Pub Date : 2024-09-19DOI: 10.1088/2058-9565/ad53fa
Ge Bai and Iman Marvian
We study quantum circuits constructed from gates and, more generally, from the entangling gates that can be realized with the XX + YY interaction alone. Such gates preserve the Hamming weight of states in the computational basis, which means they respect the global U(1) symmetry corresponding to rotations around the z axis. Equivalently, assuming that the intrinsic Hamiltonian of each qubit in the system is the Pauli Z operator, they conserve the total energy of the system. We develop efficient methods for synthesizing circuits realizing any desired energy-conserving unitary using XX + YY interaction with or without single-qubit rotations around the z axis. Interestingly, implementing generic energy-conserving unitaries, such as CCZ and Fredkin gates, with two-local energy-conserving gates requires the use of ancilla qubits. When single-qubit rotations around the z-axis are permitted, our scheme requires only a single ancilla qubit, whereas with the XX+YY interaction alone, it requires two ancilla qubits. In addition to exact realizations, we also consider approximate realizations and show how a general energy-conserving unitary can be synthesized using only a sequence of gates and two ancillary qubits, with arbitrarily small error, which can be bounded via the Solovay–Kitaev theorem. Our methods are also applicable for synthesizing energy-conserving unitaries when, rather than the XX + YY interaction, one has access to any other energy-conserving two-body interaction that is not diagonal in the computational basis, such as the Heisenberg exchange interaction. We briefly discuss the applications of these circuits in the context of quantum computing, quantum thermodynamics, and quantum clocks.
我们研究由门构造的量子电路，更广泛地说，是由仅通过 XX + YY 相互作用就能实现的纠缠门构造的量子电路。这种门保留了计算基础中状态的汉明权重，这意味着它们尊重与绕 Z 轴转动相对应的全局 U(1) 对称性。等效地，假设系统中每个量子比特的内在哈密顿是保利 Z 算子，它们就能保持系统的总能量。我们开发了高效的方法，利用 XX + YY 相互作用（无论是否存在绕 Z 轴的单量子比特旋转）合成电路，实现任何所需的能量守恒单元。有趣的是，使用双局域能量守恒门实现通用能量守恒单元（如 CCZ 门和 Fredkin 门）需要使用 ancilla 量子位。当允许围绕 Z 轴进行单量子比特旋转时，我们的方案只需要一个 ancilla 量子比特，而如果仅使用 XX+YY 相互作用，则需要两个 ancilla 量子比特。除了精确实现外，我们还考虑了近似实现，并展示了如何只用一串门和两个辅助量子比特就能合成一般的能量守恒单元，而且误差可以任意小，并可通过索洛维-基塔耶夫定理对误差进行约束。我们的方法也适用于合成能量守恒单体，当我们可以利用计算基础中不对角的任何其他能量守恒双体相互作用，如海森堡交换相互作用，而不是 XX + YY 相互作用时。我们简要讨论了这些电路在量子计算、量子热力学和量子钟方面的应用。
{"title":"Synthesis of energy-conserving quantum circuits with XY interaction","authors":"Ge Bai and Iman Marvian","doi":"10.1088/2058-9565/ad53fa","DOIUrl":"https://doi.org/10.1088/2058-9565/ad53fa","url":null,"abstract":"We study quantum circuits constructed from gates and, more generally, from the entangling gates that can be realized with the XX + YY interaction alone. Such gates preserve the Hamming weight of states in the computational basis, which means they respect the global U(1) symmetry corresponding to rotations around the z axis. Equivalently, assuming that the intrinsic Hamiltonian of each qubit in the system is the Pauli Z operator, they conserve the total energy of the system. We develop efficient methods for synthesizing circuits realizing any desired energy-conserving unitary using XX + YY interaction with or without single-qubit rotations around the z axis. Interestingly, implementing generic energy-conserving unitaries, such as CCZ and Fredkin gates, with two-local energy-conserving gates requires the use of ancilla qubits. When single-qubit rotations around the z-axis are permitted, our scheme requires only a single ancilla qubit, whereas with the XX+YY interaction alone, it requires two ancilla qubits. In addition to exact realizations, we also consider approximate realizations and show how a general energy-conserving unitary can be synthesized using only a sequence of gates and two ancillary qubits, with arbitrarily small error, which can be bounded via the Solovay–Kitaev theorem. Our methods are also applicable for synthesizing energy-conserving unitaries when, rather than the XX + YY interaction, one has access to any other energy-conserving two-body interaction that is not diagonal in the computational basis, such as the Heisenberg exchange interaction. We briefly discuss the applications of these circuits in the context of quantum computing, quantum thermodynamics, and quantum clocks.