july 18-20, 2018 - › sites › › ...3:30 – 4:00 coffee 4:00 – 4:30 stefan willitsch...
TRANSCRIPT
Quantum
thermodynamics
Harvard-Smithsonian Center for AstrophysicsITAMP
MS-14, B-32660 Garden Street
Cambridge, MA 02138 USA
Few-body and CollectiveMany-body Behavior with Charge
Impurities in Atomic Quantum Gases
July 18-20, 2018
Organizers: Svetlana Kotochigova
NIST /Temple UniversityJohannes Hecker Denschlag
Ulm UniversityTommaso Calarco
Ulm University
Sponsored by:Institute for Theoretical Atomic, Molecular and Optical Physics*
Integrated Quantum Science and Technology
Sant Feliu de Guixols, Spain
https://www.cfa.harvard.edu/itamp
Abstracts, Program, Participants*Funded by the National Science Foundation
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INDEX
Notes
Abstracts
Synopsis ....................................................................................................4Participants ...............................................................................................5Program ....................................................................................................8Notes........................................................................................................41
Kenneth R. Brown..................................................................................12Robin Côté..............................................................................................13Eugene Demler........................................................................................14Johannes Hecker Denschlag....................................................................15Olivier Dulieu..........................................................................................16Rosario González-Férez..........................................................................18Rene Gerritsma.......................................................................................19Chris H. Greene......................................................................................20Eric Hudson.............................................................................................21Zbigniew Idziaszek..................................................................................22Paul Julienne............................................................................................23Thomas Killian........................................................................................24Ming Li....................................................................................................25Florian Meinert.......................................................................................26 Takashi Mukaiyama.................................................................................27Roee Ozeri.............................................................................................. 28Brian Odom.............................................................................................29Trey Porto................................................................................................30Jesús Pérez-Ríos.......................................................................................31Sadiq Rangwala.......................................................................................32 Tobias Schätz...........................................................................................33Peter Schmelcher..................................................................................... 34Mark Saffman..........................................................................................35Michael Tomza........................................................................................36Roland Wester..........................................................................................37Stefan Willitsch........................................................................................38
PostersMarkus Deiß...........................................................................................39Shinsuke Haze.........................................................................................40
Notes
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Notes
Organizing Committee:
Svetlana Kotochigova NIST/Temple UniversityJohannes Hecker DenschlagUlm UniversityTommaso CalarcoUlm University
Few-body and Collective Many-body Behavior with Charge Impurities in Atomic Quantum Gases
This workshop will bring together experts in the field of quantum hybrid ion-neutral systems with controllable properties. Research on ultracold atom-ion hybrid systems is a novel field of modern science and crosses boundaries between atomic physics, chemistry, and quantum information processing. It promises to lead to fundamental understanding of cold chemistry as well as system-bath interactions in many-body physics. An ion impurity interacting with a quantum bath of atoms is a nontrivial many-body model system with wide relevance to material systems. Furthermore, the interaction between atoms and ions can be controlled, e.g. via Rydberg states.
Synops is
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Notes Par t i c ipan ts
Ruti Ben ShlomiWeizmann [email protected]
Ken BrownDuke [email protected]
Tommaso Calarco Ulm [email protected]
Robin CôtéUniversity of [email protected]
Markus DeißUniversity of [email protected]
Eugene DemlerHarvard [email protected]
Johannes Hecker DenschlagUlm [email protected]
Olivier DulieuLaboratoire Aime Cotton, [email protected]
Rene GerritsmaUniversity of [email protected]
Rosario González-FérezGranada [email protected]
Chris GreenePurdue [email protected]
Shinsuke HazeUlm [email protected]
Eric [email protected]
Zbigniew IdziaszekUniversity of [email protected]
Krzysztof JachymskiUniversity of [email protected]
Paul JulienneJoint Quantum [email protected]
Thomas KillianRice [email protected]
Svetlana KotochigovaNIST/Temple [email protected]
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Notes Par t i c ipan ts
Haggai LandaIpht., Cea, Univ. [email protected]
Ming LiTemple [email protected]
Constantinos MakridesJQI, University of [email protected]
Florian MeinertUniversity of [email protected]
Takashi MukaiyamaOsaka [email protected]
Niranjan MyneniRaman Research [email protected]
Brian OdomNorthwestern [email protected]
Roee OzeriWeizmann Institute of [email protected]
Jesús Pérez-RíosPurdue [email protected]
Trey PortoUniversity of Maryland/[email protected]
Sadiq RangwalaRaman Research [email protected]
Hossein [email protected]
Mark SaffmanUniversity of [email protected]
Tobias SchätzUniversity of [email protected]
Peter SchmelcherZOQ - University of Hamburgpeter.schmelcher
Michal SmialkowskiUniversity of [email protected]
Eite TiesingaUniversity of Maryland/JQI/[email protected]
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Par t i c ipan ts Posters
Michael TomzaUniversity of [email protected]
Marios TsatsosUniversity of Sao [email protected]
Andrey VilesovUniversity of Southern [email protected]
Vladan VuleticMassachusetts Institute of [email protected]
Pascal Weckesser University Of [email protected]
Roland WesterUniversität [email protected]
Stefan WillitschUniversity of [email protected]
Rydberg spectroscopy in an atom-ion hybrid trap
Shinsuke Haze,1 Joschka Wolf,1 Limei Wang,1 Markus Deiß,1 Georg Raithel,2 Christian Fey,3 Florian Meinert,4 and
Johannes Hecker Denschlag1
1Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology IQST, Universität Ulm, 89069 Ulm, Germany
2Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA3Zentrum für Optische Quantentechnologien, Universität Hamburg
Luruper Chaussee 149, 22761 Hamburg, Germany4Physikalisches Institut and Center for Integrated Quantum Science and Technology,
Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
Hybrid atom-ion trap has been a key technology for intriguing applications such as cold chemistry, molecular physics and so on. The good controllability of ion’s and atomic states provides an opportunity for studying atom-ion interaction in an unprecedented regime. Here, we demonstrate Rydberg spectroscopy of rubidium atoms within an atom-ion hybrid trap, where an optical dipole trap and a Paul trap are combined for simultaneous trapping of neutral and charged particles. This versatility enables for capturing an ionized product following an optical excitation to Rydberg states. The trapped ions elastically collide with the rubidium atoms leading to an atom loss, which gives rise to a high sensitivity of observing the underlying Rydberg excitation. In this presentation, we show results for spectroscopy of Rydberg states, including a signature for butterfly molecular bound states and avoided level crossings. We discuss our preliminary results on Stark maps. This work opens up a potential application of atom-ion hybrid trap to be used as a novel detection tool for precision spectroscopy for Rydberg atoms.
