Ultrafast, all-optical coherence of molecular electron spins in room-temperature, aqueous solution

TL;DR

This paper demonstrates ultrafast optical detection of electron spin coherence in molecules at room temperature, significantly advancing the temporal resolution and revealing new regimes of molecular quantum coherence.

Contribution

It introduces a pump-probe polarization spectroscopy method for detecting molecular electron spin coherence with femtosecond resolution at room temperature.

Findings

Detection of few-picosecond free induction decay in aqueous molecules.

Viscosity significantly affects decoherence lifetimes.

Achieved up to five orders of magnitude improvement in experimental time resolution.

Abstract

The tunability and spatial precision of paramagnetic molecules makes them attractive for quantum sensing. However, usual microwave-based detection methods have poor temporal and spatial resolution, and optical methods compatible with room-temperature solutions have remained elusive. Here, we utilize pump-probe polarization spectroscopy to initialize and track electron spin coherence in a molecule. Designed to efficiently couple spins to light, aqueous $K_{2}IrCl_{6}$ enables detection of few-picosecond free induction decay at room temperature and micromolar concentrations. Viscosity is found to strongly vary decoherence lifetimes. This work redefines the meaning of room-temperature coherence by improving experimental time resolution by up to five orders of magnitude. Doing so unveils a new regime of electron spin coherence, opening the door to new synthetic design and applications of molecular quantum bits.