Groups | Seminars || Courses | Outreach

Seminars

Seminars will be held in room S-141 in the Physics and Astronomy Department building on Mondays at 4:00 PM, unless noted otherwise. When necessary, virtual seminar Zoom login instructions will be sent out via email. 

Fall 2023

September 18, 2023, 3:00 PM Prof. Balakrishnan Naduvalath Department of Chemistry, University of Nevada, Las Vegas Chemistry in the Extreme Quantum Regime (Host: Jesús Pérez Ríos)

A central goal in chemistry is the absolute control of quantum states of both reactants and products. This is not achievable at normal temperatures due to a thermal population of internal quantum states. By cooling atoms and molecules to temperatures close to absolute zero and confining them in electromagnetic traps controlled chemistry experiments can be performed between trapped atoms and molecules in the deep quantum regime. This allows unprecedented level of control over initial quantum states, molecular orientation, and even final states in certain cases. I will discuss recent theoretical progress in describing chemical reactions and molecular interactions in this regime and the prospects and challenges ultracold molecules offer in uncovering many aspects of chemistry that are yet to be revealed at its most fundamental level.

September 25, 2023 Dr. Patricia Vindel Zandbergen New York University Quantum and Classical Nuclei: Balancing Efficiency and Accuracy in Molecular Motion Description (Host: Jesús Pérez Ríos )

Understanding the structure and dynamics of chemical processes at the molecular level is a key step toward the design of materials with the desired properties, or the efficient control of chemical reactions. Their fundamentally correct and detailed description can be obtained by solving the Schrödinger equation, but this is only feasible for small molecules as the computational effort scales exponentially with the number of particles. To model realistic systems, we clearly need to make approximations. The Born-Oppenheimer approximation -which separates the nuclear and electronic motions- is widely used and works well when there is not much excitation in the system, e.g., starting in equilibrium, or ground state dynamics. However, this approximation fails when modeling ultrafast processes, such as the dynamics of photoexcited molecules or subject to some external field, as they involve several electronic states and thus, highly correlated electron and nuclear motions. But still, approximate methods are needed, and the most natural ones would be to treat nuclei classically but coupled to the quantum treatment of electrons (semiclassical approximations). But the question arises: what would the feedback (couplings) between the classical and quantum systems be? What force is driving the nuclei and what is their effect on the potential driving the electrons? On the other hand, many chemically interesting processes involve quantum nuclear motions and a fundamentally correct theoretical description based on quantum mechanics is needed. For instance, non-covalent, hydrogen-bonded and van der Waals (vdW) interactions, involve quantum nuclear motions which are delocalized over multiple potential energy wells. These large-amplitude motions, in addition to the high dimensionality of the vibrational problem represent a hurdle to the current (ro)vibrational methodology. In this talk, I will present two methodologies that have been recently proposed to tackle these different challenges. In the first part, I will introduce the exact equations for describing the coupled electron and nuclear dynamics. These equations serve as a rigorous starting point for the systematic development of semiclassical approximations offering a solution to accurately capture correlated electron-nuclear interactions in scenarios where traditional mixed-quantum classical methods fail. In the second part, I will explain a novel approach that provides a comprehensive and rigorous description of the intermolecular rovibrational level structure of molecular complexes. A. Abedi, N.T. Maitra, and E.K.U. Gross, PRL 105, 123002 (2010) F. Agostini, A. Abedi, Y. Suzuki, S. K. Min, N. T. Maitra, and E. K. U. Gross, JCP. 142, 084303 (2015) J. K. Ha, I. S. Lee, S. K. Min. JPCL, 9, 1097 (2018) P. Vindel-Zandbergen, L.M. Ibele, J. K. Ha, S. K.Min, B.F. E. Curchod, N.T. Maitra. JCTC, 17, 3852 (2021) P. Vindel-Zandbergen, S.Matsika and N.T. Maitra. JPCL 13, 1785 (2022) E.Villaseco-Arribas, P.Vindel-Zandbergen, S.Roy, N.T. Maitra. PCCP (2023) P.M. Felker and Z. Bačić. JCP, 156, 064301 (2022), JCP, 158, 234109 (2023) P.Vindel-Zandbergen et al. JCP (2023)

September 19, 2023, 4:15 PM SCGP Prof. Serge Haroche Nobel Laureate, Physics (2012) College de France and Laboratoire Kastler Brossel Quantum Science with Giant Atoms (CN Yang Colloquium Series)

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September 28, 2023, 11:00 AM Prof. Roland Wester University of Innsbruck Quantum collisions of cold molecular ions in traps (Host: Jesús Pérez Ríos)

Cryo-cooled radiofrequency ion traps have become a widespread tool for spectroscopic and collisional studies of a wide range of molecular ions at low temperatures. In recent years negatively charged molecular ions have drawn a lot of attention, because negative ions have been detected in different interstellar molecular clouds. We have developed photodetachment spectroscopy into a tool to probe rotational and vibrational quantum states of cold negative ions. In this talk I will show how we used this to study rotational state-changing collisions and perform rotational terahertz spectroscopy. Furthermore, I will present results on the spectroscopic characterization of a possible laser-cooling transition in the carbon dimer anion. Recently, we also achieved to measure the extremely low rate of the H^- + HD reaction, which occurs by quantum tunneling.

