We re-analyze the problem of thermally activated phase slips (TAPS) which can dominate the behavior of sufficiently thin superconducting wires at temperatures close to $T_C$. With the aid of an effective action approach we evaluate the TAPS rate which turns out to exceed the rate found by D.E. McCumber and B.I. Halperin, Phys. Rev. B {\bf 1}, 1054 (1970) within the TDGL analysis by the factor $\sim (1-T/T_C)^{-1} \gg 1$. Additional differences in the results of these two approaches arise at bias currents close to the Ginzburg-Landau critical current where the TAPS rate becomes bigger. We also derive a simple formula for the voltage noise across the superconducting wire in terms of the TAPS rate. Our results can be verified in modern experiments with superconducting nanowires.
We have experimentally compared the critical current, dark count rate and photo-response of 100nm wide superconducting nanowires with different bend designs. Enhanced critical current for nanowires with optimally rounded bends, and thus with no current crowding, are observed. Furthermore, we find that the optimally designed bend significantly reduces the dark counts without compromising the photo-response of the device. The results can lead to major improvements in superconducting nanowire single photon detectors.
We present the preparation and measurements of nanowires of single-crystal NbSe$_2$. These nanowires were prepared on ultrathin ($\lesssim10\text{ nm}$) flakes of NbSe$_2$ mechanically exfoliated from a bulk single crystal using a process combining electron beam lithography and reactive plasma etching. The electrical contacts to the nanowires were prepared using Ti/Au. Our technique, which overcomes several limitations of methods developed previously for fabricating superconducting nanowires, also allows for the preparation of complex superconducting nanostructures with a desired geometry. Cur…
We report on magnetoresistance oscillations in superconducting NbNx nanowires synthesized through ammonia gas annealing of NbSe3 precursor nanostructures. Even though the transverse dimensions of the nanowires are much larger than the superconducting coherence length, the voltage-current characteristics of these nanowires at low temperatures are reminiscent of one-dimensional superconductors where quantum phase slips are associated with the origin of dissipation. We show that both the magnetoresistance oscillations and voltage-current characteristics observed in this work result from the granu…
A superconducting thin film with uniform properties is the key to realize nanowire superconducting single-photon detectors (SSPDs) with high performance and high yield. To investigate the uniformity of NbN films, we introduce and characterize simple detectors consisting of short nanowires with length ranging from 100nm to 15μm. Our nanowires, contrary to meander SSPDs, allow probing the homogeneity of NbN at the nanoscale. Experimental results, endorsed by a microscopic model, show the strongly inhomogeneous nature of NbN films on the sub-100nm scale.
The emergence of superconductivity-induced phase-controlled forces in the (0.01-0.1) nN range, and of magnetization oscillations, in nanowire junctions, is discussed. A giant magnetic response to applied weak magnetic fields, is predicted in the ballistic Josephson junction formed by a superconducting tip and a surface, bridged by a normal metal nanowire where Andreev states form.
Superconducting nanowire single-photon detectors (SNSPDs) have an absolute advantage over other types of single photon detectors except the low operating temperature. Therefore, many efforts have been devoted to find high-temperature superconducting materials that are suitable for preparing SNSPDs. Copper-based and MgB2 ultra-thin superconducting nanowires have been already reported. However, the transport properties of iron-based ultra-thin superconducting nanowires have not been studied. In this work, a 10 nm thick 200 nm wide 30 μm long high quality superconducting nanowire was fabricated f…
We have fabricated disordered superconducting nanowires of molybdenium silicide. A molybdenium nanowire is first deposited on top of silicon, and the alloy is formed by rapid thermal annealing. The method allows tuning of the crystal growth to optimise, e.g., the resistivity of the alloy for potential applications in quantum phase slip devices and superconducting nanowire single-photon detectors. The wires have effective diameters from 42 to 79 nm, enabling the observation of crossover from conventional superconductivity to regimes affected by thermal and quantum fluctuations. In the smallest …
Magnetoresistance oscillations were observed on networks of superconducting ultrathin Nb nanowires presenting evidences of either thermal or quantum activated phase slips. The magnetic transport data, discussed in the framework of different scenarios, reveal that the system behaves coherently in the temperature range where the contribution of the fluctuations is important.
