Penn FoQuS 2026 Event Program

Abstract: Quantum metrology enables ultrasensitive measurements with transformative potential for the life sciences, yet translating qubit sensors into practical biological devices remains challenging. In this talk, I present new strategies that combine quantum engineering and molecular biology to create quantum sensors compatible with living systems. I will discuss advances in biocompatible diamond sensors, engineered core–shell nanodiamonds, and a new class of genetically encodable protein qubits—optically addressable spins in fluorescent proteins with coherence and readout comparable to solid-state defects.

Abstract: From its initial proposal, Quantum Computing (QC) has had captivating potential, and scientists have worked on advancing toward that potential. QC has now reached an interesting and important inflection point. The Algorithms-to-Devices gap in QC refers to the orders of magnitude difference between the resource quantity/quality needed by QC algorithms, and what has been successfully built today. Computing research can help QC systems close this gap, by develop the crucial intermediate tool flows and hybrid classical-quantum techniques that can move towards practical quantum utility. I will discuss our recent advances in these topic areas, and more broadly advocate for the role that computer scientists must play for QC to reach its full potential.

Abstract: Quantum interferences, where two electronic pathways “compete” in a manner akin to the interference of separate propagating waves, are often exploited in atomic systems to realize a variety of exotic phenomena, such as electromagnetically induced transparency, slow light and lasing without inversion. In crystalline materials, quantum interferences can sometimes be difficult to discern with conventional probes, even if their consequences may be just as profound. In this talk, I will discuss how optical second harmonic generation spectroscopy reveals a hidden quantum interference in the LnAlSi (Ln = lanthanide) family of Weyl semimetals, a class of topologically ordered matter defined by massless, chiral quasiparticles, and I will discuss how this previously concealed feature of their shared band structure plays a fundamental role in their magnetic and optical properties.

Abstract: Spin-based quantum sensors offer advantages including optical addressability and chemical tunability. We demonstrate vector AC field sensing using the photoexcited spin triplet of deuterated pentacene at zero field and room temperature. Three-dimensional microwave fields are reconstructed by measuring Rabi frequencies of anisotropic spin-triplet transitions from two pentacene orientations. We further present a comprehensive experimental and theoretical study of spin decoherence and demonstrate a spin-protection protocol based on nuclear spin hyperpolarization.

Abstract: Multiterminal Josephson junctions provide a powerful platform for emulating topological phases in synthetic dimensions defined by superconducting phase differences. In these systems, Andreev bound states form a multidimensional band structure on a compact phase torus, where independent phase biases act as quasimomenta and enable phase-coherent control of quantum states.

Here, we present phase-resolved spectroscopic measurements of Andreev bands in graphene-based three-terminal Josephson junctions, revealing signatures of higher-order Cooper pair transport and emergent topology. We observe sharp resonances in the differential conductance that lock to specific linear combinations of superconducting phases, corresponding to coherent quartet processes. These resonances trace quantized trajectories across the two-dimensional phase space, forming closed winding paths on the torus that encode topological invariants of the multipair transport. At the intersections of distinct winding sectors, we identify avoided crossings arising from coherent hybridization of Andreev bound states, demonstrating the quantum nature of the underlying Andreev band structure beyond classical winding arguments. These results establish multiterminal Josephson junctions as a tunable platform for emulating topological phases in superconducting quantum systems, where phase-controlled transport enables the design of synthetic band structures with nontrivial topology.

Abstract: Inability to communicate poses a major challenge to coordination in multi-agent systems. It is well known that, for certain multi-player games with no communication, shared quantum entanglement allows strategies that outperform any classical strategy. We extend this to sequential decision-making by introducing the first framework for training multi-agent reinforcement learning policies that exploit entanglement as a coordination resource. As entanglement distribution technology becomes a practical reality, extending ideas of Bell nonlocality to settings that approach realistic applications becomes relevant. We suggest that coordination in multi-agent systems be considered as a guiding application for the field of quantum networking, alongside well-studied applications like distributed quantum computing and secure communication.

