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David Dentelski

Publications and source records attributed to David Dentelski.

10 recordsLinked to original sources
arXiv2026

Blueprint for a fault-tolerant compound photon-atom quantum architecture

Fault-tolerant quantum computing requires architectures that simultaneously address scalability, connectivity, and error correction under realistic noise constraints. We present a compound photonic-atomic quantum computing platform that uses cavity QED to realize near-deterministic entangling operations between flying photonic qubits and stationary atomic qubits. Photons provide long-range connectivity and scalability via measurement-based quantum computing (MBQC), while atoms supply reusable, near-deterministic resources for photon generation and entanglement, overcoming the inefficiency of purely photonic platforms. The core primitive is a symmetrized Duan-Kimble photon-atom controlled-phase (CZ) gate, robust to experimental imperfections and high-fidelity. Using single $^{87}$Rb atoms coupled to optical cavities, we give protocols for state preparation, measurement, photon generation, and entangling gates on tens-of-nanosecond timescales, and show how large-scale cluster states with effectively unrestricted connectivity and reduced overhead can be generated through atomic reuse. We analyze fault tolerance on the Raussendorf-Harrington-Goyal (RHG) lattice with a hardware-aware noise model capturing asymmetric loss and correlated photonic-atomic errors. Logical memory simulations yield a photon-loss threshold near $2.6\%$ per physical gate ($\sim$15\% total per trajectory). The full Clifford set -- Hadamard, phase, CNOT -- is implementable transversally or fold-transversally at thresholds matching the identity channel, and we propose two non-Clifford resource-state routes (code teleportation and magic state cultivation) within the foliated cluster-state architecture.

quant-ph↗
arXiv2026

Neural network decoder confidence as a learned proxy for the logical gap

To utilize quantum error-correcting codes, a decoder must infer the logical sector from the measured syndrome. Beyond a hard logical decision, some decoders provide soft information estimating its reliability. For minimum-weight perfect matching (MWPM), a common confidence measure is the complementary, or logical, gap. Neural-network decoders trained with binary cross entropy naturally output a different score, the logit, whose relation to the matching gap remains unclear. Here, we test whether the logit of a graph neural network (GNN) decoder behaves as a learned proxy for the logical gap. Using a pretrained GNN for the rotated surface code under uniform circuit-level noise [PRR, 7(2):023181, 2025], we compare its logit with the MWPM gap shot by shot on identical syndromes. The native GNN decoder-logit pair yields a lower post-selected logical error rate than the native MWPM decoder-gap pair over the operationally relevant range of acceptance rates. Exchanging the scores between decoders isolates score discrimination from hard-decision accuracy and shows that both contribute to the advantage. At larger distances each score best ranks failures of its own decoder, whereas at small distance, where the bounded matching gap saturates, the learned confidence better discriminates MWPM failures than the gap itself. Finally, GNN confidence is substantially better described by the posterior logistic form implied by an ideal log-likelihood ratio, while the MWPM gap shows systematic departures. Thus, a neural-network decoder trained only on syndromes and logical labels learns a gap-like confidence proxy whose native scale more closely follows the expected posterior calibration form, supporting learned soft output when MWPM gap estimates are unavailable, costly, or insufficiently expressive.

quant-ph↗
arXiv2023

Proximitized insulators from disordered superconductors

We present an experimental study of bilayers of a disordered Ag metal layer close to the metal-insulator transition and an Indium Oxide film which is on the insulating side of the superconductor-insulator-transition. Our results show that superconducting fluctuations within the indium-oxide film, that proximitize the underlying metal layer, induce insulating rather than superconducting behavior. This is ascribed to suppression of density of states (due to the superconducting energy gap) for quasiparticles in the proximitized regions. Our results present a novel manifestation of the proximity effect phenomenon and provide important insight into the nature of the insulating phase of the disorder driven superconductor-insulator-transition.

cond-mat.supr-con↗
arXiv2021

Statistical Floquet prethermalization of the Bose-Hubbard model

The manipulation of many-body systems often involves time-dependent forces that cause unwanted heating. One strategy to suppress heating is to use time-periodic (Floquet) forces at large driving frequencies. For quantum spin systems with bounded spectra, it was shown rigorously that the heating rate is exponentially small in the driving frequency. Recently, the exponential suppression of heating has also been observed in an experiment with ultracold atoms, realizing a periodically driven Bose-Hubbard model. This model has an unbounded spectrum and, hence, is beyond the reach of previous theoretical approaches. Here, we study this model with two semiclassical approaches valid, respectively, at large and weak interaction strengths. In both limits, we compute the heating rates by studying the statistical probability to encounter a many-body resonance, and obtain a quantitative agreement with the exact diagonalization of the quantum model. Our approach demonstrates the relevance of statistical arguments to Floquet perthermalization of interacting many-body quantum systems.

