arXiv subjects

A. S. Averkin

Publications and source records attributed to A. S. Averkin.

8 recordsLinked to original sources

arXiv2026

Strongly nonlinear regime of Josephson transmission lines revealed by two-tone spectroscopy

We present experimental and theoretical studies of the off-resonant and strongly nonlinear regime of Josephson transmission lines (JTLs) with galvanically-coupled nonlinear elements. The transition from the weakly to the strongly nonlinear regime of a JTL induced by increasing the input power of the pump is probed via two-tone spectroscopy. Measurements of the phase of the transmission coefficient for a weak probe signal reveal a large increase and pronounced oscillations in the phase length variation as a function of the microwave power of the pump. Experimental observations are explained on the basis of the developed theoretical approach suitable for the description of the nonlinear response of strongly driven JTLs. Using the derived nonlinear wave equation, we show that the behavior of the phase length variation is associated with the oscillatory dependence of the Josephson inductances on the microwave power. It is demonstrated that the dissipation-induced propagation losses increase in the strongly nonlinear regime and also lead to smearing out the phase length oscillations. The developed theoretical analysis is in good agreement with experimental observations.

cond-mat.supr-con↗

arXiv2019

Two-tone spectroscopy of a SQUID metamaterial in the nonlinear regime

Compact microwave resonantors made of superconducting rings containing Josephson junctions (SQUIDs) are attractive candidates for building frequency tunable metamaterials with low losses and pronounced nonlinear properties. We explore the nonlinearity of a SQUID metamaterial by performing a two-tone resonant spectroscopy. The small-amplitude response of the metamaterial under strong driving by a microwave pump tone is investigated experimentally and theoretically. The transmission coefficient $S_{21}$ of a weak probe signal is measured in the presence of the pump tone. Increasing the power of the pump, we observe pronounced oscillations of the SQUID's resonance frequency $f_{\textrm{res}}$. The shape of these oscillations varies significantly with the frequency of the pump tone $f_{\textrm{dr}}$. The response to the probe signal displays instabilities and sidebands. A state with strong second harmonic generation is observed. We provide a theoretical analysis of these observations, which is in good agreement with the experimental results.

physics.app-ph↗

arXiv2018

Phase-sensitive imaging of microwave currents in superconductive circuits

The contemporary superconductive electronics is widely using planar circuits with micrometer-scale elements for a variety of applications. With the rise of complexity of a circuit and increased number of its components, a simple impedance measurement are often not efficient for diagnostics of problems, nor for clarifying the physics underlying the circuit response. The established Scanning Laser Microscope (LSM) technique generates the micrometer-scale images of the amplitude of the microwave currents in a planar superconductive circuit, but not the phase of the oscillating currents. Here we present a novel, more powerful type of LSM imaging containing the signal phase information. We employ a fast optical modulator in order to synchronize the phase of the laser intensity oscillation with the phase of the probing microwave signal. The loss induced in laser illuminated area strongly depends on the phase difference between the RF probing signal and the laser beam modulation. We explain the detection principle of the phase sensitive LSM and experimentally demonstrate the capability of this method using superconductive microwave resonators. The described technique facilitates understanding of complex RF current distributions in superconductive circuits.

physics.app-ph↗

arXiv2018

Superconductive Ultra-compact Magnetically Coupled Resonator with Twin-spiral Structure

We describe a practical design of an ultra-compact on-chip superconductive micro-resonator as a potential magnetic element of metamaterial. The achieved resonator size with respect to the wavelength in our experiment is about λ/ 14400. The resonator consists of two superconducting Nb spirals, sandwiched face to face, with a small gap filled with dielectric. The spirals are turning in opposite directions: one clockwise, another counter-clockwise. We study the resonator spectral response and its inner modes using numerical simulation in HFSS. In experiment with a Laser Scanning Microscope (LSM) we confirm the predictions for the resonance frequencies of Nb superconductive resonator and its inner modes structures. Small size and the ease of manufacturing make the two-spiral resonator an attractive solution for superconductive filters, coupling circuits, and as a magnetic component of a metamaterial.

