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Quantum Mixtures of Ytterbium and Lithium

The precise tools of experimental atomic physics allow the preparation, manipulation and study of trapped atomic gases at temperatures near absolute zero (less than one microKelvin), where their behavior is dominated by quantum mechanics. Thus, fundamental quantum few and many-body theory can be tested and novel quantum systems can be engineered. In this project we apply the tools of ultracold atom production simultaneously on two atomic species - lithium and ytterbium, to study quantum phenomena in ultracold mixtures and in ultracold polar molecules formed by linking lithium and ytterbium. We have created quantum degenerate mixtures of these atoms in our lab and measured their low-temperature (s-wave) scattering cross-section [1,2].

Feshbach Resonances

Resonances in two-body scattering can be used to control interactions between atoms. Feshbach resonances occur when the energy of two free atoms is very close to that of a bound state of the two atoms. The manipulation of atomic internal structure can allow the tuning of this energy difference by using an external magnetic field. Thus, interactions can be turned on and off, made positive or negative, by setting the ambient magnetic field to particular values. This control of two-body interactions can have profound effects on the many-body system. One example is the realization of fermion pairing analogous to the physics in superconductors. Another application of the Feshbach resonance is in the production of ultracold molecules. A review of Feshbach resonances in the context of ultracold atoms can be found in [3]. Our recent work on the dynamics of lithium Feshbach molecules in an ultracold lithium-ytterbium mixture can be found here [4]. Current work is focussed on identifying and manipulating Feshbach resonances between lithium and ytterbium atoms. This can lead to studies of the interesting three-body (Efimov) physics of particles with large mass ratio and the production of diatomic LiYb molecules.

Ultracold Molecules

Samples of cold trapped molecules can be used for studies of dipolar quantum matter, applications in quantum information science, and sensitive tests of time-reversal invariance and time-variations of fundamental constants. A recent review can be found here [5]. We plan to use the techniques pioneered in [6,7] to produce LiYb molecules. Such molecules will possess both an electric and a magnetic dipole moment.

Ultracold Chemical Reactions

A great strength of ultracold atomic physics lies in the availability of particles which can be held for long periods of time (minutes). Such a long lifetime is a result of weak inelastic interactions (and ultra-high vacuum) and is a key factor in precise diagnostics and measurement. Additionally the study of interactions (both elastic and inelastic) are fascinating by themselves, elucidating subtleties in our quantum description of matter. Within the new field of ultracold molecules, chemical reactions are a new inelastic phenomenon which have to be understood and controlled. This subject also leads directly into the area of controlled chemistry. We plan to study and control the chemical reactions associated with the production and stabilization of LiYb molecules.

Trapping and Quantum Simulation in Optical Lattices

A standing-wave of laser light can act as an optical lattice for trapped atoms. This can be exploited to demonstrate phenomena analogous to electrons in a solid-state lattice. Many-body Hamiltonians can be engineered and thus simulated. A review of the impact of ultracold gases on many-body physics can be found here [8]. Yb and Li atoms simultaneously trapped in an optical lattice form an intriguing system for simulating condensed matter phenomena, for instance pattern formation. A major goal is quantum simulation with lattice-trapped molecules. A proposal for utilizing paramagetic polar molecules for simulations of lattice-spin models, and relevant applications in quantum information science can be found here [9]. The LiYb molecule being studied in our lab is paramagnetic and polar, and a candidate system for these applications.

Our experiments are financially supported by grants from the National Science Foundation, Air Force Office of Scientific Research, and a MURI grant from the Army Research Office.

[1] A. Hansen, A. Khramov, W. Dowd, A. Jamison, V. Ivanov, and S. Gupta, Quantum Degenerate Mixture of Ytterbium and Lithium Atoms, Phys. Rev. A 84, 011606(R) (2011).
[2] V. Ivanov, A. Khramov, A. Hansen, W. Dowd, F. Muenchow, A. Jamison, and S. Gupta, Sympathetic cooling in an optically trapped mixture of alkali and spin-singlet atoms, Phys. Rev. Lett. 106, 153201 (2011).
[3] C. Chin, R. Grimm, P. Julienne, and E. Tiesinga Feshbach resonances in ultracold gases, Rev. Mod. Phys. 82, 1225 (2010).
[4] A. Khramov, A. Hansen, A. Jamison, W. Dowd, and S. Gupta, Dynamics of Feshbach molecules in an ultracold three-component mixture, Phys. Rev. A 86, 032705 (2012).
[5] L. Carr, D. DeMille, R. Krems, and J. Ye, Cold and ultracold molecules: science, technology, and applications, New J. Phys.11, 055049 (2009).
[6] K.-K. Ni, S. Ospelkaus, M. de Miranda, A. Pe’er, B. Neyenhuis, J. Zirbel, S. Kotochigova, P. Julienne, D. Jin, and J. Ye. A high phase-space-density gas of polar molecules, Science 322, 231 (2008).
[7] J. Danzl, E. Haller, M. Gustavsson, M. Mark, R. Hart, N. Bouloufa, O. Dulieu, H. Ritsch, and H.-C. Nagerl. Quantum gas of deeply bound ground state molecules, Science 321, 1062 (2008).
[8] I. Bloch, J. Dalibard, and W. Zwerger, Many-body physics with ultracold gases, Rev. Mod. Phys. 80, 885 (2008).
[9] A. Micheli, G. Brennen, and P. Zoller, A toolbox for lattice-spin models with polar molecules, Nature Physics 2, 341 (2006).

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