High Resolution Image Download MS PowerPoint Slide Planar Josephson junctions (JJs) based on InSb nanoflags have recently emerged as an intriguing platform in superconducting electronics. The knowledge of the current-phase relationship (CPR) of such hybrid junctions is crucial for their applications. This letter presents the fabrication and investigation of superconducting quantum interference devices (SQUIDs) employing InSb nanoflag JJs. The observed features are well reproduced through numerical simulations. By measuring interference patterns in both symmetric and asymmetric SQUID configurations, we extract unprecedented details of the junctions’ CPRs. Our results demonstrate the skewness of the CPR, showing significant contributions from higher harmonics. We explore the magnetic field response of the devices across a wide range of fields (±30 mT). Finally, we assess the flux-to-voltage sensitivity of the SQUIDs to evaluate their performance as magnetometers, identifying a magnetic flux noise of S Φ 1 / 2 = 4.4 × 1 0 − 6 Φ 0 / √ H z . These results showcase potential applications in nanoscale magnetometry.
High Resolution Image Download MS PowerPoint Slide Planar Josephson junctions (JJs) based on InSb nanoflags have recently emerged as an intriguing platform in superconducting electronics. The knowledge of the current-phase relationship (CPR) of such hybrid junctions is crucial for their applications. This letter presents the fabrication and investigation of superconducting quantum interference devices (SQUIDs) employing InSb nanoflag JJs. The observed features are well reproduced through numerical simulations. By measuring interference patterns in both symmetric and asymmetric SQUID configurations, we extract unprecedented details of the junctions’ CPRs. Our results demonstrate the skewness of the CPR, showing significant contributions from higher harmonics. We explore the magnetic field response of the devices across a wide range of fields (±30 mT). Finally, we assess the flux-to-voltage sensitivity of the SQUIDs to evaluate their performance as magnetometers, identifying a magnetic flux noise of S Φ 1 / 2 = 4.4 × 1 0 − 6 Φ 0 / √ H z . These results showcase potential applications in nanoscale magnetometry.
Superconducting quantum interference devices (SQUIDs) based on nanobridge junctions (NBJs) are promising platforms for highly sensitive magnetic detection. The SQUID performance is influenced by the non-sinusoidal current-phase relation (CPR) of NBJs. In this work, we measured the flux modulation of 10 asymmetric Nb SQUIDs based on three-dimensional NBJs, along with the CPR response in each device, which is mainly determined by the junction with the smaller critical current. By studying the CPR parameters (skewness Δ θ , critical current I c1 , and effective junction inductance L j ), together with the SQUID modulation characteristics (voltage modulation amplitude Δ I c R n and current modulation ratio Δ I c /2 I c1 ), we found that as I c1 increases from 0.6 μA to 6.6 μA and L j correspondingly decreases from 106 pH to 70 pH, the CPR skewness Δ θ increases from 0.2 rad to 1.5 rad. Over this range, Δ I c /2 I c1 decreases from 1.2 to 0.5, while Δ I c R n increases from about 0.06 mV to 0.22 mV. More specifically, Δ I c R n increases while Δ I c /2 I c1 decreases with increasing I c1 , whereas both quantities decrease with increasing L j . These results reveal a trade-off between intrinsic SQUID response and tolerance to readout noise, suggesting that improved performance can be achieved by engineering NBJs with increased I c1 and smaller L j .
We report on the fabrication and characterization of micrometer-sized superconducting quantum interference devices (SQUIDs) based on nanoscale vanadium/copper/vanadium Josephson weak links. Magnetically driven quantum interference patterns have been measured for temperatures in the 0.24–2 K range. As DC SQUIDs, these devices obtain flux-to-voltage transfer function values as high as 450 μV/Φ0 leading to promising magnetic flux resolution ΦN<3 μΦ0/Hz, being here limited by the room temperature preamplification stage. Significant improvement in the flux noise performance figures is expected with the adoption of cryogenic preamplification. The presented devices are suitable for operation as small-area SQUIDs at sub-Kelvin temperature, but their design can also be upscaled to include input coils enabling their use as sensitive magnetometers via the adoption of optimized electronic readout stages based on flux feedback schemes.
