Regularized dynamical decoupling noise spectroscopy - a decoherence descriptor for radicals in glassy matrices

Area of Science:

• Quantum Information Science
• Materials Science
• Spectroscopy

Background:

• Decoherence in quantum systems originates from fluctuating spin environments, characterized by their noise spectrum S(ω).
• Dynamical decoupling (DD) uses nπ pulses to extend dephasing times by attenuating S(ω) via its filter function.
• Current DD noise spectroscopy (DDNS) reconstructs S(ω) but is limited to systems with long dephasing times or many pulses.

Purpose of the Study:

• To introduce regularized DDNS to overcome limitations of standard DDNS.
• To infer the noise spectrum S(ω) from DD traces of paramagnetic centers in various matrices.
• To characterize spin dynamics and decoherence descriptors in glassy and liquid matrices.

Main Methods:

• Development and application of regularized DDNS for noise spectrum reconstruction.
• Recording DD traces for paramagnetic centers (nitroxide radicals) in glassy o-terphenyl and water-glycerol matrices with n ≤ 5 pulses.
• Utilizing deuteration to distinguish matrix- and spin center-induced spectral features at low temperatures.

Main Results:

• Regularized DDNS successfully infers S(ω) from DD traces, extending applicability beyond traditional limits.
• Identified matrix-specific cut-off frequencies characterizing nuclear spin diffusion, driven by methyl group rotational tunneling.
• Observed classical methyl group reorientation dominating S(ω) at elevated temperatures, revealing distinct dynamic processes.

Conclusions:

• Regularized DDNS provides a powerful method to visualize and quantify spin environment variations.
• The study elucidates the role of molecular dynamics (rotational tunneling, reorientation) in spin decoherence.
• S(ω) serves as a crucial descriptor for understanding and quantifying electron spin couplings and underlying spin dynamics.