Jonathan Hess (University of Pennsylvania)
Mridul Pushp (University of Pennsylvania)
Noah Johnson (University of Pennsylvania)
Seong Woo Oh (University of Pennsylvania)
Robert Spivey (University of Pennsylvania)
Anthony Sigillito (University of Pennsylvania)

A vital component in any quantum computing paradigm is an efficient method for entangling qubits with high fidelity [1]. In this poster, we report our process to achieve a high-fidelity entanglement via a decoupled CZ (DCZ) gate. These experiments were conducted on a Loss-DiVincenzo spin qubit fabricated on a Si/SiGe heterostructure, with the two qubit gates being generated by the exchange interaction [2]. After careful tuning of the entangling gate, we report Bell State fidelities over 90%. Along with previous work in initialization, readout, and one qubit gates, we demonstrate a complete set of operations for universal quantum computation.

[1] Bremner et al. A practical scheme for quantum computation with any two-qubit gate. Phys. Rev. Lett. 89, 247902 (2002)
[2] Loss, D. DiVincenzo, D.P. Quantum computation with quantum dots. Phys. Rev. A 56, 120-126 (1998).

Tarush Tandon (Drexel University)

In recent times, quantum topological materials have garnered significant attention in the fields of energy-efficient electronics, spintronics, and even quantum computing. The topological kagome magnet Fe3Sn2 hosts interesting features such as van Hove singularities, flat bands, and Dirac cones in its electronic band structure. In bulk, Fe3Sn2 is described as a frustrated soft ferromagnet with a reported Curie temperature of 640 K, with spins oriented parallel to the c-axis of the lattice at 300 K. There have been several reports on the Berry-phase induced (intrinsic) giant anomalous Hall effect (AHE) in Fe3Sn2 with an anomalous Hall resistivity of 5 μΩcm reported in bulk single crystals, which is almost 20 times greater than that in traditional ferromagnets like Fe and Ni. In this work, I investigate the AHE in thin films of Fe3Sn2 of varying thicknesses grown on (0001) – oriented Al2O3 substrates with an Fe (110) buffer layer via molecular beam epitaxy (MBE).

The AHE effect is known to have both intrinsic and extrinsic factors contributing to its origin in ferromagnets. It has been shown that the anomalous Hall resistivity (ρAxy), arising from both contributions, demonstrates a strong dependence on the longitudinal resistivity (ρxx) of the material. Recently, a theory unifying both intrinsic and extrinsic contributions to the AHE in ferromagnets has been proposed.

In this work, I demonstrate the epitaxial growth of crystalline, phase-pure, and laterally continuous thin films of Fe3Sn2 via MBE, supported by X-ray diffraction and reflectivity measurements. Using data collected from magnetometry experiments, I reveal a thickness-dependent behavior of the magnetization of the samples, where films below 11 nm exhibit a suppressed saturation magnetization. Through electronic transport measurements, I demonstrate that ρxx of Fe3Sn2 films is dependent on the film thickness in a non-trivial manner, with thinner films seemingly exhibiting a lower resistivity, which is attributed to enhanced conductivity at the Fe/Fe3Sn2 interface. I show that the anomalous Hall resistivity of these films can be understood within the context of the unified AHE theory of ferromagnets, exhibiting both intrinsic and extrinsic origins depending on the material thickness.

Yichi Zhang (University of Pennsylvania)

Classical and quantum technologies have traditionally been viewed as orthogonal, with classical systems being deterministic and quantum systems inherently probabilistic. This distinction hinders the development of a scalable quantum internet even as the global internet continues expanding. We report a classical-decisive quantum internet architecture in which the integration of quantum information into advanced photonic technologies enables efficient entanglement distribution over a commercially deployed fiber network. On-chip precise synchronization between classical headers and quantum payloads enables dynamic routing and networking of high-fidelity entanglement guided by classical light. The quantum states are preserved through real-time error mitigation, relying solely on classical signal readout without disturbing quantum information. These classical-decisive features demonstrate a practical path to a scalable quantum internet using existing network infrastructure and operating systems.

