Groups | Seminars || Courses | Outreach

Seminars

Seminars will continue to be held in room S-141 on Mondays at 4:00PM in-person and over Zoom, unless noted otherwise. Check your email for login instructions!

Spring 2022

February 14, 2022 (9AM, Zoom) Dr. Bharath Hebbe Madhusudhana, LMU Munich Quantum simulation of many-body non-equilibrium dynamics in a Fermi-Hubbard model (Host: Matt Dawber)

Identifying and understanding realistic applications of noisy intermediate scale quantum (NISQ) devices such as quantum computers and neutral atom quantum simulators is a topical problem. An area of research that involves problems with a unique blend of computational complexity and practical importance is quantum many-body physics. Consequently, these problems constitute one of the most exciting present-day applications of NISQ devices. In particular, the study of highly correlated quantum many-body systems, which is computationally very challenging,  could lead to the discovery of new quantum materials with profound and exotic properties. In this work, we show how a state-of-the-art quantum simulator can be used to mathematically solve for the dynamics of a quantum many-body system, which is beyond the limits of existing classical computational methods [1]. We use a quantum simulator to develop a new efficient classical approximation algorithm for a many-body system. Considering localized 1D Fermi-Hubbard systems, we use an approximation ansatz to develop a new numerical method that facilitates efficient classical simulations in such regimes. The method is based on approximations that are well suited to describe localized one-dimensional Fermi-Hubbard systems. Since this new method does not have an error estimate and is not valid in general, we use a neutral-atom Fermi-Hubbard quantum simulator with L_exp = 290 lattice sites to benchmark its performance in terms of accuracy and convergence for evolution times up to 700 tunneling times. We use the tilted Fermi Hubbard model [2] for the benchmarking. Our approximation method also offers novel insights into the microscopic processes that lead to the observed dynamics.  In the limit of large tilts, we identify these microscopic processes. And show that they constitute an effective Hamiltonian and we experimentally show its validity [3]. This effective Hamiltonian features the novel phenomenon of Hilbert space fragmentation. Finally, we characterise the many-body problems that lie further outside the  accessible range of this new method and discuss technical advancements to our quantum simulator that are necessary to be able to simulate them. [1.] Bharath Hebbe Madhusudhana et. al. PRX Quantum 2, 040325. [2.] Sebastian Scherg et al. Nature Communications 12 (1), 1-8 [3.] Thomas Kohlert et al. arXiv:2106.15586

February 16, 2022 (9 AM, Zoom) Dr. Yinyu Liu, Harvard University Quantum information processing based on spins in semiconductor quantum dots (Host: Matt Dawber)

The field of Quantum Information is of great excitement in both fundamental physics and industry. One promising platform for quantum computing is gate-defined quantum dots in semiconductors. The greatest limiting factor currently is that delicate quantum states can lose their quantum nature due to interactions with their environment. Other open challenges are to coherently control large-scale spin qubits and develop methods to entangle quantum bits that are separated by significant distances. Silicon-based materials are promising due to the long lifetimes of electrons’ quantum states, but also challenging due to the difficulty in fabrication and valley degeneracy. I will report a singlet-triplet qubit with a qubit gate that is assisted by the valley states. This work would potentially relax the design and fabrication requirement for scaling. Moreover, strong coupling between electron spins and photons in hybrid circuit-QED architecture has been achieved in this research field. Quantum optics, long-distance quantum entanglement, and communication via photons are promised. To address that, I will present my project on indium arsenate (InAs) double quantum dots (DQD) that are embedded in circuit-QED architecture. We demonstrated the direct evidence of photon emission from a DQD in the microwave regime. By achieving stimulated emission from one DQD in these works, we invented a semiconductor single atom maser that can be tuned in situ.  I will demonstrate that a semiconductor-based quantum dot is a promising platform for quantum information as well as for fundamental physics.

