Colloquium

Zoom Link: https://oklahoma.zoom.us/j/4881880273

Host: Arne Schwettmann

Title: "Engineering coherent quantum systems in atomic qubit platforms"

Abstract: Advances in quantum computation and simulation rely critically on the ability to precisely control complex, interacting atomic systems while maintaining long coherence times. In this talk, I will present my work on engineering high-fidelity quantum control across two leading atomic platforms — trapped ions and neutral atom arrays — highlighting approaches to controlling internal and motional degrees of freedom under realistic experimental constraints.

I will first describe techniques developed during my PhD work in trapped-ion systems for robust multi-qubit operations, including control of collective motional modes, pulse-design strategies that mitigate sensitivity to experimental imperfections, and quantum simulation using motional modes of a long ion chain. I will then discuss my postdoctoral work on neutral ytterbium atom arrays, where long-lived atomic states and flexible optical control enable new opportunities for scalable quantum computation and simulation. I will present recent experimental advances in coherent control, non-destructive readout, and atom–photon interfaces. Together, these results illustrate a platform-spanning approach to precision quantum control and motivate future directions toward scalable atomic quantum systems that integrate computation, simulation, and modular architectures.

Host: Kieran Mullen

Title: "Molecular Design Principles for Organic and Hybrid Materials: Insights into Topological States and Beyond"

Abstract: Organic frameworks (COFs & MOFs) have emerged as versatile platforms for exploring new electronic and quantum phenomena. Their modular “bottom-up” design, structural tunability, and chemical diversity make them ideal candidates for realizing tailored electronic structures and even unconventional topological states. Clear and predictive rules that connect molecular building blocks to emergent electronic behavior in extended lattices remain a central challenge. In this talk, I will discuss our efforts to build such connections and to adopt them for the rational design of quantum functionalities in organic materials. I will begin by introducing an effective theoretical framework that enables controlled band engineering in polymer networks. It reveals the fundamental relationships among lattice symmetries, frontier molecular orbitals, and the resulting electronic properties of COFs [1]. Building on this foundation, I will then present our discovery of a topological Dirac semimetal phase in a phthalocyanine-based COF composed solely of light elements, where external strain drives a transition from a trivial insulator to a topological semimetal [2]. I will then focus on heterotriangulene-based COFs and show how variations in the core heteroatoms and linker chemistry can promote higher-order topological insulating state [3]. Additionally, I will briefly overview other studies that broaden the scope of my research. These include investigations of the structure-property relationships in the highly conductive n-type polymer, poly(benzodifurandione) [4,5], as well as uncovering how organic cation engineering and quantum confinement govern the properties of low-dimensional hybrid perovskites [6,7]. These efforts demonstrate a unified molecular-level strategy for designing organic and hybrid materials with tailored properties and quantum states, offering fundamental insight into the molecular-to-materials relationships.

References:
1. Ni, X.; Li, H.; Liu, F.; Bredas, J.L. Mater. Horiz. 2022, 9, 88–98.
2. Ni, X.; Huang, H.; Bredas, J.L. Chem. Mater. 2022, 34, 3178–3184.
3. Ni, X.; Huang, H.; Bredas, J.L. J. Am. Chem. Soc. 2022, 144, 22778–22786.
4. Ni, X.; Li, H., Bredas, J.L. Chem. Mater. 2023, 35, 5886–5894.
5. Ni, X., Li, H., Coropceanu, S., Bredas, J.L. ACS Mater Lett 2024, 6, 2569.
6. Ni, X.; Li, H.; Bredas, J.L. ACS Mater Lett 2024, 6, 3436.
7. Zhong, X.†; Ni, X.†; Sidhik, S.; Li, H.; Mohite, A.D.; Bredas, J.L; Kahn, A. Adv. Energy Mater. 2022, 12, 2202333. (†Equal contribution)

Host: Kieran Mullen

Title: "Beyond Twistronics: Flat Bands Without Magic"

Abstract: Flat electronic bands have emerged as a powerful route to correlated and topological quantum matter, but in moiré systems they rely on extreme geometric fine tuning. I present an alternative paradigm in which externally imposed superlattice potentials generate flat bands in a deterministic and broadly tunable way, without requiring magic angles. Using graphene multilayers as a representative platform, I show that superlattice modulation produces both topological flat bands and stacked flat bands with favorable quantum geometry over extended parameter regimes. Band flatness, topology, and geometry can be controlled via superlattice symmetry, period, and displacement fields, offering direct access to conditions relevant for fractional Chern insulators and other correlated phases. This establishes superlattice engineering as a general and experimentally realistic platform for designing flat-band quantum matter beyond twistronics.

