A physic package for an atomic clock comprising: a block made of optical glass, a glass ceramic material or another suitable material that includes a plurality of faces on its exterior and a plurality of angled borings that serve as a vacuum chamber cavity, light paths and measurement bores; mirrors fixedly attached using a vacuum tight seal to the exterior of the block at certain locations where two light paths intersect; optically clear windows fixedly attached using a vacuum tight seal to the block's exterior over openings of the measurement bores and at one location where two light paths intersect; and fill tubes fixedly attached using a vacuum tight seal to the exterior of the block over the ends of the vacuum chamber cavity. This physics package design makes possible atomic clocks having reduced size and power consumption and capable of maintaining an ultra-high vacuum without active pumping.