Groups | Seminars || Courses | Outreach

Seminars

Seminars will be held held at room S-141 in the Physics and Astronomy Department building on Mondays at 4:00 PM, unless noted otherwise.

Fall 2015

September 14, 2015 Dr. Robert Konik Brookhaven National Laboratory Quantum stutter: arrested expansion without a lattice and impurity snaking (Host: Dominik Schneble)

We consider the real time dynamics of an initially localized distinguishable impurity injected into the ground state of the Lieb-Liniger model. Focusing on the case where integrability is preserved, we numerically compute the time evolution of the impurity density operator in regimes far from analytically tractable limits. We find that the injected impurity undergoes a stuttering motion as it moves and expands. For an initially stationary impurity, the interaction-driven formation of a quasibound state with a hole in the background gas leads to arrested expansion -- a period of quasistationary behavior. When the impurity is injected with a finite center of mass momentum, the impurity moves through the background gas in a snaking manner, arising from a quantum Newton's cradle-like scenario where momentum is exchanged back-and-forth between the impurity and the background gas.

September 21, 2015 Dr. Cornelius Hempel IQI Innsbruck, Austria Exploring magnetism and chemistry with a trapped-ion quantum simulator (Host: Hal Metcalf)

Quantum computers & simulators promise access to previously inaccessible states and properties of many-body quantum systems with potential use in fields ranging from material science to pharmaceutical chemistry. Current experimental investigations are mainly focused on analog quantum simulations as full quantum error correction is still under development. In this talk, I will first introduce the trapped-ion platform and present its capabilities in the context of quantum gates and analog simulations. Next, I will report on work in which we investigate the dynamical behavior of one-dimensional spin chains. Building on recent experiments that examined how entanglement and information travels around an interacting quantum system [1], we have implemented a new spectroscopy technique to directly measure the system's dispersion relation and reveal interactions between the emergent quasi-particles [2]. I will briefly touch upon ongoing work on ways to efficiently characterize [3] such quantum systems with up to 20 particles. Lastly, I will describe a recent experiment in which we realized a novel quantum chemistry algorithm [4] in a fully scalable way. Here, we joined quantum and classical resources in a hybrid approach, which allows us to simulate properties of small molecular systems on a noisy quantum processor without error correction using only a small number of quantum gates. [1] P. Jurcevic et al, Nature 511, 202 (2014). [2] P. Jurcevic et al, PRL 115, 100501 (2015). [3] M. Cramer et al, Nat. Commun. 1, 149 (2010). [4] A. Peruzzo et al. Nat. Commun. 5, 4213 (2014).ba

September 28, 2015 Dr. Oliver Gessner Lawrence Berkeley Nat'l Laboratory Monitoring Interfacial Charge-Transfer Dynamics and Quantum Hydrodynamics with Ultrafast X-ray Tools (Host: Tom Allison)

At the heart of many emerging sunlight-to-fuel and molecular photovoltaic concepts are interfacial processes that require an optimized, concerted flow of charge and energy on a molecular level. We introduce a new approach to characterize the location of a migrating electron at a molecule-semiconductor interface with sub-nanometer spatial sensitivity and sub-picosecond temporal resolution. Time-resolved X-ray photoelectron spectroscopy (tr-XPS) at the LCLS is used to monitor the pathways of charge carriers in a film of N3 dye-sensitized ZnO nanocrystals on an atomic scale and with a temporal resolution that is commensurate with the timescales of interfacial electron motion.^1 Femtosecond time-resolved XPS experiments at the LCLS are complemented by picosecond time-domain studies at the Advanced Light Source (ALS).^2 Using a novel time stamping technique in combination with a high-power picosecond laser system, tr-XPS experiments can be performed in all operating modes of the ALS. The measurements monitor charge separation and recombination processes at the dye-semiconductor interface from the perspectives of both the N3 dye molecules and the ZnO substrate simultaneously, with distinct site specificity, picosecond time resolution, and up to millisecond dynamic ranges. Observations will be discussed with respect to the correlated electronic dynamics in the electron donors and acceptors as a result of interfacial charge transfer. Most recently, the technique has been extended to monitor charge-transfer dynamics in layered model systems for organic photovoltaics.^3 First steps toward the implementation of ultrafast X-ray spectroscopy tools as real-time in operando X-ray probes of interfacial photo-electrochemical processes will be outlined.^4 Much of our understanding of quantum hydrodynamics has emerged from experiments on macroscopic quantities of bulk superfluid helium. More recently, helium nanodroplets are attracting increasing attention as ideal, isolated model systems for the study of strongly correlated quantum fluids. The study of motion, however, in these sub-micron scale clusters has been hampered by their size and, in particular, their fleeing nature. A recent series of single-shot X-ray coherent diffractive imaging experiments at the Linac Coherent Light Source (LCLS) captured the first snapshots of rotational motion in pure and doped helium nanodroplets.^5 The images provide unequivocal evidence for the superfluid nature of the clusters through the observation of quantum vortex lattices. Observed rotational frequencies exceed previously achievable values by at least five orders of magnitude, granting experimental access to new regimes of quantum rotation. References [1] K. R. Siefermann et al., “Atomic Scale Perspective of Ultrafast Charge Transfer at a Dye-Semiconductor Interface”, J. Phys. Chem. Lett. 5, 2753 (2014). [2] S. Neppl et al., “Capturing interfacial photo-electrochemical dynamics with picosecond time-resolved X-ray photoelectron spectroscopy”, Faraday Discuss. 171, 219 (2014). [3] T. Arion et al., “Site-specific probing of charge transfer dynamics in organic photovoltaics”, Appl. Phys. Lett. 106, 121602 (2015). [4] S. Neppl et al., in Ultrafast Phenomena XIX, (Springer, 2015), 325 (2014). [5] L. Gomez et al., “Shapes and Vorticities of Superfluid Helium Nanodroplets”, Science 345, 906 (2014).

