Colloquia

Physics

Unless otherwise specified, all lectures will take place in CTLM102 from 4:00 PM to 5:00 PM.
Pre-Seminar Snacks in CoorsTek 140/150 from 3:30 PM to 4:00 PM.
For more information, please contact Barbara Shellenberger.
April 8, 2025 – Physics colloquium – Nanfang Yu, Columbia University - Flat Optics

Nanfang Yu

Nanfang Yu

Associate Professor of Applied Physics and Applied Mathematics
Columbia University – NY
Flat Optics

Abstract: In this talk, I will share with the audience recent and on-going work in my lab on metasurfaces and biophotonics. Metasurfaces utilize strong interactions between light and nanostructured thin films to control light with subwavelength precision. I will describe how we use metasurface as a technology platform to innovate free-space optics, integrated photonics, and neuromorphic computing, with examples including holographic metasurfaces for trapping ultracold atoms, mm-wave flat-knit metasurface reflect-arrays, leaky-wave metasurfaces for interconnecting integrated and free-space optics, and metasurface-based neural networks for facial verification. I will also describe on-going work on characterizing and understanding the color and polarization vision of living butterflies.

Short-Bio: Nanfang Yu is an Associate Professor of Applied Physics at the Department of Applied Physics and Applied Mathematics, Columbia University. His lab conducts experimental research on metasurfaces, integrated photonics, and biophotonics. Yu was previously a Research Associate in the School of Engineering and Applied Sciences at Harvard University from 2009 to 2012. He received the Ph.D. degree in Engineering Sciences from Harvard University in 2009, and the B.S. degree from the Department of Electronics at Peking University, Beijing, China, in 2004. Yu is the recipient of 2023 Moore Foundation Experimental Physics Investigators Award, 2022 OPTICA Fellow, 2017 Defense Advanced Research Projects Agency (DARPA) Director’s Fellowship, 2016 Office of Naval Research Young Investigator Program Award, and 2015 DARPA Young Faculty Award.

April 8, 2025 – Physics colloquium – Nanfang Yu, Columbia University - Flat Optics

Nanfang Yu

Nanfang Yu

Associate Professor of Applied Physics and Applied Mathematics
Columbia University – NY
Flat Optics

Abstract: In this talk, I will share with the audience recent and on-going work in my lab on metasurfaces and biophotonics. Metasurfaces utilize strong interactions between light and nanostructured thin films to control light with subwavelength precision. I will describe how we use metasurface as a technology platform to innovate free-space optics, integrated photonics, and neuromorphic computing, with examples including holographic metasurfaces for trapping ultracold atoms, mm-wave flat-knit metasurface reflect-arrays, leaky-wave metasurfaces for interconnecting integrated and free-space optics, and metasurface-based neural networks for facial verification. I will also describe on-going work on characterizing and understanding the color and polarization vision of living butterflies.

Short-Bio: Nanfang Yu is an Associate Professor of Applied Physics at the Department of Applied Physics and Applied Mathematics, Columbia University. His lab conducts experimental research on metasurfaces, integrated photonics, and biophotonics. Yu was previously a Research Associate in the School of Engineering and Applied Sciences at Harvard University from 2009 to 2012. He received the Ph.D. degree in Engineering Sciences from Harvard University in 2009, and the B.S. degree from the Department of Electronics at Peking University, Beijing, China, in 2004. Yu is the recipient of 2023 Moore Foundation Experimental Physics Investigators Award, 2022 OPTICA Fellow, 2017 Defense Advanced Research Projects Agency (DARPA) Director’s Fellowship, 2016 Office of Naval Research Young Investigator Program Award, and 2015 DARPA Young Faculty Award.

April 15, 2025 – Physics colloquium – Phil Richerme, Indiana University at Bloomington - title to be announced

Dr. Phil Richerme

Phil Richerme

Associate Professor of Physics
Indiana University at Bloomington
April 15, 2025 – Physics colloquium – Phil Richerme, Indiana University at Bloomington - title to be announced

Dr. Phil Richerme

Phil Richerme

Associate Professor of Physics
Indiana University at Bloomington
April 22, 2025 – Physics colloquium – Lu Lu, University of Wisconsin at Madison - title to be announced

Dr. Lu Lu

Lu Lu

Associate Professor of Physics
University of Wisconsin – Madison
April 22, 2025 – Physics colloquium – Lu Lu, University of Wisconsin at Madison - title to be announced

Dr. Lu Lu

Lu Lu

Associate Professor of Physics
University of Wisconsin – Madison
January 14, 2025 – Physics colloquium – No-Go Theorem of Hidden Variable Theory and Quantum Machine Learning

