Thermally condensing photons into a coherently split state of light

• Published in: Science (American Association for the Advancement of Science) Vol. 366; no. 6467; pp. 894 - 897
• Main Authors: Kurtscheid, Christian, Dung, David, Busley, Erik, Vewinger, Frank, Rosch, Achim, Weitz, Martin
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 15.11.2019; The American Association for the Advancement of Science
• Subjects: Beam splitters; Bifurcations; Coherence; Computer simulation; Control methods; Dimpling; Dyes; Entangled states; Fluorescent dyes; Fluorescent indicators; Ground state; Optical components; Optical properties; Photons; Prisms; Quantum computing; Quantum phenomena; Recombination; Room temperature; Thermalization (energy absorption); Wave packets
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.aay1334

The quantum state of light plays a crucial role in a wide range of fields, from quantum information science to precision measurements. Whereas complex quantum states can be created for electrons in solid-state materials through mere cooling, optical manipulation and control builds on nonthermodynamic methods. Using an optical dye microcavity, we show that photon wave packets can be split through thermalization within a potential with two minima subject to tunnel coupling. At room temperature, photons condense into a quantum-coherent bifurcated ground state. Fringe signals upon recombination show the relative coherence between the two wells, demonstrating a working interferometer with the nonunitary thermodynamic beam splitter. Our energetically driven optical-state preparation method provides a route for exploring correlated and entangled optical many-body states.