Seminars

Title:  Electron Transport in Nanodevices:  Quantum dragons; tatty devices;  order-amidst-disorder; universal scaling  

Mark Novotny, Mississippi State University

Tuesday, Septmember 10th, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  The standard short-ranged single-orbital tight binding model, analyzed using standard NEGF (Non-Equilibrium Green’s Function) methods, is used to study electron transport in unconventional 2D, 3D, and 2D+3D nanodevices.  Quantum dragon nanodevices, and nanodevices that are almost quantum dragons, are studied.  A quantum dragon nanodevice [1] has the coherent electron transport transmission probability T(E)=1 for all injected electron energies E that propagate through attached thin leads, even though the device may have strong disorder in the tight binding parameters.  Starting from a thin 2D nano-ribbon and using allowed operations of cutting, twisting, sewing, and braiding can give very tatty quantum dragon nanodevices.  Quantum dragon nanodevices may exhibit order-amidst-disorder [2], where the Hamiltonian is strongly disordered but commonly measured quantities such as bond currents and the projected local density of states (LDOS) are ordered.  We derive and demonstrate two different regimes of universal scaling for all nanodevices that are almost quantum dragon nanodevices. 
 
[1] M.A. Novotny, Phys. Rev B 90, 165103 (2014).
[2] M.A. Novotny, G. Inkoom, and T. Novotný, EuroPhysics Lett. 143, 26005 (2023).
 

Title: Integrated Photonics for Sensing and Computing with Artificial Intelligence and Machine Learning Applications

Ray Chen, Univerity of Texas, Austin

Friday, Septmember 27th, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  The advancement of sensing, interconnects and computing in the last one hundred years is mainly from the R&D works on electrons and photons, which carry drastically different characteristics defining different technology roadmaps.  Due to the saturation of the Moore’s law, the advantages of photon-based devices provide solutions with the unprecedented performance.  In this talk, we will present the integrated photonic devices covering near and mid-IR wavelengths for biosensing, SERS and spectroscopy sensing for Methane, Nitrogen Dioxide, CO, Ethanol, Ammonia, and TEP.  Mid-IR Lidar Chip centered at 4.6 micron will also presented.  Silicon photonics for both digital and analog computing will be introduced with low latency, high bandwidth and multi-wavelength operations for AI and ML applications.

Title:  Quantum chemistry on a quantum computer

October 1st, 2024: Susanne Yelin, Harvard University. 

Tuesday, October 1st, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  Simulations of quantum chemistry and quantum materials are believed to be among the most important potential applications of quantum information processors, but realizing practical quantum advantage for such problems is challenging. In this talk, I will introduce a simulation framework for strongly correlated quantum systems modeled by spin Hamiltonians, focusing on practical applications in quantum chemistry and materials. Our approach uses reconfigurable qubit architectures to simulate real-time dynamics and employs an algorithm for extracting chemically relevant spectral properties through classical co-processing. We develop a digital-analog simulation toolbox, utilizing digital Floquet engineering and hardware-optimized multi-qubit operations to realize complex spin-spin interactions, demonstrated via a proposal based on Rydberg atom arrays. This method allows for extracting detailed spectral information, such as excitation energies and finite-temperature susceptibilities, from a single dataset. I will also highlight how this framework can be applied to compute key properties of polynuclear transition-metal catalysts and 2D magnetic materials.

Title: High-efficiency, superconducting single-photon detectors from ultraviolet to long-wavelength infrared wavelengths

Richard Mirin, Quantum Nanophotonics Group, NIST

Tuesday, October 15th, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  The development of high performance superconducting single-photon detectors has been a key development in the advancement of photonic quantum information science. Both transition edge sensors (TESs) and superconducting nanowire single-photon detectors (SNSPDs) have demonstrated system detection efficiencies approaching 100% at wavelengths around 1550 nm.  In 2015, both of these detectors were used in landmark demonstrations of loophole-free Bell experiments that conclusively showed that quantum entanglement cannot be explained by hidden local variables.  Both of these detectors have been used for demonstrations of photonic quantum computing. There are many applications beyond quantum information science, such as medical imaging, semiconductor characterization, laboratory astrophysics, and exoplanet detection that are enabled by these detectors. I will describe some of the latest innovations in these superconducting single-photon detectors, including the development of SNSPD arrays with 400,000 pixels, from the Quantum Nanophotonics Group/Faint Photonics Group in the Applied Physics Division of NIST.