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Program Posters
Few-body and collective many-body behavior with charge impurities in atomic quantum gases
July18-20, 2018Sant Feliu de Guixols, Spain
Wednesday, July 18, 2018
AM Session Chair: Hossein Sadeghpour
9:00 – 9:10 Arrival & Welcome Svetlana Kotochigova, Johannes Hecker Denschlag
9:10 –9:40 Chris Greene “Novel quantum states and dynamics of ions, atoms, and electrons”
9:40 – 10:10 Peter Schmelcher “Dynamics and Bound State Formation of Charged Impurities in Ultracold Bosonic Gases”
10:10 – 10:40 Thomas Killian “Rydberg Impurities in Strontium Quantum Gases”
10:40 – 11:10 Coffee
11:10 – 11:40 Roee Ozeri “A search for quantum signatures in ultracold atom-ion collisions”
11:40 – 12:10 Florian Meinert “Rydberg Atoms in a Bose-Einstein-Condensate From Electron to Ion Impurities”
12:10 – 2:00 Lunch
State-to-state chemistry for three-body recombination with resolution of magnetic
quantum numbers
Markus Deiß1, Joschka Wolf1, Artjom Krükow1, Eberhard Tiemann2, Brandon P. Ruzic3, Yujun Wang4, José P. D’Incao5,Paul S. Julienne3, and Johannes Hecker Denschlag1
1Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology IQST, Universität Ulm, D-89069 Ulm, Germany
2Institut für Quantenoptik, Leibniz Universität Hannover, 30167 Hannover, Germany3Joint Quantum Institute, University of Maryland, and NIST, College Park
MD 20742, USA4American Physical Society, Ridge, NY 11961, USA
5JILA, NIST, and the Department of Physics, University of ColoradoBoulder, CO 80309, USA
I will present our results on state-to-state chemistry for three-body recombination of ultracold rubidium atoms. In this chemical process three neutral atoms collide to form a diatomic molecule which, together with the remaining atom, carries away the released binding energy. We prepare a precisely-defined quantum state of the reactants and observe the resulting molecular products with a resolution of the vibrational, the rotational, the hyperfine [1], and more recently, the magnetic quantum numbers. For this we have developed a method in a hybrid atom-ion setup [1,2] that combines state-selective ionization of freshly formed molecules in the atom cloud using laser light with the high sensitivity of molecular ion detection in a Paul trap. Besides qualitative assignment of product states the method allows for quantitatively determining the production rates for molecules in the individual states. On the basis of that we extract propensity rules for the given three-body recombination process.
References[1] J. Wolf, M. Deiß, A. Krükow, E. Tiemann, B. P. Ruzic, Y. Wang, J. P. D’Incao, P. S. Julienne, and J. Hecker Denschlag, Science 358, 921 (2017).[2] A. Härter, A. Krükow, M. Deiß, B. Drews, E. Tiemann, and J. Hecker Denschlag, Nat. Phys. 9, 512 (2013).
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Par t i c ipan ts Abst rac ts
PM Session Chair: Svetlana Kotochigova
2:00 – 2:30 Eugene Demler “New theoretical approaches to quantum impurity problems”
2:30 – 3:00 Mark Saffman “Exited state interactions between heterogeneous elements and objects”
3:00 – 3:30 Trey Porto “Dark state optical lattice with sub-wavelength spatial structure and nanoscale probing of atomic wave function”
3:30 – 4:00 Coffee
4:00 – 4:30 Stefan Willitsch “Superstatistical properties of an ion in an ultracold buffer gas”
4:30 – 5:00 Brian Odom “Non-Destructive Analysis of Single-Ion Chemical Reaction”
Reception
Thursday, July 19, 2018
Am Session Chair: Eite Tiesinga
9:00 – 9:30 Rene Gerritsma “Prospects of reaching the quantum regime in Li-Yb+ mixtures”
9:30 – 10:00 Eric Hudson “The road to entanglement of freely-rotating molecular ions”
Superstatistical properties of an ion in anultracold buffer gas
Stefan WillitschDepartment of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
An ion in a radiofrequency ion trap interacting with a buffer gas of ultracold neutral atoms is a driven dynamical system which has been found to develop a non-thermal energy distribution with a power law tail. The exact analytical form of this distribution has often been represented empirically by q-exponential (Tsallis) functions. Based on the concepts of superstatistics, we introduce a framework for the statistical mechanics of an ion trapped in an RF field subject to collisions with a buffer gas [1,2]. We derive analytic ion secular energy distributions from first principles both neglecting and including the effects of the thermal energy of the buffer gas. For a buffer gas with a finite temperature, we show that Tsallis statistics emerges from the combination of a constant heating term and multiplicative energy fluctuations. We show that the resulting distributions essentially depend on experimentally controllable parameters paving the way for an accurate control of the statistical properties of ion-atom hybrid systems. Our treatment can also be extended to include and characterize the effects of additional external forces caused by, e.g., stray electric fields which are ubiquitous in ion trapping.
