Experimental Search for Quantum Advantages in Thermodynamics

Project Information

ESQuAT

Grant agreement ID: 101041744

DOI

10.3030/101041744

EC signature date 4 October 2022

Start date 1 January 2023

End date 31 December 2027

Funded under

• European Research Council (ERC)

Total cost

€ 2 124 089,00

EU contribution

€ 2 124 089,00

Coordinated by

CHALMERS TEKNISKA HOGSKOLA AB
Sweden

Periodic Reporting for period 1 - ESQuAT (Experimental Search for Quantum Advantages in Thermodynamics)

Reporting period: 2023-01-01 to 2025-06-30

Summary of the context and overall objectives of the project

The rapid technological progress of the last decades challenges long-standing concepts in thermodynamics. A central question has emerged: *can uniquely quantum mechanical resources provide tangible advantages in thermodynamic processes?* Theory suggests they might — enabling more powerful engines, faster-charging batteries, and reduced energy waste — yet experimental progress remains limited by the absence of comprehensive testbeds for quantum thermal machines.

**ESQuAT** aims to deliver the most ambitious and systematic experimental search for quantum advantages in thermodynamics to date. The project leverages **circuit quantum electrodynamics (cQED)**, augmented with a novel concept: the **engineered physical bath**. This broadband bath features an Ohmic spectral density, can be populated with arbitrary distributions, and couples to quantum thermal machines with tunable strength. Crucially, it allows spectrally resolved detection of heat flows deep in the quantum regime.

On this foundation, the project will realize three pioneering **quantum refrigerators**, each designed to isolate the role of a distinct quantum resource: (i) quantum coherence, (ii) measurement backaction, and (iii) collective effects. By systematically exploring an unprecedented parameter space and benchmarking against classical counterparts, ESQuAT will directly test recent theoretical frameworks in quantum thermodynamics.

The expected breakthroughs are twofold:

1. **Unambiguous experimental signatures of nonclassical behaviour in thermodynamic observables.**
2. **Quantitative determination of genuine quantum advantages** in the operation of thermal machines.

By providing both conceptual insights and a robust experimental platform, ESQuAT will set a new standard for the field, significantly advancing our understanding of quantum thermodynamics and its potential for future energy technologies.

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

During the reporting period, ESQuAT has successfully established a new experimental platform for quantum thermodynamics based on superconducting circuits coupled to engineered physical heat baths. The main achievements include:

Implementation of engineered physical baths: A broadband, tunable microwave environment combining thermal noise with quantum vacuum fluctuations. This setup was integrated into multiple devices and validated as a robust testbed for quantum thermal machines.

First demonstration of a useful autonomous quantum thermal machine: In Nature Physics (2025), we reported a quantum absorption refrigerator that autonomously resets a superconducting qubit. The device achieves ground-state preparation at a record effective temperature of 22 mK, demonstrating practical relevance for quantum information processing.

Noise-powered quantum refrigerator: In a second experiment (arXiv:2403.03373 under review at Nature Communications), we realized a Brownian-type refrigerator driven by controlled dephasing noise. The system can function as a refrigerator, heat engine, or thermal accelerator, and achieves a coefficient of performance close to the Carnot limit.

Ultra-sensitive heat current detection: We developed a methodology to measure photonic heat currents at sub-attowatt resolution, opening the path to fluctuation studies and higher-order thermodynamic statistics.

New directions: Building on these results, we are extending capabilities to measure heat current fluctuations (in connection with the thermodynamic uncertainty relation) and developing a microwave photodetector based on our device architecture. Both innovations will expand the experimental reach of ESQuAT and the broader community.

Together, these advances demonstrate the viability of superconducting circuits as a versatile platform for exploring quantum thermodynamics and provide the first systematic tests of autonomous quantum machines performing useful tasks.

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)

ESQuAT significantly advances the frontier of quantum thermodynamics. Prior to this project, experimental work was limited to proof-of-concept demonstrations with narrow scope. ESQuAT has gone beyond this state of the art by:

Establishing engineered physical baths that enable spectrally resolved and tunable coupling of quantum thermal machines to their environments.

Demonstrating the first autonomous quantum refrigerator with real-world utility: qubit reset at unprecedentedly low temperatures, relevant for scalable quantum computing.

Realizing the first Brownian quantum refrigerator, powered by noise-assisted transport, and showing multimode operation (engine, accelerator, refrigerator) within the same device.

Achieving record precision in photonic heat current measurements at sub-attowatt scales, enabling access to fluctuations and higher-order moments for the first time.

These results set a new experimental standard and open pathways for unambiguous observation of quantum advantages in thermodynamic observables. They also highlight the potential of quantum thermodynamics to contribute to the second quantum revolution, in analogy with how classical thermodynamics underpinned the industrial revolution.

Future uptake will benefit from further development of specialized tools (e.g. microwave photodetectors), collaborations across quantum technology initiatives, and continued theoretical–experimental integration. In the longer term, such results could inform quantum-enhanced energy technologies, including low-dissipation devices, efficient cooling protocols, and fast quantum batteries.