Molecular Spins for Quantum Technology

Project Information

MSpin

Grant agreement ID: 101077866

DOI

10.3030/101077866

EC signature date 16 February 2023

Start date 1 May 2023

End date 30 April 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 893 184,00

EU contribution

€ 1 893 184,00

Coordinated by

RHEINISCHE FRIEDRICH-WILHELMS-UNIVERSITAT BONN
Germany

Periodic Reporting for period 1 - MSpin (Molecular Spins for Quantum Technology)

Reporting period: 2023-05-01 to 2025-10-31

Summary of the context and overall objectives of the project

Spin defects in solids provide promising qubits for quantum information processing and quantum networks. However, the lack of elementary system homogeneity in the material and qubit decoherence impede the fabrication of a real-scale quantum network. Funded by the European Research Council, the MSpin project will tackle these challenges by exploiting the potential of molecules. Project researchers will develop methods to control individual nuclear spins housed in a single molecule, and demonstrate molecule-based quantum registers. Supported by organic chemistry approaches, such molecular registers can be produced at a large scale. The ultimate goal is to demonstrate – for the first time – an efficient molecular quantum network node.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

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)].

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The ability to perform spectroscopy on the triplet state with time resolution in the nanosecond scale and single photon sensitivity can be viewed as an advance beyond state-of-the-art. While fluorescence detection on molecular host-guest systems is a well-established routine, detecting emission from meta-stable triplet state has remained a challenge, as phosphorescence is known to be 10-6 to10-9 times weaker than fluorescence signal. The home-built spectrometer is tailored for isolating such small signals in both frequency and time domain, and pushes the limit for weak signal detection from quantum emitters.
A second advance beyond state-of-the-art is the prospects of single molecule host guest systems for quantum technology applications discussed in the publication [Gurlek and Wang, Phys. Rev. Research 7, 021001 (2025)]. There, we have gone beyond traditional research lines on single molecules, and discussed the prospects of using spins and phonons in the system as quantum resources, while these degrees of freedom have been considered detrimental to the optical properties of single molecules before.