A quantum device (100) includes: an interposer (112); a quantum chip (111); and a connection part (130) that is provided between the interposer (112) and the quantum chip (111) and electrically connects a wiring layer of the interposer (112) to a wiring layer of the quantum chip (111), in which the connection part (130) includes: a plurality of pillars (131) arranged on a main surface of the interposer (112); and a metal film (132) provided on a surface of the plurality of pillars (131) in such a way that it contacts the wiring layer of the quantum chip (111) and the thickness of the metal film at outer peripheral parts of the tip of each of the plurality of pillars (131) becomes larger than the thickness of the metal film at a center part of the tip of each of the plurality of pillars (131).