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.

Spring/Summer 2019

January 28, 2019 Prof. Peter D Drummond Swinburne University of Technology, Melbourne, Australia Fundamental tests of physics and simulations of exponentially complex many-body systems (Host: Jin Wang)

The physical universe is not an assembly of mechanical parts, as envisaged classically. Instead, quantum mechanics tells us that the universe is a many-body state, described by an exponentially large Hilbert space of enormous size. The standard model indicates what the components are: but what emerges when they evolve, dynamically, in time? In this colloquium, I will give results of first-principles quantum simulations of many-body systems and relate these to fundamental tests. These will include accurate, experimentally tested quantum dynamical simulations of the world's most coherent Bose-Einstein atom interferometer. These simulations are fully quantum mechanical. They include both thermal and quantum noise, as well as linear and nonlinear collisional losses, in one, two and three space dimensions. Experiments that verify the theory were carried out at Swinburne University. Evidence is obtained for genuine entanglement and steering of up to 40,000 atoms. Methods to simulate novel technologies will include: opto-mechanical entanglement, quantum memories for 'on-demand' Schrodinger Cats, and mesoscopic bright solitons in ultra-cold gases. Entanglement predictions were confirmed in electro-optic experiments at JILA. The soliton experiments are underway at Rice University using  7 Li. I will also treat a proposal to simulate the early universe using an ultracold atomic laboratory model of the quantum fluctuations in the 'Big Bang'. Who needs a ship in a bottle, when you can have a universe on a table top? True vacuum bubbles forming in an early universe simulation.

February 25, 2019 [Wang Center, 8:00am-5:00pm] SBU-BNL Quantum Immersion Workshop

The goal of this Quantum Immersion Workshop is to build a Quantum Information Science (QIS) community of researchers between Stony Brook University, Brookhaven National Laboratory, and other partners. This workshop will showcase state of the art research in QIS and provide a forum to discuss opportunities to engage in QIS research. Featuring four sessions on: Quantum Networking and Cryptography, Quantum Algorithms and Programming Environment, Analog Quantum Simulation, Quantum Devices and Quantum Materials. Provost Lecture: "Building a Quantum Computer" by Dr. Barry Sanders, Director of the Institute for Quantum Science and Technology at the University of Calgary. Provost Lecture: "Quantum Machine Learning" by Dr. Seth Lloyd, Professor of engineering, MIT

April 8, 2019 Xinjue Zhong Columbia University Probing the Electronic Properties of Superatomic Van der Waals Semiconductors (Host: Tom Allison)

Two-dimensional van der Waals materials built from clusters featuring atomic precision instead of simple atoms have attracted great attention due to their unique collective physical properties and tunable structures and functions. In this talk, I will describe two van der Waals materials derived from the Chevrel phases. The strong in-plane covalent bonding and weak interlayer interactions allow exfoliating them down to few layers. The electronic properties are characterized by using scanning tunneling microscopy/spectroscopy, photoluminescence, polarization dependent Raman spectroscopy and first principles calculations. In Re6Se8Cl2, I determine the electronic bandgap, optical bandgap and thus the exciton binding energy. The latter is as large as 100 meV, which is consistent with the partially 2D nature of the exciton. In Mo6S3Br6, I determine its robust 2D semiconducting character and strong in-plane electronic anisotropy. The complex, hierarchical structures with 2D characters in these two materials suggest an exciting new strategy to design 2D materials with multi-functionality and desired electronic properties.

April 15, 2019 Albert Liu University of Michigan Novel Electronic and Vibrational Properties of Colloidal Nanocrystals (Host: Tom Allison)

Colloidal nanocrystals (CNCs) are nanometer sized crystals grown in solution. Due to their size-tunable optical properties, CNCs have emerged as a novel material platform for numerous applications such as displays, photovoltaics, and biological tagging. However, the colloidal growth process results in an unavoidable distribution of CNC size that inhomogeneously broadens optical absorption/luminescence lineshapes. 2-D spectroscopy is a technique capable of circumventing inhomogeneous broadening by correlating absorption and emission dynamics. In this talk I will present our results from applying 2-D spectroscopy to CNCs at cryogenic temperatures. I will first discuss our experiments on conventional CdSe CNCs, in which we have simultaneously observed both bulk-like acoustic phonons and acoustic vibrations discretized by the nanocrystal geometry for the first time. We also find evidence of highly anharmonic coupling to longitudinal optical phonons. Next, I discuss our experiments on perovskite CNCs, which are a new class of materials first synthesized in 2015. We demonstrate that by coupling to discrete vibrational modes, quantum superpositions of states (coherences) are insulated from the dominant dephasing by acoustic vibrations and are “protected�. Finally, I discuss our observations of coherences between so-called bright-triplet exciton states, which are robust at high temperatures and polarization-selective. These inter-triplet coherences offer a potential nanocrystal analogue of "valleytronics"� in 2-D materials