October 5, 2015 Prof. Matthew Wright Adelphi University Control of Ultracold Collisions with Frequency-Chirped Laser Light (Host: Hal Metcalf)

We investigate the application of the techniques of coherent control to ultracold atom-atom collisions. Laser-cooled Rb atoms in a magneto-optical trap are induced to collide by pulses of frequency-chirped light. The influence of various chirp parameters on these collisions is studied, including: chirp-rate, laser intensity, center detuning of the chirp, and delay between two successive chirps. These experiments reveal two coherent processes within collisions: nearly complete rapid adiabatic passage between states and multiple interactions between the laser and atom pair within one negative frequency-chirp. In addition, we will discuss our recent theoretical results that show that control of collisional processes can be even more efficient with a modest increase in the chirp rate. We will also discuss our progress toward experimentally testing this.

October 12, 2015 Dr. Sebastian Will MIT Ultracold Quantum Matter of Strongly Dipolar Molecules (Host: Tom Bergeman)

Over the past decade, ultracold atomic quantum gases have successfully been employed as quantum simulators for strongly correlated many-body systems. However, the interactions between ultracold atoms are typically short-range in character, limiting the spectrum of quantum phenomena to be explored. Quantum particles with long-range dipolar interactions will open up new routes for quantum simulation and - beyond that - should allow for the creation of novel states of matter, such as topological superfluids and dipolar quantum crystals. Ultracold diatomic molecules offer a unique path to realize strongly dipolar quantum gases. Among several choices, the sodium-potassium (NaK) molecule stands out due to its chemical stability and its large electric dipole moment in the absolute ground state. I will report on recent progress that led us to the creation of the first ultracold dipolar gas of NaK molecules – from the preparation of a new quantum gas mixture of Na and K, over the formation of weakly bound NaK Feshbach molecules [1], to the coherent transfer of NaK into the absolute ground state [2,3]. Equipped with full control over the molecules’ degrees of freedom, the creation of novel states of matter with strongly dipolar molecules comes into experimental reach. [1] Wu et al., Phys. Rev. Lett. 109, 085301 (2012) [2] Park, Will, Zwierlein, New J. Phys. 17, 075016 (2015) [3] Park, Will, Zwierlein, Phys. Rev. Lett. 114, 205302 (2015)

October 26, 2015 Prof. Vito Scarola Virginia Tech Engineering Strongly Correlated States with Ultracold Atoms (Host: Tom Bergeman)

Optical lattices containing ultracold alkali atoms represent nearly ideal manifestations of strongly correlated models, including Hubbard models. Hubbard models are centerpieces of solid-state physics. They can, for example, reveal intriguing magnetic states that are thought to hold the key to understanding high temperature superconductivity. Optical lattice experiments can therefore be used to study quantum states of matter of fundamental importance. Some of the work in my group uses numerical modeling to help guide ultracold atom experiments in these searches. I will review our recent work that compares with ongoing optical lattice experiments trying to realize a quantum antiferromagnet in a cubic optical lattice containing fermions in particular. I will also discuss recent work in our group that examines the impact of speckle disorder on the transport properties of ultracold fermions in a strongly correlated paramagnetic state in a trapped optical lattice.  In both cases we find that the temperatures are high enough to make direct quantitative comparison with experiments.

November 2, 2015 Dr. Yuan Sun University of Wisconsin-Madison Quantum computation with a 2D neutral atom array (Host: Hal Metcalf)

Qubits encoded in hyperfine states of neutral atoms are a promising approach for scalable implementations of quantum information processing. We are developing an atomic qubit array for quantum logic experiments. The array consists of qubits encoded in Cs atom hyperfine states. Single qubit gate operations are performed using either microwave fields for global operations on the array, or focused light fields for control of individual qubits. Two-qubit entangling gates are based on Rydberg-blockade interactions.