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"34 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142275621","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-18DOI: 10.1088/2058-9565/ad7756
Florian Kayatz, Jonas Mielke and Guido Burkard
Strong charge-photon coupling allows the coherent coupling of a charge qubit, realized by a single charge carrier (either an electron or a hole) in a double quantum dot, to photons of a microwave resonator. Here, we theoretically demonstrate that, in the dispersive regime, the photons can mediate both an gate as well as a gate between two distant charge qubits. We provide a thorough discussion of the impact of the dominant noise sources, resonator damping and charge qubit dephasing on the average gate fidelity. Assuming a state-of-the art resonator decay rate and charge qubit dephasing rate, the predicted average gate fidelities are below 90%. However, a decrease of the charge qubit dephasing rate by one order of magnitude is conjectured to result in gate fidelities surpassing 95%.
{"title":"Resonator-mediated quantum gate between distant charge qubits","authors":"Florian Kayatz, Jonas Mielke and Guido Burkard","doi":"10.1088/2058-9565/ad7756","DOIUrl":"https://doi.org/10.1088/2058-9565/ad7756","url":null,"abstract":"Strong charge-photon coupling allows the coherent coupling of a charge qubit, realized by a single charge carrier (either an electron or a hole) in a double quantum dot, to photons of a microwave resonator. Here, we theoretically demonstrate that, in the dispersive regime, the photons can mediate both an gate as well as a gate between two distant charge qubits. We provide a thorough discussion of the impact of the dominant noise sources, resonator damping and charge qubit dephasing on the average gate fidelity. Assuming a state-of-the art resonator decay rate and charge qubit dephasing rate, the predicted average gate fidelities are below 90%. However, a decrease of the charge qubit dephasing rate by one order of magnitude is conjectured to result in gate fidelities surpassing 95%.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"193 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-18DOI: 10.1088/2058-9565/ad7881
Philipp Stammer, Tomás Fernández Martos, Maciej Lewenstein and Grzegorz Rajchel-Mieldzioć
In the domain of quantum metrology, cat states have demonstrated their utility despite their inherent fragility with respect to losses. Here, we introduce noise robust optical cat states which exhibit a metrological robustness for phase estimation in the regime of high photon numbers. These cat states are obtained from the intense laser driven process of high harmonic generation (HHG), and show a resilience against photon losses. Focusing on a realistic scenario including experimental imperfections we opt for the case in which we can maximize the lower bound of the quantum Fisher information (QFI) instead of analyzing the best case scenario. We show that the decrease of the QFI in the lossy case is suppressed for the HHG-cat state compared to the even and odd counterparts. In the regime of small losses of just a single photon, the HHG-cat state remains almost pure while the even/odd cat state counterparts rapidly decohere to the maximally mixed state. More importantly, this translates to a significantly enhanced robustness for the HHG-cat against photon loss, demonstrating that high photon number optical cat states can indeed be used for metrological applications even in the presence of losses.
