Imaging spontaneous currents in superconducting arrays of pi-junctions

Superconductors separated by a thin tunneling barrier exhibit the Josephson effect that allows charge transport at zero voltage, typically with no phase shift between the superconductors in the lowest energy state. Recently, Josephson junctions with ground state phase shifts of pi proposed by theory three decades ago have been demonstrated. In superconducting loops, pi-junctions cause spontaneous circulation of persistent currents in zero magnetic field, analogous to spin-1/2 systems. Here we image the spontaneous zero-field currents in superconducting networks of temperature-controlled pi-junctions with weakly ferromagnetic barriers using a scanning SQUID microscope. We find an onset of spontaneous supercurrents at the 0-pi transition temperature of the junctions Tpi = 3 K. We image the currents in non-uniformly frustrated arrays consisting of cells with even and odd numbers of pi-junctions. Such arrays are attractive model systems for studying the exotic phases of the 2D XY-model and achieving scalable adiabatic quantum computers.Comment: Pre-referee version. Accepted to Nature Physic

Ferromagnetic Josephson Junctions for High Performance Computation

Josephson junctions drive the operation of superconducting qubits and they are the key for the coupling and the interfacing of superconducting qubit components with other quantum platforms. They are the only means to introduce non linearity in a superconducting circuit and offer direct solutions to tune the properties of a superconducting qubit, thus enlarging the possible qubit layouts. Junctions performances and tunability can take advantage of using a large variety of barriers and their special functionalities. We mention pertinent results on the advances in understanding the properties of ferromagnetic junctions, which make possible the use of these devices either as memory elements and as core circuit elements

Ferromagnetic Josephson switching device with high characteristic voltage

We develop a fast Magnetic Josephson Junction (MJJ) - a superconducting ferromagnetic device for a scalable high-density cryogenic memory compatible in speed and fabrication with energy-efficient Single Flux Quantum (SFQ) circuits. We present experimental results for Superconductor-Insulator-Ferromagnet-Superconductor (SIFS) MJJs with high characteristic voltage IcRn of >700 uV proving their applicability for superconducting circuits. By applying magnetic field pulses, the device can be switched between MJJ logic states. The MJJ IcRn product is only ~30% lower than that of conventional junction co-produced in the same process, allowing for integration of MJJ-based and SIS-based ultra-fast digital SFQ circuits operating at tens of gigahertz.Comment: 10 pages, 4 figure

Properties of ferromagnetic Josephson junctions for memory applications

In this work we give a characterization of the RF effect of memory switching on Nb-Al/AlOx-(Nb)-Pd$_{0.99}$Fe$_{0.01}$-Nb Josephson junctions as a function of magnetic field pulse amplitude and duration, alongside with an electrodynamical characterization of such junctions, in comparison with standard Nb-Al/AlOx-Nb tunnel junctions. The use of microwaves to tune the switching parameters of magnetic Josephson junctions is a step in the development of novel addressing schemes aimed at improving the performances of superconducting memories.Comment: IEEE Trans. Appl. Supercond. Special Issue ISEC201

Ultrastrong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers

The critical step for future quantum industry demands realization of efficient information exchange between different-platform hybrid systems that can harvest advantages of distinct platforms. The major restraining factor for the progress in certain hybrids is weak coupling strength between the elemental particles. In particular, this restriction impedes a promising field of hybrid magnonics. In this work, we propose an approach for realization of on-chip hybrid magnonic systems with unprecedentedly strong coupling parameters. The approach is based on multilayered microstructures containing superconducting, insulating, and ferromagnetic layers with modified photon phase velocities and magnon eigenfrequencies. The enhanced coupling strength is provided by the radically reduced photon mode volume. Study of the microscopic mechanism of the photon-to-magnon coupling evidences formation of the long-range superconducting coherence via thick strong ferromagnetic layers in superconductor/ferromagnet/superconductor trilayer in the presence of magnetization precession. This discovery offers new opportunities in microwave superconducting spintronics for quantum technologies

THERMOELECTRIC, UNEQUILIBRIUM AND PHASE-COHERENT PHENOMENA IN LAMINATED SUPERCONDUCTOR - NORMAL METAL - SUPERCONDUCTOR SYSTEMS

The thermoelectric and acoustoelectric analogs of the Josephson effects and also analogs of the Seebeck and Nernst effects in the distributed Josephson transitions were firstly observed in experiment; a possibility to excitate the Josephson generation in the SNS-transition by an unequilibrium electric field has been shown in experiment. The new dimensional transition in the multi-layer SNS-structure from quasi-two-dimensional state into the 20-strong-connected one has been discovered; this transition explains the anomal behaviour of the lower critical field in these structures; the multiple increase of the voltage in the resonant Shapiro stages at subdivision of the Josephson transitions in the multi-layer SNS-structures during 3D-2D dimensional transition has been discovered. The discovered effects and measured characteristics can be a base of the following principial-new converters and registrating devices: transducer of heat flow; modulated heat flow - voltage and modulated sonic wave - voltage converters enabling to record the amplitude and frequency of the modulation; "heat squid" converting the heat flow into quantized magnetic flux. Two author's certificate for the heat flow transducer and resistive squid have been obtained.Available from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Proximity effect in superconductor–ferromagnet heterostructures

We discuss the particularities of the proximity effect in superconductor–ferromagnet systems: the damped oscillatory behavior of the Cooper pair wave function, the oscillations of the critical temperature in S/F bilayers and multilayers and the conditions for the π-Josephson junctions formation. Also we outline the possibility of the formation of the novel type of the Josephson junction, intermediate between the 0 and π junction