We study optimization of superconducting properties of inhomogeneous nanowires. The main goal of this research is to find an optimized geometry that allows one to maximize the desired property of superconductors, such as the maximum value of local superconducting gap or total condensation energy. We consider axially symmetric design of multi-layered nanowires with possibility to adjust and change the layers thickness. We use numerical solution of the Bogoliubov-de Gennes equations to obtain the local superconducting gap for different arrangements of the inhomogeneous structures. The value of t…
Superconducting nanowires undergoing quantum phase-slips have potential for impact in electronic devices, with a high-accuracy quantum current standard among a possible toolbox of novel components. A key element of developing such technologies is to understand the requirements for, and control the production of, superconducting nanowires that undergo coherent quantum phase-slips. We present three fabrication technologies, based on using electron-beam lithography or neon focussed ion-beam lithography, for defining narrow superconducting nanowires, and have used these to create nanowires in niob…
We present the results from an experimental study of the magneto-transport of superconducting wires of amorphous Indium-Oxide, having widths in the range 40 - 120 nm. We find that, below the superconducting transition temperature, the wires exhibit clear, reproducible, oscillations in their resistance as a function of magnetic field. The oscillations are reminiscent of those which underlie the operation of a superconducting quantum interference device.
Robust porous silicon substrates were employed for generating interconnected networks of superconducting ultrathin Nb nanowires. Scanning electron microscopy analysis was performed to investigate the morphology of the samples, which constitute of polycrystalline single wires with grain size of about 10 nm. The samples exhibit nonzero resistance over a broad temperature range below the critical temperature, fingerprint of phase slippage processes. The transport data are satisfactory reproduced by models describing both thermal and quantum fluctuations of the superconducting order parameter in t…
We derived the I-V characteristics of short nanowire in the circuit with and without resistive and inductive shunt. For that we used numerical calculations in the framework of time-dependent Ginzburg-Landau equations with different relaxation times for the amplitude and phase dynamics. We also derived dependence of the I-V characteristics on flux in superconducting quantum interference device (SQUID) made of such two weak links.
We have fabricated 5 nm ultra-thin NbN nanowires that form a dense and regular array in the linear channels of mesoporous SBA-15 silica substrates. Bulk NbN is a well-known classical superconductor with Tc of 16 K. We show that, by being incorporated into this nanostructure, the composite material exhibits typical quasi-one-dimensional characteristics. We compare the superconducting properties with those of superconducting Pb nanowires of same dimensionality in identical configuration within the linear SBA-15 pores. While Pb nanowire arrays show a pronounced crossover from 1D superconductivity…
Nanoimprint lithography (NIL) is an attractive nonconventional lithographic technique in the fabrication of superconducting nanowires for superconducting nanowire single-photon detectors (SNSPDs) with large effective detection areas or multi-element devices consisting of hundreds of SNSPDs, due to its low cost and high throughput. In this work, NIL was used to pattern superconducting nanowires with meander-type structures based on ultra-thin (~4 nm) Nb films deposited by DC-magnetron sputtering at room temperature. A combination of thermal-NIL and UV-NIL was exploited to transfer the meander p…
Controlling thermal transport is important for a range of devices and technologies, from phase change memories to next-generation electronics. This is especially true in nano-scale devices where thermal transport is altered by the influence of surfaces and changes in dimensionality. In superconducting nanowire single-photon detectors, the thermal boundary conductance (TBC) between the nanowire and the substrate it is fabricated on influences most of the performance metrics that make these detectors attractive for applications. This includes the maximum count rate, latency, jitter, and quantum …
We present the characteristics of superconducting nanowire single photon detectors (SNSPDs) fabricated from amorphous Mo0.75Ge0.25 thin-films. Fabricated devices show a saturation of the internal detection efficiency at temperatures below 1 K, with system dark count rates below 500 counts per second. Operation in a Gifford-McMahon (GM) cryocooler at 2.5 K is possible with system detection efficiencies (SDE) exceeding 20% for SNSPDs which have not been optimized for high detection efficiency.
