Majorana Bound States Enabled by Skyrmion Crystals Offer Quantum Advantage

Researchers demonstrate Majorana bound states within a planar Josephson junction coupled to a skyrmion crystal, eliminating the need for external magnetic fields or phase biasing. This configuration supports these states at elevated temperatures and enables protocols for manipulating their non-Abelian statistics, facilitating experimental verification.

The pursuit of stable quantum computation necessitates physical systems resilient to environmental disturbances. A promising avenue lies in topological quantum computing, which encodes information in quasiparticles exhibiting non-Abelian statistics – meaning their exchange alters the quantum state in a way distinct from conventional particles. Realising this requires manipulating Majorana bound states (MBS), exotic quasiparticles predicted to exist at the boundaries of certain superconducting materials. A new theoretical study, led by Pankaj Sharma and Narayan Mohanta from the Department of Physics at the Indian Institute of Technology Roorkee, details a pathway to braid and fuse these MBS within a planar Josephson junction without reliance on external magnetic fields – a significant practical limitation in current designs. Their work, entitled “Magnetic field-free braiding and nontrivial fusion of Majorana bound states in high-temperature planar Josephson junctions”, proposes utilising a junction coupled to a skyrmion crystal to generate and manipulate MBS, potentially offering a route towards more robust and scalable topological quantum devices.

Majorana Bound States and Topological Superconductivity in Planar Josephson Junctions

Planar Josephson junctions are currently under intense investigation as potential platforms for realising and manipulating Majorana bound states (MBS), a critical component in the pursuit of fault-tolerant topological quantum computation. This research focuses on inducing topological superconductivity – an exotic state of matter characterised by non-trivial topological properties – within semiconductor-superconductor heterostructures. Common material combinations include indium arsenide (InAs), germanium (Ge), and graphene, paired with aluminium (Al) to form junctions where MBS may emerge.

A key requirement for establishing topological superconductivity is Rashba spin-orbit coupling (RSOC). This phenomenon, arising from structural inversion asymmetry, effectively links an electron’s spin to its momentum, and is crucial for generating the necessary conditions for MBS formation. Alongside RSOC, meticulous control over material quality and interface characteristics is paramount. Disorder within the heterostructure can significantly degrade MBS stability, and researchers actively seek mitigation strategies and protective measures.

Theoretical modelling plays a complementary role, simulating junction behaviour and aiding interpretation of experimental data. These simulations predict optimal device parameters and refine understanding of planar Josephson junction (PJJ) behaviour. Recent studies demonstrate the potential to generate MBS without the application of external magnetic fields. This is achieved through the utilisation of skyrmion crystals – topologically protected magnetic textures – to induce the conditions necessary for topological superconductivity, representing a notable advance in field-free platform development.

Researchers are exploring strategies to minimise the detrimental effects of magnetic fields on the proximity-induced superconductivity – the transfer of superconducting properties from a superconductor to a neighbouring material. Protocols for manipulating multiple MBS within these planar junctions are also under development, including non-trivial fusion, exchange, and braiding operations. Detailed self-consistent calculations performed on periodic lattices, coupled with analysis of quasiparticle energy spectra, confirm the stability and manipulability of the Majorana states within the proposed geometries.

The use of high-temperature superconductors with specific pairing symmetries is also being investigated as a means of supporting MBS at elevated temperatures. Techniques such as supercurrent measurements and quasiparticle spectroscopy are employed to identify the presence of these elusive states.

Furthermore, researchers are exploring advanced concepts like the integration of skyrmion crystals, offering a potential mechanism for generating and manipulating MBS without reliance on external magnetic fields or phase biasing.