Dr. Xun Gao

Xun Gao

Assistant Professor of Physics
University of Colorado – Boulder
No-Go Theorem of Hidden Variable Theory and Quantum Machine Learning
Abstract: Generative models in machine learning have gained a lot of attention for their practical applications. In this talk, we explore how quantum correlations can enhance these models and investigate the potential quantum advantage based on the no-go theorem of hidden variable theory. Unlike other quantum machine learning theories that focus on sample complexity directly, our focus is on the expressive power of the learning models. We give an example showing how quantum correlations—specifically, contextuality—can define a quantum neural network that outperforms any reasonable classical neural network in terms of the number of hidden neurons required for a language translation task. This includes a proof for artificially constructed data and numerical results for real-world data. We will also briefly mention a possible mathematical framework that could solidify this claim. This direction is still in its early stages, and I hope this talk will inspire others to make more connections from foundational research in quantum information to practically useful problems in machine learning.
Bio: Xun Gao is an assistant professor at University of Colorado Boulder and an associate fellow at JILA. He got his PhD from Tsinghua University. Then he was a postdoc at Harvard University. His research interests are quantum computational advantage and quantum machine learning.
January 14, 2025 – Physics colloquium – No-Go Theorem of Hidden Variable Theory and Quantum Machine Learning

Dr. Xun Gao

Xun Gao

Assistant Professor of Physics
University of Colorado – Boulder
No-Go Theorem of Hidden Variable Theory and Quantum Machine Learning
Abstract: Generative models in machine learning have gained a lot of attention for their practical applications. In this talk, we explore how quantum correlations can enhance these models and investigate the potential quantum advantage based on the no-go theorem of hidden variable theory. Unlike other quantum machine learning theories that focus on sample complexity directly, our focus is on the expressive power of the learning models. We give an example showing how quantum correlations—specifically, contextuality—can define a quantum neural network that outperforms any reasonable classical neural network in terms of the number of hidden neurons required for a language translation task. This includes a proof for artificially constructed data and numerical results for real-world data. We will also briefly mention a possible mathematical framework that could solidify this claim. This direction is still in its early stages, and I hope this talk will inspire others to make more connections from foundational research in quantum information to practically useful problems in machine learning.
Bio: Xun Gao is an assistant professor at University of Colorado Boulder and an associate fellow at JILA. He got his PhD from Tsinghua University. Then he was a postdoc at Harvard University. His research interests are quantum computational advantage and quantum machine learning.
January 21, 2025 – Physics colloquium – Obadiah Reed, NREL - How Driving Force & Charge Transfer Distance Control Free Carrier Generation at Donor/Acceptor Interfaces

Dr. Obadiah Reed

Obadiah Reed

Associate Research Professor
University of Colorado – Boulder, NREL
How Driving Force & Charge Transfer Distance Control Free Carrier Generation at Donor/Acceptor Interfaces
Abstract: Charge separation in organic photovoltaics appears to follow several mechanisms depending on the molecular details of the system in question. In this talk I present evidence from photoinduced absorption-detected magnetic resonance (PADMR) that charge transfer between phthalocyanine family donor molecules and a fullerene acceptor results in a driving force dependent distribution of charge-transfer distances, and that this behavior correlates well with the free charge generation yield measured via time-resolved microwave conductivity. We show that the highest driving force sample possesses both the lowest free charge yield and the shortest average charge transfer distance, as evinced by the relative strength of the magnetic dipole and isotropic exchange coupling. Conversely, the sample that displays optimal free charge yield at an intermediate driving force exhibits the weakest exchange coupling suggesting that the average charge transfer distance is substantially larger. These results are consistent with a charge separation model wherein a distribution of charge transfer distances governs whether the product state is free mobile carriers or a bound charge-transfer state. We suggest this as a parallel pathway that can allow free charge generation without the need for engineering specific intermolecular orientations, or necessarily including large amounts of disorder to drive charge separation.
Bio: Obadiah Reid earned a PhD in Physical Chemistry from the University of Washington in 2010. He joined NREL in 2010 and also held a research position at CU Boulder since 2014. His research interests include charge generation, transport, and recombination processes in organic semiconductors; development of new analytical tools and methods; and the convergent application of experimental and theoretical approaches.
January 21, 2025 – Physics colloquium – Obadiah Reed, NREL - How Driving Force & Charge Transfer Distance Control Free Carrier Generation at Donor/Acceptor Interfaces