Statistical studies on the performance of different superconducting nanowire single-photon detectors (SNSPDs) on one chip suggested that random constrictions existed in the nanowire that were barely registered by scanning electron microscopy. With the aid of advanced e-beam lithography, artificial geometric constrictions were fabricated on SNSPDs as well as single nanowires. In this way, we studied the influence of artificial constrictions on SNSPDs in a straight forward manner. By introducing artificial constrictions with different wire widths in single nanowires, we concluded that the dark c…
Quantum phase slip (QPS) is the particular manifestation of quantum fluctuations of the order parameter of a current-biased quasi-1D superconductor. The QPS event(s) can be considered a dynamic equivalent of tunneling through conventional Josephson junction containing static in space and time weak link(s). At low temperatures T<<Tc the QPS effect leads to finite resistivity of narrow superconducting channels and suppresses persistent currents in tiny nanorings. Here we demonstrate that the quantum tunneling of phase may result in Coulomb blockade: superconducting nanowire, imbedded in high-Ohm…
The voltage-carrying state of superconducting NbTiN nanowires, used for single-photon detectors, is analyzed. Upon lowering the current, the wire returns to the superconducting state in a steplike pattern, which differs from sample to sample. Elimination of geometrical inhomogeneities, such as sharp corners, does not remove these steplike features. They appear to be intrinsic to the material. Since the material is strongly disordered, electronic inhomogeneities are considered as a possible cause. A thermal model, taking into account random variations of the electronic properties along the wire…
An external magnetic field is needed to drive a nanowire in proximity to an s-wave superconductor into a topological regime which supports Majorana end states. However, a magnetic field generally suppresses the proximity superconducting gap induced on the nanowire. In recent experiments using InSb nanowires coupled to Al, the induced proximity gap vanishes at magnetic fields B~1T. This results in a small superconducting gap on the wire and a narrow topological regime which is proportional to the strength of the magnetic field. In this work, we show that by placing nanowires in proximity to rec…
Many superconducting technologies such as rapid single flux quantum computing (RSFQ) and superconducting quantum interference devices (SQUIDs) rely on the modulation of nonlinear dynamics in Josephson junctions for functionality. More recently, however, superconducting devices have been developed based on the switching and thermal heating of nanowires for use in fields such as single photon detection and digital logic. In this paper, we use resistive shunting to control the nonlinear heating of a superconducting nanowire and compare the resulting dynamics to those observed in Josephson junctio…
We report on the transport properties of an array of N about 30 interconnected Nb nanowires, grown by sputtering on robust porous Si substrates. The analyzed system exhibits a broad resistive transition in zero magnetic field, H, and highly nonlinear V(I) characteristics as a function of H which can be both consistently described by quantum tunneling of phase slips.
Microwave Fabry-Perot resonators containing nonlinear mesoscopic elements (such as superconducting nanowires) can be used to explore many-body circuit QED. Here, we report on observations of a superconductor-normal pulsing regime in microwave (GHz) coplanar waveguide resonators consisting of superconducting MoGe films interrupted by a gap that is bridged by one or more suspended superconducting nanowires. This regime, which involve MHz-frequency oscillations in the amplitude of the supercurrent in the resonator, are achieved when the steady-state amplitude of the current in the driven resonato…
We estimate the depairing current of superconducting nanowire single photon detectors (SNSPDs) by studying the dependence of the nanowires kinetic inductance on their bias current. The kinetic inductance is determined by measuring the resonance frequency of resonator style nanowire coplanar waveguides both in transmission and reflection configurations. Bias current dependent shifts in the measured resonant frequency correspond to the change in the kinetic inductance, which can be compared with theoretical predictions. We demonstrate that the fast relaxation model described in the literature ac…
We use external magnetic field to probe the detection mechanism of superconducting nanowire single photon detector. We argue that the hot belt model (which assumes partial suppression of the superconducting order parameter $Δ$ across the whole width of the superconducting nanowire after absorption of the single photon) does not explain observed weak field dependence of the photon count rate (PCR) for photons with $λ$=450 nm and noticeable {\it decrease} of PCR (with increasing the magnetic field) in some range of the currents for photons with wavelengths $λ$ =450-1200 nm. Found experimental re…
Anderson's theorem states that non-magnetic impurities do not change the bulk properties of conventional superconductors. However, as the dimensionality is reduced, the effect of impurities becomes more significant. Here we investigate superconducting nanowires with diameter less than the superconducting coherence length by using a microscopic description based on the Bogoliubov-de Gennes method. We find that: 1) impurities strongly affect the superconducting properties, 2) the effect is impurity position-dependent, and 3) it exhibits opposite behavior for resonant and off-resonant wire widths…