February 17, 2022 (9 AM, Zoom) Dr. Ye Wang, Duke University Trapped-Ion Quantum Computing and Data-Driven Quantum Approximate Optimization Algorithms (Host: Matt Dawber)

Quantum computing is expected to deliver exponential speedup over classical computing on various computational tasks such as quantum simulation,number factoring and solving linear systems of equations. But practical implementations of these quantum algorithms demand near-perfect qubit operations.This talk will introduce my work to mitigate errors in trapped-ion systems atboth gate and circuit levels. Topics include the demonstration of high-fidelity entangling gates in an ion chain, hidden-inverse error mitigation in quantum circuits, crosstalk suppression with local controls, and dephasing-noise-optimized robust entangling gates. These efforts allow us to identify key hardware upgrades and push the system to reach the quantum advantage and fault-tolerant quantum computing requirement.The second part of this talk will introduce our recent progress on the quantum approximate optimization algorithm (QAOA) implemented in a cyberphysical power system to help resilience. Our heuristic strategy extends the previews work (arXiv:1812.04170 (2018)) to show the parameter transferability between random weighted graphs. We show that our data-driven QAOA could outperform the Goemans-Williamson algorithm for some 24-vertex random weighted graphs with a realistic noise model in the current quantum processors. Our work shows the great potential of heuristic approaches on Variational Quantum Algorithms, which may be one of the most promising early candidates for achieving quantum advantage on NISQ systems

February 21, 2022 (9 AM, Zoom) Dr. Alisa Javadi, University of Basel Harnessing Light-Matter Interaction for Photonic Quantum Technologies (Host: Matt Dawber)

Photonic quantum technologies have a unique potential for applications such as large-scale quantum networks and quantum-enhanced sensing. Furthermore, photons provide new paradigms for quantum simulations and a testbed for benchmarking the advantage of quantum simulators over classical ones. These applications demand novel resources suchas efficient single-photon sources, clusters of entangled photons, and nonlinear optical gates. At the current stage, solid-state quantum optics can strongly impact photonic quantum information processing.Solid-state quantum emitters can generate the necessary single photons and more sophisticated cluster states deterministically, currently posing a significant bottleneck for photonic quantum information processing. In this talk, I will discuss our progress in realizing some of these elements using solid-state quantum emitters. In the first part, I will present an efficient source of indistinguishable single photons [1]. I will show that we achieve an end-efficiency of 57 %, 2.3 times higher than the state-of-the-art, and discuss the significance of this improvement for photonic quantum technologies.In the second part, I will present our recent progress in developing a scalable platform for quantum photonics. I will show that we can generate highly coherent photons from GaAs quantum dots [2]. Furthermore, I will show that photons emitted by remote GaAs quantum dots exhibit excellent quantum interference, laying the foundations for scalable quantum photonics. At the end of my talk, I will give an overview of my future research direction and my vision for quantum computing and quantum networking using optical photons. [1] Tomm, Javadi, Antoniadis, Najer, Löbl, Korsch, Schott,Valentin, Wieck, Ludwig, Warburton, “A bright and fast source of coherentsingle photons”, Nat. Nanotechnol. 16,399 (2021). [2] Zhai, Nguyen, Spinnler,Ritzmann, Löbl, Wieck, Ludwig, Javadi, Warburton, “Quantum Interferenceof Identical Photons from Remote Quantum Dots”, arXiv:2106.03871 (2021).

February 21, 2022 Prof. Murray Holland, JILA, University of Colorado Boulder Using Machine Learning for the Quantum Design of a Matter-Wave Interferometer (Host: Hal Metcalf)

In this talk, I will discuss the application of machine learning for the design of an inertial measurement device capable of measuring accelerations and rotations with extreme sensitivity. The system this is based on consists of ultracold atoms in an optical lattice potential created by interfering laser beams. Our approach uses reinforcement learning, a branch of machine learning that allows us to generate specific protocols needed to realize lattice-based analogs of optical components including a beam splitter, a mirror, and a recombiner. The performance of these components can be evaluated by comparison with their optical analogs, and the machine learned protocols are found to offer significant advantages. The resulting interferometer's sensitivity surpasses that of standard Bragg interferometry, demonstrating a rich future potential for this type of design methodology.

February 22, 2022 (Colloquium) Prof. Murray Holland JILA, University of Colorado Boulder Extreme sensing, clocks, and squeezing atoms and molecules with light (Host: Hal Metcalf)

I will describe recent ideas for lowering the temperature of ensembles of ultracold atoms and molecules into the extreme quantum regime, for using interactions to entangle atoms and molecules into non-classical quantum states, and for using these non-classical states to realize quantum advantages for metrology, clocks, and matter-wave interferometry. One such topic is a new experimentally demonstrated idea for laser cooling by Sawtooth Wave Adiabatic Passage (SWAP). This is mostly relevant to atoms and molecules that possess narrow linewidth transitions, such as the ultranarrow clock transitions, and promises to be an important extension to the toolbox of AMO physics for laser cooling and trapping. We are exploring ways to use optical cavities and cavity-mediated interactions to entangle atoms so that we may improve optical clock performance, make repeated quantum measurements beyond the standard quantum limit, and continuously track squeezed quantum phases. These approaches take full advantage of the powerful combination of the extreme optical coherence that is possible using atomic clocks, with the rich possibilities offered by many-body physics that arises when the atoms interact strongly. Atomic clocks have already progressed to the point that understanding how to take advantage of quantum effects will be crucial in order to progress to the next generation of devices.

