Gold Surface State Qubits for Scalable Majorana Zero Mode Verification
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Solution Overview
Problem
Current methods for generating Majorana zero modes (MZMs) in semiconductor nanowires and atomic chains face challenges such as the lack of direct evidence for non-locality, scalability issues, and difficulty in verifying zero bias peaks at both ends, making it hard to create an ensemble of qubits for topological quantum computing.
Innovation Solution
A platform using thin gold (111) films coupled to a superconductor with a magnetic insulator like europium sulfide (EuS) is introduced, where nanostructures of EuS are patterned on the gold film, allowing MZMs to appear simultaneously at both ends under an applied magnetic field, and this platform is scalable to hundreds or thousands of islands, enabling the creation of complex circuit networks for Majorana-based qubits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If semiconductor nanowires or atomic chains are used to generate MZMs, then MZMs can be formed at the ends of the structure, but it is difficult to verify simultaneous appearance at both ends and scalability is limited
Solution Approach 1:
The invention divides the verification process into separate, independently accessible ends of the nanostructure. By creating a linear atomic chain where both ends can be individually probed with STM tips, the system enables independent measurement at each end, allowing verification of simultaneous MZM appearance without the limitations of previously inaccessible configurations.
Solution Approach 2:
The atomic chain structure serves multiple functions: it generates MZMs at both ends, allows independent electrical contact at each end for verification, and provides a scalable platform that can be replicated to create ensembles of qubits. The universal design enables both measurement and scalability goals to be achieved simultaneously.
2Ease of manufacture
If gate-controlled tunnel barriers with smooth variation are used, then the system can be fabricated, but theory suggests two MZMs can exist in close proximity near one end coupling very differently across the tunnel barrier, mimicking isolated MZM signal
Solution Approach 1:
Instead of using smooth, gate-controlled tunnel barriers that cause differential coupling, the invention inverts the approach by using abrupt, well-defined tunnel barriers at each end of the atomic chain. This allows both MZMs to couple similarly and equally to the tunnel barriers, enabling clear verification of their simultaneous presence and non-locality without the confounding effects of differential coupling.
3Ease of manufacture
If one end of the atomic chain is attached to an island, then the structure can be formed, but the other end is not easily accessible making it challenging to verify ZBP appearance
Solution Approach 1:
The invention segments the atomic chain into two symmetrically accessible ends, each capable of independent measurement. By designing the structure so that both ends are equally accessible to STM tips, it eliminates the accessibility problem while maintaining the ability to form the atomic chain structure on suitable substrates.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the scalable generation of MZMs at both ends of nanostructures, facilitating the creation of Majorana-based qubits and overcoming the limitations of previous methods by providing a platform that is readily fabricable and capable of forming complex networks for topological quantum computing.
Implementation Method 1
The superconductor is on a clean, flat substrate and is thick enough to induce superconductivity in the gold film
Implementation Method 2
The surface of the gold film is covered with a magnetic insulator, such as europium sulfide (EuS) that is two atomic layers thick
Implementation Method 3
MZMs can appear simultaneously at both ends of the nanostructure under an applied magnetic field
Implementation Method 4
The free surface of the conductive film has a Rashba spin-orbit splitting of at least 1 meV
Data Source
AI summary
Under certain conditions, a fermion in a superconductor can separate in space into two parts known as Majorana zero modes, which are immune to decoherence from local noise sources and are attractive building blocks for quantum computers. Here we disclose a metal-based heterostructure platform to produce these Majorana zero modes which utilizes the surface states of certain metals in combination with a ferromagnetic insulator and a superconductor. This platform has the advantage of having a robust energy scale and the possibility of realizing complex circuit designs using lithographic methods. The Majorana zero modes are interrogated using planar tunnel junctions and electrostatic gates to selectively tunnel into designated pairs of Majorana zero modes. We give example of qubit designs and circuits that are particularly suitable for the metal-based heterostructures.