We observed a novel voltage peak in the proximity effect induced superconducting gold (Au) nanowire while cooling the sample through the superconducting transition temperature. The voltage peak turned into dip in the warming process. The voltage peak (or dip) was found to be closely related to the emergence (vanishing) of the proximity induced superconductivity in the Au nanowire. The amplitude of the voltage signal depends on the temperature scanning rate and it cannot be detected when the temperature is changed slower than 0.03 K/min. This transient feature suggests the non-equilibrium prope…
Nanowires of two-dimensional (2D) crystals of type-II superconductor NbSe$_2$ prepared by electron-beam lithography were studied, focusing on the effect of the motion of Abrikosov vortices. We present magnetoresistance measurements on these nanowires and show features related to vortex crossing, trapping, and pinning. The vortex crossing rate was found to vary non-monotonically with the applied field, which results in non-monotonic magnetoresistance variations in agreement with theoretical calculations in the London approximation. Above the lower critical field, $H_{c1}$, the crossing rate is …
We investigate the detection efficiency of a spiral layout of a Superconducting Nanowire Single-Photon Detector (SNSPD). The design is less susceptible to the critical current reduction in sharp turns of the nanowire than the conventional meander design. Detector samples with different nanowire width from 300 to 100 nm are patterned from a 4 nm thick NbN film deposited on sapphire substrates. The critical current IC at 4.2 K for spiral, meander, and simple bridge structures is measured and compared. On the 100 nm wide samples, the detection efficiency is measured in the wavelength range 400-17…
Superconducting nanowires can be synthesised in high-throughput chemical routes and hold great promise as a low-dissipative material for superconducting devices. The applicability of superconducting nanowires, however, has been limited due to the lack of an adequate method to fit the nanowires into given electronic circuits. One of the biggest obstacles is to connect metal terminals to superconducting nanowires in order to establish electric contacts. One attractive method to surmount this difficulty is to synthesise superconducting nanowires directly upon metal terminals such that the nanowir…
We show in this paper that it is possible to induce superconducting vortices in a gold nanowire connected to superconducting electrodes. The gold nanowire acquires superconductivity by the proximity effect. The differential magnetoresistance of the nanowire beyond a critical magnetic field shows uniform oscillations with increasing field with a period of \phi0/(2\pir^2) (\phi0 = h/2e is the superconducting flux quantum, r = 35 nm is the radius of the nanowire). We demonstrate that these periodic oscillations are the signatures of the sequential generation and moving of vortices across the gold…
Thorough spectral study of the intrinsic single-photon detection efficiency in superconducting TaN and NbN nanowires with different widths shows that the experimental cut-off in the efficiency at near-infrared wavelengths is most likely caused by the local deficiency of Cooper pairs available for current transport. For both materials the reciprocal cut-off wavelength scales with the wire width whereas the scaling factor quantitatively agrees with the hot-spot detection models. Comparison of the experimental data with vortex-assisted detection scenarios shows that these models predict a stronge…
Reduction of the critical current in narrow superconducting NbN lines with sharp and rounded bends with respect to the critical current in straight lines was studied at different temperatures. We compare our experimental results with the reduction expected in the framework of the London model and the Ginsburg-Landau model. We have experimentally found that the reduction is significantly less than either model predicts. We also show that in our NbN lines the bends mostly contribute to the reduction of the critical current at temperatures well below the superconducting transition temperature.
Nanostructuring of superconducting materials to form dense arrays of thin parallel nanowires with significantly large transverse Josephson coupling has proven to be an effective way to increase the upper critical field of superconducting elements by as much as two orders of magnitude as compared to the corresponding bulk materials and, in addition, may cause considerable enhancements in their critical temperatures. Such materials have been realized in the linear pores of mesoporous substrates or exist intrinsically in the form of various quasi-1D crystalline materials. The transverse coupling …
We study experimentally the low temperature resistance of superconducting nanowires connected to normal metal reservoirs. We find that a substantial fraction of the nanowires is resistive, down to the lowest temperature measured, indicative of an intrinsic boundary resistance due to the Andreev-conversion of normal current to supercurrent. The results are successfully analyzed in terms of the kinetic equations for diffusive superconductors.
We report on several low temperature experiments supporting the presence of Majorana fermions in superconducting lead nanowires fabricated with a scanning tunneling microscope. These nanowires are the connecting bridges between the STM tip and the sample resulting from indentation processes. We show here that by a controlled tuning of the geometry of the nanowire region, in which superconductivity is confined by applied magnetic fields, the conductance curves obtained in these situations are indicative of topological superconductivity and Majorana fermions. The most prominent feature of this b…
We have used a neon focused-ion-beam to fabricate both nanoscale Nb Dayem bridges and NbN phase-slip nanowires located at the short-circuited end of quarter-wavelength coplanar waveguide resonators. The Dayem bridge devices show flux-tunability and intrinsic quality factor exceeding 10,000 at 300 mK up to local fields of at least 60 mT. The NbN nanowires show signatures of incoherent quantum tunnelling of flux at 300 mK.