February 25, 2022 (9 AM, Zoom) Dr. Nathan Schine, University of Colorado Boulder Quantum Science with Photons and Atoms (Host: Matt Dawber)

Can a material be made of light? Can quantum mechanics help us measure time? These are two questions in quantum science that I directly address using the tools of atomic physics and quantum optics. We first explore the requirements to make a quantum Hall material made of light. We trap photons inside of a curved-mirror non-planar optical resonator to confine the transverse motion of photons and imbue them with an effective mass and an effective magnetic field for photons. We add strong repulsive interactions by hybridizing resonator photons with Rydberg excitations of a cold atomic gas, and we observe the formation of the ground state of highly correlated topological matter made of light. We next turn to a broad effort in quantum science—to help us to compute more efficiently and to measure the world more precisely. In an optical-tweezer-trapped array of strontium atoms, we leverage recent ideas developed in quantum information processing for related metrological goals. We demonstrate nearly a minute of atomic coherence on an optical-frequency clock transition. We then generate metrologically useful entanglement between clock-transition qubits using Rydberg excitations, and we show that this entanglement persists for approximately four seconds. Beyond enabling quantum-enhanced optical clocks, this work opens the door to studies of interacting spin and Hubbard models, efficient computing architectures, and database search algorithms.

February 28, 2022 (9 AM, Zoom) Dr. Alexander Burgers, Princeton University Advancing Quantum Science with Ytterbium Atom Arrays (Host: Matt Dawber)

Neutral atom arrays are a rapidly developing platform for quantum science. Rydberg-mediated entanglement between atoms has led to numerous advances in quantum computing and quantum simulation using this platform. An emerging frontier within this field is the use of alkaline earth-like atoms (AEAs) such as ytterbium (Yb). The rich internal structure of these atoms affords numerous unique capabilities, including efficient Doppler cooling, optical clock transitions for metrology applications, efficient control of Rydberg gate operations using light shifts from ion core transitions, and the capability to encode qubits in the nuclear spin of the J = 0 electronic ground state of fermionic AEA isotopes. In this talk I will describe our experimental platform for trapping and manipulating Yb atoms in optical tweezer arrays. I will discuss our recent results utilizing transitions in the Yb+ion core to generate light shifts that control excitations to the Rydberg state, which can be used for efficient local control of quantum gate operations [1]. I will then present our work demonstrating a universal set of quantum gate operations, including two-qubit gates through the Rydberg state, using qubits encoded in the nuclear spin of171Yb [2]. We observe long qubit coherence times, T2* = 1.24 s, as well as high-fidelity single-qubit operations, F1Q = 0.99959. These results mark the first such demonstration of a universal set of quantum gates for nuclear qubits in AEAs and lay the foundation for scalable quantum computing architectures with Yb atom arrays. [1] A P Burgers et al. arXiv: 2110.06902 (2021) [2] S Ma*, A P Burgers* et al. arXiv: 2112.06799 (2021)

March 1, 2022 (9 AM, Zoom) Dr. Erhan Saglamyurek, University of Alberta Engineering photon-matter interfaces for quantum networks (Host: Matt Dawber)

TThe realization of a future quantum Internet relies on processing and storage of quantum information at local nodes and interconnecting distant nodes using photons [1]. Photon-matter interfaces constitute building blocks for such networks, allowing reversible transfer of quantum information between “stationary” atoms and “flying” photons. Despite impressive progress over the past two decades, practical realizations of photon-matter quantum interfaces still face a lot of challenges. In my talk, I will address these challenges in view of requirements of large-scale quantum networks, and present our experimental efforts towards overcoming them. Particularly, I will focus on integrated light-matter interfaces based on rare-earth ion doped solids, and show our demonstrations including the storage of photonic entanglement in these devices [2-4]. Furthermore, I will present a novel approach to develop a broadband spin-photon interface for long-lived storage and manipulation of light along with the proof-of-principle implementations of this technique in an ensemble of laser-cooled atoms [5] and a Bose-Einstein condensate [6]. Finally, I will discuss my ongoing research and future plans towards building quantum networks and potential applications, including distributed and modular quantum computing, and remote quantum sensing. 1. H. J. Kimble. Nature, 453 1023-1030 (2008). 2. E. Saglamyurek et al. Nature 469, 512-515, (2011). 3. E. Saglamyurek et al. Nature Photonics 9, 83-87 (2015). 4. E. Saglamyurek et al. Nature Communications 7, 11202 (2016). 5. E. Saglamyurek et al. Nature Photonics 12, 774-782 (2018). 6. E. Saglamyurek et al. New Journal of Physics 23, 043028 (2021).

