Using Near-Flat-Band Electrons for Read-Out of Molecular Spin Qubit Entangled States

While molecular spin qubits (MSQs) are a promising platform for quantum computing, read-out has been largely limited to electron paramagnetic resonance, which is often slow and requires a global system drive. Moreover, because one prerequisite for the Elzerman and Pauli spin blockade read-out mechanisms typical of semiconductor spin qubits is tunneling of electrons between sites, these read-out modalities are unavailable in MSQs. Here, we theoretically demonstrate electrical read-out of entangled MSQs via driven many-electron spin-unpolarized currents. In particular, using a time-dependent density matrix renormalization group approach, we simulate a maximally entangled MSQ pair between two electronic leads. Driving itinerant electrons between the two leads, we find that the conductance is greater when the MSQs are in the entangled singlet state compared to the entangled triplet state. This contrast in conductance is enhanced when the electronic density of states at the Fermi energy is large and for a narrow bandwidth. Our results are readily applicable to molecules supramolecularly functionalizing semiconductors with relatively flat bands, such as single-wall carbon nanotubes under a magnetic field.