Engineer­ing Covalent Quantum Model Systems

The project is devel­op­ing covalently linked porphyrin spin chains on ultra­thin insula­tors to create designer quantum model systems. Using low-energy electro­spray ion beam deposi­tion (LEIBD), mass-selected metal-tetraphenyl­por­phyrin fragments are selec­tively deposited onto MgO/Ag(100) or NaCl/Au(111) substrates and linked into short 1‑D chains (2–6 units). Using ESR-STM and pulsed ESR techniques (Rabi, Ramsey, Echo), the g‑factor, exchange, and dipole couplings are deter­mined and the spins are coher­ently controlled, creat­ing a versa­tile platform for molec­u­lar quantum simulators.

The project aims to fabri­cate covalently linked porphyrin‑spin chains on ultra­thin insulat­ing films and to employ them as designer quantum‑model systems. Conven­tional on‑surface synthe­sis on Au(111) can produce atomi­cally precise spin lattices, but the strong hybridi­s­a­tion with the metal substrate dramat­i­cally short­ens spin lifetimes. In contrast, thin insulat­ing layers such as MgO/Ag(100) or NaCl/Au(111) decou­ple the spins from the conduc­tive substrate, enabling electron‑spin‑resonance scanning tunnelling microscopy (ESR‑STM) with MHz‑wide linewidths; however, these insula­tors do not support the metal‑catalysed coupling reactions required to build extended struc­tures. The central challenge there­fore is to create chemi­cally defined, covalent spin chains that reside on a decou­pling surface while preserv­ing long coher­ence times.

The integra­tion of mass‑selected ion soft‑landing with ESR‑STM repre­sents a method­olog­i­cal break­through that is not avail­able at any single site today. It provides a modular platform on which arbitrary molec­u­lar build­ing blocks can be arranged with controlled spin coupling, and the approach is readily exten­si­ble to larger biomol­e­cules such as metal­lo­pro­teins. In the long term the project will deliver an open toolbox for the commu­nity, linking funda­men­tal surface physics with quantum‑information and sensing appli­ca­tions and laying the founda­tion for the next gener­a­tion of molec­u­lar quantum simulators.