Scanning SQUID-on-tip nanomagnetometry and nanothermometry of quantum systems
Energy dissipation is a fundamental process governing the dynamics of physical systems. In condensed matter physics, in particular, scattering mechanisms, loss of quantum information, or breakdown of topological protection are deeply rooted in the intricate details of how and where the dissipation occurs. Despite its vital importance, direct imaging of dissipation in quantum systems is currently impossible because the existing thermal imaging methods lack the necessary sensitivity and are unsuitable for low temperature operation.
We developed a scanning nanoSQUID with sub 50 nm diameter that resides at the apex of a sharp pipette  that can act simultaneously as nanomagnetometer with single spin sensitivity and as nanothermometer providing cryogenic thermal imaging with four orders of magnitude improved thermal sensitivity of below 1 µK/Hz1/2 . The non-contact non-invasive thermometry allows thermal imaging of very low nanoscale energy dissipation down to the fundamental Landauer limit of 40 fW for continuous readout of a single qubit at 1 GHz at 4.2 K. These advances enable observation of changes in dissipation due to single electron charging of individual quantum dots in carbon nanotubes. Our thermal imaging study of hBN encapsulated graphene reveals a fascinating dissipation mechanism due to resonant localized states at the edges of graphene providing the first visualization of inelastic electron scattering mechanism on the nanoscale, opening the door to direct imaging of microscopic dissipation processes in quantum matter.
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