Pub Date : 2023-05-15DOI: 10.1088/2058-9565/acd576
Ji-kun Xie, Huaiyang Yuan, Shengli Ma, Shaoyan Gao, Fuli Li, R. Duine
Generating and manipulating magnon quantum states for quantum information processing is a central topic in quantum magnonics. The conventional strategy amplifies the nonlinear interaction among magnons to manifest their quantum correlations at cryogenic temperatures, which is challenging for magnets with vanishingly small nonlinearities. Here we propose an unconventional approach to prepare entangled states of two distant magnon modes by applying a two-tone Floquet field to each magnet inside a microwave cavity. The Floquet driving can effectively generate parametric interaction between magnons and photons, and thus opens an indirect entanglement channel between the two magnon modes mediated by cavity photons. By optimizing the relative ratio of the magnon–photon coupling and the detuning between the magnon modes, the two magnon modes can reach a stationary and robust entanglement, of which the strength is enhanced compared with entanglement generated via magnetic nonlinearities. Furthermore, one-way steering between the two magnets is realized by engineering unequal damping rates of the two magnets while the steering asymmetry can be efficiently modulated by tuning the coupling strength of magnons and cavity photons. The essential physics of our findings universally applies to a wide class of magnets with small nonlinearities and may find promising applications in engineering robust magnon quantum states for quantum information science.
{"title":"Stationary quantum entanglement and steering between two distant macromagnets","authors":"Ji-kun Xie, Huaiyang Yuan, Shengli Ma, Shaoyan Gao, Fuli Li, R. Duine","doi":"10.1088/2058-9565/acd576","DOIUrl":"https://doi.org/10.1088/2058-9565/acd576","url":null,"abstract":"Generating and manipulating magnon quantum states for quantum information processing is a central topic in quantum magnonics. The conventional strategy amplifies the nonlinear interaction among magnons to manifest their quantum correlations at cryogenic temperatures, which is challenging for magnets with vanishingly small nonlinearities. Here we propose an unconventional approach to prepare entangled states of two distant magnon modes by applying a two-tone Floquet field to each magnet inside a microwave cavity. The Floquet driving can effectively generate parametric interaction between magnons and photons, and thus opens an indirect entanglement channel between the two magnon modes mediated by cavity photons. By optimizing the relative ratio of the magnon–photon coupling and the detuning between the magnon modes, the two magnon modes can reach a stationary and robust entanglement, of which the strength is enhanced compared with entanglement generated via magnetic nonlinearities. Furthermore, one-way steering between the two magnets is realized by engineering unequal damping rates of the two magnets while the steering asymmetry can be efficiently modulated by tuning the coupling strength of magnons and cavity photons. The essential physics of our findings universally applies to a wide class of magnets with small nonlinearities and may find promising applications in engineering robust magnon quantum states for quantum information science.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"5 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90310671","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 : 2023-04-27DOI: 10.1088/2058-9565/acd0d1
Junbin Guo, Bang-Ying Tang, Tingqin Lai, Xiaolin Liang, Siyuan Zhang, Zhiyu Tian, Jinquan Huang, Xuelin Yuan, Wan-Rong Yu, Bo Liu, Shaobo Luo, S. Sun
Quantum key distribution (QKD) gives a way to generate unconditionally secure keys for two remote users, Alice and Bob. Information reconciliation (IR), which can correct the errors caused by the imperfections of the QKD systems, is a critical component in QKD. Due to the high-security requirements and large volumes of data processing, robustness and efficiency are two main factors that must be considered for the implementation of IR. The polar codes-based IR has several potential advantages, such as capacity to reach Shannon-limit, high IR efficiency, and low computational complexity. Although CPU-based IR is always implemented in most of the previous works, it is not the optimal implementation in terms of performance and power dissipation. To the best of our knowledge, there is still no work to build a special-purpose hardware module for polar codes-based IR. In this paper, a dedicated design of hardware accelerator is first proposed for polar codes-based IR, in which the block-checked successive cancellation list (SCL) algorithm is used to verify the consistency of the sifted keys, and the overall failure probability of IR is significantly reduced. The proposed design is constructed into a partially-unrolled parallel architecture to accelerate the core decoder as well as balance the resource utilization. Furthermore, the hardware implementation is completed based on Xilinx Zynq UltraScale+ XCZU5EV MPSoC platform and achieves an IR throughput of 15 Mbps with a block length of 212, while less than 20% of the amount of on-chip resources are used in other previous designs of SCL decoder. The proposed design can provide a real-time, low-cost solution for IR in QKD systems, and enhance the performance of QKD.