Host: Kieran Mullen

Title: "Square-planar nickelates: where nickelate superconductivity began"

Abstract: Superconductivity is one of the most fascinating phases of matter, with fundamental significance and transformative technological potential. However, superconductivity at ambient pressure typically occurs at temperatures far too low for widespread applications. As a result, the design, prediction, and discovery of new superconducting materials with higher critical temperatures remain central challenges in condensed matter physics. In this colloquium, I will review the landscape of high-temperature (high-Tc) superconductivity in the cuprate materials and discuss recent breakthroughs in square-planar superconducting nickelates. Using ab initio electronic structure methods combined with many-body approaches, I will show how these nickelates can be understood as close analogs of the cuprates, while also highlighting key distinctions that make them a new platform for exploration. I will conclude by offering a perspective on the future directions and open questions in the nascent field of nickelate superconductivity.

Host: Arne Schwettmann

Title: "Expanding the quantum toolbox for atomic and molecular systems"

Abstract: Progress in atomic, molecular, and optical (AMO) physics has been driven by a powerful paradigm: leveraging simple, well-understood quantum systems together with prec ise control techniques to realize and explore complex many-body dynamics. While the intrinsic coherence and predictability of atoms, molecules, and ions provide an exceptional foundation, it is the continual expansion of the quantum toolbox, the methods for preparing, controlling, and measuring quantum systems, that ultimately defines these platforms and enables applications in quantum simulation, quantum computing, quantum sensing, quantum networking, and beyond. In this talk, I present two complementary examples of quantum toolbox extensions from my work. First, I describe the development of a new platform based on ultracold dipolar molecules in optical tweezers. Rather than attempting to control molecules directly, we leverage mature atomic cooling and control techniques to coherently associate individual atoms into ultracold molecules, realizing a flexible "molecule assembler". Second, I introduce a set of tools that add mid-circuit measurement and reset capabilities to trapped-ion quantum computers with minimal hardware complexity and time overhead. Together, these examples illustrate how expanding the quantum toolbox broadens the scope of quantum science and technology in AMO physics.

Host: Arne Schwettmann

Title: "Spin-photon entanglement of Yb-171 atom array in the telecom band"

Abstract: Entanglement greatly enhances precision measurements by reducing noise and boosting signal gain. Expanding entanglement from the microscopic to the macroscopic scale unlocks numerous applications, including quantum key distribution, blind or distributed quantum computing, and advanced atom interferometers and magnetometers.

To achieve long-range entanglement up to thousands of kilometers, atom-photon entanglement is the key technology because photons carry quantum information with minimal loss through single-mode fiber. The neutral Yb-171 atom is a great candidate for both quantum computing and quantum communication since its level structure provides high fidelity quantum memories, gate operations, measurements, and strong coupling to a telecom wavelength photon.

In this talk I will introduce our recent work generating the atom-photon entanglement of the Yb-171 at 1389 nm (fibre loss coefficient < 0.3 dB/km). We demonstrate the high-fidelity (raw ~90(1)%) time-bin encoded spin photon entanglement and measurements using an unbalanced Mach-Zehnder interferometer. Additionally, by imaging our atom array onto an optical fiber array, we demonstrate a parallelized networking protocol that could provide an N × boost in the remote entanglement rate. Finally, we demonstrate the ability to preserve coherence on a memory qubit while performing networking operations on communications qubits.

In the outlook section, I will present a novel method for generating entangled atom pairs over macroscopic distances using a transportable atomic array, which promises to be an invaluable asset for quantum computing and precision measurements.

Host: Kieran Mullen

Host: Arne Schwettmann

Title: "From Laser Pulses to Learning Algorithms: Engineering Trapped-Ion Quantum Computers"

Abstract: Trapped-ion platforms are among the highest-performing quantum computing technologies today and have already transitioned into industrial systems. In this talk, I outline how we engineer and operate a trapped-ion platform at Duke as a reliable, application-driven system, and how we translate atomic-physics-level control into a software execution stack that automates scheduling, monitoring, and calibration to enable reproducible experiments at scale.

In the next part, I will focus on the digital regime, where universal gate sets enable programmable circuits and closed-loop hybrid quantum-classical optimization under finite-shot constraints. This gate-based workflow supports a broad range of applications on the same hardware. I will show how it enables (i) Hamiltonian learning, including a symmetry-protected signature that isolates genuine three-body interactions even in the presence of unknown lower-body terms; (ii) molecular energy estimation using CAFQA-initialized variational quantum eigensolver, reducing the amount of on-hardware variational tuning needed; and (iii) quantum machine learning methods that leverage the structure of Hilbert space to learn useful representations from data.

Finally, in contrast to the digital regime, I discuss the analog regime, where we program the device by engineering an effective Hamiltonian and using the ions’ native interactions directly. For many sensing and learning tasks, this approach captures the relevant physics with substantially lower control overhead than gate-based decompositions and can be potentially be more expressive.

Host: Kieran Mullen

Host: Mukremin Kilic

Host: Mukremin Kilic

Host: Mukremin Kilic

Host: Mukremin Kilic

Host: Mukremin Kilic

Host: Mukremin Kilic

Host: Kuver Sinha

2026 Spring Fling: Annual awards ceremony for the department of physics and astronomy.