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Nanobridge SQUIDs as multilevel memory elements

Date: 2023-12-13
Time: 10:30
Venue: MA505
Speaker: Prof. Joris Van de Vondel

KU Leuven





Multilevel memory systems are technologically appealing, for instance, due to an increase in storage density. In past years, alternative non-semiconducting materials were proposed as non-volatile multilevel memories in photonic and antiferromagnetic systems. With the development of novel computing schemes working at cryogenic temperatures, superconducting memory elements have become essential. In this context, superconducting quantum interference devices (SQUIDs) are promising candidates, as they may trap different discrete amounts of magnetic flux. This implies that information can be stored in the SQUID’s different vorticity states. Indeed, flux based qubits and memory elements relying on phase-slip physics have already been proposed [1, 2]. In addition, a yTron current combiner can be used for non-destructive current readout and is capable of differentiating between discrete magnetic flux values trapped in superconducting loops[3].

For a fully superconducting device, we previously demonstrated that the kinetic induction of the junctions may be tuned via nanofabrication, allowing control over the Ic(B) characteristics of the device [4]. We have demonstrated that a field-assisted writing scheme allows such a device to operate as a multilevel memory by the readout of eight distinct vorticity states at zero magnetic field [5, 6]. We present an alternative mechanism based on single phase slips which allows to switch the vorticity state while preserving superconductivity. This mechanism provides a possibly deterministic channel for flux control in SQUID-based memories, under the condition that the field-dependent energy of different vorticity states are nearby.

1. E. Ilin et al., Appl. Phys. Lett. 118, 112603 (2021)

2. N. Ligato et al., Nat Commun. 12, 5200 (2021)

3. A. N. McCaughan et al., Nano Lett. 16, 7626 (2016)

4. H. Dausy et al., Phys. Rev. Appl. 16, 024013 (2021)

5. L. Nulens, et al, Phys. Rev. B 106, 134518 (2022)

6. D.A.D. Chaves et al., Phys. Rev. Appl. 19, 034091 (2023)


Joris Van de Vondel (JVdV) obtained his PhD degree from KU Leuven in 2007 in the group of Prof. Moshchalkov, who is a pioneer in the investigation of superconductivity at the nanoscale.  In 2010, he moved to the group of Prof. S.O. Valenzuela (Universitat Autonoma de Barcelona) to work on spin transport in graphene-based structures. In this group, he initiated research on graphene-based spintronics and obtained the first results on the fabrication and characterization of high quality non-local spin valves.  At the end of 2011, he obtained a tenure track position at the KUL, which gave him the opportunity to start his own research group.  His research group (team of 7 PhD students) established an in-depth expertise regarding nanofabrication and a variety of low-temperature measurements.

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