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Seminars

Seminars are held on Mondays at 4:00PM, unless noted otherwise.

Due to the ongoing need to maintain social distancing during the COVID-19 pandemic, seminars will be held virtually on Zoom. Check your email for login instructions!

Spring 2021

February 8, 2021 Prof. Bryan Spring Northeastern University Single tumor biomarker-targeted and cell-activated photoimmunotherapy and its development towards multiplexed precision photomedicine (Host: Tom Allison)

This biomedical physics talk will introduce concepts of targeted photodynamic therapy with microscale fidelity using clinical antibody–photosensitizer conjugates. These initially quenched (“off”) photoimmunoconjugates target tumor cell-surface biomarkers and become activated upon cell-internalization (“on”). Present efforts to further develop these concepts for precision treatment of heterogenous human ovarian cancer will be discussed. Along the way we will discuss a few notes regarding femtosecond fiber laser and miniature fiber scanning microscopy technology with potential to facilitate image-guided, adaptive therapy of dynamic drug-resistant cancer cell populations.

February 22, 2021 Prof. Hrovje Petek University of Pittsburgh Seeing light differently (Host: Tom Allison)

Light excites quantum transitions in matter, but it can do much more. Light has a dual particle-wave character; it carries quanta of energy, and spin, but also it can be structured to posses orbital angular momentum. When interacting with matter, it will induce quantum transitions, but we must also consider it also as carrying the Coulomb field and undergoing spin-orbit interaction. The notions of energy-time uncertainty and the Abbe limit of diffraction are so ingrained that we build billion dollar fabs for nanolithographic manufacturing of semiconductor chips that increasingly push the edge of these constraints. But should we not more fully understand the light-matter interactions better before dropping another billion? Can we use the properties of light more fully to transcend these limitations?     I will describe our research involving ultrafast photoemission electron spectroscopy and microscopy to investigate light-matter interactions on the attosecond-femtosecond time scale and nanometer spatial scale. Einstein explained the concept of photons inducing quantum transitions, but I will show that light can also interact in a non-Einsteinian fashion to induce plasmonic photoemission by local light-matter fields. At moderate intensities femtosecond light pulses carry and probe the time-periodic Coulomb field that interacts with the space-periodic one of a crystalline lattice dressing them into time-crystalline bands on the attosecond time scale. Finally, I will show that light spin-orbit interaction creates new plasmonic meron and Skyrmion quasiparticles with distinct spin textures that enable nanofemto, light-matter interactions beyond the Abbe limit.

March 8, 2021 Dr. James P. Cryan SLAC National Accelerator Laboratory Studying Attosecond Electron Dynamics with X-ray Free Electron Lasers (Host: Tom Weinacht)

Electron motion is a key ingredient of all chemical reactions. The natural timescale for such electronic motion is set by the electron's binding energy to be in the range of tens to hundreds of attoseconds. Consequently, the study of ultrafast electronic phenomena requires the generation of laser pulses shorter than 1 fs, and of sufficient intensity to interact with their target with high probability. Free Electron Lasers (FELs), such as the Linac Coherent Light Source (LCLS), offer interesting opportunities to achieve these conditions, allowing for the probing of electrons on this natural time scale, elucidating the earliest processes involved in chemical change. In this talk, I will present our first results showing isolated attosecond soft X-ray pulses from the FEL. Such high power pulses open the door for nonlinear spectroscopies such as pump/probe spectroscopy, and X-ray wave mixing. We have demonstrated the preparation of a coherent electronic wavepacket by driving stimulated X-ray Raman scattering in gas phase molecules. Combing attosecond X-ray pulses with an external laser field we are able to time-resolve the photoemission dynamics of core-level electrons in molecules, and observe coherent electron motion in core-excited molecules.

