Manipulation of a Single Spin in a Superconductor

Project MASSS – Marie-Sklodowska Curie Action by Leandro Tosi


Welcome everybody! This is the web page of the Marie-Sklodowska Curie Action that I have been running the last two years in the Quantronics Group. I invite you to read about the project, ask questions if you don't understand something and comment! The heart of the project is explained in the next paragraph and then details can be found in the different sections.


The MASSS project’s goal is to single-out an electronic spin within a superconducting structure and perform the coherent manipulation of this dedree of freedom. As a first step in this direction, we have shown that combining the appropriate ingredients in a hybrid superconducting circuit, electronic states with different spin polarization can be resolved. Most of the information below is about these recent results which show that a spin two-level system is at reach.  


Microwave spectroscopy reveals distinctive fine structure in the absorption spectrum of a superconducting electrical circuit.

Atomic spectra contain fine structure—split spectral lines that arise from the coupling of the spin of the electron with its orbital motion around the nucleus. Here, we show analogous fine structure in the quantized excitation spectrum of a superconducting electrical circuit that includes a semiconducting nanowire with strong spin-orbit coupling. Remarkably, the spin state of a single electron in the nanowire has a measurable impact on the electrical properties of the circuit, which contains over a trillion electrons.

The circuit consists of a submicron indium arsenide (InAs) nanowire enclosed by a superconducting aluminum loop. Discrete localized states, known as "Andreev bound states," form in the nanowire due to coupling to the superconductor. When absorption of a photon induces a transition between two of these states, the loop inductance changes. We have measured the absorption spectrum of the circuit by monitoring the resulting frequency shift of a microwave resonator inductively coupled to the loop. The spectrum shows a fine structure of spin-split Andreev states, well accounted for by a simple model with spin-orbit coupling as the key ingredient.

On the longer term, the challenge will be to manipulate an individual spin in a superconductor—the spin of a single quasiparticle that is physically located at the same place as the many electrons forming the superconducting ground state. Here, we have done the first step: showing that there are spin-resolved states.




Go to the open-access publication: arXiv, PRX


You can check here some pictures that are beyond a scientific explanation!

About Me

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Technical support from P. Sénat is gratefully acknowledged. We thank A. Reynoso for providing us codes related to his work and for useful discussions. We thank P. Orfila and S. Delprat for nanofabrication support. This work has been supported ANR contract JETS, by the Renatech network. and by the Marie Sklodowska-Curie individual fellowship grant 705467.

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