Periodic Reporting for period 2 - NONLOCAL (Foundations of nonlocal and nonabelian condensed-matter systems)
Période du rapport: 2022-05-01 au 2023-10-31
Nonlocality of quantum states and nonabelian statistics are intimately connected properties. Both properties are predicted to appear in certain topologically nontrivial macroscopic quantum states, one of the most well-known being topological superconductors with Majorana bound states.
To date, the nonlocal nature of these states has not been demonstrated experimentally. If demonstrated in the laboratory, it would constitute a fundamentally new type of phenomenology where the quantum mechanical state of the system cannot be revealed by any local probe. The separation of information between different physical locations is, of course, a simple concept in our classical world, but in the quantum world it is more profound and opens the possibility of encoding entangled states nonlocally. Even small topological systems, as long as they have more than two states, can encode entangled states in a way that shields them from measurement by any local perturbation. For example, in the case of Majorana bound states, the dimension of the ground state manifold is doubled for each pair of MBSs.
The program involves design and implementation of systems with multiple MBSs and quantum dots, thus taking advantage of well-known quantum systems for diagnostics of the topological properties of MBSs, including spinful quantum dots, charge sensing and quantum capacitance measurements.
To summarize the state-of-the art for this project, what is known at this time is that zero bias peaks consistent with Majorana interpretations are more or less routinely observed and have been reported in a number of papers. Moreover, superconductor islands made from the proximitized nanowires consistently show a transition from only accepting electron pairs – as expected for a trivial superconductor – to a regime where the even and odd occupied states of a superconducting island are degenerated. The latter is consistent with a transition to a topologically non-trivial state. In addition, there are many details in the transport spectroscopy that support the MBS interpretation. On the theory side, the agreement with experiments is based on effective models that include the main ingredients, spin-orbit coupling and induced pairing. However, the exact microscopic nature of both ingredients is to a large extend still not understood. In this project, we introduce a joint experimental and theoretical research program with the objective of investigating the physics of nonlocal and nonabelian particles using MBSs as candidate particles.
To date, the nonlocal nature of these states has not been demonstrated experimentally. If demonstrated in the laboratory, it would constitute a fundamentally new type of phenomenology where the quantum mechanical state of the system cannot be revealed by any local probe. The separation of information between different physical locations is, of course, a simple concept in our classical world, but in the quantum world it is more profound and opens the possibility of encoding entangled states nonlocally. Even small topological systems, as long as they have more than two states, can encode entangled states in a way that shields them from measurement by any local perturbation. For example, in the case of Majorana bound states, the dimension of the ground state manifold is doubled for each pair of MBSs.
The program involves design and implementation of systems with multiple MBSs and quantum dots, thus taking advantage of well-known quantum systems for diagnostics of the topological properties of MBSs, including spinful quantum dots, charge sensing and quantum capacitance measurements.
To summarize the state-of-the art for this project, what is known at this time is that zero bias peaks consistent with Majorana interpretations are more or less routinely observed and have been reported in a number of papers. Moreover, superconductor islands made from the proximitized nanowires consistently show a transition from only accepting electron pairs – as expected for a trivial superconductor – to a regime where the even and odd occupied states of a superconducting island are degenerated. The latter is consistent with a transition to a topologically non-trivial state. In addition, there are many details in the transport spectroscopy that support the MBS interpretation. On the theory side, the agreement with experiments is based on effective models that include the main ingredients, spin-orbit coupling and induced pairing. However, the exact microscopic nature of both ingredients is to a large extend still not understood. In this project, we introduce a joint experimental and theoretical research program with the objective of investigating the physics of nonlocal and nonabelian particles using MBSs as candidate particles.
The project was kicked-off with a series of meetings to create synergy between experimentalists and theorists. The meetings led to a strategy for which experiments and designs of devices to pursue. At the same time the ERC Synergy supported dilution refrigerator was installed and tested with new and old devices.
The project consists of four themes exploring improved platforms for topological Majorana bound states. We have revisited the various material platforms and decided to devote a major part of the effort on the epitaxial superconductor-on-semiconductor platform. This platform is currently the most promising and advanced platform, which prior to the start of the ERC project was used by some participants and others to investigate evidence of topological superconductor transitions. We also concluded that parity-to-charge conversion is the best way to investigate the properties of Majorana bound states.
In the first reporting period, the already published papers include, among other key points, theory on measurement setup for the important parity-to-charge conversion plus protocols for investigation of the nonabelian and nonlocal properties. Preprint papers include experimental papers on the same topic as well as novel superconductor-semiconductor hybrid systems.
The project consists of four themes exploring improved platforms for topological Majorana bound states. We have revisited the various material platforms and decided to devote a major part of the effort on the epitaxial superconductor-on-semiconductor platform. This platform is currently the most promising and advanced platform, which prior to the start of the ERC project was used by some participants and others to investigate evidence of topological superconductor transitions. We also concluded that parity-to-charge conversion is the best way to investigate the properties of Majorana bound states.
In the first reporting period, the already published papers include, among other key points, theory on measurement setup for the important parity-to-charge conversion plus protocols for investigation of the nonabelian and nonlocal properties. Preprint papers include experimental papers on the same topic as well as novel superconductor-semiconductor hybrid systems.
If successful in achieving the objectives, the results would give fundamentally new insight into a novel class of macroscopic quantum phenomena of topological origin and it is not difficult to imagine applications in the form of quantum computation or quantum information storage.