Quantum fluctuations in quasi-one-dimensional superconducting channels leading to spontaneous changes of the phase of the order parameter by $2π$, alternatively called quantum phase slips (QPS), manifest themselves as the finite resistance well below the critical temperature of thin superconducting nanowires and the suppression of persistent currents in tiny superconducting nanorings. Here we report the experimental evidence that in a current-biased superconducting nanowire the same QPS process is responsible for the insulating state -- the Coulomb blockade. When exposed to RF radiation, the i…
We report the fabrication of strongly coupled nanohybrid superconducting junctions using PbS semiconductor nanowires and Pb0.5In0.5 superconducting electrodes. The maximum supercurrent in the junction reaches up to ~15 μA at 0.3 K, which is the highest value ever observed in semiconductor-nanowire-based superconducting junctions. The observation of microwave-induced constant voltage steps confirms the existence of genuine Josephson coupling through the nanowire. Monotonic suppression of the critical current under an external magnetic field is also in good agreement with the narrow junction mod…
Quantum phase slippage (QPS) in a superconducting nanowire is a new candidate for developing a quantum bit. It has also been theoretically predicted that the occurrence of QPS significantly changes the current-phase relationship (CPR) of the wire due to the tunneling between topologically different metastable states. We present studies on the microwave response of the superconducting nanowires to reveal their CPRs. First, we demonstrate a simple nanowire fabrication technique, based on commercially available adhesive tapes, which allows making thin superconducting wire from different metals. W…
We report microwave transmission measurements of superconducting Fabry-Perot resonators (SFPR), having a superconducting nanowire placed at a supercurrent antinode. As the plasma oscillation is excited, the supercurrent is forced to flow through the nanowire. The microwave transmission of the resonator-nanowire device shows a nonlinear resonance behavior, significantly dependent on the amplitude of the supercurrent oscillation. We show that such amplitude-dependent response is due to the nonlinearity of the current-phase relationship (CPR) of the nanowire. The results are explained within a no…
We present low-temperature measurements of low-loss superconducting nanowire-embedded resonators in the low-power limit relevant for quantum circuits. The superconducting resonators are embedded with superconducting nanowires with widths down to 20nm using a neon focused ion beam. In the low-power limit, we demonstrate an internal quality factor up to 3.9x10^5 at 300mK [implying a two-level-system-limited quality factor up to 2x10^5 at 10 mK], not only significantly higher than in similar devices but also matching the state of the art of conventional Josephson-junction-embedded resonators. We …
We report on simulation results that shows optimum photon absorption by superconducting nanowires can happen at a fill-factor that is much less than 100%. We also present experimental results on high performance of our superconducting nanowire single photon detectors realized using NbTiN on oxidized silicon.
We investigate the properties of a weak link between two Rashba-based superconducting nanowires with geometric misalignment. By applying an external magnetic field the system can be driven into a topological non-trivial regime. We demonstrate that the Josephson current can be modulated in amplitude and sign through the variation of the applied field and, remarkably, via the angle controlling the spin-orbit locking mismatch at the interface of the nanowires. The proposed setup with misaligned coplanar nanowires provides the building block configuration for the manipulation of coherent transport…
Superconducting devices are prone to reduced performance caused by impurities and defects along the edges of their wires, which can lead to local current crowding. In this study, we explored the use of helium ion irradiation to modify the lattice structure of the superconducting material to change its intrinsic properties. The process will allow us to directly pattern devices and potentially improve the quality of the nanowires. To achieve this, we used the ion beam from a scanning helium ion microscope (HIM) to localize damage on a superconducting material to create a nanowire. Two experiment…
The anti-proximity effect, where the superconductivity in superconducting nanowires is suppressed or weakened when contacted by bulk superconducting electrodes, first revealed in arrays of Zn nanowires by tuning the electrodes from the superconducting to the normal state by means of an external magnetic field, has been confirmed in single crystal Aluminum nanowires. The critical current at zero magnetic field of an individual aluminum nanowire contacted by superconducting electrodes was found to be significantly smaller than that with normal electrodes showing that the effect is not a conseque…
We study the rate of quantum phase slips in an ultranarrow superconducting nanowire exposed to weak electromagnetic radiations. The superconductor is in the dirty limit close to the superconducting-insulating transition, where fluxoids move in strong dissipation. We use a semiclassical approach and show that external radiation stimulates a significant enhancement in the probability of quantum phase slips. This can help to outline a new type of detector for microwave to submillimetre radiations based on stimulated quantum phase slip phenomenon.