Title: Tunneling and Interlayer Coherence in Twist-Controlled van der Waals Heterostructures

Emanuel Tutuc, University of Texas, Austin

Friday, October 25th, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  Van der Waals (vdW) heterostructures of two-dimensional materials offer an unprecedented playground to combine materials with different electronic properties, without the constraints of lattice matching associated with epitaxial growth. Recent years have witnessed the emergence of interlayer twist as a new parameter that controls the electronic properties of vdW heterostructures, and allows the realization of flat energy bands.  This presentation will provide an overview of experimental techniques to control interlayer twist, with an emphasis on twist-controlled double layers.  We show that interlayer tunnelling serves as unique tool to probe interlayer coherence in twist-aligned, closely spaced double layers where interaction leads to a coherent superposition of electronic states in individual layers, with Josephson junction-like tunnelling characteristics robust to temperature, and layer density detuning.  We describe a novel tunneling spectroscopy technique in twist-aligned double layers, where momentum-conserving tunneling between different energy bands serves as an energy filter for the tunneling carriers, and allows a measurement of the quasi-particle state broadening at well-defined energies with respect to the Fermi level.  

Title: Strain engineering of epitaxial BiFeO₃ film under biaxial tensile strain

In-Tae Bae, The Aerospace Corporation

Friday, November  1st, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  BiFeO₃ (BFO) has been known as the only multiferroic material that exhibits ferroelectricity and antiferromagnetism simultaneously well above room temperature since 1970s. The resurgence of BFO as a multiferroic material was triggered by the revelation of its true bulk ferroelectricity (= ~90 mC/cm²) in the mid-2000s.¹ Subsequently, with the availability of high quality single crystal oxide substrates, BFO films are grown epitaxially on a variety of single crystal substrates in an attempt to further improve its physical properties by imparting epitaxial strains.[1]^,[2] Since the crystal symmetry and microstructural characteristics caused by the epitaxial strains dominate the multiferroic property changes in BiFeO₃, substantial efforts have been devoted to understand the relationship between the crystal symmetry and ferroelectric domain structure in epitaxially strained BFO films. As a result, a number of strain-induced new crystal structures were proposed by experiments and theoretical calculations. However, details about strain-induced structural modifications remain elusive owing to: (1) the remarkably complex nature of BiFeO₃, (2) its willingness to adapt unusually high lattice strain of over ~6 %,[3] and (3) the use of pseudocubic notation to describe the equilibrium BFO phase of rhombohedral (space group: R3c). In this talk, I discuss: (1) how the use of hexagonal notation (that represents the true symmetry in equilibrium BFO phase) helps unambiguously identify the crystal symmetry and subsequent quantitative strain measurement in epitaxially strained BiFeO₃,[4]^-[7](2) the relationship between spontaneous polarization and the crystallographic orientations in ferroelectric domains.[8] In addition, how electron probe used within scanning transmission electron microscope affects the spontaneous polarization orientation measurement is discussed as well.[9] 

References

[1] J. Wang et al., Science 299, 1719 (2003)

[2] R. J. Zech et al., Science 326, 977 (2009)

[3] D. Sando, B. Xu, B. Bellaiche and V. Nagarajan, Appl. Phys. Rev. 3, 011106 (2016)

[4] I.-T. Bae, H. Naganuma, T. Ichinose, K. Sato, Phys. Rev. B, 93, 064115 (2016) 

[5] I.-T. Bae et al. Sci. Rep. 7, 46498 (2017)

[6] I.-T. Bae et al. Sci. Rep. 8, 893 (2018)

[7] I.-T. Bae et al. Sci. Rep. 9, 6715 (2019)

[8] I.-T. Bae, Z. R. Lingley, B. J. Foran, and H. Paik, Sci. Rep. 13, 19018 (2023)

[9] I.-T. Bae, B. J. Foran, and H. Paik, Sci. Rep. 14, 15513 (2024)

