arXiv subjects

A. L. Pankratov

Publications and source records attributed to A. L. Pankratov.

14 recordsLinked to original sources

arXiv2025

Observation of thermal microwave photons with a Josephson junction detector

When measuring electromagnetic radiation of frequency $f$, the most sensitive detector is the one that counts the single quanta of energy $h f$. Single photon detectors (SPDs) were demonstrated from $γ$-rays to infrared wavelengths, and extending this range down to the microwaves is the focus of intense research. The energy of $10\,\mathrm{GHz}$ microwave photon, about $40\,\mathrm{μeV}$ or $7\, \mathrm{yJ},$ is enough to force a superconducting Josephson junction into its resistive state, making it suitable to be used as a sensor. In this work, we use an underdamped Josephson junction to detect single thermal photons stochastically emitted by a microwave copper cavity at millikelvin temperatures. After characterizing the source and detector, we vary the temperature of the resonant cavity and measure the increased photon rate. The device shows an efficiency up to 40% and a dark count rate of $0.1\,\mathrm{Hz}$ in a bandwidth of several gigahertz. To confirm the thermal nature of the emitted photons we verify their super-Poissonian statistics, which is also a signature of quantum chaos. We discuss detector application in the scope of Dark Matter Axion searches, and note its importance for quantum information, metrology and fundamental physics.

quant-ph↗

arXiv2024

Response of a Cold-Electron Bolometer in a coplanar antenna system

Cold electron bolometers have shown their suitability for use in modern fundamental physical experiments. Fabrication and measurements of the samples with cold-electron bolometers integrated into coplanar antennas are performed in this study. The bolometric layer was made using combined aluminum-hafnium technology to improve quality of aluminum oxide layer and decrease the leakage current. The samples of two types were measured in a dilution cryostat at various temperatures from 20 to 300 mK. The first sample with Ti/Au/Pd antenna shows response in the two frequency bands, at 7--9 GHz with bandwidth of about 20%, and also at 14 GHz with 10% bandwidth. The NEP below 10 aW/Hz^1/2 is reached at 300 mK for 7.7 GHz signal. The second sample with aluminum made antenna shows response in the frequency range 0.5--3 GHz due to the effect of kinetic inductance of superconducting aluminum.

cond-mat.supr-con↗

arXiv2016

Observation of photon noise by cold-electron bolometers

We have measured a response to a black body radiation and noise of the cold-electron bolometers. The experimental results have been fitted by theoretical model with two heat-balance equations. The measured noise has been decomposed into several terms with the help of theory. It is demonstrated that the photon noise exceeds any other noise components, that allows us to conclude that the bolometers see the photon noise. Moreover, a peculiar shape of the noise dependence on the absorbed power originates completely from the photonic component according to the theory. In the additional experiment on heating of the cryostat plate together with the sample holder we have observed nearly independence of the noise on the electron temperature of the absorber, which has provided another proof of the presence of the photon noise in the first experiment.

physics.ins-det↗

arXiv2015

Quasioptical qualification of parallel/series arrays of cold-electron bolometers with a cross-slot antenna

We perform experimental and theoretical study of the parallel-series arrays of Cold-Electron Bolometers (CEBs) integrated into a cross-slot antenna and composed with an immersion silicon lens. The purpose is to determine the absorption efficiency, the responsivity and the noise equivalent power (NEP) of the bolometers. The absorbed power has been found in two independent ways. The comparison of two approaches gives better understanding of the system and secures from misinterpretations. The first approach is fitting of the bolometer IV curves with solutions of heat-balance equations. The second approach is modeling of electromagnetic properties of the system, including an antenna, lens, optical can, band-pass filters and black body source. The difference between both methods does not exceed $30\%$. The optimization of experimental setup is proposed to approach the photon limited detection mode.

physics.ins-det↗

arXiv2014

Nonreciprocal transmission of microwaves through a long Josephson junction

Nonreciprocal microwave transmission through a long Josephson junction in the flux-flow regime is studied analytically and numerically within the framework of the perturbed sine-Gordon model. We demonstrate that the maximum attenuation of the transmitted power occurs when the direction of the flux flow is opposite to the direction of the microwave propagation. This attenuation is nonreciprocal with respect to the flux-flow direction and can be enhanced by increasing the system length and proper impedance matching of the junction ends to external transmission line.

cond-mat.supr-con↗

arXiv2014

"Quick and dirty" technology for fabrication of a single BiSrCaCuO mesas

The technology of wet etching allowing fabrication of standalone BiSrCaCuO mesa structures was proposed. The produced mesas can be produced much thicker than ones usually being studied. The time required for the fabrication is much smaller in comparison with the standard method of ion milling. The process used is controllable which provides acceptable precision of mesa fabrication. The current-voltage characteristics of the sample showing Josephson nature were obtained. The qualitative comparison with characteristics of similar structures fabricated by other groups was carried out.

cond-mat.supr-con↗

arXiv2011

The effect of bias feed profile on spectral properties of noisy Josephson flux flow oscillator

For creation of a noisy non-stationary spectrometer working in the subTHz frequency range the power and spectral characteristics of a flux flow oscillator (FFO), based on a long Josephson junction are studied. The effect of various bias current profiles on the spectral linewidth of long overlap Josephson junction are investigated and comparison with the inline junction geometry is outlined. It has been demonstrated that the spectral linewidth can be increased by a factor of three with the moderate reduction of emitted power.

