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Check-probe spectroscopy of lifetime-limited emitters in bulk-grown silicon carbide 体生长碳化硅中寿命限制发射体的检查探针光谱
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-22 DOI: 10.1038/s41534-025-00985-3
G. L. van de Stolpe, L. J. Feije, S. J. H. Loenen, A. Das, G. M. Timmer, T. W. de Jong, T. H. Taminiau
{"title":"Check-probe spectroscopy of lifetime-limited emitters in bulk-grown silicon carbide","authors":"G. L. van de Stolpe, L. J. Feije, S. J. H. Loenen, A. Das, G. M. Timmer, T. W. de Jong, T. H. Taminiau","doi":"10.1038/s41534-025-00985-3","DOIUrl":"https://doi.org/10.1038/s41534-025-00985-3","url":null,"abstract":"<p>Solid-state single-photon emitters provide a versatile platform for exploring quantum technologies such as optically connected quantum networks. A key challenge is to ensure the optical coherence and spectral stability of the emitters. Here, we introduce a high-bandwidth ‘check-probe’ scheme to quantitatively measure (laser-induced) spectral diffusion and ionisation rates, as well as homogeneous linewidths. We demonstrate these methods on single V2 centres in commercially available bulk-grown 4H-silicon carbide. Despite observing significant spectral diffusion under laser illumination (<span>≳</span>GHz s<sup>−1</sup>), the optical transitions are narrow (~35 MHz), and remain stable in the dark (<span>≳</span>1 s). Through Landau-Zener-Stückelberg interferometry, we determine the optical coherence to be near-lifetime limited (<i>T</i><sub>2</sub> = 16.4(4) ns), hinting at the potential for using bulk-grown materials for developing quantum technologies. These results advance our understanding of spectral diffusion of quantum emitters in semiconductor materials, and may have applications for studying charge dynamics across other platforms.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"23 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143473551","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}
引用次数: 0
Direct entanglement detection of quantum systems using machine learning 使用机器学习的量子系统直接纠缠检测
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-20 DOI: 10.1038/s41534-025-00970-w
Yulei Huang, Liangyu Che, Chao Wei, Feng Xu, Xinfang Nie, Jun Li, Dawei Lu, Tao Xin
{"title":"Direct entanglement detection of quantum systems using machine learning","authors":"Yulei Huang, Liangyu Che, Chao Wei, Feng Xu, Xinfang Nie, Jun Li, Dawei Lu, Tao Xin","doi":"10.1038/s41534-025-00970-w","DOIUrl":"https://doi.org/10.1038/s41534-025-00970-w","url":null,"abstract":"<p>Entanglement plays a crucial role in advancing quantum technologies and exploring quantum many-body simulations. Here, we introduce a protocol aided by neural networks for measuring entanglement in both equilibrium and non-equilibrium states of local Hamiltonians, with a favorable amount of training data. Our numerical simulations across various Hamiltonian models and qubit configurations reveal that this approach can predict comprehensive entanglement metrics, such as Rényi entropy, for up to 100 qubits using only single-qubit and two-qubit Pauli measurements. Excitingly, future entanglement dynamics beyond the measurement window can be predicted based solely on previous single-qubit traces. Experimentally, we utilize a nuclear spin quantum processor and a neural network to measure entanglement in the ground and dynamical states of a one-dimensional spin chain. The results demonstrate the feasibility of our method in practical experiments. Therefore, our approach offers a promising method for experimentally measuring entanglement in systems with dozens to hundreds of qubits.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"13 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462757","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}
引用次数: 0
Parallel circuit implementation of variational quantum algorithms 变分量子算法的并行电路实现
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-19 DOI: 10.1038/s41534-025-00982-6
Michele Cattelan, Sheir Yarkoni, Wolfgang Lechner