Title: Doing more with the same: using metastable states of trapped ions

Tuesday, November 5th, 2024: Jameson O'Reilly, University of Oregon 

Tuesday, November 5th, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  Today’s most advanced ion trap quantum computers have at most one qubit per ion, each defined within the ground state manifold. Additional non-qubit ions provide sympathetic cooling to keep the computational ions cold enough to perform many rounds of high-fidelity coherent operations. Typically, the two subsets of ions must be different species to prevent cooling light from disturbing the computation. To bypass this added system complexity, we can instead promote our computational ions to a long-lived excited state that is isolated from the ground-state cooling transitions. This promotion also enables new features including erasure conversion and projective state preparation. We will discuss two recent efforts to develop this architecture: entangling gates between metastable qubits and sympathetic cooling of a metastable ion by a ground-state ion. Finally, we will take advantage of the larger metastable manifold to explore high-fidelity qudit control.

Title: TBA

Igal Brener, Sandia National Lab

Friday, November  15th, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  TBA

Title: TBA

Martin Scheutz, Amazon Web Services

Friday, November  22nd, 2024

2:00-3:00pm,  105 Lin Hall

Abstract:  TBA

Title:  Topological quantum synchronization: A case study of  robust collective quantum dynamics

 Christopher W. Wächtler,  University of California, Berkeley

Tuesday, January 23rd, 2024

2:30-3:30pm, 105 Lin Hall

Abstract:  Classical synchronization is ubiquitous across various systems, and it is just natural to ask how it is modified in the quantum world. Most of our current understanding in this emerging field arises from ad-hoc analysis of a few exemplary systems. However, these revealed a prominent obstacle: Synchronization in locally coupled networks is often only stable for fine-tuned parameters and initial conditions. This limits its applicability for future quantum devices. Moreover, genuine quantum effects of synchronization are currently quite elusive. The combination of synchronization with topological concepts offers the opportunity to advance in both of these directions: enhancing the robustness of synchronized dynamics and exploring novel quantum effects. The first half of my talk focuses on quantum van der Pol oscillators, which reduce to their classical analogues at the mean-field level and thus allow studying both the classical and quantum regime. I will discuss the emergence of topological synchronization in the classical scenario and demonstrated its persistence when quantum fluctuations are considered. In the second half, I will discuss an example of a purely quantum effect: Synchronization of fractionalized spins.  In the gapped symmetric phase of the AKLT chain, the synchronized spin dynamics is significantly more robust than for previously investigated spin models. These results open the avenue to synchronization not only of microscopic but also emerging degrees of freedom. 

Title:   Harnessing Quantum Fluctuations: Novel Approaches to Controlling Casimir Forces and Torques

Jeremy Munday,  University of California, Davis

Tuesday, February 13th, 2024

2:30-3:30pm, 105 Lin Hall

Abstract:  While the classical vacuum of empty space is static, the reality of the quantum vacuum is anything but boring. Electromagnetic fields are constantly fluctuating and can give rise to measurable consequences. One striking effect is the Casimir force, where quantum fluctuations between two charge neutral plates give rise to an attractive interaction between them. In this seminar, we will trace the historical evolution of this phenomenon, highlighting advancements in measuring the Casimir force and related phenomena like the Casimir torque, and highlight our recent research leveraging anisotropic materials, epsilon-near-zero materials, and magnetic materials to manipulate and modify the Casimir force and torque. We will discuss broad applications spanning nanoscale physics, engineering, chemistry, and biology, while pointing towards promising future directions.

Title:    (Dis)entangling atoms for quantum simulations on quantum computers

Susan Atlas, University of New Mexico

Tuesday, February 27th, 2024

2:30-3:30pm, 105 Lin Hall

Abstract:  As the NISQ (noisy intermediate-scale quantum) era evolves into the new era of fault-tolerant quantum computing, there is growing interest in developing methods for achieving practical quantum advantage in real applications.  In the spirit of Feynmann’s original vision—simulating the quantumness of nature via a quantum computer—we are exploring novel approaches for mapping two key problems of molecular and materials physics onto quantum architectures, at scale, by exploiting the chemical concept of an atom-in-molecule: (1) improved functionals for describing electron correlation in density functional theory; and (2) ensemble charge-transfer force fields for describing bond formation and breaking in atomistic simulations of macromolecules and complex materials.  In addition to improved simulation accuracy, the atom-in-molecule framework opens the prospect of exploiting natural fault tolerance effected by formal constraints on the electron density, and reinterpreting bond formation and breaking as an electronic phase transition.

