The Interdisciplinary Quantum Seminar is run by the Brown Quantum Initiative (BQI) with the support of several Departments at Brown University. The seminar is focused on inviting Brown and external speakers who work across the many fields that intersect in Quantum Science and Engineering. To get emails about upcoming seminars, events, and other news about Quantum Science and Engineering at Brown, you can request to join our mailing list/Google Group by following this link.
Proposing a talk
If you would like to give a talk, please reach out to the BQI via email! We welcome presentations from Faculty, Postdocs, and Senior Graduate Students. Some previous talks can also be found in our YouTube channel.
2026-2027 Schedule
Time and Location: All talks are held in Barus & Holley 190 unless otherwise stated.
| Date | Speaker | Title | Abstract | Recording |
|---|---|---|---|---|
| October 22 (Thu) | James Daniel Whitfield | Why Quantum Chemistry? The Trouble with Fermions | Why has quantum chemistry motivated so much effort across classical and quantum computing? Fermions offer a setting in which indistinguishability, antisymmetry, and interactions combine to create computational challenges. Our work explores the boundary between what is easy and hard, both with and without quantum computational resources. This includes the difference between simulating dynamics and finding ground states, robust qubit representations of fermions, and how orbital choices can change a problem’s apparent difficulty. These results inform how to use a quantum computer, how not to, and which problems are likely to yield in the near and medium term. |
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| October 28 (Wed) | David Kagan | Playing the CHSH Game with Causally Local Indivisible Systems | The CHSH game is a theoretical tool that probes constraints on statistical correlations between spatially separated systems. Bell’s theorem tells us that the CHSH game players can expect to win a maximum of 75% of the time, under some reasonable-seeming assumptions about locality and causality. Quantum entanglement opens up new strategies that allow players to win about 85% of the time, a value known as Tsirelson’s bound. But why are quantum theory’s apparent violations of locality limited? Why aren’t players able to win 100% of the time? By reformulating the CHSH game as a stochastic process, we provide a more physically transparent account of Tsirelson’s bound, showing that it follows from the existence of indivisible evolution and a new, more precise notion of causal locality. |
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Previous Schedules
2025-2026 Schedule
| Date | Speaker | Title | Abstract | Recording |
|---|---|---|---|---|
| October 1 (Wed) | Mathew Coley-O’Rourke | Entanglement (and lack thereof) in two dimensional arrays of ultracold atoms | Recent experimental advances have stimulated interest in the use of large, two-dimensional arrays of Rydberg atoms as a platform for quantum information processing and to study exotic many-body quantum states. However, the native long-range interactions between the atoms complicate experimental analysis and precise theoretical understanding of these systems. In this talk, I will use new tensor network algorithms capable of including all long-range interactions to study the ground state quantum phase diagram of Rydberg atoms in a two-dimensional square lattice array. We find a greatly altered phase diagram from earlier numerical and experimental studies, revealed by studying the phases on the bulk lattice and their analogs in experiment-sized finite arrays. We further describe a previously unknown region with a nematic phase stabilized by short-range entanglement and an order from disorder mechanism. Broadly our results yield a conceptual guide for future experiments, while our techniques provide a blueprint for converging numerical studies in other lattices. |
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| October 8 (Wed) | Kaavya Sahay | High Performance Quantum Error Corrections Tailored to Hardware | Universal quantum computation with error-prone hardware will entail the use of quantum error correction (QEC), incurring significant overhead. The requirements for fault-tolerant QEC can be reduced by leveraging properties of the underlying hardware. In this talk, we present two realizations of this principle: first, utilizing the structure of noise, and second, utilizing the ability to perform nonlocal multi-qubit gates. We first identify a new type of structured noise motivated by neutral atom qubits: biased erasure errors. We show that using qubits with dominant biased erasures improves QEC thresholds by over a factor of 8. Next, we propose a scheme to prepare high fidelity non-Clifford resource states, or magic states, for universal quantum computation in non-local architectures. Based on measuring a fold transversal operator of the surface code, this approach reduces the spacetime overhead for magic state preparation by an order of magnitude. |
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| October 15 (Wed) | Avikar Periwal | Laser-cooled molecules for quantum science | TBD |
