Pub Date : 2025-11-26DOI: 10.1109/TASC.2025.3637852
Jing Li;Xinyu Wu;Jiajun Zhong;Songlin Li;Ruichen Wang;Jingwei Chai;Pengbo Zhou;Yalin Zhao;Guangtong Ma
This study focuses on the development of a high-efficiency computational model for predicting the magnetic field of high-temperature superconducting (HTS) magnets, which is crucial for the design and optimization of HTS-based devices. A fast-computational model for magnetic field was proposed, leveraging the feature extraction capabilities of the deep residual neural network. To validate the effectiveness and reliability of the proposed model, a prototyped HTS magnet system was employed for experimental verification. The comparison between the calculation results and the experimental data demonstrated a high degree of consistency, confirming the practical applicability of the model. Subsequently, an enhanced linear adaptive genetic algorithm was introduced for the optimization design of a 3 T magnetic resonance imaging magnet utilizing rare-Earth barium copper oxide superconducting tapes. The optimized magnet is composed of 60 double-pancake coils, operating at a cryogenic temperature of 30 K and featuring a coil inner diameter of 600 mm. An active shielding technique was adopted, which involves the strategic arrangement of additional coils to counteract the stray magnetic fields. Through this approach, the fringing field was effectively suppressed. In terms of field homogeneity, the magnet achieved 74 parts per million within a 250 mm diameter spherical volume.
{"title":"Fast Electromagnetic Design of the MRI Superconducting Magnet Via Deep Residual Neural Networks","authors":"Jing Li;Xinyu Wu;Jiajun Zhong;Songlin Li;Ruichen Wang;Jingwei Chai;Pengbo Zhou;Yalin Zhao;Guangtong Ma","doi":"10.1109/TASC.2025.3637852","DOIUrl":"https://doi.org/10.1109/TASC.2025.3637852","url":null,"abstract":"This study focuses on the development of a high-efficiency computational model for predicting the magnetic field of high-temperature superconducting (HTS) magnets, which is crucial for the design and optimization of HTS-based devices. A fast-computational model for magnetic field was proposed, leveraging the feature extraction capabilities of the deep residual neural network. To validate the effectiveness and reliability of the proposed model, a prototyped HTS magnet system was employed for experimental verification. The comparison between the calculation results and the experimental data demonstrated a high degree of consistency, confirming the practical applicability of the model. Subsequently, an enhanced linear adaptive genetic algorithm was introduced for the optimization design of a 3 T magnetic resonance imaging magnet utilizing rare-Earth barium copper oxide superconducting tapes. The optimized magnet is composed of 60 double-pancake coils, operating at a cryogenic temperature of 30 K and featuring a coil inner diameter of 600 mm. An active shielding technique was adopted, which involves the strategic arrangement of additional coils to counteract the stray magnetic fields. Through this approach, the fringing field was effectively suppressed. In terms of field homogeneity, the magnet achieved 74 parts per million within a 250 mm diameter spherical volume.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 1","pages":"1-9"},"PeriodicalIF":1.8,"publicationDate":"2025-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145778395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-24DOI: 10.1109/TASC.2025.3636612
Javier Navarro Montilla;Ryan C. Stephenson;Arnaud Barbier;Nikita Klimovich;Yves Bortolotti;Eduard F. C. Driessen;Peter K. Day;Boon-Kok Tan
At microwave frequencies, Josephson junction arrays have been widely employed to create metamaterials exhibiting a third-order ($chi ^{(3)}$) nonlinearity, analogous to the Kerr effect in optics. These nonlinear metamaterials enable parametric amplification, as in Josephson travelling-wave parametric amplifiers (JTWPAs), which achieve quantum-limited noise performance over multigigahertz bandwidths. The exceptional properties of JTWPAs make them ideal for the sensitive readout of weak microwave signals, with applications in quantum computing, astrophysics, and fundamental physics experiments. Extending JTWPAs to higher frequencies, such as the W-band (70–110 GHz), holds promise for first-stage amplification in astronomical receivers, lowering system noise; as well as for reading out emerging superconducting qubit architectures at these frequencies. In this work, we investigate the $chi ^{(3)}$ nonlinear properties of Josephson arrays operating in the W-band as a step toward realizing parametric gain at these frequencies. We designed and fabricated an array composed of 704 Nb/Al-AlO$_{mathrm{x}}$/Nb tunnel junctions and experimentally demonstrated four-wave mixing via idler tone generation, providing clear evidence of third-order nonlinearity. These results mark an important step toward novel millimetre-wave and submillimetre-wave parametric-amplifier-based receiver technologies.
