Vladimir Manucharyan: Superinductance: engineering and characterization.

He reports about large inductances realized with series arrays of Josephson-junctions and means to characterize them. The experimental techniques used may very well be useful to characterize large inductances realized with highly disordered superconductors.

He starts by showing a catalogue of commercially available inductors (Coilcraft) and shows that they always have a failure mode, which implies that the impedance will never exceed the quantum resistance. This is due to the finestructure constant, which he blames to be too small.

Large inductance circuits are useful for 1; enhanced coupling in QED systems 2; electrical current metrology with Bloch oscillations in JJ’s. 3; Topologically protected quantum states in network of JJ’s. 4; eliminate flux noise in flux qubits (cf. Kerman’s poster).

One could use disordered superconductors, which requires a careful choice of controllable material and of which as of today the electrodynamics is poorly understood. Instead the ‘workhorse’ of superconducting quantum-engineering is used, the Al tunneljunction. A chain of JJ’s can act as an inductor, even tunable because of its dependence on the bias current.

In designing the most useful inductor one needs to consider a long list of possible failures, which are not a priori trivially known. Therefore it is very important to be able to measure and characterize the inductor thoroughly.

He describes 2 methods, of which one of them is easy to implement for highly disordered superconductors. The other one requires integration in a high-Q qubit structure, which is less readily available. The outcome is that coherent quantum phase slip is resolved down to 100 kHz, which connects his presentation to the first two of the workshop by Hans Mooij and Oleg Astafiev, although the QPS is realized in a series array of JJ’s (like by Pop, .., Guichard et al from Grenoble. )

The speaker believes that the highly disordered superconductors are potentially very useful for compact high-Q resonators coupled to semiconductor quantum dots, Rydberg atoms on a chip, polar molecules, or anything with a small dipole moment and a long life time.

Blogged by Teun Klapwijk