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The recently proposed Josephson traveling-wave parametric amplifier (JTWPA) based on a ladder transmission line consisting of radio-frequency superconducting quantum interference devices and exploiting three-wave mixing has great potential in achieving both a gain of 20 dB and a flat bandwidth of at least 4 GHz. To realize this concept in practical amplifiers, we model the advanced JTWPA circuit with periodic modulation of the circuit parameters (engineered dispersion loadings), which allow the basic mixing process, i.e., ω s = ω p − ω i , where ω s , ω p , and ω i are the signal, the pump, and the idler frequencies, respectively, and efficiently suppress propagation of unwanted higher tones, including ω 2 p = 2 ω p , ω p + s = ω p + ω s , ω p + i = ω p + ω i , etc. The engineered dispersion loadings allow achieving a sufficiently wide 3 dB-bandwidth from 3 to 9 GHz combined with a reasonably small ripple (± 2 dB) in the gain-vs-frequency dependence. [ABSTRACT FROM AUTHOR]

Research describing the supercurrent-phase relation of niobium-aluminum based Josephson junctions is presented. Impedance measurements of superconductor-insulator-normal conductor-insulator-superconductor elements are analysed.

A novel method for preparing deep submicron Nb/AlOx/Nb tunnel junctions is presented. The proposed method employs reactive ion etching using e-beam lithography to structure the Nb/AlOx/Nb sandwich and the Nb wiring layer and spin-on glass planarization to create insulation between the base electrode and the wiring layer. The fabricated deep submicron Nb/AlOx/Nb tunnel junctions were observed to exhibit typical superconductive and normal tunneling properties.

We develop the concept of quasi-phasematching (QPM) by implementing it in the recently proposed Josephson traveling-wave parametric amplifier (JTWPA) with three-wave mixing (3WM). The amplifier is based on a ladder transmission line consisting of flux-biased radio frequency superconducting quantum interference devices (SQUIDs) whose nonlinearity is of χ (2) -type. QPM is achieved in the 3WM process, ω p = ω s + ω i (where ωp, ωs, and ωi are the pump, signal, and idler frequencies, respectively) due to designing the JTWPA to include periodically inverted groups of these SQUIDs that reverse the sign of the nonlinearity. Modeling shows that the JTWPA bandwidth is relatively large (∼ 0.4 ω p ) and flat, while unwanted modes, including ω 2 p = 2 ω p , ω + = ω p + ω s , and ω − = 2 ω p − ω s , are strongly suppressed with the help of engineered dispersion. [ABSTRACT FROM AUTHOR]

Josephson junction transistors and 50-junction arrays with linear junction dimensions from 200 nm down to 70 nm were fabricated from standard Nb/AlOx/Nb trilayers. The fabrication process includes electron beam lithography, dry etching, anodization, and planarization by chemical-mechanical polishing. The samples were characterized at temperatures down to 25 mK. In general, all junctions are of high quality and their I-U characteristics show low leakage currents and high superconducting energy gap values of Δ≈1.35 meV. The characteristics of the transistors and arrays exhibit some features in the subgap area, associated with tunneling of Cooper pairs, quasiparticles, and their combinations due to the redistribution of the bias voltage between the junctions. Total island capacitances of the transistor samples ranged from 1.5 fF to 4 fF, depending on the junction sizes. Devices made of junctions with linear dimensions below 100 nm×100 nm demonstrate a remarkable single-electron behavior in both superconducting and normal state. We also investigated the area dependence of the junction capacitances for transistor and array samples. [ABSTRACT FROM AUTHOR]

We investigate low-temperature and low-voltage-bias charge transport in a superconducting Al single electron transistor in a dissipating environment, realized as on-chip high-ohmic Cr microstrips. In samples with relatively large charging energy Ec>EJ, where EJ is the Josephson coupling energy, two transport mechanisms were found to be dominant, both based on discrete tunneling of individual Cooper pairs: Depending on the gate voltage Vg, either sequential tunneling of pairs via the transistor island [in the conducting state of the transistor around the points Qg≡CgVg=e mod (2e), where Cg is the gate capacitance] or their cotunneling through the transistor (for Qg away of these points) was found to prevail in the net current. As the conducting state of our transistors had been found to be subject to quasiparticle poisoning, high-frequency gate cycling (at f∼1 MHz) was applied to study the sequential tunneling mechanism. A simple model based on the master equation was found to be in a good agreement with the experimental data. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Develops a quantum-statistical theory of microwave and millimeter-wave detection using superconducting tunnel junctions. Details of the problem of noise characterization in the quantum sensitivity range; Analysis of noise performance of various modes of the detection; Types of junction nonlinearity that can be used for different modes of microwave detection; Role of power dissipation in real microwave detectors; Steps in analyzing linear circuit.

