EPJ Quantum Technology最新文献

{"title":"Reinforcement learning assisted recursive QAOA","authors":"Yash J. Patel,&nbsp;Sofiene Jerbi,&nbsp;Thomas Bäck,&nbsp;Vedran Dunjko","doi":"10.1140/epjqt/s40507-023-00214-w","DOIUrl":"10.1140/epjqt/s40507-023-00214-w","url":null,"abstract":"<div><p>In recent years, variational quantum algorithms such as the Quantum Approximation Optimization Algorithm (QAOA) have gained popularity as they provide the hope of using NISQ devices to tackle hard combinatorial optimization problems. It is, however, known that at low depth, certain locality constraints of QAOA limit its performance. To go beyond these limitations, a non-local variant of QAOA, namely recursive QAOA (RQAOA), was proposed to improve the quality of approximate solutions. The RQAOA has been studied comparatively less than QAOA, and it is less understood, for instance, for what family of instances it may fail to provide high-quality solutions. However, as we are tackling <span>NP</span>-hard problems (specifically, the Ising spin model), it is expected that RQAOA does fail, raising the question of designing even better quantum algorithms for combinatorial optimization. In this spirit, we identify and analyze cases where (depth-1) RQAOA fails and, based on this, propose a reinforcement learning enhanced RQAOA variant (RL-RQAOA) that improves upon RQAOA. We show that the performance of RL-RQAOA improves over RQAOA: RL-RQAOA is strictly better on these identified instances where RQAOA underperforms and is similarly performing on instances where RQAOA is near-optimal. Our work exemplifies the potentially beneficial synergy between reinforcement learning and quantum (inspired) optimization in the design of new, even better heuristics for complex problems.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"11 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00214-w","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139481568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Improved parameter targeting in 3D-integrated superconducting circuits through a polymer spacer process","authors":"Graham J. Norris,&nbsp;Laurent Michaud,&nbsp;David Pahl,&nbsp;Michael Kerschbaum,&nbsp;Christopher Eichler,&nbsp;Jean-Claude Besse,&nbsp;Andreas Wallraff","doi":"10.1140/epjqt/s40507-023-00213-x","DOIUrl":"10.1140/epjqt/s40507-023-00213-x","url":null,"abstract":"<div><p>Three-dimensional device integration facilitates the construction of superconducting quantum information processors with more than several tens of qubits by distributing elements such as control wires, qubits, and resonators between multiple layers. The frequencies of resonators and qubits in flip-chip-bonded multi-chip modules depend on the details of their electromagnetic environment defined by the conductors and dielectrics in their vicinity. Accurate frequency targeting therefore requires precise control of the separation between chips and minimization of their relative tilt. Here, we describe a method to control the inter-chip separation by using polymer spacers. With the spacers, we measure a mean tilt of (76 ± 36) μrad, and a mean deviation of (0.4 ± 0.8) μm from the target inter-chip separation of 10 μm. We apply this process to coplanar waveguide resonator samples and observe chip-to-chip resonator frequency variations below 50 MHz (<span>(approx 1%)</span>). We measure internal quality factors of <span>(5times10^{5})</span> at the single-photon level, suggesting that the added spacers are compatible with low-loss device fabrication.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"11 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2024-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00213-x","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139419562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"ResQNets: a residual approach for mitigating barren plateaus in quantum neural networks","authors":"Muhammad Kashif,&nbsp;Saif Al-Kuwari","doi":"10.1140/epjqt/s40507-023-00216-8","DOIUrl":"10.1140/epjqt/s40507-023-00216-8","url":null,"abstract":"<div><p>The barren plateau problem in quantum neural networks (QNNs) is a significant challenge that hinders the practical success of QNNs. In this paper, we introduce residual quantum neural networks (ResQNets) as a solution to address this problem. ResQNets are inspired by classical residual neural networks and involve splitting the conventional QNN architecture into multiple quantum nodes, each containing its own parameterized quantum circuit, and introducing residual connections between these nodes. Our study demonstrates the efficacy of ResQNets by comparing their performance with that of conventional QNNs and plain quantum neural networks through multiple training experiments and analyzing the cost function landscapes. Our results show that the incorporation of residual connections results in improved training performance. Therefore, we conclude that ResQNets offer a promising solution to overcome the barren plateau problem in QNNs and provide a potential direction for future research in the field of quantum machine learning.