Quantum mechanics in the 20th century was a like nagging parent, telling 
physicist what they could NOT do: "you can't know position and momentum 
simultaneously", "you can't measure a system without disturbing it", "you 
can't describe measurement outcomes by local random variables".  Quantum 
mechanics of the 21st century is an enabler, allowing information 
processing capabilities that would be impossible in a world described by 
classical physics.  To tap into this resource, new tools must be 
developed, allowing us to control the way quantum systems behave.  In this 
colloquium, I will describe recent developments along these lines, using 
ultracold atomic spins as our basic platform.  Examples include the 
ability to reconstruct a quantum state in a continuous measurement and 
exploration of the signatures of chaos in quantum correlations.