{"title":"Investigating the $chi ^{(3)}$ Nonlinearity of a Josephson Junction Array for Travelling-Wave Parametric Amplification in the W-Band","authors":"Javier Navarro Montilla;Ryan C. Stephenson;Arnaud Barbier;Nikita Klimovich;Yves Bortolotti;Eduard F. C. Driessen;Peter K. Day;Boon-Kok Tan","doi":"10.1109/TASC.2025.3636612","DOIUrl":"https://doi.org/10.1109/TASC.2025.3636612","url":null,"abstract":"At microwave frequencies, Josephson junction arrays have been widely employed to create metamaterials exhibiting a third-order (<inline-formula><tex-math>$chi ^{(3)}$</tex-math></inline-formula>) nonlinearity, analogous to the Kerr effect in optics. These nonlinear metamaterials enable parametric amplification, as in Josephson travelling-wave parametric amplifiers (JTWPAs), which achieve quantum-limited noise performance over multigigahertz bandwidths. The exceptional properties of JTWPAs make them ideal for the sensitive readout of weak microwave signals, with applications in quantum computing, astrophysics, and fundamental physics experiments. Extending JTWPAs to higher frequencies, such as the W-band (70–110 GHz), holds promise for first-stage amplification in astronomical receivers, lowering system noise; as well as for reading out emerging superconducting qubit architectures at these frequencies. In this work, we investigate the <inline-formula><tex-math>$chi ^{(3)}$</tex-math></inline-formula> nonlinear properties of Josephson arrays operating in the W-band as a step toward realizing parametric gain at these frequencies. We designed and fabricated an array composed of 704 Nb/Al-AlO<inline-formula><tex-math>$_{mathrm{x}}$</tex-math></inline-formula>/Nb tunnel junctions and experimentally demonstrated four-wave mixing via idler tone generation, providing clear evidence of third-order nonlinearity. These results mark an important step toward novel millimetre-wave and submillimetre-wave parametric-amplifier-based receiver technologies.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 1","pages":"1-11"},"PeriodicalIF":1.8,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145674844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-24DOI: 10.1109/TASC.2025.3636228
Zhiwen Cheng;Jianglan Li;Xian Li;Mengyu Liu;Liang Li;Qiuliang Wang;Yunxing Song
A 9.0-T frameless conduction-cooled superconducting magnet has been successfully developed in Wuhan National High Magnetic Field Center. The electromagnetic design was accomplished using a hybrid global optimization method. The magnet features a cold clear bore of 95 mm. Compared with the first 9.0 T conduction-cooled superconducting magnet with frames developed previously, the frameless design reduces superconducting wire consumption by 17% and lowers the total magnet weight by 29%, while preserving the same cold clear bore size and homogeneity in the 10-mm diameter of spherical volume. Low temperature is achieved using one pulse tube cryocooler, enabling the magnet to reach temperatures below 4.2 K from room temperature. The vertical magnet comprises five coaxial NbTi superconducting coils connected in series, operating at a current of 79.73 A for a magnetic field intensity of 9.0 T, with a total magnetic energy storage of 0.14 MJ. A passive quench protection system is implemented by subdividing the coils, which protects the magnet by enabling the quench to propagate to more coils. The frameless design eliminates sliding interfaces between the coils and structural frames, preventing friction-induced joule heating during excitation and significantly reducing the occurrence of training quenches. This novel design demonstrates improved efficiency and reliability for conduction-cooled superconducting magnet systems.
