The Nobel Prize in Physics: Quantum Mechanics Comes of Age
Quantum mechanics is one of the most devilishly confusing theories ever devised. Cats that are simultaneously alive and dead, objects that are both particles and waves, subatomic particles that know whether you are looking at them or not—and, most bafflingly, these quantum effects can be erased when individual atoms, electrons, and photons interact with their environment.
That is what makes Serge Haroche and David Wineland’s Nobel Prize-winning work in physics so remarkable: They have achieved mastery of the microrealm. Both of them have spent decades trying to generate systems in which a single atom or a single photon can be studied.
David Wineland, at the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder, is an expert at trapping individual atoms using electric fields and by keeping them in an ultra-high vacuum. The mastery of individual atoms is possible by artfully employing laser beams and laser pulses. The laser beams can cool the motion of the atoms and even can transfer quantum information about the atom’s location to the location of electrons inside the atom. This is an extraordinary achievement.
Serge Haroche, of the Collége de France and the Ecole Normale Supérieure, Paris, essentially does the opposite. He uses atoms to study individual photons. Using superconducting niobium, he creates the two most reflective mirrors ever achieved. With the mirrors placed about an inch apart, he introduces a single photon, which bounces back and forth for over a tenth of a second until it eventually hits an imperfection in the mirror and is absorbed. While the photon is bouncing, it travels a distance equivalent to circling the entire globe.
In order to measure the photon, Haroche fires single rubidium atoms through his equipment. These atoms are of a special class called “Rydberg atoms,” in which the electrons “orbit” very far from the atomic nucleus. (Though we now know that atoms do not operate as mini solar systems, the analogy of orbits can still be a useful one.) By measuring the configuration of the Rydberg atom before and after it travels through his apparatus, Haroche can determine if there is a photon inside his equipment without absorbing or altering the photon.
These techniques have made it possible to probe quantum mechanics in more detail than ever before, with Haroche’s work making it possible to effectively make a movie of the transition of a photon from one state to another, a process that scientists call “the collapse of the wave function." But these two scientists’ work has more practical applications. For instance, if we are able to put equipment into a quantum state and read that state without destroying it, this opens the possibility of quantum computing. The potential power of quantum computing is enormous and if we are able to actually accomplish it, this will change computing in the same degree that ordinary computing has changed the world since the 1940s. Quantum computing is still a ways in the future, but Haroche and Wineland’s work has brought it closer to fruition.
Wineland's work has also made possible a new generation of clocks that are 100 times more accurate than the best timekeepers in the world. These new clocks are precise to one part in 1017. To give some context, if these clocks were started when the universe began 13.7 billion years ago, by now they would be off by a mere four seconds. Such accuracy is useful for communication and navigation, and could also enable even more stringent tests of Einstein’s theory of general relativity, which states that time runs slower in stronger gravitational fields. When people think about this effect, they usually invoke the mind-bending gravitational fields surrounding black holes, but these new clocks are so precise that the effect of time dilation due to gravity would be obvious if one of them were raised a mere foot off the surface of the Earth.
Haroche and Wineland’s work is of the highest caliber, with potential society-changing implications. In this year’s Nobel Ceremony on December 10, they will rightfully join their peers in the pantheon of great scientists.
Author's picks for further reading
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