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Identification of quantum resources in thermodynamic systems

Periodic Reporting for period 1 - QQT (Identification of quantum resources in thermodynamic systems)

Reporting period: 2018-04-03 to 2020-04-02

The QQT project mainly lies in the field of quantum thermodynamics, which investigates the laws governing engines, refrigerators and other machines at the smallest possible scale. The project had three main overlapping objectives, reported here with their corresponding context:

Context 1: there is urgent need to connect different approaches into a coherent framework to avoid the risk of fragmentation and inward focus of the sub-communities into excessively specialised problems.

Obj. 1: Add realistic experimental constraints to the abstract quantum information approach to thermodynamics and clarify the relation between the disparate frameworks existing within the field.

Context 2: Many results in the field are essentially semiclassical, hence unable to capture strong quantum features.

Obj. 2: Investigate extreme quantum regimes by singling out quantum effects and devising new thermodynamics protocols and experimental proposals.

Context 3: Essentially no result exists able to certify that a quantum machine cannot be emulated by classical means, a necessary milestone towards proving their conjectured superiority over classical machines.

Obj. 3: Provide tools to assess the presence of true quantum signatures in a thermodynamic engine.

The action broadly met its stated objectives and paves to exciting developments in the field of quantum thermodynamics and beyond.
In summary, this action has contributed to the creation of new general tools that allow to analyse quantum thermodynamics protocols independently of the specific setup and yet able to include relevant practical constraints. It contributed to the development of a common language within a previously fragmented community, by
1. publications bridging the gap between disparate subfields [1,2] and
2. writing comprehensive reviews for the broad community [3,4].

These works, also thanks to the useful feedback of several members of the community, have contributed to the creation of a common ground in the field of quantum thermodynamics. These considerations also led to a general framework to understand the role of memory as a thermodynamic resource [2].

The action also put forward new experimental proposals for the technologically relevant problem of cooling [1,5] by devising new optimal heat-bath algorithmic cooling schemes. This is a class of cooling protocols that have been investigated for many years, and our twist has been to show that control over the interaction with the environment leads to strong improvements over the best known schemes. We also advanced the understanding of experimentally relevant thermodynamic constraints by investigating quantum thermodynamics and specifically cooling in Gaussian quantum systems, one of the most readily available and widespread quantum physics platforms.

Furthermore, we clarified the role of quantum effects in thermodynamics [2,6,8] by exploring limitations and opportunities of exploiting two resources in a thermodynamic setting: superposition and entanglement. We also presented a new framework to understand quantum heat and work fluctuations [7] and provided tools to certify quantum signatures in thermal machines against classical emulations [9]. The latter is a necessary milestone towards proving the conjectured superiority of thermal machines over their classical counterpart.

In the attempt to solve thermodynamic problems, this action sparked to advances in various other areas. In particular we clarified a long-standing debate on the status of a class of quantum measurements known as weak measurements [10]; we identified a quantum advantage in an important primitive known as “cloning” [11] and we identified new quantum advantages in the simulation of classical processes [2].

2.1 Dissemination
All these results were disseminated in seminar and talks in prestigious physics departments all over the world. I presented the results of this action in Bilbao (conference Quantum Speed Limits and Thermodynamics 2019), ICTQ (University of Gdansk), QuTech (Fault-tolerant Quantum Computing group, TU Delft), CWI (Amsterdam), USI (Cryptography and Quantum information group, Lugano), University of Milan (12th Italian Quantum Information Conference), GIQ group (Universitat Autonoma de Barcelona), Centre for Engineered Quantum Systems (University of Sydney), Istituto Nazionale Ricerca Metrologica (Turin), Institute for Quantum Optics and Quantum Information (Vienna), Kavli Institute for Theoretical Physics (Quantum Thermodynamics conference, University of California, Santa Barbara), Perimeter Institute for Theoretical Physics. The results appeared in top level journals, including Physical Review Letters (2), Quantum (2), Rep. Prog. Phys., PRR, PRA, with more under review.
Beyond the main results and their consequences discussed above, the project had other impacts.

3.2 Teaching, outreach, career

In January 2020 I taught a course on Quantum Mechanics (30 hours + exercise sessions) at the African Institute for Mathematical Sciences in Limbe, Cameroon. It has been a wonderful personal experience as well as a great opportunity to learn important teaching skills. As described in the technical report, this is potentially the start of a longer term collaboration strengthening science programs in developing countries [12].

For the whole period of the project I co-supervised the PhD student Chung-Yun Hsieh. Two of the projects we worked on together resulted in a publication and we are keeping in contact for the continuation of his PhD.

In the summer of 2019 I mentored 3 first-year undergraduate students from the ACER program for an intensive one week school on quantum theory, quantum computation and nonlocality.

I gave a series of Theory Lectures at ICFO Barcelona (8-29 May 2018), introducing the resource theory framework to quantum thermodynamics to students and researchers of the institute. This led to an introductory review to the quantum information framework to thermodynamics for students and scientists working on different approaches to quantum thermodynamics. There I presented scope, motivation and core assumptions of the theory in a pedagogical manner. I also discussed the relation with complementary approaches, as per objective 1. This work appeared on Reports on Progress in Physics [4] and is freely available on the arXiv.

The action gave me the opportunity of building up an international network of collaborations and develop into a fully independent researcher.

3.1 Broader societal implications

The core applications and their potential relevance for the broader society are the following:

A) The identification of true quantum effects in thermodynamic machines is a necessary step towards showing their conjectured technological advantage over classical machines.
B) Since cooling is a necessary prerequisite in most quantum computing platforms, devising new protocols can contribute to the development of quantum technologies, whose potential impact on the wider society is well-known.

The extent of the impact on the wider society beyond fundamental science are directly connected to the future technological impact of the whole field of quantum thermodynamics. At the present stage, that prospect is still uncertain.
I have already discussed the opportunity the action gave me to join the lecturing program and mentoring students at AIMS-Cameroon.