Long Coherence Times in Nuclear Spin-Free Vanadyl Qubits

Area of Science:

• Quantum information science
• Molecular quantum computing
• Materials science for quantum technologies

Background:

• Quantum information processing (QIP) requires robust qubits with long coherence times (T2) and spin-lattice relaxation times (T1).
• Vanadium-based complexes have shown promise as molecular qubits, with previous work achieving millisecond T2 times in tris(dithiolene) complexes.
• Integrating long T2 with surface compatibility is crucial for practical QIP applications.

Purpose of the Study:

• To investigate vanadyl complexes as potential molecular qubits, combining surface compatibility with long coherence times.
• To explore the impact of ligand design and solute-solvent interactions on qubit performance (T1 and T2).
• To establish new design principles for enhancing T1 and T2 in molecular qubits.

Main Methods:

• Synthesis and characterization of four novel vanadyl complexes: (Ph4P)2[VO(C8S8)2] (1), (Ph4P)2[VO(β-C3S5)2] (2), (Ph4P)2[VO(α-C3S5)2] (3), and (Ph4P)2[VO(C3S4O)2] (4).
• Pulsed electron paramagnetic resonance (EPR) spectroscopy was used to measure T1 and T2 values.
• Comparison of vanadyl complex performance with previously reported vanadium tris(dithiolene) complexes in SO2 solvent.

Main Results:

• Vanadyl complexes 1-4 in SO2 exhibited T2 values up to 152(6) μs, comparable to leading molecular qubit candidates.
• A significant, order-of-magnitude increase in T1 was observed for vanadyl species compared to tris(dithiolene) analogues, attributed to enhanced solute-solvent interactions.
• A slight decrease in T2 for vanadyl complexes was noted, attributed to the reduced shielding from solvent nuclear spins due to ligand modification.

Conclusions:

• Vanadyl complexes represent promising candidates for molecular qubits, offering long T1 times due to strong solute-solvent interactions.
• Ligand design plays a critical role in tuning both T1 and T2, balancing solute-solvent interactions with shielding effects.
• These findings provide valuable insights for designing next-generation molecular qubits with optimized coherence and relaxation properties for QIP.