About

Long Doan is a professor affiliated with the University of Maryland, specializing in sociology with a focus on social psychology, emotions, and sexualities. His research encompasses a broad range of topics including the social dynamics of sexual minority populations, health and well-being disparities, family roles and responsibilities, and the impact of societal structures on marginalized groups. Doan's work often explores the intersections of formal rights and informal privileges, particularly in the context of same-sex couples, and investigates how social attitudes and emotional attributions influence perceptions and treatment of sexual minorities. His scholarship also addresses the effects of the COVID-19 pandemic on sexual minority health and family violence, highlighting the nuanced ways in which living arrangements and social environments affect mental health and well-being. Through his extensive publication record and collaborations with other scholars, Doan contributes to advancing understanding of social inequalities, identity disclosure, and the role of emotions in shaping social attitudes and behaviors.

Research topics

• Quantum mechanics
• Physics
• Statistical physics
• Condensed matter physics
• Mathematics
• Combinatorics
• Materials science
• Mathematical analysis
• Engineering
• Electrical engineering
• Theoretical physics

Selected publications

• Anomalies of Global Symmetries on the Lattice

  Physical Review X · 2026-01-02

  articleOpen access

  of global symmetries play a fundamental role in quantum many-body systems and quantum field theory (QFT). In this paper, we make a systematic analysis of —the analog of ’t Hooft anomalies in lattice systems—for which we give a precise definition. Crucially, a lattice anomaly is not a feature of a specific Hamiltonian but rather is a topological invariant of the symmetry action. The controlled setting of lattice systems allows for a systematic and rigorous treatment of lattice anomalies, shorn of the technical challenges of QFT. We find that lattice anomalies reproduce the expected properties of QFT anomalies in many ways but also have crucial differences. In particular, lattice anomalies and QFT anomalies are not, contrary to a common expectation, in one-to-one correspondence, and there can be nontrivial anomalies on the lattice that are : They admit symmetric trivial gapped ground states and map to trivial QFT anomalies at low energies. Nevertheless, we show that lattice anomalies (including IR-trivial ones) have a number of interesting consequences in their own right, including connections to commuting projector models, phases of many-body-localized systems, and quantum cellular automata. We make substantial progress on the classification of lattice anomalies and develop several theoretical tools to characterize their consequences on symmetric Hamiltonians. Our work places symmetries of quantum many-body lattice systems into a unified theoretical framework and may also suggest new perspectives on symmetries in QFT.

  PublisherDOI

• Probing Hilbert space fragmentation using controlled dephasing

  arXiv (Cornell University) · 2025-06-16

  preprintOpen access

  Dynamical constraints in many-body quantum systems can lead to Hilbert space fragmentation, wherein the system's evolution is restricted to small subspaces of Hilbert space called Krylov sectors. However, unitary dynamics within individual sectors may also be slow or non-ergodic, which limits experiments' ability to measure the properties of the entire sector. We show that additional controlled dephasing reliably mixes the system within a single Krylov sector, and that simple observables can differentiate these sectors. For example, in the strongly interacting XXZ chain with dephasing, the spin imbalance between even and odd sublattices distinguishes sectors. For appropriate choices of initial states, the imbalance begins positive, decays to a negative minimum value at intermediate times, and eventually returns to zero. The minimum reflects the average imbalance of the Krylov sector associated to the initial state. We compute the size of the minimum analytically in the limit of strong interactions, and validate our results with simulations at experimentally relevant interaction strengths.

  PublisherDOI

• Topological phases of many-body localized systems: Beyond eigenstate order

  Physical review. B./Physical review. B · 2025-10-14 · 2 citations

  article1st authorCorresponding

  Many-body localization (MBL) lends remarkable robustness to nonequilibrium phases of matter. Such phases can show topological and symmetry-breaking order in their ground and excited states, but they may also belong to an anomalous localized topological phase (ALT phase). All eigenstates in an ALT phase are trivial, in that they can be deformed to product states, but the entire Hamiltonian cannot be deformed to a trivial localized model without going through a delocalization transition. Using a correspondence between MBL phases with short-ranged entanglement and locality-preserving unitaries, called quantum cellular automata (QCA), we reduce the classification of ALT phases to that of QCA. This method extends to periodically (Floquet) and quasiperiodically driven ALT phases, and captures anomalous Floquet phases within the same framework as static phases. We considerably develop the study of the topology of QCA, allowing us to classify static and driven ALT phases in low dimensions. The QCA framework further generalizes to include symmetry-enriched ALT phases (SALT phases), which we also classify in low dimensions, and provides a large class of soluble models suitable for realization in quantum simulators. In systematizing the study of ALT phases, we both greatly extend the classification of interacting nonequilibrium systems and clarify a confusion in the literature which implicitly equates nontrivial Hamiltonians with nontrivial ground states.