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"11 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2024-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00216-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139412336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The deterministic pattern matching based on the parameterized quantum circuit","authors":"Lu Liu,&nbsp;Xing-Yu Wu,&nbsp;Chu-Yao Xu,&nbsp;Lu-Fan Zhang,&nbsp;Chuan Wang","doi":"10.1140/epjqt/s40507-023-00215-9","DOIUrl":"10.1140/epjqt/s40507-023-00215-9","url":null,"abstract":"<div><p>Grover quantum algorithm is an unstructured search algorithm that can run on a quantum computer with the complexity of O<span>(sqrt{N})</span>, and is one of the typical algorithms of quantum computing. Recently, it has served as a routine for pattern-matching tasks. However, the original Grover search algorithm is probabilistic, which is not negligible for problems involving determinism. Besides that, efficient data loading is also a key challenge for the practical applications of the Grover algorithm. Here in this work, we propose a modified pattern-matching scheme with Long’s quantum search algorithm, in which the quantum circuit structure search algorithm requires fewer multi-qubit quantum gates, and can obtain the desired results deterministically. Then, the comparison of the performance of our scheme and the previous algorithms is presented through numerical simulations, indicating our algorithm is feasible with current quantum technologies which is friendly to noisy intermediate-scale quantum (NISQ) devices.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"11 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00215-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139406782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Rydberg atom-based amplitude-modulated receiver using the dual-tone microwave field","authors":"Jinpeng Yuan,&nbsp;Ting Jin,&nbsp;Yang Yan,&nbsp;Liantuan Xiao,&nbsp;Suotang Jia,&nbsp;Lirong Wang","doi":"10.1140/epjqt/s40507-023-00212-y","DOIUrl":"10.1140/epjqt/s40507-023-00212-y","url":null,"abstract":"<div><p>We propose a Rydberg atom-based receiver for amplitude-modulation (AM) reception utilizing a dual-tone microwave field. The pseudo-random binary sequence (PRBS) signal is encoded in the basic microwave field (B-MW) at the frequency of 14.23 GHz. The signal can be decoded by the atomic receiver itself but more obvious with the introduction of an auxiliary microwave (A-MW) field. The receiver’s amplitude variations corresponding to microwave field are simulated by solving density matrices to give this mechanism theoretical support. An appropriate AM frequency is obtained by optimizing the signal-to-noise ratio, guaranteeing both large data transfer capacity (DTC) and high fidelity of the receiver. The power of two MW fields, along with the B-MW field frequency, is studied to acquire larger DTC and wider operating bandwidth. Finally, the readout of PRBS signals is performed by both the proposed and conventional mechanisms, and the comparison proves the obvious increment of DTC with the proposed scheme. This proof-of-principle demonstration exhibits the potential of the dual-tone scheme and offers a novel pathway for Rydberg atom-based microwave communication, which is beneficial for long-distance communication and weak signal perception outside the laboratory.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"11 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2024-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00212-y","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139079063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Soft-controlled quantum gate with enhanced robustness and undegraded dynamics in Rydberg atoms","authors":"Qiaolin Wu,&nbsp;Jun Xing,&nbsp;Hongda Yin","doi":"10.1140/epjqt/s40507-023-00211-z","DOIUrl":"10.1140/epjqt/s40507-023-00211-z","url":null,"abstract":"<div><p>Rydberg atoms have exhibited excellent potentials to become a competent platform of implementing quantum computation, which demands to execute various quantum gates fast and faithfully. We propose a dynamic mechanism of two interacting Rydberg atoms for implementing a high-fidelity SWAP gate on ground-state manifolds, where the amplitude modulation and