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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Fabrication and characterization of physically-linked large-scale josephson junction test arrays
摘要： The efforts of National Institute of Metrology (NIM) towards large scale Nb/ NbxSi1-x /Nb Josephson junction arrays for the quantum voltage standards are presented in this paper. Physically-linked arrays with 10,000 and 20,000 junctions (corresponding to 1 and 2 junctions vertically) are fabricated. DC I-V characteristics of different stacked arrays are measured and experimental results are discussed. Focusing ion beam (FIB) together with scanning electron microscope (SEM) are used to examine the cross-section of three types of junction stacks which vertically contains 2, 3, and 4 junctions respectively. It is shown that grain boundary defects in the niobium wiring layer exist for all of these junction stacks. A method which potentially could solve this problem is proposed.
关键词： superconducting device fabrication,Josephson junctions,quantum voltage,superconducting
更新于2025-09-23 15:22:29
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Study on the phase shifter in josephson junctions embedded microwave circuits
摘要： In a programmable Josephson voltage standard device which contains multiple branches of Josephson junction (JJ) array, the microwave reflection in arrays may result in a decrease in the Shapiro step margin. According to most of the previous designs, 90° phase shifter is used to cancel microwave reflection from branches to improve the performance of the device. This paper reports our study of the phase shifter in JJ array device with a 2-stage Wilkinson power divider. At first we designed and fabricated JJ array circuits with the phase shifters. Measurement results indicate that unequal powers have been reached to arrays. We then deleted the phase shifters in another design. Identical Shapiro step margins for 4 JJ array branches are achieved.
关键词： phase shifter,Josephson junctions,quantum voltage,superconducting
更新于2025-09-23 15:22:29
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Supercurrent and Multiple Andreev Reflections in InSb Nanosheet SNS Junctions
摘要： In this study, the realization of mesoscopic Josephson junctions based on free-standing InSb nanosheet grown by molecular-beam epitaxy is reported. Below the critical temperature of superconducting aluminium electrodes ((cid:1)1.1 K), the high transparency of the contacts gives rise to proximity-induced superconductivity. A dissipationless supercurrent which can be modulated by a gate voltage acting on the electron density in the nanosheet flows through the superconducting weak links. At finite bias voltage, subharmonic energy-gap structures (SGS) originating from multiple Andreev reflections (MARs) are observed, indicating a highly transparent InSb nanosheet–superconductor interface. At last, a superconducting hybrid device with niobium electrodes is shown, suitable for further higher temperature and magnetic field transport measurements.
关键词： supercurrent,InSb nanosheets,Josephson junctions,multiple Andreev reflections
更新于2025-09-23 15:22:29
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Magnetic field compatible circuit quantum electrodynamics with graphene Josephson junctions
摘要： Circuit quantum electrodynamics has proven to be a powerful tool to probe mesoscopic effects in hybrid systems and is used in several quantum computing (QC) proposals that require a transmon qubit able to operate in strong magnetic fields. To address this we integrate monolayer graphene Josephson junctions into microwave frequency superconducting circuits to create graphene based transmons. Using dispersive microwave spectroscopy we resolve graphene’s characteristic band dispersion and observe coherent electronic interference effects confirming the ballistic nature of our graphene Josephson junctions. We show that the monoatomic thickness of graphene renders the device insensitive to an applied magnetic field, allowing us to perform energy level spectroscopy of the circuit in a parallel magnetic field of 1 T, an order of magnitude higher than previous studies. These results establish graphene based superconducting circuits as a promising platform for QC and the study of mesoscopic quantum effects that appear in strong magnetic fields.
关键词： transmon qubit,magnetic field resilience,quantum computing,Circuit quantum electrodynamics,graphene Josephson junctions
更新于2025-09-23 15:21:01
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[IEEE 2018 48th European Microwave Conference (EuMC) - Madrid (2018.9.23-2018.9.27)] 2018 48th European Microwave Conference (EuMC) - Dispersion of THz Modes Localized on Layered Superconductor Controlled by DC Magnetic Field
摘要： Being materials that support terahertz waves propagation, layered superconductors attract great attention of many researchers. The Josephson plasma modes localized on a slab of layered superconductor can possess an anomalous dispersion. The possibility of anomalous dispersion manipulation opens wide perspectives for applications. One of the tools that can flexibly change the electromagnetic properties of layered superconductors is the external DC magnetic field. The effect of the DC magnetic field on the spectrum of the localized modes is a subject of the present paper. We present the derivation and analysis of the dispersion relations and discuss some interesting corollaries such as resonant amplification of wave transmission induced by the internal excitation of the localized modes and the possibility of the internal reflection of the localized modes controlled by the external DC magnetic field.