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| November 12 (Wed) | Weiyuan Gong | Reconstructing Hamiltonians from Real-time Evolution Under Experimental Constraints | Learning the unknown interactions that govern a quantum system is crucial for quantum information processing, device benchmarking, and quantum sensing. The problem, known as Hamiltonian learning, aims at reconstructing a Hamiltonian from querying the corresponding real-time dynamics. Despite major progress in Hamiltonian learning, many rigorous protocols assume access to digital quantum gates. Yet this assumption can be inherently circular: in leading condensed-matter and cold-atom platforms, high-fidelity gates are themselves products of calibration and are only available after the native Hamiltonian H has been identified. In reality, the only robust primitives one can assume access to prior to identifying H is to prepare a Z-basis state, evolve under H for a chosen time, and measure in the Z basis. In this work, we investigate this gate-free setting and establish its learning-theoretic foundations. Our core technical tool is a local Walsh–Hadamard “parity filtering” that converts short-time, Z-basis transition data into constant-size polynomial constraints on nearby couplings, uniquely identifying the Hamiltonian up to unlearnable Z-conjugations and time-reversal symmetries. Our results demonstrate that mathematically rigorous Hamiltonian learning is achievable within the minimal experimental primitives of quantum platforms. |
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| April 8 (Wed) | Jacob Barandes | Quantum Theory, Indivisible Stochastic Processes, and the Tsirelson Bound | The textbook axioms of quantum theory, as formally laid down by Dirac and von Neumann in the 1930s, feature two categorically different rules for time evolution. When an external observer carries out a measurement, the system probabilistically collapses to a specific outcome. By contrast, when the system is not being measured, it evolves according to a rule that does not feature probabilities or a specific outcome, whether the system is closed or open to its environment. Deciding which evolution rule to apply depends on undefined terms like “external observer” and “measurement.” This manifest problem with the axioms is called the measurement problem, and it has become an increasingly pressing issue for a number of research programs, including quantum gravity. As Bohm realized in the early 1950s, decoherence by itself, without changes to the axioms, is not capable of solving the measurement problem, because decoherence alone does not produce probabilities or a specific measurement outcome. Most modern attempts to resolve the measurement problem (and other problems) rely on trying to extend the non-probabilistic form of time evolution to cover the entire theory, but these approaches run into several significant obstacles that I will describe in my talk, including rigorously accounting for Born’s formula for the probabilities of measurement outcomes. I will then lay out an alternative approach that extends the probabilistic evolution rule to cover the entire theory, down to the microscale, leading to a stochastic reformulation of quantum theory with a number of interesting features. Among these features are new ways to think about superposition, interference, entanglement, and causal influence, as well as a first-principles argument for the Tsirelson bound, which refers to the precise degree to which quantum theory violates the Bell inequality. |
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| April 9 (Thu) | Garnet Chan | Quantum Chemistry from a Classical and Quantum Algorithms Perspective | I will describe some of the intuition behind the (classical) algorithms that we use to simulate quantum chemistry today. I will then relate this to the capabilities of rigorous quantum algorithms for quantum chemistry and the prospects for quantum advantage. I will close with some discussion of future quantum heuristic algorithms for chemistry. |
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| April 9 (Thu) | Ryan LaRose | Measurement reduction, generalized Clifford groups, and neural quantum phase estimation | I will talk about three recent and ongoing results for accelerating the timeline to useful computation with Megaquop computers [1]. First, I will present new methods for the problem of efficiently and accurately estimating observables from quantum computers [2-5]. Next, I will present ongoing work generalizing Clifford groups for reducing T counts, as well as generalizing Clifford+T simulators [6]. Finally, I will present a new method to offload resources in quantum phase estimation to neural networks [7], building on previous work [8] using phase retrieval algorithms to perform phase estimation without controlled unitaries. In addition to reducing quantum hardware resources to just time evolution, this approach has embedded robustness to certain errors (algorithmic error mitigation), making current and near-term implementations feasible. References [1] Preskill, Beyond NISQ: The Megaquop Machine, ACM Trans. Quantum Comput. 6 3, 18 1-7. [2] DalFavero et al., Measurement reduction for expectation values via fine-grained commutativity, Phys. Rev. A 112, 052407 [3] Sawaya et al., Non-Clifford diagonalization for measurement shot reduction in quantum expectation value estimation, https://arxiv.org/abs/2408.11898. [4] Rowland et al., Overlapped groupings for quantum energy estimation: Maximal variance reduction and deterministic algorithms for reducing variance, in preparation. [5] LaRose et al., The cost of quantum algorithms for biochemistry: A case study in metaphosphate hydrolysis, https://arxiv.org/abs/2601.19059. [6] Belagali et al., Reducing T count by Clifford group restructuring, in preparation. [7] LaRose et al., Neural quantum phase estimation, in preparation. [8] Clinton et al., Quantum phase estimation without controlled unitaries, https://arxiv.org/abs/2410.21517. |
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| April 23 (Thu) | Mafalda Ramôa | State-of-the-Art of Adaptive Variational Quantum Algorithms | Simulating quantum systems is one of the most promising applications of quantum computers, but fully quantum algorithms for this purpose require larger and better devices than we have today. Variational quantum algorithms (VQAs) are a popular solution where the quantum computer is used exclusively to evaluate expectation values and supplemented with a classical computer that performs an optimization. The hybrid quantum-classical nature of these algorithms results in less strict quantum hardware requirements. One of the most important components of a VQA is the state preparation circuit, also called the ansatz. Without the use of suitable heuristics for its creation, the algorithm is likely to suffer from trainability issues that prevent it from finding the solution. In this talk, I will discuss the state-of-the-art of ADAPT-VQE, a promising approach for near-term quantum simulation. This algorithm creates the state preparation circuit from scratch based on measurements performed on the quantum computer during the execution, resulting in cost-efficient, noise-resilient, and accurate ansätze. |
