Time-connected phase slips in current-driven two-band superconducting wires

Cadorim L.R., Sardella E., Domínguez D., Berger J.

Foltyn M., Norowski K., Savin A., Zgirski M.

We demonstrate complete control over dynamics of a single superconducting vortex in a nanostructure, which we coin the Single Vortex Box. Our device allows us to trap the vortex in a field-cooled aluminum nanosquare and expel it on demand with a nanosecond pulse of electrical current. Using the time-resolving nanothermometry we measure 4 · 10 - 19 joules as the amount of the dissipated heat in the elementary process of the single-vortex expulsion. Our experiment enlightens the thermodynamics of the absorption process in the superconducting nanowire single-photon detectors, in which vortices are perceived to be essential for a formation of a detectable hotspot. The demonstrated opportunity to manipulate a single superconducting vortex reliably in a confined geometry comprises a proof of concept of a nanoscale nonvolatile memory cell with subnanosecond write and read operations, which offers compatibility with quantum processors based either on superconducting qubits or on rapid single-flux quantum circuits.

Ishizu H., Yamamori H., Arisawa S., Nishio T., Tokiwa K., Tanaka Y.

A direct current superconducting quantum interference device (SQUID) fixed on a recently developed superconducting bilayer disc is effective for studying fractional magnetic quantum and fractional vortices. However, such devices cannot magnetically image fractional vortices. To overcome this limitation, we compared the bilayer SQUID signal with and without a pinhole to experimentally investigate the vortex arrangement. We measured the amount of flux passing through the SQUID ring via the SQUID signal phase shift, which reflected the vortex locations. We measured the voltages of a series of 100 SQUIDs in which the bilayer discs were present under each SQUID. When we applied a constant bias current of 5.5 μA and swept the external magnetic field, a voltage appeared when the amount of magnetic flux passing through the SQUID ring became close to half of the flux quantum. A sharp voltage peak was obtained for the bilayers with a pinhole, whereas these peaks were broader for the bilayers without a pinhole. We evaluated the amount of the flux originating from the vortices trapped in the bilayer discs and estimated the vortex locations from the peak position. When the amount of flux originating from the trapped vortices increased, the bilayer discs without a pinhole exhibited reduced amounts of flux originating from the trapped vortices by approximately 15% compared to the bilayer discs with a pinhole. When no pinhole was present, the vortex locations varied inside the SQUID ring. The results indicated that the vortices were located at the same position for all 100 bilayer discs with a pinhole; therefore, we concluded that the pinholes must trap the vortices.

Gümüş E., Majidi D., Nikolić D., Raif P., Karimi B., Peltonen J.T., Scheer E., Pekola J.P., Courtois H., Belzig W., Winkelmann C.B.

Josephson junctions are a central element in superconducting quantum technology; in these devices, irreversibility arises from abrupt slips of the quantum phase difference across the junction. This phase slip is often visualized as the tunnelling of a flux quantum in the transverse direction to the superconducting weak link, which produces dissipation. Here we detect the instantaneous heat release caused by a phase slip in a Josephson junction, signalled by an abrupt increase in the local electronic temperature in the weak link and subsequent relaxation back to equilibrium. Beyond the advance in experimental quantum thermodynamics of observing heat in an elementary quantum process, our approach could allow experimentally investigating the ubiquity of dissipation in quantum devices, particularly in superconducting quantum sensors and qubits. Superconducting currents around a loop containing a weak link can be quantized and only change during discrete events called phase slips. Now, the heat generated by a single phase slip and the subsequent relaxation have been experimentally observed.

Kato K., Takagi T., Tanabe T., Moriyama S., Morita Y., Maki H.

We study the manipulation of thermal/quantum phase slips (tPSs/qPSs) in ultra-thin niobium-nitride superconducting nanowires (scNW) grown on carbon-nanotube templates. These NWs exhibit resistive steps in current–voltage (I–V) characteristics, and the number of phase slip centers (PSCs) in an NW can be tuned by the NW length. Under microwave (MW) radiation, emergence of each single PSC can be precisely controlled by varying the MW power. For thin and short scNW, a dip structure between the qPS-dominated low-temperature region and the tPS-dominated high-temperature region were observed owing to anti-proximity effect by electrodes.

Vargunin A., Silaev M.A., Babaev E.

Dremov V.V., Grebenchuk S.Y., Shishkin A.G., Baranov D.S., Hovhannisyan R.A., Skryabina O.V., Lebedev N., Golovchanskiy I.A., Chichkov V.I., Brun C., Cren T., Krasnov V.M., Golubov A.A., Roditchev D., Stolyarov V.S.

Josephson vortices play an essential role in superconducting quantum electronics devices. Often seen as purely conceptual topological objects, 2π-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. Josephson vortices (JVs) play an important role in superconducting quantum devices, but they remain difficult to be observed and manipulated. Here, Dremov et al. report magnetic fingerprint of JVs in magnetic force microscopy experiments, which paves a way to generate and control JVs.

Marychev P.M., Vodolazov D.Y.

Using time-dependent Ginzburg-Landau theory we find oscillations of critical current density $j_c$ as a function of the length $L$ of the bridge formed from two-band superconductor. We explain this effect by appearance of the phase solitons in the bridge at $j

Madan I., Buh J., Baranov V.V., Kabanov V.V., Mrzel A., Mihailovic D.

First observation of the photoinduced transition between dynamical superconducting states and hidden dynamical states.

Mosquera Polo A.S., da Silva R.M., Vagov A., Shanenko A.A., Deluque Toro C.E., Aguiar J.A.

