Molecular One- and Two-qubit Systems with very Long Coherence Times.

General-purpose quantum computation and quantum simulation require multi-qubit architectures with precisely defined, robust interqubit interactions, coupled with local addressability. This is an unsolved challenge, primarily due to scalability issues. These issues often derive from poor control over interqubit interactions. Molecular systems are promising materials for the realization of large-scale quantum architectures, due to their high degree of positionability and the possibility to precisely tailor interqubit interactions. The simplest quantum architecture is the two-qubit system, with which quantum gate operations can be implemented. To be viable, a two-qubit system must possess long coherence times, the interqubit interaction must be well defined and the two qubits must also be addressable individually within the same quantum manipulation sequence. Here we present results on the investigation of the spin dynamics of chlorinated triphenylmethyl organic radicals, in particular perchlorotriphenylmethyl (PTM) radical, a mono-functionalized PTM and a biradical PTM dimer. We find extraordinarily long ensemble coherence times up to 148 μs at all temperatures below 100 K. We demonstrate two-qubit and, importantly, individual qubit addressability in the biradical system. These results underline the potential of molecular materials for the development of quantum architectures. This article is protected by copyright. All rights reserved.