1,720,991 research outputs found
Numerical analysis of Josephson junction arrays for multi-order quantum voltage steps
Full text linkThe dynamics of overdamped Josephson junctions under varying microwave-driving conditions have been studied through numerical simulations using the resistively-shunted junction model, with a focus on primary voltage metrology applications, where a significantly high number of series-connected junctions and stringent uniformity of their electrical parameters are required. The aim is to determine the optimal junction characteristics and external microwave (rf) parameters that maximize the width of quantum voltage levels (Shapiro steps) from order n = 0 to n > 1. Both the rf and dc power requirements, along with the junction parameter spread and power attenuation, are analyzed as key factors that need to be optimized for improved performance of the quantum device. This work aims to advance the development of next-generation programmable Josephson voltage standards with logic architectures that surpass the conventional binary and ternary codifications used in present quantum voltage arrays, while significantly reducing the overall number of junctions as well as the number of sub-arrays and bias lines. Existing technologies exploiting n = 0 and n=+/- 1 voltage steps are first discussed and analyzed to verify the validity of the simulation model. They are then further investigated to extend their usability with multi-order quantum steps for n up to 3. From the simulation results, it follows that present junction technologies may be employed with no modifications for the simultaneous operation of quantum steps up to n = 2, although optimal power efficiency would require a retrimming of the junction's electrical parameters. On the contrary, extending the highest step order to n = 3 strictly requires the junction's characteristic parameters to be properly adjusted to maintain sustainable power levels as well as acceptable quantum-locking ranges
Josephson devices for ac quantum voltage standard
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Using a Josephson junction as an effective on-chip temperature sensor
Full text linkTemperature sensing and control are essential in experiments running in cryocooled systems, as with the case of liquid helium-free superconducting devices. A Josephson junction as on-chip temperature sensor operated in ac provides the highest sensitivity and minimal power loading to the cryogenic environment, thanks to the noise rejection of lock-in detection. To demonstrate the advantages of on-chip sensing, we tested it with a Josephson voltage standard array in cryocooler and compared with the conventional case of a sensor on the cold surface of the refrigerator, showing that the power dissipated within the chip may further increment the device temperature up to some tenths of kelvin. An ac Josephson junction sensor is proven to be capable of directly stabilizing the temperature of the superconductive circuit from fluctuations of dissipated power during operation. Reliability issues related to flux trapping are discussed and solutions are proposed suited to different applications. Overall, on-chip control with ac Josephson temperature sensing has the advantage of avoiding the complexities in minimization of cryogenic thermal links, virtually reducing to zero the contact resistance and keeping the operating temperature of the superconductor constant, independently of instantaneous operating power
Non-Conventional PJVS Exploiting First and Second Steps to Reduce Junctions and Bias Lines
Full text linkQuantum digital-to-analog converters (DACs) based on programmable Josephson array [Programmable Josephson Voltage Standard (PJVS)] represent the most widely used quantum standard in ac voltage calibrations. The extension of PJVS frequency above the kilohertz range appears to be arduous; however, some enhancements are still practicable. In this work, we demonstrate the possibility to advantageously operate a conventional binary-divided PJVS array with a reduced number of bias lines. This feature is achieved by exploiting both the first and the second Shapiro steps along with nonconventional DAC codings. Two newly devised bias techniques are described in detail and preliminary experimental tests on waveform synthesis have been carried out and are presented here
Recent advancements and perspectives of INRiM’s time-dependent Josephson voltage standards
Full text linkData of cryocooler temperature dynamical response to time-varying power inputs at 4 K
Full text linkData presented here deal with the measurement of a two-stage Gifford-McMahon cryocooler dynamical thermal response to programmed square wave and sine wave power inputs around 4 K. Square response data report the raw temperature data points measured by the sensor. Properly filtered data are also presented and results of exponential decays fitting analyses are shown as well. Sine response data were acquired with two different experimental setups and at several frequencies; data report the frequencies of the input stimulus, the measured temperature variation and the phase between input and output signals for both setups. More details about the experimental background can be found in the related research article, “Experimental analysis of the thermal behavior of a GM cryocooler based on linear system theory” (Sosso and Durandetto, in press)
Quantum sampling AC standard for electrical power metrology based on programmable Josephson junction series array
Full text linkOn-chip Josephson junction-based sensor for temperature control of a cryocooled quantum standard
No full textIn this paper we show how an overdamped Josephson junction can be exploited as temperature sensor in a closedloop circuit to control the operating point of a cryocooled device, e.g. a quantum standard. The resistance of a Josephson junction is measured at the desired temperature with a commercial ac resistance meter, that then uses this value to regulate the chip temperature via its own PID control functionality. Experimental setup and measurement methods are described here. Moreover, the temperature sensitivity of an ideal junction has been determined for different bias-current values
A modular and customizable open-source package for quantum voltage standards operation and control.
Full text linkThis paper presents an open-source package developed in Python that controls and drives a programmable Josephson array to synthesize dc and ac quantum-accurate voltages. Programmable arrays are devices subdivided into independent subsections, each counting a number of series connected Josephson junctions that follows a binary sequence (1, 2, 4, 8, …) to control the output voltage. Our software allows to independently measure the current-voltage characteristics of each subsection by means of a set of arbitrary waveform generators and a nanovoltmeter that measures the voltage across the whole array with high sensitivity. A quantization test tool is also provided to check with sub-microvolt resolution whether the array is operating on its quantum margins. The code is modular and easily expandable with the support of many libraries, allowing prompt reconfiguration for different calibration and testing purposes. It is aimed at being a starting point for cooperation between National Metrology Institutes towards the realization of a shared quantum voltage calibration infrastructure
Determination of the temperature vs power dynamic behavior of a cryocooler via two independent methods in time and frequency domain
Full text linkThis report deals with the analysis of a cryocooler as a linear dynamical system around a set point, over a range of temperatures where the thermal properties can be considered constant.The accurate knowledge of the cryocooler temperature dependence with a time dependent power stimulus allows to analyze the thermodynamical properties of the system and understand the power flow related, for example, to the cryocooler temperature fluctuations. This is useful for the design of efficient thermal dampers that are necessary for the thermal stabilization of the device under test Sosso et al. [1], Trinchera et al. [2]. Two different and independent methods for deriving the cooler dynamic (i.e. non-stationary) behavior are described using the two main approaches to mathematically represent a dynamical system: step response and transfer function. • Using both approaches we were able to cross check results and provide an estimate of the accuracy of each method. • The instrumentation required is typically available in physics and engineering laboratories. • These results provide insights on cryocooler thermodynamics and design tools for cryocooler engineering. Method name: Temperature to power dynamic response of a cryocooler with both time and frequency domain analyses, Keywords: Cryocooler analysis, Transfer function, Step respons
- …