{"title":"Metrological robustness of high photon number optical cat states","authors":"Philipp Stammer, Tomás Fernández Martos, Maciej Lewenstein and Grzegorz Rajchel-Mieldzioć","doi":"10.1088/2058-9565/ad7881","DOIUrl":"https://doi.org/10.1088/2058-9565/ad7881","url":null,"abstract":"In the domain of quantum metrology, cat states have demonstrated their utility despite their inherent fragility with respect to losses. Here, we introduce noise robust optical cat states which exhibit a metrological robustness for phase estimation in the regime of high photon numbers. These cat states are obtained from the intense laser driven process of high harmonic generation (HHG), and show a resilience against photon losses. Focusing on a realistic scenario including experimental imperfections we opt for the case in which we can maximize the lower bound of the quantum Fisher information (QFI) instead of analyzing the best case scenario. We show that the decrease of the QFI in the lossy case is suppressed for the HHG-cat state compared to the even and odd counterparts. In the regime of small losses of just a single photon, the HHG-cat state remains almost pure while the even/odd cat state counterparts rapidly decohere to the maximally mixed state. More importantly, this translates to a significantly enhanced robustness for the HHG-cat against photon loss, demonstrating that high photon number optical cat states can indeed be used for metrological applications even in the presence of losses.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"475 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245178","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-16DOI: 10.1088/2058-9565/ad77ef
A Duspayev, C Owens, B Dash and G Raithel
We analyze an optical atomic clock using two-photon transitions in rubidium. Four one- and two-color excitation schemes to probe the and fine-structure states are considered in detail. We compare key characteristics of Rb and two-photon clocks. The clock features a high signal-to-noise ratio due to two-photon decay at favorable wavelengths, low dc electric and magnetic susceptibilities, and minimal black-body shifts. Ac Stark shifts from the clock interrogation lasers are compensated by two-color Rabi-frequency matching. We identify a 'magic' wavelength near 1060 nm, which allows for in-trap, Doppler-free clock-transition interrogation with lattice-trapped cold atoms. From our analysis of clock statistics and systematics, we project a quantum-noise-limited relative clock stability at the -level, with integration time τ in seconds, and a relative accuracy of . We describe a potential architecture for implementing the proposed clock using a single telecom clock laser at 1550 nm, which is conducive to optical communication and long-distance clock comparisons. Our work could be of interest in efforts to realize small and portable Rb clocks and in high-precision measurements of atomic properties of Rb -states.
{"title":"An optical atomic clock using 4 D J ...","authors":"A Duspayev, C Owens, B Dash and G Raithel","doi":"10.1088/2058-9565/ad77ef","DOIUrl":"https://doi.org/10.1088/2058-9565/ad77ef","url":null,"abstract":"We analyze an optical atomic clock using two-photon transitions in rubidium. Four one- and two-color excitation schemes to probe the and fine-structure states are considered in detail. We compare key characteristics of Rb and two-photon clocks. The clock features a high signal-to-noise ratio due to two-photon decay at favorable wavelengths, low dc electric and magnetic susceptibilities, and minimal black-body shifts. Ac Stark shifts from the clock interrogation lasers are compensated by two-color Rabi-frequency matching. We identify a 'magic' wavelength near 1060 nm, which allows for in-trap, Doppler-free clock-transition interrogation with lattice-trapped cold atoms. From our analysis of clock statistics and systematics, we project a quantum-noise-limited relative clock stability at the -level, with integration time τ in seconds, and a relative accuracy of . We describe a potential architecture for implementing the proposed clock using a single telecom clock laser at 1550 nm, which is conducive to optical communication and long-distance clock comparisons. Our work could be of interest in efforts to realize small and portable Rb clocks and in high-precision measurements of atomic properties of Rb -states.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"94 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142235243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-15DOI: 10.1088/2058-9565/ad7498
Alessandro Candeloro, Zahra Pazhotan and Matteo G A Paris
We study the role of probe dimension in determining the bounds of precision and the level of incompatibility in multi-parameter quantum estimation problems. In particular, we focus on the paradigmatic case of unitary encoding generated by and compare precision and incompatibility in the estimation of the same parameters across representations of different dimensions. For two- and three-parameter unitary models, we prove that if the dimension of the probe is smaller than the number of parameters, then simultaneous estimation is not possible (the quantum Fisher matrix is singular). If the dimension is equal to the number of parameters, estimation is possible but the model exhibits maximal (asymptotic) incompatibility. However, for larger dimensions, there is always a state for which the incompatibility vanishes, and the symmetric Cramér-Rao bound is achievable. We also critically examine the performance of the so-called asymptotic incompatibility (AI) in characterising the difference between the Holevo-Cramér-Rao bound and the Symmetric Logarithmic Derivative one, showing that the AI measure alone may fail to adequately quantify this gap. Assessing the determinant of the Quantum Fisher Information Matrix is crucial for a precise characterisation of the model’s nature. Nonetheless, the AI measure still plays a relevant role since it encapsulates the non-classicality of the model in one scalar quantity rather than in a matrix form (i.e. the Uhlmann curvature).