Title:   Spintronic Phenomena for Reversible, Neuromorphic, Reservoir, and Secure Computing

Joseph Friedman, University of Texas, Dallas.

Tuesday, March 12th, 2024

2:30-3:30pm, 105 Lin Hall

Abstract: The rich physics present in a wide range of spintronic materials and devices provide opportunities for a variety of computing applications. This presentation will describe six distinct proposals to leverage spintronic phenomena for reversible computing, neuromorphic computing, reservoir computing, and hardware security. The presentation will begin with a solution for reversible computing in which magnetic skyrmions propagate and interact in a scalable system with the potential for energy dissipation below the Landauer limit, followed by a paradigm for operating Boolean logic at terahertz clock frequencies utilizing the magnetoresistance of low-dimensional materials. Three neuromorphic systems for emulating neurobiological behavior with spintronic phenomena will then be presented: a purely-spintronic system that enables unsupervised learning with magnetic domain wall neurons and synapses, a reservoir computing system based on the dynamics of frustrated nanomagnets, and an approach for unsupervised learning that marks the first experimental demonstration of a neuromorphic network directly implemented with MTJ synapses. This presentation will conclude with a logic locking paradigm based on nanomagnet logic, the first logic locking system that is secure against both physical and algorithmic attacks.

Title:   Robust Classical Shadow Tomography in Shallow Circuits

 Yizhuang You, UCSD

Friday, March 15th, 2024

2:30-3:30pm, 105 Lin Hall

Abstract: Extracting information efficiently from quantum systems is a major component of quantum information processing tasks. Randomized measurements, or classical shadows, enable predicting many properties of arbitrary quantum states using few measurements. While random single-qubit measurements are experimentally friendly and suitable for learning low-weight Pauli observables, they perform poorly for nonlocal observables. Prepending a shallow random quantum circuit before measurements maintains this experimental friendliness but also has favorable sample complexities for observables beyond low-weight Paulis, including high-weight Paulis and global low-rank properties such as fidelity. However, in realistic scenarios, quantum noise accumulated with each additional layer of the shallow circuit biases the results. To address these challenges, we propose the robust shallow shadows protocol. Our protocol uses Bayesian inference to learn the experimentally relevant noise model and mitigate it in postprocessing. This mitigation introduces a bias-variance trade-off: correcting for noise-induced bias comes at the cost of a larger estimator variance. Despite this increased variance, as we demonstrate on a superconducting quantum processor, our protocol correctly recovers state properties such as expectation values, fidelity, and entanglement entropy, while maintaining a lower sample complexity compared to the random single-qubit measurement scheme. We also theoretically analyze the effects of noise on sample complexity and show how the optimal choice of the shallow shadow depth varies with noise strength. This combined theoretical and experimental analysis positions the robust shallow shadow protocol as a scalable, robust, and sample-efficient protocol for characterizing quantum states on current quantum computing platforms.

Title:   Tunable Quantum Dissipation: Opportunities and Challenges

Archana Kamal, Univ. of Massachusetts., Lowell

Friday, March 29th, 2024

2:30-3:30pm, 105 Lin Hall

Abstract:   Dissipation engineering is a powerful paradigm for correcting errors and realizing stable quantum coherences autonomously. The basic idea is to tailor the dissipation seen by a system, such that it relaxes and sustains the system in a desired target state. With growing capabilities in quantum information platforms this idea can now be realized in conjunction with parametric interactions that enable rapid tunability and in-situ reconfigurability for implementing strong dissipative couplings between spatially remote and off-resonant qubits. The resultant platform with tunable quantum dissipation offers novel functionalities for quantum state preparation and control, along with new opportunities for exploring fundamental physics of open systems. As an example, I will first discuss trade off-free protocols for robust and scalable entanglement generation using parametrically tunable dissipation. Next, motivated by the optimal regime of dissipation engineering, I will discuss our recent efforts on expanding the analytical and numerical framework of these platforms and some recent surprises for Lindblad renormalization and Zeno physics in the presence of strong dissipation. 

