One of the major challenges for the future of quantum computation is the drastic reduction of the error rate associated with quantum decoherence phenomena. Robust topological qubits, as realized by Majorana states, may ultimately provide a solution and constitute a new direction of topological quantum computation [1,2]. However, an unambiguous identification of Majorana states requires well defined model-type platforms and appropriate experimental tools for their investigation.

Our experimental approach is based on the use of STM-based single atom manipulation techniques in order to fabricate well-defined defect-free 1D atomic chains as well as 2D arrays of magnetic adatoms on s-wave superconductor substrates with high spin-orbit coupling [3-7]. The spin structure of these low-dimensional adatom arrays is characterized by spin-polarized STM [8,9], while scanning tunneling spectroscopy measurements reveal the evolution of the spatially and energetically resolved local density of states as well as the emergence of zero-energy bound states at both chain ends above a critical chain length [3,10]. In order to confirm the interpretation of the zero-energy states as Majorana quasiparticles, we use Bogoliubov quasiparticle interference (QPI) mapping of the 1D magnet-superconductor hybrid systems for directly probing the non-trivial band structure of the topological phases as well as the bulk-boundary correspondence [11]. Such experiments constitute the ultimate test and rigorous proof for the existence of topologically non-trivial zero-energy modes [12]. Concepts for the atomic-scale manipulation of Majorana quasiparticles will be discussed [13].

[1] C. Nayak et al., Rev. Mod. Phys. 80, 1083 (2008).

[2] J. Alicea et al., Nature Phys. 7, 412 (2011).

[3] H. Kim et al., Science Advances 4, eaar5251 (2018). 

[4] L. Schneider et al., Nature Commun. 11, 4707 (2020).

[5] A. Kamlapure et al., Nature Commun. 9, 3253 (2018).

[6] Ph. Beck et al., arXiv:2205.10062.

[7] L. Schneider et al., arXiv:2211.00561.

[8] R. Wiesendanger, Rev. Mod. Phys. 81, 1495 (2009). 

[9] L. Schneider et al., Science Advances 7, eabd7302 (2021).

[10] L. Schneider et al., Nature Nanotechnol. 17, 384 (2022).

[11] L. Schneider et al., Nature Physics 17, 943 (2021).

[12] D. Crawford et al., npj Quantum Materials 7, 117 (2022).

[13] D. Crawford et al., arXiv:2210.11587.