  PublisherDOI

• Autonomous Stabilization of Floquet States Using Static Dissipation

  Physical Review X · 2025-07-07 · 2 citations

  articleOpen access

  Floquet engineering, in which the properties of a quantum system are modified through the application of strong periodic drives, is an indispensable tool in atomic and condensed matter systems. However, it is inevitably limited by intrinsic heating processes. We describe a simple autonomous scheme, which exploits a coupling between the driven system and a lossy auxiliary, to cool large classes of Floquet systems into desired states. We present experimental and theoretical evidence for the stabilization of a chosen state in a strongly modulated transmon qubit coupled to an auxiliary microwave cavity with fixed frequency and photon loss. The scheme naturally extends to Floquet systems with multiple degrees of freedom. As an example, we demonstrate the stabilization of topological photon pumping in a driven cavity-QED system numerically. The coupling to the auxiliary cavity increases the average photon current and the fidelity of nonclassical states, such as high-photon-number Fock states, that can be prepared in the system cavity.

  PublisherDOI

• Strong-driving toolkit for topological Floquet energy pumps with superconducting circuits

  Physical review. A/Physical review, A · 2025-10-06

  article

  Topological Floquet energy pumps, which use periodic driving to create a topologically protected quantized energy current, have been proposed and studied theoretically, but have never been observed directly. Previous work [D. M. Long et al., Phys. Rev. Lett. 128, 183602 (2022)] proposed that such a pump could be realized with a strongly driven superconducting qubit coupled to a cavity. Here, we experimentally demonstrate that the proposed hierarchy of energy scales and drive frequencies can be realized using a transmon qubit. We develop an experimental toolkit to realize the adiabatic driving field required for energy pumping using coordinated frequency modulation of the transmon and amplitude modulation of an applied resonant microwave drive. With this toolkit, we measure adiabatic evolution of the qubit under the applied field for times comparable to ${T}_{1}$, which far exceed the bare qubit dephasing time. This result paves the way for direct experimental observation of topological energy pumping.

  PublisherDOI

• Probing Hilbert space fragmentation using controlled dephasing

  Physical review. B./Physical review. B · 2025-10-09 · 1 citations

  articleOpen access

  Dynamical constraints in many-body quantum systems can lead to Hilbert space fragmentation, wherein the system's evolution is restricted to small subspaces of Hilbert space called Krylov sectors. However, unitary dynamics within individual sectors may also be slow or nonergodic, which limits experiments' ability to measure the properties of the entire sector. We show that additional controlled dephasing reliably mixes the system within a single Krylov sector, and that simple observables can differentiate these sectors. For example, in the strongly interacting XXZ chain with dephasing, the spin imbalance between even and odd sublattices distinguishes sectors. For appropriate choices of initial states, the imbalance begins positive, decays to a negative minimum value at intermediate times, and eventually returns to zero. The minimum reflects the average imbalance of the Krylov sector associated to the initial state. We compute the size of the minimum analytically in the limit of strong interactions, and validate our results with simulations at experimentally relevant interaction strengths.

  PublisherOA PDFDOI

• Edge theories for anyon condensation phase transitions

  Physical review. B./Physical review. B · 2024-02-20 · 4 citations

  article1st authorCorresponding

  The algebraic tools used to study topological phases of matter are not clearly suited to studying processes in which the bulk energy gap closes, such as phase transitions. We describe an elementary two edge thought experiment, which reveals the effect of an anyon condensation phase transition on the robust edge properties of a sample, bypassing a limitation of the algebraic description. In particular, the two edge construction allows some edge degrees of freedom to be tracked through the transition, despite the bulk gap closing. The two edge model demonstrates that bulk anyon condensation induces symmetry breaking in the edge model. Further, the construction recovers the expected result that the number of chiral current carrying modes at the edge cannot change through anyon condensation. We illustrate the construction through detailed analysis of anyon condensation transitions in an achiral phase, the toric code, and in chiral phases, the Kitaev spin liquids.

