Quantum Error Correction: Surface Code & Fault-Tolerant Computing
Quantum error correction news: logical qubits, surface code, fault-tolerant quantum computing, QEC. Error mitigation & suppression.
Quantum error correction (QEC) is the critical enabler for fault-tolerant quantum computing, protecting quantum information from environmental noise through redundant encoding across multiple physical qubits. Recent breakthroughs demonstrated below-threshold error correction where logical qubit error rates fall below physical qubit rates.
The 2D surface code is the leading QEC approach due to high error threshold (~1%), local nearest-neighbor interactions, and compatibility with superconducting chip designs. Recent breakthroughs include Google's Willow demonstrating below-threshold surface code scaling, and IBM's Heavy Hex optimizing qubit connectivity for surface code implementation.
India's Quantum Error Correction Research
India's National Quantum Mission includes quantum error correction in its basic science research component. The Foundation for QC Innovation at IISc Bengaluru addresses error correction as part of its quantum computing development. The Harish-Chandra Research Institute (HRI) and Institute of Mathematical Sciences (IMSc) conduct theoretical research on quantum error correction codes.
The NQM targets developing intermediate-scale quantum computers with 50-1000 physical qubits, requiring error mitigation and eventually error correction to achieve quantum advantage. The mission includes development of indigenous control electronics and error mitigation techniques.
quantum-computingBit flips, saturation, and quantum chaos in dissipative cat qubits
--> Quantum Physics arXiv:2605.24100 (quant-ph) [Submitted on 22 May 2026] Title:Bit flips, saturation, and quantum chaos in dissipative cat qubits Authors:Filippo Ferrari, Joachim Cohen, Vincenzo Savona, Fabrizio Minganti View a PDF of the paper titled Bit flips, saturation, and quantum chaos in dissipative cat qubits, by Filippo Ferrari and Joachim Cohen and Vincenzo Savona and Fabrizio Minganti View PDF HTML (experimental) Abstract:Bosonic cat qubits promise hardware-efficient quantum error correction because their logical bit-flip rate is exponentially suppressed with the photon number of the cat state. However, several experiments report a saturation of this suppression at large photon numbers, thus limiting the achievable protection. Combining quantum-trajectory simulations, semiclassical analysis, and Liouvillian spectral methods, we investigate the properties of bit flips in realistic dissipative cat qubits, where a memory mode hosting quantum information interacts with a dissipative buffer cavity. We show that bit flips are dynamical processes inherently involving both the memory and buffer, and therefore cannot be captured by single-mode approximate descriptions. We identify a reflection symmetry, resulting in a phase-locking condition at the semiclassical level and for quantum trajectories, as the main requirement for regular bit-flip dynamics. Its breakdown is the origin of the saturation, and we find that it occurs when two conditions are met. First, the adiabatic approximation, where the state of the buffer instantaneously follows that of the memory, must not be valid, which typically happens at large photon numbers. Second, key parameters such as the cross-Kerr interaction and dephasing must be present, leading to irregular dynamics in which memory fluctuations are amplified by the buffer during bit flips. In this regime, we find that bit flips manifest as chaotic bursts within otherwise regular dynamics, as evidenced by both changes in the topology o
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quantum-computingQuantum Sensing and Quantum Error Correction: Two Sides of the Same Coin
--> Quantum Physics arXiv:2605.24120 (quant-ph) [Submitted on 22 May 2026] Title:Quantum Sensing and Quantum Error Correction: Two Sides of the Same Coin Authors:Zhuoran Bao, Daniel F. V. James View a PDF of the paper titled Quantum Sensing and Quantum Error Correction: Two Sides of the Same Coin, by Zhuoran Bao and Daniel F. V. James View PDF HTML (experimental) Abstract:Quantum metrology has been making amazing progress in the past decades. It is always in researchers' interest to search for new optimal states that improve parameter estimation. In this paper, we point out a connection between the code's error correcting capacity and its ability to act as a sensor. We backed our claim by providing an example that relates the Absorption emission code to the sensor state for arbitrary state rotation. It is hoped that, in building such a unified theory, one can draw inspiration from error correction to develop promising quantum sensors. Comments: Subjects: Quantum Physics (quant-ph); Optics (physics.optics) Cite as: arXiv:2605.24120 [quant-ph] (or arXiv:2605.24120v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2605.24120 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Zhuoran Bao [view email] [v1] Fri, 22 May 2026 18:25:54 UTC (17 KB) Full-text links: Access Paper: View a PDF of the paper titled Quantum Sensing and Quantum Error Correction: Two Sides of the Same Coin, by Zhuoran Bao and Daniel F. V. JamesView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph < prev | next > new | recent | 2026-05 Change to browse by: physics physics.optics References & Citations INSPIRE HEP NASA ADSGoogle Scholar Semantic Scholar export BibTeX citation Loading... BibTeX formatted citation × loading... Data provided by: Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the