References:[1] I. Rouse and S. Willitsch, Phys. Rev. A 97 (2018), 042712[2] I. Rouse and S. Willitsch, Phys. Rev. Lett. 118 (2017), 143401
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Program Abst rac ts
10:00 – 10:30 Ming Li “Excitation-Assisted Charge-Exchange Reaction in a Mixed Atom-Ion systems”
10:30 – 11:00 Coffee
11:00 – 11:30 Ken Brown “Ion-Atom Hybrid System: Ca+ and K”
11:30 – 12:00 Takashi Mukaiyama “Collisional properties of ultracold 6Li-40Ca+ mixture”
12:00– 2:00 Lunch
PM Session Chair: Constantinos Makrides
2:00 – 2:30 Roland Wester “Cooling trapped molecular anions with ultracold atoms”
2:30 – 3:00 Paul Julienne “Calculations of state-to-state ultra-cold three- body collision rates in gases and lattice”
3:00 – 3:30 Rosario González-Férez “Controlling ultracold p-wave collisions with non- resonant light: Predictions of an asymptotic model for the generalized scattering volume”
3:30 – 4:00 Coffee
4:00 – 4:30 Poster session 4:30 – 5:00 Brian Odom “Non-Destructive Analysis of Single-Ion Chemical Reaction”
Cooling trapped molecular anions withultracold atoms
Roland Westera, O. Lakhmanskayaa, M. Simpsona, S. Murauera, Markus Nötzolda, V. Kokooulinec, Bastian Höltkemeierb, Henry López-
Carrerab, Saba Zia Hassanb, Jonas Tauchb, Jan Trautmannb, Eric Endresa,b, Matthias Weidemüllerb
a Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Austriab Physikalisches Institut, Universität Heidelberg, Germany
c Department of Physics, University of Central Florida, Orlando, [email protected]
The study of cold molecular ions and ionic complexes in ion traps has attacted a lot of interest for precision spectroscopy, quantum collision dynamics, and astrochemistry. Translational and internal rovibrational cooling of the trapped molecular ions is usually achieved by cryogenic helium buffer gas cooling. Radiofrequency multipole ion traps, such as octupole or 22-pole ion traps, are employed, because the larger field free region compared to quadrupole traps is more suitable for buffer gas cooling. To achieve cooling to lower temperatures than 4 Kelvin, we investigate the interaction of molecular ions in a cloud of laser-cooled rubidium [1]. Here, I will present recent advances on molecular ion terahertz spectroscopy in a cryogenic radiofrequency ion trap [2] and on cooling molecular anions with ultracold rubidium.
[1] J. Deiglmayr, A. Göritz, T. Best, M. Weidemüller, R. Wester, Phys. Rev. A 86, 043438 (2012)[2] O. Lakhmanskaya, M. Simpson, S. Murauer, M. Nötzold, E. Endres, V. Kokoouline, R. Wester, Phys. Rev. Lett. 120, 253003 (2018)
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Program Abst rac ts
Friday, July 20, 2018
AM Session Chair: Johannes Hecker Denschlag
9:00–9:30 Zbigniew Idziaszek “Trap-induced shape resonances in an ultracold system of an atom and static impurities”
9:30 – 10:00 Olivier Dulieu “Probing three-body collisions induced by a charge impurity in an ultracold gas”
10:00 – 10:30 Jesús Pérez-Ríos “Relaxation process of cold molecular ions in highly vibrational states in the presence of an ultracold gas “
10:30 – 11:00 Coffee
11:00 – 11:30 Sadiq Rangwala “Ion-Atom Interactions in Hybrid Traps”
11:30 – 12:00 Michael Tomza “Cold interactions and collisional dynamics in novel atomic and molecular ion-neutral systems”
12:00– 12:30 Robin Côté “The interplay between short-range and long-range interactions in cold samples containing charges”
12:30-2:00 Lunch
PM Session Chair: Olivier Dulieu
2:00 – 2:30 Tobias Schätz “Optical trapping of ions”
2:30– 3:00 Johannes Hecker Denschlag Rydberg spectroscopy in the electrical field of an ion”
Adjournment
Cold interactions and collisional dynamics in novel atomic and molecular ion-neutral systems
Michael TomzaFaculty of Physics, University of Warsaw, Warsaw, Poland
Hybrid systems of laser-cooled trapped ions and ultracold atoms combined in a single experimental setup have recently emerged as a new platform for fundamental research in quantum physics and chemistry [1]. Reaching ultracold quantum regime is one of the most important challenges in this field at the moment. Unfortunately, the lowest attainable temperatures in experiments using the Paul ion trap are limited by the potential rf-field-induced heating related to the micromotion [2]. I will discuss possible solutions to this problem. The first approach, which can allow reaching the s-wave regime, is the use of ion-atom mixtures with the large ion/atom mass ratio [3,4]. The second approach is the use of a Rydberg molecule with a small reduced mass to initialize the scattering event [5]. I will present how ab initio quantum chemistry calculations can support and guide such quantum physics experiments. I will also present our theoretical proposals of novel systems for cold ion-atom experiments using ions or atoms other than alkali-metal or alkaline-earth-metal ones [6,7].