{"title":"Design and Performance Evaluation of a 9.0-T Frameless Conduction-Cooled Superconducting Magnet","authors":"Zhiwen Cheng;Jianglan Li;Xian Li;Mengyu Liu;Liang Li;Qiuliang Wang;Yunxing Song","doi":"10.1109/TASC.2025.3636228","DOIUrl":"https://doi.org/10.1109/TASC.2025.3636228","url":null,"abstract":"A 9.0-T frameless conduction-cooled superconducting magnet has been successfully developed in Wuhan National High Magnetic Field Center. The electromagnetic design was accomplished using a hybrid global optimization method. The magnet features a cold clear bore of 95 mm. Compared with the first 9.0 T conduction-cooled superconducting magnet with frames developed previously, the frameless design reduces superconducting wire consumption by 17% and lowers the total magnet weight by 29%, while preserving the same cold clear bore size and homogeneity in the 10-mm diameter of spherical volume. Low temperature is achieved using one pulse tube cryocooler, enabling the magnet to reach temperatures below 4.2 K from room temperature. The vertical magnet comprises five coaxial NbTi superconducting coils connected in series, operating at a current of 79.73 A for a magnetic field intensity of 9.0 T, with a total magnetic energy storage of 0.14 MJ. A passive quench protection system is implemented by subdividing the coils, which protects the magnet by enabling the quench to propagate to more coils. The frameless design eliminates sliding interfaces between the coils and structural frames, preventing friction-induced joule heating during excitation and significantly reducing the occurrence of training quenches. This novel design demonstrates improved efficiency and reliability for conduction-cooled superconducting magnet systems.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 1","pages":"1-6"},"PeriodicalIF":1.8,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145729297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-24DOI: 10.1109/TASC.2025.3636496
R. Niu;K. Han;V. J. Toplosky;J. Toth
We performed tension-tension fatigue tests in stress control mode on cold-rolled Cu-Zr alloy sheets with various levels of tensile strength (TS). We then compared the fatigue properties of these sheets to those of cold-rolled Cu sheets. Fatigue life increased as TS increased. We separated our Cu-Zr sheets according to their mechanical strength levels, designating those with their TS ∼490 MPa as “H”, those with TS around 448 $ pm $ 5 MPa as “M”, and those with TS < 440 MPa as “L”. The “H” sheets exhibited the longest life, followed by the “M” sheets, and the “L” sheets, all outperforming Cu. At 390 MPa. “H” Cu-Zr’s fatigue life was ∼3 times that of Cu. Both the Cu-Zr and the Cu showed cyclic hardening. The presence of Zirconium improved fatigue life by stabilizing microstructure and retarding the formation of cracks during fatigue cycling, thus positioning Cu-Zr alloys as much stronger candidates than Cu for resistive magnet conductors.
{"title":"Fatigue Properties of Cold-Rolled Cu-Zr Alloy Sheets","authors":"R. Niu;K. Han;V. J. Toplosky;J. Toth","doi":"10.1109/TASC.2025.3636496","DOIUrl":"https://doi.org/10.1109/TASC.2025.3636496","url":null,"abstract":"We performed tension-tension fatigue tests in stress control mode on cold-rolled Cu-Zr alloy sheets with various levels of tensile strength (TS). We then compared the fatigue properties of these sheets to those of cold-rolled Cu sheets. Fatigue life increased as TS increased. We separated our Cu-Zr sheets according to their mechanical strength levels, designating those with their TS ∼490 MPa as “H”, those with TS around 448 <inline-formula><tex-math>$ pm $</tex-math></inline-formula> 5 MPa as “M”, and those with TS < 440 MPa as “L”. The “H” sheets exhibited the longest life, followed by the “M” sheets, and the “L” sheets, all outperforming Cu. At 390 MPa. “H” Cu-Zr’s fatigue life was ∼3 times that of Cu. Both the Cu-Zr and the Cu showed cyclic hardening. The presence of Zirconium improved fatigue life by stabilizing microstructure and retarding the formation of cracks during fatigue cycling, thus positioning Cu-Zr alloys as much stronger candidates than Cu for resistive magnet conductors.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 3","pages":"1-5"},"PeriodicalIF":1.8,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145778155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-24DOI: 10.1109/TASC.2025.3636601
Tessa Hall;Coenrad J. Fourie
Quantized magnetic flux trapped during cooldown in superconducting integrated circuits, particularly in thin-film ground planes, couples to nearby circuit structures. The coupling from such fluxons is known to degrade circuit operating margins, or to cause outright operational failure. Measurement of the likely location of one or more trapped fluxons during circuit operation, as well as before and after defluxing steps, can help improve defluxing methods and increase circuit operating margins. A bi-SQUID is a device consisting of three Josephson junctions, which demonstrates improved linearity in the voltage–flux response over conventional dc SQUIDs. Conventional dc SQUIDs are being considered as a means of implementing trapped flux detection. Due to the improved linearity of bi-SQUIDs, we investigate their suitability for the same purpose. We present simulation results comparing the sensitivity of different bi-SQUID designs and layout structures to trapped flux and compare bi-SQUID results with a conventional dc SQUID.
