Phys. Rev. Lett. 104, 195302 (2010)Lett. 104, 195302 (2010)

Collective interaction using Collective interaction using coherent Rydberg dressed BECcoherent Rydberg dressed BEC

Honer et al, PRL Honer et al, PRL 105,105, 160404 (2010) 160404 (2010)

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Thank youThank you

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Rosensweig instability in Rosensweig instability in classical ferrofluidclassical ferrofluid

Competition betweenCompetition betweenthe magnetic interaction the magnetic interaction with Gravity and surfacewith Gravity and surfacefree energy free energy

Surface waveSurface wave C. Gollwitzer et al.,, J. Fluid Mech. (2006)C. Gollwitzer et al.,, J. Fluid Mech. (2006)

Similar pattern in a quantum gas would lead to a supersolid stateSimilar pattern in a quantum gas would lead to a supersolid state

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dipolar interaction in a BECdipolar interaction in a BEC

Field in y-directionField in y-direction

Field in Z-directionField in Z-direction

J. Stuhler et al., Phys. Rev. Lett. J. Stuhler et al., Phys. Rev. Lett. 95 95 , 150406 (2005), 150406 (2005)