Credit: Yusuke Morita, Kosuke Yoshioka and Makoto Kuwata-Gonokami, The University of Tokyo
A close-up picture of the apparatus in a cryogen-free dilution refrigerator. A dark red-colored cubic crystal in the center of the picture is cuprous oxide. A zinc selenide meniscus lens placed behind the crystal is an objective lens. A rod and a stage below the crystal is used for generation of an inhomogeneous strain field in the crystal that acts as a trap potential for excitons.