{"title":"Analysis on the Suitability of Bi-SQUIDs for the Detection of Trapped Flux in Superconducting Circuits","authors":"Tessa Hall;Coenrad J. Fourie","doi":"10.1109/TASC.2025.3636601","DOIUrl":"https://doi.org/10.1109/TASC.2025.3636601","url":null,"abstract":"Quantized magnetic flux trapped during cooldown in superconducting integrated circuits, particularly in thin-film ground planes, couples to nearby circuit structures. The coupling from such fluxons is known to degrade circuit operating margins, or to cause outright operational failure. Measurement of the likely location of one or more trapped fluxons during circuit operation, as well as before and after defluxing steps, can help improve defluxing methods and increase circuit operating margins. A bi-SQUID is a device consisting of three Josephson junctions, which demonstrates improved linearity in the voltage–flux response over conventional dc SQUIDs. Conventional dc SQUIDs are being considered as a means of implementing trapped flux detection. Due to the improved linearity of bi-SQUIDs, we investigate their suitability for the same purpose. We present simulation results comparing the sensitivity of different bi-SQUID designs and layout structures to trapped flux and compare bi-SQUID results with a conventional dc SQUID.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 4","pages":"1-5"},"PeriodicalIF":1.8,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146026624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-21DOI: 10.1109/TASC.2025.3635186
André E. Botha;Ilhom R. Rahmonov
We develop a discrete model for a hypothetical metamaterial consisting of an annular array of underdamped superconductor–ferromagnet–superconductor $varphi _{0}$ Josephson junctions. In this model, the magnetization in the F-layer is directly coupled to the Josephson current, producing $varphi _{0}$ phase shift that is proportional to the product of the spin-orbit coupling parameter of the ferromagnetic material and the component of magnetization perpendicular to the gradient of the asymmetric spin-orbit potential. In addition, the effective field felt by the magnetization now includes the surface current and fluxon-induced components. We show that this additional coupling can lead to the occurrence of magnetization waves that can reduce the critical current and significantly change the branching structure of the zero-field steps.
{"title":"Simulations of a Josephson Metamaterial Based on the S-F-S $varphi _{0}$ Josephson Junction","authors":"André E. Botha;Ilhom R. Rahmonov","doi":"10.1109/TASC.2025.3635186","DOIUrl":"https://doi.org/10.1109/TASC.2025.3635186","url":null,"abstract":"We develop a discrete model for a hypothetical metamaterial consisting of an annular array of underdamped superconductor–ferromagnet–superconductor <inline-formula><tex-math>$varphi _{0}$</tex-math></inline-formula> Josephson junctions. In this model, the magnetization in the F-layer is directly coupled to the Josephson current, producing <inline-formula><tex-math>$varphi _{0}$</tex-math></inline-formula> phase shift that is proportional to the product of the spin-orbit coupling parameter of the ferromagnetic material and the component of magnetization perpendicular to the gradient of the asymmetric spin-orbit potential. In addition, the effective field felt by the magnetization now includes the surface current and fluxon-induced components. We show that this additional coupling can lead to the occurrence of magnetization waves that can reduce the critical current and significantly change the branching structure of the zero-field steps.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 4","pages":"1-7"},"PeriodicalIF":1.8,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146026622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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}
To obtain the design basis for the dynamic characteristic parameters of bridges commonly used in superconducting electromagnetic suspension transportation, a refined magnetic force calculation model is established to analyze the dynamic load characteristics of null-flux coils. The dynamic response laws of simply supported beams under four types of equivalent train loads are compared, demonstrating that concentrated superconducting coil load sequences provide sufficient accuracy for bridge dynamic factor analysis. Furthermore, parametric analyses are conducted to investigate the effects of vehicle spacing, bridge spans, and train formations on bridge dynamic factors, and the preferred range of common bridge spans and strategies for regulating dynamic factors are discussed. The results show that the optimal range for common bridge spans is 1.5 to 1.75 times the vehicle spacing. When the ratio of bridge span to vehicle distance is 1.5, first-order resonance of the bridge is suppressed, and the dynamic factors of first-order superharmonic resonance increase with the number of train formations. When the ratio is 1.75, it is necessary to increase the vertical fundamental frequency of the bridge to avoid first-order resonance within the range of train operating speeds. Matching a 24.3 m vehicle spacing with a 37.8 m span bridge, under a 14-car formation, both the first-order resonance and superharmonic resonance dynamic factors of the bridge are less than 1.8. This configuration represents the optimal design scheme for high-speed superconducting electrodynamic suspension systems in terms of vehicle spacing and standardized bridge spans.