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quantum-computingOptimal Quantum Differential Privacy via Fisher Information Spectral Analysis
--> Quantum Physics arXiv:2605.24166 (quant-ph) [Submitted on 22 May 2026] Title:Optimal Quantum Differential Privacy via Fisher Information Spectral Analysis Authors:Justice Owusu Agyemang, Jerry John Kponyo, Elliot Amponsah, Godfred Manu Addo Boakye View a PDF of the paper titled Optimal Quantum Differential Privacy via Fisher Information Spectral Analysis, by Justice Owusu Agyemang and 3 other authors View PDF HTML (experimental) Abstract:The Quantum Fisher Information (QFI) metric governs a fundamental duality: it quantifies both how precisely a parameter can be estimated (metrology) and how distinguishable two quantum states are (privacy). We exploit this duality to establish a geometry-aware framework for quantum differential privacy (DP) that replaces isotropic depolarizing noise with direction-dependent noise aligned to the QFI eigenstructure of the quantum embedding. We prove six principal theorems: (1) the minimax-optimal mechanism concentrates the noise budget in the dominant QFI eigenmode, achieving $\varepsilon = (\Delta^2/2)\lambda_{\max}(1-c\gamma)$ with $O(d/\lambda_{\max})$ advantage; (2) mixed-state QFI decomposition reveals that dephasing in the adversary's basis $\textit{increases}$ accessible information, while misaligned-basis dephasing provides constructive privacy amplification from hardware noise; (3) a tight privacy $-$ utility uncertainty relation $\varepsilon \cdot (1 - F) \ge \frac{\Delta^2}{2}\frac{\operatorname{Tr}(F)}{d}$; (4) adaptive QFI estimation converging at $O(1/\sqrt{n})$ yields $1.92\times$ tighter bounds; (5) QFI-aligned composition saturates at $O(1)$ versus $O(k)$ for standard composition; and (6) hardware noise can be harnessed for privacy amplification. Adversarial vulnerabilities, Wasserstein guarantees, subspace projection, and a zero-knowledge audit protocol follow as corollaries. Results are validated on Qiskit Aer GPU simulations, IBM Quantum hardware (ibm_fez, 156 qubits), and against classical DP baselines, achiev
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Towards Scalable Quaternary Message-Passing Decoding for Quantum Error Correction
--> Quantum Physics arXiv:2605.24177 (quant-ph) [Submitted on 22 May 2026] Title:Towards Scalable Quaternary Message-Passing Decoding for Quantum Error Correction Authors:Boqing Zhang, Henry D. Pfister, Hanwen Yao, Siyuan Niu View a PDF of the paper titled Towards Scalable Quaternary Message-Passing Decoding for Quantum Error Correction, by Boqing Zhang and 3 other authors View PDF Abstract:The scalability and interpretability of message-passing (MP) decoding, such as (quaternary) Belief Propagation, remain open challenges in quantum error correction. Even for surface codes, arguably the first testbed for decoding methods, studies of improved MP decoders have mostly been restricted to small distances ($d \lesssim 19$). Moreover, the mismatch with established message-passing theory limits the decoder's interpretability, making it unclear whether MP decoding can sustain its effectiveness at large system sizes. This work takes a step toward a more principled and interpretable MP decoding framework, with the goal of making MP-based decoding more reliable and bridging theory and practice. We introduce a dilution method, which allows a quaternary Min-Sum (MS) decoder to exhibit an apparent depolarizing threshold of $16\%$ up to distance $20$, outperforming Minimum-Weight Perfect Matching in finite-length regimes. Notably, for $X$-noise, the standard MS decoder under dilution has worst-case complexity $O(N \log^2 d)$ and outperforms BP-OSD at $d=65$. The observed $\sim 9\%$ threshold may correspond to a true asymptotic threshold. Finally, we give a graph-dilution argument that interprets the success of the dilution method and offers insight into when MP algorithms can genuinely scale. Taken together, these results provide encouraging progress toward scalable and interpretable MP decoding in quantum error correction. Subjects: Quantum Physics (quant-ph); Information Theory (cs.IT) Cite as: arXiv:2605.24177 [quant-ph] (or arXiv:2605.24177v1 [quant-ph] for this version
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quantum-computingQuantum-Adaptive KS($\varphi$): A Parameterized Three-Qubit Gate Family Embedding Toffoli with Measurement-Free Phase Kickback and Intrinsic Error Non-Amplification