References
[1] M. Tomza, K. Jachymski, R. Gerritsma, A. Negretti, T. Calarco, Z. Idziaszek, P. S. Julienne, arXiv:1708.07832[2] M. Cetina, A. T. Grier, and V. Vuletic, Phys. Rev. Lett. 109, 253201 (2012)[3] M. Tomza, C. P. Koch, R. Moszynski, Phys. Rev. A 91, 042706 (2015)[4] J. Joger, H. Furst, N. Ewald, T. Feldker, M. Tomza, R. Gerritsma, Phys. Rev. A 96,030703(R) (2017)[5] T. Schmid, C. Veit, N. Zuber, T. Dieterle, R, Löw, T. Pfau, M. Tarana, M. Tomza, Phys. Rev. Lett. 120, 153401 (2018)[6] M. Tomza, Phys. Chem. Chem. Phys. 19, 16512 (2017)[7] M. Lisaj, M. Tomza, in preparation
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Ion-Atom Hybrid System: Ca+ and K
Kenneth R. BrownDuke University
I will present initial results from our experimental apparatus combining a K MOT with trapped laser-cooled Ca+ ions. The system switches between K and Ca+ cooling lasers to prevent the photoionization of the K. Reaction rates are determined by looking for charge exchange and molecular products with a time-of-flight mass spectrometer. I will conclude with a discussion of prospects for rotationally cooling CaH+ using the K MOT.
Exited state interactions between heterogeneous elements and objects
Mark SaffmanUniversity of Wisconsin
Motivated by applications in quantum information processing we have been studying interactions, both one to one and one to many, between heterogeneous atomic elements. In one application we will use Cs atoms as computational qubits and Rb atoms as couplers for measurement and communication. We have prepared single cold Rb and Cs atoms in an optical dipole trap and measured hyperfine changing collision rates. From the measurements we extract interspecies collisional cross sections and compare with other measurements and calculations. Nonlocal interspecies interactions can be achieved by excitation to Rydberg states. We will outline progress towards a dual species Rydberg interaction and entanglement measurement.
Work supported by the ARL CDQI.
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The interplay between short-range and long-range interactions in cold samples containing charges
Robin CôtéPhysics Department, University of Connecticut, Storrs, CT 06269-3046, USA
In recent years, several studies of cold and ultracold hybrid systems involving atomic and molecular ions interacting with neutral atoms or molecules have led to rapid progress towards reaching the quantum regime, where a few partial waves contribute to the behavior of the system.
In this work, we explore the effect of long-range interactions on the inelastic processes taking place at ultracold temperatures. We study how these long-range interactions couple to the shorter-range potential energy surfaces (PES) and can be used to explain /control the outcome of scattering events at low energy. In particular, we explore how the state of the projectile can influence the type of long-range interaction, leading to barriers that reduce or even prevent reactions in some cases, or accentuate the attractive polarization interaction that increase reaction rates in other cases. We present results on two polyatomic molecular ions reacting with excited Ca atoms, namely BaOCH3
+ and BaCl+. For reactions to take place, Ca needs to be in an excited state, and the reaction rate depends strongly on the spin state of the excited state of Ca, i.e. either 1P or 3P.
We also discuss a different approach to affect charge exchange in atom-ion collision, namely using Feshbach resonance. This is a different example of using spin-states to affect reactions.
Finally, we present a simple formulation for the charge exchange in the case of resonant processes, linking the s-wave regime to higher temperatures. The expression is valid for resonant scattering processes in general (charge transfer, spin-flip, excitation exchange) under appropriate conditions, and could be used for quasi-resonant processes as well.
Partially supported by the MURI US Army Research Office Grant No. W911NF-14-1-0378.
Dynamics and Bound State Formation of Charged Impurities in Ultracold Bosonic Gases
Peter SchmelcherCentre for Optical Quantum Technologies and Hamburg Centre for Ultrafast Imaging,
University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, GermanyE-mail: [email protected]
Cold and ultracold atom-ion mixtures represent an intriguing platform for the formation of me- soscopic structures and their dynamics. This particularly due to the additional length scale which stems from the polarization interaction of the ions with the neutral atoms. The latter allow not only to polarize the immediate neighbourhood of ions but lead also to bound states which can be multiply occupied, depending on the quantum statistics (fermions or bosons) of the neutral species. We review aspects of our recent work in this direction addressing among others how a single ion can bind multiple atoms on mesoscopic scales, forming a correlated bound many-body compound. We explore these mesoscopic molecular ions from weak to strong atomic repulsion, thereby taking atom-ion and atom-atom correlations fully into account. Above a critical neutral atom number dissociation occurs resulting in an unbound fraction which forms a background gas for the mesoscopic bound molecule. Self-localization, and effective quasiparticle approaches are discussed and their limitations are revealed. The most recent developments and results of ongoing projects are summarized. Our study is carried out by means of the Multi Layer Multi-Configuration Time-Dependent Hartree method for Bosons (ML-MCTDHB), an ab initio approach to simulate the correlated quantum many-body dynamics and to compute the bound states of mixtures.
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New theoretical approaches to quantumimpurity problems
Eugene DemlerHarvard University
New variational approach to the analysis of dynamics of quantum impurities will be discussed. This method is based on a generalized canonical transformation that decouples the impurity from the bath degrees of freedom. This transformation introduces long-range multi-particle interactions between the bath degrees of freedom, which can be analyzed using Gaussian variational states. I will discuss applications of this method to a broad class of problems, including Anderson impurity and Kondo models, calculation of the RF spectra of impurities in ultracold atoms. Extensions to finite temperature problems will be presented.