cond-mat.supr-con↗

arXiv2010

Noise-induced effects in magnetization reversal and chirality control of circular array of single-domained nanomagnets

The effect of noise on the process of high-speed remagnetization of vortex state of a pentagonal array of five circular magnetic nanoparticles is studied by means of computer simulation of Landau-Lifshits model. The mean switching time and its standard deviation of the reversal between the counterclockwise and clockwise vorticities have been computed. It has been demonstrated that with the reversal by the pulse with sinusoidal shape, the optimal pulse duration exists, which minimizes both the mean switching time (MST) and the standard deviation (SD). Besides, both MST and SD significantly depend on the angle between the reversal magnetic field and pentagon edge, and the optimal angle roughly equals 10 degrees. Also, it is demonstrated that the optimization of the angle, duration and the amplitude of the driving field leads to significant decrease of both MST and SD. In particular, for the considered parameters, the MST can be decreased from 60 ns to 2-3 ns. Such a chain of magnetic nanoparticles can effectively be used as an element of magnetoresistive memory, and at the temperature 300K the stable operation of the element is observed up to rather small size of nanoparticles with the raduis of 20 nm.

cond-mat.mes-hall↗

arXiv2010

Spectral characteristics of noisy Josephson flux flow oscillator

The current-voltage and spectral characteristics of a flux flow oscillator (FFO), based on a long Josephson junction, are studied. The investigations are performed in the range of small bias currents and magnetic fields, where the FFO radiates a quasi-chaotic signal with extremely large radiation linewidth, and the displaced linear slope (DLS) is observed at the current-voltage characteristic. By direct numerical simulation of the sine-Gordon equation it is demonstrated that for large lengths of the Josephson junction or in the case of finite matching of the FFO with external waveguide system, the DLS with extremely large linewidth is transformed into Fiske steps with very narrow linewidth. While there is the common belief that the chaotic regime of the FFO is due to excitation of the internal oscillation modes in the "soft" fluxon chain, it is demonstrated that this regime is inspired by multiple reflections of the traveling waves from junction ends.

cond-mat.supr-con↗

arXiv2008

Influence of length on the noise delayed switching of long Josephson junctions

The transient dynamics of long overlap Josephson junctions in the frame of the sine-Gordon model with a white noise source is investigated. The effect of noise delayed decay is observed for the case of overdamped sine-Gordon equation. It is shown that this noise induced effect, in the range of small noise intensities, vanishes for junctions lengths greater than several Josephson penetration length.

cond-mat.supr-con↗

arXiv2008

Lifetime of metastable states and suppression of noise in Interdisciplinary Physical Models

Transient properties of different physical systems with metastable states perturbed by external white noise have been investigated. Two noise-induced phenomena, namely the noise enhanced stability and the resonant activation, are theoretically predicted in a piece-wise linear fluctuating potential with a metastable state. The enhancement of the lifetime of metastable states due to the noise, and the suppression of noise through resonant activation phenomenon will be reviewed in models of interdisciplinary physics: (i) dynamics of an overdamped Josephson junction; (ii) transient regime of the noisy FitzHugh-Nagumo model; (iii) population dynamics.

cond-mat.stat-mech↗

arXiv2008

Noise-induced effects in high-speed reversal of magnetic dipole

The effect of noise on the reversal of a magnetic dipole is investigated on the basis of computer simulation of the Landau-Lifshits equation. It is demonstrated that at the reversal by the pulse with sinusoidal shape, there exists the optimal duration, which minimizes the mean reversal time (MRT) and the standard deviation (jitter). Both the MRT and the jitter significantly depend on the angle between the reversal magnetic field and the anisotropy axis. At the optimal angle the MRT can be decreased by 7 times for damping $α$=1 and up to 2 orders of magnitude for $α$=0.01, and the jitter can be decreased from 1 to 3 orders of magnitude in comparison with the uniaxial symmetry case.

cond-mat.other↗

arXiv2007

Minimizing the linewidth of the Flux-Flow Oscillator

For the first time the linewidth of Flux-Flow Oscillator has been calculated by direct computer simulation of the sine-Gordon equation with noise. Nearly perfect agreement of the numerical results with the formula derived in [Phys. Rev. B, {\bf 65}, 054504 (2002)] has been achieved. It has been demonstrated that for homogeneous bias current distribution the linewidth actually does not depend on the junction length for practically interesting parameters range. Depending on the length of the unbiased tail, the power may be maximized and the linewidth may be minimized in a broad range of bias currents. The linewidth can be decreased further by 1.5 times by proper load matching.

cond-mat.supr-con↗

arXiv2006

Life time of superconductive state in long overlap Josephson junction

The computer simulations of fluctuational dynamics of the long overlap Josephson junction in the frame of the sine-Gordon model with a white noise source have been performed. It has been demonstrated that for the case of constant critical current density the mean life time (MLT) of superconductive state increases with increasing the junction's length and for homogeneous bias current distribution MLT tends to a constant, while for inhomogeneous current distribution MLT quickly decreases after approaching of a few Josephson lengths. The mean voltage versus junction length behaves inversely in comparison with MLT.

cond-mat.supr-con↗