Dr. Obadiah Reed

Obadiah Reed

Associate Research Professor
University of Colorado – Boulder, NREL
How Driving Force & Charge Transfer Distance Control Free Carrier Generation at Donor/Acceptor Interfaces
Abstract: Charge separation in organic photovoltaics appears to follow several mechanisms depending on the molecular details of the system in question. In this talk I present evidence from photoinduced absorption-detected magnetic resonance (PADMR) that charge transfer between phthalocyanine family donor molecules and a fullerene acceptor results in a driving force dependent distribution of charge-transfer distances, and that this behavior correlates well with the free charge generation yield measured via time-resolved microwave conductivity. We show that the highest driving force sample possesses both the lowest free charge yield and the shortest average charge transfer distance, as evinced by the relative strength of the magnetic dipole and isotropic exchange coupling. Conversely, the sample that displays optimal free charge yield at an intermediate driving force exhibits the weakest exchange coupling suggesting that the average charge transfer distance is substantially larger. These results are consistent with a charge separation model wherein a distribution of charge transfer distances governs whether the product state is free mobile carriers or a bound charge-transfer state. We suggest this as a parallel pathway that can allow free charge generation without the need for engineering specific intermolecular orientations, or necessarily including large amounts of disorder to drive charge separation.
Bio: Obadiah Reid earned a PhD in Physical Chemistry from the University of Washington in 2010. He joined NREL in 2010 and also held a research position at CU Boulder since 2014. His research interests include charge generation, transport, and recombination processes in organic semiconductors; development of new analytical tools and methods; and the convergent application of experimental and theoretical approaches.
January 28, 2025 – No Physics colloquium - Career Days
February 4, 2025 – Physics colloquium – Markus B. Raschke, CU Boulder - Ultrafast Nano-Imaging Resolving Structure, Coupling, & Dynamics of Matter on its Natural Length & Time Scales

Markus B. Raschke

Dr. Markus B. Raschke

Physics Professor
University of Colorado – Boulder
Ultrafast Nano-Imaging Resolving Structure, Coupling, & Dynamics of Matter on its Natural Length & Time Scales
Abstract: Understanding and ultimately controlling the properties of matter, from molecular to quantum systems, requires imaging the elementary excitations on their natural time and length scales. To achieve this goal, we developed scanning probe microscopy with ultrafast and shaped laser pulse excitation for multiscale spatio-temporal optical nano-imaging. In corresponding ultrafast movies, we resolve the fundamental quantum dynamics from the few-femtosecond coherent to the thermal transport regime. I will discuss specific examples visualizing in space and time the nanoscale heterogeneity in competing structural and electronic dynamic processes in matter. In photovoltaic perovskites with far-from equilibrium excitation we visualize the polaron dynamics and its spatial, temporal and fluence dependence on the nanoscale, reflecting the elementary processes underling their photoresponse. In the extension to coherent nonlinear nanoimaging, we resolve competing ultrafast intra- and interlayer dynamic processes in graphene and 2D semiconductors and their heterostructures. As a perspective I will show that we are reaching the ultimate goal of functional imaging and control, to link macroscopic properties to microscopic interactions in materials at their fundamental spatio-temporal scales.
Bio: Markus Raschke is professor at the Department of Physics and JILA at the University of Colorado at Boulder. His research is on the development and application of nano-scale nonlinear and ultrafast spectroscopy to control the light-matter interaction on the nanoscale. These techniques allow for imaging structure and dynamics of molecular and quantum matter with nanometer spatial resolution. He received his PhD in 2000 from the Max-Planck Institute of Quantum Optics and the Technical University in Munich, Germany. Following research appointments at the University of California at Berkeley, and the Max-Born-Institute in Berlin, he became faculty member at the University of Washington in 2006, before moving to Boulder in 2010. He is fellow of the Optical Society of America, the American Physical Society, he American Association for the Advancement of Science, and the Explorers Club.
February 4, 2025 – Physics colloquium – Markus B. Raschke, CU Boulder - Ultrafast Nano-Imaging Resolving Structure, Coupling, & Dynamics of Matter on its Natural Length & Time Scales

Markus B. Raschke

Dr. Markus B. Raschke

Physics Professor
University of Colorado – Boulder
Ultrafast Nano-Imaging Resolving Structure, Coupling, & Dynamics of Matter on its Natural Length & Time Scales
Abstract: Understanding and ultimately controlling the properties of matter, from molecular to quantum systems, requires imaging the elementary excitations on their natural time and length scales. To achieve this goal, we developed scanning probe microscopy with ultrafast and shaped laser pulse excitation for multiscale spatio-temporal optical nano-imaging. In corresponding ultrafast movies, we resolve the fundamental quantum dynamics from the few-femtosecond coherent to the thermal transport regime. I will discuss specific examples visualizing in space and time the nanoscale heterogeneity in competing structural and electronic dynamic processes in matter. In photovoltaic perovskites with far-from equilibrium excitation we visualize the polaron dynamics and its spatial, temporal and fluence dependence on the nanoscale, reflecting the elementary processes underling their photoresponse. In the extension to coherent nonlinear nanoimaging, we resolve competing ultrafast intra- and interlayer dynamic processes in graphene and 2D semiconductors and their heterostructures. As a perspective I will show that we are reaching the ultimate goal of functional imaging and control, to link macroscopic properties to microscopic interactions in materials at their fundamental spatio-temporal scales.
Bio: Markus Raschke is professor at the Department of Physics and JILA at the University of Colorado at Boulder. His research is on the development and application of nano-scale nonlinear and ultrafast spectroscopy to control the light-matter interaction on the nanoscale. These techniques allow for imaging structure and dynamics of molecular and quantum matter with nanometer spatial resolution. He received his PhD in 2000 from the Max-Planck Institute of Quantum Optics and the Technical University in Munich, Germany. Following research appointments at the University of California at Berkeley, and the Max-Born-Institute in Berlin, he became faculty member at the University of Washington in 2006, before moving to Boulder in 2010. He is fellow of the Optical Society of America, the American Physical Society, he American Association for the Advancement of Science, and the Explorers Club.
February 11, 2025 – Physics colloquium - JiHyun Kim, University of Utah – Investigations into the Mysteries of Ultra-High Energy Cosmic Rays by the Telescope Array

