{"title":"Uncovering quantum many-body scars with quantum machine learning","authors":"Jia-Jin Feng, Bingzhi Zhang, Zhi-Cheng Yang, Quntao Zhuang","doi":"10.1038/s41534-025-01005-0","DOIUrl":"https://doi.org/10.1038/s41534-025-01005-0","url":null,"abstract":"<p>Quantum many-body scars are rare eigenstates hidden within the chaotic spectra of many-body systems, representing a weak violation of the eigenstate thermalization hypothesis (ETH). Identifying these scars, as well as other non-thermal states in complex quantum systems, remains a significant challenge. Besides exact scar states, the nature of other non-thermal states lacking simple analytical characterization remains an open question. In this study, we employ tools from quantum machine learning—specifically, (enhanced) quantum convolutional neural networks (QCNNs), to explore hidden non-thermal states in chaotic many-body systems. Our simulations demonstrate that QCNNs achieve over 99% single-shot measurement accuracy in identifying all known scars. Furthermore, we successfully identify new non-thermal states in models such as the xorX model, the PXP model, and the far-coupling Su-Schrieffer-Heeger model. In the xorX model, some of these non-thermal states can be approximately described as spin-wave modes of specific quasiparticles. We further develop effective tight-binding Hamiltonians within the quasiparticle subspace to capture key features of these many-body eigenstates. Finally, we validate the performance of QCNNs on IBM quantum devices, achieving single-shot measurement accuracy exceeding 63% under real-world noise and errors, with the aid of error mitigation techniques. Our results underscore the potential of QCNNs to uncover hidden non-thermal states in quantum many-body systems.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"56 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143589661","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shubham Kumar, Narendra N. Hegade, Anne-Maria Visuri, Balaganchi A. Bhargava, Juan F. R. Hernandez, E. Solano, F. Albarrán-Arriagada, G. Alvarado Barrios
{"title":"Digital-analog quantum computing of fermion-boson models in superconducting circuits","authors":"Shubham Kumar, Narendra N. Hegade, Anne-Maria Visuri, Balaganchi A. Bhargava, Juan F. R. Hernandez, E. Solano, F. Albarrán-Arriagada, G. Alvarado Barrios","doi":"10.1038/s41534-025-01001-4","DOIUrl":"https://doi.org/10.1038/s41534-025-01001-4","url":null,"abstract":"<p>High-fidelity quantum simulations demand hardware-software co-design architectures, which are crucial for adapting to complex problems such as strongly correlated dynamics in condensed matter. By leveraging co-design strategies, we can enhance the performance of state-of-the-art quantum devices in the noisy intermediate quantum (NISQ) and early error-correction regimes. In this direction, we propose a digital-analog quantum algorithm for simulating the Hubbard–Holstein model, describing strongly correlated fermion-boson interactions, in a suitable architecture with superconducting circuits. It comprises a linear chain of qubits connected by resonators, emulating electron–electron (e–e) and electron–phonon (e–p) interactions, as well as fermion tunneling. Our approach is adequate for digital-analog quantum computing (DAQC) of fermion-boson models, including those described by the Hubbard–Holstein model. We show the reduction in the circuit depth of the DAQC algorithm, a sequence of digital steps and analog blocks, outperforming the purely digital approach. We exemplify the quantum simulation of a half-filled two-site Hubbard–Holstein model. In this example, we obtain time-dependent state fidelities larger than 0.98, showing that our proposal is suitable for studying the dynamical behavior of solid-state systems. Our proposal opens the door to computing complex systems for chemistry, materials, and high-energy physics.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"91 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143589827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nico Hauser, Matthias J. Bayerbach, Simone E. D’Aurelio, Raphael Weber, Matteo Santandrea, Shreya P. Kumar, Ish Dhand, Stefanie Barz