{"title":"The implementation of Shannon-limited polar codes-based information reconciliation for quantum key distribution","authors":"Junbin Guo, Bang-Ying Tang, Tingqin Lai, Xiaolin Liang, Siyuan Zhang, Zhiyu Tian, Jinquan Huang, Xuelin Yuan, Wan-Rong Yu, Bo Liu, Shaobo Luo, S. Sun","doi":"10.1088/2058-9565/acd0d1","DOIUrl":"https://doi.org/10.1088/2058-9565/acd0d1","url":null,"abstract":"Quantum key distribution (QKD) gives a way to generate unconditionally secure keys for two remote users, Alice and Bob. Information reconciliation (IR), which can correct the errors caused by the imperfections of the QKD systems, is a critical component in QKD. Due to the high-security requirements and large volumes of data processing, robustness and efficiency are two main factors that must be considered for the implementation of IR. The polar codes-based IR has several potential advantages, such as capacity to reach Shannon-limit, high IR efficiency, and low computational complexity. Although CPU-based IR is always implemented in most of the previous works, it is not the optimal implementation in terms of performance and power dissipation. To the best of our knowledge, there is still no work to build a special-purpose hardware module for polar codes-based IR. In this paper, a dedicated design of hardware accelerator is first proposed for polar codes-based IR, in which the block-checked successive cancellation list (SCL) algorithm is used to verify the consistency of the sifted keys, and the overall failure probability of IR is significantly reduced. The proposed design is constructed into a partially-unrolled parallel architecture to accelerate the core decoder as well as balance the resource utilization. Furthermore, the hardware implementation is completed based on Xilinx Zynq UltraScale+ XCZU5EV MPSoC platform and achieves an IR throughput of 15 Mbps with a block length of 212, while less than 20% of the amount of on-chip resources are used in other previous designs of SCL decoder. The proposed design can provide a real-time, low-cost solution for IR in QKD systems, and enhance the performance of QKD.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"75 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78258423","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 : 2023-04-20DOI: 10.1088/2058-9565/accec5
Ki‐Sung Jin, Gyuil Cha
Quantum error correction is likely to be key in obtaining near term quantum advantage. We propose a novel method for providing multiple logical qubits in the correction of quantum errors using classical computers. The core idea of our work is built upon two main pillars: dividing the Hilbert space into reduced Hilbert spaces with individual logical qubits and synthesizing the reduced Hilbert spaces through a mathematical collaborating between classical bits and logical quantum states. We demonstrate that our method supports at least 20 logical qubits in a surface code with a code distance of 3. Furthermore, we generate entangled states of multiple logical qubits from lattice surgery-based surface codes using only physical qubit operations. This approach enables classical computers to support a larger number of logical qubits using less memory and perform faster simulations.