Dr. Jihyun Kim

Dr. Jihyun Kim

Physics Professor
University of Utah – Salt Lake City
Department of Physics and Astronomy
Investigations into the Mysteries of Ultra-High Energy Cosmic Rays by the Telescope Array
Abstract: Ultra-high energy cosmic rays (UHECRs) are energetic charged particles with E > 1018 eV that impinge on Earth’s atmosphere from outer space. Their energies are much higher than those that can be achieved in laboratories such as the Large Hadron Collider. By exploring the nature and origin of UHECRs, we hope to better understand where they are coming from and how they achieve such high energy, thereby giving us a window to understanding the most violent objects in the universe. The Cosmic Ray Physics Group at the University of Utah hosts the Telescope Array experiment in Delta, Utah, which is the largest observatory for UHECRs in the northern hemisphere. In this presentation, I will introduce the experiment, highlight its key findings, and discuss future prospects in the field of UHECRs.
February 11, 2025 – Physics colloquium - JiHyun Kim, University of Utah – Investigations into the Mysteries of Ultra-High Energy Cosmic Rays by the Telescope Array

Dr. Jihyun Kim

Dr. Jihyun Kim

Physics Professor
University of Utah – Salt Lake City
Department of Physics and Astronomy
Investigations into the Mysteries of Ultra-High Energy Cosmic Rays by the Telescope Array
Abstract: Ultra-high energy cosmic rays (UHECRs) are energetic charged particles with E > 1018 eV that impinge on Earth’s atmosphere from outer space. Their energies are much higher than those that can be achieved in laboratories such as the Large Hadron Collider. By exploring the nature and origin of UHECRs, we hope to better understand where they are coming from and how they achieve such high energy, thereby giving us a window to understanding the most violent objects in the universe. The Cosmic Ray Physics Group at the University of Utah hosts the Telescope Array experiment in Delta, Utah, which is the largest observatory for UHECRs in the northern hemisphere. In this presentation, I will introduce the experiment, highlight its key findings, and discuss future prospects in the field of UHECRs.
February 18, 2025 – No Physics colloquium - Presidents' Day Break
February 25, 2025 – Physics colloquium – Walter Pettus, Indiana University at Bloomington - 2β or No-v 2β: The Search for Matter Creation with Ge-76

Dr. Walter C. Pettus

Walter C. Pettus

Assistant Professor of Physics
Indiana University -Bloomington
2β or No-ν 2β: The Search for Matter Creation with 76Ge

Motivated by the search for neutrinoless double beta decay, – the bizarre process wherein neutrinos are their own antiparticles – the high purity germanium detector technology has advanced as an increasingly sensitive discovery platform. These experiments operate deep underground in the cleanest and most radio-pure environments, with exquisite discovery potential to rare event signals. Building on the success of the Majorana Demonstrator and GERDA, the currently operating LEGEND-200 experiment is rapidly advancing sensitivity by integrating existing technical progress from its predecessor programs. In this talk, I will review recent science results from these experiments, highlighting the broad science reach and focusing on the first results from LEGEND-200. These results set the stage for the next-generation LEGEND-1000, the tonne-scale culmination of the germanium program achieving sensitivity beyond 1028 years and covering the allowed neutrino inverted mass ordering range.

Walter C. Pettus is an Assistant Professor in the Department of Physics at Indiana University, where he joined the faculty in 2020. He had previously conducted postdoctoral work at the University of Washington and Yale University after receiving his Ph.D. from University of Wisconsin. His current research focus is neutrino properties related to the neutrino mass – both direct detection and neutrinoless double beta decay – with a focus on detectors and instrumentation.

February 25, 2025 – Physics colloquium – Walter Pettus, Indiana University at Bloomington - 2β or No-v 2β: The Search for Matter Creation with Ge-76

Dr. Walter C. Pettus

Walter C. Pettus

Assistant Professor of Physics
Indiana University -Bloomington
2β or No-ν 2β: The Search for Matter Creation with 76Ge

Motivated by the search for neutrinoless double beta decay, – the bizarre process wherein neutrinos are their own antiparticles – the high purity germanium detector technology has advanced as an increasingly sensitive discovery platform. These experiments operate deep underground in the cleanest and most radio-pure environments, with exquisite discovery potential to rare event signals. Building on the success of the Majorana Demonstrator and GERDA, the currently operating LEGEND-200 experiment is rapidly advancing sensitivity by integrating existing technical progress from its predecessor programs. In this talk, I will review recent science results from these experiments, highlighting the broad science reach and focusing on the first results from LEGEND-200. These results set the stage for the next-generation LEGEND-1000, the tonne-scale culmination of the germanium program achieving sensitivity beyond 1028 years and covering the allowed neutrino inverted mass ordering range.

