We present a study of a cold strontium Rydberg gas. Using a high-resolution step-scanning technique, we perform detailed measurements of the Stark maps of selected Rydberg states. We find excellent agreement between the measured Stark maps and a numerical calculation based on an independent electron model. Finally we show that excitation of the second valence electron can be used to probe the dynamics of the Rydberg gas with nanosecond temporal resolution via autoionization. This coherence can be destroyed on sub-microsecond timescales by the application of even very small amounts of electrical noise at a rate that depends markedly on the spectral characteristics of the noise.

The mechanisms responsible for decoherence are discussed with the aid of classical and quantum simulations. The results of these simulations are in good accord with the experimental data. We have performed classical and quantum calculations for a hydrogen atom in a strong magnetic field exposed to a parallel electric field that linearly increases with time. The calculations were performed for the situation where the electron is launched from near the nucleus and for a microcanonical ensemble. For the case of low angular momentum, the classical and quantum calculations are compared.

We show that there exist stable classical trajectories at positive energy and that these contribute to the possibility of the atom surviving to strong electric fields. Since their first experimental observation, ultralong-range Rydberg molecules consisting of a highly excited Rydberg atom and a ground state atom [1, 2] have attracted the interest in the field of ultracold chemistry [3, 4]. Especially the intriguing properties such as size, polarizability and type of binding they inherit from the Rydberg atom are of interest.

An open question in the field is the reduced lifetime of the molecules compared to the corresponding atomic Rydberg states [2]. We show that the lifetimes depend on the density of ground state atoms and that this can be described in the frame of a classical scattering between the molecules and ground state atoms. We also find that the excited molecular state has an even more reduced lifetime compared to the ground state which can be attributed to an inward penetration of the bound atomic pair due to imperfect quantum reflection that takes place in the special shape of the molecular potential [5].

The internal electric field of a Rydberg atom electron can bind a polar molecule to form a giant ultralong-range stable polyatomic molecule. Such molecules not only share their properties with Rydberg atoms such as long lifetimes and large sizes but they also possess huge permanent electric dipole moments and in addition allow for coherent control of the polar molecule orientation.

In this work, we include additional Rydberg manifolds which couple to the nearly degenerate set of Rydberg states employed in the previous work S T Rittenhouse and H R Sadeghpour Phys. Ultimately, these avoided crossings enable the formation of the giant polyatomic Rydberg molecules with standard two-photon laser photoassociation techniques. We explore long-range interactions between two atoms excited into high principal quantum number n Rydberg states, and present calculated potential energy curves for various symmetries of doubly excited n s and n p rubidium atoms.

We present n -scaling relations for both the depth D e of the wells and the equilibrium separations R e of these macrodimers, and explore their response to small electric fields and stability with respect to predissociation. The behaviour of interacting ultracold Rydberg atoms in both constant electric fields and laser fields is important for designing experiments and constructing realistic models of them.

In this paper, we briefly review our prior work and present new results on how electric fields affect interacting ultracold Rydberg atoms. Specifically, we address the topics of constant background electric fields on Rydberg atom pair excitation and laser-induced Stark shifts on pair excitation. Ultracold atomic gases have been used extensively in recent years to realize textbook examples of condensed matter phenomena. Recently, phase transitions to ordered structures have been predicted for gases of highly excited, 'frozen' Rydberg atoms.

Such Rydberg crystals are a model for dilute metallic solids with tunable lattice parameters, and provide access to a wide variety of fundamental phenomena. We investigate theoretically how such structures can be created in four distinct cold atomic systems, by using tailored laser excitation in the presence of strong Rydberg—Rydberg interactions. We study in detail the experimental requirements and limitations for these systems and characterize the basic properties of small crystalline Rydberg structures in one, two and three dimensions.

We investigate the spectral properties of a finite laser-driven lattice of ultracold Rydberg atoms exploiting the dipole blockade effect in the frozen Rydberg gas regime. Uniform one-dimensional lattices as well as lattices with variable spacings are considered. In the case of a weak laser coupling, we find a multitude of many-body Rydberg states with well-defined excitation properties which are adiabatically accessible starting from the ground state. A comprehensive analysis of the degeneracies of the spectrum as well as of the single- and pair-excitation numbers of the eigenstates is performed.