--> Quantum Physics arXiv:2605.24182 (quant-ph) [Submitted on 22 May 2026] Title:Quantum-Adaptive KS($φ$): A Parameterized Three-Qubit Gate Family Embedding Toffoli with Measurement-Free Phase Kickback and Intrinsic Error Non-Amplification Authors:Kripa Sankaranarayanan, Marek Perkowski View a PDF of the paper titled Quantum-Adaptive KS($\varphi$): A Parameterized Three-Qubit Gate Family Embedding Toffoli with Measurement-Free Phase Kickback and Intrinsic Error Non-Amplification, by Kripa Sankaranarayanan and 1 other authors View PDF Abstract:We introduce Quantum-Adaptive KS($\varphi$) ($K$ = kickback, $S$ = sandwich), a parameterized three-qubit gate family that structurally embeds the Toffoli (CCX) gate within two additional components: (1)a palindromic Hadamard sandwich on the first control qubit $q_0$ that conjugates $Z$-type errors to $X$-type in the CCX frame, providing simultaneous sensitivity to both error types without ancilla overhead; and (2)a controlled-phase (CP) gate whose quantum phase kickback propagates post-CCX target-state information into the control-qubit phase without measurement. The term Quantum- Adaptive refers to amplitude steering conditioned by the compile-time parameter $\varphi$ via a Quantum Neural Cellular Automaton (QNCA) majority-inspired bias rule; the gate does not self-modify at runtime. Two QA-KS($\pi$) gates chained on a shared control qubit $q_0$ produce outputs completely orthogonal to two sequential CCX gates on $q_0$=1 inputs (output fidelity F=0.000), while agreeing exactly on $q_0$=0 inputs (F=1.000). This subspace-dependent divergence is the direct computational signature of coherent phase retention across gate boundaries -- impossible for CCX-only circuits. On the $q_1$ = 0 subspace the gate acts deterministically (up to a relative phase), providing intrinsic error non-amplification. On the $q_1$ = 1 subspace it produces four-component entangled superpositions, making it a strictly distinct quantum-native primitive from
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quantum-computingDigital twins for compact hybrid quantum classical learning in FMCW radar detection
--> Quantum Physics arXiv:2605.24187 (quant-ph) [Submitted on 22 May 2026] Title:Digital twins for compact hybrid quantum classical learning in FMCW radar detection Authors:Sebastian Ratto Valderrama, Ahmed N. Sayed, Arien Sligar, Jose R. Rosas-Bustos, Omar M. Ramahi, George Shaker View a PDF of the paper titled Digital twins for compact hybrid quantum classical learning in FMCW radar detection, by Sebastian Ratto Valderrama and 5 other authors View PDF HTML (experimental) Abstract:Frequency-modulated continuous-wave radar sensing often relies on labeled measurements that are costly, restricted, or difficult to collect at scale. This work evaluates physics-informed digital twins as controlled testbeds for early-stage quantum-classical radar learning. Two synthetic radar benchmarks are considered: unmanned aerial vehicle classification from range-Doppler maps and human fall detection from Doppler-time spectrograms. For both tasks, inputs are standardized, reduced using principal component analysis, and classified using either a radial basis function support vector classifier or a quantum support vector classifier. All quantum-kernel results are obtained using noiseless classical simulation; no quantum hardware is used, and no quantum-advantage claim is made. Across five random seeds, the quantum support vector classifier improves the UAV benchmark from four principal components onward, reaching an accuracy of 0.941 +/- 0.012 at eight components, compared with 0.880 +/- 0.029 for the classical baseline. On the fall-detection benchmark, both classifiers perform similarly, with a small quantum-kernel improvement at higher feature dimensions. A Gaussian-noise robustness study shows limited performance degradation across the tested noise levels, while preserving the UAV quantum-kernel gain. These results support digital twins as useful, controlled environments for radar-QML benchmarking prior to measured-data validation and hardware execution. Comments: Subjects: Quantum
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quantum-computingHybrid Quantum-Classical Machine Learning Algorithms for Multi-Output Time-Series Forecasting at Utility Scale
--> Quantum Physics arXiv:2605.24252 (quant-ph) [Submitted on 22 May 2026] Title:Hybrid Quantum-Classical Machine Learning Algorithms for Multi-Output Time-Series Forecasting at Utility Scale Authors:Mackenson Polché, Varun Puram, Aditi Lal, Weronika Golletz, Joan Étude Arrow, Vardaan Sahgal, Kumar Ghosh, Giorgio Cortiana, Corey O'Meara View a PDF of the paper titled Hybrid Quantum-Classical Machine Learning Algorithms for Multi-Output Time-Series Forecasting at Utility Scale, by Mackenson Polch\'e and 8 other authors View PDF HTML (experimental) Abstract:Multi-output time-series forecasting in energy systems is challenging because of nonlinear dynamics, multi-scale seasonality, and strong dependencies across correlated series. In this work, we investigate two hybrid quantum-classical frameworks for multi-stream time-series forecasting on a real Smart Meter dataset comprising 103 household electricity consumption time-series, with experiments executed on the $ibm\_marrakesh$ superconducting quantum processor. The first model, Kernelized Quantum Reservoir Computing with Repeated Measurement (KQRC-RM), combines coupled quantum reservoirs, ancilla-assisted repeated measurement, and kernelized