Join the dots

Abstract

A new variation on an old theme in atomic physics, a spectral distortion known as the Fano effect, has been revealed — not in an atom, but in an artificial nanostructure known as a quantum dot. The Fano effect is a spectral distortion arising from quantum-mechanical resonance or interference between two competing optical pathways. It is ubiquitous in optical spectroscopy of atoms, solids and semiconductor heterostructures. It indicates how discrete energy states, for example of an atom, are coupled to the continuum of states in its environment. The effect has been widely studied, but usually in a linear regime at low excitation power. A new study uses semiconductor quantum dots to explore the physics of the nonlinear Fano regime. Clear Fano resonances are observed, and they can be tuned by changing the device design or with applied voltages. In the nonlinear regime, visibility of Fano interferences increases dramatically, which could be used as a sensitive probe of the degree of coupling between discrete states and the continuum, which is relevant for example for qubits where coupling to the environment needs to be kept to a minimum.