Researchers from the Moscow Institute of Physics and Technology (MIPT), together with their French colleagues, have experimentally shown that if impurities are added to certain semiconductors, the electrons of the impurity atoms will retain the direction of their spin (their own magnetic moment) for a long time (by quantum standards, this is several nanoseconds). Thanks to the long spin coherence time, such atomic systems can be used as qubits in a quantum computer.
In a new study, scientists from the Center for Advanced Methods of Mesophysics and Nanotechnology at MIPT replaced some of the tellurium atoms in molybdenum ditelluride (2H-MoTe2) with bromine atoms and used electron paramagnetic resonance and tunneling scanning microscopy to study the structure of the electrons of the impurity atom and estimate the coherence time of the system.
If a single foreign atom placed in a single crystal leads to the localization of a spin-polarized state, then it can become a qubit. In transition metal dichalcogenides, strong spin-orbit interaction creates just such conditions. The only question is how to work with such qubits, because this is the most atomic scale, about 0.3 nm. In our studies, we added bromine impurities to the molybdenum telluride semiconductor. This impurity has an energy position inside the forbidden zone of the material, that is, its electrons are localized. In this work, we show that the quantum properties of these impurities can be studied; for this, we used the method of measuring electron spin resonance and low-temperature scanning tunneling spectroscopy. We have shown that these atoms have spin-valley states inherited from the material with nanosecond spin coherence times.
Thus, scientists have demonstrated the possibility of using real atoms as qubits and theoretically explained the long coherence time by constructing the electronic structure of the material.
So far, this is a relatively pioneering work, which shows in principle that impurity atoms have signs of long-lived localized electronic states - an atom a la qubit. The message of the work is that it is necessary to further study the possibility of using real atoms in a solid-state matrix to create qubits. We plan to improve the methodology; now my graduate student Valeria Sheina, the first author of the work, is also trying to transfer impurity atoms to an excited state. To do this, we need to introduce a source of high-frequency radiation directly under the needle into the tunneling microscope, which would transfer the qubit from the ground state to the excited state. And this is the next stage. In many ways, its success depends on the choice of material and impurity.