Pub Date : 2024-06-21DOI: 10.1038/s41534-024-00846-5
You Zhou, Zhenhuan Liu
Estimating nonlinear functions of quantum states, such as the moment ({{{rm{tr}}}}({rho }^{m})), is of fundamental and practical interest in quantum science and technology. Here we show a quantum-classical hybrid framework to measure them, where the quantum part is constituted by the generalized swap test, and the classical part is realized by postprocessing the result from randomized measurements. This hybrid framework utilizes the partial coherent power of the intermediate-scale quantum processor and, at the same time, dramatically reduces the number of quantum measurements and the cost of classical postprocessing. We demonstrate the advantage of our framework in the tasks of state-moment estimation and quantum error mitigation.
{"title":"A hybrid framework for estimating nonlinear functions of quantum states","authors":"You Zhou, Zhenhuan Liu","doi":"10.1038/s41534-024-00846-5","DOIUrl":"https://doi.org/10.1038/s41534-024-00846-5","url":null,"abstract":"<p>Estimating nonlinear functions of quantum states, such as the moment <span>({{{rm{tr}}}}({rho }^{m}))</span>, is of fundamental and practical interest in quantum science and technology. Here we show a quantum-classical hybrid framework to measure them, where the quantum part is constituted by the generalized swap test, and the classical part is realized by postprocessing the result from randomized measurements. This hybrid framework utilizes the partial coherent power of the intermediate-scale quantum processor and, at the same time, dramatically reduces the number of quantum measurements and the cost of classical postprocessing. We demonstrate the advantage of our framework in the tasks of state-moment estimation and quantum error mitigation.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141436063","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 : 2024-06-19DOI: 10.1038/s41534-024-00852-7
Mats Volmer, Tom Struck, Arnau Sala, Bingjie Chen, Max Oberländer, Tobias Offermann, Ran Xue, Lino Visser, Jhih-Sian Tu, Stefan Trellenkamp, Łukasz Cywiński, Hendrik Bluhm, Lars R. Schreiber
In Si/SiGe heterostructures, the low-lying excited valley state seriously limits the operability and scalability of electron spin qubits. For characterizing and understanding the local variations in valley splitting, fast probing methods with high spatial and energy resolution are lacking. Leveraging the spatial control granted by conveyor-mode spin-coherent electron shuttling, we introduce a method for two-dimensional mapping of the local valley splitting by detecting magnetic field-dependent anticrossings of ground and excited valley states using entangled electron spin-pairs as a probe. The method has sub-μeV energy accuracy and a nanometer lateral resolution. The histogram of valley splittings spanning a large area of 210 nm by 18 nm matches well with statistics obtained by the established but time-consuming magnetospectroscopy method. For the specific heterostructure, we find a nearly Gaussian distribution of valley splittings and a correlation length similar to the quantum dot size. Our mapping method may become a valuable tool for engineering Si/SiGe heterostructures for scalable quantum computing.
在硅/硅锗异质结构中,低洼激发谷态严重限制了电子自旋量子比特的可操作性和可扩展性。为了描述和了解谷分裂的局部变化,目前还缺乏具有高空间和能量分辨率的快速探测方法。利用传送带模式自旋相干电子穿梭所赋予的空间控制能力,我们引入了一种二维绘制局部谷分裂图的方法,即使用纠缠电子自旋对作为探针,通过探测磁场依赖的基态和激发态的反交叉来绘制谷分裂图。该方法具有亚微伏能量精度和纳米级横向分辨率。跨越 210 纳米 x 18 纳米大面积的谷分裂直方图与通过成熟但耗时的磁谱法获得的统计数据非常吻合。对于特定的异质结构,我们发现谷分裂近似高斯分布,相关长度与量子点尺寸相似。我们的制图方法可能会成为用于可扩展量子计算的硅/硅锗异质结构工程设计的重要工具。
{"title":"Mapping of valley splitting by conveyor-mode spin-coherent electron shuttling","authors":"Mats Volmer, Tom Struck, Arnau Sala, Bingjie Chen, Max Oberländer, Tobias Offermann, Ran Xue, Lino Visser, Jhih-Sian Tu, Stefan Trellenkamp, Łukasz Cywiński, Hendrik Bluhm, Lars R. Schreiber","doi":"10.1038/s41534-024-00852-7","DOIUrl":"https://doi.org/10.1038/s41534-024-00852-7","url":null,"abstract":"<p>In Si/SiGe heterostructures, the low-lying excited valley state seriously limits the operability and scalability of electron spin qubits. For characterizing and understanding the local variations in valley splitting, fast probing methods with high spatial and energy resolution are lacking. Leveraging the spatial control granted by conveyor-mode spin-coherent electron shuttling, we introduce a method for two-dimensional mapping of the local valley splitting by detecting magnetic field-dependent anticrossings of ground and excited valley states using entangled electron spin-pairs as a probe. The method has sub-μeV energy accuracy and a nanometer lateral resolution. The histogram of valley splittings spanning a large area of 210 nm by 18 nm matches well with statistics obtained by the established but time-consuming magnetospectroscopy method. For the specific heterostructure, we find a nearly Gaussian distribution of valley splittings and a correlation length similar to the quantum dot size. Our mapping method may become a valuable tool for engineering Si/SiGe heterostructures for scalable quantum computing.