Enhancing spin coherence in optically addressable molecular qubits through host-matrix engineering*

Molecular ‘color centers’ seek to combine key features of solid-state color centers–e.g., an optically addressable ground-state spin–with a versatile molecular architecture [1]. The modularity of molecular systems means these color centers can be ported across different environments e.g., host matrices, and engineering this environment enables qubit properties to be tuned. Here we demonstrate such environmental control with chromium(IV)-based molecular spins. Inserting these molecular color centers into a non-isostructural host matrix significantly enhances their spin coherence compared to using an isostructural host. This behavior results from the environment-induced breaking of the qubit’s symmetry, which generates a significant transverse zero-field splitting, creating transitions which are insensitive to magnetic-field noise. We model this behavior from first principles using cluster-correlation expansion methods, and further experimentally demonstrate enhanced optical contrast and spin-lattice relaxation times for host-matrix engineered molecular color centers. These results highlight the portability and environmental tunability of molecular color centers, indicating their promise for applications in quantum information science.

[1] Bayliss*, Laorenza* et al. Science 370, 1309 (2020)