A quantum interference device includes an atomic cell, a light source, a light detector, a package, and a reflective portion. The atomic cell has alkali metal atoms disposed within, and the light source emits light to excite the alkali metal atoms in the atomic cell. The light detector detects light transmitted through the atomic cell. The package defines an internal space and houses at least the light source. The reflective portion is provided between an inner surface of the package and the light source, and has reflectance to an electromagnetic wave having a wavelength of 4 μm, where the reflectance is greater than or equal to 50%.