readouts to model temporal dynamics and cross-stream correlations jointly. For a 3-stream time-series input and output, the KQRC-RM model using 114 qubits achieves an MAE of 0.0811 on MPS simulator (36.92\% improvement over its classical analog) whereas performance degrades to an MAE of 0.1524 on hardware. The second, a Projected Quantum Kernel Gaussian Process (QGP), replaces fidelity-based kernels with projected kernels constructed from local reduced-state statistics. Using a topology-aware 100-qubit QGP model to predict 100 multi-output time-series values, we observe 49\% of time-series outputs achieve high-accuracy predictions (MAE $<0.15$), with an average MAE of $0.082$ for this low-error group. The medium-error regime (MAE $0.15$-$0.35$) has an average MAE of $0.229$, wh
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quantum-computingQuantum non-demolition measurements as a practical primitive for fault-tolerant computation against biased noise
--> Quantum Physics arXiv:2605.24262 (quant-ph) [Submitted on 22 May 2026] Title:Quantum non-demolition measurements as a practical primitive for fault-tolerant computation against biased noise Authors:Christophe Vuillot, Diego Ruiz, Jérémie Guillaud, Mazyar Mirrahimi View a PDF of the paper titled Quantum non-demolition measurements as a practical primitive for fault-tolerant computation against biased noise, by Christophe Vuillot and Diego Ruiz and J\'er\'emie Guillaud and Mazyar Mirrahimi View PDF Abstract:Leveraging noise bias, where phase-flip errors dominate over bit-flips, can drastically reduce the hardware overhead of fault-tolerant quantum computation, but existing approaches require bias-preserving CNOT gates whose implementation remains experimentally challenging and is provably impossible for strictly two-dimensional systems. We show that high-fidelity quantum non-demolition (QND) multi-qubit Pauli $Z$ measurements provide an equally powerful yet more accessible primitive. We demonstrate that such measurements can fully replace bias-preserving CNOT gates for compiling all operations required by bias-tailored error correction, including stabilizer measurements for repetition codes, XZZX surface codes, and LDPC codes. We propose concrete physical implementations of this primitive for two platforms: solid-state nuclear spins coupled to electron spin ancillas, and dissipatively stabilized superconducting cat qubits. Through circuit-level numerical simulations, we show that an asymmetric XZZX surface code implemented with weight-four QND $Z$ measurements achieves a phase-flip threshold of $\sim\!1.25\%$ and provides a qubit overhead reduction of up to $6\times$ compared to a bias-unaware surface code at noise bias $\eta = 10^4$. In the regime of very large bias, a repetition code with QND $Z$ measurements attains a threshold of $\sim\!2.3\%$ and achieves overhead comparable to that of a bias-preserving CNOT scheme, without requiring such a gate. Our results
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quantum-computingMultiple fidelities and joint numerical range
--> Quantum Physics arXiv:2605.24360 (quant-ph) [Submitted on 23 May 2026] Title:Multiple fidelities and joint numerical range Authors:Pei Li, Bang-Hai Wang View a PDF of the paper titled Multiple fidelities and joint numerical range, by Pei Li and Bang-Hai Wang View PDF HTML (experimental) Abstract:We investigate the effectiveness of entanglement detection based on multiple fidelities via the geometry of the joint separable numerical range. When all reference states are product states, we derive a necessary and sufficient criterion for such detection: either some pair of reference states has nontrivial moduli of the local inner products on both subsystems, or the orthogonal complement of the span of the reference states is completely entangled. We further show that there exist sets of reference product states for which no proper subset is effective for entanglement detection, whereas the full set is. A typical example of this phenomenon is provided by unextendible product bases. Moreover, for a pair of reference product states on a bipartite system with arbitrary local dimensions, we characterize both the joint numerical range and the joint separable numerical range, showing that the joint separable numerical range is determined solely by their local fidelities, as illustrated by a representative two-qubit example. Our results offer a systematic approach to designing effective entanglement witnesses and lay the groundwork for extensions to higher-dimensional and multipartite scenarios. Comments: Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2605.24360 [quant-ph] (or arXiv:2605.24360v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2605.24360 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Bang-Hai Wang [view email] [v1] Sat, 23 May 2026 02:52:12 UTC (108 KB) Full-text links: Access Paper: View a PDF of the paper titled Multiple fidelities and joint numerical range, by Pei Li and Bang
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quantum-computingPodcast with Klea Dhimitri of Hamamtsu Photonics
