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 extent 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 project aims to study these phenomena in both extended topological systems and in small systems where fine-tuned sweet spots can possibly mimic the behavior of the larger systems. In addition, the project explores other new phenomena which the super-semi platform offers. For example, the control of dissipation and the possibility to connect larger arrays of superconductors via tunable semiconductor junctions.