April 22, 2019 Prof. Phillip L. Gould University of Connecticut Binding Ultracold Atoms into Molecules Using Frequency-Chirped Light (Host: Hal Metcalf)

Ultracold molecules are currently a topic of great interest in AMO physics, with potential applications ranging from ultracold chemistry to quantum computing. One method for forming such molecules is photoassociation, where two colliding ultracold atoms absorb a photon and are thereby bound into an excited molecule. We examine an extension of this process in Rb dimers, using frequency-chirped light on the nanosecond time scale. Within a single chirped pulse, the photoassociation process is followed by stimulated emission which transfers the excited molecule to a bound level of the electronic ground state. We show that this two-step process can be enhanced by a judicious shape of the chirp. Quantum simulations of the molecular formation are not only in good agreement with the experimental results, but also give insight into the enhancement mechanism. Our method for producing the nanosecond frequency-chirped pulses will also be briefly described.

April 23, 2019 (Tues, 2:00PM) Prof. Phillip L. Gould University of Connecticut Pushing Molecules with Light: The Bichromatic Force (Host: Hal Metcalf)

Manipulating and cooling molecules are topics of significant current interest, with potential applications ranging from ultracold chemistry to precision measurements to quantum computing. Tremendous progress has recently been realized in slowing, cooling, and trapping of molecules using radiation pressure forces. However, these forces are limited in magnitude by the photon scattering rate. Larger forces would be beneficial, especially for more efficient loading of traps from molecular beams. A potential agent for large deceleration is the bichromatic force, whereby a two-frequency standing wave allows stimulated emission to significantly enhance the momentum transfer. I will describe experiments using the bichromatic force to transversely deflect a beam of CaF. A force approximately four times that of radiation pressure has been observed. The large magnitude of this force, coupled with the reduced rate of spontaneous emission, indicates its potential utility in the slowing and manipulation of molecular beams.

April 29, 2019 Alice Kunin University of California at Berkeley Ultrafast dynamics of electron accommodation in nucleobases (Host: Tom Allison)

Low energy electrons have been shown to attach to DNA and induce single and double strand breaks. Theoretical work has implicated the formation of transient negative ions (TNIs) of nucleobases as the initial step in the damage mechanism, but these short-lived electronic resonances are challenging to probe experimentally. Iodide-nucleobase clusters studied by time-resolved photoelectron spectroscopy (TRPES) are an opportune model system to examine ultrafast electron attachment to nucleobases as well as the subsequent relaxation and photodissociation processes. By initiating charge transfer from iodide to the nucleobase with the TRPES pump pulse and following the dynamics of the nascent TNIs, the formation and time-evolution of both dipole-bound and valence-bound TNIs of several nucleobase species have been measured. This talk will explore in detail our recent work investigating the effects of microhydration on iodide-nucleobase clusters to provide insight into the role of water and solvation on the dynamics of electron accommodation and photodissociation.

May 1, 2019 [YITP Seminar, 2:30pm, YITP Common Room] Prof. Andrea Trombettoni CNR & SISSA,Trieste, Italy Dr. Nicolo Defenu University of Heidelberg, Germany Equilibrium and Dynamical Properties of Quantum Long-Range Spin Systems (Host: Tzu-Chieh Wei )

Several recent experiments in atomic, molecular and optical systems motivated a huge interest in the study of quantum long-range spin systems. In the first part of the talk [by Andrea Trombettoni] we discuss a general description of their critical behavior and phases, devising a treatment valid in d dimensions, with an exponent d+\sigma for the power-law decay of the couplings in the presence of an O(N) symmetry. Results for the correlation length exponent, the dynamical critical exponent z and a comparison with numerical findings for them are  presented. In the second part of the talk [30minutes, by Nicolo' Defenu], the goal is to present a discussion of dynamical properties of quantum long-range systems, focusing on slow quenches. In systems with short-range interactions the heat exhibits universal power-law scaling as a function of the quench rate, known as Kibble-Zurek scaling. Slow quenches of the magnetic field in quantum long-range quantum systems are then analyzed, showing that it is possible to analytically determine the quantum contribution to the residual heat as a function of the quench rate by means of a Holstein-Primakoff expansion about the mean-field value.