In the strong laser regime, analytical solutions for the pseudo-fermionic eigenmodes are derived. Perturbative energy corrections for this approximative approach are provided. We explore the prospects for confining alkaline-earth Rydberg atoms in an optical lattice via optical dressing of the secondary core—valence electron.

Focussing on the particular case of strontium, we identify experimentally accessible magic wavelengths for simultaneous trapping of ground and Rydberg states. A detailed analysis of relevant loss mechanisms shows that the overall lifetime of such a system is limited only by the spontaneous decay of the Rydberg state, and is not significantly affected by photoionization or autoionization.

The van der Waals C 6 coefficients for the Sr 5s n s 1 S 0 Rydberg series are calculated, and we find that the interactions are attractive. Finally we show that the combination of magic-wavelength lattices and attractive interactions could be exploited to generate many-body Greenberger—Horne—Zeilinger states.

In such a Rydberg chain, similar to molecular aggregates, an electronic excitation is delocalized due to long-range dipole—dipole interactions among the atoms. The transport of an exciton that is initially trapped by a chain dislocation is strongly coupled to nuclear dynamics, forming a localized pulse of combined excitation and displacement.

This pulse transfers entanglement between dislocated atoms adiabatically along the chain. Details about the interaction and the preparation of the initial state are discussed. We also present evidence that the quantum dynamics of this complex many-body problem can be accurately described by selected quantum—classical methods, which greatly simplify investigations of excitation transport in flexible chains.

We investigate coherent and incoherent excitation transfer in a random network with dipole—dipole interactions as a model system describing energy transport, e. For this purpose, we introduce and compare two different measures the maximum output probability and the average transfer time for the efficiency of transport from the input to the output site.

We especially focus on optimal configurations which maximize the transfer efficiency and the impact of dephasing noise on the transport dynamics. For most configurations of the random network, the transfer efficiency increases when adding noise, giving rise to essentially classical transport. These noise-assisted configurations are, however, systematically less efficient than the optimal configurations.

The latter reach their highest efficiency for purely coherent dynamics, i. Collective effects, such as waves and instabilities, are integral to our understanding of most plasma phenomena. We have been able to study these in ultracold neutral plasmas by shaping the initial density distribution through spatial modulation of the ionizing laser intensity.

We describe a relay imaging system for the photoionization beam that allows us to create higher resolution features and its application to extend the observation of ion acoustic waves to shorter wavelengths. Gabbanini, R. Bisset, L. Santos, G. John Sous, Edward Grant. Many-body physics with ultracold plasmas: quenched randomness and localization. New Journal of Physics , 21 4 , Lin, L. Jin, Z. Symmetry protected topological phases characterized by isolated exceptional points. Sorantin, Irakli Titvinidze, Walter Hofstetter. Density-wave steady-state phase of dissipative ultracold fermions with nearest-neighbor interactions.

Giudici, A. Angelone, G. Magnifico, Z. Zeng, G. Giudice, T. Mendes-Santos, M. Diagnosing Potts criticality and two-stage melting in one-dimensional hard-core boson models. Cooper, J. Dalibard, I. Topological bands for ultracold atoms. Beyond-mean-field corrections for dipolar bosons in an optical lattice. Torsten Hartmann, Torben A. Schulze, Kai K.

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## Ultracold molecules hold promise for quantum computing | MIT News

Voges, Philipp Gersema, Matthias W. Tobias, Jacob P. Covey, Jun Ye. A degenerate Fermi gas of polar molecules. Science , , Prasad, T. Bland, B. Mulkerin, N. Parker, A. Annalen der Physik , 2 , Brendan C. Leggett mode in a two-component Fermi gas with dipolar interactions. Vortex patterns in rotating dipolar Bose—Einstein condensate mixtures with squared optical lattices. Ultracold molecules for quantum simulation: rotational coherences in CaF and RbCs. Quantum Science and Technology , 4 1 , Nirav P. Mehta, Kaden R. Hazzard, Christopher Ticknor. Model for scattering with proliferating resonances: Many coupled square wells.

