Probing many-body correlations using quantum-cascade correlation spectroscopy

• Published in: Nature physics Vol. 20; no. 2; pp. 214 - 218
• Main Authors: Scarpelli, Lorenzo, Elouard, Cyril, Johnsson, Mattias, Morassi, Martina, Lemaitre, Aristide, Carusotto, Iacopo, Bloch, Jacqueline, Ravets, Sylvain, Maxime, Richard, Volz, Thomas
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 18.12.2022; Nature Publishing Group
• Subjects: Bell's inequality; Emission analysis; Energy levels; Excitation; Excitons; Photon emission; Photons; Physics; Physics - Mesoscale and Nanoscale Physics; Physics - Optics; Physics - Quantum Physics; Polaritons; Quantum entanglement; Quantum optics; Quantum phenomena; Quantum Physics; Semiconductor materials; Spectral emittance; Spectrum analysis; Optics; Mesoscale and Nanoscale Physics
• ISSN: 1745-2473; 2331-8422; 1476-4636
• DOI: 10.48550/arxiv.2212.09047

The radiative quantum cascade, i.e. the consecutive emission of photons from a ladder of energy levels, is of fundamental importance in quantum optics. For example, the two-photon cascaded emission from calcium atoms was used in pioneering experiments to test Bell inequalities. In solid-state quantum optics, the radiative biexciton-exciton cascade has proven useful to generate entangled-photon pairs. More recently, correlations and entanglement of microwave photons emitted from a two-photon cascaded process were measured using superconducting circuits. All these experiments rely on the highly non-linear nature of the underlying energy ladder, enabling direct excitation and probing of specific single-photon transitions. Here, we use exciton polaritons to explore the cascaded emission of photons in the regime where individual transitions of the ladder are not resolved, a regime that has not been addressed so far. We excite a polariton quantum cascade by off-resonant laser excitation and probe the emitted luminescence using a combination of spectral filtering and correlation spectroscopy. Remarkably, the measured photon-photon correlations exhibit a strong dependence on the polariton energy, and therefore on the underlying polaritonic interaction strength, with clear signatures from two- and three-body Feshbach resonances. Our experiment establishes photon-cascade correlation spectroscopy as a highly sensitive tool to provide valuable information about the underlying quantum properties of novel semiconductor materials and we predict its usefulness in view of studying many-body quantum phenomena.