{"title":"Boosted Bell-state measurements for photonic quantum computation","authors":"Nico Hauser, Matthias J. Bayerbach, Simone E. D’Aurelio, Raphael Weber, Matteo Santandrea, Shreya P. Kumar, Ish Dhand, Stefanie Barz","doi":"10.1038/s41534-025-00986-2","DOIUrl":"https://doi.org/10.1038/s41534-025-00986-2","url":null,"abstract":"<p>Fault-tolerant fusion-based photonic quantum computing (FBQC) greatly relies on entangling two-photon measurements, called fusions. These fusions can be realized using linear-optical projective Bell-state measurements (BSMs). These linear-optical BSMs are limited to a success probability of 50%, greatly reducing the performance of FBQC schemes. The performance of FBQC can be improved using boosting, thus achieving higher success probabilities by adding additional resources. Here, we realize a boosted BSM using a 4 × 4 multiport splitter and an additional entangled photon pair, allowing for a success probability of up to 75%. In our experiment, we obtain a success probability for our boosted BSM of (69.3 ± 0.3)%, clearly exceeding the 50% limit. We further demonstrate the significance of our boosted BSM for FBQC, showing a threefold increase in robustness to photon loss and a significant reduction of the logical error rates.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"28 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143576275","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Arnav Arora, Siddhant Midha, Alexander Zyuzin, Pertti Hakonen, Bhaskaran Muralidharan
{"title":"Steady-state dynamics and nonlocal correlations in thermoelectric Cooper pair splitters","authors":"Arnav Arora, Siddhant Midha, Alexander Zyuzin, Pertti Hakonen, Bhaskaran Muralidharan","doi":"10.1038/s41534-025-00966-6","DOIUrl":"https://doi.org/10.1038/s41534-025-00966-6","url":null,"abstract":"<p>Recent experiments on Cooper pair splitters using superconductor-quantum dot hybrids have embarked on creating entanglement in the solid-state, by engineering the sub-gap processes in the superconducting region. Using the thermoelectric Cooper pair splitter setup [Nat. Comm., 12, 21, (2021)] as a prototype, we present a comprehensive analysis of the fundamental components of the observed transport signal, aiming to critically clarify the operating regimes and confirm the nonlocal and nonclassical nature of correlations arising from crossed Andreev processes. By making a nexus with quantum discord, we identify operating points of nonlocal quantum correlations in the CPS device—information that cannot be extracted from the transport signal alone. A notable consequence of our analysis is the finding that contact-induced level broadening of the quantum dot’s discrete energy spectrum, along with its hybridization with the superconducting segment, can lead to shifted resonances in the crossed Andreev process as well as a parity reversal in the thermoelectric current. Our work thereby provides detailed insights into the gate voltage control of the quantum correlations in superconducting-hybrid Cooper pair splitters, revealing new avenues for harnessing quantum correlations in solid-state systems.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"12 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143575307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
György P. Gehér, Marcin Jastrzebski, Earl T. Campbell, Ophelia Crawford
{"title":"To reset, or not to reset—that is the question","authors":"György P. Gehér, Marcin Jastrzebski, Earl T. Campbell, Ophelia Crawford","doi":"10.1038/s41534-025-00998-y","DOIUrl":"https://doi.org/10.1038/s41534-025-00998-y","url":null,"abstract":"<p>Whether to reset qubits, or not, during quantum error correction experiments is a question of both foundational and practical importance for quantum computing. Text-book quantum error correction demands that qubits are reset after measurement. However, fast qubit reset has proven challenging to execute at high fidelity. Consequently, many cutting-edge quantum error correction experiments are opting for the no-reset approach, where physical reset is not performed. It has recently been postulated that no-reset is functionally equivalent to reset procedures, as well as being faster and easier. For memory experiments, we confirm numerically that resetting provides no benefit. On the other hand, we identify a remarkable difference during logical operations. We find that unconditionally resetting qubits can reduce the duration of fault-tolerant logical operation by up to a factor of two as the number of measurement errors that can be tolerated is doubled. We support this with numerical simulations. However, our simulations also reveal that the no-reset performance is superior if the reset duration and infidelity exceed given thresholds. For example, with the noise model we considered, we find the no-reset performance to be superior when the reset duration is greater than approximately 100 ns and the physical error probability is greater than approximately 10<sup>−2.5</sup> ≈ 0.003. Lastly, we introduce two novel syndrome extraction circuits that can reduce the time overhead of no-reset approaches. Our findings provide guidance on how experimentalists should design future experiments.