Pub Date : 2025-11-28DOI: 10.1038/s41534-025-01136-4
Yuxuan Yan, Zhenyu Du, Junjie Chen, Xiongfeng Ma
Finding solid and practical quantum advantages via noisy quantum devices without error correction is a critical but challenging problem. Conversely, comprehending the fundamental limitations of the state-of-the-art is equally crucial. In this work, we consider the class of strictly contractive unital noise and derive its analytical representation by decomposition. Under such noise, we observe the polynomial-time indistinguishability of n -qubit devices from random coins when circuit depths exceed $$Omega (log (n))$$Ω(log(n)) . Even with classical processing, we demonstrate the absence of computational advantage in polynomial-time algorithms with super-logarithmic noisy circuit depths. These results impact variational quantum algorithms, error mitigation, and quantum simulation with polynomial depth. Furthermore, we consider noisy quantum devices with a restricted gate topology. For one-dimensional noisy qubit circuits, we rule out super-polynomial quantum advantages in all-depth regimes. We also establish upper limits on entanglement generation: $$O(log (n))$$O(log(n)) for one-dimensional circuits and $$O(sqrt{n}log (n))$$O(nlog(n)) for two-dimensional circuits. Our findings underscore the computational capacity and entanglement scalability constraints in noisy quantum devices.
通过无纠错的噪声量子器件寻找固体和实用的量子优势是一个关键但具有挑战性的问题。相反，理解最先进技术的基本局限性同样至关重要。在这项工作中，我们考虑了一类严格压缩的单位噪声，并通过分解导出了它的解析表示。在这种噪声下，当电路深度超过$$Omega (log (n))$$ Ω （log (n)）时，我们观察到n量子位器件与随机硬币的多项式时间不可区分性。即使使用经典处理，我们也证明了在具有超对数噪声电路深度的多项式时间算法中缺乏计算优势。这些结果影响了变分量子算法、误差缓解和多项式深度的量子模拟。此外，我们考虑具有受限门拓扑的噪声量子器件。对于一维噪声量子比特电路，我们排除了在全深度区域的超多项式量子优势。我们还建立了纠缠产生的上限：一维电路的$$O(log (n))$$ O （log (n)）和二维电路的$$O(sqrt{n}log (n))$$ O （n log (n)）。我们的发现强调了噪声量子器件的计算能力和纠缠可扩展性限制。
{"title":"Limitations of noisy quantum devices in computing and entangling power","authors":"Yuxuan Yan, Zhenyu Du, Junjie Chen, Xiongfeng Ma","doi":"10.1038/s41534-025-01136-4","DOIUrl":"https://doi.org/10.1038/s41534-025-01136-4","url":null,"abstract":"Finding solid and practical quantum advantages via noisy quantum devices without error correction is a critical but challenging problem. Conversely, comprehending the fundamental limitations of the state-of-the-art is equally crucial. In this work, we consider the class of strictly contractive unital noise and derive its analytical representation by decomposition. Under such noise, we observe the polynomial-time indistinguishability of <jats:italic>n</jats:italic> -qubit devices from random coins when circuit depths exceed <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$Omega (log (n))$$</jats:tex-math> <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:mi>Ω</mml:mi> <mml:mo>(</mml:mo> <mml:mi>log</mml:mi> <mml:mo>(</mml:mo> <mml:mi>n</mml:mi> <mml:mo>)</mml:mo> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> </jats:alternatives> </jats:inline-formula> . Even with classical processing, we demonstrate the absence of computational advantage in polynomial-time algorithms with super-logarithmic noisy circuit depths. These results impact variational quantum algorithms, error mitigation, and quantum simulation with polynomial depth. Furthermore, we consider noisy quantum devices with a restricted gate topology. For one-dimensional noisy qubit circuits, we rule out super-polynomial quantum advantages in all-depth regimes. We also establish upper limits on entanglement generation: <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$O(log (n))$$</jats:tex-math> <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:mi>O</mml:mi> <mml:mo>(</mml:mo> <mml:mi>log</mml:mi> <mml:mo>(</mml:mo> <mml:mi>n</mml:mi> <mml:mo>)</mml:mo> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> </jats:alternatives> </jats:inline-formula> for one-dimensional circuits and <jats:inline-formula> <jats:alternatives> <jats:tex-math>$$O(sqrt{n}log (n))$$</jats:tex-math> <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:mi>O</mml:mi> <mml:mo>(</mml:mo> <mml:msqrt> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> </mml:msqrt> <mml:mi>log</mml:mi> <mml:mo>(</mml:mo> <mml:mi>n</mml:mi> <mml:mo>)</mml:mo> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> </jats:alternatives> </jats:inline-formula> for two-dimensional circuits. Our findings underscore the computational capacity and entanglement scalability constraints in noisy quantum devices.","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"59 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145611511","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}
Pub Date : 2025-11-27DOI: 10.1038/s41534-025-01132-8
Robert J. P. T. de Keijzer, Luke Y. Visser, Oliver Tse, Servaas J. J. M. F. Kokkelmans