Optically Trapping and Isolating Ions for Seconds
Tobias SchätzAlbert Ludwigs University Freiburg, 79104 Freiburg, Germany
Isolating ions and atoms from the environment is essential for experiments, especially if we aim to study quantum effects. For decades, this has been achieved by trapping ions with radiofrequency (rf) fields and neutral particles with optical fields. We are trapping ions by the interaction with light and electrostatic fields, in absence of any rf-fields. We take our results as starting point for studying how to combine the advantages of optical trapping and ions. We aim to demonstrate the prospects of our approach in the context of interaction and reaction at ultra-low temperatures as a showcase. Following the seminal work in the groups of Vuletic, Koehl and Denschlag in hybrid traps, we plan to embed optically trapped ions into quantum gases to reach lowest temperatures, circumventing the currently inevitable excess kinetic energy in hybrid traps, where ions are kept but also driven by rf-fields. It might permit to enter the temperature regime where quantum effects are predicted to dominate. I will report about our recent results on optically trapping 138Ba+ in a bi-chromatic far-off-resonant dipole trap sufficiently isolated and providing lifetimes of seconds. In addition, I aim to discuss the prospects for Coulomb Crystals within optical traps.
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Rydberg spectroscopy in the electrical field of an ion
Johannes Hecker DenschlagUlm University
I report on experiments where we carry out Rydberg spectroscopy of neutral Rb atoms in the environment of an ion trap. The atoms are trapped with a far detuned optical dipole trap. When we optically excite atomic and molecular Rydberg states they are sensitively detected after ionization. We observe a range of butterfly states of which the spectra vary strongly as we go from one n quantum number to the next. Furthermore, we observe Stark spectra due to the presence of the electrical fields of the Paul trap and trapped ions. These signals consist of characteristic step functions which indicate the positions of avoided crossings in the Stark spectrum.
Ion-Atom Interactions in Hybrid Traps
Sadiq RangwalaRaman Research Institute
The simple act of placing a single ion within a cloud of ultracold atoms creates a system with a distinct impurity. While both, trapped ultracold atoms and ions can be produced and manipulated with great precision, the hybrid combination of these traps have thrown up challenges in realizing the equally pliable hybrid systems. In experimental realizations, a number of fascinating studies on binary interactions between trapped ions and atoms have resulted. A key experimental objective is the equilibration of the ion within the cloud of ultracold atoms, so that the combined system can be studied in a regime where quantum processes dominate. However, theory and experiments have shown the central role of binary interactions in the understanding and therefore potentially realizing the desired quantum system in experiments, going forward.In the domain where the collisions between trapped ions and atoms are fairly energetic, several interesting consequences arise, and have been studied in detail over the years at RRI. The dynamically trapped ion can cool by elastic collisions with atoms, even when the mass of the ion is significantly smaller than the atomic mass. In such a scenario, whether the ions steady state energy is determined by the spatial size of the atomic ensemble or the atom temperature is also subject to the ion trap curvature. Further, in the event when the ion is the daughter of the trapped atom, the mechanism of resonant charge exchange is accessible, and is measured to be approximately 100 times more efficient at cooling the ion in a single collision, as compared to elastic collisions. Finally the new experiment building up at RRI in a drive for lower temperatures for the ion-atom system will be discussed.
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Probing three-body collisions induced by a charge impurity in an ultracold gas*
H. da Silva Jr1, M. Raoult1, R. Vexiau1, A. Mohammadi2, Artjom Krükow2, Markus Deiss2, J. H. Denschlag2, and O. Dulieu1
1Laboratoire Aimé Cotton, CNRS, Univ. Paris-Sud, ENS Paris-Saclay, Univ. Paris-Saclay, 91400 Orsay, France
2Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology, Universität Ulm, Germany
Investigating atom-ion interactions in hybrid setups merging a cold atom trap and a cold ion trap has revealed to be one of the novel developments of research on ultracold matter. Beside elastic or inelastic binary collisions, charge exchange, or three-body collisions, the formation of cold molecular ions has been directly observed by one group [1], while they are predicted to be created in most experiments of this kind [2]. In the Ulm group, the formation of cold RbBa+ molecular ions induced by the presence of a single Ba+ ion immersed in a dense (≈ 1012 atoms/cm3) cloud of ultracold Rb atoms is investigated [3]. The experiment reveals formation rates compatible with a three-body collision facilitated by both the high atomic density and the long-range interaction between Ba+ and Rb. The molecular ions are detected destructively by photodissociation provoked by the relatively intense 1064 nm laser used in the dipole trap beam [3]. Here we will present our model for the photodissociation mechanism. The potential energy curves and all the relevant transition electric dipole moments for numerous electronic states in all symmetries are first calculated with a semiempirical methodology that we used elsewhere [4]. Briefly, both atoms are represented as one-electron systems, where the valence electron is moving in the field of a relativistic effective core potential with a core-polarization potential correction. The RbBa+ electronic structure is thus reduced to an effective two-electron problem. These two valence electrons are considered to calculate the Hartree-Fock and the excitation determinants, in an atom-centered large Gaussian basis set. Finally, a full configuration interaction is achieved. With these data we computed the state-to-state absorption cross section, σΛνj(v), of a RbBa+ ro-vibrational level (νj) in the Λ electronic state, induced by a laser with frequency ν, towards accessible electronic states Λ’, reaching continuum states with angular momentum j’ and energy ħk. The main
Vibrational quenching and reactive processes of weakly bound molecular ion-atom collisions
at cold temperatures
Jesús Pérez-RíosSchool of Natural Sciences and Technology, Universidad del Turabo
Gurabo, PR00778, USA
We present a study of vibrational quenching and chemical processes of molecular ions immersed in an ultracold cloud of neutrals by means of the quasi-classical trajectory (QCT) method. The developed theoretical approach is applied to BaRb+(ν) + Rb at cold temperatures, revealing a highly efficient energy transfer between the translational and internal degrees of freedom of the molecular ion, which translates to a large vibrational quenching cross section following the Langevin capture model prediction. In particular, we study three different reactions as a function of the available collision energy and internal state of the molecular ion: vibrational quenching, dissociation (three free atoms as the product state) and substitution reactions.