Walter C. Pettus is an Assistant Professor in the Department of Physics at Indiana University, where he joined the faculty in 2020. He had previously conducted postdoctoral work at the University of Washington and Yale University after receiving his Ph.D. from University of Wisconsin. His current research focus is neutrino properties related to the neutrino mass – both direct detection and neutrinoless double beta decay – with a focus on detectors and instrumentation.

March 4, 2025 – Physics colloquium – Joel Eaves, CU Boulder -Singlet Fission as a Quantum Resource and Integral Decimation

Dr. Joel Eaves

Joel Eaves

Professor of Chemistry
University of Colorado – Boulder
Singlet Fission as a Quantum Resource and Integral Decimation

Abstract: Quantum computing promises advances last seen in the digital age, but noise in quantum circuits severely limits the realization of quantum logic devices. My group uses theory and simulation to discover new materials for quantum information applications. In this talk, I will discuss some of our work using singlet fission, a process that splits one exciton into a spin-entangled triplet pair, as a quantum resource near room temperature. I will also discuss how integral decimation, a numerical method we developed, can model realistic noise in quantum circuits. Such simulations are critical to predicting the resources required to error-correct quantum circuits, but integral decimation has a wide range of uses, from classical statistical mechanics to quantum and classical stochastic differential equations, and I will conclude by discussing those examples as well.

Bio: Joel Eaves received his Ph.D. from MIT in 2005 working with Phill Geissler and Andrei Tokmakoff on the coherent multidimensional infrared spectroscopy of liquid water. He then joined David Reichman’s group at Columbia University as a postdoc working on quantum relaxation phenomena and the glass transition. He is a professor in the chemistry department at the University of Colorado, Boulder, where he develops theory to describe basic processes in nanoscience, spectroscopy, and nonequilibrium statistical mechanics.

March 4, 2025 – Physics colloquium – Joel Eaves, CU Boulder - Singlet Fission as a Quantum Resource and Integral Decimation

Dr. Joel Eaves

Joel Eaves

Professor of Chemistry
University of Colorado – Boulder
Singlet Fission as a Quantum Resource and Integral Decimation

Abstract: Quantum computing promises advances last seen in the digital age, but noise in quantum circuits severely limits the realization of quantum logic devices. My group uses theory and simulation to discover new materials for quantum information applications. In this talk, I will discuss some of our work using singlet fission, a process that splits one exciton into a spin-entangled triplet pair, as a quantum resource near room temperature. I will also discuss how integral decimation, a numerical method we developed, can model realistic noise in quantum circuits. Such simulations are critical to predicting the resources required to error-correct quantum circuits, but integral decimation has a wide range of uses, from classical statistical mechanics to quantum and classical stochastic differential equations, and I will conclude by discussing those examples as well.

Bio: Joel Eaves received his Ph.D. from MIT in 2005 working with Phill Geissler and Andrei Tokmakoff on the coherent multidimensional infrared spectroscopy of liquid water. He then joined David Reichman’s group at Columbia University as a postdoc working on quantum relaxation phenomena and the glass transition. He is a professor in the chemistry department at the University of Colorado, Boulder, where he develops theory to describe basic processes in nanoscience, spectroscopy, and nonequilibrium statistical mechanics.

March 11, 2025 – Physics colloquium – Jonathan Bird, SUNY Buffalo - Strange Things Happen When Nanomaterials are Driven Far From Equilibrium

Dr. Jonathan Bird

Jonathan Bird

Professor and Department Chair
Electrical Engineering
SUNY – Buffalo
Strange Things Happen When Nanomaterials are Driven Far From Equilibrium

Abstract: The past two decades have witnessed an explosion of interest in functional nanomaterials, whose rich physical properties reflect their reduced dimensionality, the importance of spin- and charge-based interactions, and the existence of complex correlated phases. The application of these materials in various technologies – that span from clean energy to quantum computing – is premised upon a deep understanding of their physical properties. Specifically, the behavior that they exhibit when driven out of equilibrium, by strong electric and/or optical fields, can be crucial to many of these applications.

In my presentation, I summarize some of the experiments that we have performed in recent years to investigate the behavior exhibited by a variety of different nanomaterials that are driven electrically far from equilibrium. In many situations, this driving gives rise to fundamentally new behavior, not associated with the material in its near-equilibrium state. Just a few such examples include the emergence of robust one-dimensional transport in narrow semiconductor channels subject to strong phonon emission [1]; negative-mass amplification in the narrow conduction-band states of transition-metal trichalcogenide nanowires [2]; Landau-Zener tunneling across the minibands of (graphene/h-BN) van der Waals heterostructures [3]; and dynamic resistive-switching phenomena associated with charge-density wave evolution in layered transition-metal dichalcogenides [4,5]. I will provide an overview of some of these phenomena in my presentation, focusing on the use of time-resolved, transient, electrical measurements to probe the nonequilibrium dynamics with sub-nanosecond resolution.