我们研究了探测维度在多参数量子估计问题中决定精度界限和不相容程度的作用。特别是，我们将重点放在由单元编码生成的典型案例上，并比较不同维度的表征在估计相同参数时的精度和不兼容性。对于两参数和三参数单元模型，我们证明，如果探针的维度小于参数数，那么同步估计是不可能的（量子费雪矩阵是奇异的）。如果维数等于参数数，则可以进行估计，但模型会表现出最大（渐近）不相容性。然而，对于更大的维度，总有一种不相容消失的状态，对称克拉梅-拉奥约束是可以实现的。我们还批判性地考察了所谓渐进不相容（AI）在描述 Holevo-Cramér-Rao 约束与对称对数衍射约束之间的差异时的表现，结果表明仅用 AI 度量可能无法充分量化这一差距。评估量子费雪信息矩阵的行列式对于精确描述模型的性质至关重要。尽管如此，人工智能度量仍然发挥着重要作用，因为它以一个标量而不是矩阵形式（即乌尔曼曲率）概括了模型的非经典性。
{"title":"Dimension matters: precision and incompatibility in multi-parameter quantum estimation models","authors":"Alessandro Candeloro, Zahra Pazhotan and Matteo G A Paris","doi":"10.1088/2058-9565/ad7498","DOIUrl":"https://doi.org/10.1088/2058-9565/ad7498","url":null,"abstract":"We study the role of probe dimension in determining the bounds of precision and the level of incompatibility in multi-parameter quantum estimation problems. In particular, we focus on the paradigmatic case of unitary encoding generated by and compare precision and incompatibility in the estimation of the same parameters across representations of different dimensions. For two- and three-parameter unitary models, we prove that if the dimension of the probe is smaller than the number of parameters, then simultaneous estimation is not possible (the quantum Fisher matrix is singular). If the dimension is equal to the number of parameters, estimation is possible but the model exhibits maximal (asymptotic) incompatibility. However, for larger dimensions, there is always a state for which the incompatibility vanishes, and the symmetric Cramér-Rao bound is achievable. We also critically examine the performance of the so-called asymptotic incompatibility (AI) in characterising the difference between the Holevo-Cramér-Rao bound and the Symmetric Logarithmic Derivative one, showing that the AI measure alone may fail to adequately quantify this gap. Assessing the determinant of the Quantum Fisher Information Matrix is crucial for a precise characterisation of the model’s nature. Nonetheless, the AI measure still plays a relevant role since it encapsulates the non-classicality of the model in one scalar quantity rather than in a matrix form (i.e. the Uhlmann curvature).","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"8 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142234096","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-10DOI: 10.1088/2058-9565/ad7169
Alexander Pitchford, Andrey A Rakhubovsky, Rick Mukherjee, Darren W Moore, Frédéric Sauvage, Daniel Burgarth, Radim Filip and Florian Mintert
Nonclassical correlations provide a resource for many applications in quantum technology as well as providing strong evidence that a system is indeed operating in the quantum regime. Optomechanical systems can be arranged to generate nonclassical correlations (such as quantum entanglement) between the mechanical mode and a mode of travelling light. Here we propose automated optimization of the production of quantum correlations in such a system, beyond what can be achieved through analytical methods, by applying Bayesian optimization to the control parameters. A two-mode optomechanical squeezing experiment is simulated using a detailed theoretical model of the system and the measurable outputs fed to the Bayesian optimization process. This then modifies the controllable parameters in order to maximize the non-classical two-mode squeezing and its detection, independently of the inner workings of the model. We focus on a levitated nano-sphere system, but the techniques described are broadly applicable in optomechanical experiments, and also more widely, especially where no detailed theoretical treatment is available. We find that in the experimentally relevant thermal regimes, the ability to vary and optimize a broad array of control parameters provides access to large values of two-mode squeezing that would otherwise be difficult or intractable to discover via analytical or trial and error methods. In particular we observe that modulation of the driving frequency around the resonant sideband allows for stronger nonclassical correlations. We also observe that our optimization approach finds parameters that allow significant squeezing in the high temperature regime. This extends the range of experimental setups in which non-classical correlations could be generated beyond the region of high quantum cooperativity.
