Atomic Physics Seminars

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Monday, October 25, 2021
9:00 AM
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"Single-site and single-atom imaging of Lithium-7 atoms in an optical lattice."


Dr. Jae-yoon Choi , KAIST South Korea
[Host: Peter Schauss]
ABSTRACT:

Imaging and addressing individual atoms in optical lattices with single-site resolution constitute a new approach to the study of quantum many-body problems. It provides microscopic information of quantum many-body states, such as correlation functions, and one can engineer arbitrary density patterns for the study of non-equilibrium quantum dynamics. Here, we report the first realization of the quantum gas microscope of Lithium-7 atoms in a square two-dimensional optical lattice and observation of the unity filling Mott insulator with few thousand atoms. We implement the Raman sideband cooling in the lattice and about 4,000 photons per atom are detected by high numerical aperture (NA=0.65) objective lens. The point spread function (PSF) of the imaging system is measured to be 630 nm (full width half maximum), small enough to resolve the lattice spacing (752 nm). In the talk, we will also introduce our journey (both successful and failed stories) when implementing the state-of-the-art imaging system.

Atomic
Monday, July 26, 2021
4:00 PM
Physics Building, Room 204

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ABSTRACT:

A recent experiment, conducted in the group of Cass Sackett at the University of Virginia, implemented a dual-Sagnac atom interferometer (AI) for rotation sensing using a BoseEinstein condensate (BEC) confined in a TOP-trap potential. The BEC was split twice by laser light to create two pairs of counter-orbiting clouds in a harmonic potential trap where each cloud pair acted as a separate Sagnac interferometer. After one orbit the two overlapping cloud pairs were split a final time and the population of atoms in the zero momentum state were measured. We have studied the impact of the presence of anharmonic potential terms and atom-atom interactions on the performance of this rotation sensor. Our studies have been carried out using a variational model that approximates the rotating-frame Gross-Pitaevskii equation. We have used this model to study the impacts of using larger-number condensates and multiple-orbit protocols on sensor performance.

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Monday, April 26, 2021
4:00 PM
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"Demonstration of RF Electrometer Based on EIT Spectroscopy of Non-Resonantly Dressed Rydberg Atoms"


Lingyun Chai , University of Virginia - Department of Physics
[Host: Peter Schauss]
ABSTRACT:

We present a technique for measuring the amplitude of weak microwave/rf fields of arbitrary frequency. The method uses Rydberg atoms in a vapor cell as a detection medium, and electromagnetically induced transparency (EIT) spectroscopy as an optical readout. Unlike other schemes that rely on resonant coupling between Rydberg states [1], our electrometer is based on non-resonant dressing of the Rydberg atoms in combined AC and DC fields. We demonstrate the technique in a room temperature Rb cell, where mixing of the AC and DC fields through the second-order Stark shift produces sidebands in the EIT signal, flanking the primary resonance feature associated with the optical 5p – 32s transition. The spectral location of the sidebands reveals the frequency of the AC field. The ratio of the sideband intensity to that of the central EIT feature gives the AC field amplitude through calculation. Field amplitudes less than 200 mV/cm have been measured at frequencies from 20 to 100 MHz.  

[1] J. A. Sedlacek et al., Nat. Phys. 8, 819 (2012). 

Special Atomic Seminar

 

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Friday, April 23, 2021
2:00 PM
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"Realising the Symmetry-Protected Haldane Phase in Fermi-Hubbard Ladders"


Timon Hilker , Max Planck Institute of Quantum Optics
[Host: Peter Schauss]
ABSTRACT:

The spin-1 Haldane chain is the paradigmatic example of symmetry protected topological (SPT) phases, which are characterized by non-local order and edge states. In my talk, I will report on the experimental realization of such a phase using ultracold fermions in optical lattices (arXiv:2103.10421). 

Using the full spin and density resolution of our Fermi-gas microscope, we detect a finite non-local string correlator in the bulk of a Heisenberg two-leg ladder system and image localized spin-1/2 states at its edges. We find the phase to be robust to perturbations that preserve the spin symmetry. 

Going beyond the spin model, we then study the effects of charge fluctuations on the SPT phase in the more general Hubbard ladder. Finally, I will compare the non-local order seen here to spin-charge separation in doped spin-1/2 chains. 

 

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Monday, April 19, 2021
4:00 PM
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"Engineering Long-Range Interactions Between Ultracold Atoms"


Brian J. DeSalvo , Indiana University Bloomington
[Host: Peter Schauss]
ABSTRACT:

Throughout many fields of physics, particle exchange plays an important role in the understanding of long-range interactions. From the exchange of massive bosons yielding the Yukawa potential to the phonon exchange underpinning Cooper pairing in superconductors, such mediated interactions can have profound consequences on the ground state of a many-body system. When a Bose-Einstein condensate (BEC) is immersed in a degenerate Fermi gas, exchange of a particle-hole pair of fermions gives rise to an attractive mediated interaction between bosons. These mediated interactions are analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism in condensed matter and are expected to give rise to novel magnetic phases and supersolids. In this talk, I will describe how we experimentally realize these mediated interactions in a quantum degenerate mixture of Li and Cs. We show that for suitable conditions, these mediated interactions can become dominant and convert a stable BEC into a train of \Bose-Fermi solitons". In the time remaining, prospects for other methods of engineering long-range interactions in quantum gases will also be discussed.
 

