[time-nuts] Team of physicists repeats tvb Project GREAT

[jimlux]

On 2/14/18 6:51 PM, Tim Lister wrote:
> On Feb 14, 2018 19:47, "Chris Caudle" <chris at chriscaudle.org> wrote:
> 
> On Wed, February 14, 2018 7:06 pm, jimlux wrote:
>> At substantially more expense, and with an experimental lattice clock,
> 
> Does that schematic figure in the paper imply that the "transportable"
> strontium and ytterbium clocks are built into trailers instead of the
> traditional rack enclosure?
> Actually now that I look more closely it looks like maybe two trailers.
> Doesn't seem like something that Jim is going to be flying any time soon.
> 
> 
> Yes. From the Nature article text:
> "The transportable 87Sr lattice clock is (compared with laboratory clocks)
> designed to be compact, with robust optical parts12
> <https://www.nature.com/articles/s41567-017-0042-3#ref-CR12>. The physics
> package is less than 0.6 m3 in size, and we use laser breadboards with
> mechanical stress-resistant fibre couplers21
> <https://www.nature.com/articles/s41567-017-0042-3#ref-CR21>. All
> components except the reference cavity of the interrogation laser are
> rigidly mounted in a car trailer (size 2.2 m × 3 m × 2.2 m), and vibration
> isolation is provided by rubber dampers. The trailer interior is
> temperature stabilized, while the small volume of the trailer hinders air
> exchange and generates hot spots with more than 10 K temperature rise.
> However, the optics and the physics package are placed apart and shielded
> from these and are stable to within 0.4 K after an initial temperature rise
> of about 1 K. The transportable ultrastable reference cavity for the clock
> interrogation lasers is rigidly mounted to endure transport12
> <https://www.nature.com/articles/s41567-017-0042-3#ref-CR12>. It was placed
> next to the trailer to avoid its performance being degraded by vibrations
> induced in the trailer’s air conditioning system. The vibration amplitudes
> in the trailer are a factor of ten larger than under typical laboratory
> conditions, leading to a corresponding increase in clock instability. A
> reference resonator with lower acceleration sensitivity or an active
> feed-forward system may in the future remedy this inconvenience22
> <https://www.nature.com/articles/s41567-017-0042-3#ref-CR22>."
> 


We have discussed the desirability of suitable caves for operation of 
high quality clocks many times on this list.
Clearly this is another instance.

With respect to flying such things in space - this is the continual 
challenge - DSAC (the trapped mercury ion clock) was a couple of benches 
in a special time keeping lab when I first saw it, oh, a decade ago?. 
It will fly later this year and it's probably about the size of an 
airplane carry-on.
https://www.jpl.nasa.gov/missions/deep-space-atomic-clock-dsac/

Cold Atom Laboratory basically takes several optical benches operated by 
a team of post-docs that makes Bose Einstein Condensates (BEC) and turns 
it into a box the size of a dorm refrigerator that goes "ping" when you 
press a button and makes a BEC (in either Rb or K, as you choose).

https://coldatomlab.jpl.nasa.gov/mission/

Just as a rule of thumb, I've found that it takes about 10-20 times the 
cost to get from "benchtop prototype"(TRL 5) to "flyable unit" (TRL 6), 
as it cost to get from idea to benchtop prototype.