References

  1. Lee, J. E. Han, S. Xiao, J. Song, J. L. Reno, and J. P. Bird, Nat. Nanotechnol. 9, 101 (2014).
  2. Randle, …, J. P. Bird, Nat. Materials, under review (2025).
  3. Nathawat, …, J. P. Bird, Nat. Communs. 14, 1507 (2023).
  4. A Mohammadzadeh, …, J. P. Bird, Appl. Phys. Lett. 118, 093102 (2021).
  5. Yin, …, J. P. Bird, Adv. Phys. Res. 3, 2400033 (2024).

Biosketch: Jonathan Bird joined the UB Department of Electrical Engineering as full professor in 2004. He currently serves as chair of that department and as director of the UB Center for Advanced Semiconductor Technologies. Jonathan obtained his BSc (First-Class Honors) and PhD degrees in physics from the University of Sussex (UK) in 1986 and 1990, respectively. He was JSPS Visiting Fellow at the University of Tsukuba (Japan, 1991 – 1992) and a member of the Frontier Research Program of the Institute of Physical and Chemical Research (RIKEN, Japan, 1992 – 1997). Professor Bird’s research is in the area of nanoelectronics; he is currently supported by the Coherent/II-VI Foundation, the US Air Force Office of Scientific Research and the National Science Foundation.

March 11, 2025 – Physics colloquium – Jonathan Bird, SUNY Buffalo - Strange Things Happen When Nanomaterials are Driven Far From Equilibrium

Dr. Jonathan Bird

Jonathan Bird

Professor and Department Chair
Electrical Engineering
SUNY – Buffalo
Strange Things Happen When Nanomaterials are Driven Far From Equilibrium

Abstract: The past two decades have witnessed an explosion of interest in functional nanomaterials, whose rich physical properties reflect their reduced dimensionality, the importance of spin- and charge-based interactions, and the existence of complex correlated phases. The application of these materials in various technologies – that span from clean energy to quantum computing – is premised upon a deep understanding of their physical properties. Specifically, the behavior that they exhibit when driven out of equilibrium, by strong electric and/or optical fields, can be crucial to many of these applications.

In my presentation, I summarize some of the experiments that we have performed in recent years to investigate the behavior exhibited by a variety of different nanomaterials that are driven electrically far from equilibrium. In many situations, this driving gives rise to fundamentally new behavior, not associated with the material in its near-equilibrium state. Just a few such examples include the emergence of robust one-dimensional transport in narrow semiconductor channels subject to strong phonon emission [1]; negative-mass amplification in the narrow conduction-band states of transition-metal trichalcogenide nanowires [2]; Landau-Zener tunneling across the minibands of (graphene/h-BN) van der Waals heterostructures [3]; and dynamic resistive-switching phenomena associated with charge-density wave evolution in layered transition-metal dichalcogenides [4,5]. I will provide an overview of some of these phenomena in my presentation, focusing on the use of time-resolved, transient, electrical measurements to probe the nonequilibrium dynamics with sub-nanosecond resolution.

References

  1. Lee, J. E. Han, S. Xiao, J. Song, J. L. Reno, and J. P. Bird, Nat. Nanotechnol. 9, 101 (2014).
  2. Randle, …, J. P. Bird, Nat. Materials, under review (2025).
  3. Nathawat, …, J. P. Bird, Nat. Communs. 14, 1507 (2023).
  4. A Mohammadzadeh, …, J. P. Bird, Appl. Phys. Lett. 118, 093102 (2021).
  5. Yin, …, J. P. Bird, Adv. Phys. Res. 3, 2400033 (2024).

Biosketch: Jonathan Bird joined the UB Department of Electrical Engineering as full professor in 2004. He currently serves as chair of that department and as director of the UB Center for Advanced Semiconductor Technologies. Jonathan obtained his BSc (First-Class Honors) and PhD degrees in physics from the University of Sussex (UK) in 1986 and 1990, respectively. He was JSPS Visiting Fellow at the University of Tsukuba (Japan, 1991 – 1992) and a member of the Frontier Research Program of the Institute of Physical and Chemical Research (RIKEN, Japan, 1992 – 1997). Professor Bird’s research is in the area of nanoelectronics; he is currently supported by the Coherent/II-VI Foundation, the US Air Force Office of Scientific Research and the National Science Foundation.