May 6, 2019 Prof.Joseph Subotnik University of Pennsylvania Electrodynamics for the Chemist: How should a photochemist think about the electromagnetic radiation fields? (Host: Tom Weinacht)

Within the physics and chemistry communities, there is currently an enormous interest in the phenomena of strong light-matter coupling. Whether in cavities or in plasmonic materials, there is today clear evidence that the quantum nature of light and matter can become entangled in very interesting ways, and moreover there is hope that this entanglement can be exploited and lead to new devices  In order to predict light-matter behavior, one outstanding question is: how can we best model light-matter systems in a predictive manner so that we can model large, realistic systems and gain intuition for quantum electrodynamics? In this talk, I will highlight our recent attemptsto semiclassically merge the Schrodinger equation with Maxwell's equations so as to recover the essential effects of strong light-matter coupling (that are not captured classically).  This work in semiclassical electrodynamics draws on much older (and more developed) work in semiclassical nonadiabatic molecular dynamics, highlighting the fact that many outstanding questions remains at the intersection of chemical and atomic physics.

May 7, 2019 [Nuclear Physics Group Seminar,1pm, C-120] Prof. Yannick Meurice University of Iowa Quantum Field Theory with Cold Atoms? (Host: Dmitri Kharzeev)

We review tensorial formulations of lattice gauge/spin theories and algorithmic aspects of their coarse graining. We discuss truncations and show that they preserve the symmetries of the original lattice models (arXiv:1903.01918). We show that tensor reformulations fit the needs of quantum computation. We discuss concrete proposals of quantum simulation experiments with cold atoms for the Abelian Higgs model  and other simple models in 1+1 dimensions.  We discuss methods to measure the second order Renyi entanglement entropy with cold atoms.  We report recent calculations for real time scattering for the quantum Ising model (arXiv:1901.05944) and  discuss the errors associated with the Trotter step size and gate errors for existing or near term quantum computers (such as IBM or trapped ions devices).

May 20, 2019 Prof.Jiehang Zhang New York University Quantum Many-Body Spin Systems Engineered from Trapped Atomic Ions (Host: Tom Weinacht)

Quantum mechanics prescribes exponential scaling of the Hilbert space dimension in many-body systems, which presents both challenges and new opportunities for understanding strongly correlated matter, especially since novel custom-built systems are now available. I will describe such efforts on engineering quantum systems atom by atom, precisely controlling them with laser-driven interactions, and increasing the system size up to a regime where the capabilities of classical computers are challenged. I will focus on the platform of trapped atomic ions, where a combination of excellent coherence time and high-fidelity measurements has enabled many applications, ranging from simulating condensed matter physics, to quantum computation. We represent spin qubits with electronic levels of ions in a Coulomb crystal, and entangle them through tailored laser pulses. I will present recent experiments using these systems to study dynamical phase with individual resolution for more than 50 spins [1], as well as non-equilibrium driven matter such as discrete time crystals [2]. I then conclude with some future prospects. [1] J. Zhang, et al., Observation of a many-body dynamical phase transition with a 53-qubit quantum simulator, Nature, vol. 551, p. 601, Nov. 2017   [2] J. Zhang, et al. Observation of a discrete time crystal, Nature, vol. 543, pp. 217–220, Mar. 2017

August 19, 2019 Prof. Agnes Vibok University of Debrecen, Hungary Classical and Quantum Field-Dressed Spectra of the Sodium Molecule (Host: Tom Weinacht)

In classical laser fields with frequencies resonant with the electronic excitation in molecules, it is by now known that conical intersections are induced by the field and are called light-induced conical intersections LICIs). As optical cavities have become accessible their quantized modes could also lead to the appearance of LICIs. In the present work theoretical frameworks are formulated for the investigation of LICIs of diatomics in such a classical and quantum light circumstances. As an example by employing a weak measuring pulse the dressed state absorption spectra of the Na2 molecule are investigated both in a cavity and in an optical lattice.

2019