  PublisherDOI

• Topological Phases of Many-Body Localized Systems: Beyond Eigenstate Order

  arXiv (Cornell University) · 2024-08-01

  preprintOpen access1st authorCorresponding

  Many-body localization (MBL) lends remarkable robustness to nonequilibrium phases of matter. Such phases can show topological and symmetry breaking order in their ground and excited states, but they may also belong to an anomalous localized topological phase (ALT phase). All eigenstates in an ALT phase are trivial, in that they can be deformed to product states, but the entire Hamiltonian cannot be deformed to a trivial localized model without going through a delocalization transition. Using a correspondence between MBL phases with short-ranged entanglement and locality preserving unitaries - called quantum cellular automata (QCA) - we reduce the classification of ALT phases to that of QCA. This method extends to periodically (Floquet) and quasiperiodically driven ALT phases, and captures anomalous Floquet phases within the same framework as static phases. We considerably develop the study of the topology of QCA, allowing us to classify static and driven ALT phases in low dimensions. The QCA framework further generalizes to include symmetry-enriched ALT phases (SALT phases) - which we also classify in low dimensions - and provides a large class of soluble models suitable for realization in quantum simulators. In systematizing the study of ALT phases, we both greatly extend the classification of interacting nonequilibrium systems and clarify a confusion in the literature which implicitly equates nontrivial Hamiltonians with nontrivial ground states.

  PublisherOA PDFDOI

• Absence of disordered Thouless pumps at finite frequency

  Physical review. B./Physical review. B · 2024-11-04 · 1 citations

  article

  A Thouless pump is a slowly driven one-dimensional band insulator, which pumps charge at a quantized rate. Previous study showed that pumping persists in weakly disordered chains, and separately in clean chains at finite drive frequency. We study the interplay of disorder and finite frequency, and show that the pump rate always decays to zero because of nonadiabatic transitions between the instantaneous eigenstates. However, the decay is slow, occurring on a timescale that is exponentially large in the period of the drive. In the adiabatic limit, the band gap in the instantaneous spectrum closes at a critical disorder strength above which pumping ceases. We predict the scaling of the pump rate around this transition from a model of scattering between rare states near the band edges. Our predictions can be experimentally tested in ultracold atomic and photonic platforms.

  PublisherDOI

• Phenomenology of the Prethermal Many-Body Localized Regime

  Physical Review Letters · 2023 · 56 citations

  1st authorCorresponding
  • Physics
  • Statistical physics
  • Quantum mechanics

  The dynamical phase diagram of interacting disordered systems has seen substantial revision over the past few years. Theory must now account for a large prethermal many-body localized regime in which thermalization is extremely slow, but not completely arrested. We derive a quantitative description of these dynamics in short-ranged one-dimensional systems using a model of successive many-body resonances. The model explains the decay timescale of mean autocorrelators, the functional form of the decay-a stretched exponential-and relates the value of the stretch exponent to the broad distribution of resonance timescales. The Jacobi method of matrix diagonalization provides numerical access to this distribution, as well as a conceptual framework for our analysis. The resonance model correctly predicts the stretch exponents for several models in the literature. Successive resonances may also underlie slow thermalization in strongly disordered systems in higher dimensions, or with long-range interactions.

  PublisherOA PDFDOI

Frequent coauthors

• Andrew C. Doherty

  University of Sydney

  24 shared

• Anushya Chandran

  Harvard University

  16 shared

• Philip J. D. Crowley

  Harvard University

  13 shared

• Richard Kueng

  8 shared

• Steven T. Flammia

  4 shared

• S. Das Sarma

  Joint Quantum Institute

  4 shared

• Dominik Vuina

  4 shared

• Yi-Ting Tu

  Joint Quantum Institute

  4 shared

Labs

• Long DoanPI

Education

• Ph.D., Physics

  Boston University

  2023

• Bachelor of Science (Advanced) (Honours), Physics

  University of Sydney

  2017