March 18, 2025 – No Physics colloquium - Spring Break
March 25, 2025 – Physics colloquium –Shuo Sun, CU Boulder - Quantum Optics with Artificial Atoms

Dr, Shuo Sun

Shuo Sun

Assistant Professor of Physics
University of Colorado – Boulder
Associate Fellow – JILA
Quantum Optics with Artificial Atoms

Abstract: The 2023 Nobel Prize in Chemistry was awarded for the discovery and synthesis of quantum dots, often referred to as “artificial atoms”, due to their discrete electronic energy levels resembling those of natural atoms. Since their discovery, quantum dots have been widely utilized in bioimaging, energy harvesting, illumination, displays, machine vision, and communications. Recently, significant progress has been made in creating single artificial atoms with excellent quantum coherence properties, enabling the development of quantum devices based on these artificial atoms.

In this talk, I will discuss several ongoing experiments in my group that showcase the unique advantages of solid-state artificial atoms in studying quantum optics and advancing quantum technologies. A key feature of solid-state artificial atoms is their compatibility with various devices (e.g., photonic, acoustic, electronic) defined on their host material. This compatibility allows us to experimentally investigate the resonance fluorescence of a strongly driven atom in novel regimes, where the atom is simultaneously influenced by both longitudinal (σz-driven) and transverse (σx-driven) fields. Remarkably, our observations reveal distinct features in the resonance fluorescence spectrum as we modulate the Rabi frequency of the σx drive across the frequency of the σz drive field, including the cancellation of the central spontaneous spectral line and the anti-crossing of different sidebands. The experimental results align well with our theoretical calculations and can be effectively explained using a dynamically-dressed-state framework. Additionally, I will discuss another ongoing experiment that leverages strong light-matter interactions in a quantum nanophotonic device to develop a deterministic source of photonic graph states. These photonic graph states are crucial resources in optical quantum computing and all-photonic quantum repeaters. I will discuss our experimental progresses, as well as our theory proposal for generating loss-tolerant photonic graph states using only a single quantum dot.

Moving forward, solid-state artificial atoms also offer tremendous opportunities for studying quantum many-body physics. I will discuss some of these opportunities at the end of my talk, including the study of photon-mediated many-body interactions defined by a structured photonic bath, and electron-spin mediated interactions among a bath of nuclear spins.

Bio: Shuo Sun is an Assistant Professor of Physics and an Associate Fellow of JILA at the University of Colorado Boulder. Before joining the University of Colorado Boulder in Fall 2020, he worked at Stanford University as a postdoctoral fellow and later as a research scientist in the Ginzton Lab. Sun received his B.S. in Zhejiang University (2011), and his M.S. (2015) and Ph.D. (2016) from the University of Maryland College Park. Sun is a recipient of the NSF CAREER award (2024), Sloan Research Fellowship (2022), and the Ralph E. Powe Junior Faculty Enhancement Award (2021).

March 25, 2025 – Physics colloquium –Shuo Sun, CU Boulder - Quantum Optics with Artificial Atoms

Dr, Shuo Sun

Shuo Sun

Assistant Professor of Physics
University of Colorado – Boulder
Associate Fellow – JILA
Quantum Optics with Artificial Atoms

Abstract: The 2023 Nobel Prize in Chemistry was awarded for the discovery and synthesis of quantum dots, often referred to as “artificial atoms”, due to their discrete electronic energy levels resembling those of natural atoms. Since their discovery, quantum dots have been widely utilized in bioimaging, energy harvesting, illumination, displays, machine vision, and communications. Recently, significant progress has been made in creating single artificial atoms with excellent quantum coherence properties, enabling the development of quantum devices based on these artificial atoms.

In this talk, I will discuss several ongoing experiments in my group that showcase the unique advantages of solid-state artificial atoms in studying quantum optics and advancing quantum technologies. A key feature of solid-state artificial atoms is their compatibility with various devices (e.g., photonic, acoustic, electronic) defined on their host material. This compatibility allows us to experimentally investigate the resonance fluorescence of a strongly driven atom in novel regimes, where the atom is simultaneously influenced by both longitudinal (σz-driven) and transverse (σx-driven) fields. Remarkably, our observations reveal distinct features in the resonance fluorescence spectrum as we modulate the Rabi frequency of the σx drive across the frequency of the σz drive field, including the cancellation of the central spontaneous spectral line and the anti-crossing of different sidebands. The experimental results align well with our theoretical calculations and can be effectively explained using a dynamically-dressed-state framework. Additionally, I will discuss another ongoing experiment that leverages strong light-matter interactions in a quantum nanophotonic device to develop a deterministic source of photonic graph states. These photonic graph states are crucial resources in optical quantum computing and all-photonic quantum repeaters. I will discuss our experimental progresses, as well as our theory proposal for generating loss-tolerant photonic graph states using only a single quantum dot.

Moving forward, solid-state artificial atoms also offer tremendous opportunities for studying quantum many-body physics. I will discuss some of these opportunities at the end of my talk, including the study of photon-mediated many-body interactions defined by a structured photonic bath, and electron-spin mediated interactions among a bath of nuclear spins.

