Centre de Physique Théorique


Jeudi 5 décembre 2019

16h00 – 17h00, Amphi 5 du CPT

Many-Body States through Quantum Noise : Non-Equilibrium Quantum Criticality and an Unpaired Majorana Zero Mode

Harold Baranger (Duke University, USA)

Abstract : It is natural to suppose that decoherence produced by quantum noise will suppress quantum effects, and in particular inhibit or destroy interesting quantum states. In contrast, I shall discuss how quantum noise can be used as a resource to create delicate many-body states. Quantum dot systems are particularly advantageous for such effects : they exhibit impurity quantum criticality, they are amenable to detailed experimental study, and they are simple enough theoretically that extensive results can be obtained. First, I shall present one such experimental system : a quantum dot connected to resistive leads via tunable tunnel barriers. A quantum critical point of the two-channel Kondo type occurs when the dot is symmetrically coupled to the leads and a level in the dot is resonant. Second, I summarize our theoretical results for the non-equilibrium I-V curve. Theory and experiment are compared in a parameter-free way, and the agreement is excellent. Finally, I argue that these results are a manifestation of a decoupled Majorana mode in the charge degree of freedom of the dot. Introducing an additional topological superconducting wire with a nonlocal fermion shared between its ends, the dot Majorana can hybridize with the topological non-local fermion. In this way, at the other end of the topological wire, one obtains a single decoupled Majorana zero mode.