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Monday, April 5, 2021
4:00 PM
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"Quantum optical frequency comb on a chip "


Professor Xu Yi , University of Virginia - ECE and Physics
[Host: Peter Schauss]
ABSTRACT:

Scalability is the central challenge in universal quantum computing, which has long established revolutionary premises, such as exponential speedup of difficult to near-impossible computations. A promising platform towards scalable quantum computing is the quantum optical frequency comb, which leverages optical frequency multiplexing and produces thousands of unconditional EPR entanglement in a single oscillator. In this talk, I will present our recent work to miniaturize the quantum optical frequency comb to a photonic chip for the first time. Our work brings the power of microfabrication to quantum optical applications, and could enable low cost mass-production, which promises additional scalability. I will also briefly discuss the roadmap and the challenges towards scalable quantum computing with integrated photonic frequency combs. 

 

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Monday, March 22, 2021
9:00 AM
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"Single-site-resolved imaging of rubidium atoms in a triangular lattice"


Takeshi Fukuhara , RIKEN, Japan
[Host: Peter Schauss]
ABSTRACT:

Ultracold atoms in optical lattices provide an excellent platform to study many-body quantum systems. Especially, a quantum gas microscope, which enables us to observe and control atoms at the single-site level, is a powerful tool for such studies. Our target is a quantum simulation of frustrated systems, which are expected to exhibit various phenomena and non-trivial quantum states such as quantum spin liquids. The simplest example of frustrated systems can be realized with a triangular lattice. In this talk, I will present single-site-resolved fluorescence imaging of ultracold rubidium-87 atoms in a triangular optical lattice [1].
Experimental parameters for the fluorescence imaging have been automatically optimized by using a machine learning technique. I will also introduce experimental results [1,2] of automatic optimization based on the Bayesian optimization.


[1] R. Yamamoto et al., “Single-site-resolved imaging of ultracold atoms in a triangular optical lattice,” New Journal of Physics 22, 123028 (2020).
[2] I. Nakamura et al., “Non-standard trajectories found by machine learning for evaporative cooling of 87Rb atoms,” Optics Express 27, 20435 (2019).

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Monday, February 22, 2021
4:00 PM
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"Quantum state engineering with photon-number-resolved detection"


Miller Eaton , University of Virginia - Department of Physics
[Host: Olivier Pfister]
ABSTRACT:

Quantum information science promises to hold substantial advantages over classical information by allowing for secure communication, measurement precision below standard limits, and an exponential increase in certain computational problems. Although there have been several recent advances, such as the claims at quantum supremacy with discrete quantum computation (QC), many challenges still remain. One large obstacle is the prevention of decoherence in large entangled systems, which leads to a scalability problem in qubit-based QC. The scalability problem can be solved with cluster states using continuous-variable (CV) quantum-optics, but this comes with its own difficulties. In order to achieve a quantum advantage and allow for error correction with CV systems, it is necessary to include quantum states with non-Gaussian distribution functions.  In this talk, I will discuss several experimentally accessible ways one can generate useful non-Gaussian states with photon-number-resolved detection. Some of these states are desirable for CVQC while others show potential for Heisenberg-limited metrology. I will then introduce our method of efficient quantum state characterization utilizing the photon-number-resolving measurement capabilities in our lab.

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Monday, November 16, 2020
4:00 PM
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"Ultracold strontium for condensed-matter simulations and quantum sensing"


Julio Barreiro , University of California San Diego
[Host: Peter Schauss]
ABSTRACT:

Systems of ultracold particles with strong interactions and correlations lie at the heart of many areas of the physical sciences, from atomic, molecular, optical, and condensed-matter physics to quantum chemistry. In condensed matter, strong interactions determine the formation of topological phases giving materials unexpected physical properties that could revolutionize technology through robustness to noise and disorder. In this talk I will report on our work towards the realization of a fractional Chern insulator state using our experimental apparatus producing degenerate Fermi gases of strontium. Our simulation of the topological insulating state will follow an optical flux approach, which engineers the lattice in reciprocal space through polychromatic beams driving a manifold of stimulated Raman transitions, and will benefit from ultracold strontium's low temperatures and reduced heating by spontaneous emission.

On the other hand, systems of ultracold particles without interactions reveal matter-wave properties with enhanced interferometric sensitivity. I will discuss our ongoing efforts to trap ultracold strontium atoms on the evanescent fields of nanophotonic waveguides and nanotapered optical fibers. The existence of magic blue and red detuned wavelengths lead to a trapping volume that can be continuously and robustly loaded with ultracold strontium via a transparency beam. Fundamental studies of Casimir and Casimir-Polder physics as well as several applications, such as field sensors and matter-wave interferometers, will be possible with these platforms.

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To add a speaker, send an email to ps5nw@Virginia.EDU Include the seminar type (e.g. Atomic Physics Seminars), date, name of the speaker, title of talk, and an abstract (if available). [Please send a copy of the email to phys-speakers@Virginia.EDU.]