cond-mat.supr-con↗

arXiv2014

Design and experimental study of superconducting left-handed transmission lines with tunable dispersion and improved impedance match

We continue detailed study of microwave properties of a superconducting left-handed tunable CPW transmission line (LHTL). The line consists of a central conductor, loaded with series of Josephson junctions as fixed inductors; the line is shunted with SQUIDs as tunable inductors. The inductance of the SQUIDs is varied in the range of 0.08-0.5 nH by applying an external dc magnetic field. The circuit is designed to have left- and right-handed transmission bands separated by a variable rejection band. At zero magnetic field, we observed only one pass-band between 8 and 10 GHz within the frequency range of 8-12 GHz. The rejection band is anticipated to appear between 10 GHz and 11 GHz by design, and it has been detected in our previous work. To solve the problem of standing waves and RF leak in measurements of our experimental 20-cell LHTL, we have designed a high-ratio (5-50 Ohm) wideband (8-11 GHz) impedance transformer integrated at the chip, along with improved sample holder. The experimental data are compared with numerical simulations.

cond-mat.supr-con↗

arXiv2014

Electrodynamics of a planar Archimedean spiral resonator

We present a theoretical and experimental study of electrodynamics of a planar spiral superconducting resonator of a finite length. The resonator is made in the form of a monofilar Archimedean spiral. By making use of a general model of inhomogeneous alternating current flowing along the resonator and specific boundary conditions on the surface of the strip, we obtain analytically the frequencies $f_n$ of resonances which can be excited in such system. We also calculate corresponding inhomogeneous RF current distributions $ψ_n (r)$, where $r$ is the coordinate across a spiral. We show that the resonant frequencies and current distributions are well described by simple relationships $f_n=f_1 n$, and $ψ_n(r)\simeq \sin[πn (r/R_e)^2]$, where $n=1,2...$, and $R_e$ is the external radius of the spiral. Our analysis of electrodynamic properties of spiral resonators' is in good accord with direct numerical simulations and measurements made using specifically designed magnetic probe and laser scanning microscope.

cond-mat.supr-con↗

arXiv2014

Broadband Sample Holder for Microwave Spectroscopy of Superconducting Qubits

We present a practical design and implementation of a broadband sample holder suitable for microwave experiments with superconducting integrated circuits at millikelvin temperatures. Proposed design can be easily integrated in standard dilution cryostats, has flat pass band response in a frequency range from 0 to 32 GHz, allowing the RF testing of the samples with substrate size up to 4x4 mm. The parasitic higher modes interference in the holder structure is analyzed and prevented via design considerations. The developed setup can be used for characterization of superconducting parametric amplifiers, bolometers and qubits. We tested the designed sample holder by characterizing of a superconducting flux qubit at 20 mK temperature.

cond-mat.supr-con↗

arXiv2013

Design and experimental study of superconducting left-handed transmission lines with tunable dispersion

We study microwave properties of a superconducting tunable coplanar waveguide (CPW). Pairs of Josephson junctions are forming superconducting quantum interference devices (SQUIDs), which shunt the central conductor of the CPW. The Josephson inductance of the SQUIDs is varied in the range of 0.08-0.5 nH by applying an external dc magnetic field. The central conductor of the CPW contains Josephson junctions connected in series that provide extra inductances; the magnetic field controlling the SQUIDs is weak enough not to influence the inductance of the chain of the single junctions. The circuit is designed to have left- and right-handed transmission properties separated by a variable rejection band; the band edges can be tuned by the magnetic field. We present transmission measurements on CPWs based on up to 120 Nb-AlOx-Nb Josephson junctions. At zero magnetic field, we observed no rejection band in the frequency range of 8-11 GHz. When applying the magnetic field, a rejection band between 7 GHz and 9 GHz appears. The experimental data are compared with numerical simulations.

cond-mat.supr-con↗