In order to be able to use a molecule as a qubit, the computing unit of quantum computers, it needs a spin state that lasts long enough for information to be entered and read from outside. And, of course, this spin state must be able to be manipulated from the outside. A research team led by Professor Winfried Plass at the University of Jena has developed a molecule that fulfils this condition.
It is a so-called coordination compound, i.e. it contains organic and metallic components. The organic material forms a framework in which the metal ions arrange themselves in a very specific way. In the case at hand, this is a trinuclear copper complex. The special feature is that the copper ions form an exactly equilateral triangle within the molecule. Only in this way can the electron spins of the three copper centres interact strongly enough with each other for the molecule to develop a spin state that makes it an externally addressable qubit.
“Even though we already knew what our molecule should theoretically look like, the synthesis was quite a big challenge,” says Benjamin Kintzel, one of the researchers in the Jena team. “And it is difficult to predict how such a particle will behave in the crystal. However, with different chemical tools and different fine tunings during the manufacturing process, it has been possible to produce the desired result – it can be addressed, described and read from the outside.
According to theoretical predictions, the molecule offers another elementary advantage over other qubits. Based on the theoretical blueprint of the copper compound, its spin state can be controlled by electric fields at the molecular level. Up to now, magnetic fields have mainly been used here, but they cannot be used to focus on individual molecules, explains Plass. A research group in Oxford, which cooperates with the Jena chemists, is currently investigating this property of the synthesized molecule through various experiments.
The research team at the University of Jena is convinced that its molecule meets the requirements to be used as a qubit. However, it is difficult to predict whether it will actually be used as a computing unit. There is still no ultimate solution as to how molecules can actually be integrated into quantum computers.
They report on their work in the current issue of the research magazine “Chemical Communications”.
More information: https://www.chemgeo.uni-jena.de/en/Institutes.html