Our predictions are tested against the state of the art cold chemistry experiments. In particular, a single laser cooled Ba^+ ion is brought in contact with a dense ultracold cloud of Rb atoms held by a dipole trap, leading to molecular formation through three-body recombination. Then, different laser light sources are employed to characterized the time evolution of the internal state of the molecular ion, which evolution is consistent with our theoretical approach.
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photodissociation channels are identified. The results indicate that the lifetime of the molecular ions is strongly limited by the presence of laser light in the experiment, in agreement with Ref. [5]. We currently extend this investigation toward similar systems formed by an alkali atom (Li to Cs) and a Ca+ ion, for which preliminary results will be presented.
References
[1] F. H. J. Hall et al. Phys. Rev. Lett. 107, 243202 (2011)[2] H. da Silva Jr et al. New J. Phys. 17, 045015 (2015)[3] A. Krükow et al. Phys. Rev. A 94, 030701 (R) (2016)[4] M. Aymar et al. J. Chem. Phys. 135, 064305 (2011)[5] S. Jyothi et al. hys. Rev. Lett. 117, 213002 (2016)
*This research is supported by the Marie-Curie Initial Training Network ‘COMIQ: Cold Molecular Ions at the Quantum limit’ of the European Commission under the Grant Agreement 607491.
Dark state optical lattice with sub-wavelength spatial structure and nanoscale probing of
atomic wave functions
Trey PortoUniversity of Maryland/JQI
Optical trapping and imaging of cold atoms are typically constrained by the diffraction limit to length scales on the order of the wavelength of the trapping or imaging light. The nonlinear response of three-level atoms can result in spatially dependent dark states, with spatial structure much smaller than the wavelength. I will discuss the experimental use of such dark state spatial structure to create conservative optical potentials and to image atomic wave functions trapped in those potentials, both with sub-wavelength resolution. The optical potential physically realizes a Kronig-Penney lattice of near delta-function barriers with widths below 10nm. We directly measure the wave function density of atoms trapped in the lattice with similar resolution.
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Controlling ultracold p-wave collisions with non-resonant light: Predictions of an asymptotic
model for the generalized scattering volumen
R. González-Férez Instituto Carlos I de Física Teórica y Computacional and Departamento de Física
Atómica, Molecular y Nuclear, Universidad de Granada18071 Granada, Spain
Interactions in a spin-polarized ultracold Fermi gas are governed by p-wave collisions and can be characterized by the p-wave scattering volume. Control of these collisions by Feshbach resonances is hampered by huge inelastic losses. We suggest non-resonant light control of p-wave collisions, exploiting the anisotropic coupling of non-resonant light to the polarizability of the atoms [1]. The generalized p-wave scattering volume can be controlled by strong non-resonant light [2], in close analogy to the s-wave scattering length [3]. For collision partners that are tightly trapped, the non-resonant light induces an energy shift directly related to the generalized scattering volumen [2]. In this talk we will also discuss that controlling the generalized scattering volume could allow to control, at least roughly, the relative orientation at short distance of the interparticle axis and of the polarization of the light. Our proposal is based on an asymptotic model and introduces explicitly the anisotropic dipole-dipole interaction which governs the ultracold collision dynamics at long-range [2,3].
[1] A. Crubellier, R. González-Férez, C. P. Koch, and E. Luc-Koenig, preprint (2018).[2] A. Crubellier, R. González-Férez, C. P. Koch, and E. Luc-Koenig, preprint (2018).[3] A. Crubellier, R. González-Férez, C. P. Koch, and E. Luc-Koenig, Phys. Rev. A 95, 023405 (2017).
Single molecular ion quantum control and readout
Brian OdomNorthwestern University
Obtaining control over the rotational and vibrational quantum state is a prerequisite for many applications of trapped molecular ions. I will discuss a technique to optically cool rotations of certain species of trapped molecular ions, using a single spectrally shaped broadband laser. I will also discuss our progress toward reading out the internal state of a single trapped molecular ion using a relatively simple nondestructive photon recoil technique. Finally, I will discuss prospects for measurement of time-varying fundamental constants using spectroscopy of a single trapped molecular ion.
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Prospects of reaching the quantum regime in Li-Yb+ mixtures
H. Fürst1, N. V. Ewald1, T. Feldker1, H. Hirzler1, J. Joger1, M. Tomza2 and R. Gerritsma1
Institute of Physics, University of Amsterdam, NetherlandsFaculty of Physics, University of Warsaw
Recent experiments have shown that the time-dependent trapping field of the ions can cause heating in hybrid atom-ion systems [e.g. 1]. One way to mitigate this problem is to employ ion-atom combinations with a large mass ratio [2]. The highest mass ratio - for species that still allow for straightforward laser cooling - is achieved by using the combination 174Yb and 6Li. Here, we present experimental results on cold collisions between 6Li atoms and Yb+ ions. We find that for atoms and ions prepared in the S1/2 ground state, the rate of collisions that result in charge exchange or molecular association is suppressed by a factor ≤ 10−3, as compared to the Langevin collision rate [3]. Furthermore, we measure fast spin-exchange collisions between Yb+ ions and Li atoms [4]. We discuss the prospects for our system to reach the quantum regime and the possibility to observe atom-ion Feshbach resonances in it [5,6].
[1] Z. Meir et al., Phys. Rev. Lett. 117, 243401 (2016).[2] M. Cetina et al., Phys. Rev. Lett. 109, 253201 (2012).[3] J. Joger et al., Phys. Rev. A 96, 030703(R) (2017).[4] H. Fürst et al., arXiv:1712.07873 (2017).[5] M. Tomza, C.P. Koch and R. Moszynski, Phys. Rev. A 91, 042706 (2015).[6] H. Fürst et al., arXiv:1804.04486 (2018).