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141425322","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 : 2024-06-15DOI: 10.1038/s41534-024-00857-2
Ting Zhang, Graeme Smith, John A. Smolin, Lu Liu, Xu-Jie Peng, Qi Zhao, Davide Girolami, Xiongfeng Ma, Xiao Yuan, He Lu
Entanglement and coherence are fundamental properties of quantum systems, promising to power near-future quantum technologies, such as quantum computation, quantum communication, and quantum metrology. Yet, their quantification, rather than mere detection, generally requires reconstructing the spectrum of quantum states, i.e., experimentally challenging measurement sets that increase exponentially with the system size. Here, we demonstrate quantitative bounds to operationally useful entanglement and coherence that are universally valid, analytically computable, and experimentally friendly. Specifically, our main theoretical results are lower and upper bounds to the coherent information and the relative entropy of coherence in terms of local and global purities of quantum states. To validate our proposal, we experimentally implement two purity detection methods in an optical system: shadow estimation with random measurements and collective measurements on pairs of state copies. The experiment shows that both the coherent information and the relative entropy of coherence of pure and mixed unknown quantum states can be bounded by purity functions. Our research offers an efficient means of verifying large-scale quantum information processing.
{"title":"Quantification of entanglement and coherence with purity detection","authors":"Ting Zhang, Graeme Smith, John A. Smolin, Lu Liu, Xu-Jie Peng, Qi Zhao, Davide Girolami, Xiongfeng Ma, Xiao Yuan, He Lu","doi":"10.1038/s41534-024-00857-2","DOIUrl":"https://doi.org/10.1038/s41534-024-00857-2","url":null,"abstract":"<p>Entanglement and coherence are fundamental properties of quantum systems, promising to power near-future quantum technologies, such as quantum computation, quantum communication, and quantum metrology. Yet, their quantification, rather than mere detection, generally requires reconstructing the spectrum of quantum states, i.e., experimentally challenging measurement sets that increase exponentially with the system size. Here, we demonstrate quantitative bounds to operationally useful entanglement and coherence that are universally valid, analytically computable, and experimentally friendly. Specifically, our main theoretical results are lower and upper bounds to the coherent information and the relative entropy of coherence in terms of local and global purities of quantum states. To validate our proposal, we experimentally implement two purity detection methods in an optical system: shadow estimation with random measurements and collective measurements on pairs of state copies. The experiment shows that both the coherent information and the relative entropy of coherence of pure and mixed unknown quantum states can be bounded by purity functions. Our research offers an efficient means of verifying large-scale quantum information processing.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141329510","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 : 2024-06-10DOI: 10.1038/s41534-024-00855-4
Joshua Ramette, Josiah Sinclair, Nikolas P. Breuckmann, Vladan Vuletić
One of the most promising routes toward scalable quantum computing is a modular approach. We show that distinct surface code patches can be connected in a fault-tolerant manner even in the presence of substantial noise along their connecting interface. We quantify analytically and numerically the combined effect of errors across the interface and bulk. We show that the system can tolerate 14 times higher noise at the interface compared to the bulk, with only a small effect on the code’s threshold and subthreshold behavior, reaching threshold with ~1% bulk errors and ~10% interface errors. This implies that fault-tolerant scaling of error-corrected modular devices is within reach using existing technology.
