Tunable Cr⁴⁺ Molecular Color Centers

Area of Science:

• Quantum Information Science
• Materials Chemistry
• Molecular Engineering

Background:

• Synthetic chemistry offers precise control over molecular structures for quantum technologies.
• Optically addressable molecular qubits are essential for quantum sensing, networking, and computing.
• Tuning paramagnetic molecular qubits with optical-spin initialization and readout is a key challenge.

Purpose of the Study:

• To demonstrate the translation of electronic structures enabling optical-spin initialization and readout from Cr(aryl)4 to Cr(alkyl)4 compounds.
• To investigate the impact of ligand fields on ground and excited state properties of chromium-based molecular qubits.
• To lay the groundwork for designing structurally precise, optically addressable molecular qubits.

Main Methods:

• Synthesis and characterization of Cr(aryl)4 and Cr(alkyl)4 compounds.
• Electronic absorption and emission spectroscopy to confirm electronic structures and photoluminescence.
• Coherent spin manipulation studies at X-band microwave frequencies.
• Theoretical calculations to elucidate bonding interactions and electronic structures.

Main Results:

• Successful translation of optical-spin initialization and readout capabilities from aryl to alkyl chromium complexes.
• Small ground state zero-field splitting (<5 GHz) in Cr(alkyl)4 compounds (4-6) enabling coherent spin manipulation.
• Observation of photoluminescence in the 897-923 nm range for Cr(alkyl)4 compounds.
• Theoretical insights into the varied bonding interactions influenced by ligand fields.

Conclusions:

• The ligand field significantly impacts both ground state spin structure and excited state manifold in Cr(IV) compounds.
• Cr(alkyl)4 compounds are promising candidates for molecular qubits with optical addressability.
• This study provides a foundation for the rational design of bespoke molecular qubits.