arXiv subjects

V. A. Tulin

Publications and source records attributed to V. A. Tulin.

32 records · Page 2Linked to original sources

arXiv2006

Investigation of possibility of creation of a superconductor quantum register

Multiple and single measurements of quantum states of mesoscopic superconducting loops are carried out in order to investigate a possibility of macroscopic quantum superposition and of creation of a superconductor quantum register. Asymmetric superconducting rings are used in order to be convinced that single measurement gives result corresponding to one of permitted states and multiple one gives an average value on these states. We have measured magnetic dependencies of resistance, rectified voltage and critical current on these rings. The observed quantum oscillations of the resistance and the rectified voltage, corresponding to multiple measurement of quantum states, give evidence of two permitted states at the magnetic flux inside the ring divisible by half of the flux quantum. But the observed quantum oscillations of the critical current, corresponding to single measurement, not only does not confirm these two quantum states, but are in a direct contradiction with the observed oscillations of the resistance. It is assumed that the observed contradiction between the results of measurements made on the same ring can testify to violation of the principle of realism on the mesoscopic level that is a necessary condition for an opportunity of creation of a quantum computer.

cond-mat.supr-con↗

arXiv2006

Multiple and single measurements of a mesoscopic quantum system with two permitted states

Mesoscopic loop is proposed in many works as possible solid-state quantum bit, i.e. two-state quantum system. The quantum oscillations of resistance and of rectified voltage observed on asymmetric superconducting loops give evidence of the two states at magnetic flux divisible by half of the flux quantum. But our measurements of quantum oscillations of the critical current of these loops have given results coming into irreconcilable contradictions with result of the observations of the quantum oscillations of resistance.

cond-mat.supr-con↗

arXiv2006

Could two degenerate energy states be observed for a superconducting ring at $Φ_{0}$/2?

The Little-Parks oscillations of the resistance and the quantum oscillations of the rectified voltage observed for asymmetric superconducting Al rings give experimental evidence of two degenerate energy states at the magnetic flux $Φ_{0}$/2. The quantum oscillations of the critical current as a function of magnetic field have also been measured. On the one hand, these oscillations confirm that the quantum oscillations of the rectified voltage are a consequence of periodical dependence of the asymmetry of the current-voltage curves and, on the other hand, comparison of the oscillations with Little-Parks measurements results in contradiction.

cond-mat.supr-con↗

arXiv2006

Calibration of quantum detector of noise based on a system of asymmetric superconducting loops

The quantum oscillations of the dc voltage are induced on segments of asymmetric superconducting loops by an external ac current or noise. The dependencies of the amplitude of the quantum oscillations on amplitude of inducing ac current are measured at different temperatures below superconducting transition Tc on aluminum asymmetric loops and systems of the loops connected in series. The measured values of the maximum amplitude of the quantum oscillations, the amplitude of the ac current inducing this maximum dc voltage and the critical amplitude of the ac current decrease with temperature increase to Tc. The extrapolation of these measured dependencies to the region near superconducting transition allows to make a calibration of asymmetric superconducting loops as quantum detector of noise. The calibration restores an amplitude profile of the noise pulses from a measured temperature dependence of an amplitude of the quantum oscillations induced by this noise. It is found that rectification efficiency, determined as relation of the maximum amplitude of the quantum oscillations to the ac current amplitude inducing it, decreases near superconducting transition Tc. High efficiency of rectification observed below Tc is consequence of irreversibility of the current-voltage curves. Increase of the rectification efficiency is achieved in multiple series connected loop structures.

cond-mat.supr-con↗

arXiv2006

Quantum detector of noise based on a system of asymmetric Al superconducting rings

The quantum rectification effect observed on asymmetric superconducting loops is proposed to use as a basic of a noise detector with maximum sensitivity. The measurements show that a critical amplitude of noise or ac current decreases down to zero near superconducting transition, Tc, just as superconducting critical current. Therefore any how weak noise, right down to the equilibrium one, can induce the quantum oscillations of the dc voltage near Tc. The transformation of the power of random noise into the dc power observed on asymmetric superconducting loops gives very important advantage: even very weak noise can give enough high output power in a system with large number of loops.

cond-mat.supr-con↗

arXiv2006

Quantum oscillations of the rectified voltage and the critical current of asymmetric mesoscopic superconducting loops

The current-voltage curves and magnetic dependence of the critical current of asymmetric superconducting loops are measured. It was found that sign and value of the asymmetry of the current-voltage curves changes with value of magnetic field, periodically for single loop and system of identical loops. The obtained results allow to explain the quantum oscillation of the dc voltage, observed below superconducting transition in the previous works, as rectification of ac current or noise.

cond-mat.supr-con↗

arXiv2005

Quantum Oscillations of the Critical Current of Asymmetric Aluminum Loops in Magnetic Field