{"title":"Parallel circuit implementation of variational quantum algorithms","authors":"Michele Cattelan, Sheir Yarkoni, Wolfgang Lechner","doi":"10.1038/s41534-025-00982-6","DOIUrl":"https://doi.org/10.1038/s41534-025-00982-6","url":null,"abstract":"<p>We present a framework to split quantum circuits of variational quantum algorithms (VQAs) to allow for parallel training and execution to solve problems larger than the number of available qubits in a quantum device. We apply this method to combinatorial optimization problems, where inherent structures can be identified, and show how to implement these parallelized quantum circuits. We show how to formulate an objective function for the classical optimizer to guide the optimization towards meaningful solutions. We test our framework by creating a parallelized version of the Quantum Approximate Optimization Algorithm and a variational version of quantum annealing and explain how our framework applies to other quantum optimization algorithms. We provide results obtained both from simulation and experiments on real hardware. Our results show that the information lost by splitting the quantum circuits can be partially recovered by optimizing a global objective function evaluated with the separate circuit samples.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"26 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143452191","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}
引用次数: 0
Maximal steady-state entanglement in autonomous quantum thermal machines 自主量子热机中的最大稳态纠缠
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-19 DOI: 10.1038/s41534-025-00981-7
Shishir Khandelwal, Björn Annby-Andersson, Giovanni Francesco Diotallevi, Andreas Wacker, Armin Tavakoli
{"title":"Maximal steady-state entanglement in autonomous quantum thermal machines","authors":"Shishir Khandelwal, Björn Annby-Andersson, Giovanni Francesco Diotallevi, Andreas Wacker, Armin Tavakoli","doi":"10.1038/s41534-025-00981-7","DOIUrl":"https://doi.org/10.1038/s41534-025-00981-7","url":null,"abstract":"<p>We devise an autonomous quantum thermal machine consisting of three pairwise-interacting qubits, two of which are locally coupled to thermal reservoirs. The machine operates autonomously, as it requires no time-coherent control, external driving or quantum bath engineering, and is instead propelled by a chemical potential bias. Under ideal conditions, we show that this out-of-equilibrium system can deterministically generate a maximally entangled steady-state between two of the qubits, or any desired pure two-qubit entangled state, emerging as a dark state of the system. We study the robustness of entanglement production with respect to several relevant parameters, obtaining nearly-maximally-entangled states well-away from the ideal regime of operation. Furthermore, we show that our machine architecture can be generalised to a configuration with 2<i>n</i> − 1 qubits, in which only a potential bias and two-body interactions are sufficient to generate genuine multipartite maximally entangled steady states in the form of a W state of <i>n</i> qubits.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"49 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143451502","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}
引用次数: 0
Stabilization of Kerr-cat qubits with quantum circuit refrigerator 用量子电路制冷机稳定Kerr-cat量子比特
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-15 DOI: 10.1038/s41534-025-00974-6
Shumpei Masuda, Shunsuke Kamimura, Tsuyoshi Yamamoto, Takaaki Aoki, Akiyoshi Tomonaga
{"title":"Stabilization of Kerr-cat qubits with quantum circuit refrigerator","authors":"Shumpei Masuda, Shunsuke Kamimura, Tsuyoshi Yamamoto, Takaaki Aoki, Akiyoshi Tomonaga","doi":"10.1038/s41534-025-00974-6","DOIUrl":"https://doi.org/10.1038/s41534-025-00974-6","url":null,"abstract":"<p>A periodically driven superconducting nonlinear resonator can implement a Kerr-cat qubit, which provides a promising route to a quantum computer with a long lifetime. However, the system is vulnerable to pure dephasing, which causes unwanted excitations outside the qubit subspace. Therefore, we require a refrigeration technology that confines the system in the qubit subspace. We theoretically study on-chip refrigeration for Kerr-cat qubits based on photon-assisted electron tunneling at tunneling junctions, called quantum circuit refrigerators (QCR). Rates of QCR-induced deexcitations of the system can be changed by more than four orders of magnitude by tuning a bias voltage across the tunneling junctions. Unwanted QCR-induced bit flips are greatly suppressed due to quantum interference in the tunneling process, and thus the long lifetime is preserved. The QCR can serve as a tunable dissipation source that stabilizes Kerr-cat qubits.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"14 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143417726","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}
引用次数: 0
Contextual subspace variational quantum eigensolver calculation of the dissociation curve of molecular nitrogen on a superconducting quantum computer 超导量子计算机上分子氮解离曲线的上下文子空间变分量子特征解算
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-12 DOI: 10.1038/s41534-024-00952-4
Tim Weaving, Alexis Ralli, Peter J. Love, Sauro Succi, Peter V. Coveney