{"title":"Multilayered logical qubits and synthesized quantum bits","authors":"Ki‐Sung Jin, Gyuil Cha","doi":"10.1088/2058-9565/accec5","DOIUrl":"https://doi.org/10.1088/2058-9565/accec5","url":null,"abstract":"Quantum error correction is likely to be key in obtaining near term quantum advantage. We propose a novel method for providing multiple logical qubits in the correction of quantum errors using classical computers. The core idea of our work is built upon two main pillars: dividing the Hilbert space into reduced Hilbert spaces with individual logical qubits and synthesizing the reduced Hilbert spaces through a mathematical collaborating between classical bits and logical quantum states. We demonstrate that our method supports at least 20 logical qubits in a surface code with a code distance of 3. Furthermore, we generate entangled states of multiple logical qubits from lattice surgery-based surface codes using only physical qubit operations. This approach enables classical computers to support a larger number of logical qubits using less memory and perform faster simulations.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"82 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90496005","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 : 2023-04-17DOI: 10.1088/2058-9565/accd92
Gabriele Lo Monaco, L. Innocenti, Dario Cilluffo, D. A. Chisholm, S. Lorenzo, G. Palma
Quantum information scrambling (QIS), from the perspective of quantum information theory, is generally understood as local non-retrievability of information evolved through some dynamical process, and is often quantified via entropic quantities such as the tripartite information. We argue that this approach comes with a number of issues, in large part due to its reliance on quantum mutual informations, which do not faithfully quantify correlations directly retrievable via measurements, and in part due to the specific methodology used to compute tripartite informations of the studied dynamics. We show that these issues can be overcome by using accessible mutual informations, defining corresponding ‘accessible tripartite informations’, and provide explicit examples of dynamics whose scrambling properties are not properly quantified by the standard tripartite information. Our results lay the groundwork for a more profound understanding of what QIS represents, and reveal a number of promising, as of yet unexplored, venues for further research.
量子信息置乱(Quantum information scrambling, QIS)，从量子信息论的角度来看，通常被理解为信息经过某种动态过程演化而来的局部不可检索性，通常通过三方信息等熵量来量化。我们认为，这种方法带来了许多问题，在很大程度上是由于它依赖于量子互信息，不能忠实地量化通过测量直接检索的相关性，部分是由于用于计算所研究动力学的三方信息的特定方法。我们证明了这些问题可以通过使用可访问的互信息来克服，定义相应的“可访问的三方信息”，并提供了其置乱特性不能被标准三方信息适当量化的动态的明确例子。我们的研究结果为更深刻地理解QIS所代表的内容奠定了基础，并揭示了一些有前途的，尚未探索的，进一步研究的场所。
{"title":"Quantum scrambling via accessible tripartite information","authors":"Gabriele Lo Monaco, L. Innocenti, Dario Cilluffo, D. A. Chisholm, S. Lorenzo, G. Palma","doi":"10.1088/2058-9565/accd92","DOIUrl":"https://doi.org/10.1088/2058-9565/accd92","url":null,"abstract":"Quantum information scrambling (QIS), from the perspective of quantum information theory, is generally understood as local non-retrievability of information evolved through some dynamical process, and is often quantified via entropic quantities such as the tripartite information. We argue that this approach comes with a number of issues, in large part due to its reliance on quantum mutual informations, which do not faithfully quantify correlations directly retrievable via measurements, and in part due to the specific methodology used to compute tripartite informations of the studied dynamics. We show that these issues can be overcome by using accessible mutual informations, defining corresponding ‘accessible tripartite informations’, and provide explicit examples of dynamics whose scrambling properties are not properly quantified by the standard tripartite information. Our results lay the groundwork for a more profound understanding of what QIS represents, and reveal a number of promising, as of yet unexplored, venues for further research.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"71 1 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79306108","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 : 2023-04-11DOI: 10.1088/2058-9565/acd1a9
Rodolfo Carobene, Stefano Barison, Andrea Giachero
We propose an extension of the variational quantum eigensolver (VQE) that leads to more accurate energy estimations and can be used to study excited states. The method is based on the introduction of a sequence of increasing penalties in the cost function. This approach does not require circuit modifications and thus can be applied with no additional depth cost. Through numerical simulations, we show that we are able to produce variational states with desired physical properties, such as total spin and charge. We assess its performance both on classical simulators and on currently available quantum devices, calculating the potential energy curves of small molecular systems in different physical configurations. Finally, we compare our method to the original VQE and to another extension, obtaining a better agreement with exact simulations for both energy and targeted physical quantities.
