The CsIII Project Homepage

Content: Goals of the Experiment  /  Status of Research  /  References  /  Status of the Project  /  What's New  /  Support

Goals of the Experiment

The goals of this project (begin: Sept. 1^st 2003) are

1. to develop a new generation Cs BEC apparatus which incorporates the experience gained from first generation setup (see LevT-project) and to implement major improvements to create a high particle number Cs BEC with optimum optical access, greatly increased magnetic switching speed, and with much improved shielding from external perturbations such as fluctuating magnetic fields,

2. to use the new source of quantum matter for matter-wave interferometry with the aim to perform a precision measurement of the fine structure constant α at the level of 1 ppb. This fundamental constant can be determined from a measurement of the photon recoil frequency using e.g. so-called contrast interferometry. An interferometer with Cs matter-waves would benefit from the control of the self-interaction and the long interrogation times possible with levitated atoms,

3. and to add a three-dimensional lattice potential for creating a tunable Mott insulator phase for preparing non-classical states of the matter wave. For example, placing precisely two atoms at each lattice site will allow for a direct measurement of collisional phases or to study the formation of ultracold dimer molecules (see LevT-project) . Placing precisely three atoms at each site, in combination with a variation of the scattering length, should allow a rigorous experimental study of three-body dynamics and of the Efimov effect.

Status of Research

The field of quantum gases has seen remarkable progress during the last years. More species have been put into the state of a Bose-Einstein condensate (BEC), adding to the richness of the available systems for future quantum gas studies (for more information, see a list of atoms trap experiments worldwide). For example, quantum gases with Cs atoms [1] feature wide magnetic tunability of interaction properties, allowing the realization of weakly and strongly interacting matter waves and the coupling to molecular systems. The creation of pure samples of dimer molecules  within the 3D-Cs-BEC experimental effort of our group (LevT-Project) [2] has helped to initiate a whole new field of research on its own, namely the field of molecular quantum gases. The molecules are created in the zero-temperature limit via magnetically induced Feshbach resonances which couple atomic to high-lying molecular states. A primary goal of the research with molecular systems is the creation of molecular BECs. This goal has been achieved for the case of dimers composed of fermionic atoms [3,4], owing to the remarkable collisional stability of such molecules (see e.g. the Li-project of our group). A recent highlight has been the observation of the BEC-to-BCS crossover [5,6] for these systems. For dimers made of bosonic atoms, the quantum degenerate regime has been reached [2,7], but definite measurements on the hydrodynamic, superfluid and coherence properties are still lacking. Future experiments will determine the collisional stability of the molecules near appropriately chosen Feshbach resonances. A primary goal is the investigation of chemical reactions in the quantum degenerate regime, and in particular the observation of the quantum phase transition from an atomic to a molecular BEC [8].

The creation of ultracold molecules and molecular quantum gases has opened up various exciting directions for the present and future research. It is now possible to study molecular interactions and few-body quantum systems in the zero-temperature limit. For example, our group has been able to observe Feshbach-like resonances between molecules [9] as a result of coupling to tetramer states, and recently we found experimental evidence for Efimov trimer states in an ultracold gas of thermal Cs atoms [10]. A new level of quantum control has been reached by combining the techniques of Feshbach association and quantum gases in optical lattice potentials. Long-lived ground-state molecules could be produced in a 3D lattice [11], opening the road towards full control of the molecule formation process. In our lab ultracold molecules have found first applications in molecular spectroscopy and in molecular matter wave interferometers [12].

Presently we are supporting three experimental setups with ultracold Cs atoms in the matter wave regime in our group. Each BEC-machine has its specific scientific orientation. The BEC-machines are located in a separate laboratories together with their entire infrastructure (laser systems etc.). The machines called 3D-Cs-BEC (the LevT-Project) and 2D-Cs-BEC (the GOST-project) are part of the Spezialforschungsbereich 15 (SFB 15)  funded by the Austrian Science Fund (FWF) within project P16, the third machine called CsIII is funded by the START-project Y227-N20. The 3D-Cs-BEC-machine is the first-generation Cs BEC apparatus [1] with its present focus on Feshbach dimers, their interactions, and their relation to Efimov trimers [2,9,10]. For this machine it is planned to extend the investigations to mixtures of Cs and Rb quantum gases as proposed within the SFB-application. The 2D-Cs-BEC-machine is optimized to study quantum gases in two dimensions in surface traps and it has recently been rebuilt to allow for larger 2D condensates [13]. The CsIII-machine is in the final stages of completion. Its present focus is on precision measurements with tunable quantum gases in atom interferometers and in three-dimensional lattice potentials.

