Atomic Physics Seminar

Optical trapping and imaging of atoms plays an essential role in cold-atom physics, ranging from precision measurement to the study of correlated many body systems. Due to the diffraction limit, trapping and imaging are typically limited to length scales on the order of the wavelength of the light. The nonlinear response of three-level atoms, however, supports a dark state with spatial structures much smaller than the wavelength. In this talk, I will present the experimental use of such dark state spatial structure to both create optical potentials and probe the atomic wave function with a resolution of lambda/50, far below the diffraction limit. The optical potential physically realizes a Kronig-Penney lattice of near delta-function barriers with widths below 10nm. The coherent nature of our approach also provides a fast temporal resolution (500 ns), with which we could observe the quantum motion of atoms inside the unit cell of an optical lattice.
Host: 
Saffman
Speaker: Dr. Yang Wang Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland

 

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Room and Building: 
5310 Chamberlin Hall
The rich internal structures of diatomic molecules enable a wide range of experiments in regimes not accessible with atoms. Uses of molecules range from measurement of symmetry-violating effects that probe interesting phenomena in nuclear and particle physics, to the study of highly correlated quantum systems, to the control of novel phenomena in chemical reactions. Despite this broad interest, methods for cooling and trapping molecules have been far less advanced than those for atoms. In particular, direct laser cooling of molecules was long considered infeasible: the same complex internal structure that makes molecules useful also makes laser cooling more difficult. Over the past several years, our group and others have found methods to overcome this obstacle. Now, most of the standard tools of atomic laser cooling and trapping have been demonstrated to work, with appropriate modifications and for certain molecules. In this talk I will review progress in laser cooling and trapping of molecules, and give an outlook for future directions enabled by these rapidly-developing methods.
Host: 
Saffman
Speaker: Prof. David DeMIlle Yale University

 

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Room and Building: 
5310 Chamberlin Hall
Controllable, coherent quantum many-body systems can provide insights into fundamental properties of quantum matter, enable the realization of exotic quantum phases, and ultimately offer a platform for quantum information processing that could surpass any classical approach. Recently, reconfigurable arrays of neutral atoms with programmable Rydberg interactions have become promising systems to study such quantum many-body phenomena, due to their isolation from the environment, and high degree of control. Using this approach, we demonstrate high fidelity manipulation of individual atoms and entangled atomic states. Furthermore, we realize a programmable Ising-type quantum spin model with tunable interactions and system sizes up to 51 qubits. Within this model, we observe transitions into ordered states that break various discrete symmetries. Varying the rate at which the quantum phase transition is crossed allows us to observe the power-law scaling of the correlation length, as predicted by the Kibble-Zurek mechanism. The scaling exponent observed is consistent with theoretical predictions for the Ising universality class when sweeping into a Z2-ordered phase, and with the 3-state Chiral Clock Model for transitions into the Z3-ordered phase. An alternative, hybrid approach for engineering interactions is the coupling of atoms to nanophotonic structures in which guided photons mediate interactions between atoms. I will discuss our progress towards entangling two atoms that are coupled to a photonic crystal cavity and outline the exciting prospects of scaling these systems to many qubits and to quantum networks over large distances.
Host: 
Saffman
Speaker: Prof. Hannes Bernien University of Chicago

 

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Room and Building: 
5310 Chamberlin Hall
Understanding the ionization properties of diatomic molecules is of fundamental importance to chemical physics and many spectroscopic applications. Here, I present rotational-state-selective field ionization spectra of highly excited triplet nd H2 Rydberg states. A fast 6 keV beam of metastable c3∏u- 2pπ molecules is excited to v = 0, R(1)nd1 (n = 17-27) Rydberg states by a frequency-doubled tunable dye laser and ionized by a static electric field as large as ~35 kV/cm. For each Rydberg state, we observe, as expected, an ion yield that corresponds to diabatic field ionization into the N+ = 1 continuum. At higher fields, we observed an additional ion yield. A model, which considers a diabatic traverse of the Stark map, expects the N+ = 1 ion yield and allows for characterization of the second ion yield as ionization into the N+ = 3 continuum and the result of a rotational-state population transfer. Candidates for the population-transfer mechanism are discussed.
Host: 
Shimon Kolkowitz
Speaker: William Setzer Thomas Morgan's group, Wesleyan University

 

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Room and Building: 
Chamberlin 5310
What sets the boundaries of what humans can perceive? From time and frequency standards, to molecular biology, the limits of what we can measure depend on two related factors:

1. How much information we get in a single measurement

2. How well we can combine and average these measurements.

I will tell two stories from these two different fields of metrology.