Using a Josephson junction interferometer (DC SQUID) as a microwave source for irradiating a single-electron trap, both devices fabricated on the same chip, we study the process of photonassisted tunneling as an effective mechanism of single photon detection. High sensitivity down to a very small oscillation amplitude vJ 10 nV ⪡ Eact ≲hfJ and down to low photon absorption rates Γph(1-50) Hz, as well as a clear threshold type of operation with an activation energy Eact∼400 μeV, is demonstrated for the trap with respect to the microwave photons of frequency fJ∼(100-200) GHz. Tunable generation is demonstrated with respect to the power and frequency of the microwave signal produced by the SQUID source biased within the subgap voltage range. A much weaker effect is observed at the higher junction voltages along the quasiparticle branch of the I-V curve; this response mostly appears due to the recombination phonons. [ABSTRACT FROM AUTHOR]

The present work addresses quantum interaction phenomena of microwave radiation with a single-electron tunneling system. For this study, an integrated circuit is implemented, combining on the same chip a Josephson junction (Al/AlOx/Al) oscillator and a single-electron transistor (SET) with the superconducting island (Al) and normal-conducting leads (AuPd). The transistor is demonstrated to operate as a very sensitive photon detector, sensing down to a few tens of photons per second in the microwave frequency range around ƒ ~ 100 GHz. On the other hand, the Josephson oscillator, realized as a two-junction SQUID and coupled to the detector via a coplanar transmission line (Al), is shown to provide a tunable source of microwave radiation: controllable variations in power or in frequency were accompanied by significant changes in the detector output, when applying magnetic flux or adjusting the voltage across the SQUID, respectively. It was also shown that the effect of substrate-mediated phonons, generated by our microwave source, on the detector output was negligibly small. [ABSTRACT FROM AUTHOR]

We investigate electric transport and noise properties of microstrip-type submicron direct current superconducting quantum interference devices (dc SQUIDs) based on Nb thin films and overdamped Josephson junctions with a HfTi barrier. The SQUIDs were designed for optimal spin sensitivity Sμ1/2 upon operation in intermediate magnetic fields B (tens of mT), applied perpendicular to the substrate plane. Our, so far, best SQUID can be continuously operated in fields up to B≈±50 mT with rms flux noise S[uppercase_phi_synonym],w1/2≤250 n[uppercase_phi_synonym]0/Hz1/2 in the white noise regime and spin sensitivity Sμ1/2≤29 μB/Hz1/2. Furthermore, we demonstrate operation in B = 0.5 T with high sensitivity in flux S[uppercase_phi_synonym],w1/2≈680 n[uppercase_phi_synonym]0/Hz1/2 and in electron spin Sμ1/2≈79 μB/Hz1/2. We discuss strategies to further improve the nanoSQUID performance. [ABSTRACT FROM AUTHOR]

We propose a transistorlike circuit including two serially connected segments of a narrow superconducting nanowire joint by a wider segment with a capacitively coupled gate in between. This circuit is made of amorphous NbSi film and embedded in a network of on-chip Cr microresistors ensuring a sufficiently high external electromagnetic impedance. Assuming a virtual regime of quantum phase slips (QPS) in two narrow segments of the wire, leading to quantum interference of voltages on these segments, this circuit is dual to the dc SQUID. Our samples demonstrated appreciable Coulomb blockade voltage (analog of critical current of the SQUIDs) and periodic modulation of this blockade by an electrostatic gate (analog of flux modulation in the SQUIDs). The model of this QPS transistor is discussed. [ABSTRACT FROM AUTHOR]

We propose a threshold detector with an operating principle based on a parametric period-doubling bifurcation in an externally pumped nonlinear resonance circuit. The ac-driven resonance circuit includes a dc-current-biased Josephson junction ensuring parametric frequency conversion (period-doubling bifurcation) due to its quadratic nonlinearity. A sharp onset of oscillations at the half-frequency of the drive allows for the detection of small variations of an effective inductance and, therefore, the readout of the quantum state of a coupled Josephson qubit. The bifurcation characteristics of this circuit are compared with those of the conventional Josephson bifurcation amplifier, and its possible advantages are discussed. [ABSTRACT FROM AUTHOR]