Klea Dhmitri of Hamamatsu joins Yuval to discuss the company’s role as a photonic component provider for trapped-ion and neutral-atom quantum computers. She explains key technologies such as photomultiplier tubes (PMTs), SPADs, and quantitative CMOS cameras, and how scaling to larger qubit arrays changes requirements for speed, resolution, and integration. Klea also shares how customer demand is pushing product innovation, reflects on her unconventional path into quantum, and offers advice for those looking to build careers in photonics and quantum technologies. Transcript Yuval: Hello, Klea. Thank you for joining me today. Klea: Hi, Yuval. I’m glad to be here. Yuval: So who are you and what do you do? Klea: Hi, yes, happy to introduce myself. So I’m Klea Dhmitri and I work for Hamamatsu Corporation, which is the North American subsidiary of Hamamatsu Photonics. And I will be with Hamamatsu eight years in June. And what I do here is I lead our quantum computing and quantum communication project here in North America. And so what that means is I engage a lot with the community in helping, you know, folks from academia to industry find solutions of the product, help them find photonic solutions of the current products that they’re building, but also keeping in mind their next generation. And this is really where I work closely with our R&D colleagues in Japan and bringing these maybe R&D or prototype solutions and detection, modulation, and even lasers to these customers. And I also do a lot of marketing as well. So you’ll find me at trade shows, doing webinars, and really creating content that explains where Hamamatsu plays in this space. And so maybe a bit of a sort of a fun tidbit is actually this role in this project did not exist when I joined the company. So it was a bit serendipitous. So I’m happy to jump into that later in the conversation if you’d like to learn more. Yuval: What kind of components does Hamamatsu provide to qua
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quantum-computingRan a compiler-generated 3-qubit bit-flip code on Rigetti's Cepheus-1-108Q via Braket, syndrome correctly identified the injected error in 87% of shots, 94.5% logical error recovery under hardware noise
I've been building QSHL (Quantum Self-Healing Language), a small compiler that emits OpenQASM 3.0 with error-correction circuits generated from a high-level specification rather than hand-wired syndrome logic. I wanted to validate the syndrome extraction on real hardware, not just simulators. Setup: 3-qubit bit-flip repetition code Two parity syndromes: s0 = parity(q0,q1) s1 = parity(q1,q2) Syndrome extraction via ancilla qubits Deliberate X error injected on q0 Expected syndrome: "10" Execution: Rigetti Cephus-1-108Q via Amazon Braket 100 shots Observed syndrome distribution: 10 (expected): 87% 11: 5% 00: 5% 01: 3% Using post-process syndrome decoding, the logical recovery rate was 94.5%. The non-ideal outcomes are consistent with real hardware effects: readout noise gate infidelity decoherence routing/SWAP overhead across the device topology For comparison, the same circuit executed deterministically on SV1 (1000/1000 expected outcomes), so the spread here is clearly hardware-driven. Important caveats: this is post-process decoding, not active fault tolerance not closed-loop real-time correction not a logical memory lifetime experiment distance-1 repetition code only Next steps are: mid-circuit measurement + conditional feedback repeated syndrome cycles higher-distance codes cross-hardware benchmarking Happy to answer questions about the compiler or lowering pipeline. submitted by /u/DestinyInDepth [link] [comments]
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Imec builds world's first High-NA EUV-fabricated quantum dot qubit device — breakthrough could pull quantum computing onto the same manufacturing roadmap as next-gen AI processors, compressing timelines - Tom's Hardware
Imec builds world's first High-NA EUV-fabricated quantum dot qubit device — breakthrough could pull quantum computing onto the same manufacturing roadmap as next-gen AI processors, compressing timelines Tom's Hardware
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quantum-computingSample-efficient benchmarking of shallow all-to-all random quantum circuits
--> Quantum Physics arXiv:2605.22909 (quant-ph) [Submitted on 21 May 2026] Title:Sample-efficient benchmarking of shallow all-to-all random quantum circuits Authors:Gregory Bentsen, Bill Fefferman, Soumik Ghosh, Michael J. Gullans, Yinchen Liu View a PDF of the paper titled Sample-efficient benchmarking of shallow all-to-all random quantum circuits, by Gregory Bentsen and Bill Fefferman and Soumik Ghosh and Michael J. Gullans and Yinchen Liu View PDF HTML (experimental) Abstract:Random circuit sampling (RCS) remains one of the most competitive frameworks for demonstrating quantum advantage in near-term noisy intermediate-scale quantum (NISQ) hardware. Unfortunately, absent error-correction, existing benchmarks to characterize these experiments, like linear cross-entropy, have been classically spoofed due to noise. Because of this, there are interesting regimes, like shallow-depth random quantum circuits, where sampling is plausibly classically intractable, but no existing benchmark