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1. Efficiently Verifiable Quantum Advantage on Near-Term Analog Quantum Simulators

   https://doi.org/10.1103/PRXQuantum.6.010341  

   Liu, Zhenning; Devulapalli, Dhruv; Hangleiter, Dominik; Liu, Yi-Kai; Kollár, Alicia J; Gorshkov, Alexey V; Childs, Andrew M (March 2025, PRX Quantum)

   Existing schemes for demonstrating quantum computational advantage are subject to various practical restrictions, including the hardness of verification and challenges in experimental implementation. Meanwhile, analog quantum simulators have been realized in many experiments to study novel physics. In this work, we propose a quantum advantage protocol based on verification of an analog quantum simulation, in which the verifier need only run an $O\left({\lambda }^2\right)$-time classical computation, and the prover need only prepare $O\left(1\right)$samples of a history state and perform $O\left({\lambda }^2\right)$single-qubit measurements, for a security parameter $\lambda$. We also propose a near-term feasible strategy for honest provers and discuss potential experimental realizations. Published by the American Physical Society2025 

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2. Low leakage current in heteroepitaxial ${\mathrm{Al}}_{0.7}{\mathrm{Sc}}_{0.3}\mathrm{N}$ ferroelectric films on $\mathrm{Ga}\mathrm{N}$

   https://doi.org/10.1103/PhysRevApplied.23.014036  

   Yazawa, Keisuke; Evans, Charles; Dickey, Elizabeth C; Tellekamp, M Brooks; Brennecka, Geoff L; Zakutayev, Andriy (January 2025, Physical Review Applied)

   Wurtzite $(\mathrm{Al},\mathrm{Sc})\mathrm{N}$ferroelectrics are attractive for microelectronics applications due to their chemical and structural compatibility with wurtzite semiconductors, such as $\mathrm{Ga}\mathrm{N}$and $(\mathrm{Al},\mathrm{Ga})\mathrm{N}$. However, the leakage current in epitaxial stacks reported to date should be reduced for reliable device operation. Here, we demonstrate low leakage current in epitaxial ${\mathrm{Al}}_{0.7}{\mathrm{Sc}}_{0.3}\mathrm{N}$films on $\mathrm{Ga}\mathrm{N}$with well-saturated ferroelectric hysteresis loops that are orders of magnitude lower (i.e., 0.07 A ${\mathrm{cm}}^{-2}$) than previously reported films (1–19 A ${\mathrm{cm}}^{-2}$) having similar or better structural characteristics. We also show that, for these high-quality epitaxial $(\mathrm{Al},\mathrm{Sc})\mathrm{N}$films, structural quality (edge and screw dislocations), as measured by diffraction techniques, is not the dominant contributor to leakage. Instead, the small leakage in our films is limited by thermionic emission across the interfaces, which is distinct from the large leakage due to trap-mediated bulk transport in the previously reported $(\mathrm{Al},\mathrm{Sc})\mathrm{N}$films. To support this conclusion, we show that ${\mathrm{Al}}_{0.7}{\mathrm{Sc}}_{0.3}\mathrm{N}$on lattice-matched ${\mathrm{In}}_{0.18}{\mathrm{Ga}}_{0.82}\mathrm{N}$buffers with improved structural characteristics but higher interface roughness exhibit increased leakage characteristics. This demonstration of low leakage current in heteroepitaxial $(\mathrm{Al},\mathrm{Sc})\mathrm{N}$films and understanding of the importance of interface barrier and surface roughness can guide further efforts toward improving the reliability of wurtzite ferroelectric devices. Published by the American Physical Society2025 

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3. A QCD $R$ -axion

   https://doi.org/10.1103/PhysRevD.111.015048  

   Unwin, James; Yildirim, Tom (January 2025, Physical Review D)

   $R$-parity can be extended to a continuous global $\mathrm{U}(1{)}_R$symmetry. We investigate whether an anomalous $\mathrm{U}(1{)}_R$can be identified as the Peccei-Quinn symmetry suitable for solving the strong $CP$problem within supersymmetric extensions of the Standard Model. In this case, $\mathrm{U}(1{)}_R$is broken at some intermediate scale and the quantum chromodynamics axion is the $R$-axion. Moreover, the $R$-symmetry can potentially be gauged via the Green-Schwarz mechanism within completions to supergravity, in order to evade the axion quality problem. Obstacles to realizing this scenario are highlighted and phenomenologically viable approaches are identified. Published by the American Physical Society2025 

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4. Noninvertible Symmetry-Protected Topological Order in a Group-Based Cluster State

   https://doi.org/10.1103/PhysRevX.15.011058  

   Fechisin, Christopher; Tantivasadakarn, Nathanan; Albert, Victor V (March 2025, Physical Review X)

   Despite growing interest in beyond-group symmetries in quantum condensed matter systems, there are relatively few microscopic lattice models explicitly realizing these symmetries, and many phenomena have yet to be studied at the microscopic level. We introduce a one-dimensional stabilizer Hamiltonian composed of group-based Pauli operators whose ground state is a $G\times \mathrm{Rep}\left(G\right)$-symmetric state: the $G$-cluster state introduced by Brell []. We show that this state lies in a symmetry-protected topological (SPT) phase protected by $G\times \mathrm{Rep}\left(G\right)$symmetry, distinct from the symmetric product state by a duality argument. We identify several signatures of SPT order, namely, protected edge modes, string order parameters, and topological response. We discuss how $G$-cluster states may be used as a universal resource for measurement-based quantum computation, explicitly working out the case where $G$is a semidirect product of Abelian groups. Published by the American Physical Society2025 

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5. Optimization Tools for Distance-Preserving Flag Fault-Tolerant Error Correction

   https://doi.org/10.1103/PRXQuantum.5.020336  

   Pato, Balint; Tansuwannont, Theerapat; Huang, Shilin; Brown, Kenneth R (May 2024, PRX Quantum)

   Lookup-table decoding is fast and distance preserving, making it attractive for near-term quantum computer architectures with small-distance quantum error-correcting codes. In this work, we develop several optimization tools that can potentially reduce the space and time overhead required for flag fault-tolerant quantum error correction (FTQEC) with lookup-table decoding on Calderbank-Shor-Steane (CSS) codes. Our techniques include the compact lookup-table construction, the meet-in-the-middle technique, the adaptive time decoding for flag FTQEC, the classical processing technique for flag information, and the separate $X$- and $Z$-counting technique. We evaluate the performance of our tools using numerical simulation of hexagonal color codes of distances 3, 5, 7, and 9 under circuit-level noise. Combining all tools can result in an increase of more than an order of magnitude in the pseudothreshold for the hexagonal color code of distance 9, from $(1.34\pm 0.01)\times {10}^{-4}$to $(1.43\pm 0.07)\times {10}^{-3}$. Published by the American Physical Society2024 

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