Nanoscale thermal imaging of dissipation in quantum systems

A cryogenic thermal imaging technique that uses a superconducting quantum interference device fabricated on the tip of a sharp pipette can be used to image the thermal signature of extremely low power nanometre-scale dissipation processes. The details of how and where energy is dissipated are fundamental to the microscopic behaviour of quantum systems. Dorri Halbertal et al. have developed a cryogenic thermal imaging technique that promises to help to elucidate these details. The key component of their method is a superconducting quantum interference device mounted on the tip of a sharp pipette, which they show can be used to image the thermal signature of extremely low-energy nanoscale dissipation processes. The potential of the system is demonstrated in preliminary studies of systems including nanotubes and grapheme; future investigations will target more exotic states of matter, such as those associated with quantum Hall systems. Energy dissipation is a fundamental process governing the dynamics of physical, chemical and biological systems. It is also one of the main characteristics that distinguish quantum from classical phenomena. In particular, in condensed matter physics, 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. Yet the microscopic behaviour of a system is usually not formulated in terms of dissipation because energy dissipation is not a readily measurable quantity on the micrometre scale. Although nanoscale thermometry has gained much recent interest1,2,3,4,5,6,7,8,9,10,11,12,13,14,15, existing thermal imaging methods are not sensitive enough for the study of quantum systems and are also unsuitable for the low-temperature operation that is required. Here we report a nano-thermometer based on a superconducting quantum interference device with a diameter of less than 50 nanometres that resides at the apex of a sharp pipette: it provides scanning cryogenic thermal sensing that is four orders of magnitude more sensitive than previous devices—below 1 μK Hz−1/2. This non-contact, non-invasive thermometry allows thermal imaging of very low intensity, nanoscale energy dissipation down to the fundamental Landauer limit16,17,18 of 40 femtowatts for continuous readout of a single qubit at one gigahertz at 4.2 kelvin. These advances enable the observation of changes in dissipation due to single-electron charging of individual quantum dots in carbon nanotubes. They also reveal a dissipation mechanism attributable to resonant localized states in graphene encapsulated within hexagonal boron nitride, opening the door to direct thermal imaging of nanoscale dissipation processes in quantum matter.