Maxwell's demon in the quantum Zeno regime

March 7, 2018 by Lisa Zyga, feature
maxwells demon
Two reservoirs are connected by a quantum dot. The Maxwell’s demon monitors the quantum dot and adjusts the tunnel barriers, generating a current. Credit: Engelhardt and Schaller. Published in the New Journal of Physics

In the original Maxwell's demon thought experiment, a demon makes continuous measurements on a system of hot and cold reservoirs, building up a thermal gradient that can later be used to perform work. As the demon's measurements do not consume energy, it appears that the demon violates the second law of thermodynamics, although this paradox can be resolved by considering that the demon uses information to perform its sorting tasks.

It's well-known that when a quantum system is continuously measured, it freezes, i.e., it stops changing, which is due to a phenomenon called the quantum Zeno effect. This leads to the question: what might happen when Maxwell's demon enters the quantum Zeno regime? Will the demon's continuous measurements cause the quantum system to freeze and prevent work extraction, or will the demon still be able to influence the system's dynamics?

In a paper published in the New Journal of Physics, physicists Georg Engelhardt and Gernot Schaller at the Technical University of Berlin have theoretically implemented Maxwell's demon in a single-electron transistor in order to investigate the actions of the demon in the quantum Zeno regime.

In their model, the single-electron transistor consists of two electron reservoirs coupled by a quantum dot, with a demon making continuous measurements on the system. The researchers demonstrated that, as predicted by the quantum Zeno effect, the demon's continuous measurements block the flow of current between the two reservoirs. As a result, the demon cannot extract work.

However, the researchers also investigated what happens when the demon's measurements are not quite continuous. They found that there is an optimal measurement rate at which the measurements do not cause the system to freeze, but where a chemical gradient builds up between the two reservoirs and work can be extracted.

"The key significance of our findings is that it is necessary to investigate the transient short-time dynamics of thermoelectric devices, in order to find the optimal performance," Engelhardt told "This could be important for improving nanoscale technological devices."

The physicists explain that this intermediate regime lies between the quantum regime in which genuine quantum effects occur and the classical regime. What's especially attractive about this regime is that, due to the demon's measurements, the total energy of the system decreases so that no external energy needs to be invested to make the demon work.

"Due to the applied non-Markovian method, we have been able to find a working mode of the demon, at which—besides the build-up of the chemical gradient—it also gains work due the measurement," Engelhardt explained.

Going forward, it may be possible to extract work from the chemical gradient and use it, for example, to charge a battery. The researchers plan to address this possibility and others in the future.

"In our future research, we aim to investigate potential applications," Engelhardt said. "Feedback processes are important, for example, in many biological processes. We hope to identify and analyze quantum transport processes from a feedback viewpoint.

"Furthermore, we are interested in of topological band structures. As topological effects strongly rely on coherent dynamics, measurements seem to be an obstacle for feedback control. However, for an appropriate weak measurement, which only partly destroys the coherent state, a feedback manipulation might be reasonable."

Explore further: Maxwell's demon extracts work from quantum measurement

More information: G Engelhardt and G Schaller. "Maxwell's demon in the quantum-Zeno regime and beyond." New Journal of Physics. DOI: 10.1088/1367-2630/aaa38d

Related Stories

Maxwell's demon extracts work from quantum measurement

July 10, 2017

(—Physicists have proposed a new type of Maxwell's demon—the hypothetical agent that extracts work from a system by decreasing the system's entropy—in which the demon can extract work just by making a measurement, ...

Physicists read Maxwell's Demon's mind

July 5, 2017

Pioneering research offers a fascinating view into the inner workings of the mind of 'Maxwell's Demon', a famous thought experiment in physics.

Physicists create first photonic Maxwell's demon

February 12, 2016

(—Maxwell's demon, a hypothetical being that appears to violate the second law of thermodynamics, has been widely studied since it was first proposed in 1867 by James Clerk Maxwell. But most of these studies have ...

Maxwell's demon can use quantum information to generate work

December 18, 2013

( —In theory, Maxwell's demon can decrease the entropy of a system by opening and closing a door at appropriate times to separate hot and cold gas molecules. But as physicist Leó Szilárd pointed out in 1929, ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

Physicists reveal why matter dominates universe

March 21, 2019

Physicists in the College of Arts and Sciences at Syracuse University have confirmed that matter and antimatter decay differently for elementary particles containing charmed quarks.

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

How heavy elements come about in the universe

March 19, 2019

Heavy elements are produced during stellar explosion or on the surfaces of neutron stars through the capture of hydrogen nuclei (protons). This occurs at extremely high temperatures, but at relatively low energies. An international ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Mar 07, 2018
There is no need for the demon to accumulate information. It only needs two simple rules and it can change the entropy, assuming that it does not require any energy to operate.

The rules are:
1) That one side is arbitrarily assigned as the hot side;
2) If a particle approaching the door from the colder side is hotter than a particle approaching from the hot side then allow them to pass.

Information does not have to be stored beyond this.

A second strategy is even simpler. According to Boltzmann, all configurations of the gas are equally probable. Therefore configurations of the gas whereby one side is hotter than the other must occur periodically. The demon only need wait for such a configuration and then close the door. The length of time the demon has to wait is irrelevant as there is no declared limit to the interval of the experiment eg billions of years would be allowable. Measurement of the condition of the gas can be achieved with a bi-metal thermostat.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.