soft quantum control of lasers driving ground-Rydberg state transitions are elaborately matched with the interaction strength between atoms so as to engineer the desired transformation of atomic states. Compared with the recent Rydberg-atom SWAP gate scheme, the present one possesses the undegraded first-order dynamics and shows an interference-induced suppression of the doubly-excited Rydberg state, so it costs shorter gate time and exhibits greater robustness against atomic decay and deviations in the interatomic separation (interaction strengths). The present mechanism of implementing a SWAP gate on interacting Rydberg atoms could facilitate high-fidelity demonstrations of atomic ground state transformation and further exploitation of peculiar dynamics.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"11 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2024-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00211-z","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139079007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Secret key rate bounds for quantum key distribution with faulty active phase randomization","authors":"Xoel Sixto,&nbsp;Guillermo Currás-Lorenzo,&nbsp;Kiyoshi Tamaki,&nbsp;Marcos Curty","doi":"10.1140/epjqt/s40507-023-00210-0","DOIUrl":"10.1140/epjqt/s40507-023-00210-0","url":null,"abstract":"<div><p>Decoy-state quantum key distribution (QKD) is undoubtedly the most efficient solution to handle multi-photon signals emitted by laser sources, and provides the same secret key rate scaling as ideal single-photon sources. It requires, however, that the phase of each emitted pulse is uniformly random. This might be difficult to guarantee in practice, due to inevitable device imperfections and/or the use of an external phase modulator for phase randomization in an active setup, which limits the possible selected phases to a finite set. Here, we investigate the security of decoy-state QKD when the phase is actively randomized by faulty devices, and show that this technique is quite robust to deviations from the ideal uniformly random scenario. For this, we combine a novel parameter estimation technique based on semi-definite programming, with the use of basis mismatched events, to tightly estimate the parameters that determine the achievable secret key rate. In doing so, we demonstrate that our analysis can significantly outperform previous results that address more restricted scenarios.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"10 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00210-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138678787","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Improvement of response bandwidth and sensitivity of Rydberg receiver using multi-channel excitations","authors":"Jinlian Hu,&nbsp;Yuechun Jiao,&nbsp;Yunhui He,&nbsp;Hao Zhang,&nbsp;Linjie Zhang,&nbsp;Jianming Zhao,&nbsp;Suotang Jia","doi":"10.1140/epjqt/s40507-023-00209-7","DOIUrl":"10.1140/epjqt/s40507-023-00209-7","url":null,"abstract":"<div><p>We investigate the response bandwidth of a superheterodyne Rydberg receiver at a room-temperature vapor cell, and present an architecture of multi-channel lasers excitation to increase the response bandwidth and keep sensitivity, simultaneously. Two microwave fields, denoted as a local oscillator (LO) <span>(E_{text{LO}})</span> and a signal field <span>(E_{text{SIG}})</span>, couple two Rydberg states transition of <span>(|52D_{5/2}rangle to |53P_{3/2}rangle )</span>. In the presence of the LO field, the frequency difference between two fields can be read out as an intermediate frequency (IF) signal using Rydberg electromagnetically induced transparency (EIT) spectroscopy. The bandwidth of the Rydberg receiver is obtained by measuring the output power of IF signal versus the frequency difference between two fields. The bandwidth dependence on the Rabi frequency of excitation lasers is presented, which shows the bandwidth decrease with the probe Rabi frequency, while it is quadratic dependence on the coupling Rabi frequency. Meanwhile, we investigate the effect of probe laser waist on the bandwidth, showing that the bandwidth is inversely proportional to the laser waist. We achieve a maximum response bandwidth of the receiver about 6.8 MHz. Finally, we design an architecture of multi-channel lasers excitation for increasing the response and keeping the sensitivity, simultaneously. Our work has the potential to extend the applications of Rydberg atoms in communications.