The periodical dependencies in magnetic field of the asymmetry of the current-voltage curves of asymmetric aluminum loop are investigated experimentally at different temperatures below the transition into the superconducting state T < Tc. The obtained periodical dependencies of the critical current on magnetic field allow to explain the quantum oscillations of the dc voltage as consequence of the rectification of the external ac current and to calculate the persistent current at different values of magnetic flux inside the loop and temperatures.

cond-mat.supr-con↗

arXiv2004

Thin-Film Aluminum Microstructure as a Hot-Electron Microwave Radiation Detector

We have found that the thin film aluminum structures shaped into a chain of micron sized islands connected by narrow isthmuses, can modify their electrical and structural properties under microwave radiation. As a result, at the temperature of 4.2 K the film structures turn into a kind of lateral periodic structure N-S-N, where N is for normal islands, S is for superconducting isthmuses. Current-voltage characteristics of the samples, as well as changes of these characteristics under low power radiation, have been studied over the temperature range from 1.3 to 10 K. The sensitivity of a structure as a microwave detector runs 10^{5} V/W.

cond-mat.supr-con↗

arXiv2004

Temperature dependence of the resistance of a phase-slip line in a thin superconducting film

An experimental investigation was made of the temperature dependence of the first step of a phase-slip line in a thin superconducting tin film. The depth of penetration of a nonequilibrium longitudinal electric field into the superconductor was determined near the critical temperature. A comparison was made with theoretical investigations of one-dimensional structures containing phase-slip centers. The experimental results were found to be in good agreement with the theory when the mechanism of mixing of electron-like and hole-like branches of the quasiparticle spectrum was governed by the elastic scattering of the excitations. This was one more experimental confirmation that a phase-slip line is a two-dimensional analog of a phase-slip center.

cond-mat.supr-con↗

arXiv2004

Induction of phase-slip lines in a thin, wide superconducting film by an rf electromagnetic field

The appearance of phase-slip lines, induced by an rf field, was observed experimentally in wide superconducting films in which the destruction of superconductivity by a dc current is associated with the formation of phase-slip lines. The characteristics of the separation of the film into superconducting and nonuniform, isothermal, nonequilibrium regions (phase-slip lines) under electromagnetic irradiation were studied.

cond-mat.supr-con↗

arXiv2004

Synchronization of high-frequency oscillations of phase-slip centers in a tin whisker under microwave radiation

Current-voltage characteristics of a system with a variable number of phase-slip centers resulting from phase separation in a tin whisker under external microwave field with a frequency Ω/2π\=35-45 GHz have been studied experimentally. Emergence and disappearance of steps with zero slope in a whisker's current-voltage characteristic at U_{m/n}=(m/n)U_Ω, where m and n are integers and U_Ω is determined by Josephson's formula \hbarΩ=2eU_Ω, have been investigated. Microwave field generated by phase-slip centers is nonharmonic, and the system of phase-slip centers permits synchronization of internal oscillations at a microwave frequency by an external field with a frequency which is the n-th harmonic of internal oscillations. The estimated microwave power generated by a whisker is 10^{-8} W. Stimulation of superconductivity in a current-carrying whisker has been detected.

cond-mat.supr-con↗

arXiv2004

Observation of a nonmonotonic transverse voltage induced by vortex motion in a superconducting thin film

A vortex-induced transverse voltage in a superconducting film, previously predicted theoretically, has been seen experimentally for the first time. The magnitude of this voltage and its nonmonotonic current dependence are explained on the basis of a curvature of the trajectory of vortices resulting from their interaction. A good agreement between theory and experiment is found.

cond-mat.supr-con↗

arXiv2004

Conversion of phase-slip lines into elementary resistive domains in a current-carrying superconducting thin film

A nonmonotonic dependence of the differential resistance of the first step of a phase-slip line on the heat-reservoir temperature near Tc has been observed experimentally for the first time in a superconducting tin film. This behavior is interpreted as a conversion of the phase-slip line into an elementary resistive domain as the result of a deviation from the isothermal conditions.

cond-mat.supr-con↗

arXiv2000

Nonlinear electron transport in normally pinched-off quantum wire

Nonlinear electron transport in normally pinched-off quantum wires was studied. The wires were fabricated from AlGaAs/GaAs heterostructures with high-mobility two-dimensional electron gas by electron beam lithography and following wet etching. At certain critical source-drain voltage the samples exhibited a step rise of the conductance. The differential conductance of the open wires was noticeably lower than e^2/h as far as only part of the source-drain voltage dropped between source contact and saddle-point of the potential relief along the wire. The latter limited the electron flow injected to the wire. At high enough source-drain voltages the decrease of the differential conductance due to the real space transfer of electrons from the wire in GaAs to the doped AlGaAs layer was found. In this regime the sign of differential magnetoconductance was changed with reversing the direction of the current in the wire or the magnetic field, whet the magnetic field lies in the heterostructure plane and is directed perpendicular to the current. The dependence of the differential conductance on the magnetic field and its direction indicated that the real space transfer events were mainly mediated by the interface scattering.

cond-mat.soft↗