Jeiko Pujols (University of Pennsylvania)

Colloidal quantum dots (CQDs) are an emerging platform in quantum information science, offering unique advantages in scalable fabrication and tunable physical properties. Their size, composition, and surface chemistry characteristics enable precise control over optical and electronic behavior. CQDs have been widely explored as fluorescent probes for imaging and as hosts for optically active defect states. This poster highlights recent advances in CQD synthesis and defect engineering, with a focus on their application in quantum sensing and spin-based qubits. By tailoring defect environments within CQDs, these systems show promise as versatile platforms for quantum technologies.

Noah Johnson (University of Pennsylvania)
Vatsal Bandaru (University of Pennsylvania)

Abstract TBD

Joseph Minnella (University of Pennsylvania)

Multipartite entanglement is an essential aspect of quantum systems, needed to execute quantum algorithms, implement error correction, and achieve quantum-enhanced sensing. In solid-state quantum registers such nitrogen-vacancy (NV) centers in diamond, entangled states are typically created using sequential, pairwise gates between the central electron and individual nuclear qubits. This sequential approach is slow and suffers from crosstalk errors. Here, we demonstrate a parallelized multi-qubit entangling gate to generate a four-qubit GHZ state using a room-temperature NV center in only 14.8µs — 10 times faster than using sequences of two-qubit gates and close to the fundamental limit set by the hyperfine coupling frequencies. Parallel three-qubit gates are also realized with all nuclear-qubit subsets. The entangled states are verified by measuring multiple quantum coherences. The four-qubit parallel gate has a fidelity of 0.92(4), whereas the sequential four-qubit gate fidelity is only 0.69(3). The approach is generalizable to other solid-state platforms, and it lays the foundation for scalable generation and control of entanglement in practical devices.

Muyao Zhu (University of Pennsylvania)

We present a current-tunable 3D microwave cavity system for dynamic control of the quality factor (Q). A superconducting chip integrated within the cavity couples to the cavity magnetic field, enabling tunable coupling through an applied bias current. By varying the current, the effective interaction between the cavity and the chip is modified, resulting in controlled changes in the cavity Q. This approach provides a flexible method for engineering dissipation and coupling in microwave systems, with potential applications in quantum circuits and tunable resonator architectures.

Augustin Braun (Columbia University)

Nanodiamonds are a platform of growing interest for quantum sensing at the nanoscale owing to the environment-sensitivity of the color centers that they host. Under high pressure and high temperature, we managed to synthesize highly crystalline and faceted nanodiamonds from molecular precursors and we controlled their size by tuning the temperature. Upon irradiation/annealing/oxidation, we observed the formation of negatively charged nitrogen vacancy color centers suitable for optically detected magnetic resonance, with an electron spin coherence time in the µs range. New milder surface chemistry will improve the coherence time of these nanodiamonds. This controlled synthesis allowed us to investigate quantum confinement in nanodiamonds which can be used as a synthetic parameter to stabilize color centers within the band gap of wide band gap materials.

Nicolò Dal Fabbro (University of Pennsylvania)
John Gardiner (Nasdaq)
Orlando Romero (Nasdaq)

The inability to communicate poses a major challenge to coordination in multi-agent reinforcement learning (MARL). Prior work has explored correlating local policies via shared randomness, sometimes in the form of a correlation device, as a mechanism to assist in decentralized decision-making. In contrast, this work introduces the first framework for training MARL agents to exploit shared quantum entanglement as a coordination resource, which permits a larger class of communication-free correlated policies than shared randomness alone. This is motivated by well-known results in quantum physics which posit that, for certain single-round cooperative games with no communication, shared quantum entanglement enables strategies that outperform those that only use shared randomness. In such cases, we say that there is quantum advantage. Our framework is based on a novel differentiable policy parameterization that enables optimization over quantum measurements, together with a novel policy architecture that decomposes joint policies into a quantum coordinator and decentralized local actors. To illustrate the effectiveness of our proposed method, we first show that we can learn, purely from experience, strategies that attain quantum advantage in single-round games that are treated as black box oracles. We then demonstrate how our machinery can learn policies with quantum advantage in an illustrative multi-agent sequential decision-making problem formulated as a decentralized partially observable Markov decision process (Dec-POMDP).