{"title":"Fault-tolerant connection of error-corrected qubits with noisy links","authors":"Joshua Ramette, Josiah Sinclair, Nikolas P. Breuckmann, Vladan Vuletić","doi":"10.1038/s41534-024-00855-4","DOIUrl":"https://doi.org/10.1038/s41534-024-00855-4","url":null,"abstract":"<p>One of the most promising routes toward scalable quantum computing is a modular approach. We show that distinct surface code patches can be connected in a fault-tolerant manner even in the presence of substantial noise along their connecting interface. We quantify analytically and numerically the combined effect of errors across the interface and bulk. We show that the system can tolerate 14 times higher noise at the interface compared to the bulk, with only a small effect on the code’s threshold and subthreshold behavior, reaching threshold with ~1% bulk errors and ~10% interface errors. This implies that fault-tolerant scaling of error-corrected modular devices is within reach using existing technology.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141304329","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 : 2024-06-10DOI: 10.1038/s41534-024-00829-6
Denis Janković, Jean-Gabriel Hartmann, Mario Ruben, Paul-Antoine Hervieux
As qubit-based platforms face near-term technical challenges in terms of scalability, qudits, d-level bases of quantum information, are being implemented in multiple platforms as an alternative for Quantum Information Processing (QIP). We compare the infidelity scalings of single qudit and multiqubit systems within identical Hilbert space dimensions and noisy environments in the Lindblad formalism. We find them to be gate-independent to first-order and present an analytically-derived critical curve (({d}^{2}-1)/3{log }_{2}(d)) that benchmarks the operational time efficiency of qudits and qubits relative to their decoherence times. This comparison reveals conditions under which qudits offer competitive gate efficiencies compared to leading qubit platforms. Our findings, supported by numerical simulations testing the applicability and limits of the linear response formalism, highlight the relevance of qudits in near-term QIP. This provides a benchmark for evaluating qudit platforms, specifically those with lower dimensionality, in terms of their operational efficiency relative to the qubit state-of-the-art.
由于基于量子比特的平台在可扩展性方面面临短期技术挑战,量子信息的 d 级基础--量子比特正在多个平台中实现,作为量子信息处理(QIP)的替代方案。我们在林德布拉德形式主义中比较了相同希尔伯特空间维度和噪声环境下单量子比特和多量子比特系统的不保真扩展。我们发现它们与一阶门无关,并提出了一条分析得出的临界曲线(({d}^{2}-1)/3{log }_{2}(d)),它是量子比特和量子比特相对于其退相干时间的运行时间效率的基准。这种比较揭示了在哪些条件下,与领先的量子比特平台相比,量子比特能提供具有竞争力的门效率。我们的发现得到了测试线性响应形式的适用性和极限的数值模拟的支持,突出了量子比特在近期 QIP 中的相关性。这为评估量子比特平台,特别是维度较低的量子比特平台的运行效率提供了一个基准。
{"title":"Noisy qudit vs multiple qubits: conditions on gate efficiency for enhancing fidelity","authors":"Denis Janković, Jean-Gabriel Hartmann, Mario Ruben, Paul-Antoine Hervieux","doi":"10.1038/s41534-024-00829-6","DOIUrl":"https://doi.org/10.1038/s41534-024-00829-6","url":null,"abstract":"<p>As qubit-based platforms face near-term technical challenges in terms of scalability, qudits, <i>d</i>-level bases of quantum information, are being implemented in multiple platforms as an alternative for Quantum Information Processing (QIP). We compare the infidelity scalings of single qudit and multiqubit systems within identical Hilbert space dimensions and noisy environments in the Lindblad formalism. We find them to be gate-independent to first-order and present an analytically-derived critical curve <span>(({d}^{2}-1)/3{log }_{2}(d))</span> that benchmarks the operational time efficiency of qudits and qubits relative to their decoherence times. This comparison reveals conditions under which qudits offer competitive gate efficiencies compared to leading qubit platforms. Our findings, supported by numerical simulations testing the applicability and limits of the linear response formalism, highlight the relevance of qudits in near-term QIP. This provides a benchmark for evaluating qudit platforms, specifically those with lower dimensionality, in terms of their operational efficiency relative to the qubit state-of-the-art.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141304444","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 : 2024-06-08DOI: 10.1038/s41534-024-00854-5
Andrew Zhao, Akimasa Miyake
Estimating expectation values is a key subroutine in quantum algorithms. Near-term implementations face two major challenges: a limited number of samples required to learn a large collection of observables, and the accumulation of errors in devices without quantum error correction. To address these challenges simultaneously, we develop a quantum error-mitigation strategy called symmetry-adjusted classical shadows, by adjusting classical-shadow tomography according to how symmetries are corrupted by device errors. As a concrete example, we highlight global U(1) symmetry, which manifests in fermions as particle number and in spins as total magnetization, and illustrate their group-theoretic unification with respective classical-shadow protocols. We establish rigorous sampling bounds under readout errors obeying minimal assumptions, and perform numerical experiments with a more comprehensive model of gate-level errors derived from existing quantum processors. Our results reveal symmetry-adjusted classical shadows as a low-cost strategy to mitigate errors from noisy quantum experiments in the ubiquitous presence of symmetry.