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2024–2025 Schedule
| Date | Speaker | Title | Abstract | Recording |
|---|---|---|---|---|
| July 9 (Tue) | Jacob Barandes | Quantum Theory & Indivisible Stochastic Processes | The notion of an ‘indivisible’ stochastic process, which generalizes the textbook non-Markovian case, appeared only recently in the research literature. In this talk, I will explain how any quantum system can be understood as an indivisible stochastic process unfolding on an old-fashioned configuration space, without a fundamental role for Hilbert spaces or wave functions. On the one hand, this connection demystifies and deflates many of the exotic features of quantum systems, like interference, superposition, decoherence, entanglement, and noncommutative measurement outcomes. On the other hand, this stochastic-quantum correspondence opens up new possibilities for modeling non-Markovian stochastic processes efficiently on quantum hardware. I will also explain how this correspondence leads to a new microphysical definition of causal influences, which can be used to challenge the premises of various no-go theorems, including Bell’s theorem, with potentially significant consequences for locality and local causality. |
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| October 16 (Wed) | Yusong Bai | Designing and probing exciton quantum phase transitions in two-dimensional semiconductors | Designing and harnessing quantum phases of matter is a central goal in modern physical sciences and information technologies. These quantum phases are predominantly characterized as interacting many-body systems, where quantum phase transitions occur due to the competition between many-body Coulomb potentials and the particles’ kinetic energy. In this context, interlayer excitons in 2D transition metal dichalcogenides (TMDC) with type-II-aligned heterostructures offer a versatile bosonic system for realizing quantum phases of matter, given by their large out-of-plane dipole moments that enable long-range Coulomb interactions. By constructing a symmetric WSe2/MoSe2/WSe2 heterotrilayer, we have realized ordered phases of interlayer excitons. This ordered phase is characterized by sharp photoluminescence persisting at an exciton density of ~10¹² cm⁻², an electric-field-driven exciton Mott transition, and negligible exciton mobility. More recently, we have further regulated the competition between exciton many-body Coulomb potentials and kinetic energy by constructing a WS2/WS2/WSe2/WSe2 hetero-twisted double homobilayer. This system hosts emergent heavy excitons with distinct photoluminescence compared to that observed in regular heterobilayers, originating from the Coulomb binding of highly hybridized electrons and holes residing in each twisted homobilayer. Our experimental observations underscore that multilayer interlayer excitons can be explored as a capable model bosonic system for programming a range of quantum phases of matter. |
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| November 1 (Fri) | Jia Leo Li | Bilayer excitons as a new type of quantum particle | Quantum statistics underpins our understanding of various quantum phases of matter, a cornerstone of condensed matter research. Beyond the well-known fermions and bosons, an exotic class of particles called anyons emerges from the fractional quantum Hall effect, characterized by fractional quantum statistics. Decades of research have uncovered a profound connection between fractional braiding phases and Coulomb-driven charge fractionalization. In this talk, I will focus on a distinct quantum particle: the bilayer exciton, generally defined as a charge-neutral bound state of electrons and holes. Typically, excitons act as bosons, with their low-temperature ground state forming a Bose-Einstein condensate. I will discuss experimental observations of this condensate phase within quantum Hall bilayer systems and then delve into more exotic forms of bilayer excitons that exhibit anyonic properties. The discovery of anyonic excitons challenges two longstanding paradigms: (i) that excitons are inherently bosonic and (ii) that anyons must carry fractional electronic charge. These breakthroughs have profound implications for future quantum science research and open new avenues for potential applications in quantum computation. |
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| November 15 (Fri) | Dima Feldman | Beyond bosons and fermions: How to detect and use anyons | According to basic quantum mechanics, all particles are classified as either bosons or fermions. Yet, two-dimensional topological systems allow another type of quasiparticles called anyons. Non-Abelian anyons are particularly interesting since, if found in nature, they would allow building a topological quantum computer that needs no error correction. The talk will review recent experimental and theoretical developments in the search for anyons with the emphasis on the discovery and probes of non-Abelian particles. |