Amelia Klein (University of Pennsylvania)

Europium-doped gallium nitride (GaN:Eu) is a promising platform for classical and quantum optoelectronic applications due to its bright red emission and narrow optical linewidths. Such applications demand highly efficient and homogeneous emission, and for this goal it is necessary to optimize the formation of desired Eu incorporation sites and efficient energy transfer into their emissive excited states. In this work, we perform site-selective spectroscopy to characterize the photoluminescence properties of delta-doped structures with alternating Eu-doped and undoped layers of varying layer thickness. We demonstrate that samples with few-nm-thick doped layers show greater PL intensity per Eu concentration as well as more efficient energy transfer to the majority site, which are both highly desirable properties for creating power-efficient LEDs. In a sample with 1nm doped layers, we observe only a single Eu incorporation site, with a narrow, homogeneous emission spectrum that is highly desirable for applications in quantum technologies. This result highlights the potential of delta-doping as a broadly applicable approach to engineering defect properties in rare-earth–doped semiconductors.

Deven Carmichael (University of Pennsylvania)

Quantum control of the many-body wavefunction is a central challenge in quantum materials research, as it could yield a precise control knob to manipulate emergent phenomena. Floquet engineering, the coherent dressing of quantum states with periodic non-resonant optical fields, has become an important strategy for quantum control. Most applications to solid-state systems have targeted weakly interacting or single-ion states, leaving the manipulation of many-body wavefunctions largely unexplored. Here we use Floquet engineering to achieve quantum control of a strongly correlated Hubbard exciton in the one-dimensional Mott insulator Sr2CuO3. A non-resonant mid-infrared optical field coherently dresses the exciton wavefunction, driving its rotation between bright and dark states. We use resonant third-harmonic generation to quantify ultrafast π/2 rotations on the Bloch sphere spanned by these exciton states. Our work advances the quest towards programmable control of correlated states and exciton-based quantum sensing.

Wai Ting Tai (University of Pennsylvania)

In correlated electronic systems with a well-defined band gap, conventional pictures of light-matter coupling suggest that electrons only excite within active band manifolds. However, this standard band-projection approach fails in the presence of nontrivial quantum geometry, where interband current matrix elements remain unsuppressed at large band gap, creating finite contributions from virtual interband processes. I present a quantum-geometric gauge theory that resolves this problem by dressing both single-particle hopping and electron-electron interactions with a Wilson-line phase factor, equivalent to a light-induced deformation of maximally-localized Wannier orbitals. This mechanism is non-perturbative in the drive and can dominate responses in flat-band and moiré systems with poor Wannier localization. I illustrate these predictions on a strongly-interacting topological chain and a two-orbital flat-band model, and discuss implications for spectroscopy in moiré heterostructures. Building on this picture, I develop a perturbative Raman scattering theory for obstructed quantum materials: even when the intraband current vanishes exactly in a flat band, a finite symmetry-resolved Raman response survive. The response decomposes naturally in terms of the quantum geometric tensor — Berry curvature and the Fubini-Study metric each control distinct polarization channels — alongside renormalized non-resonant and resonant contributions from virtual interband Coulomb scattering.

Svetlana Kotochigova (Temple University)
Anna Linnik (Temple University)
Eite Tiesinga (NIST)

The discovery of the C60 fullerene opened new horizons to design carbon nanostructures with targeted electronic structure as well as transport and optical properties. For example, endohedral 12C60 molecules were proposed as candidates for functional quantum architectures to store and manipulate encased atomic and molecular qubits. Recent advances in cryogenic buffer-gas cooling and frequency-comb spectroscopy have enabled rovibrational quantum-state-resolved measurements of gas-phase 12C60, revealing rotational fine structure reflecting its high icosahedral symmetry. Here, we present a perturbative quantum description of the 12C60 molecule interacting with a buffer gas of 40Ar atoms at temperatures of order 150 K, including a detailed analysis of their electronic structure, their interaction anisotropies, and the collision-induced rotational quenching of 12C60 in its vibrational and electronic ground state. The role of the icosahedral symmetry on the collisional dynamics is emphasized leading to a complex dependence on the 12C60 rotational quantum number. Finally, we compute the isotropic and anisotropic static and dynamic dipole polarizability of 12C60 in its absolute ground state in order to evaluate the long-range, van der Waals interaction between 12C60 and 40Ar.