References

complete list of publications of our group

1. Bose-Einstein Condensation of Cesium
   T. Weber, J. Herbig, M. Mark, H.-C. Nägerl, and R. Grimm
   Science 299, 232 (2003); published online 5 Dec 2002 (10.1126/science.1079699)
2. Preparation of a Pure Molecular Quantum Gas
   J. Herbig, T. Kraemer, M. Mark, T. Weber, C. Chin, H.-C. Nägerl, and R. Grimm
   Science 301, 1510 (2003); published online 21 Aug 2003 (10.1126/science.1088876)
3. Bose-Einstein condensation of molecules
   S. Jochim, M. Bartenstein, A. Altmeyer, G. Hendl, S. Riedl, C. Chin, J. Hecker Denschlag, and R. Grimm
   Science 302, 2101 (2003); published online 13 Nov 2003 (10.1126/science.1093280)

4. M. Greiner, C. A. Regal, D. S. Jin, Nature 426, 537 (2003)

5. Observation of the pairing gap in a strongly interacting Fermi gas
   C. Chin, M. Bartenstein, A. Altmeyer, S. Riedl, S. Jochim, J. Hecker Denschlag, and R. Grimm
   Science 305, 1128 (2004); published online 22 July 2004 (10.1126/science.1100818). cond-mat/0405632

6. M. W. Zwierlein, J. R. Abo-Shaeer, A. Schirotzek, C. H. Schunck, W. Ketterle, Nature 435, 1047 (2005)

7. K. Xu, T. Mukaiyama, J. R. Abo-Shaeer, J. K. Chin, D. E. Miller, W. Ketterle, Phys. Rev. Lett. 91, 210402 (2003)

8. M. W. J. Romans, R. A. Duine, S. Sachdev, H. T. C. Stoof, Phys. Rev. Lett. 93, 020405 (2004)

9. Observation of Feshbach-like resonances in collisions between ultracold molecules
   C. Chin, T. Kraemer, M. Mark, J. Herbig, P. Waldburger, H.-C. Nägerl, and R. Grimm
   Phys. Rev. Lett. 94, 123201 (2005) . cond-mat/0411258

10. Experimental evidence for Efimov quantum states
    T. Kraemer, M. Mark, P. Waldburger, J. G. Danzl, C. Chin, B. Engeser, A. D. Lange, K. Pilch, A. Jaakkola, H.-C. Naegerl and R. Grimm
    submitted, cond-mat/0512394

11. Long-lived Feshbach molecules in a 3D optical lattice
    G. Thalhammer, K. Winkler, F. Lang, S. Schmid,R. Grimm, and J. Hecker Denschlag
    submitted, cond-mat/0510755

12. Internal-state interferometry with ultracold molecules
    T. Kraemer, M. Mark, P. Waldburger, J. Herbig, C. Chin, H.-C. Nägerl, R. Grimm
    manuscript in preparation

13. Two-dimensional Bose-Einstein condensate in an optical surface trap
    D. Rychtarik, B. Engeser, H.-C. Nägerl, and R. Grimm
    Phys. Rev. Lett. 92, 173003 (2004). cond-mat/0309536

Status and Results of the Project (January 2006)

The setup of the new CsIII-machine  is currently nearing completion. The following intermediate goals have been met:

• Setup of an ultra-high vacuum chamber consisting of a central high-quality quartz cell (pressure <10^-11 mbar) together with Cs-dispenser and atomic beam section, Zeeman slower section, and main pumping section together with various magnetic field coils for magnetic offset, gradient, and compensation fields.

• Implementation of a new home-built modular and economical experimental timing system which can presently address 64 digital and 16 analog channels at high update rates and which can easily be upgraded to more channels.

