Nanoscale thermal imaging of dissipation in quantum systems

Abstract: Energy dissipation is a fundamental process governing the dynamics of physical, chemical, and biological systems. It is also one of the main characteristics distinguishing quantum and classical phenomena. 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 the microscopic behavior of a system is usually not formulated in terms of dissipation because the latter is not a readily measureable quantity on the microscale. Although nanoscale thermometry is gaining much recent interest, the existing thermal imaging methods lack the necessary sensitivity and are unsuitable for low temperature operation required for study of quantum systems. Here we report a superconducting quantum interference nano-thermometer device with sub 50 nm diameter that resides at the apex of a sharp pipette and provides scanning cryogenic thermal sensing with four orders of magnitude improved thermal sensitivity of below 1 {\mu}K/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 dissipation due to single electron charging of individual quantum dots in carbon nanotubes and reveal a novel dissipation mechanism due to resonant localized states in hBN encapsulated graphene, opening the door to direct imaging of nanoscale dissipation processes in quantum matter.

Nanoscale Thermal Imaging of Dissipation in Quantum Systems

The research presented in the paper focuses on developing and utilizing a superconducting quantum interference device (SQUID) based thermometer with an exceptionally small diameter of under 50 nm positioned at the apex of a sharp pipette. This SQUID-on-tip (SOT) is employed for nanoscale thermal imaging, providing a breakthrough in thermal sensitivity and spatial resolution, which enables novel insights into energy dissipation mechanisms within quantum systems. Notably, the device exhibits four orders of magnitude better thermal sensitivity compared to existing methods, detecting minute energy dissipations below the Landauer limit of 40 fW, which is relevant for operations such as single-qubit readouts at 4.2 K.

Methodological Advances

The superconducting quantum interference nano-thermometer discussed in this paper is notable for its cryogenic thermal sensing capabilities and sub-50 nm spatial resolution. The notable thermal sensitivity of below 1 µK/Hz^1/2 allows for the detailed examination of energy dissipation at the nanoscale, a crucial factor in understanding both quantum and classical systems. The tSOT's non-invasive thermometry characteristic makes it particularly suitable for imaging delicate quantum states, a domain where traditional thermometry techniques may fail due to their invasiveness or lack of sensitivity.

Key Findings and Implications

The application of the tSOT technique demonstrates significant experimental findings:

1. Carbon Nanotubes and Quantum Dots: Through imaging thermometry, the research reveals dissipation patterns in carbon nanotubes linked to the charging dynamics of quantum dots. This includes resonant effects indicative of single-electron processes. The ability to visualize such processes underscores the tSOT's potential for fault detection and its utility in engineering tasks within nanodevices.

2. Graphene Devices: The paper details observations in hBN-encapsulated graphene where localized resonant states at the graphene edges act as significant centers for energy dissipation. This discovery has profound implications for understanding the thermoelectric properties and electron-phonon interactions in graphene, which could influence the development of graphene-based electronic and optoelectronic devices.

Theoretical and Practical Implications

The implications of these findings are substantial for both theoretical physics and practical applications. The ability to directly observe and measure dissipation processes at such fine scales opens up new avenues for investigating the quantum behaviors of materials and the underlying physics governing dissipation in quantum systems. The exceptional sensitivity of the tSOT could revolutionize the study of thermoelectric phenomena, potentially impacting areas such as quantum computing, where heat dissipation control is crucial.

Future Prospects

The paper suggests further exploration into utilizing the tSOT's scanning gate thermometry capabilities, which may provide additional insights into quantum dot behavior and dissipation mechanisms in other quantum systems. Moreover, the potential to integrate with other quantum systems and expand the operational temperature range opens up possibilities for wider application across various materials and phenomena, including Weyl semimetals and topologically protected surface states. The potential for scanning magnetometry in conjunction with thermal imaging further expands the future scope, ensuring the tool's versatility in exploring new quantum states and pioneering new approaches in heat and energy management at the smallest scales, critical for the ongoing advancement of nanotechnology and quantum information systems.