March 2, 2022 (9 AM, Zoom) Dr. Pankaj Jha, Caltech Engineering Defects in Flatland for Quantum Information Science and Technologies (Host: Matt Dawber)

Single photon sources (SPSs) are one of the building blocks for quantum technologies, including optical quantum computing, quantum communications, and sensing and metrology. In the past two decades, various systems have been explored, including heralded SPSs, atoms and atom-like systems as quantum emitters, and highly attenuated lasers. However, both fundamental and technological challenges need to be resolved to achieve a reliable SPS which is scalable and capable of generating single photons on demand with high purity, indistinguishability, and repetition rate. In this seminar, I will highlight atomic defects (also known as color centers) in van der Waals crystals of wide-bandgap material such as hexagonal boron nitride (hBN) as a promising candidate for quantum light sources owing to its enticing properties, such as high stability and brightness from cryogenic temperatures to 800 K, convenient integration with flexible substrates, fiber optics, and on-chip photonic devices. In the first part of the talk, I will address two fundamental questions about hBN color centers: (1) Where are these color centers located in any multi-layered flake and (2) What is the orientation of their dipole moment?  I will show our experimental results on nanometric axial localization (down to ~7 nm) of these color centers with 3Dcharacterization of their dipole orientation using the phase change material,vanadium dioxide.  In the second part of my talk, I will discuss our ongoing work which utilizes these color centers as a quantum module for photon addition quantum technology, applied to the interferometric imaging, LIDAR enhancement for astronomical, military, and other applications. Finally, I will conclude by presenting my vision for this quantum hardware platform, outlining its usages,including metrology of single photon detectors, generation of intensity squeezed light at room temperature as well as interfacing machine learning with quantum information for intelligent light detection and characterization.

March 28, 2022 Prof. Daniel Rolles, Kansas State University Gas-phase photochemistry studies with free-electron lasers (Host: Tom Weinacht)

X-ray free-electron lasers provide intense, short-pulse, short-wavelength radiation that can be used to study ultrafast electronic and structural dynamics in gas-phase molecules with unprecedented spatial and temporal resolution. I will present recent examples of experiments utilizing a variety of different techniques such as time-resolved photoelectron spectroscopy [1] and Coulomb explosion imaging [2,3]. The results are compared to similar experiments performed with other ultrafast techniques such as ultrafast electron diffraction and strong-field ionization based experiments with near-infrared laser sources in order to highlight strengths and limitations of each technique. References [1] S. Pathak et al., Nat. Chem. 12, 795 (2020) [2] R. Boll et al., Nat. Phys. (2022); doi.org/10.1038/s41567-022-01507-0 [3] S. Pathak et al., J. Phys. Chem. Lett. 11, 10205 (2020)

March 30, 2022 Prof. Kyung Soo Choi (SBU 2006), University of Waterloo Many-body QED with atoms and photons (Host: Hal Metcalf)

An exciting frontier in quantum information science is the creation and manipulation of quantum systems that are built and controlled quanta by quanta. In this context, there is active research worldwide to achieve strong and coherent coupling between light and matter as the building block of complex quantum systems. Despite the range of physical behaviors accessible by these QED systems, the low-energy description is often masked by small fluctuations around the mean fields. In contrast, we describe our theory/experimental program towards novel forms of light-matter quantum systems, where a highly-correlated Rydberg quantum material is strongly coupled to a cavity field. We call this new domain of strong coupling quantum optics, "many-body quantum electrodynamics." I describe our laboratory efforts towards the exploration of new physics in this uncharted territory, where locally-gauged quantum materials are entirely driven by the QED vacuum. We find that genuinely surprising phenomena arise from the universal features of non-perturbative physics of many-body QED, including the stabilization of topological spin liquids and self-correcting quantum memories.

