Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Controlling Thermal and Particle Currents by Quantum Observation

12.07.2017

Researchers from the Theory Department of the MPSD have realized the control of thermal and electrical currents in nanoscale devices by means of quantum local observations.

Measurement plays a fundamental role in quantum mechanics. At the same time, it also constitutes one of the main problems regarding the interpretation of this whole field. The best-known illustration of the principles of superposition and entanglement is Schrödinger’s cat. Not being visible from the outside, the cat resides in a coherent superposition of two states: it is alive and dead at the same time.


Artistic illustration of the role of a quantum observer in a nanodevice

© K. Aranburu

By means of a measurement, this superposition collapses to a concrete state: the cat is now either dead or alive. In this famous thought experiment a measurement of the “quantum cat” can be seen as an interaction with a macroscopic object collapsing the superposition onto a concrete state by destroying its coherence.

In their new article published in Nature PJ Quantum Materials, researchers from the MPSD (Max Planck Institute for the Structure and Dynamics of Matter) at CFEL (Center for Free-Electron Laser Science) in Hamburg together with collaborators from the University of the Basque Country (UPV/EHU) in San Sebastian and the Bremen Center for Computational Materials Science (BCCMS) discovered how a microscopic quantum observer is able to control thermal and electrical currents in nanoscale devices. Local quantum observation of a system can induce continuous and dynamic changes in its quantum coherence, which allows better control of particle and energy currents in nanoscale systems.

Classical non-equilibrium thermodynamics was developed to understand the flow of particles and energy between multiple heat and particle reservoirs. The best-known example is Clausius’ formulation of the second law of thermodynamics stating that when two objects with different temperatures are brought in contact, heat will exclusively flow from the hotter to the colder one.

In macroscopic objects, the observation of this process does not influence the flow of energy and particles between them. However, in quantum devices, thermodynamical concepts need to be revisited. When a classical observer measures a quantum system, this interaction destroys most of the coherence inside the system and alters its dynamical response.

Instead, if a quantum observer acts only locally, the system quantum coherence changes continuously and dynamically, thus providing another level of control of its properties. Depending on how strong and where these local quantum observations are performed, novel and surprising quantum transport phenomena arise.

The group of Prof.Dr. Angel Rubio at the Theory Department of the MPSD along with their colleagues have demonstrated how the concept of quantum measurements can offer novel possibilities for a thermodynamical control of quantum transport (heat and particle). This concept offers possibilities far beyond the ones obtained using standard classical thermal reservoirs.

The scientists studied this idea in a theoretical quantum ratchet. Within this system, the left and right side are connected to hot and cold thermal baths, respectively. This configuration forces the energy to flow from hot to cold and the particles to flow clockwise inside the ratchet. The introduction of a quantum observer, however, inverts the particle ring-current against the natural direction of the ratchet - a phenomenon caused by the localized electronic state and the disruption of the system’s symmetry.

Furthermore, the quantum observation is also able to invert the direction of the heat flow, contradicting the second law of thermodynamics. “Such heat and particle current control might open the door for different strategies to design quantum transport devices with directionality control of the injection of currents. There could be applications in thermoelectricity, spintronics, photonics, and sensing, among others. These results have been an important contribution to my PhD thesis.” says Robert Biele, first author of the paper.

From a more fundamental point of view this work highlights the role of a quantum observer: In contrast to Schrödinger’s cat, where the coherent state is destroyed via the interaction with a macroscopic “observer”, here by introducing a local quantum observer, the coherence is changed locally and dynamically, allowing to tune between the coherent states of the system. “This shows how thermodynamics is very different in the quantum regime. Schrödinger’s cat paradox leads to new thermodynamic forces never seen before,” adds César A. Rodríguez Rosario.

In the near future, the researchers will apply this concept to control spins for applications in spin injection and novel magnetic memories. Angel Rubio suggests that “The quantum observer - besides controlling the particle and energy transfer at the nanoscale - could also observe spins, select individual components, and give rise to spin-polarized currents without spin-orbit coupling. Observation could be used to write a magnetic memory.”

This work was carried out in a collaboration of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg with the NanoBio Spectroscopy Group at the University of the Basque Country in San Sebastian (UPV/EHU) and the Bremen Center for Computational Materials Science (BCCMS). It was funded by the European Research Council Advanced Grant “Qspec-Newmat”, Grupos Consolidados del Gobierno Vasco and the Marie Skłodowska-Curie Actions – Individual Fellowships.

Contacts: Dr. César Alberto Rodriguez Rosario, Postdoc, Telephone: +49 (0)40 8998-6643 cesar-a.rodriguez-rosario@mpsd.mpg.de

Prof. Dr. Angel Rubio, Managing Director MPSD: Telephone: +49 (0)40 8998-6550 angel.rubio@mpsd.mpg.de

Full picture caption: "Artistic illustration of the role of a quantum observer in a nanodevice: When observing only the right part of the figure (covering the left part with the hand the water appears to flow down the channel, instead, by looking at the whole painting the water actually flows uphill. This apparent paradox mimics the coherent superposition of two quantum states (water flowing up and down). By observing at specific parts of our system we are able to tune between these two states and hence change the ‘physical response of the nanodevice’ in a controlled way."

Weitere Informationen:

https://www.nature.com/articles/s41535-017-0043-6 (original publication)
http://www.mpsd.mpg.de/419754/2017-07-THERMOELECTRICS_Observe_control (MPSD-web site)

Jenny Witt | Max-Planck-Institut für Struktur und Dynamik der Materie

More articles from Physics and Astronomy:

nachricht Artificial agent designs quantum experiments
19.01.2018 | Universität Innsbruck

nachricht Only an atom thick: Physicists succeed in measuring mechanical properties of 2D monolayer materials
17.01.2018 | Universität des Saarlandes

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

More genes are active in high-performance maize

19.01.2018 | Life Sciences

How plants see light

19.01.2018 | Life Sciences

Artificial agent designs quantum experiments

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>