TOpological Spin ChAins by ESR-STM – TOSCA_by_ESR-STM

Topological edge-states, such as the fractional S=1/2 spin excitations in the Haldane chain and the Majorana states in the Shiba chain, are protected against decoherence and constitute a possible platform for quantum information processing. The Haldane spin chain, an archetypal example of quantum magnetism, is constituted of anti-ferromagnetically coupled S=1 spins and hosts at its extremities fractional S=1/2 edge excitations. This spin-chain provides a promising entangled resource state for measurement-based quantum computation (MBQC), robust quantum memories and perfect quantum wires. The Shiba chain is constituted of spins coupled with a superconductor and host at its extremities zero-energy Majorana bound states. Theoretical works suggest that the coupling of the Majorana modes with two-level systems such as single spins could provide a mean for reading and braiding Majorana modes. Recently, both Shiba/Majorana and Haldane spin-chains have been fabricated through the self-organization of magnetic adatoms and molecules into chains on various substrates in Ultra-High Vacuum (UHV). While previous studies focus on standard Scanning Tunneling Microscopy and Spectroscopy (STM/STS) characterization of these spin-chains, we propose to analyze their spin dynamic as recent advances in Electron Spin Resonance-STM (ESR-STM) are now making possible the study of spin resonance on single atoms. Furthermore, pulsed ESR-STM has been developed to manipulate quantum spin states through microwave sequences, as well known in standard NMR/ESR. The principle of ESR-STM consists of measuring the spin-polarized tunnel current as function of the frequency of a microwave signal (DC- 40 GHz), which enables the identification of the Larmor frequency of a paramagnetic center located below the tip. In this project, we will self-assemble molecular spin chains on insulator (MgO) and superconductors (Re,Ta-Ox,Nb/MgO) to obtain Haldane and Shiba/Majorana chains. The molecular spin-chains will be obtained from either transition metal-organic complexes or polycyclic aromatic molecules. Using Continuous-Wave (CW) ESR-STM with atomic resolution, we will obtain spatial maps of the magnetic excitation frequency spectrum along the chain. With pulsed ESR-STM, we will extract crucial physical parameters for these spin chains by acquiring spatial maps of the spin-lattice relaxation (T1) and spin memory phase coherence (T2) lifetimes. These measurements will allow to test not only the existence of the topological excitations but also to test the improvement in quantum coherence time endowed by the topological protection.