April 18, 2022 Prof. Viatcheslav Kokoouline, University of Central Florida Recent progress in theoretical description of excitation and dissociative processes in collisions of electrons with molecular ions (Host: Jesús Pérez Ríos)

The talk gives a short overview of recent progress in successful theoretical description of various processes taken place in collisions of electrons with molecular ions at energies below a few eV: dissociative recombination, rotational, vibrational, and electronic excitation of the ions, molecular photoionization. The theory based on first principles only (and, sometimes, heavy numerical calculations) is now able to give reliable cross sections for these processes for ions having up to approximately 10 atoms. The progress in the theoretical description of the processes is crucial for various applications where molecular plasma is involved.

June 3, 2022 Prof. Emily Grace, Northwestern College Building the Island Cure: Iowa Stony Brook Lasers ANd DNA Course-Based Undergraduate Research Experience (Host: Eric Jones)

ISLAND CURE is a new collaborative project that uses multi-disciplinary approaches in science experimental design and science pedagogy. This collaborative interdisciplinary CURE project includes faculty and students from the physics, chemistry, and biology departments at Northwestern College (NWC) and the Laser Teaching Center (LTC) at Stony Brook University. Comparisons will be made between NWC and LTC students who seek out independent research experiences, students enrolled in a class with a "cookbook" lab versus a CURE-based lab component. ISLAND CURE will have a central focus on using optical methods to measure biochemical processes. Students will engage in original research involving cutting-edge and relevant technologies (e.g., optical tweezing, DNA cloning, and protein expression). The research goals include (1) understanding how to use CURE methods to guide students in developing the skills needed to effectively engage in scientific practices in physics, chemistry, and biology, (2) comparing the outcomes of CURE students to traditional independent student project results, and (3) exploring the impact and sustainability of CURE scholarship for faculty at small colleges. This talk will lay out the development of this collaboration, and present progress.

June 20, 2022 Dr. Ruaridh Forbes, SLAC Sensitivity of X-ray photoelectron spectroscopy and Coulomb explosion imaging to excited state dynamics in polyatomic molecules (Host: Tom Weinacht)

The UV photochemistry of gas-phase CS2 exhibits many general features of complex excited state dynamics: vibrational mode coupling, internal conversion, intersystem crossing, and dissociation. The molecule initially undergoes bending and symmetric stretching motion before coupling to asymmetric stretch motion leading to dissociation of atomic sulfur. In this talk, I will explore the ability of time-resolved X-ray photoelectron spectroscopy and Coulomb explosion imaging, at the sulfur 2p site, to investigate such complex photodynamics. The results of a 200 nm UV pump + 180 eV soft X-ray probe experiment at the FLASH free-electron laser (FEL) will be presented. By utilizing a soft X-ray probe ionization at S 2p edge (~170 eV binding energy) can be performed providing a site selective view on the photoinduced dynamics. Ions and electrons following ionization were simultaneously collected in a double-sided velocity map imaging (VMI) instrument. The momenta of the Coulomb-exploded ions probed the molecular geometry at the time of ionization, while the measured photoelectrons yielded information about the evolving electronic and nuclear structure through shifts in the S 2p binding energy. The low repetition rate, high count rate experimental conditions prevent the use of coincidence techniques to separate overlapping contributions to the photoelectron spectrum from the various ionization channels. To overcome this, we have employed electron-ion covariance to associate sulfur 2p binding energy shifts to particular ionization channels and molecular geometries. We find a sulfur 2p binding energy shift of ~2 eV in covariance with low-momentum S^2+ associated with dissociated atomic sulfur, and a transient enhancement in the production of higher-momentum S^+ ions following photoexcitation and an associated broadening of the covariance photoelectron spectrum, indicating some effect on the core-level chemical shift from either the photoexcitation or the vibrational motion prior to photodissociation. Our experimental results are supported by simulations of the neutral CS2 photodynamics and core ionization. Preliminary results on the use of electron-photon covariances to achieve sub-bandwidth spectral resolution will also be presented. These result pave the way for performing high-resolution electron spectroscopy measurements at SASE FEL despite the inherently large (several eV) bandwidths of these machines.

July 6, 2022 (10:30 AM) Dr. Dan Herman NIST, University of Colorado, Boulder Applications of Deployable Open-Path Infrared Dual-Comb Spectrometers (Host: Tom Allison)

Dual frequency comb spectroscopy (DCS) is an emerging technique that achieves high spectral resolution across wide optical bandwidths. In this talk, I will summarize the development of portable, remote-controlled, open-path DCS systems for measurement in the near-infrared and mid-infrared spectral regions. I will also examine several applications where the benefits of the DCS technique are highlighted, including calibration-free agricultural gas flux quantification, greenhouse gas source attribution, and air quality monitoring.

2022