{"title":"Sequence of penalties method to study excited states using VQE","authors":"Rodolfo Carobene, Stefano Barison, Andrea Giachero","doi":"10.1088/2058-9565/acd1a9","DOIUrl":"https://doi.org/10.1088/2058-9565/acd1a9","url":null,"abstract":"We propose an extension of the variational quantum eigensolver (VQE) that leads to more accurate energy estimations and can be used to study excited states. The method is based on the introduction of a sequence of increasing penalties in the cost function. This approach does not require circuit modifications and thus can be applied with no additional depth cost. Through numerical simulations, we show that we are able to produce variational states with desired physical properties, such as total spin and charge. We assess its performance both on classical simulators and on currently available quantum devices, calculating the potential energy curves of small molecular systems in different physical configurations. Finally, we compare our method to the original VQE and to another extension, obtaining a better agreement with exact simulations for both energy and targeted physical quantities.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"56 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83909649","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 : 2023-03-31DOI: 10.1088/2058-9565/acef54
Daniel Q. L. Nguyen, Irina Heinz, G. Burkard
Two-qubit gates between spin qubits are often performed using a rectangular or an adiabatic exchange interaction pulse resulting in a CZ gate. An oscillating exchange pulse not only performs a CZ gate, but also enables the iSWAP gate, which offers more flexibility to perform quantum algorithms. We provide a detailed description for two-qubit gates using resonant and off-resonant exchange pulses, give conditions for performing the respective gates, and compare their performance to the state-of-the-art static counterpart. We find that for relatively low charge noise the gates still perform reliably and can outperform the conventional CZ gate.
{"title":"Quantum gates with oscillating exchange interaction","authors":"Daniel Q. L. Nguyen, Irina Heinz, G. Burkard","doi":"10.1088/2058-9565/acef54","DOIUrl":"https://doi.org/10.1088/2058-9565/acef54","url":null,"abstract":"\u0000 Two-qubit gates between spin qubits are often performed using a rectangular or an adiabatic exchange interaction pulse resulting in a CZ gate. An oscillating exchange pulse not only performs a CZ gate, but also enables the iSWAP gate, which offers more flexibility to perform quantum algorithms. We provide a detailed description for two-qubit gates using resonant and off-resonant exchange pulses, give conditions for performing the respective gates, and compare their performance to the state-of-the-art static counterpart. We find that for relatively low charge noise the gates still perform reliably and can outperform the conventional CZ gate.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"25 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72715428","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 : 2023-03-29DOI: 10.1088/2058-9565/ace0d5
Rui Li, J. Qian, Weiping Zhang
Rydberg quantum gate serving as an indispensable computing unit for neutral-atom quantum computation, has attracted intense research efforts for the last decade. However, the state-of-the-art experiments have not reached the high gate fidelity as predicted by most theories due to the unexpected large loss remaining in Rydberg and intermediate states. In this paper, we report our findings in constructing a native two-qubit controlled-NOT gate based on pulse optimization. We focus on the method of commonly-used two-photon Rydberg excitation with smooth Gaussian-shaped pulses which is straightforward for experimental demonstration. By utilizing optimized pulse shapes the scheme reveals a remarkable reduction in the decays from Rydberg and intermediate states, as well as a high-tolerance to the residual thermal motion of atoms. We extract a conservative lower bound for the gate fidelity >0.9921 after taking into account the experimental imperfections. Our results not only reduce the gap between experimental and theoretical prediction because of the optimal control, but also facilitate the connectivity of distant atomic qubits in a larger atom array by reducing the requirement of strong blockade, which is promising for developing multiqubit quantum computation in large-scale atomic arrays.
