Josephson vortices play an essential role in superconducting quantum electronics devices. Often seen as purely conceptual topological objects, 2 π -phase singularities, their observation and manipulation are challenging. Here we show that in Superconductor—Normal metal—Superconductor lateral junctions Josephson vortices have a peculiar magnetic fingerprint that we reveal in Magnetic Force Microscopy (MFM) experiments. Based on this discovery, we demonstrate the possibility of the Josephson vortex generation and manipulation by the magnetic tip of a MFM, thus paving a way for the remote inspection and control of individual nano-components of superconducting quantum circuits.

Vortices in quantum condensates exist owing to a macroscopic phase coherence. Here we show, both experimentally and theoretically, that a quantum vortex with a well-defined core can exist in a rather thick normal metal, proximized with a superconductor. Using scanning tunneling spectroscopy we reveal a proximity vortex lattice at the surface of 50 nm—thick Cu-layer deposited on Nb. We demonstrate that these vortices have regular round cores in the centers of which the proximity minigap vanishes. The cores are found to be significantly larger than the Abrikosov vortex cores in Nb, which is related to the effective coherence length in the proximity region. We develop a theoretical approach that provides a fully self-consistent picture of the evolution of the vortex with the distance from Cu/Nb interface, the interface impedance, applied magnetic field, and temperature. Our work opens a way for the accurate tuning of the superconducting properties of quantum hybrids.

Superconducting proximity devices using low-dimensional semiconducting elements enable a ballistic regime in the proximity transport. The use of topological insulators in such devices is considered promising owing to the peculiar transport properties these materials offer, as well the hope of inducing topological superconductivity and Majorana phenomena via proximity effects. Here we demonstrate the fabrication and superconducting properties of proximity Josephson devices integrating nanocrystals single of Bi 2 Te 2.3 Se 0.7 with a thickness of a few unit cells. Single junctions display typical characteristics of planar Josephson devices; junctions integrating two nanocrystals behave as nanodimensional superconducting quantum interference devices. A peculiar temperature and magnetic field evolution of the Josephson current along with the observed excess current effect point towards the ballistic proximity regime of topological channels. This suggests the proposed devices are promising for testing topological superconducting phenomena in two-dimensions.

We report on a fabrication method and electron-transport measurements for submicron Josephson junctions formed by Cu nanowires coupling to superconducting planar Nb electrodes. The Cu nanowires with a resistivity of ρCu≃1 μΩ cm at low temperatures consisting of single-crystalline segments have been obtained by templated electrodeposition using anodic aluminum oxide as a porous matrix. The current-voltage characteristics of the devices have been studied as a function of temperature and magnetic field. For all junctions, the critical current monotonically decreases with a magnetic field. The measured temperature and magnetic field dependencies are consistent with the model for one-dimensional diffusive superconductor/normal metal/superconductor (SNS) Josephson junctions within the quasiclassical theory of superconductivity.

In this work, we briefly overview various options for Josephson junctions, which should be scalable down to nanometer range for utilization in nanoscale digital superconducting technology. Such junctions should possess high values of critical current, I c , and normal state resistance, R N . Another requirement is the high reproducibility of the junction parameters across a wafer in a fabrication process. We argue that superconductor-normal metal-superconductor (SN -N -NS) Josephson junction of "variable thickness bridge" geometry is a promising choice to meet these requirements. Theoretical analysis of the SN -N -NS junction is performed in the case where the distance between the S electrodes is comparable to the coherence length of the N material. The restriction on the junction geometrical parameters providing the existence of superconductivity in the S electrodes is derived for the current flowing through the junction of an order of I c . The junction heating, as well as available mechanisms for the heat removal, is analyzed. The obtained results show that a SN -N -NS junction with a high (submillivolt) value of I c R N product can be fabricated from a broadly utilized combination of materials like Nb/Cu using well-established technological processes. The junction area can be scaled down to that of semiconductor transistors fabricated in the frame of a 40-nm process.

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Magnetic flux quantization in superconductors allows the implementation of fast and energy-efficient digital superconducting circuits. However, information representation in magnetic flux severely limits the functional density and is a long-standing problem. Here, we introduce the concept of superconducting digital circuits that do not utilize magnetic flux and have no inductors. We argue that neither the use of geometric nor kinetic inductance is promising for the scaling down of superconducting circuits. The key idea of our approach is the utilization of bistable Josephson junctions, allowing the representation of information through the Josephson energy. Since the proposed circuits are composed only of Josephson junctions, they can be called all-Josephson junction (all-JJ) circuits. We present a methodology for the design of circuits consisting of conventional and bistable junctions. We analyze the principles of the circuit's functioning, ranging from simple logic cells to an 8-bit parallel adder. The utilization of bistable junctions in the all-JJ circuits is promising for the simplification of schematics and a decrease of the JJ count, leading to space efficiency.

We have developed planar nanoSQUID with nanobridge-type Josephson junctions based on the oxidation resistant and high H c2 MoRe alloy. The objective of the research was to reduce size of the SQUID loop with the aim being to reduce magnetic flux noise and improve the spatial resolution of the SQUID sensors. Employing RF-magnetron sputtering, electron-beam lithography, and reactive ion etching in CHF 3 + O 2 plasma using Al hard masks, we have realized nanoSQUIDs with Josephson junctions in the form of 30 − 50 nm wide nanobridges and an effective magnetic flux capture radius of ~95 nm. The critical temperature of the fabricated devices was T c = 7.9 K. The I(V)-characteristics demonstrated critical current I 0 ≃ 114 µA at 4.2 K and modulation period in magnetic fields of ~700 Oe.