We report an algorithm that is able to tailor qubit interactions for individual variational quantum algorithm problems. The algorithm leverages the unique ability of a neutral atom tweezer platform to realize arbitrary qubit position configurations. These configurations determine the degree of entanglement available to a variational quantum algorithm via the interatomic interactions. Good configurations will accelerate pulse optimization convergence and help mitigate barren plateaus. As gradient-based approaches are ineffective for position optimization due to the divergent R−6 nature of Rydberg interactions, we opt to use a consensus-based algorithm. By sampling configuration space instead of using gradient information, the consensus-based algorithm is able to successfully optimize the positions, yielding adapted variational quantum algorithm ansatzes that lead to both faster convergence and lower errors. We show that these optimized configurations generally result in large improvements in the system’s ability to solve ground state minimization problems for both random Hamiltonians and small molecules.
{"title":"Consensus-based qubit configuration optimization for variational algorithms on neutral atom quantum systems","authors":"Robert J. P. T. de Keijzer, Luke Y. Visser, Oliver Tse, Servaas J. J. M. F. Kokkelmans","doi":"10.1038/s41534-025-01132-8","DOIUrl":"https://doi.org/10.1038/s41534-025-01132-8","url":null,"abstract":"We report an algorithm that is able to tailor qubit interactions for individual variational quantum algorithm problems. The algorithm leverages the unique ability of a neutral atom tweezer platform to realize arbitrary qubit position configurations. These configurations determine the degree of entanglement available to a variational quantum algorithm via the interatomic interactions. Good configurations will accelerate pulse optimization convergence and help mitigate barren plateaus. As gradient-based approaches are ineffective for position optimization due to the divergent <jats:italic>R</jats:italic> <jats:sup>−6</jats:sup> nature of Rydberg interactions, we opt to use a <jats:italic>consensus-based</jats:italic> algorithm. By sampling configuration space instead of using gradient information, the consensus-based algorithm is able to successfully optimize the positions, yielding adapted variational quantum algorithm ansatzes that lead to both faster convergence and lower errors. We show that these optimized configurations generally result in large improvements in the system’s ability to solve ground state minimization problems for both random Hamiltonians and small molecules.","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"194 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145608802","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}
Pub Date : 2025-11-27DOI: 10.1038/s41534-025-01144-4
Chuanzhou Zhu, Peter J. Ehlers, Hendra I. Nurdin, Daniel Soh
{"title":"Minimalistic and scalable quantum reservoir computing enhanced with feedback","authors":"Chuanzhou Zhu, Peter J. Ehlers, Hendra I. Nurdin, Daniel Soh","doi":"10.1038/s41534-025-01144-4","DOIUrl":"https://doi.org/10.1038/s41534-025-01144-4","url":null,"abstract":"","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"118 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145609423","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}
Pub Date : 2025-11-27DOI: 10.1038/s41534-025-01130-w
Abhikbrata Sarkar, Pratik Chowdhury, Xuedong Hu, Andre Saraiva, A. S. Dzurak, A. R. Hamilton, Rajib Rahman, Dimitrie Culcer
{"title":"Effect of disorder and strain on the operation of planar Ge hole spin qubits","authors":"Abhikbrata Sarkar, Pratik Chowdhury, Xuedong Hu, Andre Saraiva, A. S. Dzurak, A. R. Hamilton, Rajib Rahman, Dimitrie Culcer","doi":"10.1038/s41534-025-01130-w","DOIUrl":"https://doi.org/10.1038/s41534-025-01130-w","url":null,"abstract":"","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"20 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145608801","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}
Pub Date : 2025-11-25DOI: 10.1038/s41534-025-01128-4
Oskar Leimkuhler, K. Birgitta Whaley
Electronic ground states are of central importance in chemical simulations, but have remained beyond the reach of efficient classical algorithms except in cases of weak electron correlation or one-dimensional spatial geometry. We introduce a hybrid quantum-classical eigenvalue solver that constructs a wavefunction ansatz from a linear combination of matrix product states in rotated orbital bases, enabling the characterization of strongly correlated ground states with arbitrary spatial geometry. The energy is converged via a gradient-free generalized sweep algorithm based on quantum subspace diagonalization, with a potentially exponential speedup in the off-diagonal matrix element contractions upon translation into compact quantum circuits of linear depth in the number of qubits. Chemical accuracy is attained in numerical experiments for both a stretched water molecule and an octahedral arrangement of hydrogen atoms, achieving substantially better correlation energies compared to a unitary coupled-cluster benchmark, with orders of magnitude reductions in quantum resource estimates and a surprisingly high tolerance to shot noise. This proof-of-concept study suggests a promising new avenue for scaling up simulations of strongly correlated chemical systems on near-term quantum hardware.
