A modular design of molecular qubits to implement universal quantum gates

The physical implementation of quantum information processing relies on individual modules - qubits - and operations that modify such modules either individually or in groups - quantum gates. Two examples of gates that entangle pairs of qubits are the controlled NOT-gate (CNOT) gate, which flips the state of one qubit depending on the state of another, and the √iSWAP gate that brings a two-qubit product state into a superposition involving partially swapping the qubit states. Here we show that through supramolecular chemistry a single simple module, molecular Cr7 Ni rings, which act as the qubits, can be assembled into structures suitable for either the CNOT or √iSWAP gate by choice of linker, and we characterize these structures by electron spin resonance spectroscopy. We introduce two schemes for implementing such gates with these supramolecular assemblies and perform detailed simulations, based on the measured parameters including decoherence, to demonstrate how the gates would operate.