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"10 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2023-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00209-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138454565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vector—towards quantum key distribution with small satellites","authors":"Alexander V. Miller,&nbsp;Liubov V. Pismeniuk,&nbsp;Alexey V. Duplinsky,&nbsp;Vitaly E. Merzlinkin,&nbsp;Aleksandr A. Plukchi,&nbsp;Kseniia A. Tikhonova,&nbsp;Ivan S. Nesterov,&nbsp;Dmitry O. Sevryukov,&nbsp;Sergey D. Levashov,&nbsp;Vladimir V. Fetisov,&nbsp;Sergei V. Krasnopejev,&nbsp;Ruslan M. Bakhshaliev","doi":"10.1140/epjqt/s40507-023-00208-8","DOIUrl":"10.1140/epjqt/s40507-023-00208-8","url":null,"abstract":"<div><p>A satellite-constellation based global quantum network could allow secure quantum communication between remote users worldwide. Such a constellation could be formed of micro- or even nanosatellites, which have the advantage of being more cost-effective than larger expensive spacecrafts. At the same time, the features of quantum communication impose a number of technical requirements that are more difficult to meet when using small satellites. Full-fledged quantum communication has been demonstrated with neither a micro- nor a nanosatellite so far. The authors took up this challenge and have developed a 6U CubeSat weighting 9.5 kg. The satellite is to be launched in 2023 and has already successfully passed all the pre-flight tests. The mission is not yet intended for fully quantum communication. Nevertheless, the authors are testing such key functional elements as polarization reference-frame synchronization and acquisition, pointing and tracking system on it. Besides that, the payload accommodates a full-duplex telecommunication system operating at a bit rate of 50 Mbit/s: an up- and a downlink at wavelengths of 808 and 850 nm. After the satellite is launched, the main goal to be achieved is to demonstrate stable connection between it and an optical ground station and carry out multiple communication sessions. In quantum communication, generating secret keys from raw measurement data implies two-way exchange of significant amount of information and therefore availability of a classical communication channel with a high bandwidth is one of the crucial things. In the following mission, which envisages an overall quantum key distribution system, we plan to use the free-space optical link for such an exchange of data, whereas the RF link will only be used for telemetry and telecommand.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"10 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2023-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00208-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138454572","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Demonstration of 75 km-fiber quantum clock synchronization in quantum entanglement distribution network","authors":"Bang-Ying Tang,&nbsp;Ming Tian,&nbsp;Huan Chen,&nbsp;Hui Han,&nbsp;Han Zhou,&nbsp;Si-Chen Li,&nbsp;Bo Xu,&nbsp;Rui-Fang Dong,&nbsp;Bo Liu,&nbsp;Wan-Rong Yu","doi":"10.1140/epjqt/s40507-023-00207-9","DOIUrl":"10.1140/epjqt/s40507-023-00207-9","url":null,"abstract":"<div><p>The quantum entanglement distribution network, serviced as the communication infrastructure which distributes quantum information among remote users, enables many applications beyond the reach of classical networks. Recently, the applications such as quantum key distribution and quantum secure direct communication, have been successfully demonstrated in the quantum entanglement distribution network. In this article, we propose a multi-user round-trip quantum clock synchronization (QCS) scheme in the quantum network, which can be implemented with one single entangled photon source located at the server. The server distributes the entangled photons to remote multiple users with the wavelength division multiplexing strategy, and each user feeds partial received photons back to the server. The clock difference between the server and each user is calculated from the one-way and round-trip propagation times, which are determined according to the time correlation of entangled photons. Afterwards, the demonstration has been conducted between the server and a user over a 75-km-long fiber link, where the measured clock difference uncertainty is 4.45 ps, and the time deviation is 426 fs with an average time of 4000 s. Furthermore, the proposed QCS scheme is linearly scalable to many users, with respect to user hardware and number of deployed fibers.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"10 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2023-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-023-00207-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138431587","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}