{"title":"A quantum eigenvalue solver based on tensor networks","authors":"Oskar Leimkuhler, K. Birgitta Whaley","doi":"10.1038/s41534-025-01128-4","DOIUrl":"https://doi.org/10.1038/s41534-025-01128-4","url":null,"abstract":"Electronic ground states are of central importance in chemical simulations, but have remained beyond the reach of efficient classical algorithms except in cases of weak electron correlation or one-dimensional spatial geometry. We introduce a hybrid quantum-classical eigenvalue solver that constructs a wavefunction ansatz from a linear combination of matrix product states in rotated orbital bases, enabling the characterization of strongly correlated ground states with arbitrary spatial geometry. The energy is converged via a gradient-free generalized sweep algorithm based on quantum subspace diagonalization, with a potentially exponential speedup in the off-diagonal matrix element contractions upon translation into compact quantum circuits of linear depth in the number of qubits. Chemical accuracy is attained in numerical experiments for both a stretched water molecule and an octahedral arrangement of hydrogen atoms, achieving substantially better correlation energies compared to a unitary coupled-cluster benchmark, with orders of magnitude reductions in quantum resource estimates and a surprisingly high tolerance to shot noise. This proof-of-concept study suggests a promising new avenue for scaling up simulations of strongly correlated chemical systems on near-term quantum hardware.","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"17 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145593349","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}
Pub Date : 2025-11-25DOI: 10.1038/s41534-025-01145-3
Guorui Zhu, Joel Bierman, Jianfeng Lu, Yingzhou Li
{"title":"Quantum circuit for non-unitary linear transformation of basis sets","authors":"Guorui Zhu, Joel Bierman, Jianfeng Lu, Yingzhou Li","doi":"10.1038/s41534-025-01145-3","DOIUrl":"https://doi.org/10.1038/s41534-025-01145-3","url":null,"abstract":"","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"163 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145593350","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}
Pub Date : 2025-11-21DOI: 10.1038/s41534-025-01143-5
I. Arrazola, P. Bertet, Y. Chu, P. Rabl
We study a generic cavity QED setup under conditions where the coupling between the two-level systems and a single bosonic mode is significantly degraded by low-frequency noise. To overcome this problem, we identify pulsed dynamical decoupling strategies that suppress the effects of noise while still allowing for a coherent exchange of excitations between the individual subsystems. The corresponding pulse sequences can be further designed to realize either Jaynes-Cummings, anti-Jaynes-Cummings, or Rabi couplings, as well as different types of cavity-mediated interactions between the two-level systems. A detailed analysis of the residual imperfections demonstrates that this decoupling strategy can boost the effective cooperativity of the cavity QED system by several orders of magnitude and improve the fidelity of quantum-technologically relevant operations accordingly.
