The 2012 Nobel Prize in Physics is awarded "for ground-breaking experimental methods that enable measuring & manipulation of individual quantum systems" with the prize awarded jointly to David Wineland and Serge Haroche.
Quantum physics is a notoriously tricky thing to measure at the most fundamental level. Quantum systems retain their more intriguing properties only when they are allowed to stay in a state of quantum superposition, but any measurement of the system tends to cause the system to collapse out of a superposition state into a single definite state, through a process called decoherence. By developing and refining experimental methods that allow atoms to interact in precise ways with photons, these two experimental physicists have helped to perform quantum measurements in new and innovative ways.
About David Wineland:
David Wineland is a physicist at the National Institutes of Standards and Technology (NIST) laboratory in Boulder, CO. Dr. Wineland's work has focused on how to capture an ion, which he and his team has done through a process known as "laser cooling." This work has helped expand our understanding of quantum mechanics and has significant implications for the development of a quantum computer.
About Serge Haroche:
French physicist Serge Haroche, along with his team, have worked extensively on developing methods to capture light between mirrors and then to use atoms to interact with that light. These methods are significant because they allow the atoms to interact with and measure the quantum state of the light without destruction of individual photons which, in the words of the Nobel presenter, is actually a very hard thing to do. This work was performed at the Ecole Normale Superieure in Paris in 1996.
Interesting Trivia Fact:
Both of this year's Nobel Laureates in Physics were born in 1944.