Boning Li (Massachusetts Institute of Technology)

Quantum sensors based on electronic spins have emerged as powerful probes of microwave-frequency fields. Among other solid-state platforms, spins in molecular crystals offer a range of advantages, from high spin density to functionalization via chemical tunability. Here, we demonstrate microwave vector magnetometry using the photoexcited spin triplet of deuterated pentacene molecules, operating at zero external magnetic field and room temperature. We achieve full three-dimensional microwave field reconstruction by detecting the Rabi frequencies of anisotropic spin-triplet transitions associated with two crystallographic orientations of pentacene in naphthalene crystals. We further introduce a phase alternated protocol that extends the rotating-frame coherence time by an order of magnitude and enables sensitivities of with sub-micrometer spatial resolution. These results establish pentacene-based molecular spins as a practical and high-performance platform for microwave quantum sensing, and the control techniques are broadly applicable to other molecular and solid-state spin systems.

Hongkun Chen (Princeton University)

Decoding stabilizer codes such as the surface and toric codes involves evaluating free-energy differences in a disordered statistical mechanics model, in which the randomness comes from the observed pattern of error syndromes. We study the statistical distribution of logical failure rates across observed syndromes in the toric code, and show that, within the coding phase, logical failures are predominantly caused by exponentially unlikely syndromes. Therefore, postselecting on not seeing these exponentially unlikely syndrome patterns offers a scalable accuracy gain. In general, the logical error rate can be suppressed from pf to pbf, where b≥2 in general; in the specific case of the toric code with perfect syndrome measurements, we find numerically that b=3.1(1). Our arguments apply to general topological stabilizer codes, and can be extended to more general settings as long as the decoding failure probability obeys a large deviation principle.

Ellie Han (Temple University)

A major challenge in realizing scalable quantum computing with superconducting qubits is achieving long coherence time, a key measure of qubit performance. Niobium thin films are important components in superconducting qubits, but impurities in its native oxide are a significant source of decoherence. Recent studies suggest that Ta forms a cleaner native oxide with fewer impurities, making it a promising candidate to replace Nb or serve as a capping layer to Nb after the oxide removal. In this study, we utilize low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) to investigate the superconducting properties of Ta foil and the efficacy of surface preparation processes. We focus on inhomogeneity in the superconducting gap and the density of states near the Fermi energy, as well as the nature and distribution of surface defects. These measurements provide valuable insight optimizing surface preparation and defect mitigation strategies to improve the coherence times of transmon qubits.

Junki Makita (Temple University)

Niobium thin films are key components in superconducting quantum qubit devices; however, the formation of a native oxide layer on Nb surface introduces losses that can limit qubit coherence. One promising approach to mitigate these losses is the removal of the oxide layer followed by capping Nb with a metallic overlayer. In this work, we employ low-temperature scanning tunneling microscopy and spectroscopy (STM/S) to investigate the superconducting properties of Nb films capped with metallic layers, focusing on Au and Re. STM/S provides direct access to the local density of states, providing detailed characterization of proximity-induced superconductivity in the capping layers as well as presence of sub-gap quasiparticle states that may contribute to losses. We examine spatial variations in the superconducting gap and quasiparticle density of states in comparison to bare Nb films. Our measurements highlight the role of metallic overlayers in modifying the electronic structure near the Fermi level and suppressing sub-gap states. These results demonstrate the utility of STM/S as a powerful tool for evaluating and optimizing capping-layer materials and provide insights into surface and interface engineering strategies for improving the performance of superconducting qubit devices.

Naifeng Zhang (Carnegie Mellon University)

Understanding the high-level functionality encoded in low-level quantum circuits remains a fundamental challenge in quantum computing. We present a semantics lifting approach that automatically extracts high-level mathematical specifications from quantum circuits by applying semantics-preserving transformations over structured operators. As a proof of concept, we demonstrate successful lifting of a 2-qubit quantum program that implements modular addition, underscoring the potential of semantics lifting for automated verification and re-optimization of quantum programs.

