Molecule-based coherent light-spin interfaces for quantum information processing -- optical spin state polarization in a binuclear Europium complex

TL;DR

This study demonstrates that a binuclear Europium complex can be used as a molecular optical spin interface, showing narrow spectral holes and long-lived spin polarization, advancing quantum information processing with REI molecules.

Contribution

It provides the first evidence that REI molecules can serve as coherent light-spin interfaces, with measurable spectral and spin properties suitable for quantum applications.

Findings

Narrow spectral holes with linewidth 22 MHz in Eu(III) complex

Homogeneous linewidth corresponds to T2 of 14.5 ns at 1.4 K

Long-lived spectral holes enable efficient nuclear spin polarization

Abstract

The success of the emerging field of solid-state optical quantum information processing (QIP) critically depends on the access to resonant optical materials. Rare-earth ions (REIs) are suitable candidates for QIP protocols due to their extraordinary photo-physical and magnetic quantum properties such as long optical and spin coherence lifetimes ($T_2$). However, molecules incorporating REIs, despite having advantageous properties such as atomically exact quantum tunability, inherent scalability, and large portability, have not yet been studied for QIP applications. As a first testimony of the usefulness of REI molecules for optical QIP applications, we demonstrate in this study that narrow spectral holes can be burned in the inhomogeneously broadened $^5$D$_0\to^7$F$_0$ optical transition of a binuclear Eu(III) complex, rendering a homogeneous linewidth ($\Gamma_h$) = 22 $\pm$ 1 MHz, which translates as $T_2 = 14.5$ $\pm$ 0.7 ns at 1.4 K. Moreover, long-lived spectral holes are observed, demonstrating efficient polarization of Eu(III) ground state nuclear spins, a fundamental requirement for all-optical spin initialization and addressing. These results elucidate the usefulness of REI-based molecular complexes as versatile coherent light-spin interfaces for applications in quantum communications and processing.