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"67 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143570453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jack Raymond, Mohammad H. Amin, Andrew D. King, Richard Harris, William Bernoudy, Andrew J. Berkley, Kelly Boothby, Anatoly Smirnov, Fabio Altomare, Michael Babcock, Catia Baron, Jake Connor, Martin H. Dehn, Colin Enderud, Emile Hoskinson, Shuiyuan Huang, Mark W. Johnson, Eric Ladizinsky, Trevor Lanting, Allison J. R. MacDonald, Gaelen Marsden, Reza Molavi, Travis Oh, Gabriel Poulin-Lamarre, Hugh Ramp, Chris Rich, Berta Trullas Clavera, Nicholas Tsai, Mark Volkmann, Jed D. Whittaker, Jason Yao, Niclas Heinsdorf, Nitin Kaushal, Alberto Nocera, Marcel Franz, Jacek Dziarmaga
{"title":"Quantum error mitigation in quantum annealing","authors":"Jack Raymond, Mohammad H. Amin, Andrew D. King, Richard Harris, William Bernoudy, Andrew J. Berkley, Kelly Boothby, Anatoly Smirnov, Fabio Altomare, Michael Babcock, Catia Baron, Jake Connor, Martin H. Dehn, Colin Enderud, Emile Hoskinson, Shuiyuan Huang, Mark W. Johnson, Eric Ladizinsky, Trevor Lanting, Allison J. R. MacDonald, Gaelen Marsden, Reza Molavi, Travis Oh, Gabriel Poulin-Lamarre, Hugh Ramp, Chris Rich, Berta Trullas Clavera, Nicholas Tsai, Mark Volkmann, Jed D. Whittaker, Jason Yao, Niclas Heinsdorf, Nitin Kaushal, Alberto Nocera, Marcel Franz, Jacek Dziarmaga","doi":"10.1038/s41534-025-00977-3","DOIUrl":"https://doi.org/10.1038/s41534-025-00977-3","url":null,"abstract":"<p>Quantum error mitigation (QEM) presents a promising near-term approach to reducing errors when estimating expectation values in quantum computing. Here, we introduce QEM techniques tailored for quantum annealing, using zero-noise extrapolation (ZNE). We implement ZNE through zero-temperature and zero-time extrapolations. The practical zero-time extrapolation developed exploits the Kibble-Zurek mechanism so that only problem-Hamiltonian rescaling is required. We conduct experimental investigations into the quantum critical and post-critical dynamics of a transverse-field Ising spin chain by examining statistics with weak and strong post-critical dynamics. We demonstrate successful mitigation of thermal noise and non-thermal errors through both of these extrapolation techniques.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"16 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143560620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Simone E. D’Aurelio, Matthias J. Bayerbach, Stefanie Barz
{"title":"Boosted quantum teleportation","authors":"Simone E. D’Aurelio, Matthias J. Bayerbach, Stefanie Barz","doi":"10.1038/s41534-025-00992-4","DOIUrl":"https://doi.org/10.1038/s41534-025-00992-4","url":null,"abstract":"<p>Quantum teleportation has proven to be fundamental for many quantum information and communication processes. The core concept can be exploited in many tasks, from the transmission of quantum states, quantum repeaters, to quantum computing. However, for linear-optical systems, the efficiency of teleportation is directly linked to the success probability of the involved Bell-state measurement (BSM). In most implementations, this is realized by linear optics with an intrinsically limited success probability of 50%. Here, we demonstrate quantum teleportation surpassing this limit. We achieve an average fidelity of the teleported states of 0.8677 ± 0.0024, leading to an overall acceptance rate of the teleportation of 69.71 ± 0.75%. We obtain this boosted success probability by generating ancillary photonic states that are interfered with the Bell states. Thus, our work demonstrates the boosting BSMs in quantum-technology applications and our scheme could directly be applied to, e.g., quantum repeaters.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"67 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143546361","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Peiyu Yang, Guzhi Bao, Jun Chen, Wei Du, Jinxian Guo, Weiping Zhang