Robert Spivey (University of Pennsylvania)
Seong Woo Oh (University of Pennsylvania)

Semiconductor quantum dot qubits have reached the error threshold regime, yet many scaling challenges remain. To support the network topologies needed for quantum error correction coherent transport of spin qubits between quantum processing regions is required. Spin qubit shuttling schemes demonstrated to date rely on patterned interdigitated gates across the length of the shuttle lowering fabrication yield. We present a novel device which could simplify the structure needed to achieve coherent qubit shuttling. Two double quantum dots (DQD) with accompanying sensor dots are connected by a micron-scale resistive top gate. Two material platforms have been explored for the device: a Niobium-Silicon top gate on a Si/SiGe platform and a polysilicon top gate on a MOS platform, both top gate materials exhibit high resistivity at millikelvin temperatures. The top gate connecting the DQDs creates a channel which can store charge, and be emptied of charge allowing a path for single electrons to travel. The large resistivity allows for a potential difference to be established imparting a force on single charges while adding minimally to the heat load. In theory nanosecond scale transit times can be achieved. Two platforms are discussed and initial data is presented about the behavior of the device.

Jordan Gusdorff (University of Pennsylvania)

The narrow optical linewidths and long-lived nuclear spin of Eu3+ make a promising candidate for a solid-state spin qubit system. Ceria (CeO2) nanocrystals provide a spin-free host that may be controllably placed on a substrate. There are currently no studies of CeO2:Eu nanocrystals with low doping concentrations (<1% Eu), which will be essential for quantum applications. This work focuses on understanding ensemble optical properties of CeO2:0.2 Eu by investigating optical dynamics and isolating optical transitions. We demonstrate Eu emission activation via annealing, variation in incorporation sites, and temperature-dependent processes.

Xiang Lu (University of Pennsylvania)

Abstract TBD

Spenser Talkington (University of Pennsylvania)

Coherently coupling photons at low power remains a key obstacle for interfaces to superconducting hardware, quantum sensing, and spectroscopy of low-energy matter. Here we propose a method to generate photonic non-nonlinearities that act on, or create, single terahertz photons by leveraging cavity-material coupling to the collective modes found in superconductors and charge density waves. In these materials, selection rules suppress single-photon absorption; they instead couple to light through two-photon absorption; in a cavity, this leads to the formation of a Higgs polariton. For input frequencies between polaritonic branches, a blockade forms, leading to perfect antibunching, g^(2)(0) –> 0, and single photons are emitted. In the weak-coupling limit, we present an analytic solution to the photon statistics, and in the ultrastrong coupling limit, we show that single-photon emission persists over a range of parameters and identify qualitatively new features that are absent at weak coupling. We consider the example system 2H-NbSe2 and reveal the temperature- and frequency-dependent photon statistics. Overall, we propose a cavity-enabled THz single-photon source with on-demand antibunching and material-tunable frequency.

Alexander Velič (Drexel University)

Kagome structure uniquely supports both linear Dirac crossings, where electrons are highly mobile, and flat bands regions of highly corelated electron behavior. FeSn exhibits A-type antiferromagnetism and as the magnetic order depends strongly on the position of the Fermi level with respect to the flat band (i.e. the charge density per transition metal atom), multiple studies have shown the possibilities of manipulating the magnetic order via band engineering by moving the Fermi level (E_F) close to the Dirac point or flat bands as a result of hole or electron doping (doping with Mn or Co respectively). However, it is unclear how disorder influences the magnetic system of FeSn when an isoelectronic (have the same d-band filling) system such as Fe_(1-2x) Co_x Mn_x Sn is prepared. Since much of the excitement in kagome metals originates from idealized band-structure calculations, it is important to investigate how the electronic and magnetic structure evolves as the system is driven towards increasingly disordered regimes (higher x).

Mridul Pushp (University of Pennsylvania)

Abstract TBD