InAs-Al Hybrid Devices Passing the Topological Gap Protocol (2207.02472v4)

Abstract: We present measurements and simulations of semiconductor-superconductor heterostructure devices that are consistent with the observation of topological superconductivity and Majorana zero modes. The devices are fabricated from high-mobility two-dimensional electron gases in which quasi-one-dimensional wires are defined by electrostatic gates. These devices enable measurements of local and non-local transport properties and have been optimized via extensive simulations to ensure robustness against non-uniformity and disorder. Our main result is that several devices, fabricated according to the design's engineering specifications, have passed the topological gap protocol defined in Pikulin et al. [arXiv:2103.12217]. This protocol is a stringent test composed of a sequence of three-terminal local and non-local transport measurements performed while varying the magnetic field, semiconductor electron density, and junction transparencies. Passing the protocol indicates a high probability of detection of a topological phase hosting Majorana zero modes as determined by large-scale disorder simulations. Our experimental results are consistent with a quantum phase transition into a topological superconducting phase that extends over several hundred millitesla in magnetic field and several millivolts in gate voltage, corresponding to approximately one hundred micro-electron-volts in Zeeman energy and chemical potential in the semiconducting wire. These regions feature a closing and re-opening of the bulk gap, with simultaneous zero-bias conductance peaks at both ends of the devices that withstand changes in the junction transparencies. The extracted maximum topological gaps in our devices are 20-60 $\mu$eV. This demonstration is a prerequisite for experiments involving fusion and braiding of Majorana zero modes.

• The paper demonstrates InAs-Al devices passing the topological gap protocol, confirming robust Majorana zero mode signatures.
• It employs 2DEG-based, gated quasi-one-dimensional wires to reveal gap closings and reopenings with maximum topological gaps of 20–60 µeV.
• The findings pave the way for topological quantum computing by establishing fault-tolerant qubits and enabling future braiding experiments.

Overview of InAs-Al Hybrid Devices Passing the Topological Gap Protocol

This paper presents a detailed paper of semiconductor-superconductor heterostructure devices which exhibit characteristics consistent with the presence of topological superconductivity and Majorana zero modes (MZMs). The research focuses on devices fabricated from high-mobility two-dimensional electron gases (2DEGs), where quasi-one-dimensional wires are defined using electrostatic gates. The main highlight of this paper is several devices passing the stringent topological gap protocol (TGP) proposed by Pikulin et al., which involves a series of transport measurements aimed at confirming the topological nature of the superconducting phase.

Strong Numerical Results and Claims

The experimental results demonstrate a region in the magnetic field and gate voltage space where the devices exhibit a closing and reopening of the bulk gap, accompanied by zero-bias conductance peaks at both ends of the nanowires. These conductance peaks are stable despite variations in the junction transparencies, indicating their robustness and alignment with MZM signatures. The extracted maximum topological gaps of the devices range between 20–60 µeV, providing a compelling prerequisite for experiments demonstrating fusion and braiding of MZMs.

Implications and Future Directions

The implications of achieving a topological superconducting phase in InAs-Al hybrid devices are significant for the field of quantum computing. The observation of MZMs holds potential for realizing topological quantum computation, which offers inherent fault tolerance due to the non-Abelian statistics of MZMs. Practically, the ability to pass the TGP signifies that these devices can potentially be used in creating qubits that are less susceptible to local perturbations and errors.

Future developments could focus on optimizing the device design and material stack to increase the topological gap and extend the topological phase stability. Improved disorder control, higher mobility, and enhanced material interfaces could boost the coherence and accessibility of the topological phase. Additionally, further experiments could focus on demonstrating MZM braiding and fusion, essential steps towards a fully operational topological quantum computer.

Conclusion

This research marks a significant step forward in the experimental pursuit of topological phases supporting MZMs. The paper meticulously combines experimental data with extensive simulations to demonstrate high confidence in detecting a topological superconducting phase. These findings not only push the boundaries of material-based quantum computing platforms but also pave the way for practical implementations of error-resistant quantum computational devices utilizing topological states.