Theoretical Prediction Contributes to New Technique for Probing Nano-Electronic Systems

A recently published scientific study reports on a new technique for probing nano-electronic systems that could be used to design better quantum devices and quantum bits. The research paper, published Jan. 14 in Nature Nanotechnology, was co-authored by Aashish Clerk, professor in molecular engineering at the Institute for Molecular Engineering at the University of Chicago.

The study began when researchers at the Weizmann Institute of Science in Israel contacted Clerk to test a theory he developed in 2011 with graduate students Jamie Gardner and Steven Bennett. Clerk’s group hypothesized that mechanical motion could be used to closely study the "quantum tunneling" of electrons in a nano-electronic system.

Clerk was looking for a way to probe nano-scale electronic systems and states without having to pass an electrical current through them, then the most common way to study these systems. Using a current can be problematic because many interesting and important states don’t carry a current, or are so small and inaccessible that it is not feasible to make a current measurement. Using motion, they theorized, could be a viable alternative.

“Our theory described how quantum-mechanical tunneling of just a single electron could have noticeable effects on the vibrations of a mechanical object,” Clerk said. Tunneling could change the frequency and quality of the vibrations, giving a way to sensitively probe this process. 

The experiments, which took place at the Weizmann Institute, used a double quantum dot formed in a carbon nanotube. The double quantum dot can be thought of as a box for electrons, where there is a barrier separating the left and right halves of the box. A single electron can be trapped in this structure, on either the left or right. However, it can quantum-mechanically "tunnel" through the barrier to the other side.

Clerk’s co-authors, Ilya Khivrich and Shahal Ilani from the Weizmann Institute, implemented a setup and measurement protocol that made it possible to directly measure how tunneling changes the vibrations of the carbon nanotube. This allowed them to directly measure the effects predicted in Clerk’s theory. 

The implications of this research could prove far-reaching. The technique introduced in the study could be a powerful way to probe more complex types of quantum electronic devices and states—those in which it’s difficult to measure currents directly. This is exciting for scientists because it means it may be possible to characterize new types of quantum bits, or qubits, as well as design better quantum devices.

“The new states that can be probed are of fundamental interest as they may reveal new physical phenomena, and they could also form the basis of new quantum devices.” Clerk said.

Citation: “Nanomechanical pump–probe measurements of insulating electronic states in a carbon nanotube,” Ilya Khivrich, Aashish A. Clerk, and Shahal Ilani. Nature Nanotechnology, January 14, 2019. doi: 10.1038/s41565-018-0341-6

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