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John O | July 2017

Researchers control thermal and electric currents in nanoscale devices


researchers from the max planck institute for the structure and dynamics of matter (mpsd) and the center for free-electron laser science (cfel), both in hamburg, germany, have demonstrated that using a microscopic quantum observer can control thermal and electrical currents in nanoscale devices, according to an article on the mpsd website.

 


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.
(k. aranburu)

 

the article explained, “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.”

 

in studying thermal interactions at the quantum scale, researchers discovered that a classical observer would impact the way the system functioned. “when a classical observer measures a quantum system, this interaction destroys most of the coherence inside the system and alters its dynamical response,” the article said.

 

a quantum observer, which works on a local scale, provides a level of control in the dynamics of the system and can impart new properties on the nanoscale device.

 

“the scientists studied this idea in a theoretical quantum ratchet,” the article continued. “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.”

 

the quantum observer could also invert the direction of heat flow, which goes against the laws of thermodynamics. this could impact applications ranging from thermoelectricity to spintronics to photonics and more.

 

the article noted, “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.”

 

the research was recently published in quantum materials. the abstract read:

 

“we demonstrate that in a standard thermo-electric nanodevice the current and heat flows are not only dictated by the temperature and potential gradient, but also by the external action of a local quantum observer that controls the coherence of the device. depending on how and where the observation takes place, the direction of heat and particle currents can be independently controlled.

 

“in fact, we show that the current and heat flow in a quantum material can go against the natural temperature and voltage gradients. dynamical quantum observation offers new possibilities for the control of quantum transport far beyond classical thermal reservoirs.

 

“through the concept of local projections, we illustrate how we can create and directionality control the injection of currents (electronic and heat) in nanodevices. this scheme provides novel strategies to construct quantum devices with application in thermoelectrics, spintronic injection, phononics, and sensing among others.

 

“in particular, highly efficient and selective spin injection might be achieved by local spin projection techniques.”

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