A new regime of rf-SQUID

I. M. Dmitrenko, Georgy M. Tsoi, V. I. Shnyrkov +1 more

Oleg V. Snigirev

Boris Chesca

At a time when the supremacy of SQUIDs as the most sensitive magnetometers is being challenged by the recent progress of optically pumped atomic magnetometers operating at room temperature, looking into new opportunities to further improve SQUIDs sensitivity would probably be most welcomed by the SQUID community. By far the most promising such opportunity is to operate a double (D) rf SQUID (an rf-SQUID in which a dc-SQUID is used instead of a single Josephson junction) in a non-adiabatic regime at frequencies of about a few GHz. At these relatively high frequencies required to assure an ultra-high SQUID sensitivity the SQUID-design complexity and the cost of the electronics involved (current generator and SQUID amplifier) are still kept at reasonable levels. The advantages of using this concept, as presented in my contribution in more detail now, are overwhelming. Ironically, although this idea in its preliminary shape has been around for some time now [1], the opportunity has never been explored experimentally! I am just wondering what else needs to be done to get this message across the SQUID community and have this concept finally tested experimentally?

Helen Prance

In this paper we consider new and remarkable dynamical behavior displayed by a strongly hysteretic SQUID (Superconducting QUantum Interference device)-a single Josephson weak link enclosed by a thick superconducting ring inductively coupled to a radio frequency (rf) parallel LC tank circuit resonator. Experimentally, we show that in the strongly hysteretic regime this coupled system can display remarkable level structure in its dynamics, quite different to that normally associated with rf driven SQUID ring systems. We demonstrate theoretically that this level structure arises when the SQUID ring responds non-adiabatically to time dependent changes in its potential, i.e. so that the ring no longer stays at or very close to the minimum in this potential as it changes in time.

L. D. Jackel, Robert A. Buhrman

Robert M. Weisskoff, Gregory P. Lafyatis, Kevin Robert Boyce +3 more

We have designed and constructed a novel superconducting detector sensitive enough to detect the axial motion of a single, trapped ion. This detector employs a tuned, superconducting transformer matched to a rf SQUID (superconducting quantum interference device) to yield an effective current sensitivity of 2.7×10−15A/(Hz)1/2 at 160 kHz. To optimize the detection system, we have used existing small-signal equivalent circuit models, and thus have tested these models in a new regime. We include details of our superconducting circuitry and of the modifications required to stabilize the commerical SQUID controls at 160 kHz. Finally, we present typical detected signals from trapped ions.