{"title":"Changing Laws and Regulation Strategies of Dynamic Factors of Bridges With Common Spans for Superconducting EDS Maglev Transportation","authors":"Zhonglin He;Chunfa Zhao;Yang Feng;Kai Li;Jing Yang;Ruodan Yu","doi":"10.1109/TASC.2025.3633799","DOIUrl":"https://doi.org/10.1109/TASC.2025.3633799","url":null,"abstract":"To obtain the design basis for the dynamic characteristic parameters of bridges commonly used in superconducting electromagnetic suspension transportation, a refined magnetic force calculation model is established to analyze the dynamic load characteristics of null-flux coils. The dynamic response laws of simply supported beams under four types of equivalent train loads are compared, demonstrating that concentrated superconducting coil load sequences provide sufficient accuracy for bridge dynamic factor analysis. Furthermore, parametric analyses are conducted to investigate the effects of vehicle spacing, bridge spans, and train formations on bridge dynamic factors, and the preferred range of common bridge spans and strategies for regulating dynamic factors are discussed. The results show that the optimal range for common bridge spans is 1.5 to 1.75 times the vehicle spacing. When the ratio of bridge span to vehicle distance is 1.5, first-order resonance of the bridge is suppressed, and the dynamic factors of first-order superharmonic resonance increase with the number of train formations. When the ratio is 1.75, it is necessary to increase the vertical fundamental frequency of the bridge to avoid first-order resonance within the range of train operating speeds. Matching a 24.3 m vehicle spacing with a 37.8 m span bridge, under a 14-car formation, both the first-order resonance and superharmonic resonance dynamic factors of the bridge are less than 1.8. This configuration represents the optimal design scheme for high-speed superconducting electrodynamic suspension systems in terms of vehicle spacing and standardized bridge spans.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 1","pages":"1-10"},"PeriodicalIF":1.8,"publicationDate":"2025-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145729437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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}
A superconducting quantum interference device (SQUID) consists of a superconducting loop interrupted by one or two Josephson junctions. Overdamped Josephson junctions, characterized by a Stewart–McCumber parameter (βc) below 1, are typically required as the key element of SQUIDs due to their nonhysteretic I–V characteristics. In the overdamped limit, the junction's shunt resistance is only a few ohms, leading to a SQUID voltage swing of just tens of μV. Consequently, connecting the SQUID to readout circuitry necessitates a complex noise-matching electronic circuit, such as those using flux modulation, adaptive positive feedback, or a SQUID bootstrap circuit. Here, we present a weakly damped SQUID designed for direct connection to the readout circuitry. This is achieved first by incorporating a submicron, low-capacitance Josephson junction, which allows the shunt resistance to be increased to tens of ohms. Second, the shunt resistance is increased further, resulting in a βc greater than 1, defining what is known as a weakly damped junction. This design achieves a high flux-to-voltage transfer coefficient of over 1 mV/Φ0, attributable to the increased voltage swing and a quasi-rectangular signal shape. As a result, the noise contribution from the preamplifier of the direct readout circuitry becomes negligible compared to the SQUID's intrinsic noise.
{"title":"Weakly Damped SQUID With Submicron Josephson Junctions","authors":"Guofeng Zhang;Shumin Yu;Yifeng Pei;Jun Wu;Yongliang Wang;Longqing Qiu;Hui Dong;Liangliang Rong;Y. Zhang;Xiaoming Xie","doi":"10.1109/TASC.2025.3631487","DOIUrl":"https://doi.org/10.1109/TASC.2025.3631487","url":null,"abstract":"A superconducting quantum interference device (SQUID) consists of a superconducting loop interrupted by one or two Josephson junctions. Overdamped Josephson junctions, characterized by a Stewart–McCumber parameter (<italic>β</i><sub>c</sub>) below 1, are typically required as the key element of SQUIDs due to their nonhysteretic I–V characteristics. In the overdamped limit, the junction's shunt resistance is only a few ohms, leading to a SQUID voltage swing of just tens of <italic>μ</i>V. Consequently, connecting the SQUID to readout circuitry necessitates a complex noise-matching electronic circuit, such as those using flux modulation, adaptive positive feedback, or a SQUID bootstrap circuit. Here, we present a weakly damped SQUID designed for direct connection to the readout circuitry. This is achieved first by incorporating a submicron, low-capacitance Josephson junction, which allows the shunt resistance to be increased to tens of ohms. Second, the shunt resistance is increased further, resulting in a <italic>β</i><sub>c</sub> greater than 1, defining what is known as a weakly damped junction. This design achieves a high flux-to-voltage transfer coefficient of over 1 mV/Φ<sub>0</sub>, attributable to the increased voltage swing and a quasi-rectangular signal shape. As a result, the noise contribution from the preamplifier of the direct readout circuitry becomes negligible compared to the SQUID's intrinsic noise.","PeriodicalId":13104,"journal":{"name":"IEEE Transactions on Applied Superconductivity","volume":"36 4","pages":"1-5"},"PeriodicalIF":1.8,"publicationDate":"2025-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146026623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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