A portable high-voltage (HV) pulsed generator has been designed for rock fragmentation experiments. The generator can be used also for other technological applications. The installation consists of low voltage block, HV block, coaxial transmission line, fragmentation chamber, and control system block. Low voltage block of the generator, consisting of a primary capacitor bank (300 μF) and a thyristor switch, stores pulse energy and transfers it to the HV block. The primary capacitor bank stores energy of 600 J at the maximum charging voltage of 2 kV. HV block includes HV pulsed step up transformer, HV capacitive storage, and two electrode gas switch. The following technical parameters of the generator were achieved: output voltage up to 300 kV, voltage rise time of ∼50 ns, current amplitude of ∼6 kA with the 40 Ω active load, and ∼20 kA in a rock fragmentation regime (with discharge in a rock-water mixture). Typical operation regime is a burst of 1000 pulses with a frequency of 10 Hz. The operation process can be controlled within a wide range of parameters. The entire installation (generator, transmission line, treatment chamber, and measuring probes) is designed like a continuous Faraday's cage (complete shielding) to exclude external electromagnetic perturbations. [ABSTRACT FROM AUTHOR]

High operation speed and low energy consumption may allow the superconducting digital single-flux-quantum circuits to outperform traditional complementary metal–oxide–semiconductor logic. The remaining major obstacle towards high element densities on-chip is a relatively large cell size necessary to hold a magnetic flux quantum Φ0. Inserting a π-type Josephson junction in the cell is equivalent to applying flux Φ0/2 and thus makes it possible to solve this problem. Moreover, using π-junctions in superconducting qubits may help to protect them from noise. Here we demonstrate the operation of three superconducting circuits—two of them are classical and one quantum—that all utilize such π-phase shifters realized using superconductor/ferromagnet/superconductor sandwich technology. The classical circuits are based on single-flux-quantum cells, which are shown to be scalable and compatible with conventional niobium-based superconducting electronics. The quantum circuit is a π-biased phase qubit, for which we observe coherent Rabi oscillations. We find no degradation of the measured coherence time compared to that of a reference qubit without a π-junction. [ABSTRACT FROM AUTHOR]

Pulsed current generator was developed for experiments with current carrying pulsed plasma. Main parts of the generator are capacitor bank, low inductive current driving lines, and central load part. Generator consists of four identical sections, connected in parallel to one load. Capacitor bank is assembled from 24 capacitor blocks (100 kV, 80 nF), connected in parallel. It stores 9.6 kJ at 100 kV charging voltage. Each capacitor block incorporates a multigap spark switch, which is able to commute by six parallel channels. Switches operate in dry air at atmospheric pressure. The generator was tested with an inductive load and a liner load. At 17.5 nH inductive load and 100 kV of charging voltage it provides 650 kA of current amplitude with 390 ns rise time with 0.6 Ω damping resistors in discharge circuit of each capacitor block. The net generator inductance without a load was optimized to be as low as 15 nH, which results in extremely low impedance of the generator (∼0.08 Ω). It ensures effective energy coupling with a low impedance load such as Z pinch. The generator operates reliably without any adjustments in 70–100 kV range of charging voltage. Jitter in delay between output pulse and triggering pulse is less than 5 ns at 70–100 kV charging voltage. Operation and handling are very simple, because no oil or purified gases are required for the generator. The generator has dimensions 5.24×1.2×0.18 m3 and total weight about 1400 kg, thus manifesting itself as simple, robust, and cost effective apparatus. [ABSTRACT FROM AUTHOR]

High voltage, high current, and high Coulomb transfer closing switches are required for many high power pulsed systems. There are a few alternatives for closing switches, for example, ignitrons, vacuum switches, solid-state switches, high pressure gas switches (spark gaps), and some others. The most popular closing switches up to date are spark gaps due to relatively simple design, robustness, easily field maintenance, and repair. Main drawback of spark gaps is limited lifetime, which is related directly or indirectly to erosion of the electrodes. Multichannel switches and switches with moving arc have been proposed to prevent the electrodes erosion. This study investigates switches, where a spark channel is initiated in a three-electrode layout and then the spark accelerates due to electrodynamic force and moves along the extended electrodes. At a given current amplitude, the diameter of the extended electrodes allows to control the spark velocity and hence, the erosion of the electrodes providing the required lifetime. The first switch is designed for 24 kV charging voltage and ∼4 C total charge transfer. This spark gap was tested at 25 kA peak current in 40 000 shots in a single polarity discharge and in 20 000 shots in bipolar discharge. Second spark gap is designed for 24 kV charging voltage and ∼70 C total charge transfer. It was tested in 22 000 shots, at a current of 250 kA with a pulse length of 360 μs. In this paper, we present design of these spark gaps and trigger generator, describe the test bed, and present the results of the tests. [ABSTRACT FROM AUTHOR]