{"title":"Engineering protected cavity-QED interactions through pulsed dynamical decoupling","authors":"I. Arrazola, P. Bertet, Y. Chu, P. Rabl","doi":"10.1038/s41534-025-01143-5","DOIUrl":"https://doi.org/10.1038/s41534-025-01143-5","url":null,"abstract":"We study a generic cavity QED setup under conditions where the coupling between the two-level systems and a single bosonic mode is significantly degraded by low-frequency noise. To overcome this problem, we identify pulsed dynamical decoupling strategies that suppress the effects of noise while still allowing for a coherent exchange of excitations between the individual subsystems. The corresponding pulse sequences can be further designed to realize either Jaynes-Cummings, anti-Jaynes-Cummings, or Rabi couplings, as well as different types of cavity-mediated interactions between the two-level systems. A detailed analysis of the residual imperfections demonstrates that this decoupling strategy can boost the effective cooperativity of the cavity QED system by several orders of magnitude and improve the fidelity of quantum-technologically relevant operations accordingly.","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"9 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145559874","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}
Pub Date : 2025-11-20DOI: 10.1038/s41534-025-01119-5
Fenglei Gu, Shankar G. Menon, David Maier, Antariksha Das, Tanmoy Chakraborty, Wolfgang Tittel, Hannes Bernien, Johannes Borregaard
{"title":"Hybrid quantum repeaters with ensemble-based quantum memories and single-spin photon transducers","authors":"Fenglei Gu, Shankar G. Menon, David Maier, Antariksha Das, Tanmoy Chakraborty, Wolfgang Tittel, Hannes Bernien, Johannes Borregaard","doi":"10.1038/s41534-025-01119-5","DOIUrl":"https://doi.org/10.1038/s41534-025-01119-5","url":null,"abstract":"","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"165 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145554226","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}
Pub Date : 2025-11-20DOI: 10.1038/s41534-025-01124-8
Hao-En Li, Yongtao Zhan, Lin Lin
Dissipative engineering is a powerful tool for quantum state preparation, and has drawn significant attention in quantum algorithms and quantum many-body physics in recent years. In this work, we introduce a novel approach using the Lindblad dynamics to efficiently prepare the ground state for general ab initio electronic structure problems on quantum computers, without variational parameters. These problems often involve Hamiltonians that lack geometric locality or sparsity structures, which we address by proposing two generic types of jump operators for the Lindblad dynamics. Type-I jump operators break the particle number symmetry and should be simulated in the Fock space. Type-II jump operators preserves the particle number symmetry and can be simulated more efficiently in the full configuration interaction space. For both types of jump operators, we prove that in a simplified Hartree-Fock framework, the spectral gap of our Lindbladian is lower bounded by a universal constant. For physical observables such as energy and reduced density matrices, the convergence rate of our Lindblad dynamics with Type-I jump operators remains universal, while the convergence rate with Type-II jump operators only depends on coarse grained information such as the number of orbitals and the number of electrons. To validate our approach, we employ a Monte Carlo trajectory-based algorithm for simulating the Lindblad dynamics for full ab initio Hamiltonians, demonstrating its effectiveness on molecular systems amenable to exact wavefunction treatment.
{"title":"Dissipative ground state preparation in ab initio electronic structure theory","authors":"Hao-En Li, Yongtao Zhan, Lin Lin","doi":"10.1038/s41534-025-01124-8","DOIUrl":"https://doi.org/10.1038/s41534-025-01124-8","url":null,"abstract":"Dissipative engineering is a powerful tool for quantum state preparation, and has drawn significant attention in quantum algorithms and quantum many-body physics in recent years. In this work, we introduce a novel approach using the Lindblad dynamics to efficiently prepare the ground state for general ab initio electronic structure problems on quantum computers, without variational parameters. These problems often involve Hamiltonians that lack geometric locality or sparsity structures, which we address by proposing two generic types of jump operators for the Lindblad dynamics. Type-I jump operators break the particle number symmetry and should be simulated in the Fock space. Type-II jump operators preserves the particle number symmetry and can be simulated more efficiently in the full configuration interaction space. For both types of jump operators, we prove that in a simplified Hartree-Fock framework, the spectral gap of our Lindbladian is lower bounded by a <jats:italic>universal</jats:italic> constant. For physical observables such as energy and reduced density matrices, the convergence rate of our Lindblad dynamics with Type-I jump operators remains universal, while the convergence rate with Type-II jump operators only depends on coarse grained information such as the number of orbitals and the number of electrons. To validate our approach, we employ a Monte Carlo trajectory-based algorithm for simulating the Lindblad dynamics for full ab initio Hamiltonians, demonstrating its effectiveness on molecular systems amenable to exact wavefunction treatment.","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":"1 1","pages":""},"PeriodicalIF":7.6,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145554228","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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