can distinguish between a noisy quantum computer and an adversarial classical spoofer. In this paper, we demonstrate that the nonlinear cross-entropy provides a sample-efficient benchmark for shallow-depth all-to-all random quantum circuits whose score cleanly separates noisy quantum computers from state-of-the-art classical spoofers, even in the presence of depolarizing noise. Further, we develop a binary classifier based on the notion of heavy output generation that features logarithmic sample complexity at short depth. Our evidence comes from exact analytic expressions for all-to-all Brownian circuit ensembles derived using replica tricks, and numerical simulations that corroborate these results for discrete Haar-random unitary circuits. Comments: Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2605.22909 [quant-ph] (or arXiv:2605.22909v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2605.22909 Focus to learn more arXiv-issued DOI via DataCite Submission
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quantum-computingEstimating Green's functions with a robust quantum Arnoldi method
--> Quantum Physics arXiv:2605.22920 (quant-ph) [Submitted on 21 May 2026] Title:Estimating Green's functions with a robust quantum Arnoldi method Authors:Jacob S. Nelson, Andrew B. Baczewski View a PDF of the paper titled Estimating Green's functions with a robust quantum Arnoldi method, by Jacob S. Nelson and Andrew B. Baczewski View PDF HTML (experimental) Abstract:Many applications of Green's functions (GFs) require their evaluation over intervals or at multiple points, motivating quantum algorithms that return an efficiently computable functional representation rather than mere point estimates. We introduce a robust quantum Arnoldi method (ROQAM) that achieves this goal. Its robustness is derived from formulation in terms of orthogonal polynomials, which preserves the upper-Hessenberg structure of the projected matrices despite finite-precision estimation. We also show that as the iteration depth increases, the precision required for matrix-element estimation can be reduced. Resource estimates for the spectral function of a quantum impurity model indicate that ROQAM outperforms pointwise estimation via quantum singular value transformation by multiple orders of magnitude. Finally, we show that the ROQAM can be used to estimate GFs at nonzero temperatures using only a single Krylov subspace. Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2605.22920 [quant-ph] (or arXiv:2605.22920v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2605.22920 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Jacob Nelson [view email] [v1] Thu, 21 May 2026 18:00:41 UTC (1,108 KB) Full-text links: Access Paper: View a PDF of the paper titled Estimating Green's functions with a robust quantum Arnoldi method, by Jacob S. Nelson and Andrew B. BaczewskiView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph < prev | next > new | recent | 2026-05 Referen
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quantum-computingAbsorbing Many-Body Correlations into Core-Optimized Orbitals
--> Quantum Physics arXiv:2605.22977 (quant-ph) [Submitted on 21 May 2026] Title:Absorbing Many-Body Correlations into Core-Optimized Orbitals Authors:Hao Zhang, Matthew Otten View a PDF of the paper titled Absorbing Many-Body Correlations into Core-Optimized Orbitals, by Hao Zhang and 1 other authors View PDF HTML (experimental) Abstract:The cost of simulating quantum many-body systems - on classical or quantum hardware - scales with the number of variational parameters, so progress at fixed computational budget hinges on more parameter-efficient ansätze. Configuration Interaction (CI) is widely dismissed as parameter-heavy; we show this verdict is an artifact of the orbital basis. Co-optimizing the orbital basis with a sparse CI wavefunction - a method we call Core-Optimized Orbitals (COO) - absorbs a large fraction of the dynamical correlation directly into the single-particle basis, cutting the determinant count by several orders of magnitude beyond the already compact TrimCI ansatz on which it builds. On [Fe$_4$S$_4$] (54e, 36o), a billion-determinant TrimCI+COO wavefunction reaches accuracy that would require $3\!\times\!10^{14}$ determinants in a localized basis. At matched accuracy, it is $8\times$ more compact than the largest unrestricted-DMRG benchmark ($25\times$ with PT2). Across the iron-sulfur series - from [Fe$_2$S$_2$] (30e,20o) to the P-cluster (114e,73o) - TrimCI+COO is $10$-$100\times$ more compact than SU(2)-adapted DMRG with entanglement-minimized orbitals at matched accuracy. A tunable Hubbard-on-graph model factorizes the advantage into an orbital-basis gain and an ansatz gain, the latter capturing multi-center entanglement that resists MPS localization. COO therefore changes the picture of CI efficiency: sparse CI with optimized orbitals can outperform state-of-the-art tensor networks on strongly correlated multi-center systems. Comments: Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); Chemical Physics
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quantum-computingAutomatic De-Quantization of Quantum Programs Using Constant Propagation
