I'm pretty sure this is "Noise Level" by Raymond F. Jones.

http://www.sf-encyclopedia.com/entry/jones_raymond_f:
>"Noise Level" (December 1952 Astounding), an archetypal Astounding tale of Conceptual Breakthrough, scientific advance taking place through destruction of a previous paradigm: Scientists are told that Antigravity exists, and so proceed to invent it. 

"Noise Level" [on ISFDB][1] 


  [1]: https://www.isfdb.org/cgi-bin/title.cgi?55972