Optical Spin Polarization of a Narrow‐Linewidth Electron‐Spin Qubit in a Chromophore/Stable‐Radical System

Abstract

Photoexcited organic chromophores appended to stable radicals can serve as qubit and/or qudit candidates for quantum information applications. 1,6,7,12‐Tetra‐(4‐ tert‐butylphenoxy)‐perylene‐3,4 : 9,10‐bis(dicarboximide) (tpPDI) linked to a partially deuterated α,γ‐bisdiphenylene‐β‐phenylallyl radical (BDPA‐ d ₁₆) was synthesized and characterized by time‐resolved optical and electron paramagnetic resonance (EPR) spectroscopies. Photoexcitation of tpPDI‐BDPA‐ d ₁₆ results in ultrafast radical‐enhanced intersystem crossing to produce a quartet state ( Q) followed by formation of a spin‐polarized doublet ground state ( D ₀). Pulse‐EPR experiments confirmed the spin multiplicity of Q and yielded coherence times of T _m=2.1±0.1 μs and 2.8±0.2 μs for Q and D ₀, respectively. BDPA‐ d ₁₆ eliminates the dominant ¹H hyperfine couplings, resulting in a single narrow line for both the Q and D ₀ states, which enhances the spectral resolution needed for good qubit addressability.

Abstract

A promising approach to molecular qubits employs a photoexcited chromophore covalently linked to a deuterated stable radical (C−R⋅). Photoexcitation of the C within C−R⋅ results in ultrafast intersystem crossing to produce the spin‐polarized quartet state ( Q) that decays to the spin‐polarized ground state ( D ₀ ). Both Q and D ₀ have narrow linewidths that allow facile addressability using microwave pulses.