5 ms·

A super fascinating journal would be mit failed experiments. And what happened.

• CamperBob2 5y ago
  One semi-famous example from MIT would be Jerrold Zacharias's attempt to build a cesium fountain clock ( https://en.wikipedia.org/wiki/Atomic_fountain https://en.wikipedia.org/wiki/Atomic_fountain ). It took decades of additional research before anyone managed to make fountain clocks work. Norman Ramsey's biography of Zacharias at http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/zacharias-jerrold.pdf http://www.nasonline.org/publications/biographical-memoirs/m... (.pdf link) talks a little about it: Zacharias at this time became interested in developing atomic clocks and pursued two versions concurrently. One was a cesium atomic beam clock using my (Ramsey's) separated oscillatory field method, well engineered for reliability and commercial applications, including a source and vacuum system that could be operated for years rather than hours. He cooperated with the National Company in developing a commercial clock known as the Atomichron. The availability of this highly successful cesium atomic beam clock contributed greatly to the adoption of atomic time and to the international definition of the second as 9,192,631,770 oscillations of the cesium atom. His other version had the potential for much greater accuracy but the risk of total failure. A very slow beam of atomic cesium was directed upward and allowed to fall as a fountain, with separated oscillatory field excitation on the way up and down. The half second required for the roundtrip in the fountain was approximately fifty times greater than that for an atom to traverse the oscillatory field region of a conventional atomic beam apparatus, so the resonance width, by the Heisenberg uncertainty principle, would be fifty times narrower with correspondingly increased clock accuracy. Despite valiant efforts by Zacharias and his associates, the fountain experiment failed because the numbers of ultraslow atoms in the beam were far below theoretical predictions, probably due to scattering in the nonequilibrium region between the slits. It is of interest to note that thirty years later, in 1989, Steven Chu succeeded in making an atomic fountain by using the new laser cooling techniques to produce ultra-slow atoms. The atomic fountain with laser cooling is now one of the most promising prospects for increasing the accuracy of clocks and frequency standards.
• Xpol 5y ago
  What the MIT group achieved was implementing spin-squeezing to clock operation, but their results are not QPN-limited (in fact, they made it above the SQL, so they actually make things worse instead of making it better) [1]. They attributed their major obstacle as their laser phase noise, and they claimed if they subtract the estimated laser noise from the result they would get sub-SQL. But hey, that's not how things work. If you think you can make it, you just make it. [1] : https://www.nature.com/articles/s41586-020-3006-1 https://www.nature.com/articles/s41586-020-3006-1