November 3, 2015 [Wed, 12pm] Boris Braverman MIT Progress toward a spin-squeezed optical atomic clock beyond the standard quantum limit (Host: Eden Figueroa)

State of the art optical lattice atomic clocks have reached a relative inaccuracy level of order $10^{-18}$, making them the most stable time references in existence. One of the limitations to the precision of these clocks is the quantum projection noise caused by the measurement of the atomic state. This limit, known as the standard quantum limit (SQL), can be overcome by entangling the atoms. By performing spin squeezing, it is possible to robustly generate such entanglement and therefore surpass the SQL of precision in optical atomic clocks. I will report on recent experimental progress toward realizing spin squeezing in an ${}^{171}$Yb optical lattice clock. A high-finesse micromirror-based optical cavity operating in the strong coupling regime of cavity quantum electrodynamics mediates the atom-atom interaction necessary for generating the entanglement. By exceeding the SQL in this state of the art system, we are aiming to advance precision time metrology and expand the boundaries of quantum control and measurement.

November 9, 2015 Prof. Shu Jia SBU (Biomedical Engineering) Optical Imaging at the Nano Scale (Host: Hal Metcalf)

Super-resolution fluorescence imaging techniques have overcome the optical diffraction limit (~λ/2) of conventional fluorescence microscopy, allowing visualization of biological structures and processes with near-molecular-scale resolution. In recent years, these emerging techniques have significantly empowered studies in molecular, cellular and neurobiology. However, the complexity of biological systems ranges from small structures organized at molecular precision to large volumes of connected networks extending across multi-cellular organisms. This poses a strong desire for imaging systems that possess spatial resolution at the sub-cellular or molecular level, temporal resolution that captures rapid bio-dynamics, and imaging depth that penetrates deep tissues. To address these challenges, the Jia Laboratory works on the forefront of super-resolution optical microscopy, developing and applying advanced imaging tools to study complex, dynamic biological systems. This talk will present a host of new biophotonic technologies, combining optical wavefront engineering, single-molecule biophysics, adaptive optics, image processing, and advanced instrumentation, aiming to enable the extraction of structural, molecular and functional information from cells and tissues at the nanometer scale.

December 21, 2015 Prof. Dimitris Angelakis Technical University of Crete, Greece, Centre for Quantum Tech., Singapore and KITP Many-body physics and quantum simulations with light (Host: Eden Figueroa)

In this talk, I will try to review in a pedagogic way the works in the area of many-body physics and quantum simulation with light starting from the early theoretical proposals for realising  equilibrium models all the way to the more recent works in driven dissipative platforms. I will start by describing the founding works on the Jaynes-Cummings lattice or Jaynes-Cummings-Hubbard model and the corresponding photon-blockade induced Mott transition. I will continue by briefly discussing how to realize effective spin models and Fractional Hall states  in coupled nonlinear resonator arrays (CRAs) and then discuss the recent efforts to study out-of-equilibrium many-body effects using driven CRAs, including the predictions for photon fermionization and crystallization. If time, I will also try to summarize the work in realizing strongly correlated Tonks gases, Luttinger liquids, and interacting relativistic fermionic models with photons in slow light set ups. I will review the major theory results and also briefly outline recent developments in ongoing experimental efforts involving different platforms in circuit QED, Rydberg polaritons and nanophotonic platforms. 1.D. G. Angelakis, Marcelo F. Santos, Sougato Bose, Photon blockade induced Mott transitions and XY spin models in coupled cavity arrays�, Phys. Rev. A (Rap. Com.) vol. 76, 031805 (2007) 2. Jaeyoon Cho, Dimitris G. Angelakis, Sougato Bose, Fractional Quantum Hall state in coupled cavities�. Phys. Rev. Lett. 101, 246809 (2008). 3.D. G. Angelakis, M. Huo, E. Kyoseva, LC Kwek, Luttinger liquid photons and spin-charge separation in hollow-core fibers'. Phys. Rev. Lett.106, 153601 (2011).  4.D. G. Angelakis, M. Huo, D. Chang, LC Kwek, V. Korepin, Mimicking interacting relativistic theories with light'. Phys. Rev. Lett. 110, 100502 (2013) 5.R. Keil, C. Noh, A. Rai, S. Stutzer, S. Nolte, D. G. Angelakis, A. Szameit "Experimental simulation of charge conservation violation and Majorana dynamics", Optica 2,454 (2015)

December 22, 2015 (4pm) Dr. Maxim Scherbakov Lomonosov Moscow State University Nonlinear optics of semiconductor metasurfaces (Host: Sasha Abanov)

Subwavelength Mie-resonant nanostructures have recently emerged as new building blocks for artificially nanostructured surfaces with tailorable optical properties, or metasurfaces. With negligible intrinsic losses, they are especially relevant and attractive when the nonlinear-optical regime is set. In my talk, I will cover our recent experimental results in harmonic generation spectroscopy and all-optical switching in silicon-based metasurfaces. The stress will be put on magnetic dipolar Mie resonances in particular, for they possess the smallest relative mode volume of all the Mie modes. I will show that the third harmonic output from an array of silicon nanodisks is enhanced by a factor of 100 if compared with a bulk silicon slab. Pump-probe experiments on the nanodisks show the possibility of all-optical switching with the pulse-limited switching time of 65 fs with no apparent free-carrier contribution. Our studies establish the low loss Mie-resonant nanostructures under study as a prospective new platform for active nanophotonics.

2015