O. G. Turutanov

Spatially resolved characterization of superconducting films and cryoelectronic devices by means of low temperature scanning laser microscope

Abstract The work describes the low temperature scanning laser microscopy technique used for spatially resolved characterization of superconducting films and film-based cryoelectronic circuits in the temperature range from 2 to 300 K. The determination of superconducting parameters for separate elements of a high T c Josephson junctions array and imaging of the resistive transition in a high T c superconducting polycrystalline film are demonstrated. The spatial evolution of the resistive state of a Sn thin film strip associated with the phase slip lines formation is visualized.

Stochastic resonance in superconducting loops containing Josephson junctions. Numerical simulation

A numerical simulation of the stochastic resonance is carried out in the adiabatic approximation in overdamped systems based on superconducting loops closed by a weak link. The systems under consideration include a single-ring rf SQUID, two rings coupled by a common magnetic flux, and a ring closed by a 4-terminal Josephson junction. It is shown that coupling of single SQUID rings enhances the gain and the signal-to-noise ratio. These effects can be used to create new stochastic SQUID antennas for measurements of harmonic and quasi-harmonic signals. The stochastic resonance in 4-terminal SQUIDS exists even at values of the dimensionless inductance l<1.

A low temperature system with a pulse UV laser for scribing HTSC films and single crystals

Abstract A simple laser scribing equipment used to pattern high-Tc films and single crystals within a micron accuracy is described. A focused beam of a UV pulsed laser serves as a cutting tool. A low temperature attachment enables all operations to be performed at sample temperatures ranging from 65 to 300 K. Thus it provides a means to fit the critical current of any element in a cryoelectronic circuit to a desirable value during its operational conditions.

Superposition of states in flux qubits with a Josephson junction of the ScS type (Review Article)

The consequences of the transition to a quantum description of magnetic flux motion in the superconducting ring closed by an ScS type Josephson junction are considered. Here we review the principal results regarding macroscopic quantum tunneling (MQT) of Bose condensate consisting of a macroscopically large number of Cooper electron pairs. These phenomena are illustrated by the original data obtained from the study of MQT and coherent states in a modified flux qubit with energy level depletion ΔE01 ≈ 2·10–23 J (ΔE01/h ≈ 30 GHz). State superposition properties in a two-well potential and the issues associated with quantum measurements of local curvature of qubits’ superposition energy levels are analyzed.

Stochastic resonance in an RF SQUID with shunted ScS junction

Using a point (superconductor–constriction–superconductor, ScS) contact in a single-Josephson-junction superconducting quantum interference device (RF SQUID) provides stochastic resonance conditions at any arbitrary small value of loop inductance and contact critical current, unlike SQUIDs with more traditional tunnel (superconductor–insulator–superconductor, SIS) junctions. This is due to the unusual potential energy of the ScS RF SQUID which always has a barrier between two wells, thus making the device bistable. This paper presents the results of a numerical simulation of the stochastic dynamics of the magnetic flux in an ScS RF SQUID loop affected by band-limited white Gaussian noise and low-frequency sine signals of small and moderate amplitudes. The difference in stochastic amplification of RF SQUID loops incorporating ScS and SIS junctions is discussed.

Isolation of a Josephson qubit from the electromagnetic environment

We consider two aspects of isolation of a Josephson flux (charge-flux) qubit from the external dissipative electromagnetic environment: (i) selecting an optimal topology of the superconducting qubit circuit and (ii) passive filtering of Planck radiation at the input of the qubit-state detection circuit. When reading the state of a macroscopic quantum object (“Schrodingers cat”) with the weak continuous measurement technique, the coupling to the environment, both direct and through the connected circuits, is the cause of the rapid loss of coherence of the superposition states. The coefficients of coupling to the external electromagnetic environment are discussed, as well as the problem of their minimization for flat (2D) and bulk (3D) designs of the qubit quantization loops. The analysis of the characteristics of low-temperature combined broadband filters designed to effectively reduce the electromagnetic noise in the control and measurement circuits is carried out. It is shown experimentally that a cryog...

Stochastic-parametric amplification of narrow-band signals in a single-junction SQUID interferometer

The features of the response of a single-junction superconducting quantum interferometer to a low-frequency harmonic signal in the presence of noise and a high-frequency electromagnetic field are investigated through numerical solution of the equations of motion. It is shown that in this situation a system described by a double-well potential will display stochastic-parametric amplification of weak harmonic signals owing to the cooperative effects of noise and the high-frequency field. The gain is a nonmonotonic function of the amplitude of the high-frequency field and the variance of the noise flux and passes through a maximum. A detailed numerical analysis of the dependence of the gain on the noise intensity and on the frequency and amplitude of the high-frequency field is carried out in the stochastic, parametric, and stochastic-parametric amplification regimes. It is shown that at optimal amplitude of the high-frequency field the gain for a weak harmonic signal reaches rather high values (10–30). The ...

Direct measurement of critical currents of individual weak links in DC interferometerby scanning laser microscope

Abstract This paper describes the non-destructive technique of in situ measurement of critical currents Ic of individual weak links in thin film superconducting quantum do interferometers (dc SQUDs). The low temperature scanning laser microscope (LTLSM) is used to study the SQUID resistive response to the laser radiation and to measure the critical currents I c1 and I c2 of the weak links separately.

Frequency-tuned microwave photon counter based on a superconductive quantum interferometer

Various types of single-photon counters operating in infrared, ultraviolet, and optical wavelength ranges are successfully used to study electromagnetic fields, analyze radiation sources, and solve problems in quantum informatics. However, their operating principles become ineffective at millimeter band, S-band, and ultra-high frequency bands of wavelengths due to the decrease in quantum energy by 4–5 orders of magnitude. Josephson circuits with discrete Hamiltonians and qubits are a good foundation for the construction of single-photon counters at these frequencies. This paper presents a frequency-tuned microwave photon counter based on a single-junction superconducting quantum interferometer and flux qutrit. The control pulse converts the interferometer into a two-level system for resonance absorption of photons. Decay of the photon-induced excited state changes the magnetic flux in the interferometer, which is measured by a SQUID magnetometer. Schemes for recording the magnetic flux using a DC SQUID or...