March 15, 2021 Dr. Ruaridh Forbes SLAC National Accelerator Laboratory Time resolved X-ray induced Coulomb explosion imaging of multi-channel non-adiabatic photodissociation dynamics (Host: Tom Weinacht)

My talk will focus on opportunities to exploit high-event rate velocity map imaging experiments at soft X-ray Free Electrons Lasers (FELs) to track non-adiabatic and photodissociation dynamics in polyatomic molecules. By exploiting the Pixel Imaging Mass Spectrometry (PImMS) camera, developed at Oxford University, at FEL facilities ion vector momenta following Coulomb explosion (CE) can be utilized to extracted detailed correlated information about the target. In the FLASH results, predissociation of the B-state in methyl iodide is investigated and time-dependent photofragment angular distributions are extracted from three-dimensional ion velocity map images. At SACLA, strong-field ionization was used to initiate dissociative ionization in methyl iodide. Distance-dependent X-ray induced charge transfer processes were tracked using charge-state resolved ion-yields and signatures of multiple pathways were evident in the data. Our recent progress on utilizing time-resolved recoil-frame covariance imaging to extract coincidence-like information will also be outlined.

March 22, 2021, 10:00AM Dr. Jesús Pérez Ríos Fritz Haber Institute of the Max Planck Society, Berlin Theoretical Atomic, Molecular and Optical Physics: from Ultracold Systems to Fundamental Physics (Host: Sasha Abanov)

We present new avenues that theoretical atomic, molecular, and optical physics may bring to different physics disciplines in this talk. For example, we present our results about the physics of a charged impurity in an ultracold bath relevant to condensed matter physics. In particular, the dynamics of the impurity in the ultracold bath is treated from a few-body perspective, including the time-dependent trapping potential holding the impurity or the role of external laser sources holding the particles of the bath. As a result, it is possible to elucidate reactive processes affecting the charged impurity's nature required for a comprehensive many-body approach. To finalize, we discuss future projects driven by our findings and curiosity.

March 24, 2021, 10:00AM Dr. Wen Wei Ho Stanford University Exploring Non-equilibrium Many-body Physics in the Age of Quantum Simulators (Host: Sasha Abanov)

The advent of quantum simulators -- controllable, programmable quantum systems of many particles, such as trapped ions, cold atoms, superconducting qubits, color defects etc. -- has excitingly unlocked new paradigms in information processing and communication. They also enable fresh insights into hard-to-simulate strongly correlated many-body phases of matter. In this talk, I want to discuss some recent theoretical developments in non-equilibrium many-body physics, a frontier direction of condensed matter physics which has been opened by quantum simulators. I will touch upon the discovery of a weak ergodicity-breaking phenomenon termed quantum many-body scarring, first seen in experiments utilizing arrays of neutral Rydberg atoms, which challenge our understanding of thermalization and the applicability of statistical mechanics in closed quantum systems. I will next present a mathematically rigorous framework by which strong external driving, either periodically or quasi-periodically, can induce robust, emergent symmetries of a quantum many-body system, which survive in a long-lived, "prethermal" dynamical regime. This can in turn be used to define novel phases of matter far from thermodynamic equilibrium, which include the discrete time-crystal and more generally the discrete time-quasicrystal, states characterized by universal dynamical correlations with no equilibrium analog. The implications of these results for applications in quantum information science as well as broad future research directions will also be discussed.

March 26, 2021, 10:00AM Dr. Kanupriya Sinha Princeton University Atom-Field Interactions in Nanoscale Quantum Optical Systems (Host: Sasha Abanov)

Interactions between atoms or atom-like emitters and electromagnetic fields are at the core of nearly all quantum optical phenomena and quantum information applications. With growing efforts towards miniaturization, both with the fundamental motivation to explore strong light-matter coupling regimes and the practical goal of making quantum devices more modular, understanding and controlling atom-field interactions at nanoscales becomes increasingly relevant. When interfacing atoms with surfaces of waveguides and photonic structures at nanoscales, quantum fluctuation phenomena such as Casimir-Polder forces, surface-modified dissipation and decoherence become an inevitable element of consideration. I will present an overview of various ways to engineer fluctuation-induced phenomena in nanoscale quantum optical systems, and discuss how collective effects can modify Casimir-Polder forces. Furthermore, when connecting multiple atoms prepared in correlated states at long distances, memory effects of the electromagnetic environment become pronounced in the presence of strong atom-field couplings and retardation, necessitating a non-Markovian treatment of the system. I will discuss retardation-induced modifications to collective atom-field interactions in a model system of two distant correlated emitters coupled to a waveguide. We demonstrate that such a system can exhibit surprisingly rich non-Markovian dynamics, with collective spontaneous emission rates exceeding those of Dicke superradiance (‘superduperradiance’), formation of delocalized atom-photon bound states and frequency-comb-like features in the output spectrum. We also find that the cooperativity of the system, an important figure of merit in quantum information applications, can decrease exponentially with distance, which calls for a careful consideration of retardation effects in long-distance quantum networks. [1] K. Sinha, B. P. Venkatesh, and P. Meystre, Collective Effects in Casimir-Polder Forces, Phys.Rev.Lett. 121, 183605 (2018). [2] K. Sinha, P. Meystre, E. Goldschmidt, F. K. Fatemi, S. L. Rolston, P. Solano, Non-Markovian collective emission from macroscopically separated emitters, Phys.Rev.Lett. 124, 043603 (2020). [3] K. Sinha, A. Gonzalez-Tudela, Y. Lu, and P. Solano, Collective radiation from distant emitters, Phys.Rev.A 102, 043718 (2020).