The first story is about a new atomic clock design aimed at measuring time to the 19th decimal place. By using a Fermi-degenerate gas in a three-dimensional optical lattice, we controlled all quantum degrees of freedom of our atomic frequency references and suppressed atomic interactions. This allowed us to increase our single-shot frequency sensitivity by both extending the atom-light coherence time and by using more atoms to reduce the quantum projection noise. This new technology enabled new records in clock stability and the corresponding improvements in our ability to evaluate and stabilize systematic shifts.

The second story is about pushing the limits of cryogenic transmission electron microscopy (cryo-EM). Cryo-EM is rapidly usurping x-ray crystallography for determining protein structure, as it allows the visualization of molecules in their native environments, without the need for crystallization. Information from the nearly-transparent specimen manifests as a small phase shift on the electron wavefunction, which goes undetected unless the microscope is intentionally defocused. Defocusing compromises resolution and still results in low contrast at low spatial frequencies. Reaching atomic resolution requires using low-frequency information to align ~100,000 2D projections of randomly-oriented particles before averaging. The need for sufficient low-frequency information has limited the scope of cryo-EM to large macromolecular complexes. Zernike phase contrast converts phase to amplitude by applying a 90 degree phase shift to the unscattered electron beam, but has yet to be widely implemented, as all previous phase plate designs degrade under the charged electron beam. Laser-based electron optics offer stable, tunable operation, without material objects in the electron beam path. We phase shift the unscattered electron wavefunction via the ponderomotive force of a tightly-focused laser in a near-concentric buildup cavity, which reaches 100 GW/cm^2 continuous intensity.

This aims to be a light, introductory talk with many pictures of my cat and Fourier transforms of my cat. Pickles has a lot of 1/f noise.
Host: 
Shimon Kolkowitz
Speaker: Dr. Sara Campbell Postdoc in Holger Müller's group, UC Berkeley

 

Available Downloads:

Room and Building: 
5310, Chamberlin Hall
Triatomic molecules are deceptively simple. Even though there is only one additional atom compared to a diatomic molecule, this leads to non-trivial additional motional degrees of freedom and new associated quantum numbers. This, plus the larger density of states, realizes a quantum object whose complexity leads to new chemistry and physics research opportunities and concomitantly presents new challenges in molecular control. The science opportunities include the development of accurate and precise manipulation of chemical reactions and collisions in a qualitatively more complex species. But the reach of triatomics also includes dramatically improved, novel approaches to searches for physics beyond the Standard Model, and enhanced platforms for quantum computing using molecular tweezer arrays, both of which are aided by the low lying bending modes present in triatomic molecules. All of these research frontiers with triatomics, and their symmetric and asymmetric top brethren, either require or are greatly enhanced by chilling them to ultracold temperatures where they can be prepared in exquisitely well-defined internal and external motional states.



The recent experimental advances in direct laser cooling of diatomic molecules and triatomic molecules clearly indicates that full extension of laser tools - the creation of a magneto-optical trap (MOT) plus sub-Doppler cooling - to triatomic species should be possible. Recently in our laboratory we achieved a magneto-optical trap of diatomic molecules with CaF, sub-Doppler cooling to 40 µK, and loading of these molecules into an optical dipole trap. We also accomplished the first laser cooling and bichromatic force deflection of a polyatomic molecule, using SrOH. In addition, in 2016 we proposed the laser cooling of more complex polyatomic molecules using the methods we have now demonstrated. In particular, symmetric top molecules like CaOCH3 (and, possibly, related asymmetric top molecules) look extremely promising for direct laser cooling. The experimental prospects for a MOT of CaOH, YbOH, and CaOCH3 will be discussed.

