Energy-level quantization in YBa2Cu3O7-x phase-slip nanowires

Significant progress has been made in the development of superconducting quantum circuits, however new quantum devices that have longer decoherence times at higher temperatures are urgently required for quantum technologies. Superconducting nanowires with quantum phase slips are promising candidates for use in novel devices that operate on quantum principles. Here, we demonstrate ultra-thin YBa2Cu3O7-x nanowires with phase-slip dynamics and study their switching-current statistics at temperatures below 20 K. We apply theoretical models that were developed for Josephson junctions and show that our results provide strong evidence for energy-level quantization in the nanowires. The crossover temperature to the quantum regime is 12-13 K, while the lifetime in the excited state exceeds 20 ms at 5.4 K. Both values are at least one order of magnitude higher than those in conventional Josephson junctions based on low-temperature superconductors. We also show how the absorption of a single photon changes the phase-slip and quantum state of a nanowire, which is important for the development of single-photon detectors with high operating temperature and superior temporal resolution. Our findings pave the way for a new class of superconducting nanowire devices for quantum sensing and computing

In-plane anisotropy of electrical transport in Y0.85_{0.85}Tb0.15_{0.15}Ba2_2Cu3_3O7−x_{7-x} films

We fabricate high-quality c-axis oriented epitaxial YBa$_2$Cu$_3$O$_{7-x}$ films with 15% of yttrium atoms replaced by terbium (YTBCO) and study their electrical properties. The Tb substitution reduces the charge carrier density resulting in increased resistivity and decreased critical current density compared to the pure YBa$_2$Cu$_3$O$_{7-x}$ films. The electrical properties of the YTBCO films show an in-plane anisotropy in both the superconducting and normal state providing evidence for the twin-free film. Unexpectedly, the resistive transition of the bridges also demonstrates the in-plane anisotropy that can be explained within the framework of Tinkham's model of the resistive transition and the Berezinskii-Kosterlitz-Thouless (BKT) model depending on the sample parameters. We consider YTBCO films to be a promising platform for both the fundamental research on the BKT transition in the cuprate superconductors and for the fabrication of devices with high kinetic inductance

Josephson spectrometer with waveguide coupling for liqiud identification

AbstractFast and reliable liquid identification is possible, in principle, by Josephson spectroscopy at subterahertz and terahertz ranges, but high speed of measurements, extended frequency range and high accuracy of intensity measurements are required. Quasioptical radiation coupling used in our previous demonstrators of the identifier can not be used at low frequencies where diffraction losses increase drastically. In this paper, we describe a new spectrometer based on a frequency-selective high-Tc Josephson detector with dielectric waveguide coupling and consider its frequency scanning speed limit at a given accuracy of power measurement. According to our estimations, frequency scanning speed up to 1.3 THz/sec can be achieved if spectral resolution and power measurement error are 3GHz and 0.1%, respectively. We have developed new compact radiation coupling system based on dielectric waveguides, which extends low frequency limit of our spectrometer down to 1.75GHz. Small spread of angles of incidence of radiation and polarization control allow to recover the dielectric constants of the substance under test in a more simple way than in the case of quasioptical coupling. The results of first measurements with the new radiation coupling will be presented in our paper

Hilbert spectral analysis of THz radiation sources by high-Tc Josephson detectors

AbstractA Hilbert spectrum analyzer was developed and characterized with monochromatic radiation sources at the frequency range from 30GHz to 1 THz. The analyzer was based on a high-Tc frequency-selective Josephson detector and cooled to temperatures of 60-80K by a Stirling cryocooler. The instrumental function of the spectrum analyzer was shown to be of Lorentz type and within accuracy up to 0.1% without any harmonic and subharmonic contributions. Spectral characterization of THz sources, based on frequency multiplication of input microwave radiation by Schottky diodes, was demonstrated for input frequencies from 10 to 20GHz with a total scanning time as low as 50ms per scan. The developed Hilbert spectrum analyzer might be considered as a compact and high-speed substitute of conventional Fourier spectrometers, which are used for characterization of THz radiation sources in combination with liquid-helium-cooled silicon bolometers

Liquid indentification by Hilbert spectroscopy

Fast and reliable identification of liquids is of great importance in, for example, security, biology and the beverage industry. An unambiguous identification of liquids can be made by electromagnetic measurements of their dielectric functions in the frequency range of their main dispersions, but this frequency range, from a few GHz to a few THz, is not covered by any conventional spectroscopy. We have developed a concept of liquid identification based on our new Hilbert spectroscopy and high-T-c Josephson junctions, which can operate at the intermediate range from microwaves to THz frequencies. A demonstration setup has been developed consisting of a polychromatic radiation source and a compact Hilbert spectrometer integrated in a Stirling cryocooler. Reflection polychromatic spectra of various bottled liquids have been measured at the spectral range of 15-300 GHz with total scanning time down to 0.2 s and identification of liquids has been demonstrated

Towards Ideal High-Tc Josephson Junctions

Ext. Abstract