Bio: Shuo Sun is an Assistant Professor of Physics and an Associate Fellow of JILA at the University of Colorado Boulder. Before joining the University of Colorado Boulder in Fall 2020, he worked at Stanford University as a postdoctoral fellow and later as a research scientist in the Ginzton Lab. Sun received his B.S. in Zhejiang University (2011), and his M.S. (2015) and Ph.D. (2016) from the University of Maryland College Park. Sun is a recipient of the NSF CAREER award (2024), Sloan Research Fellowship (2022), and the Ralph E. Powe Junior Faculty Enhancement Award (2021).

April 1, 2025 – Physics colloquium – Murray Holland, CU Boulder - Programmable Atom Interferometry in a Multidimensional Optical Lattice

Dr. Murray Holland

Murray Holland

Professor of Physics
University of Colorado – Boulder
Programmable Atom Interferometry in a Multidimensional Optical Lattice

Abstract: The creation of a matter-wave interferometer can be achieved by loading Bose-Einstein condensed atoms into a crystal of light formed by interfering laser beams. It has recently been realized that by translating this optical lattice in a specific way, the traditional steps of interferometry can all be implemented, i.e., splitting, propagating, reflecting, and recombining the macroscopic quantum wavefunction. Using this concept, we have designed and built a compact experiment to sense inertial signals, including accelerations, rotations, gravity, and gravity gradients. This is a new approach, since the atoms can be supported against external forces and perturbations by the lasers, and the system can be completely programmed on-the-fly for new design goals. I will report on experimental results in which atoms are cooled in a dipole trap and subsequently loaded into an optical lattice. Protocols for obtaining interferometry steps are derived via machine learning and quantum optimal control methods. Implementing these in the lab, I will show our recent demonstrations of a vector accelerometer capable of sensitively deducing the magnitude and direction of an inertial force in a single shot. I will discuss our vision to use this platform for remote sensing of Earth as part of the recently founded NASA Quantum Pathways Institute.

Bio: Holland joined the faculty of the University of Colorado Boulder in 1996 and is a Fellow of JILA and teaches in the Department of Physics. He received his B.Sc. and M.Sc. from the University of Auckland in New Zealand, and his D.Phil. from the University of Oxford in the United Kingdom. The Holland experimental group has developed a new approach to atom interferometry whereby a quantum degenerate gas is cooled and trapped in optical lattices and controlled by artificial intelligence methods, in particular deep-learning and reinforcement learning for quantum design. The Holland theory group’s research is on the properties of quantum gases and entanglement in strongly interacting superfluids. The group is also working on superradiant cavity QED with group-II elements to develop a mHz linewidth “laser.” Holland has developed a number of courses in Boulder as part of a quantum science stream, including quantum optics, and quantum computing at both the graduate and undergraduate level.

April 1, 2025 – Physics colloquium – Murray Holland, CU Boulder - Programmable Atom Interferometry in a Multidimensional Optical Lattice

Dr. Murray Holland

Murray Holland

Professor of Physics
University of Colorado – Boulder
Programmable Atom Interferometry in a Multidimensional Optical Lattice

Abstract: The creation of a matter-wave interferometer can be achieved by loading Bose-Einstein condensed atoms into a crystal of light formed by interfering laser beams. It has recently been realized that by translating this optical lattice in a specific way, the traditional steps of interferometry can all be implemented, i.e., splitting, propagating, reflecting, and recombining the macroscopic quantum wavefunction. Using this concept, we have designed and built a compact experiment to sense inertial signals, including accelerations, rotations, gravity, and gravity gradients. This is a new approach, since the atoms can be supported against external forces and perturbations by the lasers, and the system can be completely programmed on-the-fly for new design goals. I will report on experimental results in which atoms are cooled in a dipole trap and subsequently loaded into an optical lattice. Protocols for obtaining interferometry steps are derived via machine learning and quantum optimal control methods. Implementing these in the lab, I will show our recent demonstrations of a vector accelerometer capable of sensitively deducing the magnitude and direction of an inertial force in a single shot. I will discuss our vision to use this platform for remote sensing of Earth as part of the recently founded NASA Quantum Pathways Institute.

Bio: Holland joined the faculty of the University of Colorado Boulder in 1996 and is a Fellow of JILA and teaches in the Department of Physics. He received his B.Sc. and M.Sc. from the University of Auckland in New Zealand, and his D.Phil. from the University of Oxford in the United Kingdom. The Holland experimental group has developed a new approach to atom interferometry whereby a quantum degenerate gas is cooled and trapped in optical lattices and controlled by artificial intelligence methods, in particular deep-learning and reinforcement learning for quantum design. The Holland theory group’s research is on the properties of quantum gases and entanglement in strongly interacting superfluids. The group is also working on superradiant cavity QED with group-II elements to develop a mHz linewidth “laser.” Holland has developed a number of courses in Boulder as part of a quantum science stream, including quantum optics, and quantum computing at both the graduate and undergraduate level.