Josephson junction, as the core nonlinear element underpinning superconducting electronics, is characterized by its current-phase relation (CPR), which fundamentally determines the dynamical properties and functional capabilities of superconducting quantum devices. Traditional Josephson junctions typically exhibit a traditional sinusoidal CPR; however, the junctions characterized by non-sinusoidal CPR have recently attracted considerable attention due to their distinctive physical properties and promising quantum device applications. In this work, a numerical model tailored specifically for junctions exhibiting non-sinusoidal CPR is developed by integrating experimentally measured current-voltage (I-V ) characteristics from Nb/Al-AlOx/Nb junctions into a resistively and capacitively shunted junction (RCSJ) framework. By leveraging this refined model, the influence of CPR skewness on Josephson junction dynamics is systematically investigated. Our results indicate that in underdamped junctions, the critical current significantly diminishes with the increase of CPR skewness, a behavior reminiscent of the adjustable critical currents typically observed in DC superconducting quantum interference devices (SQUIDs). Conversely, in overdamped junctions, the influence of CPR skewness on the I-V characteristics is found to be negligible. However, our numerical simulations under microwave irradiation indicate that nonsinusoidal CPRs readily promote the emergence of half-integer Shapiro steps in overdamped junctions, thereby establishing CPR skewness as a plausible microscopic origin for this phenomenon. In addition, the advanced design system (ADS) simulations is employed to model nonlinear resonators and DC SQUID circuits, offering a detailed investigation into how nonsinusoidal CPRs modulate the Josephson inductance and magnetic flux response. Our findings reveal that engineering the CPR of Josephson junctions provides substantial flexibility in the design of superconducting qubits, parametric amplifiers, and non-magnetic nonreciprocal devices. This tunability underscores significant opportunities for developing next-generation superconducting electronic components. The Josephson junctions with engineered CPR offer expanded functionality for superconducting quantum technologies. This study suggests that customized CPR can enhance control over the dynamical behavior of junctions, and promote the optimized designs of superconducting qubits, parametric amplifiers, and nonmagnetic nonreciprocal devices.
Direct current-superconducting quantum interference devices (SQUIDs) characterized by asymmetric Josephson junctions have never been used for applications. In order to demonstrate their potential advantages, a throughout numerical analysis of different asymmetric configurations has been carried out. A damping resistance has been included in the SQUID circuit and the thermal noise associated with junction and damping resistances has been considered in the numerical model. Magnetic modulations and flux noise spectral densities have been computed as a function of many parameters (bias current, asymmetry, SQUID inductance, and damping resistance) and the performance of symmetric and asymmetric devices have been compared. The results show that, by properly optimizing the SQUID design, asymmetric SQUIDs are characterized by higher magnetic flux to voltage transfer coefficient and lower flux noise. As a result, asymmetric configurations can be very useful in all the applications where high sensitivity is required.
Hybrid superconductor(S)-semiconductor(Sm) devices bring a range of functionalities into superconducting circuits. In particular, hybrid parity-protected qubits and Josephson diodes were recently proposed and experimentally demonstrated. Such devices leverage the nonsinusoidal character of the Josephson current-phase relation (CPR) in highly transparent S-Sm-S junctions. Here, we report an experimental study of superconducting quantum-interference devices (SQUIDs) embedding Josephson field-effect transistors fabricated from a SiGe/Ge/SiGe heterostructure grown on a 200-mm silicon wafer. The single-junction CPR shows up to three harmonics with gate-tunable amplitude. In the presence of microwave irradiation, the ratio of the first two dominant harmonics, corresponding to single and double Cooper-pair transport processes, is consistently reflected in relative weight of integer and half-integer Shapiro steps. A combination of magnetic-flux and gate-voltage control enables tuning the SQUID functionality from a nonreciprocal Josephson-diode regime with 27% asymmetry to a π -periodic Josephson regime suitable for the implementation of parity-protected superconducting qubits. These results illustrate the potential of Ge-based hybrid devices as versatile and scalable building blocks of superconducting quantum circuits. Published by the American Physical Society 2024
Abstract Miniaturization of superconducting quantum interference devices (SQUIDs) is of major importance for the development of sensitive scanning nanoscale magnetometry tools. The high sensitivity of nanoSQUIDs is restricted, however, to only particular periodic values of the applied magnetic field, making accurate measurements at intermediate values of the field impossible. We present a theoretical investigation of a multi-terminal, multi-junction SQUID (mSQUID) that lifts this limitation by providing electrical means for a continuous shift of the quantum interference pattern with respect to the applied field. Analysis of 4-terminal, 4-junction and 3-terminal, 3-junction mSQUIDs shows that operation at maximum sensitivity can be obtained at any value of the magnetic field by applying control current to the extra terminals. The model describes the variation and the shift of the interference pattern as a function of the control currents, junction asymmetries, and the mSQUID inductance. The mSQUID is also shown to provide a direct measurement of the current–phase relations of superconducting junctions. The derived model provides a quantitative description of the recently developed multi-terminal nanoSQUID-on-tip.