In the proposed experiment, two energy reservoirs (S and D) made of trapped ions transport energy quanta to each other by coupling to the spins in a quantum magnet placed between them. Credit: Alejandro Bermudez and Tobias Schaetz, New Journal of Physics. CC-BY-3.0
The first method to control transport of energy at the level of single energy quanta (which are mostly phonons) has been proposed. It’s theoretically possible to control the flow of single energy quanta through a quantum magnet using lasers with carefully controlled frequencies and intensities. If implemented, the method could allow researchers to explore quantum energy transport phenomena that are expected to be completely different than what is observed in macroscopic energy transport. In general, understanding energy transport in small-scale devices could lead to the development of methods for reducing the energy dissipation in shrinking computer hardware (however, researchers note hardware differs from the particular setup proposed here).
Bermudez said: “This mechanism can be considered as an analogue of Coulomb blockade in electronic nanodevices, and we have proposed to test it using experiments with crystals of self-assembled trapped atomic ions.” In the study, the scientists propose building an energy reservoir using trapped magnesium ions. By using a laser to heat and cool the ions, the ions can be made to absorb or release tiny amounts of energy, acting as tiny energy reservoirs.
Then to transport the energy, researchers propose placing a synthetic quantum magnet which consists of a long line of magnetic spins that form a chain between two energy reservoirs. When the reservoirs are coupled to the spins in the magnet, they can exchange energy with each other in the form of single phonons. In this way, quantum-scale energy transport occurs across the spin chain. The scientists explain that energy transport at the quantum level can be thought of as analogous to charge (electron) transport at the quantum level, which has already been well-documented. Just as single-electron transport is very different than bulk electron transport, quantum energy transport is expected to be very different than energy transport on a large scale.
Energy transport in quantum magnets: biased source/drain reservoirs represented by a macroscopic number of harmonic oscillators in a thermal state with temperatures T T S D > , such that an energy current through a quantum magnet is established. The quantum magnet is depicted as a chain of interacting spins that can exchange energy with the reservoirs, such that transport occurs longitudinally along the chain (a), or transversely across it (b)
One particular phenomenon associated with single-electron transport, which is not observed at larger scales, is called the Coulomb-blockade effect. In nanoscale electronic devices, electrons must gain a certain level of charging energy in order to tunnel across a barrier. When one electron manages to gain this energy and tunnel, it blocks the simultaneous tunneling of other electrons because additional electrons would require additional energy. The resulting blockade effect violates Ohm’s law of charge transport, and results in only 1 electron tunneling at a time.
In the new study, the physicists theoretically demonstrated that an analogous Coulomb-blockade effect occurs with nanoscale heat transport, which again does not appear at larger scales.
The scientists derived a quantum master equation for the transport of energy that shows that there is a “transport window” that defines the energy level needed for energy quanta to travel through a quantum magnet. Similar to the situation with electrons, energy transport is blockaded when the energy quanta do not have sufficient energy. This effect, which the researchers call the Ising blockade effect, violates Fourier’s law of heat conduction and results in the transport of only one energy quanta at a time.
If the proposed experiment can be realized, they expect to observe the Ising blockade effect along with many other interesting quantum effects in energy transport that so far have been restricted to electronic currents. At this stage, it’s difficult to tell what applications quantum energy transport may have.
“If the same effect can be shown to be more general, and applicable to other physical setups, it may yield unexpected applications similar to single-electron electronics in Coulomb-blockaded devices,” Bermudez said.
One of the biggest challenges to realizing the experiment will be to design a device that can directly measure such tiny amounts of heat energy. “We are considering exploring this type of physics in the laboratory of my coauthor, Professor Schätz, at the University of Freiburg,” Bermudez said. “Although the experimental requirements to implement the proposed scheme are stringent, Professor Schätz leads a world-class team of fantastic researchers with the required technology to face this challenge.”
http://iopscience.iop.org/article/10.1088/1367-2630/18/8/083006/pdf http://phys.org/news/2016-08-physicists-method-quanta-energy.htmljCp
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