Encoding quantum information in the degrees of freedom of molecules opens a new avenue for quantum technologies. Starting from the simpler diatomic molecules and advancing to the more complex polyatomic molecules, we are interested in studying the coherence properties of these MoleQubits (molecular qubits). We hope that these studies will shed light on fundamental questions regarding the interface between quantum and classical descriptions of our world.
We will explore new types of quantum superpositions in molecules not possible with atoms or any other type of quantum hardware. One example is putting a single molecule in a quantum superposition of two distinct total-nuclear-spin states. In other words, we will bring a molecule to a quantum state where it has both hyperfine and no-hyperfine energy levels.
The homonuclear diatomic molecule, 14N2, has rich total-nuclear-spin (TNS) configurations. 14N nuclei have a nuclear spin of 1, thus molecular nitrogen has three configurations of the TNS quantum number, I=0,1,2. The two TNS configurations of orthonitrogen (I=0,2) have a remarkably different spectrum: the I=0 molecule has no hyperfine structure, while in contrast, the I=2 molecule has a rich hyperfine structure. These two TNSs of the same molecule are considered distinct molecules. In a theoretical paper, we have shown that the electric-quadrupole hyperfine interaction leads to the mixing of the two orthonitrogen molecules. By tuning the magnetic field, a Landau-Zenner type avoided crossing of two excited rotational states occur. This mixing of TNS opens the possibility to coherently interconvert molecular nitrogen from one configuration of TNS to another and create a coherent superposition of both TNS configurations (see figure).
This project is funded by the Israel Science Foundation (ISF), grant No. 1010/22.
A molecule that has both hyperfine and no-hyperfine energy levels. This figure is based on our theoretical work in Basel. a) Each of the nuclei of the nitrogen molecule has a spin of 1; thus, the molecule has three configurations of the total-nuclear-spin quantum numbers, I=0,1,2. b) The electric-quadrupole hyperfine interactions create an avoided crossing that mixes the two different total-nuclear-spin molecules at a magnetic field of ~26 Gauss. c) Coherent transitions from a well-defined total-nuclear-spin state through the avoided crossing can interconvert and create superpositions of nitrogen with different total nuclear spins.