Exploiting Atomic Control to Show When Atoms Become Molecules

Abstract Precision‐placed atom qubits in silicon offer a unique means to confine electrons and control their spins with extreme accuracy, which can be leveraged to construct powerful quantum computers. To date atom qubits in silicon have been successfully realized using electrons hosted either on a single phosphorus atom or on a multi‐donor quantum dot. Here, a novel molecular regime is explored in which electrons are bound to two donor dots separated by ≈8 nm in a natural silicon substrate. The molecular state, provided by these spatially separated donors, is used to study with exquisite precision the impact of confinement potential on the electronic and spin properties of qubits. Unique spin filling measurements, performed on up to five electrons, confirm how electrons are shared between both sites of the molecule, forming hybridized molecular states. The precise atomic locations of the donor atoms in the silicon lattice are determined by combining the experimental electron spin resonance spectra and the state‐of‐the‐art atomistic modeling of multi‐electron wave‐functions in presence of realistic electric fields. The donor molecule studied in this work exhibits excellent qubit properties and addresses the impact that the confinement potential has, at the atomic scale, on the desired properties of electron spin qubits.