{"title":"Contextual subspace variational quantum eigensolver calculation of the dissociation curve of molecular nitrogen on a superconducting quantum computer","authors":"Tim Weaving, Alexis Ralli, Peter J. Love, Sauro Succi, Peter V. Coveney","doi":"10.1038/s41534-024-00952-4","DOIUrl":"https://doi.org/10.1038/s41534-024-00952-4","url":null,"abstract":"<p>We present an experimental demonstration of the Contextual Subspace Variational Quantum Eigensolver on superconducting hardware. Calculating the potential energy curve of molecular nitrogen proves challenging for many conventional quantum chemistry techniques, since static correlation dominates in the dissociation limit. Our quantum simulations retain good agreement with the Full Configuration Interaction energy, outperforming all benchmarked single-reference wavefunction techniques in capturing the bond-breaking appropriately. Moreover, our methodology is competitive with multiconfigurational approaches but at a saving of quantum resource, meaning larger active spaces can be treated for a fixed qubit allowance. To achieve this result, we deploy an error mitigation/suppression strategy comprised of Dynamical Decoupling, Measurement-Error Mitigation and Zero-Noise Extrapolation. Circuit parallelization also provides passive noise-averaging and improves the effective shot yield to reduce the measurement overhead. Furthermore, we introduce a modified adaptive ansatz construction algorithm that incorporates hardware awareness into our variational circuits, minimizing the transpilation cost for the target qubit topology.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"78 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143393008","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}
引用次数: 0
Remote cooling of spin-ensembles through a spin-mechanical hybrid interface 通过自旋-机械混合界面远程冷却自旋系综
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-07 DOI: 10.1038/s41534-025-00968-4
Yang Wang, Durga Bhaktavatsala Rao Dasari, Jörg Wrachtrup
{"title":"Remote cooling of spin-ensembles through a spin-mechanical hybrid interface","authors":"Yang Wang, Durga Bhaktavatsala Rao Dasari, Jörg Wrachtrup","doi":"10.1038/s41534-025-00968-4","DOIUrl":"https://doi.org/10.1038/s41534-025-00968-4","url":null,"abstract":"<p>We present a protocol for the ground-state cooling of a tripartite hybrid quantum system, in which a macroscopic oscillator acts as a mediator between a single-probe spin and a remote spin ensemble. In the presence of weak dispersive coupling between the spins and the oscillator, cooling of the oscillator and the ensemble spins can be achieved by exploiting the feedback from frequent measurements of the single-probe spin. We explore the parameter regimes necessary to cool the ensemble, the oscillator, or both to their thermal ground states. This novel cooling protocol shows that, even with only weak dispersive coupling, energy transfer-like effects can be obtained by simply manipulating the probe spin. These results not only contribute to the development of a practical solution for cooling/polarizing large spin ensembles but also provide a relatively simple means of tuning the dynamics of a hybrid system. The proposed protocol thus has broader implications for advancing various quantum technology applications, such as macroscopic quantum state generation and remote sensing.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"16 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143258565","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}
引用次数: 0
Universal validity of the second law of information thermodynamics 信息热力学第二定律的普遍有效性
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-07 DOI: 10.1038/s41534-024-00922-w
Shintaro Minagawa, M. Hamed Mohammady, Kenta Sakai, Kohtaro Kato, Francesco Buscemi
{"title":"Universal validity of the second law of information thermodynamics","authors":"Shintaro Minagawa, M. Hamed Mohammady, Kenta Sakai, Kohtaro Kato, Francesco Buscemi","doi":"10.1038/s41534-024-00922-w","DOIUrl":"https://doi.org/10.1038/s41534-024-00922-w","url":null,"abstract":"<p>Adiabatic measurements, followed by feedback and erasure protocols, have often been considered as a model to embody Maxwell’s Demon paradox and to study the interplay between thermodynamics and information processing. Such studies have led to the conclusion, now widely accepted in the community, that Maxwell’s Demon and the second law of thermodynamics can peacefully coexist because any gain provided by the demon must be offset by the cost of performing the measurement and resetting the demon’s memory to its initial state. Statements of this kind are collectively referred to as <i>second laws of information thermodynamics</i> and have recently been extended to include quantum theoretical scenarios. However, previous studies in this direction have made several assumptions, particularly about the feedback process and the demon’s memory readout, and thus arrived at statements that are not universally applicable and whose range of validity is not clear. In this work, we fill this gap by precisely characterizing the full range of quantum feedback control and erasure protocols that are overall consistent with the second law of thermodynamics. This leads us to conclude that the second law of information thermodynamics is indeed <i>universal</i>: it must hold for any quantum feedback control and erasure protocol, regardless of the measurement process involved, as long as the protocol is overall compatible with thermodynamics. Our comprehensive analysis not only encompasses new scenarios but also retrieves previous ones, doing so with fewer assumptions. This simplification contributes to a clearer understanding of the theory.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"12 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143258676","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}
引用次数: 0
Microscopic parametrizations for gate set tomography under coloured noise 彩色噪声下门集层析成像的微观参数化
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-06 DOI: 10.1038/s41534-025-00976-4
P. Viñas, A. Bermudez
{"title":"Microscopic parametrizations for gate set tomography under coloured noise","authors":"P. Viñas, A. Bermudez","doi":"10.1038/s41534-025-00976-4","DOIUrl":"https://doi.org/10.1038/s41534-025-00976-4","url":null,"abstract":"<p>Gate set tomography (GST) allows for a self-consistent characterization of noisy quantum information processors (QIPs). The standard approach treats QIPs as black boxes only constrained by the laws of physics, attaining full generality at a considerable resource cost: numerous circuits must be run in order to amplify each of the gate set parameters. In this work, we show that a microscopic parametrization of quantum gates under time-correlated noise on the driving phase, motivated by recent experiments with trapped-ion gates, enables a more efficient version of GST. Adopting the formalism of filter functions over the noise spectral densities, we discuss the minimal parametrizations of the gate set that include the effect of non-Markovian quantum evolutions during the individual gates. We compare the estimated gate sets obtained by our method and the standard long-sequence GST, discussing their accuracies and showcasing the advantages of the parametrized approach in terms of the sampling complexity.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"62 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143258677","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}
引用次数: 0
Low-error encoder for time-bin and decoy states for quantum key distribution 用于时间箱和量子密钥分发的诱饵状态的低误差编码器
IF 7.6 1区 物理与天体物理
npj Quantum Information Pub Date : 2025-02-06 DOI: 10.1038/s41534-024-00923-9
Davide Scalcon, Elisa Bazzani, Giuseppe Vallone, Paolo Villoresi, Marco Avesani
{"title":"Low-error encoder for time-bin and decoy states for quantum key distribution","authors":"Davide Scalcon, Elisa Bazzani, Giuseppe Vallone, Paolo Villoresi, Marco Avesani","doi":"10.1038/s41534-024-00923-9","DOIUrl":"https://doi.org/10.1038/s41534-024-00923-9","url":null,"abstract":"<p>Time-bin encoding is a robust method for implementing quantum key distribution (QKD) on optical fiber channels, minimizing drift-induced errors. However, interferometric structures make achieving stable and low intrinsic Quantum Bit Error Rate (QBER) challenging. A key device for decoy-state QKD is the state encoder, which must produce low-error, stable states with varying photon mean values. Here, we introduce the MacZac (<i>Mac</i>h-<i>Z</i>ehnder-S<i>a</i>gna<i>c</i>), a time-bin encoder with ultra-low QBER (&lt;2 × 10<sup>−5</sup>) and high stability. Based on nested Sagnac and Mach-Zehnder interferometers, it uses a single phase modulator for both decoy and state preparation, simplifying the optical setup. The encoder requires no active compensation and can generate states of arbitrary dimension. We experimentally tested it as a standalone component and in a QKD experiment. With its low QBER, stability, and simplicity, this device is a key building block for high-performance, low-cost QKD systems.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"50 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143191973","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}
引用次数: 0
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