April 12, 2021, 10:00AM Dr. Przemyslaw Bienias Joint Quantum Institute, University of Maryland Quantum Simulation and Computation with Synthetic Quantum Matter (Host: Sasha Abanov)

In recent decades, enormous progress has been made in the control and understanding of large quantum systems. In the future, this progress can give rise to many applications such as secure communication, powerful quantum computers, and efficient quantum simulators of nature. Efficient characterization of quantum devices is a significant challenge critical for the development of large scale quantum computers. I will consider an experimentally motivated situation in which we have a decent estimate of the Hamiltonian describing the system, and its parameters need to be characterized and fine-tuned frequently to combat drifting experimental variables. I will show that this task can be performed more efficiently using a machine learning technique known as meta-learning. In the second part of the talk, I will show that atomic, molecular, and optical systems are ideal for addressing major questions in quantum many-body physics. In particular, these systems can shed light on some of the most intriguing condensed-matter and high-energy-physics phenomena such as information scrambling and quark confinement.

April 19, 2021 Dr. Péter Sándor Wigner Research Centre for Physics Angle-dependence of strong-field ionization of CS2, CH3Br and CH3Cl (Host: Tom Weinacht)

Strong field ionization (SFI) triggers many strong-field processes of current interest, from high-harmonic generation and attosecond pulse generation to laser-induced electron diffraction for time-resolved molecular imaging. Since for molecules exposed to intense low-frequency radiation, the (SFI) rates can depend nontrivially on the alignment/orientation of the molecule relative to the direction of the applied field at the instant of ionization, it is important to understand the ionization anisotropy in molecular systems of interest. In this talk I will present the joint experimental and theoretical study of the angle-dependent ionization probability of carbonyl sulfide (CS2) and singly halogenated methane molecules (CH3Cl and CH3Br). For CS2, analysis of the simulated one-body density reveals that, when averaged over a laser cycle, the resulting hole is delocalized across the molecule for light polarized perpendicular to the molecular axis and mostly localized on the sulfur for parallel polarization. Interestingly, for the two halomethane species, we find a marked difference between the angle-dependence of the ionization yields despite the similar structure of their highest occupied molecular orbitals. The results highlight that chemical functionalization and molecular alignment are likely to be important parameters for initiating and controlling charge migration dynamics via SFI.

May 10, 2021, 10:00 AM Dr. Jie Yang Tsinghua University Methodology advancement in studying ultrafast molecular dynamics with MeV-UED (Host: Tom Weinacht)

In the past few years, Mega-electron-volt ultrafast electron diffraction (MeV-UED) has made significant progress toward recording excited state molecular dynamics with atomic spatiotemporal resolution. In this talk, I will focus on two recent methodology advancements demonstrated in SLAC MeV-UED. The first one is the simultaneous recording of nuclear and electronic dynamics using both elastic and inelastic scattering. We recorded both the S1->S0Â internal conversion and the main reaction coordinate (ring-puckering)Â in a single MeV-UED dataset. The second one is expanding MeV-UED into liquid phase samples. Using a new liquid phase MeV-UED setup, we revealed transient hydrogen bond strengthening as a key step in the vibrational relaxation of liquid water.

2020