{"title":"Bayesian optimization of non-classical optomechanical correlations","authors":"Alexander Pitchford, Andrey A Rakhubovsky, Rick Mukherjee, Darren W Moore, Frédéric Sauvage, Daniel Burgarth, Radim Filip and Florian Mintert","doi":"10.1088/2058-9565/ad7169","DOIUrl":"https://doi.org/10.1088/2058-9565/ad7169","url":null,"abstract":"Nonclassical correlations provide a resource for many applications in quantum technology as well as providing strong evidence that a system is indeed operating in the quantum regime. Optomechanical systems can be arranged to generate nonclassical correlations (such as quantum entanglement) between the mechanical mode and a mode of travelling light. Here we propose automated optimization of the production of quantum correlations in such a system, beyond what can be achieved through analytical methods, by applying Bayesian optimization to the control parameters. A two-mode optomechanical squeezing experiment is simulated using a detailed theoretical model of the system and the measurable outputs fed to the Bayesian optimization process. This then modifies the controllable parameters in order to maximize the non-classical two-mode squeezing and its detection, independently of the inner workings of the model. We focus on a levitated nano-sphere system, but the techniques described are broadly applicable in optomechanical experiments, and also more widely, especially where no detailed theoretical treatment is available. We find that in the experimentally relevant thermal regimes, the ability to vary and optimize a broad array of control parameters provides access to large values of two-mode squeezing that would otherwise be difficult or intractable to discover via analytical or trial and error methods. In particular we observe that modulation of the driving frequency around the resonant sideband allows for stronger nonclassical correlations. We also observe that our optimization approach finds parameters that allow significant squeezing in the high temperature regime. This extends the range of experimental setups in which non-classical correlations could be generated beyond the region of high quantum cooperativity.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"57 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142166216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-10DOI: 10.1088/2058-9565/ad749a
Xuejian Zhang, Yan Chang, Lin Zeng, Weifeng Xue, Lili Yan and Shibin Zhang
Due to the stringent hardware requirements and high cost, quantum computing as a service (QCaaS) is currently the main way to output quantum computing capabilities. However, the current QCaaS has significant shortcomings in privacy protection. The existing researches mainly focus on dataset privacy in some specific quantum machine learning algorithms, and there is no general and comprehensive research on privacy protection for dataset, parameter sets and algorithm models. To solve this problem, this paper defines the concept of generalized quantum homomorphic encryption and pioneers a novel method termed quantum circuit equivalence homomorphic encryption (QCEHE), aiming at protecting the privacy of the complete quantum circuits—encompassing data, parameters, and model. Based on QCEHE, a privacy protection scheme and its approximate implementation called quantum circuit equivalent substitution algorithm are proposed for any quantum algorithm, which can encrypt the complete quantum circuit on a classical computer, ensuring that the encrypted quantum circuit is physically equivalent to the original one, and does not reveal data holders’ privacy (data, parameters and model). By theoretical derivation, we prove that the proposed solution can effectively execute any quantum algorithm while protecting privacy. By applying the proposed solution to the privacy protection of the Harrow–Hassidim–Lloyd algorithm and the variational quantum classifier algorithm, the results showed that the accuracy rate before and after encryption are almost the same, which means that the proposed solution can effectively protect the privacy of data holders without impacting the usability and accuracy.
