{"title":"Nonreciprocal macroscopic tripartite entanglement in atom-optomagnomechanical system","authors":"Qianjun Zheng, Wenxue Zhong, Guangling Cheng, Aixi Chen","doi":"10.1140/epjqt/s40507-024-00218-0","DOIUrl":"10.1140/epjqt/s40507-024-00218-0","url":null,"abstract":"<div><p>We investigate how to generate the nonreciprocal macroscopic tripartite entanglement among the atomic ensemble, ferrimagnetic magnon and mechanical oscillator in a hybrid atom-optomagnomechanical system, where an ensemble of two-level atoms and a yttrium iron garnet micro-bridge supporting the magnon and mechanical modes are placed in a spinning optical resonator driven by a laser field. The phonon being the quantum of the mechanical mode interacts with the magnon and the optical photon via magnetostriction and radiation pressure, respectively, and meanwhile the photon couples to the atomic ensemble. The results show that not only all bipartite entanglements but also the genuine tripartite entanglement among the atomic ensemble, magnon and phonon could be generated at the steady state. Moreover, the nonreciprocity of atom-magnon-phonon entanglement can be obtained with the aid of the optical Sagnac effect by spinning the resonator, in which the entanglement is present in a chosen driving direction but disappears in the other direction. The nonreciprocal macroscopic tripartite entanglement is robust against temperature and could be flexibly controlled by choosing the system parameters. Our work enriches the study of macroscopic multipartite quantum states, which may have potential applications in the development of quantum information storage and the construction of multi-node chiral quantum network.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"11 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2024-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-024-00218-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139585355","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 Quantum Technology Open Master: widening access to the quantum industry","authors":"Simon Goorney, Matoula Sarantinou, Jacob Sherson","doi":"10.1140/epjqt/s40507-024-00217-1","DOIUrl":"10.1140/epjqt/s40507-024-00217-1","url":null,"abstract":"<div><p>In this article we conceive of the <i>Open Master</i>, a new form of Transnational Education, as a means of enhancing accessibility to specialist expertise in Quantum Technology. Through participatory action research conducted during the setup and operation of a pan-European pilot project, the QTEdu Open Master (QTOM), we examine the viability of this educational model to offer flexible learning opportunities to STEM Master’s students through the setup and year-long operation of an online course exchange platform. A crucial lynchpin in the Open Master model are the mechanisms of <i>local accreditation</i> available for the awarding of credit, which we divide into distinct course types varying in formality and applicability. Furthermore, we have elucidated the strategies taken by staff to successfully implement the Open Master and benefit from its transformative value, building long-lasting communities within and between faculty, and scaling up educational offerings across Europe. With this research, we reflect on a possible future for QT Education.</p></div>","PeriodicalId":547,"journal":{"name":"EPJ Quantum Technology","volume":"11 1","pages":""},"PeriodicalIF":5.3,"publicationDate":"2024-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://epjquantumtechnology.springeropen.com/counter/pdf/10.1140/epjqt/s40507-024-00217-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139561198","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}
Yash J. Patel, Sofiene Jerbi, Thomas Bäck, Vedran Dunjko
{"title":"Reinforcement learning assisted recursive QAOA","authors":"Yash J. Patel, Sofiene Jerbi, Thomas Bäck, 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}
Graham J. Norris, Laurent Michaud, David Pahl, Michael Kerschbaum, Christopher Eichler, Jean-Claude Besse, Andreas Wallraff
{"title":"Improved parameter targeting in 3D-integrated superconducting circuits through a polymer spacer process","authors":"Graham J. Norris, Laurent Michaud, David Pahl, Michael Kerschbaum, Christopher Eichler, Jean-Claude Besse, 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, 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}
Lu Liu, Xing-Yu Wu, Chu-Yao Xu, Lu-Fan Zhang, Chuan Wang
{"title":"The deterministic pattern matching based on the parameterized quantum circuit","authors":"Lu Liu, Xing-Yu Wu, Chu-Yao Xu, Lu-Fan Zhang, 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}
Jinpeng Yuan, Ting Jin, Yang Yan, Liantuan Xiao, Suotang Jia, Lirong Wang
{"title":"A Rydberg atom-based amplitude-modulated receiver using the dual-tone microwave field","authors":"Jinpeng Yuan, Ting Jin, Yang Yan, Liantuan Xiao, Suotang Jia, 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, Jun Xing, 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, Guillermo Currás-Lorenzo, Kiyoshi Tamaki, 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, Yuechun Jiao, Yunhui He, Hao Zhang, Linjie Zhang, Jianming Zhao, 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}