The stationary nano-SQUID

By Tom Sharp on June 28, 2017

This week, we take a look at a recent letter published in Journal of Physics: Condensed Matter by Jorge Berger of ORT Braude College, with his fascinating take on measuring magnetic signatures. Read on to find out more from Jorge himself:

Can we measure the magnetic signature of a state without altering that state?

The most accurate available instrument for the measurement of magnetic signatures is the SQUID (Superconducting Quantum Interference Device). The primary reason for worrying about its back action is the heat that it dissipates when it assumes a resistive state. Clever techniques have been devised to diminish this source of back action.

Eventually, the ultimate source of back action from a SQUID in the resistive state could be the electromagnetic radiation that it emits. This radiation is due to oscillations of the electric field in the superconducting wire. Oscillations arise because there is a different electric potential at each electrode, leading to different evolutions of the phases of the wave function at each electrode and thus creating gradients that periodically force interruption of superconductivity at some point in the wire.

Oscillations can be avoided in circuits with sufficiently small perimeter, provided that at least one of the electrodes is in the normal state. In this case the superconducting order parameter vanishes at the electrode and its phase becomes irrelevant. This is the situation proposed in figure 1.

Figure 1: The proposed circuit. Blue is substrate, white (SC) is superconducting, and brown (N) is normal metal. ɸ is the measured flux. There is no tunnel junction between the circuit and the normal electrode. Adapted from J. Phys.: Condens. Matter 29 (2017) 29LT01 © Jorge Braude 2017.

Electromagnetic radiation is not the largest source of back action encountered in present uses of nano-SQUIDs. A more immediate appealing feature of the proposed circuit is the absence of miniature parts in comparison to the whole of it, such as Josephson junctions, thus facilitating fabrication of nanoscale devices.

About the Author

If we reach an unexpected conclusion, should we be worried? Most probably yes, because this usually indicates that we have made a mistake. But if you are as optimistic as the author, you would prefer to see in this conclusion the potential for a discovery.

One of the favorite publications by the author is an essay entitled The fight against the second law of thermodynamics. He co-edited a book entitled Connectivity and Superconductivity and wrote a textbook in Mechanics.

At present, the author is the head of the Department of Physics and Optical Engineering at ORT Braude College, whose faculty appear in the picture. It is the only institution in Israel with a study program that leads to a BSc in Optical Engineering. You can see who is who by clicking here.