{"title":"Universal and holistic privacy protection in quantum computing: a novel approach through quantum circuit equivalence homomorphic encryption","authors":"Xuejian Zhang, Yan Chang, Lin Zeng, Weifeng Xue, Lili Yan and Shibin Zhang","doi":"10.1088/2058-9565/ad749a","DOIUrl":"https://doi.org/10.1088/2058-9565/ad749a","url":null,"abstract":"Due to the stringent hardware requirements and high cost, quantum computing as a service (QCaaS) is currently the main way to output quantum computing capabilities. However, the current QCaaS has significant shortcomings in privacy protection. The existing researches mainly focus on dataset privacy in some specific quantum machine learning algorithms, and there is no general and comprehensive research on privacy protection for dataset, parameter sets and algorithm models. To solve this problem, this paper defines the concept of generalized quantum homomorphic encryption and pioneers a novel method termed quantum circuit equivalence homomorphic encryption (QCEHE), aiming at protecting the privacy of the complete quantum circuits—encompassing data, parameters, and model. Based on QCEHE, a privacy protection scheme and its approximate implementation called quantum circuit equivalent substitution algorithm are proposed for any quantum algorithm, which can encrypt the complete quantum circuit on a classical computer, ensuring that the encrypted quantum circuit is physically equivalent to the original one, and does not reveal data holders’ privacy (data, parameters and model). By theoretical derivation, we prove that the proposed solution can effectively execute any quantum algorithm while protecting privacy. By applying the proposed solution to the privacy protection of the Harrow–Hassidim–Lloyd algorithm and the variational quantum classifier algorithm, the results showed that the accuracy rate before and after encryption are almost the same, which means that the proposed solution can effectively protect the privacy of data holders without impacting the usability and accuracy.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"23 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142166207","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-09DOI: 10.1088/2058-9565/ad7499
Francisco Ferreira da Silva, Guus Avis, Joshua A Slater and Stephanie Wehner
We perform a numerical study of the distribution of entanglement on a real-world fiber grid connecting the German cities of Bonn and Berlin. The connection is realized using a chain of processing-node quantum repeaters spanning roughly 900 kilometers. Their placement is constrained by the fiber grid we consider, resulting in asymmetric links. We investigate how minimal hardware requirements depend on the target application, as well as on the number of repeaters in the chain. We find that requirements for blind quantum computing are markedly different than those for quantum key distribution, with the required coherence time being around two and a half times larger for the former. Further, we observe a trade-off regarding how target secret-key rates are achieved when using different numbers of repeaters: comparatively low-quality entangled states generated at a high rate are preferred for higher numbers of repeaters, whereas comparatively high-quality states generated at a lower rate are favored for lower numbers of repeaters. To obtain our results we employ an extensive simulation framework implemented using NetSquid, a discrete-event simulator for quantum networks. These are combined with an optimization methodology based on genetic algorithms to determine minimal hardware requirements.
{"title":"Requirements for upgrading trusted nodes to a repeater chain over 900 km of optical fiber","authors":"Francisco Ferreira da Silva, Guus Avis, Joshua A Slater and Stephanie Wehner","doi":"10.1088/2058-9565/ad7499","DOIUrl":"https://doi.org/10.1088/2058-9565/ad7499","url":null,"abstract":"We perform a numerical study of the distribution of entanglement on a real-world fiber grid connecting the German cities of Bonn and Berlin. The connection is realized using a chain of processing-node quantum repeaters spanning roughly 900 kilometers. Their placement is constrained by the fiber grid we consider, resulting in asymmetric links. We investigate how minimal hardware requirements depend on the target application, as well as on the number of repeaters in the chain. We find that requirements for blind quantum computing are markedly different than those for quantum key distribution, with the required coherence time being around two and a half times larger for the former. Further, we observe a trade-off regarding how target secret-key rates are achieved when using different numbers of repeaters: comparatively low-quality entangled states generated at a high rate are preferred for higher numbers of repeaters, whereas comparatively high-quality states generated at a lower rate are favored for lower numbers of repeaters. To obtain our results we employ an extensive simulation framework implemented using NetSquid, a discrete-event simulator for quantum networks. These are combined with an optimization methodology based on genetic algorithms to determine minimal hardware requirements.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"5 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142160706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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}
Differential-phase-shift (DPS) quantum key distribution stands as a promising protocol due to its simple implementation, which can be realized with a train of coherent pulses and a passive measurement unit. To implement the DPS protocol, it is crucial to establish security proofs incorporating practical imperfections in users’ devices, however, existing security proofs make unrealistic assumptions on the measurement unit using a Mach–Zehnder interferometer. In this paper, we enhance the implementation security of the DPS protocol by incorporating a major imperfection in the measurement unit. Specifically, our proof enables us to use practical beam splitters with a known range of the transmittance rather than the one with exactly 50%, as was assumed in the existing security proofs. Our numerical simulations demonstrate that even with fluctuations of in the transmittance from the ideal value, the key rate degrades only by a factor of 0.57. This result highlights the feasibility of the DPS protocol with practical measurement setups.
