Quantum information science (QIS) has many types of qubits to choose from, including superconducting and trapped-ion qubits, all with their advantages and disadvantages. Although less developed than some of the other qubit platforms, molecules and molecular systems can serve as spin-qubit arrays with distinct benefits. For example, molecular synthesis can create qubits at atomically precise locations; tailor the qubits’ magnetic, optical, and electronic properties; and construct large ordered qubit arrays through self-assembly and other strategies.1
Experiments from the mid 1970s showed that when light triggers electron transfer between molecules, the electrons and the electron vacancies they leave behind—known as holes—can form entangled spin states. The presence of those spin pairs is clear from time-resolved electron paramagnetic resonance (TREPR) spectroscopy, which measures the absorption or emission of gigahertz radiation as a function of an applied magnetic field—in effect, the method probes the magnetic interactions between the electron spins. Important early...