A search for quantum signatures in ultracoldatom-ion collisions
Roee OzeriWeizmann Institute of Science
Atom-ion mixtures are studies at decreasingly lower temperatures. As the temperature range decreases, less partial waves are involved in the collision and the search for quantum signatures in scattering dynamics commences. In this talk I will describe the search for quantum signatures in two types of processes, in a cold mixture of 88Sr+ - Rb mixture: spin-exchange and non-adiabatic electronic excitation exchange
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Novel quantum states and dynamics of ions, atoms, and electrons
Chris H. GreenePurdue University
This talk will discuss some of the recent progress that has been achieved in the system of a Rydberg atom immersed in a sea of ground state neutral atoms. This is the regime where interesting molecular spectra can be observed in ultra-long-range Rydberg molecules. Such molecular states are well-known to be formed, in a number of different categories from low angular momentum to the trilobite and butterfly states that are created as superpositions of high angular momentum states. In recent years, an improved understanding has evolved in the description of the complicated spin-dependent interactions that can perturb the spectra, and some headway in treating that Hamiltonian will be addressed. Beyond the spectroscopy, rich collisional dynamics can also occur, and the mechanisms for processes such as associative ionization will also be discussed.
Elastic and inelastic collisions in a 6Li-40Ca+
co-trapped system
Takashi MukaiyamaOsaka University
Chemical properties of particles at low temperatures are expected to be quite different from those at high temperatures. To study quantum statistical features in chemical reactions, we investigate the collisional properties in an ultracold atom-ion hybrid system. In this study we choose 6Li and 40Ca+ as an atom-ion combination, which has a small atom-ion mass ratio to suppress the heating arising from the dynamical nature of the ion trap. We have been able to observe elastic collisions (thermalization) and inelastic collisions (charge-exchange and collisional quenching) in the atom-ion co-trapped system. In the talk we will present our recent experimental results on the collisional properties between 6Li atoms and 40Ca+ ions.
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The road to entanglement of freely-rotatingmolecular ions
Eric HudsonUCLA
We consider the practical feasibility of using the direct, electric dipole-dipole interaction between co-trapped molecular ions for robust quantum logic without the need for static polarizing fields. The use of oscillating dipole moments, as opposed to static electric dipoles, dynamically decouples the dipoles from laboratory fields, including the electric fields of the trap itself. Further, this implementation does not require quantum control of motion, potentially removing a major roadblock to ion trap quantum computing scalability. Since the polarizing field is electromagnetic radiation, even pairs of states with splittings in the THz regime can be fully polarized. We will also discuss recent work towards preparing cold molecular ions via sympathetic cooling, detailing a recent solution to a long-standing roadblock from unwanted chemical reactions.
Ionic Impurity in a Bose-Einstein Condensate at Submicrokelvin Temperatures
Florian MeinertPhysikalisches Institut and Center for Integrated Quantum Science and Technology,
Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
I will report on our endeavor to utilize single Rydberg impurities in a quantum gas for the exploration of ion-atom interaction. Generally, Rydberg atoms immersed in a Bose-Einstein condensate interact with the quantum gas via electron-atom and ion-atom interaction. To suppress the typically dominant electron-neutral interaction, Rydberg states with a principal quantum number up to n=190 are excited from a dense and tightly trapped micron-sized condensate. This allows us to explore a regime where the Rydberg orbit exceeds the size of the atomic sample by far. In this case, a detailed line shape analysis of the Rydberg excitation spectrum provides clear evidence for ion-atom interaction at temperatures well below a microkelvin. Moreover, the Rydberg electron effectively shields the ionic core from detrimental electric stray fields, which otherwise would cause rapid acceleration of the ionic impurity. Our results may open up ways to enter the quantum regime of ion-atom scattering for the exploration of charged quantum impurities and associated polaron physics.
Reference:K. S. Kleinbach, F. Engel, T. Dieterle, R. Löw, T. Pfau, and F. Meinert, Phys. Rev. Lett. 120, 193401 (2018).
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Trap-induced shape resonances in an ultracold system of an atom and static impurities
Marta Sroczyńska1, Tomasz Wasak1, Krzysztof Jachymski 1, 2, Tommaso Calarco3 and Zbigniew Idziaszek1
1Faculty of Physics, University of Warsaw, ul. Pasteura 5, PL-02-093 Warsaw, Poland2Institute for Theoretical Physics III & Center for Integrated Quantum Science and
Technology (IQST),University of Stuttgart, Pfaffenwaldring 57,D-70550 Stuttgart, Germany
3Institute for Complex Quantum Systems & Center for Integrated Quantum Science and Technology (IQST), Universität Ulm, Albert-Einstein-Allee 11, D-89075 Ulm, Germany
Hybrid systems of ultracold atoms and trapped ions or Rydberg atoms can be useful for quantum simulation purposes. By tuning the geometric arrangement of the impurities it is possible to mimic solid state and molecular systems. Here we study a single trapped atom interacting with a set of arbitrarily arranged static impurities and show that the problem admits an analytical solution. First I will discuss in details the case of two impurities, finding multiple trap-induced resonances which can be used for entanglement generation. In the second part of the talk I will consider the motion atoms in quasi-1D geometry in the presence of a chain of equally spaced impurities. The impurities form a periodic lattice and induce a band structure in the atoms. Such a setup can be realized for instance in a hybrid system composed of a one-dimensional crystal of trapped ions immersed into a cloud of ultracold atoms. Our results serve as a building block for the studies of quantum dynamics of more complex systems.