• Implementation of Zeeman slowing, MOT-operation, absorption imaging and Raman-sideband cooling to temperatures of 2 μK for more than 2*10⁷ atoms in the Cs absolute ground state with hyperfine quantum numbers F=3, m_F =3, all within less than 3 sec.

• Setup of a home-built state-of-the-art high-power fiber laser amplifier system capable of delivering up to 40 Watt of single-frequency light power at 1064 nm (in collaboration with IAP Jena). The system is seeded by a commercial narrow-band 1064-nm laser with up to 2 Watt. Typically, 15 Watt of light power are expected to be sufficient for operation of 3D optical lattice potentials. On the technical side, we have acquired the know-how for precision fiber polishing and packaging with a high-quality fiber polishing machine. This is particular important for fiber amplifier systems and for the production of high-power fiber patch cables which are not available commercially.

• Realization of a novel large-volume crossed dipole reservoir trap generated from a high-power multimode diode stack at 976 nm (split into 2 polarized beams with up to 40 Watt of light power each which are then directed into the glass cell at Brewsters angle) with the capability to capture more than 1*10⁷ atoms at an estimated phase space density of 10^-3 .

Recently, we have implemented a second stage of dipole trapping by crossing two 1064-nm laser beams, realizing a so-called dimple trap while the reservoir trap is on. This elongated trap with strong confinement in two directions is ideal for efficient evaporative cooling. We thus expect that a second-generation Cs BEC will soon be available (the third Cs BEC in Innsbruck and the third Cs BEC world-wide). Also, we are currently setting up the 3D optical lattice laser beams. The new Cs BEC can thus immediately be loaded into the lattice for first tests with tunable matter waves in optical lattices.

What's New About the Current CsIII-Machine?

The CsIII-machine has been built in view of the experience gained from the first generation 3D-Cs-BEC-machine (the LevT-project) . The following major changes have been introduced to allow for a new generation of future experiments:

• Realization of a new and improved Zeeman slower. This should in principle allow 100 times higher loading rates into the MOT after final optimization in comparison to the previous setup, yielding much higher experimental cycle rates.

• Four times more laser power for MOT operation and twice as much laser power for Raman sideband cooling. This yields already now significantly higher atom numbers in comparison to the first generation setup. Note that convenient high-power DBR-diode lasers as used for the 3D-Cs-BEC-machine are not commercially available anymore.

• Quartz-cell apparatus with improved optical access from all directions. In contrast to the previous stainless-steel apparatus of the 3D-Cs-BEC-machine magnetic field coils can be brought much closer to the atoms position. Also, switching of magnetic fields is not limited anymore by ring-currents induced in the vacuum chamber. In addition, shielding of magnetic field fluctuations is now possible (not implemented yet). The new Cs BEC will be the first one in a quartz-cell apparatus.

• Novel reservoir trap economically generated from a commercial high-power infrared diode laser module. To our knowledge this is the first time that an atom trap has been realized in this way. The trap depth can easily be modulated by changing the diode current. This trap disposes of cumbersome far-infrared CO₂ -laser systems and allows larger trap volumes for higher atom numbers. In the original START-application we had proposed to use two high-power fiber laser systems. The present solution is a factor 8 less expensive!

• Setup of a narrow-band high-power 1064-nm laser system for generation of 3D optical lattices. This will allow the first realization of a Mott-insulator state in a relatively far detuned optical lattice where spontaneous optical excitation is negligible. It is also expected that molecules will be sufficiently stable for single-frequency light at this wavelength.

One crucial improvement with respect to the 3D-Cs-BEC-machine is the possibility to control magnetic fields to a much higher degree with respect to switching speeds and fluc-tuations. Further, much higher field values can in principle be accessed, allowing the study of tunable matter waves near a broad Feshbach resonance at 800 G with a width of 88 G which promises new perspectives for studying the Efimov effect.

Support

This project is funded by the START-prize awarded to Hanns-Christoph Nägerl in 2003 by the Austrian Federal Ministry for Education, Science and Culture (BMBWK) and administered by the Austrian Science Fund (FWF).

last change: 09-09-20 by EH