{"title":"Proposal for practical Rydberg quantum gates using a native two-photon excitation","authors":"Rui Li, J. Qian, Weiping Zhang","doi":"10.1088/2058-9565/ace0d5","DOIUrl":"https://doi.org/10.1088/2058-9565/ace0d5","url":null,"abstract":"Rydberg quantum gate serving as an indispensable computing unit for neutral-atom quantum computation, has attracted intense research efforts for the last decade. However, the state-of-the-art experiments have not reached the high gate fidelity as predicted by most theories due to the unexpected large loss remaining in Rydberg and intermediate states. In this paper, we report our findings in constructing a native two-qubit controlled-NOT gate based on pulse optimization. We focus on the method of commonly-used two-photon Rydberg excitation with smooth Gaussian-shaped pulses which is straightforward for experimental demonstration. By utilizing optimized pulse shapes the scheme reveals a remarkable reduction in the decays from Rydberg and intermediate states, as well as a high-tolerance to the residual thermal motion of atoms. We extract a conservative lower bound for the gate fidelity >0.9921 after taking into account the experimental imperfections. Our results not only reduce the gap between experimental and theoretical prediction because of the optimal control, but also facilitate the connectivity of distant atomic qubits in a larger atom array by reducing the requirement of strong blockade, which is promising for developing multiqubit quantum computation in large-scale atomic arrays.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"54 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84469951","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 : 2023-03-27DOI: 10.1088/2058-9565/acc7c2
Hsin-Pin Lo, Takuya Ikuta, Koji Azuma, T. Honjo, W. Munro, H. Takesue
Multipartite entanglement is a critical resource in quantum information processing that exhibits much richer phenomenon and stronger correlations than in bipartite systems. This advantage is also reflected in its multi-user applications. Although many demonstrations have used photonic polarization qubits, polarization-mode dispersion confines the transmission of photonic polarization qubits through an optical fiber. Consequently, time–bin qubits have a particularly important role to play in quantum communication systems. Here, we generate a three-photon time–bin Greenberger–Horne–Zeilinger (GHZ) state using a 2 × 2 optical switch as a time-dependent beam splitter to entangle time–bin Bell states from a spontaneous parametric down-conversion source and a weak coherent pulse. To characterize the three-photon time–bin GHZ state, we performed measurement estimation, showed a violation of the Mermin inequality, and used quantum state tomography to fully reconstruct a density matrix, which shows a state fidelity exceeding 70%. We expect that our three-photon time–bin GHZ state can be used for long-distance multi-user quantum communication.
{"title":"Generation of a time–bin Greenberger–Horne–Zeilinger state with an optical switch","authors":"Hsin-Pin Lo, Takuya Ikuta, Koji Azuma, T. Honjo, W. Munro, H. Takesue","doi":"10.1088/2058-9565/acc7c2","DOIUrl":"https://doi.org/10.1088/2058-9565/acc7c2","url":null,"abstract":"Multipartite entanglement is a critical resource in quantum information processing that exhibits much richer phenomenon and stronger correlations than in bipartite systems. This advantage is also reflected in its multi-user applications. Although many demonstrations have used photonic polarization qubits, polarization-mode dispersion confines the transmission of photonic polarization qubits through an optical fiber. Consequently, time–bin qubits have a particularly important role to play in quantum communication systems. Here, we generate a three-photon time–bin Greenberger–Horne–Zeilinger (GHZ) state using a 2 × 2 optical switch as a time-dependent beam splitter to entangle time–bin Bell states from a spontaneous parametric down-conversion source and a weak coherent pulse. To characterize the three-photon time–bin GHZ state, we performed measurement estimation, showed a violation of the Mermin inequality, and used quantum state tomography to fully reconstruct a density matrix, which shows a state fidelity exceeding 70%. We expect that our three-photon time–bin GHZ state can be used for long-distance multi-user quantum communication.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"12 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84285891","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 : 2023-02-28DOI: 10.1088/2058-9565/ace6cb
A. Binai-Motlagh, Matthew L Day, N. Videnov, Noah Greenberg, C. Senko, R. Islam
Trapped ions are one of the leading platforms for quantum information processing, exhibiting the highest gate and measurement fidelities of all contending hardware. In order to realize a universal quantum computer with trapped ions, independent and parallel control over the state of each qubit is necessary. The manipulation of individual qubit states in an ion chain via stimulated Raman transitions generally requires light focused on individual ions. In this manuscript, we present a novel, guided-light individual addressing system for hyperfine Ba+ qubits. The system takes advantage of laser-written waveguide technology, enabled by the atomic structure of Ba+, allowing the use of visible light to drive Raman transitions. Such waveguides define the spatial mode of light, suppressing aberrations that would have otherwise accumulated in a free-space optics set up. As a result, we demonstrate a nearest neighbor relative intensity crosstalk on the order of 10−4, without any active aberration compensation. This is comparable to or better than other previous demonstrations of individual addressing. At the same time, our modular approach provides independent and agile control over the amplitude, frequency, and phase of each channel; combining the strengths of previous implementations.
