The work describes the capabilities of Laser Scanning Microscopy (LSM) as a spatiallyresolved method of testing high-T c materials and devices. The earlier results obtained by the authors are briefly reviewed. Some novel applications of the LSM are illustrated, including imaging the HTS responses in rf mode, probing the superconducting properties of HTS single crystals, development of two-beam laser scanning microscopy. The existence of the phase slip lines mechanism of resistivity in HTS materials is proven by LSM imaging.

The current-induced destruction of superconductivity is discussed in wide superconducting thin film strips, whose width is greater than the magnetic field penetration depth, in weak magnetic fields. Particular attention is paid to the role of the edge potential barrier (the Bean-Livingston barrier) in critical state formation and detection of the edge responsible for this critical state with different mutual orientations of external perpendicular magnetic field and transport current. Critical and resistive states of the thin film strip were visualized using the space-resolving lowtemperature laser scanning microscopy (LTLSM) method, which enables detection of critical current-determining areas on the thin film edges. Based on these observations, a simple technique was developed for investigation of the critical state separately at each film edge, and for the estimation of residual magnetic fields in cryostats. The proposed method only requires recording of the current-voltage characteristics of the thin film in a weak magnetic field, thus circumventing the need for complex LTLSM techniques. Information thus obtained is particularly important for interpretation of studies of superconducting thin film single-photon light emission detectors.

Superconducting quantum coherent circuits have opened up a novel area of fundamental lowtemperature science since they could potentially be the element base for future quantum computers. Here we report a quasi-three-level coherent system, the so-called superconducting qutrit, which has some advantages over a two-level information cell (qubit), and is based on the qutrit readout circuit intended to measure individually the states of each qubit in a quantum computer. The designed and implemented radio-frequency superconducting qutrit detector (rf SQUTRID) with atomic-size ScStype contact utilizes the coherent-state superposition in the three-well potential with energy splitting ∆E01/kB ≈ 1.5 K at the 30th quantized energy level with good isolation from the electromagnetic environment. The reason why large values of ∆E01 (and thus using atomic-size Nb-Nb contact) are required is to ensure an adiabatic limit for the quantum dynamics of magnetic flux in the rf SQUTRID.