Coupling of external electromagnetic fields to supercurrents: From SQUID to SQIF

Evgeni V. Il’ichev, Hans E. Hoenig, H.‐G. Meyer +5 more

D. Rogula, M. Sztyren

Rosanna Migliore, ANTONINO MESSINA

The dynamical behavior of a superconducting quantum interference device (an rf-SQUID) irradiated by a single-mode quantized electromagnetic field is theoretically investigated. Treating the SQUID as a flux qubit, we analyze the dynamics of the combined system within the low-lying energy Hilbert subspace both in the asymmetric and in the symmetric SQUID potential configurations. We show that the temporal evolution of the system is dominated by an oscillatory behavior characterized by more than one, generally speaking, incommensurable Rabi frequencies whose expressions are explicitly given. We find that the external parameters may be fixed in such a way to realize a control on the dynamical replay of the total system which, for instance, may be forced to exhibit a periodic evolution accompanied by the occurrence of an oscillatory disappearance of entanglement between the two subsystems. We demonstrate the possibility of generating quantum maximally entangled superpositions of the two macroscopically distinguishable states describing clockwise and counterclockwise supercurrents in the loop. The experimental feasibility of our proposal is briefly discussed.

T. M. Klapwijk, D. R. Heslinga, Wim M. van Huffelen

Le‐Man Kuang, Yiwen Wang, Mo‐Lin Ge

Dynamic evolution of a mesoscopic Josephson junction (MJJ) interacting with quantized electromagnetic fields (QEMF) is investigated. It is shown that the current-voltage steps of the MJJ can reflect quantum coherences of the external QEMF; these characteristics may be used to distinguish different types of quantum electromagnetic fields. It is found that supercurrent fluctuations exhibit periodic oscillations in the time evolution. Supercurrent correlation functions are also studied in some detail. It is shown that the thermal noise in the external electromagnetic field seriously affects the second-order correlation function of the supercurrent. \textcopyright{} 1996 The American Physical Society.

F. Couëdo, Eliana Recoba Pawlowski, Julien Kermorvant +8 more

We have fabricated arrays of High-Tc Superconducting Quantum Interference Devices (SQUIDs) with randomly distributed loop sizes as sensitive detectors for Radio Frequency (RF) waves. These subwavelength size devices known as Superconducting Quantum Interference Filters (SQIFs) detect the magnetic component of the electromagnetic field. We used a scalable ion irradiation technique to pattern the circuits and engineer the Josephson junctions needed to make SQUIDs. Here, we report on a 300 SQUID series array with the loop area ranging from 6 to 60 μm2, folded in a meander line covering a 3.5 mm × 120 μm substrate area, made out of a 150 nm thick YBa2Cu3O7 film. Operating at a temperature of T = 66 K in an unshielded magnetic environment under low DC bias current (I = 60 μA) and a DC magnetic field (B = 3 μT), this SQIF can detect a magnetic field of a few picoteslas at a frequency of 1.125 GHz, which corresponds to a sensitivity of a few hundreds of fT/Hz and shows a linear response over 7 decades in RF power. This work is a promising approach for the realization of low dissipative subwavelength gigahertz magnetometers.