Nickel(II) Metal Complexes as Optically Addressable Qubit Candidates.

Area of Science:

• Quantum Information Science
• Synthetic Chemistry
• Materials Science

Background:

• Quantum information science relies on qubits, with a need for optically readable spin states in tunable molecular systems.
• Current quantum sensing applications could be transformed by molecular systems offering optical spin readout, similar to defect-based systems.

Purpose of the Study:

• To explore nickel(II) ions in octahedral symmetry as potential candidates for optical spin readout in qubits.
• To synthesize and characterize nickel(II) complexes suitable for electron paramagnetic resonance (EPR) and optical addressability.

Main Methods:

• Identification and synthesis of two highly symmetric Ni(II) complexes: [Ni(phen)3](BF4)2 (1) and [Ni(pyr3)2](BF4)2 (2).
• Characterization using pulse EPR to determine axial zero-field splitting parameters (D).
• Spectroscopic analysis to confirm emission properties for optical readout.

Main Results:

• Two Ni(II) compounds with weak zero-field splitting (D = +0.9 cm⁻¹ for 1, D = +2.7 cm⁻¹ for 2) were identified, enabling EPR addressability.
• Both compounds exhibit emission in the near-infrared region (λmax = 938–944 nm), crucial for optical readout.
• Strong field ligands were confirmed, facilitating optical addressability.

Conclusions:

• Nickel(II)-based compounds are introduced as a new class of qubit materials.
• These findings provide a pathway for developing molecular systems with optical spin readout for quantum sensing and information processing.