A key foundational work during the initial 30 months of MSpin is the successful establishment of an experimental platform tailored for the optical and microwave manipulation of single organic molecules under cryogenic conditions. This platform integrates a narrow-linewidth laser with a helium-free cryostat and on-chip microwave circuitries to achieve high-resolution optical microscopy and spectroscopy parallel to microwave spin driving. Using this setup, we have achieved the detection and spectral characterization of individual perylene molecules, which is a key step for upcoming spin-resolved optical studies.
Based on this platform, the spectroscopic properties of perylene molecules doped in anthracene crystals have been systematically studied with a focus on their emission and absorption properties related to both singlet and triplet electronic manifolds. An optical spectrometer has been designed and constructed. The spectrometer is tailored for time-resolved spectral measurement of photons emitted from the metastable triplet states.
On the spin-manipulation side, on-chip microwave resonators which are compatible with cryogenic operation have been developed and microfabricated. These circuits are currently used to perform optically detected magnetic resonance (ODMR) measurements, where microwave transitions within the triplet sublevels of perylene molecules are driven. The ODMR measurements are performed with lock-in detection of optical signals to improve the signal-to-noise ratio.
An unforeseen challenge encountered during this starting phase relates to the purity of the host material. Perylene molecules emit in the blue wavelength region, where typical impurities in anthracene also exhibit strong absorption. This spectral overlap introduces fluorescence background and deteriorates the signal-to-noise ratio and poses obstacle for high-fidelity single-molecule detection and spin readout.
To address this, we have undertaken a focused effort on the purification of the anthracene host. After an evaluation of different purification techniques, zone refinement was identified as the most suitable method for our application. We have therefore designed and constructed a custom zone refiner, optimized for the purification of small quantities (on the order of milligrams) of organic materials. Preliminary test results indicated significant improvements in the optical quality of the host material.
Parallel to the optical and spin characterization, we have also started initial efforts in the design of monolithic Fabry-Perot optical resonators suitable for integration into the closed-cycle cryogenic platform. The fabrication of micromirrors is being planned.
Moreover, an article elaborating on the potential of single-molecule host-guest platforms for quantum technologies, with a focus on spin and phonon degrees of freedom has been published in open-access format in Physics Review Research [Gurlek and Wang, Phys. Rev. Research 7, 021001 (2025)].
