ThErmAl Probes Of fractional quantum hall Transport

Project Information

TEAPOT

Grant agreement ID: 101031655

DOI

10.3030/101031655

Project closed

EC signature date 19 March 2021

Start date 1 January 2022

End date 15 February 2024

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 203 852,16

EU contribution

€ 203 852,16

Coordinated by

CHALMERS TEKNISKA HOGSKOLA AB
Sweden

Periodic Reporting for period 1 - TEAPOT (ThErmAl Probes Of fractional quantum hall Transport)

Reporting period: 2022-01-01 to 2023-12-31

Summary of the context and overall objectives of the project

In a strong magnetic field and at extremely low temperatures, a two-dimensional sheet of electrons can transition into a strongly correlated state: the fractional quantum Hall (FQH) state. The one-dimensional edge of such a sheet is by itself a viable experimental platform for controlled studies of a wide range of quantum phenomena. In particular, recent experimental developments have enabled detailed thermal transport experiments for probing the properties of such FQH edges. Despite this progress, many pressing questions on edge energy propagation, equilibration, and redistribution have remained unanswered.

The purpose of the TEAPOT project was to theoretically address these and related questions by introducing new observables - heat noise, mixed noise, and delta-T noise for FQH edges. The main goal was to use these promising quantities as novel and complementary tools for probing emergent transport phenomena, not directly or not uniquely related to the electrical charge. To this end, TEAPOT sought to provide theoretical descriptions of the interrelated edge propagation of charge noise, heat noise, delta-T noise, and mixed noise. As a result, TEAPOT has opened up for novel types of FQH experiments, which have improved the fundamental understanding of strongly correlated quantum behaviour on the nanoscale. While primarily of fundamental interest, the acquired knowledge about strongly correlated quantum phenomena paves the way for developing future quantum technologies, e.g. small-scale thermodynamical or quantum computational applications.

TEAPOT concluded that complementary thermal probes, such as delta-T noise, heat noise, and thermal conductance, indeed provide several advantages over the conventionally used charge-based shot noise for probing fractional quantum Hall edge states as well as related, strongly correlated quantum systems.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main observable in focus of TEAPOT was delta-T noise, which is the excess electrical noise in response to only a temperature gradient and in the absence of a voltage bias. TEAPOT has provided comprehensive theoretical models for such noise in: (a) Systems comprised of weak tunneling links bridging one-dimensional, strongly correlated conductors [Physical Review B 105 195423 (2022)] (b) Non-interacting, two-terminal conductors [Phys. Rev. B 107, 075409 (2023)] and (c) Non-Abelian fractional quantum Hall states [Phys. Rev. B 107, 245301 (2023)].

TEAPOT also produced theory for temperature and equilibration-dependent thermal conductance for Abelian hole-conjugate [Nat Commun 13, 5185 (2022)] and non-Abelian [Phys. Rev. B 107, 245301 (2023)] fractional quantum Hall states, as well as for detecting the so-called quantum Hall binding transitions [Phys. Rev. B 107, 245301 (2023)]. Regarding heat noise, only theory for non-interacting conductors had been reported [Phys. Rev. B 107, 075409 (2023)] by the end of the project. Nonetheless, one project on heat noise in quantum Hall quantum point contact devices and one project on heat noise along edge states coupled to an Ohmic contact are currently in progress. The mixed noise observable was early in the project judged to be much less interesting than delta-T and heat noises since the mixed noise was found to vanish in many setups in the fractional quantum Hall regime. The mixed noise was therefore not in focus during TEAPOT and the utility of mixed noise remains an open question.

TEAPOT also provided theory for charge noise generation due to equilibration between edge states and bulk magnons in a quantum Hall ferromagnet [arXiv: 2310.08703]. Finally, a theoretical proposal to experimentally distinguish non-Abelian candidates for the fractional quantum Hall state at filling 5/2 was also developed [arXiv: 2402.02157]. This theory exploited the interplay of thermal equilibration and noise generation on conductance plateaus in a quantum point contact device to single out the so-called anti-Pfaffian candidate state. Distinguishing between non-Abelian candidate states at filling 5/2 is an outstanding problem in condensed matter physics, and TEAPOT provided a clear possibility for progress in this matter.

Apart from the scientific journal publications highlighted above, TEAPOT’s results were also disseminated as oral presentations and posters at conferences and seminars. A notable venue was an invited talk at the specialized conference “Quantum Hall edge: New results and old questions” in 2023 in Villard de Lans, Grenoble, 2023.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The results from TEAPOT go beyond state-of-the-art by providing theory that describe novel types of experiments to probe fractional quantum Hall edges and related strongly correlated quantum systems. A particularly important result of TEAPOT was that delta-T noise and heat noise provide access to excitations’ scaling dimensions, which under certain strict conditions, are further related to the excitations’ quantum exchange statistics. Due to this result, TEAPOT will impact the growing field of detecting anyons in the fractional quantum Hall effect, where pin-pointing scaling dimensions is a pressing problem to correctly infer anyonic statistics in various fractional quantum Hall states.

TEAPOT’s socio-economic impact and wider societal implications are expected to be long-term: While TEAPOT’s main contribution was to produce fundamental knowledge of low-dimensional quantum phenomena, this knowledge is paramount for developing novel quantum technologies, which in turn are expected to transform society in the coming decades.

Delta-T noise in tunneling between strongly correlated 1D systems