Excitation-Assisted Charge-Exchange Reaction in a Mixed Atom-Ion systems
Ming Li and Svetlana Kotochigova Department of Physics, Temple University, Philadelphia, PA, United States
Hybrid systems that mix laser-cooled atoms and ions often exhibit rich charge-exchange reaction dynamics that involve excited channels. We present a theoretical investigation into possible mechanisms behind such excitation-assisted reactions. In particular, we focus on Ca atoms in a magneto-optical trap (MOT) reacting with Yb+ ions in collaboration with Eric Hudson’s group in UCLA who lead the experimental effort. We find that direct non-adiabatic charge-exchange reaction between an excited Ca atom and a ground Yb+ ion is limited by the Ca excited-state population in the MOT and the spontaneous decay of the excited atom. On the other hand, an additional pathway starting from a ground Ca atom and an Yb+ ion assisted by the MOT laser can efficiently transfer population from the ground-state potentials to excited potentials at shorter internuclear separations and contribute significantly to the charge-exchange reaction rate. The light-assisted process taps into the extremely high density-of-state of the isotropic C4/R4 induction and anisotropic C3/R3 charge-quadrupole potentials that govern the long-range molecular forces as well as the large transition dipole moment associated with the excited threshold. We theoretically demonstrate that such mechanism can be replicated with an additional tunable laser and used to control and enhance the charge-exchange reaction through changing the laser detuning and intensity.
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Calculations of state-to-state ultra-cold three-body recombination rates in gases and lattices
Paul S. JulienneJoint Quantum Institute, NIST and University of Maryland, College Park MD 20742
Three-body collision rates are very important for cold gases and lattices, since the recombination of three atoms to make a diatomic molecule plus a free atom usually leads to loss of both from a shallow trap. A recent experiment with a hybrid neutral + ion trap configuration measured the specific vibrational and rotational states of the diatomic molecules produced in the case of three ultra-cold 87Rb atoms [1]. Thus, we can test the validity of a universal van der Waals (UVDW) theoretical model to calculate state-to-state near-threshold three-body recombination coefficients. The UVDW theory, known to be successful in describing Efimov physics associated with tuning the scattering length with a Feshbach resonance [2], assumes that long-range three-body forces are given by the sum of two-body potentials having the correct 2-body van der Waals coefficient and the known 2-body scattering length, but with a reduced number of bound states. We apply the UVDW model for two different cases where we can compare with experiment. The first involves the above-mentioned 87Rb one, using numerical 3-body codes developed at JILA to calculate the product distribution. The overall pattern over the last 5 vibrational levels with rotational quantum numbers R up to R = 10 show both similarities and differences between the measurement and calculations. The calculations tend to be better for the most weakly bound levels, but experiment and theory show a similar drop off of overall magnitude as the square root of the binding energy and exhibit an oscillating pattern with R. The magnitude of the calculated total recombination rate constant is about a factor of 4 smaller than the measured one, but the latter is uncertain by a factor of 2. We also apply the UVDW model to calculate the total loss rate for a JILA experiment with three unlike 87Sr fermions that differ in nuclear spin projection. Since 2 to 5 individual 87Sr atoms could be held in the ground state of a single optical lattice trapping cell and probed according to atom number, a very clean measurement of the loss rate of three-atom cells was possible. The measured and calculated values are in excellent agreement for three ground state 87Sr atoms with unlike nuclear spin [3].
[1] J. Wolf, M. Deiß, A. Krükow, E. Tiemann, B. P. Ruzic, Y. Wang, J. P. D’Incao, P. S. Julienne, J. Hecker Denschlag, Science 358, 921-924 (2017).[2] Yujun Wang and P. S. Julienne, Nat. Phys. 10, 768-773 (2014).[3] A. Goban, R. B.. Hutson, G. E. Marti. S. L. Campbell, M. A. Perlin, P. S. Julienne, J. P. D’Incao, A. M. Rey, J. Ye, arXiv:1803.11282 (2018).
Rydberg Impurities in Strontium Quantum Gases
Thomas C. KillianRice University, Department of Physics and Astronomy and Rice Center for Quantum
Materials, Houston, Texas, USA [email protected]
I will describe the excitation of Rydberg atoms in ultracold gases of bosonic and fermionic isotopes of strontium. In a few-body regime, we observe a dense, highly structured spectrum reflecting excitation of ultralong-range molecules consisting of one or more ground-state atoms bound to the Rydberg core in potential wells formed by the Rydberg-electron wave function. In a many-body regime, with hundreds of ground-state atoms within the Rydberg orbital, the Rydberg atoms can be viewed as an impurity in a quantum gas. For bosons, the spectrum for impurity excitation is explained in terms of dressing of the impurity with excitations from the background gas. In particular, detailed analysis of the red-detuned tail reveals the intrinsic excitation spectrum of objects described as Rydberg polarons. All features of the spectrum are well described using functional determinant theory to solve the many-body Hamiltonian. Rydberg excitations in a fermi gas have been explored in the few-body regime, and the excitation rate can be used to probe the effects of quantum statistics on spatial correlations.
Research supported by the AFOSR, NSF and the Robert A, Welch Foundation
Collaborators
F. B. Dunning1, F. Camargo1, J. Whalen1, R. Ding1, H. R. Sadeghpour2, R. Schmidt2,3, E. Demler3, S. Yoshida4, J. Burgdorfer4
1Rice University, Department of Physics and Astronomy and Rice Center for Quantum Materials, Houston, Texas2ITAMP, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts3Department of Physics, Harvard University, Cambridge, Massachusetts 4Institute for Theoretical Physics, Vienna University of Technology, Vienna, Austria, EU