Tijs Karman, Matthew D. Frye, John D. Reddel, Jeremy M. Near-threshold bound states of the dipole-dipole interaction. Emergent interlayer nodal superfluidity of a dipolar Fermi gas in bilayer optical lattices. Petzold, P. Kaebert, P. Gersema, T. Poll, N. Reinhardt, M. Siercke, S. Type-II Zeeman slowing: Characterization and comparison to conventional radiative beam-slowing schemes. Iran Seydi, Saeed H. Abedinpour, Reza Asgari, B. Composite quasiparticles in strongly correlated dipolar Fermi liquids. An-Bang Wang, Su Yi. Trapped Bose—Einstein condensates with quadrupole—quadrupole interactions.

Chinese Physics B , 27 12 , Yukalov, E. Influence of quadratic Zeeman effect on spin waves in dipolar lattices. Journal of Magnetism and Magnetic Materials , , Vyacheslav I. Yukalov, Elizaveta P. Spin dynamics in lattices of spinor atoms with quadratic Zeeman effect. Physical Chemistry Chemical Physics , 20 41 , International Journal of Theoretical Physics , 57 10 , Nonuniversal beyond-mean-field properties of quasi-two-dimensional dipolar Bose gases. Tijs Karman, Jeremy M. Microwave Shielding of Ultracold Polar Molecules. Singularity-free quantum tracking control of molecular rotor orientation.

Regulating spin reversal in dipolar systems by the quadratic Zeeman effect. Observation of Feshbach resonances between alkali and closed-shell atoms. Nature Physics , 14 9 , Ground state of an ultracold Fermi gas of tilted dipoles in elongated traps. New Journal of Physics , 20 9 , Klaudia Zaremba-Kopczyk, Piotr S. Magnetically tunable Feshbach resonances in ultracold gases of europium atoms and mixtures of europium and alkali-metal atoms.

### Funding & Awards

Martin Dressel, Elena S. Zhukova, Victor G. Thomas, Boris P. Quantum Electric Dipole Lattice. Journal of Infrared, Millimeter, and Terahertz Waves , 39 9 , Baier, D.

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- Fractal universality in near-threshold magnetic lanthanide dimers.
- Selling Fast: We Sold Our House in One Day, And You Can Too.
- First Ultracold Polar Molecule Gas Ready for Research?
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Hafermann, A. Toschi, A. Katanin, A. Antipov, M. Katsnelson, A. Lichtenstein, A. Rubtsov, K. Diagrammatic routes to nonlocal correlations beyond dynamical mean field theory. Orbital quantum magnetism in spin dynamics of strongly interacting magnetic lanthanide atoms. Symmetric tops in combined electric fields: Conditional quasisolvability via the quantum Hamilton-Jacobi theory. Landini, N. Dogra, K. Kroeger, L. Hruby, T.

Donner, T. Journal of Quantitative Spectroscopy and Radiative Transfer , , Local condensate depletion at trap center under strong interactions. Jesus Aldegunde, Jeremy M. Yao, M. Zaletel, D. Stamper-Kurn, A. A quantum dipolar spin liquid. Nature Physics , 14 4 , Tao Shi, Eugene Demler, J. Ignacio Cirac. Variational study of fermionic and bosonic systems with non-Gaussian states: Theory and applications.

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## Collision resonances between ultracold atom and molecules visualized for the first time

Dipolar Bose gas with three-body interactions at finite temperature. Density-wave instability and collective modes in a bilayer system of antiparallel dipoles. Journal of Physics Communications , 2 1 , Collisions of ultracold 23 Na 87 Rb molecules with controlled chemical reactivities. Science Advances , 4 1 , eaaq Enhancement of signal-to-noise ratio of ultracold polar NaCs molecular spectra by phase locking detection. Chinese Physics B , 26 12 , Hao Lee, S. Matveenko, Daw-Wei Wang, G. Fulde-Ferrell-Larkin-Ovchinnikov state in bilayer dipolar systems. Ultracold molecule assembly with photonic crystals.

New Journal of Physics , 19 12 , Optical Feshbach resonances and ground-state-molecule production in the RbHg system. Tuning the Drude weight of Dirac-Weyl fermions in one-dimensional ring traps. A cryofuge for cold-collision experiments with slow polar molecules. Manpreet Singh, Suman Mondal, B. Sahoo, Tapan Mishra. Quantum phases of constrained dipolar bosons in coupled one-dimensional optical lattices.