Quantized values of magnetic flux trapped in a superconducting loop enable a new type of passive phase shifting elements. These elements can be incorporated into digital Josephson circuits making their design compact. We have proven the functionality of such phase shifters fabricated in conventional Nb/Al trilayer technology. We report on the successful low speed operation of a Rapid Single Flux Quantum toggle flip-flop circuit with the integrated passive π-phase shifting element. [ABSTRACT FROM AUTHOR]

The GIT-32 current generator was developed for experiments with current carrying pulsed plasma. The main parts of the generator are capacitor bank, multichannel multigap spark switches, low inductive current driving lines, and central load part. The generator consists of four identical sections, connected in parallel to one load. The capacitor bank is assembled from 32 IEK-100-0.17 (0.17 μF, 40 nH, 100 kV) capacitors, connected in parallel. It stores ∼18 kJ at 80 kV charging voltage. Each two capacitors are commuted to a load by a multigap spark switch with eight parallel channels. Switches operate in ambient air at atmospheric pressure. The GIT-32 generator was tested with 10, 15, and 20 nH inductive loads. At 10 nH load and 80 kV of charging voltage it provides 1 MA of current amplitude and 490 ns rise time with 0.8 Ω damping resistors in discharge circuit of each capacitor and 1.34 MA/530 ns without resistors. The net generator inductance without a load was optimized to be as low as 12 nH, which results in extremely low self-impedance of the generator (∼0.05 Ω). It ensures effective energy coupling with low impedance loads like Z pinch. The generator operates reliably without any adjustments in 40–80 kV range of charging voltage. Maximum jitter (relative to a triggering pulse) at 40 kV charging voltage is about 7 ns and lower at higher charging voltages. Operation and handling are very simple, because no oil and no purified gases are required for the generator. The GIT-32 generator has dimensions of 3200×3200×400 mm3 and total weight of about 2500 kg, thus manifesting itself as a simple, robust, and cost effective apparatus. [ABSTRACT FROM AUTHOR]

We report here a design of the portable high current generator, which can be used for a row of experiments and applications, including, but not limited to, X pinch, plasma focus, vacuum spark, etc. The X generator consists of the capacitor bank, multigap spark switch, load chamber, and built-in high voltage triggering generator. The capacitor bank consists of 12 General Atomics 35404 type capacitors (20 nF, 25 nH, 0.2 Ω, 100 kV). It stores ∼0.8 kJ at 80 kV charging voltage. Each three capacitors are commuted to a load by the multigap spark switch, which is able to commute by eight parallel channels. Switches operate in ambient air at atmospheric pressure. At 76 kV charging voltage the generator provides ∼260 kA with 120 ns rise time and 5 nH inductive load and ∼220 kA with 145 ns rise time and 10 nH. Delay of output pulse relative to high voltage triggering pulse is ∼65 ns with 5 ns jitter. The dimensions of the generator are 1240×1240×225 mm3 and the weight is ∼250 kg, and only one high voltage power supply is required as additional equipment for the generator. The generator with a pumping system is placed on area about 0.5 m2. Operation and handling are very simple, because no oil nor purified gases are required for the generator. The X generator has been successfully employed for experiments on the Ni X pinch load. X-ray pulse duration (full width at half maximum above 1 keV) was about 5 ns. Radiation yield Wr>=500 mJ was observed in the 1.2–1.5 KeV range and Wr>=20 mJ in the 3–5 keV energy range, which is comparable to results, obtained on the nanosecond accelerators. Clearly resolved images of 6 μm wire indicate micron level size of hot spot. These results demonstrate possibility of this generator for application for x-ray backlighting. [ABSTRACT FROM AUTHOR]

Presents a study that exploited two complementary single electron tunneling devices for use in electrical current metrology. Set current source; Current steps for the R-pump with smaller junctions for different frequencies and series resistances; Summary and conclusion.

We consider the applicability of the established rf readout technique, which allows to obtain the supercurrent-phase relation of a Josephson element from impedance measurements in the phase-biased regime. In experiments on Nb-based single and double tunnel junctions, we demonstrate that this method holds even if the Josephson coupling energy is smaller than the thermal energy. Compared with conventional current-voltage measurements, we evaluate the rf technique to be favorable in particular for investigations of small supercurrents in low-capacitance Josephson elements. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]