{"title":"Quantum locking of intrinsic spin squeezed state in Earth-field-range magnetometry","authors":"Peiyu Yang, Guzhi Bao, Jun Chen, Wei Du, Jinxian Guo, Weiping Zhang","doi":"10.1038/s41534-025-00971-9","DOIUrl":"https://doi.org/10.1038/s41534-025-00971-9","url":null,"abstract":"<p>In the Earth-field range, the nonlinear Zeeman (NLZ) effect has been a bottleneck limiting the sensitivity and accuracy of atomic magnetometry from physical mechanism. To break this bottleneck, various techniques are introduced to suppress the NLZ effect. Here we revisit the spin dynamics in the Earth-field-range magnetometry with the NLZ effect and identify the existence of the intrinsic spin squeezed state (SSS), generated from the coupling between nuclear and electron spins of each individual atom, with the oscillating squeezing degree and squeezing axis. Such oscillating features of the SSS prevent its direct observation and as well, accessibility to magnetic sensing. To exploit quantum advantage of the intrinsic SSS in the Earth-field-range magnetometry, it’s essential to lock the oscillating SSS to a persistent one. Hence we develop a quantum locking technique to achieve a persistent SSS, benefiting from which the sensitivity of the Earth-field-range magnetometer is quantum-enhanced. This work presents an innovative way turning the drawback of NLZ effect into the quantum advantage and opens a new access to quantum-enhanced magnetometry in the Earth-field range.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"5 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143532859","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Chengran Yang, Marta Florido-Llinàs, Mile Gu, Thomas J. Elliott
{"title":"Dimension reduction in quantum sampling of stochastic processes","authors":"Chengran Yang, Marta Florido-Llinàs, Mile Gu, Thomas J. Elliott","doi":"10.1038/s41534-025-00978-2","DOIUrl":"https://doi.org/10.1038/s41534-025-00978-2","url":null,"abstract":"<p>Quantum technologies offer a promising route to the efficient sampling and analysis of stochastic processes, with potential applications across the sciences. Such quantum advantages rely on the preparation of a quantum sample state of the stochastic process, which requires a memory system to propagate correlations between the past and future of the process. Here, we introduce a method of lossy quantum dimension reduction that allows this memory to be compressed, not just beyond classical limits, but also beyond current state-of-the-art quantum stochastic sampling approaches. We investigate the trade-off between the saving in memory resources from this compression, and the distortion it introduces. We show that our approach can be highly effective in low distortion compression of both Markovian and strongly non-Markovian processes alike. We further discuss the application of our results to quantum stochastic modelling more broadly.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"26 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143518749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Calibrating quantum gates up to 52 qubits in a superconducting processor","authors":"Daojin Fan, Guoding Liu, Shaowei Li, Ming Gong, Dachao Wu, Yiming Zhang, Chen Zha, Fusheng Chen, Sirui Cao, Yangsen Ye, Qingling Zhu, Chong Ying, Shaojun Guo, Haoran Qian, Yulin Wu, Hui Deng, Gang Wu, Cheng-Zhi Peng, Xiongfeng Ma, Xiaobo Zhu, Jian-Wei Pan","doi":"10.1038/s41534-025-00983-5","DOIUrl":"https://doi.org/10.1038/s41534-025-00983-5","url":null,"abstract":"<p>Benchmarking large-scale quantum gates, typically involving multiple native two-qubit and single-qubit gates, is crucial in quantum computing. Global fidelity, encompassing information about inter-gate correlations, offers a comprehensive metric for evaluating and optimizing gate performance, unlike the fidelities of individual local native gates. In this work, utilizing the character-average benchmarking protocol implementable in a shallow circuit, we successfully benchmark gate fidelities up to 52 qubits. Notably, we achieved a fidelity of 63.09% ± 0.23% for a 44-qubit parallel CZ gate. Utilizing the global fidelity of the parallel CZ gate, we explore the correlations among local CZ gates by introducing an inter-gate correlation metric, enabling one to simultaneously quantify crosstalk error when benchmarking gate fidelity. Finally, we apply our methods in gate optimization. By leveraging global fidelity for optimization, we enhance the fidelity of a 6-qubit parallel CZ gate from 87.65% to 92.04% and decrease the gate correlation from 3.53% to 3.22%, compared to local gate fidelity-based optimization. The experimental results align well with our established composite noise model, incorporating depolarizing and <i>Z</i><i>Z</i>-coupling noises, and provide valuable insight into further study and mitigation of correlated noise.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"24 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143495518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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