--> Quantum Physics arXiv:2605.22980 (quant-ph) [Submitted on 21 May 2026] Title:Automatic De-Quantization of Quantum Programs Using Constant Propagation Authors:Lian Remme, Alexander Weinert, Andre Waschk, Lukas Burgholzer, Robert Wille View a PDF of the paper titled Automatic De-Quantization of Quantum Programs Using Constant Propagation, by Lian Remme and 4 other authors View PDF Abstract:Quantum computing promises to solve problems beyond the reach of classical computers, but today's quantum hardware is error-prone and much slower than classical hardware. Every quantum operation is costly, making it crucial to minimize quantum resource usage in near-term algorithms. Quantum resources should only be used when they are truly essential for quantum advantage, and not wasted on operations that can be efficiently handled by classical computation. In this work, we focus on de-quantizing quantum operations to classical computation whenever possible. The approach we propose for this is hybrid quantum-classical constant propagation, an optimization which reduces quantum operations by trading them for fast, reliable classical instructions. This is done by tracking between quantum and classical states to identify and eliminate unnecessary quantum gates and controls. We formalize a hybrid state model for quantum-classical constant propagation, implement our optimizations in the open-source MQT Core tool, and evaluate them on benchmark circuits. The obtained results show that quantum-classical constant propagation can reduce costly multi-qubit operations, making quantum programs more practical and robust for near-term devices. This opens the door to new hybrid compiler strategies that leverage the best of both quantum and classical worlds. Comments: Subjects: Quantum Physics (quant-ph); Emerging Technologies (cs.ET) Cite as: arXiv:2605.22980 [quant-ph] (or arXiv:2605.22980v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2605.22980 Focus to learn mo
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quantum-computingConstruction of EAQECCs with imperfect ebits
--> Quantum Physics arXiv:2605.23119 (quant-ph) [Submitted on 22 May 2026] Title:Construction of EAQECCs with imperfect ebits Authors:Guanmin Guo, Ruihu Li View a PDF of the paper titled Construction of EAQECCs with imperfect ebits, by Guanmin Guo and 1 other authors View PDF HTML (experimental) Abstract:We generalize the stabilizer formalism for entanglement-assisted quantum error-correcting codes with noisy ebits (EAQECCs-Ne) from the binary case to the general $q$-ary case, where $q$ is a prime power. By leveraging the structure of the generalized Pauli group over $\mathbb{F}_q$ and symplectic geometry over $\mathbb{F}_q^{2n}$, we establish a unified framework for constructing EAQECCs-Ne for qudit systems. Equivalent formulations in terms of symplectic geometry over $\mathbb{F}_q$ and additive codes over $\mathbb{F}_q^{2n}$ are derived. We further construct several families of $q$-ary EAQECCs with noise ebits and analyze their performance compared to optimal stabilizer codes. Our results demonstrate that under certain noise conditions, the proposed EAQECCs-Ne can outperform standard stabilizer codes with equivalent error-correcting capability, offering a promising approach for fault-tolerant quantum computation in high-dimensional quantum systems. Subjects: Quantum Physics (quant-ph); Information Theory (cs.IT) Cite as: arXiv:2605.23119 [quant-ph] (or arXiv:2605.23119v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2605.23119 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Guanmin Guo [view email] [v1] Fri, 22 May 2026 00:42:55 UTC (651 KB) Full-text links: Access Paper: View a PDF of the paper titled Construction of EAQECCs with imperfect ebits, by Guanmin Guo and 1 other authorsView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph < prev | next > new | recent | 2026-05 Change to browse by: cs cs.IT math math.IT References &am
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quantum-computingClassical State Preparation for Variational Quantum Algorithms via Reinforcement Learning
--> Quantum Physics arXiv:2605.23138 (quant-ph) [Submitted on 22 May 2026] Title:Classical State Preparation for Variational Quantum Algorithms via Reinforcement Learning Authors:Gino Kwun, Dhanvi Bharadwaj, Gokul Subramanian Ravi View a PDF of the paper titled Classical State Preparation for Variational Quantum Algorithms via Reinforcement Learning, by Gino Kwun and 2 other authors View PDF HTML (experimental) Abstract:Variational Quantum Algorithms (VQAs) potentially offer a pathway to practical quantum advantage, but their optimization is heavily hindered by barren plateaus and numerous local minima. While classically simulable Clifford circuits can warm-start VQAs to accelerate convergence, existing heuristic-based initialization methods struggle to scale within vast combinatorial search spaces. To overcome this bottleneck, we propose CRiSP (a Clifford Reinforcement Learning agent for State Preparation), a framework that formulates discrete prefix selection as a sequential decision-making problem. CRiSP utilizes Neural-Guided Monte Carlo Tree Search, driven by a