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We demonstrate a Josephson parametric amplifier design with a band-pass impedance matching network based on a third-order Chebyshev prototype. We measured eight amplifiers operating at 4.6 GHz that exhibit gains of 20 dB with less than 1 dB gain ripple and up to 500 MHz bandwidth. The amplifiers further achieve high output saturation powers around -73 dBm based on the use of rf-SQUID arrays as their nonlinear element. We characterize the system readout efficiency and its signal-to-noise ratio near saturation using a Sycamore processor, finding the data consistent with near quantum limited noise performance of the amplifiers. In addition, we measure the amplifiers' intermodulation distortion in two-tone experiments as a function of input power and inter-tone detuning, and observe excess distortion at small detuning with a pronounced dip as a function of signal power, which we interpret in terms of power-dependent dielectric losses., Comment: 14 pages, 10 figures

The control of a superconducting current via the application of a gate voltage has been recently demonstrated in a variety of superconducting devices. Although the mechanism underlying this gate-controlled supercurrent (GCS) effect remains under debate, the GCS effect has raised great interest for the development of the superconducting equivalent of conventional metaloxide semiconductor electronics. To date, however, the GCS effect has been mostly observed in superconducting devices made by additive patterning. Here, we show that devices made by subtractive patterning show a systematic absence of the GCS effect. Doing a microstructural analysis of these devices and comparing them to devices made by additive patterning, where we observe a GCS, we identify some material and physical parameters that are crucial for the observation of a GCS. We also show that some of the mechanisms proposed to explain the origin of the GCS effect are not universally relevant., Comment: 19 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:2302.13734

We investigate a ballistic InSb nanoflag-based Josephson junction with Nb superconducting contacts. The high transparency of the superconductor-semiconductor interfaces enables the exploration of quantum transport with parallel short and long conducting channels. Under microwave irradiation, we observe half-integer Shapiro steps that are robust to temperature, suggesting their possible non-equilibrium origin. Our results demonstrate the potential of ballistic InSb nanoflags Josephson junctions as a valuable platform for understanding the physics of hybrid devices and investigating their non-equilibrium dynamics., Comment: 37 pages, 14 figures

In conventional metal-oxide semiconductor (CMOS) electronics, the logic state of a device is set by a gate voltage (VG). The superconducting equivalent of such effect had remained unknown until it was recently shown that a VG can tune the superconducting current (supercurrent) flowing through a nanoconstriction in a superconductor. This gate-controlled supercurrent (GCS) effect can lead to superconducting logics like CMOS logics, but with lower energy dissipation. The physical mechanism underlying the GCS effect, however, remains under debate. In this review article, we illustrate the main mechanisms proposed for the GCS effect, and the material and device parameters that mostly affect it based on the evidence reported. We will come to the conclusion that different mechanisms are at play in the different studies reported so far. We then outline studies that can help answer open questions on the effect and achieve control over it, which is key for applications. We finally give insights into the impact that the GCS effect can have towards high-performance computing with low-energy dissipation and quantum technologies., Comment: 54 pages, 16 figures, 4 tables

We report evidence of non-reciprocal dissipation-less transport in single ballistic InSb nanoflag Josephson junctions, owing to a strong spin-orbit coupling. Applying an in-plane magnetic field, we observe an inequality in supercurrent for the two opposite current propagation directions. This demonstrates that these devices can work as Josephson diodes, with dissipation-less current flowing in only one direction. For small fields, the supercurrent asymmetry increases linearly with the external field, then it saturates as the Zeeman energy becomes relevant, before it finally decreases to zero at higher fields. We show that the effect is maximum when the in-plane field is perpendicular to the current vector, which identifies Rashba spin-orbit coupling as the main symmetry-breaking mechanism. While a variation in carrier concentration in these high-quality InSb nanoflags does not significantly influence the diode effect, it is instead strongly suppressed by an increase in temperature. Our experimental findings are consistent with a model for ballistic short junctions and show that the diode effect is intrinsic to this material. Our results establish InSb Josephson diodes as a useful element in superconducting electronics.

Setting up strong Josephson coupling in van der Waals materials in close proximity to superconductors offers several opportunities both to inspect fundamental physics and to develop novel cryogenic quantum technologies. Here we show evidence of Josephson coupling in a planar few-layer black Phosphorus junction. The planar geometry allows us to probe the junction behavior by means of external gates, at different carrier concentrations. Clear signatures of Josephson coupling are demonstrated by measuring supercurrent flow through the junction at milli Kelvin temperatures. Manifestation of Fraunhofer pattern with a transverse magnetic field is also reported, confirming the Josephson coupling. These findings represent the first evidence of proximity Josephson coupling in a planar junction based on a van der Waals material beyond graphene and open the way to new studies, exploiting the peculiar properties of exfoliated black phosphorus thin flakes.