{"title":"Differential-phase-shift QKD with practical Mach–Zehnder interferometer","authors":"Akihiro Mizutani, Masanori Terashita, Junya Matsubayashi, Shogo Mori, Ibuki Matsukura, Suzuna Tagawa and Kiyoshi Tamaki","doi":"10.1088/2058-9565/ad71ec","DOIUrl":"https://doi.org/10.1088/2058-9565/ad71ec","url":null,"abstract":"Differential-phase-shift (DPS) quantum key distribution stands as a promising protocol due to its simple implementation, which can be realized with a train of coherent pulses and a passive measurement unit. To implement the DPS protocol, it is crucial to establish security proofs incorporating practical imperfections in users’ devices, however, existing security proofs make unrealistic assumptions on the measurement unit using a Mach–Zehnder interferometer. In this paper, we enhance the implementation security of the DPS protocol by incorporating a major imperfection in the measurement unit. Specifically, our proof enables us to use practical beam splitters with a known range of the transmittance rather than the one with exactly 50%, as was assumed in the existing security proofs. Our numerical simulations demonstrate that even with fluctuations of in the transmittance from the ideal value, the key rate degrades only by a factor of 0.57. This result highlights the feasibility of the DPS protocol with practical measurement setups.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"6 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142160705","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-09-09DOI: 10.1088/2058-9565/ad752d
Pengcheng Liao, Bingzhi Zhang and Quntao Zhuang
The emergence of quantum sensor networks has presented opportunities for enhancing complex sensing tasks, while simultaneously introducing significant challenges in designing and analyzing quantum sensing protocols due to the intricate nature of entanglement and physical processes. Supervised learning assisted by an entangled sensor network (SLAEN) (Zhuang and Zhang 2019 Phys. Rev. X 9 041023) represents a promising paradigm for automating sensor-network design through variational quantum machine learning. However, the original SLAEN, constrained by the Gaussian nature of quantum circuits, is limited to learning linearly separable data. Leveraging the universal quantum control available in cavity quantum electrodynamics experiments, we propose a generalized SLAEN capable of handling nonlinear data classification tasks. We establish a theoretical framework for physical-layer data classification to underpin our approach. Through training quantum probes and measurements, we uncover a threshold phenomenon in classification error across various tasks—when the energy of probes exceeds a certain threshold, the error drastically diminishes to zero, providing a significant improvement over the Gaussian SLAEN. Despite the non-Gaussian nature of the problem, we offer analytical insights into determining the threshold and residual error in the presence of noise. Our findings carry implications for radio-frequency photonic sensors and microwave dark matter haloscopes.
{"title":"Quantum-enhanced learning with a controllable bosonic variational sensor network","authors":"Pengcheng Liao, Bingzhi Zhang and Quntao Zhuang","doi":"10.1088/2058-9565/ad752d","DOIUrl":"https://doi.org/10.1088/2058-9565/ad752d","url":null,"abstract":"The emergence of quantum sensor networks has presented opportunities for enhancing complex sensing tasks, while simultaneously introducing significant challenges in designing and analyzing quantum sensing protocols due to the intricate nature of entanglement and physical processes. Supervised learning assisted by an entangled sensor network (SLAEN) (Zhuang and Zhang 2019 Phys. Rev. X 9 041023) represents a promising paradigm for automating sensor-network design through variational quantum machine learning. However, the original SLAEN, constrained by the Gaussian nature of quantum circuits, is limited to learning linearly separable data. Leveraging the universal quantum control available in cavity quantum electrodynamics experiments, we propose a generalized SLAEN capable of handling nonlinear data classification tasks. We establish a theoretical framework for physical-layer data classification to underpin our approach. Through training quantum probes and measurements, we uncover a threshold phenomenon in classification error across various tasks—when the energy of probes exceeds a certain threshold, the error drastically diminishes to zero, providing a significant improvement over the Gaussian SLAEN. Despite the non-Gaussian nature of the problem, we offer analytical insights into determining the threshold and residual error in the presence of noise. Our findings carry implications for radio-frequency photonic sensors and microwave dark matter haloscopes.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"8 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142160707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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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