I’ve just returned from the EUROFLUX2008 conference in Naples. The conference dealt with two main aspects of superconducting electronics: Fundamental device progress and superconducting devices as detectors. (I was mainly in with the first bunch).
A few conference highlights:
Valery Ryazanov gave a good presenation on the progress of pi junction applications for digital and quantum logic. The measurements suggest good quality qubits containing SFS (Superconductor-Ferromagnet-Superconductor) pi junction components have been fabricated. This is something I’m really pretty interested in. For RSFQ applications, pi junctions are useful as they act as phase inverters. In the case of qubits, a pi element can introduce a phase shift across one of the Josephson junctions in the loop. The ground state of the qubit loop will then consist of a spontaneously generated circulating current, a half-integer magnetic flux quantum in the loop, and most importantly a double well potential for no applied bias (aka a free lunch). Such qubits are intrinsically thought to be more ‘quiet’ – as you do not need to apply a flux bias to bring them to the working point. The presentation at the conference gave evidence that pi-qubits may be as good as conventional ‘zero’ types. And because they are Niobium SFS, they are (somewhat) compatible with existing process technology, and the best thing is that they’re low Tc, avoiding all that HTS messiness.
I think people still slightly hesitant that magnetic materials and superconductors would ever work in harmony (I spent a year investigating spin-injection devices and came to the same conclusion), not to mention the fact that having magnetic impurities all over the place is not really ideal for a component that’s incredibly sensitive to variations in field. Yet somehow they work. Go physics. Absolutely fantastic progress in this field.
See here, here, here, here and here for a few papers on SFS junctions (there are loads more).
Maria Castellano – High Frequency coherent oscillations of a flux qubit manipulated by fast pulses. The experiment involves Niobium tunable flux qubits. A superconducting loop interrupted by a double Josephson Junction loop (DC SQUID) gives you two handles on the shape of the double well potential – the barrier height and the asymmetry (bias). The group demonstrate coherent oscillations between 6-25Ghz. Operating the qubit at high frequencies means you get more oscillations for your money, and thus more (potential) ops in those vital nanoseconds before decoherence kicks in.
See here and here for some more info.
IPHT (Jena) are developing THz cameras for security applications.
The cameras scan people passively (e.g. at airports) and can detect hidden items. Metallic items e.g. guns, knives etc. block the THz emission from the human body, causing them to appear as shadowed regions to the camera. The detector can also detect non-metallic ‘suspect’ items. These cameras are really coming along, and I perhaps fully working systems will become commonplace within the next 5 years or so. You can read more about the progress here.
SQUIDs for magnetic exploration, again from IPHT. These guys hang a cryocooler containing a SQUID from a helicopter and raster-scan the ground to detect magnetic objects. Items of interest could be unexploded landmines, large mineral deposits, or the buried remains of medieval structures.
The social event was a visit to the excavated city of Herculaneum, buried by the eruption of Mount Vesuvius in 79 AD. It was rather cool to see all the roman technology of the time.
In true Italian style, the conference dinner was an epic six-course meal. The food in general was fantastic, and the weather in Italy was also great (I think we left just before it began to get really hot). Naples itself seemed to have lots of palm trees:
It was a very useful experience overall, and the conference was small enough that nearly all the talks were relevant to my own areas of interest. The general idea of the conference was a gathering of all the people involved in superconducting electronics in Europe (although the conference was open to an international audience) to further progress in the FLUXONICS project, in the area of Niobium Josephson junction applications, and in the European RSFQ technology.