{"title":"Group-theoretic error mitigation enabled by classical shadows and symmetries","authors":"Andrew Zhao, Akimasa Miyake","doi":"10.1038/s41534-024-00854-5","DOIUrl":"https://doi.org/10.1038/s41534-024-00854-5","url":null,"abstract":"<p>Estimating expectation values is a key subroutine in quantum algorithms. Near-term implementations face two major challenges: a limited number of samples required to learn a large collection of observables, and the accumulation of errors in devices without quantum error correction. To address these challenges simultaneously, we develop a quantum error-mitigation strategy called <i>symmetry-adjusted classical shadows</i>, by adjusting classical-shadow tomography according to how symmetries are corrupted by device errors. As a concrete example, we highlight global U(1) symmetry, which manifests in fermions as particle number and in spins as total magnetization, and illustrate their group-theoretic unification with respective classical-shadow protocols. We establish rigorous sampling bounds under readout errors obeying minimal assumptions, and perform numerical experiments with a more comprehensive model of gate-level errors derived from existing quantum processors. Our results reveal symmetry-adjusted classical shadows as a low-cost strategy to mitigate errors from noisy quantum experiments in the ubiquitous presence of symmetry.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141298909","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}
Quantum computers have a potential for solving quantum chemistry problems with higher accuracy than classical computers. Quantum computing quantum Monte Carlo (QC-QMC) is a QMC with a trial state prepared in quantum circuit, which is employed to obtain the ground state with higher accuracy than QMC alone. We propose an algorithm combining QC-QMC with a hybrid tensor network to extend the applicability of QC-QMC beyond a single quantum device size. In a two-layer quantum-quantum tree tensor, our algorithm for the larger trial wave function can be executed than preparable wave function in a device. Our algorithm is evaluated on the Heisenberg chain model, graphite-based Hubbard model, hydrogen plane model, and MonoArylBiImidazole using full configuration interaction QMC. Our algorithm can achieve energy accuracy (specifically, variance) several orders of magnitude higher than QMC, and the hybrid tensor version of QMC gives the same energy accuracy as QC-QMC when the system is appropriately decomposed. Moreover, we develop a pseudo-Hadamard test technique that enables efficient overlap calculations between a trial wave function and an orthonormal basis state. In a real device experiment by using the technique, we obtained almost the same accuracy as the statevector simulator, indicating the noise robustness of our algorithm. These results suggests that the present approach will pave the way to electronic structure calculation for large systems with high accuracy on current quantum devices.