Reyhaneh Khasseh, Saeed H. Abedinpour, B. Phase diagram and dynamics of Rydberg-dressed fermions in two dimensions. Kwasigroch, N. Synchronization transition in dipole-coupled two-level systems with positional disorder. Striped states in a many-body system of tilted dipoles. Communication: General variational approach to nuclear-quadrupole coupling in rovibrational spectra of polyatomic molecules. The Journal of Chemical Physics , 14 , Erich J Mueller. Review of pseudogaps in strongly interacting Fermi gases.

Reports on Progress in Physics , 80 10 , Timur M. Rvachov, Hyungmok Son, Ariel T. Sommer, Sepehr Ebadi, Juliana J. Park, Martin W. Zwierlein, Wolfgang Ketterle, Alan O. Excitations and stability of weakly interacting Bose gases with multibody interactions. Lima, Axel Pelster. Low-lying excitation modes of trapped dipolar Fermi gases: From the collisionless to the hydrodynamic regime. Interacting in-plane molecular dipoles in a zigzag chain.

Two supersolid phases in hard-core extended Bose—Hubbard model. Journal of Physics Communications , 1 3 , Hyperfine structure of alkali-metal diatomic molecules. Christian Gross, Immanuel Bloch. Quantum simulations with ultracold atoms in optical lattices.

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- Interactions in Ultracold Gases: From Atoms to Molecules | Physics & Astronomy | Subjects | Wiley!
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John L. Cold molecules: Progress in quantum engineering of chemistry and quantum matter. Baranov, Marcello Dalmonte. Adiabatic state preparation of stripe phases with strongly magnetic atoms. Maykel L. Adimensional theory of shielding in ultracold collisions of dipolar rotors. Condensation to a strongly correlated dark fluid of two dimensional dipolar excitons. Superlattices and Microstructures , , Edler, C. Mishra, F. Nath, S. Sinha, L. Azadeh Mazloom, Saeed H. Superfluidity in density imbalanced bilayers of dipolar fermions.

Philip D. Gregory, Jacob A. Blackmore, Jesus Aldegunde, Jeremy M. Salvatore Lorenzo, Tony J. Apollaro, Andrea Trombettoni, Simone Paganelli. International Journal of Quantum Information , 15 05 , Sabari Subramaniyan. Vortex formation and hidden vortices in dipolar Bose—Einstein condensates. Theoretical study of spin-forbidden cooling transitions of indium hydride using ab initio methods. Chinese Physics B , 26 9 , Efficient production of long-lived ultracold Sr2 molecules. Multiply quantized and fractional skyrmions in a binary dipolar Bose-Einstein condensate under rotation.

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Modern Physics Letters B , 31 13 , Unconventional superfluids of fermionic polar molecules in a bilayer system. Physics Letters A , 20 , Phase diagrams of the extended Bose-Hubbard model in one dimension by Monte-Carlo simulation with the help of a stochastic-series expansion. Matthew T. Anisotropic blockade using pendular long-range Rydberg molecules.

Michael L. Wall, Nirav P. Microscopic derivation of multichannel Hubbard models for ultracold nonreactive molecules in an optical lattice. Lattice-model parameters for ultracold nonreactive molecules: Chaotic scattering and its limitations. Nondestructive detection of polar molecules via Rydberg atoms. EPL Europhysics Letters , 1 , Vortices and vortex lattices in quantum ferrofluids. Journal of Physics: Condensed Matter , 29 10 , Nikolay V.

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Svetlana A. Design of many-body spin states of Rydberg atoms excited to highly tunable magnetic sublevels. Optics Letters , 42 2 , Elliott, Yong P. Two-photon photoassociation spectroscopy of an ultracold heteronuclear molecule. Long-range transverse Ising model built with dipolar condensates in two-well arrays. New Journal of Physics , 19 1 , An experimental toolbox for the generation of cold and ultracold polar molecules. Journal of Physics: Conference Series , , Chris H.

## Ultracold gases

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