{"title":"A guided light system for agile individual addressing of Ba+ qubits with 10−4 level intensity crosstalk","authors":"A. Binai-Motlagh, Matthew L Day, N. Videnov, Noah Greenberg, C. Senko, R. Islam","doi":"10.1088/2058-9565/ace6cb","DOIUrl":"https://doi.org/10.1088/2058-9565/ace6cb","url":null,"abstract":"Trapped ions are one of the leading platforms for quantum information processing, exhibiting the highest gate and measurement fidelities of all contending hardware. In order to realize a universal quantum computer with trapped ions, independent and parallel control over the state of each qubit is necessary. The manipulation of individual qubit states in an ion chain via stimulated Raman transitions generally requires light focused on individual ions. In this manuscript, we present a novel, guided-light individual addressing system for hyperfine Ba+ qubits. The system takes advantage of laser-written waveguide technology, enabled by the atomic structure of Ba+, allowing the use of visible light to drive Raman transitions. Such waveguides define the spatial mode of light, suppressing aberrations that would have otherwise accumulated in a free-space optics set up. As a result, we demonstrate a nearest neighbor relative intensity crosstalk on the order of 10−4, without any active aberration compensation. This is comparable to or better than other previous demonstrations of individual addressing. At the same time, our modular approach provides independent and agile control over the amplitude, frequency, and phase of each channel; combining the strengths of previous implementations.","PeriodicalId":20821,"journal":{"name":"Quantum Science and Technology","volume":"21 1","pages":""},"PeriodicalIF":6.7,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73613136","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 : 2023-02-08DOI: 10.1088/2058-9565/ace474
Pablo Díez-Valle, J. Luis-Hita, Senaida Hernández-Santana, Fernando Martínez-García, Á. Díaz-Fernández, Eva Andrés, Juan José García-Ripoll, Escolástico Sánchez-Martínez, Diego Porras
Combinatorial optimization problems are ubiquitous in industry. In addition to finding a solution with minimum cost, problems of high relevance involve a number of constraints that the solution must satisfy. Variational quantum algorithms (VQAs) have emerged as promising candidates for solving these problems in the noisy intermediate-scale quantum stage. However, the constraints are often complex enough to make their efficient mapping to quantum hardware difficult or even infeasible. An alternative standard approach is to transform the optimization problem to include these constraints as penalty terms, but this method involves additional hyperparameters and does not ensure that the constraints are satisfied due to the existence of local minima. In this paper, we introduce a new method for solving combinatorial optimization problems with challenging constraints using VQAs. We propose the multi-objective variational constrained optimizer (MOVCO) to classically update the variational parameters by a multiobjective optimization performed by a genetic algorithm. This optimization allows the algorithm to progressively sample only states within the in-constraints space, while optimizing the energy of these states. We test our proposal on a real-world problem with great relevance in finance: the cash handling problem. We introduce a novel mathematical formulation for this problem, and compare the performance of MOVCO versus a penalty based optimization. Our empirical results show a significant improvement in terms of the cost of the achieved solutions, but especially in the avoidance of local minima that do not satisfy any of the mandatory constraints.
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