{"title":"Quantum computing quantum Monte Carlo with hybrid tensor network for electronic structure calculations","authors":"Shu Kanno, Hajime Nakamura, Takao Kobayashi, Shigeki Gocho, Miho Hatanaka, Naoki Yamamoto, Qi Gao","doi":"10.1038/s41534-024-00851-8","DOIUrl":"https://doi.org/10.1038/s41534-024-00851-8","url":null,"abstract":"<p>Quantum computers have a potential for solving quantum chemistry problems with higher accuracy than classical computers. Quantum computing quantum Monte Carlo (QC-QMC) is a QMC with a trial state prepared in quantum circuit, which is employed to obtain the ground state with higher accuracy than QMC alone. We propose an algorithm combining QC-QMC with a hybrid tensor network to extend the applicability of QC-QMC beyond a single quantum device size. In a two-layer quantum-quantum tree tensor, our algorithm for the larger trial wave function can be executed than preparable wave function in a device. Our algorithm is evaluated on the Heisenberg chain model, graphite-based Hubbard model, hydrogen plane model, and MonoArylBiImidazole using full configuration interaction QMC. Our algorithm can achieve energy accuracy (specifically, variance) several orders of magnitude higher than QMC, and the hybrid tensor version of QMC gives the same energy accuracy as QC-QMC when the system is appropriately decomposed. Moreover, we develop a pseudo-Hadamard test technique that enables efficient overlap calculations between a trial wave function and an orthonormal basis state. In a real device experiment by using the technique, we obtained almost the same accuracy as the statevector simulator, indicating the noise robustness of our algorithm. These results suggests that the present approach will pave the way to electronic structure calculation for large systems with high accuracy on current quantum devices.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141264823","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}
Cryogenic qubit controllers (QCs) are the key to build large-scale superconducting quantum processors. However, developing scalable QCs is challenging because the cooling power of a dilution refrigerator is too small (~10 μW at ~10 mK) to operate conventional logic families, such as complementary metal-oxide-semiconductor logic and superconducting single-flux-quantum logic, near qubits. Here we report on a scalable QC using an ultra-low-power superconductor logic family, namely adiabatic quantum-flux-parametron (AQFP) logic. The AQFP-based QC, referred to as the AQFP-multiplexed QC (AQFP-mux QC), produces multi-tone microwave signals for qubit control with an extremely small power dissipation of 81.8 pW per qubit. Furthermore, the AQFP-mux QC adopts microwave multiplexing to reduce the number of coaxial cables for operating the entire system. As a proof of concept, we demonstrate an AQFP-mux QC chip that produces microwave signals at two output ports through microwave multiplexing and demultiplexing. Experimental results show an output power of approximately −80 dBm and on/off ratio of ~40 dB at each output port. Basic mixing operation is also demonstrated by observing sideband signals.
{"title":"Microwave-multiplexed qubit controller using adiabatic superconductor logic","authors":"Naoki Takeuchi, Taiki Yamae, Taro Yamashita, Tsuyoshi Yamamoto, Nobuyuki Yoshikawa","doi":"10.1038/s41534-024-00849-2","DOIUrl":"https://doi.org/10.1038/s41534-024-00849-2","url":null,"abstract":"<p>Cryogenic qubit controllers (QCs) are the key to build large-scale superconducting quantum processors. However, developing scalable QCs is challenging because the cooling power of a dilution refrigerator is too small (~10 μW at ~10 mK) to operate conventional logic families, such as complementary metal-oxide-semiconductor logic and superconducting single-flux-quantum logic, near qubits. Here we report on a scalable QC using an ultra-low-power superconductor logic family, namely adiabatic quantum-flux-parametron (AQFP) logic. The AQFP-based QC, referred to as the AQFP-multiplexed QC (AQFP-mux QC), produces multi-tone microwave signals for qubit control with an extremely small power dissipation of 81.8 pW per qubit. Furthermore, the AQFP-mux QC adopts microwave multiplexing to reduce the number of coaxial cables for operating the entire system. As a proof of concept, we demonstrate an AQFP-mux QC chip that produces microwave signals at two output ports through microwave multiplexing and demultiplexing. Experimental results show an output power of approximately −80 dBm and on/off ratio of ~40 dB at each output port. Basic mixing operation is also demonstrated by observing sideband signals.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141236008","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 : 2024-05-31DOI: 10.1038/s41534-024-00850-9
Shi-Ning Sun, Brian Marinelli, Jin Ming Koh, Yosep Kim, Long B. Nguyen, Larry Chen, John Mark Kreikebaum, David I. Santiago, Irfan Siddiqi, Austin J. Minnich
The quantum computation of molecular response properties on near-term quantum hardware is a topic of substantial interest. Computing these properties directly in the frequency domain is desirable, but the circuits require large depth if the typical hardware gate set consisting of single- and two-qubit gates is used. While high-fidelity multipartite gates have been reported recently, their integration into quantum simulation and the demonstration of improved accuracy of the observable properties remains to be shown. Here, we report the application of a high-fidelity multipartite gate, the iToffoli gate, to the computation of frequency-domain response properties of diatomic molecules. The iToffoli gate enables a ~50% reduction in circuit depth and ~40% reduction in circuit execution time compared to the traditional gate set. We show that the molecular properties obtained with the iToffoli gate exhibit comparable or better agreement with theory than those obtained with the native CZ gates. Our work is among the first demonstrations of the practical usage of a native multi-qubit gate in quantum simulation, with diverse potential applications to near-term quantum computation.