We theoretically investigate a quantum heat diode based on two interacting flux qubits coupled to two heat baths. Rectification of heat currents is achieved by asymmetrically coupling the qubits to the reservoirs modelled as dissipative $RLC$ resonators. We find that the coherent interaction between the qubits can be exploited to enhance the rectification factor, which otherwise would be constrained by the baths temperatures and couplings. Remarkably high values of rectification ratio up to $\mathcal R \sim 3.5$ can be obtained for realistic system parameters, with an enhancement up to $\sim 230\%$ compared to the non-interacting case. The system features the possibility of manipulating both the rectification amplitude and direction, allowing for an enhancement or suppression of the heat flow to a chosen bath. For the regime of parameters in which rectification is maximized, we find a significant increase of the rectification above a critical interaction value which corresponds to the onset of a non vanishing entanglement in the system. Finally, we discuss the dependence of the rectification factor on the bath temperatures and couplings., Comment: 6 pages, 3 figures

We discuss the response of an rf-SQUID formed by anomalous Josephson junctions embedded in a superconducting ring with a non-negligible inductance. We demonstrate that a properly sweeping in-plane magnetic field can cause both the total flux and the current circulating in the device to modulate and to behave hysteretically. The bistable response of the system is analyzed as a function of the anomalous phase shift at different values of the screening parameter, in order to highlight the parameter range within which a hysteretic behavior can be observed. The magnetic flux piercing the SQUID ring is demonstrated to further modulate the hysteretical response of the system. Moreover, we show that the anomalous phase shift can be conveniently determined through the measurement of the out-of-plane magnetic field at which the device switches to the voltage state and the number of trapped flux quanta changes. Finally, we compare the response of two different device configurations, namely, a SQUID including only one or two anomalous junctions. In view of these results, the proposed device can be effectively used to detect and measure the anomalous Josephson effect., Comment: 9 pages, 6 figures

Hybrid superconductor/semiconductor devices constitute a powerful platform to investigate the emergence of new topological state of matter. Among all possible semiconductor materials, InAs represents a promising choice, owing to its high quality, large g-factor and spin-orbit component. Here, we report on InAs-based devices both in one-dimensional and two-dimensional configurations. In the former, low-temperature measurements on a suspended nanowire are presented, inspecting the intrinsic spin-orbit contribution of the system. In the latter, Josephson Junctions between two Nb contacts comprising an InAs quantum well are investigated. Supercurrent flow is reported, with Nb critical temperature up to T_c~8K. Multiple Andreev reflection signals are observed in the dissipative regime. In both systems, we show that the presence of external gates represents a useful knob, allowing for wide tunability and control of device properties, such as spin-orbit coherence length or supercurrent amplitude., Comment: 6 pages, 5 figures (Proceeding of the SPIE conference)

Semiconductor nanowires featuring strong spin-orbit interactions (SOI), represent a promising platform for a broad range of novel technologies, such as spintronic applications or topological quantum computation. However, experimental studies into the nature and the orientation of the SOI vector in these wires remain limited despite being of upmost importance. Typical devices feature the nanowires placed on top of a substrate which modifies the SOI vector and spoils the intrinsic symmetries of the system. In this work, we report experimental results on suspended InAs nanowires, in which the wire symmetries are fully preserved and clearly visible in transport measurements. Using a vectorial magnet, the non-trivial evolution of weak anti-localization (WAL) is tracked through all 3D space, and both the spin-orbit length $l_{SO}$ and coherence length $l_\varphi$ are determined as a function of the magnetic field magnitude and direction. Studying the angular maps of the WAL signal, we demonstrate that the average SOI within the nanowire is isotropic and that our findings are consistent with a semiclassical quasi-1D model of WAL adapted to include the geometrical constraints of the nanostructure. Moreover, by acting on properly designed side gates, we apply an external electric field introducing an additional vectorial Rashba spin-orbit component whose strength can be controlled by external means. These results give important hints on the intrinsic nature of suspended nanowire and can be interesting for in the field of spintronics as well as for the manipulation of Majorana bound states in devices based on hybrid semiconductors., Comment: 13 pages, 11 figures