We demonstrate that in a weak-coupled two-band superconducting slab the interaction between vortices penetrating the sample and its boundaries leads to the phenomenon of vortex splitting, which divides composite vortices and creates fractional ones. The interaction between vortices, attractive for different bands and repulsive for the same band, which is controlled by the electric current density flowing through the system, leads to an ordered alternating arrangement of the vortices. This arrangement creates nonequilibrium interband phase textures or domains with different signs of the Josephson energy of the interaction between the band condensates. Such phase textures have a significant effect on the dissipation caused by the vortex motion. In particular, in the phase-texture regime the onset of the dissipation is shifted to higher current densities.

Baumans X.D., Zharinov V.S., Raymenants E., Blanco Alvarez S., Scheerder J.E., Brisbois J., Massarotti D., Caruso R., Tafuri F., Janssens E., Moshchalkov V.V., Van de Vondel J., Silhanek A.V.

The main dissipation mechanism in superconducting nanowires arises from phase slips. Thus far, most of the studies focus on long nanowires where coexisting events appear randomly along the nanowire. In the present work we investigate highly confined phase slips at the contact point of two superconducting leads. Profiting from the high current crowding at this spot, we are able to shrink in-situ the nanoconstriction. This procedure allows us to investigate, in the very same sample, thermally activated phase slips and the probability density function of the switching current Isw needed to trigger an avalanche of events. Furthermore, for an applied current larger than Isw, we unveil the existence of two distinct thermal regimes. One corresponding to efficient heat removal where the constriction and bath temperatures remain close to each other, and another one in which the constriction temperature can be substantially larger than the bath temperature leading to the formation of a hot spot. Considering that the switching current distribution depends on the exact thermal properties of the sample, the identification of different thermal regimes is of utmost importance for properly interpreting the dissipation mechanisms in narrow point contacts.

Kimmel G., Glatz A., Aranson I.S.

Superconducting vortices and phase slips are primary mechanisms of dissipation in superconducting, superfluid, and cold atom systems. While the dynamics of vortices is fairly well described, phase slips occurring in quasi-one dimensional superconducting wires still elude understanding. The main reason is that phase slips are strongly non-linear time-dependent phenomena that cannot be cast in terms of small perturbations of the superconducting state. Here we study phase slips occurring in superconducting weak links. Thanks to partial suppression of superconductivity in weak links, we employ a weakly nonlinear approximation for dynamic phase slips. This approximation is not valid for homogeneous superconducting wires and slabs. Using the numerical solution of the time-dependent Ginzburg-Landau equation and bifurcation analysis of stationary solutions, we show that the onset of phase slips occurs via an infinite period bifurcation, which is manifested in a specific voltage-current dependence. Our analytical results are in good agreement with simulations.

Abdulrazzaq B.I., Abdul Halin I., Kawahito S., Sidek R.M., Shafie S., Yunus N.A.

A review on CMOS delay lines with a focus on the most frequently used techniques for high-resolution delay step is presented. The primary types, specifications, delay circuits, and operating principles are presented. The delay circuits reported in this paper are used for delaying digital inputs and clock signals. The most common analog and digitally-controlled delay elements topologies are presented, focusing on the main delay-tuning strategies. IC variables, namely, process, supply voltage, temperature, and noise sources that affect delay resolution through timing jitter are discussed. The design specifications of these delay elements are also discussed and compared for the common delay line circuits. As a result, the main findings of this paper are highlighting and discussing the followings: the most efficient high-resolution delay line techniques, the trade-off challenge found between CMOS delay lines designed using either analog or digitally-controlled delay elements, the trade-off challenge between delay resolution and delay range and the proposed solutions for this challenge, and how CMOS technology scaling can affect the performance of CMOS delay lines. Moreover, the current trends and efforts used in order to generate output delayed signal with low jitter in the sub-picosecond range are presented.

Buh J., Kabanov V., Baranov V., Mrzel A., Kovič A., Mihailovic D.

The superconducting state in one-dimensional nanosystems is very delicate. While fluctuations of the phase of the superconducting wave function lead to the spontaneous decay of persistent supercurrents in thin superconducting wires and nanocircuits, discrete phase-slip fluctuations can also lead to more exotic phenomena, such as the appearance of metastable superconducting states in current-bearing wires. Here we show that switching between different metastable superconducting states in δ-MoN nanowires can be very effectively manipulated by introducing small amplitude electrical noise. Furthermore, we show that deterministic switching between metastable superconducting states with different numbers of phase-slip centres can be achieved in both directions with small electrical current pulse perturbations of appropriate polarity. The observed current-controlled bi-stability is in remarkable agreement with theoretically predicted trajectories of the system switching between different limit cycle solutions of a model one-dimensional superconductor. Fluctuations of the phase of the superconducting wave function in one-dimensional nanosystems can lead to the appearance of metastable superconducting states. Here, the authors show that it is possible to manipulate the switching between such states by means of a small electrical noise in δ-MoN nanowires.

Tanaka Y., Hase I., Yanagisawa T., Kato G., Nishio T., Arisawa S.

There is a current-induced massless mode of an interband phase difference in two-band superconductors. For a thin wire, the externally applied current always invokes a finite interband phase difference when the end of the wire is terminated by a natural boundary condition, i.e., where the total current is specified but the other parameters are left as free and a finite interband phase difference is allowed. This condition can be realized by the normal state region formed by the shrinking of a cross section of the wire where the critical current density is lower than that of the other region of the wire. The interband interaction in the wire cannot completely prevent the emergence of the interband phase difference, though it reduces it somewhat. Instead, boundary conditions determine the presence of the interband phase difference. By reverting the normal state into the superconducting state at the shrunken region by decreasing the current, we may trap a rotation of integral multiples of 2π radians of the interband phase difference in the wire. After switching off the current, this rotation of integral multiples of 2π radians, which continuously spreads over the whole wire, is separated into several interband phase difference solitons (i-solitons), where one i-soliton locally generates a 2π interband phase difference.