We report on the fabrication and electrical transport properties of superconducting junctions made of β-Ag$_{2}$Se topological insulator (TI) nanowires in contact with Al superconducting electrodes. The temperature dependence of the critical current indicates that the superconducting junction belongs to a short and diffusive junction regime. As a characteristic feature of the narrow junction, the critical current decreases monotonously with increasing magnetic field. The stochastic distribution of the switching current exhibits the macroscopic quantum tunneling behavior, which is robust up to …
We expose superconducting nanowires to microwave radiation in order to study phase lock-in effects in quasi one dimensional superconductors. For sufficiently high microwave powers a resistive branch with Shapiro steps appears in the voltage-current characteristics. At frequencies in the range of 0.9-4 GHz these steps are of integer order only. At higher frequencies steps of 1/2, 1/3, 1/4 and even 1/6 order appear. We numerically model this behavior using a multi-valued current-phase relationship (CPR) for nanowires.
Properties of superconducting nanowires set the performance level for Superconducting Nanowire Single Photon Detectors (SNSPD). Reset time in commonly employed large area SNSPDs,5-10ns,is known to be limited by the nanowires kinetic inductance.On the other hand, reduction of the kinetic inductance in small area (waveguide integrated) SNSPDs prevents biasing them close to the critical current due to latching into a permanent resistive state.In order to reduce the reset time in SNSPDs, superconducting nanowires with both low kinetic inductance and fast electron energy relaxation are required. In…
Recently transport measurements have been carried out in resistively shunted long superconducting nanowires [M. W. Brenner {\it et. al.}, Phys. Rev. B {\bf{85}}, 224507 (2012)]. The measured voltage-current ($V$-$I$) characteristics was explained by the appearance of the phase slip centers in the shunted wire, and the whole wire was modeled as a single Josephson junction. The kinetic inductance of the long nanowires used in experiments is generally large. Here we argue that the shunted superconducting nanowire acts as a Josephson junction in series with an inductor. The inductance depends on t…
We demonstrate a 16-pixel array of radio-frequency superconducting nanowire single-photon detectors with an integrated and scalable frequency-division multiplexing architecture, reducing the required bias and readout lines to a single microwave feed line. The electrical behavior of the photon-sensitive nanowires, embedded in a resonant circuit, as well as the optical performance and timing jitter of the single detectors is discussed. Besides the single pixel measurements we also demonstrate the operation of the 16-pixel array with a temporal, spatial and photon-number resolution.
In a recent paper Tettamanzi et al (2009 Nanotechnology \bf{20} 465302) describe the fabrication of superconducting Nb nanowires using a focused ion beam. They interpret their conductivity data in the framework of thermal and quantum phase slips below $T_c$. In the following we will argue that their analysis is inappropriate and incomplete, leading to contradictory results. Instead, we propose an interpretation of the data within a SN proximity model.
We study the non linear response of current-transport in a superconducting diffusive nanowire between normal reservoirs. We demonstrate theoretically and experimentally the existence of two different superconducting states appearing when the wire is driven out of equilibrium by an applied bias, called global and bimodal superconducting state. The different states are identified by using two probe measurements of the wire, and measurements of the local density of states with tunneling probes. The analysis is performed within the framework of the quasiclassical kinetic equations for diffusive su…
The functionality of a nanowire integrated into a superconducting transmission line acting as a single pole single throw switch is demonstrated. The switch has an instantaneous bandwidth from 2 to 8 GHz with more than 10 dB of isolation between the open and closed states. The switch consumes no power in the closed state and $\approx 15~\rm{nW}$ in the open state. The rise and fall response time between open and closed states is approximately $370~\rm{ps}$.
The effect of quantum fluctuations on the current-voltage characteristics of Josephson junctions and superconducting nanowires is studied in the underdamped limit. Quantum fluctuations induce transitions between a Coulomb--blockade and a supercurrent branch, and can significantly modify the shape of current-voltage characteristics in the case of a highly resistive environment. Owing to the phase-charge duality, our results can be directly extended to the opposite overdamped limit.