Title:   Quantum Simulation with Non-Unitary Dynamics

Xiao Mi, Google AI

Friday, April 5th, 2024

2:30-3:30pm, 105 Lin Hall

Abstract:   Many-body quantum simulation using experimental quantum processors is a highly promising avenue toward practical quantum advantage. Traditionally, such a task is accomplished via unitary dynamics which is limited by gate fidelities and oftentimes Trotter errors. Here we explore the non-unitary dynamics arising from the interplay between unitary evolution applied to a system of qubits and an engineered dissipative environment realized by auxiliary qubits that are frequently reset to their ground states. We find that by appropriate choice of interaction between the system qubits and auxiliaries, the quantum system may be steered to an entangled steady state resembling low-temperature states of 1D and 2D transverse Ising models. Furthermore, by coupling the system to auxiliaries stabilized to different states, we discover a new, subdiffusive form of quantum transport in the Heisenberg XXZ model. These results demonstrate the feasibility of utilizing engineered dissipation toward preparing complex quantum matter, significantly enriching the capability of near-term superconducting processors. As time allows, I will also briefly discuss another complementary approach toward practical quantum advantage, namely realizing high-fidelity analog evolution using tunable-coupling transmons.

Title:   Quantum state control via light-matter interactions in cold and ultracold atoms gases: quantum memory and holonomic quantum operations

Lindsay LeBlanc, University of Alberta

Friday, April 19th, 2024

2:30-3:30pm, 105 Lin Hall

Abstract:  Neutral atomic gases provide fantastic opportunities for studying and controlling quantum phenomena, ranging from many-body physics to quantum computers. In our research, we use the well-known interactions between cold gases and electromagnetic radiation to harness various quantum degrees of freedom. Quantum memories, used for storing and manipulating photonic signals, will be a key component in quantum communications systems, especially in realizing critical quantum repeater infrastructure. In our work, we demonstrate two memory protocols in ultracold (sometimes Bose-condensed) atoms, which hold the potential for high-performance light storage: the Autler-Townes splitting (ATS) and superradiant approaches. These methods provide a path towards practical implementations in both ground- and satellite-based quantum communications systems, and we are working on both increasing performance and developing practical implementations. In a separate direction, our lab also uses ultracold ensembles to study unconventional quantum gates for quantum computing. In our work on holonomic operations, we engineer degeneracies into our system through Floquet driving, with the goal of realizing non-Abelian geometric phases. Our experiments reveal that we indeed rotate quantum states in this degenerate manifold, though we find that the naive expectation of geometric robustness to fluctuations is less resilient to real experimental issues than expected.

Title:   New Dimensions on the Interaction of Light and Matter: Quantum Materials, Quantum Light, and Quantum Control

Nathaniel Stern,  Northwestern University,

April 30th, 2024

2:30-3:30pm, 105 Lin Hall

Abstract:  The quantum conception of light consisting of particles of discrete energy, or photons, underlies its interaction with matter. For solid materials, this understanding has led to transformational applications both as conventional as sensor and display technologies and as extraordinary as lasers. Despite this ubiquity, advances in materials continue to reveal nuances in the interaction of light with matter. The emergence of layered materials of atomic-scale thickness presents a new two-dimensional (2D) landscape in which to play with the interaction between photons and matter, revealing diverse opportunities for control based on morphology, surface chemistry, and electromagnetic environment. I will describe how the unique features of layered materials can be harnessed for generating and exploring optical phenomena. The properties of 2D materials give rise to spin-polarized half-light, half-matter superpositions that can be manipulated at picosecond timescales like a two-level spin. The polarization-sensitivity of these materials can be an ingredient of chiral interactions with light when integrated with photonic circuits. Shifting from light-matter superpositions to isolable quantum emitters, I will discuss recent insights into how the surface of 2D materials can be used to manipulate and to improve quantum light emission from defects through chemical functionalization. The confluence of spin, quantum emission, and quantum control available by combining low-dimensional materials with polarized light expands the toolbox for engineering quantum optical applications.