October 20, 2023, 2:00 PM Prof. Chen-Lun Hung Purdue University Quench dynamics of low-dimensional Bose gases in an optically painted box (Host: Jesús Pérez Ríos)

A quantum gas loaded in an optical box presents a model homogeneous system for exploring quantum many-body dynamics. While trap uniformity has been the main attraction for realizing intricate many-body states or for studying non-equilibrium dynamics without suffering from inhomogeneous effects, the existence of sharp edges in a box could also lead to unexpected, but fascinating consequences in out-of-equilibrium dynamics that were not seen in conventional harmonic traps. In this talk, I will discuss several examples of novel quench dynamics from atomic superfluids trapped in two-dimensional (2D) boxes. I will first present our recent studies of interaction quenches to attractive Bose gases, where we observe instability-induced quasiparticle pair-creations and can characterize their quantum entanglement. This dynamics in a uniform trap eventually leads to fragmentation and formation of solitons among other intricate dynamics. In the second example, I will discuss quench dynamics of a repulsive Bose gas and show how the interaction with the box boundary could lead to spontaneously patterned defect formation in a superfluid--from ring dark solitons to vortex dipole necklaces - which would open a doorway towards forming complex vortex quantum matters in an optical box. I will discuss our on-going studies on out-of-equilibrium dynamics using tunable Bose gases in optically painted low-dimensional boxes, including evidence of breathing dynamics and recurrence in an attractive 1D Bose gas.

October 23, 2023, 1:00 PM Wang Center Prof. Gerhard Rempe Max Planck Institute for Quantum Optics Entanglement at its Best (Host:CDQP Inaugural Workshop)

The concept of entanglement brings out the quantum superposition principle for correlations. It is a key pillar of quantum physics and has widely been studied for two qubits. However, its full potential will develop in multi-qubit quantum systems only. The talk introduces the first technique that can efficiently engineer a plethora of multi-qubit entangled states at will. This sheds new light on measurement-based quantum computation and loss-tolerant quantum communication in quantum networks.

November 10, 2023, 10:00 AM Prof. R. Tyler Sutherland Quantinuum, UT San Antonio Cooling trapped ions with Phonon Rapid Adiabatic Passage: phRAP (Host: Jesús Pérez Ríos)

In recent demonstrations of the quantum charge-coupled device (QCCD) computer architecture circuit times have been dominated by cooling operations, which can limit operational fidelity. Some motional modes of a multi-ion crystal cool inefficiently due to laser geometry and ion mode participation, resulting in order-of-magnitude differences in the cooling times needed to address all modes. Previous work has shown that motional quanta can be transferred between modes by high-frequency modulation of local electric potentials. These techniques, however, are hindered by the voltage filters needed to suppress high frequency noise and are sensitive to drifts in mode frequencies as well as drive field amplitudes. Phonon rapid adiabatic passage (phRAP) overcomes these limitations. Analogous to adiabatic rapid passage, we quasi-statically couple harder-to-cool modes with easier ones using a DC electric field. When the crystal is adiabatically driven through an avoided crossing, we see nearly total population transfer. We demonstrate this technique by indirect ground-state cooling of all radial modes of a two-ion crystal, achieving well over an order-of-magnitude speedup in cooling times as compared with traditional sideband cooling.

November 27, 2023 Dr. Spencer Horton BAE Systems, Inc. Novel NLO Crystal Growth and Laser Development at BAE Systems (Host:Tom Weinacht)

BAE Systems Inc. is a multi-billion dollar company with a long history of integrating laser systems into hardware for the Department of Defense (DoD). We specialize in laser systems at 2 um, midwave infrared (3-6 um), and the longwave infrared (8-14 um). We deal with temporal systems from ultra-narrow linewidth (~kHz) CW systems to ultrafast laser systems. In this talk, we will discuss the growth of custom non-linear optical materials to access unique parts of the electromagnetic spectrum. Crystals like: ZGP, CSP, OP-GaAS, OP-GaP, BGS, and BGSe. On the laser side, we will talk about custom fiber and solid state laser systems we have designed and made for various DoD application.

December 22, 2023, 1:30 PM CMP Seminar Room Physics B-131 Prof. Anton Souslov Cambridge University Topological fiber optics (Host: Paul M. Goldbart )

A challenge in photonics is to create a scalable platform in which topologically protected light can be transmitted over large distances. I will talk about the design, modelling, and fabrication of photonic crystal fiber (PCF) characterized by topological invariants [1]. The fiber is made using a stack-and-draw technique in which glass capillaries are stacked, molten, and drawn to the desired size. Light propagates in glass cores, whose normal modes are analogous to atomic orbitals. Topological invariants emerge in the band structure of many coupled cores inside a periodic array. We directly measured the bulk winding-number invariant and imaged the associated boundary modes predicted to exist by bulk-boundary correspondence. The mechanical flexibility of fiber allows us to reversibly reconfigure the topological state. For example, as the fiber is bent, we find that the edge states first lose their localization and then become re-localized due to disorder. We envision fiber as a scalable platform to explore and exploit topological effects in photonic networks. [1] N. Roberts, G. Baardink, J. Nunn, P. J. Mosley, A. Souslov. Topological supermodes in photonic crystal fiber. Sci. Adv. 8, eadd3522 (2022).

2023