{"title":"Quantum computation of frequency-domain molecular response properties using a three-qubit iToffoli gate","authors":"Shi-Ning Sun, Brian Marinelli, Jin Ming Koh, Yosep Kim, Long B. Nguyen, Larry Chen, John Mark Kreikebaum, David I. Santiago, Irfan Siddiqi, Austin J. Minnich","doi":"10.1038/s41534-024-00850-9","DOIUrl":"https://doi.org/10.1038/s41534-024-00850-9","url":null,"abstract":"<p>The quantum computation of molecular response properties on near-term quantum hardware is a topic of substantial interest. Computing these properties directly in the frequency domain is desirable, but the circuits require large depth if the typical hardware gate set consisting of single- and two-qubit gates is used. While high-fidelity multipartite gates have been reported recently, their integration into quantum simulation and the demonstration of improved accuracy of the observable properties remains to be shown. Here, we report the application of a high-fidelity multipartite gate, the iToffoli gate, to the computation of frequency-domain response properties of diatomic molecules. The iToffoli gate enables a ~50% reduction in circuit depth and ~40% reduction in circuit execution time compared to the traditional gate set. We show that the molecular properties obtained with the iToffoli gate exhibit comparable or better agreement with theory than those obtained with the native CZ gates. Our work is among the first demonstrations of the practical usage of a native multi-qubit gate in quantum simulation, with diverse potential applications to near-term quantum computation.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141185239","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 : 2024-05-31DOI: 10.1038/s41534-024-00853-6
Benjamin D. Woods, Hudaiba Soomro, E. S. Joseph, Collin C. D. Frink, Robert Joynt, M. A. Eriksson, Mark Friesen
Engineering conduction-band valley couplings is a key challenge for Si-based spin qubits. Recent work has shown that the most reliable method for enhancing valley couplings entails adding Ge concentration oscillations to the quantum well. However, ultrashort oscillation periods are difficult to grow, while long oscillation periods do not provide useful improvements. Here, we show that the main benefits of short-wavelength oscillations can be achieved in long-wavelength structures through a second-order coupling process involving Brillouin-zone folding induced by shear strain. We finally show that such strain can be achieved through common fabrication techniques, making this an exceptionally promising system for scalable quantum computing.
导带谷耦合工程是硅基自旋量子比特面临的一个关键挑战。最近的研究表明,增强谷耦合的最可靠方法是在量子阱中加入 Ge 浓度振荡。然而,超短振荡周期难以增长,而长振荡周期也无法提供有用的改进。在这里,我们展示了短波长振荡的主要优势可以通过剪切应变诱导的布里渊区折叠的二阶耦合过程在长波长结构中实现。我们最终证明,这种应变可以通过普通制造技术实现,从而使其成为一种极具潜力的可扩展量子计算系统。
{"title":"Coupling conduction-band valleys in SiGe heterostructures via shear strain and Ge concentration oscillations","authors":"Benjamin D. Woods, Hudaiba Soomro, E. S. Joseph, Collin C. D. Frink, Robert Joynt, M. A. Eriksson, Mark Friesen","doi":"10.1038/s41534-024-00853-6","DOIUrl":"https://doi.org/10.1038/s41534-024-00853-6","url":null,"abstract":"<p>Engineering conduction-band valley couplings is a key challenge for Si-based spin qubits. Recent work has shown that the most reliable method for enhancing valley couplings entails adding Ge concentration oscillations to the quantum well. However, ultrashort oscillation periods are difficult to grow, while long oscillation periods do not provide useful improvements. Here, we show that the main benefits of short-wavelength oscillations can be achieved in long-wavelength structures through a second-order coupling process involving Brillouin-zone folding induced by shear strain. We finally show that such strain can be achieved through common fabrication techniques, making this an exceptionally promising system for scalable quantum computing.</p>","PeriodicalId":19212,"journal":{"name":"npj Quantum Information","volume":null,"pages":null},"PeriodicalIF":7.6,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141185241","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}