Transformer-based policy trained via self-play, to insert learned Clifford gates before fixed parameterized rotations. This enables the construction of high-quality initial states entirely through polynomial-time classical stabilizer simulation without altering the underlying circuit architecture. By integrating a curriculum learning strategy that progressively expands the search horizon, the agent efficiently scales to deep circuits. Evaluated on QAOA benchmarks of up to $22$ qubits and $1{,}370$ parameters, CRiSP outperforms state-of-the-art Clifford initialization methods by a mean of $3.17\times$ (max $45.02\times$) in average energy accuracy and $2.44\times$ (max $16.01\times$) in best-achieved energy accuracy. Assessments on VQE tasks further demonstrate the framework's robustness and generalizability. Comments: Subjects: Quantum Physics (quant-ph); Artificial Intelligence (cs.AI); Emerging Technol
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quantum-computingAnomalous Decay of Quantum Resources: The Entanglement Sudden Death Mpemba Effect
--> Quantum Physics arXiv:2605.23197 (quant-ph) [Submitted on 22 May 2026] Title:Anomalous Decay of Quantum Resources: The Entanglement Sudden Death Mpemba Effect Authors:Zhilong Liu, Zehua Tian, Jieci Wang View a PDF of the paper titled Anomalous Decay of Quantum Resources: The Entanglement Sudden Death Mpemba Effect, by Zhilong Liu and 2 other authors View PDF HTML (experimental) Abstract:In classical thermodynamics, the Mpemba effect refers to the counterintuitive observation that hot water can freeze faster than cold water, manifesting as an anomalous crossing of dynamical trajectories. While analogues of this phenomenon have been explored in quantum radiative systems and spin-chain entanglement asymmetry, its connection to the finite-time decoupling of quantum correlations remains elusive. In this Letter, we uncover a distinct quantum Mpemba effect associated with entanglement sudden death (ESD). By analyzing two qubits interacting with local amplitude damping reservoirs, we demonstrate that a more strongly entangled initial state can experience a faster collapse into a separable state than a more weakly entangled one. We provide an exact analytical derivation of the trajectory crossover dynamics and the ESD time. Finally, we map the phase diagram of initial state parameters to delineate the regime where this anomalous entanglement Mpemba effect occurs, offering insights into the control of quantum resource lifetimes in dissipative environments. Comments: Subjects: Quantum Physics (quant-ph); General Relativity and Quantum Cosmology (gr-qc) Cite as: arXiv:2605.23197 [quant-ph] (or arXiv:2605.23197v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2605.23197 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Jieci Wang [view email] [v1] Fri, 22 May 2026 03:28:53 UTC (364 KB) Full-text links: Access Paper: View a PDF of the paper titled Anomalous Decay of Quantum Resources: The Entanglement
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quantum-computingTransition-state lattice modes and the breakdown of adiabatic tunneling for hydrogen and deuterium in bcc Nb
--> Quantum Physics arXiv:2605.23212 (quant-ph) [Submitted on 22 May 2026] Title:Transition-state lattice modes and the breakdown of adiabatic tunneling for hydrogen and deuterium in bcc Nb Authors:P. Graham Pritchard, James M. Rondinelli View a PDF of the paper titled Transition-state lattice modes and the breakdown of adiabatic tunneling for hydrogen and deuterium in bcc Nb, by P. Graham Pritchard and James M. Rondinelli View PDF HTML (experimental) Abstract:Interstitial hydrogen and deuterium in body-centered-cubic metals constitute archetypal quantum tunneling systems. Their relevance has been renewed by the connection between hydrogenic tunneling in Nb and defect-induced decoherence in superconducting qubits, motivating a predictive microscopic theory. Existing theoretical treatments invoke an adiabatic separation between the light interstitial and the host lattice, an assumption whose validity has not been rigorously established for hydrogenic species. Here, we show that the experimentally measured tunnel splittings of O-trapped H and D in bcc Nb are quantitatively reproduced only within a five-dimensional (5D) Lattice-Renormalized Born-Oppenheimer (LRBO) framework. This approach treats three interstitial modes and two judiciously selected lattice modes, which includes a transition-state mode, on equal quantum footing. By recasting nested Born-Oppenheimer hierarchies within this same formalism and benchmarking against modern \textit{ab initio} potential energy surfaces, we show that adiabatic separation of the light particle from lattice dynamics is satisfied only in the positive-muon ($\mu^{+}$) mass limit. In contrast, tunneling for H and D is fundamentally a collective, nonadiabatic process mediated by anharmonic lattice couplings. Finally, we show that the breakdown of adiabaticity can be anticipated from simple energy estimates involving the ground-state light-particle energy evaluated at a small number of fixed lattice configurations, providing a practic
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