Nowadays the optical atomic clocks that can be used in vehicles are many orders of magnitude less accurate than those that are restricted to a well protected laboratory environment.
If anyone is wondering, we aren't yet to the point of having an atomic clock in the dashboard of your Toyota. But they have been reduced to ~suitcase size. Example if one being tested in a Navy ship:
The microchip miniature atomic clocks are not optical atomic clocks, but old-school microwave atomic clocks.
They are orders of magnitude less accurate than even portable optical atomic clocks and the difference is much greater in comparison with SOTA laboratory cesium clocks or hydrogen masers, which are again orders of magnitude less stable than the best laboratory optical atomic clocks.
However, these miniature atomic clocks are much smaller and cheaper than better atomic clocks and there are applications where something better than an OCXO-based quartz clock is desired.
Indeed, this clock, which uses iodine absorption cells to provide the reference frequency, is one of the kinds of already existing portable optical atomic clocks to which I was referring.
The best laboratory optical clocks, which use ion traps or optical lattices with neutral atoms, have a higher accuracy by up to 6 orders of magnitude, which makes much harder for the system that stabilizes the length of the laser cavity to keep up with it.
Minute length changes that would not matter for a less accurate iodine clock would cause unacceptable frequency shifts in a SOTA optical clock. Therefore such optical clocks are much more sensitive to their environment.
If anyone is wondering, we aren't yet to the point of having an atomic clock in the dashboard of your Toyota. But they have been reduced to ~suitcase size. Example if one being tested in a Navy ship:
https://www.geoconnexion.com/in-depth/scientists-create-new-...