Ultra-high vacuum fabrication of quantum devices with topological and superconductive elements

TO-124 • PT 1.2777 • As of 10/2023
Peter Grünberg Institute
Semiconductor Nanoelectronics (PGI-9)

Technology

Our invention presents an innovative method for producing a hybrid structure of a Majorana material and a superconductor. The term Majorana materials comprises the class of materials that can be used in combination with a superconductor to generate Majorana zero modes. The process involves two dielectric masks.

The lower mask enables selective area growth of the Majorana material (e.g., in the shape of a nanowire), the upper mask acts as a stencil mask during the deposition of superconductive material onto the Majorana material. Both masks are aligned to each other with nm-precision and are monolithically integrated onto a substrate. This allows for deposition of topological, superconductive and dielectric materials without interruption in an inert atmosphere, preferably in ultra-high vacuum.

The resulting hybrid structure consists of a structured Majorana material, a superconductive material, and a passivation layer. Our approach ensures the preservation of surface properties of the Majorana material and high interface quality between the Majorana material and the superconductor. Due to the monolithic integration, complex networks consisting of these hybrid devices can be created for various applications (see below).

Problem addressed

The surface of topological insulators and other Majorana materials, is susceptible to oxidation, which can compromise the topological protection of the spinless surface states and hence prevent the creation of Majorana zero modes in these materials. To create Majorana devices or qubits, the Majorana material needs to be structured (e.g. in nanowire), be contacted via superconducting electrodes and finally be passivated by a dielectric capping layer. Typically, these fabrication steps take place in a cleanroom facility, where exposure to ambient conditions, air, and chemicals is inevitable. Each type of exposure has the potential to alter the surface properties.

Therefore, to preserve the unique characteristics of Majorana materials and harness them in topological devices, a meticulous process is required. This process must enable the structuring of Majorana materials, their contact formation, and passivation in an inert atmosphere, ensuring pristine interfaces and surfaces.

Solution

Our approach solves above problem and enables the fabrication of high-quality hybrid structures with precise alignment between the structured Majorana material and the superconducting material in ultra-high vacuum. The process ensures the preservation of surface states, particularly important for reliable Majorana physics. Additionally, the method allows for the deposition of a protective passivation layer in a final fabrication step, preventing any damage or alteration to the surface states of the structured Majorana material when exposed to ambient conditions after fabrication. The in situ and epitaxial growth of both materials is performed in in ultrahigh vacuum, in just a few process steps. Therefore, it facilitates the creation of high-quality hybrid structures. Because the process is highly scalable, it can be used to construct complex networks of Majorana material-superconductor devices.

Benefits and Potential Use

The high-quality surfaces and interfaces provided by our technology are crucial for applications in Majorana physics and topological quantum computing. The technology allows for the fabrication of heterostructures of superconducting and Majorana materials with precise alignment, enabling the structured definition of functional devices and networks. The hybrid structures can be utilized in topological Josephson contacts, SQUIDs and complex components such as topological qubits and quantum processor units (QPUs). Our approach offers an alternative to conventional fabrication methods, that do not account for the sensitivity of topological surfaces.

Development Status and Next Steps

Forschungszentrum Jülich has extensive expertise in this field. The technology described above has already been initially verified through prototypes and is continuously being developed further. The Peter Grünberg Institute (PGI-9) – Semiconductor Nanoelectronics – already cooperates with numerous national and international scientific partners.

Forschungszentrum Jülich focuses on emerging quantum technologies. We are continuously seeking for cooperation partners and/or licensees in this and adjacent areas of research and applications.

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