关键词： high-temperature superconductors,electromagnetic fields,Terahertz metamaterials,Josephson junctions
更新于2025-09-12 10:27:22
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Stationary charge imbalance effect in a system of coupled Josephson junctions
摘要： We investigate the stationary charge imbalance e?ect in the system of coupled overdamped Josephson junctions. We show that the stationary charge imbalance in the resistive state brings to a decrease in the Josephson frequency in the junctions of the stack. The formed di?erence in frequencies leads to a nonuniform switch of junctions along the stack to the Shapiro step regime in the presence of external electromagnetic radiation. On the other hand, such nonuniform switching leads to the appearance of voltage spikes on the IV -characteristic of the stack. We show that the stationary charge imbalance is responsible for a slope in the Shapiro step due to the di?erence of the nonequilibrium potentials at the edges of the step. The obtained results have been compared with the voltage bias coupled Josephson junctions and experimental results.
关键词： nonequilibrium potentials,Shapiro step,Stationary charge imbalance,Josephson junctions
更新于2025-09-11 14:15:04
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Development and Fabrication of Improved Josephson Series Arrays with NbSi Barrier for AC Voltage Standards
摘要： Series arrays of overdamped Josephson junctions compose the basis of AC Josephson voltage standards. Presently, an advanced technology is based on Josephson junctions consisting of an NbxSi1-x barrier. Using junction stacks containing five Josephson junctions, series arrays of 15,000 junctions have been successfully fabricated at PTB for the pulse-driven Josephson Arbitrary Waveform Synthesizer (JAWS). The operation of eight arrays simultaneously enable spectrally pure waveforms with output voltages above 1 V to be synthesized.
关键词： SNS Josephson junctions,binary-divided Josephson series arrays,AC Josephson voltage standards,pulse-driven Josephson series arrays,NbSi barrier Josephson junctions
更新于2025-09-10 09:29:36
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Anomalous quantum interference effects in graphene SNS junctions due to strain-induced gauge fields
摘要： We investigate the influence of gauge fields induced by strain on the supercurrent passing through the graphene-based Josephson junctions. We show that, in the presence of a constant pseudomagnetic field BS originating from an arc-shape elastic deformation, the Josephson current is monotonically enhanced. This is in contrast with the oscillatory behavior of supercurrent (known as Fraunhofer pattern) caused by real magnetic fields passing through the junction. The absence of oscillatory supercurrent originates from the fact that strain-induced gauge fields have opposite directions at the two valleys due to the time-reversal symmetry. Subsequently the Aharonov-Bohm phases due to BS cancel out between electron and hole components of the current carrying Andreev bound states. Nevertheless, we find another phase factor coming from the pseudomagnetic fields which rotates the pseudospin and is in fact responsible for the enhancement of Josephson currents. When both magnetic and pseudomagnetic fields are present, Fraunhofer-like oscillations as a function of the real magnetic field flux are found. Intriguingly, the combination of two kinds of gauge fields results in two special fingerprints in the local supercurrent density: (i) strong localization of the Josephson current density with more intense maximum amplitudes; (ii) appearance of the inflated vortex cores—finite regions with almost diminishing Josephson currents—whose sizes increase by increasing BS. These findings reveal unexpected interference signatures of pseudomagnetic fields in graphene SNS junctions which can cause a twist in the investigations on strain-induced gauge fields.
关键词： quantum interference,supercurrent,Josephson junctions,graphene,strain-induced gauge fields
更新于2025-09-10 09:29:36
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Nanowire-Based Josephson Junctions
摘要： The combination of superconductivity and surface states in Dirac semimetal can produce a 4π-periodic supercurrent in a Josephson junction configuration, which can be revealed by the missing of odd Shapiro steps (especially the n ? 1 step). However, the suppression of the n ? 1 step is also anticipated in the high-power oscillatory regime of the ordinary 2π-periodic Josephson effect, which is irrelevant to the 4π-periodic supercurrent. Here, in order to identify the origin of the suppressed n ? 1 step, we perform the measurements of radio frequency irradiation on Nb–Dirac semimetal Cd3As2 nanowire–Nb junctions with continuous power dependence at various frequencies. Besides the n ? 1 step suppression, we uncover a residual supercurrent of first node at the n ? 0 step, which provides a direct and predominant signature of the 4π-periodic supercurrent. Furthermore, by tuning the gate voltage, we can modulate the surface and bulk state contribution and the visibility of the n ? 1 step. Our results provide deep insights to explore the topological superconductivity in Dirac semimetals.
关键词： surface states,Cd3As2 nanowire,topological superconductivity,4π-periodic supercurrent,Josephson junctions
更新于2025-09-09 09:28:46