False-colored electron microscope image of the sample, the green layers are graphene on top of the gray superconductor. The blue metal electrode is used to extract the entangled electrons. Credit: Aalto University
Quantum entanglement is the key to the next generation of computer and communications technology. Aalto researchers can now manufacture it using temperature differences.
A joint team of scientists from Finland, Russia, China and the US has shown that temperature difference can be used to entangle pairs of electrons in superconducting structures. The experimental discovery, published in Nature communication, promises powerful applications in quantum devices, bringing us one step closer to applications of the second quantum revolution.
The team, led by Professor Pertti Hakonen of Aalto University, showed that the thermo-effect offers a new method for producing entangled electrons in a new device. “Quantum entanglement is the cornerstone of the new quantum technologies. However, this concept has surprised many physicists over the years, including Albert Einstein who was very concerned about the ghostly interaction at a distance that it causes, ”says prof. Hakonen.
In quantum calculation, entanglement is used to merge individual quantum systems into one, exponentially increasing their total computational power. “Entanglement can also be used in quantum cryptography, which enables the secure exchange of information over long distances,” explains prof. Gordey Lesovik, of the Moscow Institute of Physics and Technology, who has been a visiting professor at the Aalto University School of Science several times. Given the importance of entanglement for quantum technology, the ability to create entanglement easily and controllably is an important goal for researchers.
The researchers designed a device where a superconductor is layered in layers graphene and metal electrodes. ‘Superconductivity is caused by entangled electron pairs called’ copper pairs’. With the help of a temperature difference, we let them tear, and each electron then moves to different normal metal electrodes, ‘explains doctoral student Nikita Kirsanov from Aalto University. “The resulting electrons remain entangled, even though they are separated over long distances.”
Along with the practical implications, the work has an essential fundamental importance. The experiment showed that the process of Cooper distribution works as a mechanism to change temperature difference in correlated electrical signals in superconducting structures. The developed experimental scheme can also become a platform for original quantum thermodynamic experiments.
Reference: “Thermoelectric current in a graphene Cooper pair splitter” by ZB Tan, A. Laitinen, NS Kirsanov, A. Galda, VM Vinokur, M. Haque, A. Savin, DS Golubev, GB Lesovik and PJ Hakonen, 8 January 2021 , Nature communication.
DOI: 10.1038 / s41467-020-20476-7
The work was carried out using the OtaNano research infrastructure. OtaNano provides modern work environment and equipment for nanoscience and technology and quantum technology research in Finland. OtaNano is managed by Aalto University and VTT, and is available internationally to academic and commercial users. Visit their website for more information. The work was supported by funding from QTF (Academy of Finland CoE). Gordey Lesovik’s visiting professorship funding comes from the Aalto University of Science and Zhenbing Tan’s postdoctoral fellowship comes from the Academy of Finland.