Quantum Criticality in Light-Matter Interaction, and its Use for Metrology
March 9th, 2020 LOUIS GARBE Paris-Diderot University

The last few years have seen an outstanding improvement in our ability to control light-matter interaction at the quantum level. In particular, it is now possible to experimentally achieve the ultrastrong-coupling regime, where the coupling strength becomes comparable to the bare frequency of the system. This regime is associated with many exotic properties, including phase transitions.

In this talk, I will discuss the presence of critical effects in ultrastrongly-coupled light-matter systems, and their potential applications for sensing task. First, I will discuss the two-photon Dicke model, which describes a collection of qubits interacting with a bosonic field by simultaneously exchanging two excitation quanta. I will show that this model exhibits a complex interplay between two critical effects, a phase transition and a coalescence of energy levels known as spectral collapse. Second, I will discuss how the diverging susceptibility associated with critical effects could be used for sensing applications. I will present metrological protocols which make use of a finite-size critical behavior, which has been predicted to take place in a system composed of a single qubit coupled to a single bosonic mode.

Seminar, March 9, 2020, 12:00. ICFO’s Seminar Room

Hosted by Prof. Darrick Chang