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Home > Press > Quantum engine operating at maximum power: A new experimental proof-of-concept quantum Otto cycle, using nuclear spins, has reached an efficiency close to its thermodynamic limit at maximum power

Abstract:
The so-called quantum technology relies on microscopic devices that obey the laws of quantum mechanics. But how much power will this new type of devices need in practice? How much heat will be produced? How to operate in the optimal condition dissipating minimum energy? These questions have just starting to be answered through a link between quantum information and the out-of-equilibrium thermodynamics of mesoscopic systems, besides new proof-of-principle experiments.

Quantum engine operating at maximum power: A new experimental proof-of-concept quantum Otto cycle, using nuclear spins, has reached an efficiency close to its thermodynamic limit at maximum power

Santo Amdre, Brazil | Posted on December 20th, 2019

Similar questions abounded during the Industrial Revolution, in the nineteenth century. Scientists of the epoch realized that both heat and the ability of machines to perform work are different forms of the same physical quantity, energy. When investigating the conversion of one form of energy into another, they discovered the laws of classical thermodynamics that have a profound impact in the industry and transformed completely modern society.

The theoretical concept of a quantum heat engine was first introduced sixty years ago, when Scovil and Schulz-DuBois at Bell Labs (USA), make an analogy between three-level masers and thermal machines. Since then many proposals for thermodynamic cycles at the quantum scale have appeared in scientific journals and only very recently experiments started to be performed.

In the quantum scenario, energy fluctuations play an important role. The measurement of such fluctuations in quantum devices is challenging in many aspects. Now the experimental implementation of a quantum Otto cycle was reported in Physical Review Letters by an international research team involving experts from Federal University of ABC (Brazil), Brazilian Center for Physics Research (Brazil), University of Waterloo (Canada), and Singapore University of Technology and Design (Singapore). The scientist scrutinized all energy fluctuations in work and heat, besides the irreversibility at the quantum scale. Such a tiny engine was made of nuclear spins in a molecule that absorbs and release energy from radio waves.

“Fast operation of this molecular machine produces transitions between the spin energy states, which are related to what scientists in the area call ‘quantum friction’ that reduces performance. This kind of friction is also associated with an increase in entropy. On the other hand, a very slow operation (that decreases quantum friction) will not deliver a considerable amount of extracted power”, as pointed out by John Peterson from the University of Waterloo. So, the best scenario is to conciliate some amount of power with low levels of quantum friction or entropy production, in a similar way of what modern engineering does in cars engines. In the new reported experiment, the tiny spin engine reaches an efficiency close to its thermodynamic limit at maximum power, which is much better than what car engines can do nowadays. “The quantum spin engine would not be very useful in practice since the work produced would supply a very small amount of energy to radio waves. It would only be sufficient to alter another nuclear spin. The research team is more interested in measuring how much energy it uses, how much heat it dissipates, and how much entropy is produced during operation. Another goal is to learn, in real experiments, how to optimize the operation of small quantum thermal machines and eventually build better quantum refrigerators to applications in quantum technology” explain Roberto Serra from the Federal University of ABC. The technique applied in this experiment has great potential for further developments in the emerging quantum thermodynamics.

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About Federal University of ABC
Federal University of ABC (UFABC, Brazil) was born in 2006 rooted in an innovative interdisciplinary pedagogical plan. It has no departments, fostering interaction between academic members from different backgrounds. Moreover, undergraduate freshmen are admitted into Interdisciplinary Bachelor’s Degrees, in Science and Technology (BC&T) and Science and Humanities (BC&H). At the core of the interdisciplinary experiences, students can enjoy the flexibility and freedom to build their academic pathways throughout the programs offered by the university, thus behaving as entrepreneurs of their own careers. Our main goal is to enhance independent thinking and risk-taking.

For more information, please click here

Contacts:
Roberto Serra
Federal University of ABC

Copyright © Federal University of ABC

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Full details are reported in J. P. S. Peterson, T. B. Batalhão, M. Herrera, A. M. Souza, R. S. Sarthour, I. S. Oliveira, and R. M. Serra, “Experimental Characterization of a Spin Quantum Heat Engine”, Phys. Rev. Lett. 123, 240601 (2019), that can be read at:

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