Host: 
Saffman
Speaker: Prof. John Doyle Harvard

 

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Room and Building: 
5310 Chamberlin
The interstellar medium (ISM) is multi-phase, turbulent, and magnetic. This makes the ISM an ideal laboratory for studying the multi-scale physics of star formation and galactic evolution. This unfortunately also makes the ISM a formidable foreground for cosmology experiments, such as the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background. I will discuss recent work on magnetic fields in the diffuse ISM, with a particular focus on insights from high-dynamic range observations of neutral hydrogen and polarized dust emission. Novel tools for quantifying the morphology of interstellar material are enabling new probes of the ambient magnetic field structure, and thus a better characterization of polarized cosmological foregrounds. The hunt for primordial signals is now inextricably linked to our understanding of the magnetic ISM.
Host: 
Prof Alexander Lazarian
Speaker: Susan Clark Institute for Advanced Study

 

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Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 pm, Talk begins at 3:45 pm
We present results of theoretical and experimental studies of Stark-tuned Forster resonances in Rydberg atoms. Two trapped<br>
atoms are excited into Rydberg states which are then tuned by the external electric field midway between two other Rydberg states of the opposite parity. The collective two-atom states are coupled by dipole-dipole interaction. We have proposed schemes of two-qubit gates using adiabatic passage of Forster resonances in time-dependent electric field. We have shown that radiofrequency electric fields can induce additional "inaccessible" resonances which are useful both for coherent coupling and for adiabatic passage. We have experimentally observed Borromean three-body Forster resonances for three interacting Rydberg atoms.
Host: 
Saffman
Speaker: Dr. Ilya Beterov Institute of Semiconductor Physics Novosibirsk, Russia

 

Available Downloads:

Room and Building: 
5310 Chamberlin Hall
The next generation experiments for the electric dipole moment (EDM) of the neutron search for a manifestation of yet unknown time reversal violation sources. In the Munich nEDM experiment ultra-cold neutrons are stored in two cylindrical vessels and subject to parallel and anti-parallel magnetic and electric fields. Applying Ramsey's method of separated oscillatory fields a phase proportional to the EDM is obtained from a clock comparison scheme.

The first part of this talk discusses the general scheme of nEDM experiment with respect to the upcoming 2018 measurements at the Institut Laue-Langevin. The latter part will focus on optical Cs and Hg magnetometers used to monitor and stabilize the magnetic field.
Host: 
Walker
Speaker: David Wurm TUM Munich

 

Available Downloads:

Room and Building: 
5280 Chamberlin Hall
Strong, long-range interactions between atoms in high-lying Rydberg states
make them attractive systems for the studies of ordered phases of interacting
many-body systems and simulating quantum phase transitions.

Several conceptually different approaches have been explored, both theoretically
and experimentally, for the preparation of crystalline order of Rydberg excitations
in spatially-extended ensembles of cold atoms. These include direct (near-)resonant
laser excitation of strongly-interacting Rydberg states in a two-dimensional lattice
gas, and adiabatic preparation of crystalline phases of Rydberg excitations in a
one-dimensional optical lattice by adiabatic frequency sweep of the excitation laser.
We show, however, that taking into account realistic relaxation processes affecting
the atoms severely complicates the prospects of attaining sizable crystals of Rydberg
excitations in laser-driven atomic media. Our simulations well reproduce the
experimental observations of spatial ordering of Rydberg excitations in driven
dissipative lattice gases, as well as highly sub-Poissonian probability distribution
of the excitation number. We find that the excitations essentially form liquid rather
than crystal phases with long-range order.
Host: 
Mark Saffman
Speaker: Prof. David Petrosyan Institute of Electronic Structure & Laser (IESL) Foundation for Research and Technology - Hellas (FORTH) Heraklion, Crete, GREECE

 

Available Downloads:

Room and Building: 
5310 Chamberlin Hall

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