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| December 6 (Fri) | Victoria Manfredi | From Quantum Networks to Quantum Key Distribution | This talk will overview the basics of quantum networking, which relies on entanglement swapping to securely communicate quantum information (qubits) between quantum nodes. We will then focus on a key application of quantum networks: quantum key distribution (QKD), a method that enables two parties to generate and share a secret key while detecting the presence of any eavesdroppers. By leveraging a network, the range of QKD systems can be extended. Finally, we will discuss practical approaches to improving the overall key generation rate in QKD networks. |
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| March 19 (Wed) | Madelyn Cain | Low Overhead Fault Tolerance for Universal Quantum Computation | Quantum computers have the potential to solve certain computational problems much faster than their classical counterparts. Since most known applications require extremely low error rates, quantum error correction (QEC) is believed to be essential for scalable quantum computation. Here we report recent theoretical and experimental advances in QEC. Using dynamically reconfigurable arrays of neutral atoms, we demonstrate efficient manipulation and entanglement of logical qubits using transversal gates, including improving entangling gates with code distance and simulating classically complex scrambling circuits. In performing such circuits, we observe that the performance can be substantially improved by accounting for error propagation during transversal entangling gates and decoding the logical qubits jointly. We find that by using this correlated decoding technique and correctly handling feedforward operations, the number of noisy syndrome extraction rounds in universal quantum computation can be reduced from O(d) to O(1), where d is the code distance. These techniques result in new theories of fault-tolerance and in practical reductions to the cost of large-scale quantum computation. |
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| April 2 (Wed) | William Simon | Ladder Operator Block-Encoding | We describe and analyze LOBE (Ladder Operator Block-Encoding), a framework for block-encoding second-quantized ladder operators that act upon fermionic and bosonic modes. We numerically benchmark these constructions using models arising in quantum field theories including the quartic oscillator, and phi4 and Yukawa Hamiltonians on the light front. These benchmarks show that LOBE produces block-encodings with fewer non-Clifford operations, fewer block-encoding ancillae and overall number of qubits, and lower rescaling factors for various second-quantized operators as compared to block-encoding frameworks that expand the ladder operators in the Pauli basis. The LOBE constructions also demonstrate favorable scaling with respect to key parameters, including the maximum occupation of bosonic modes, the total number of fermionic and bosonic modes, and the locality of the operators. LOBE is implemented as an open source python package to enable further applications. |
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| April 9 (Wed) | Vesna Mitrović | Creating & Manipulating Entanglement in Bio Molecules at Ambient Conditions | Nature is known to be the best and most efficient engineer. By deciphering nature’s underlining mechanisms (e.g. bee’s efficient use of space: https://doi.org/10.1038/ srep28341; aerodynamics of birds influencing plane design), we could create the most efficient bio-inspired machines. Such machines would be very effective and at the same time allow for control of biological systems. However, implementing this deciphering process that governs biology requires knowledge of the most fundamental principles, believed to be quantum in nature (https://doi.org/10.1098/rsif.2018.0640). Yet, our ability to understand the underlining quantum mechanisms that govern biological systems on the most elementary level is hindered by the complexity of the biological/chemical processes coupled to dimensionality, topology and shape of the molecules. The popular belief that quantum effects do not take place in ambient conditions further inhibits the progress. Nevertheless, the biggest obstruction to making progress in quantum biology is that on a foundational level, quantum mechanics prevents us from performing fully deterministic measurements about physical systems. Any measurement of even the simplest quantum system yields intrinsically random results and irreversibly alters the system itself. Ultimately, this deceptive image hinders our ability to both advance basic knowledge and harness quantum properties of biological systems for transformative applications and control. In this talk I will discuss our recent experimental breakthrough that allowed us to directly measure entanglement in biological molecules at ambient/physiological (wet & noisy) conditions. Furthermore, I will demonstrate how such entanglement is employed to generate universal quantum gate set and universal logical quantum bits at ambient conditions. |
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| April 16 (Wed) | Brenda Rubenstein | Studying Biology on a Quantum Computer | N/A | |
| April 23 (Wed) | John Martyn | The Unreasonable Effectiveness of Polynomials in Quantum Computing | Quantum Signal Processing (QSP) has emerged as a framework for developing quantum algorithms to solve hard computational problems. At its core, QSP works by constructing and manipulating polynomials, predicated on results in classical polynomial theory. Here we survey these developments, highlighting how QSP very simply enables the design of general quantum algorithms, parallelized quantum algorithms, and randomized quantum algorithms. This remarkable success highlights how elementary concepts in classical polynomial theory, with no intrinsic grounding in quantum mechanics, can be effectively translated over to quantum computing. Going forward, this perspective suggests ample future directions for adopting polynomial theory into quantum algorithms through the lens of QSP. |
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