cond-mat.quant-gas↗
arXiv2021

Robust Gapless Superconductivity in 4Hb-TaS$_2$

The superconducting TMD 4Hb-TaS$_2$ consists of alternating layers of H and T structures, which in their bulk form are metallic and Mott-insulating, respectively. Recently, this compound has been proposed as a candidate chiral superconductor, due to an observed enhancement of the muon spin relaxation at $T_c$. 4Hb-TaS$_2$ also exhibits a puzzling $T$-linear specific heat at low temperatures, which is unlikely to be caused by disorder. Elucidating the origin of this behavior is an essential step in discerning the true nature of the superconducting ground state. Here, we propose a simple model that attributes the $T$-linear specific heat to the emergence of a robust multi-band gapless superconducting state. We show that an extended regime of gapless superconductivity naturally appears when the pair-breaking scattering rate on distinct Fermi-surface pockets differs significantly, and the pairing interaction is predominantly intra-pocket. Using a tight-binding model derived from first-principle calculations, we show that the pair-breaking scattering rate promoted by slow magnetic fluctuations on the T layers, which arise from proximity to a Mott transition, can be significantly different in the various H-layer dominated Fermi pockets depending on their hybridization with T-layer states. Thus, our results suggest that the ground state of 4Hb-TaS$_2$ consists of Fermi pockets displaying gapless superconductivity, which are shunted by superconducting Fermi pockets that are nearly decoupled from the T-layers.

cond-mat.supr-con↗
arXiv2020

The effect of interorbital scattering on superconductivity in doped Dirac materials

Unconventional superconductivity has been discovered in a variety of doped materials, including topological insulators, semimetals and twisted bilayers. A unifying property of these systems is strong orbital hybridization, which involves pairing of states with non-trivial Bloch wave functions. In contrast to naive expectation, many of these superconductors are relatively resilient to disorder. Here we study the effects of a generic disorder on superconductivity in doped 3D Dirac systems, which serve as a paradigmatic example for the dispersion near a band crossing point. We argue that due to strong orbital hybridization, interorbital scattering processes are naturally present and must be taken into account. We calculate the reduction of the critical temperature for a variety of pairing states and scattering channels using Abrikosov-Gor'kov theory. In that way, the role of disorder is captured by a single parameter $Γ$, the pair scattering rate. This procedure is very general and can be readily applied to different band structures and disorder configurations. Our results show that interorbital scattering has a significant effect on superconductivity, where the robustness of different pairing states highly depends on the relative strength of the different interorbital scattering channels. Our analysis also reveals a protection, analogous to the Anderson's theorem, of the odd-parity pairing state with total angular momentum zero (the B-phase of superfluid $^3$He). This odd-pairty state is a singlet of partners under $\mathcal{CT}$ symmetry (rather than $\mathcal{T}$ symmetry in the standard Anderson's theory), where $\mathcal{C}$ and $\mathcal{T}$ are chiral and time-reversal symmetries, respectively. As a result, it is protected against any disorder potential that respects $\mathcal{CT}$ symmetry, which includes a family of time-reversal odd (magnetic) impurities.

cond-mat.supr-con↗
arXiv2020

Minimal model of charge and pairing density waves in X-ray scattering experiments

Competing density waves play an important role in the mystery of high-temperature superconductors. In spite of the large amount of experimental evidence, the fundamental question of whether these modulations represent charge or pairing density waves (CDWs or PDWs) is still debated. Here we present a method to answer this question using momentum and energy-resolved resonant X-ray scattering maps. Starting from a minimal model of density waves in superconductors, we identify distinctive signatures of incipient CDWs and PDWs. The generality of our approach is confirmed by a self-consistent solution of an extended Hubbard model with attractive interaction. By considering the available experimental data, we claim that the spatial modulations in cuprates have a predominant PDW character. Our work paves the way for using X-ray to identify competing and intertwined orders in superconducting materials.

cond-mat.supr-con↗
arXiv2017

Tunneling probe of fluctuating superconductivity in disordered thin films

Disordered thin films close to the superconducting-insulating phase transition (SIT) hold the key to understanding quantum phase transition in strongly correlated materials. The SIT is governed by superconducting quantum fluctuations, which can be revealed for example by tunneling measurements. These experiments detect a spectral gap, accompanied by suppressed coherence peaks that do not fit the BCS prediction. To explain these observations, we consider the effect of finite-range superconducting fluctuations on the density of states, focusing on the insulating side of the SIT. We perform a controlled diagrammatic resummation and derive analytic expressions for the tunneling differential conductance. We find that short-range superconducting fluctuations suppress the coherence peaks, even in the presence of long-range correlations. Our approach offers a quantitative description of existing measurements on disordered thin films and accounts for tunneling spectra with suppressed coherence peaks observed, for example, in the pseudo gap regime of high-temperature superconductors.

cond-mat.dis-nn↗
arXiv2016

Friedel Oscillations as a Probe of Fermionic Quasiparticles

When immersed in a see of cold electrons, local impurities give rise to density modulations known as Friedel oscillations. In spite of the generality of this phenomenon, the exact shape of these modulations is usually computed only for non-interacting electrons with a quadratic dispersion relation. In actual materials, one needs to take into account several additional factors, such as (i) the details of the band structure, (ii) the lifetime of quasiparticles, (iii) in superconductors, the presence of a pairing gap. Studying how these effects influence Friedel oscillations is a viable way to access the properties of fermionic excitations in strongly-correlated materials. In this work we analyze the signatures of Friedel oscillations in STM and X-ray scattering experiments, focusing on the concrete example of cuprates superconductors. A detailed comparison with recent experiments reveals a rich interplay between local modulation of the chemical potential and of the pairing gap.

cond-mat.str-el↗