In a described example, an apparatus includes a package substrate having a device side surface and a board side surface opposite the device side surface, a physics cell mounted on the device side surface having a first end and a second end, a first opening extending through the package substrate and lined with a conductor, aligned with the first end, a second opening extending through the package substrate and lined with the conductor, aligned with the second end, a millimeter wave transmitter module on the board side, having a millimeter wave transfer structure including a transmission line coupled to an antenna aligned with the first opening, and a millimeter wave receiver module mounted on the board side surface of the package substrate and having a millimeter wave transfer structure including a transmission line coupled to an antenna for receiving millimeter wave signals, aligned with the second opening.