Through these experiments, SpinScreen found out that the tiny size of the hybrid island favours electron bonding. The bonding depends on how strongly the electrons repel each other in the island. If the repulsion is strong, an individual electron can exist in the island besides the Cooper pairs, while if it is weak, only Cooper pairs can. Bonding occurs when the electron repulsion is sufficiently strong.
Next, SpinScreen investigated devices in which one quantum dot is coupled to two small hybrid islands. In this case, the electron in the quantum dot finds itself in an astounding dilemma. With which electron to bond, that of island #1 or that of island #2? The experiments in SpinScreen show that the electron resides in a state of quantum superposition where it bonds at the same time with the electrons in island #1 and island #2. The total spin is however not zero, in contrast to the single island case. This is an over-screened quantum state.
The experiments in SpinScreen went further, though. With the help of theoreticians for the interpretation of the data, it was found out that a new type of quantum states had been discovered. It turns out that in a superconducting island there are two forbidden energy gaps. The first one is the superconducting gap, formed by the pairing of electrons into Cooper pairs. The second one is a Coulombic gap, due to the electric (also called Coulomb) repulsion between electrons when the superconductor is made tiny as in an island. The result of this second gap is that the quantum states are no longer electron-hole symmetric, in contrast to purely superconducting quantum states. Electron-hole symmetry means that removing an electron from a superconductor costs the same energy as adding it. Superconducting Coulombic quantum states (this is the name created for these states in the project) emerge when the quantum dot is filled with even numbers of electrons. This was an unsuspected situation, with no parallel in large superconductors, and exceeded the original objective of SpinScreen.
These results were disseminated to the specialized physics community through one manuscript which has been submitted for peer-review. An additional manuscript is in preparation with the results on the two-island devices. The results were also presented in 7 international scientific conferences, 2 international workshops and 1 invited seminar at the University of Cincinnati.
The following outreach activities took place: 1) Project communications through SpinScreen’s twitter account (
https://twitter.com/SpinScreen(se abrirá en una nueva ventana)). 2) The Fellow narrated his experience as a MSCA Fellow to potential Latin American applicants at an Euraxess-LAC webinar (
https://www.youtube.com/watch?v=-Rii_Oep03s&t=1115s(se abrirá en una nueva ventana)). 3) The Fellow produced a short film showing the activities at the host laboratory, the Center for Quantum Devices (
https://video.ku.dk/video/69812637/labtour-at-center-for-quantum(se abrirá en una nueva ventana)). 4) The Fellow was panellist at the International Conference of Physics Students 2021 to answer questions from the students about the activities at the Center for Quantum Devices.
An objective of the MSCA Individual Fellowships is to train the Fellow. To aid the academic career of the Fellow, the Fellow took courses of Introduction of University Pedagogy and PhD student supervision. To advance his teaching skills, the Fellow also taught courses to MSc students on electronic quantum transport at the Niels Bohr Institute. In addition, the Fellow co-supervised four MSc students and one PhD student in their scientific projects. The projects have resulted in 2 publications, 1 manuscript submitted for peer-review, and 2 more manuscripts in preparation. These publications are/will be co-authored by the Fellow. At the end of the fellowship, the Fellow was promoted by the Niels Bohr Institute to the rank of Assistant Professor.
