David J. Wineland of the United States and Serge Haroche of France will be awarded the Nobel Prize in Physics “for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems”.
Affiliated with the National Institute of Standards and Technology, Wineland’s work allows for “optical” clocks that reach a precision of 10-17 seconds, a hundred times better than the caesium clocks that set the official time in the United States. Optical clocks use a self-referential technique—one ion is used as a clock, another is used to read the clock without altering its fragile quantum state. Their precision allows for measurement of the effects of relativity—like time dilation and gravitational shifts—even across distances as small as tens of meters. So far optical clocks have run in Wineland’s lab for “many hours and days,” he said in an interview on the Nobel Prize’s web site.
Wineland’s group has also demonstrated computing operations based on two quantum bits. Unlike conventional computers, where the basic unit of information, a bit, can take the binary values of either 1 or 0, a quantum bit can be 1, 0, or both 1 and 0 at once. Computation scales up dramatically, because n quantum bits can represent 2n states at the same time, theoretically allowing for unimaginable computational power. “Most of us feel that even though that is a long, you know, long way off before we can realize such a computer,” Wineland said, “many of us feel it will eventually happen.”
Both Nobel Laureates’ work probes the quantum properties of particles in isolation. In particular they explored a quantum phenomenon called superposition, where a particle can be in two states at once. The phenomenon was made famous by Austrian physicist Erwin Schrodinger’s thought experiment. A cat—for some reason usually shown as black—is isolated in a sealed box that also contains a vial of poison. The poison is released when the decay of a radioactive atom in the box is detected. Because radioactive decay is a quantum mechanical process, there is a level of uncertainty in when the atom decays. The system is in a state of superposition—the atom has both decayed and not decayed, so the cat is both alive and dead. Opening the box “collapses” the state and possibly kills the cat.
Schrodinger didn’t think that it would be possible to study this collapse of a quantum state in detail. In 1952, he wrote, “We never deal with just one electron or atom, or (small) molecule,” except in thought experiments.
But the work done by the Laureates did just that, describing the “progressive collapse” of the wave function of a single particle. Haroche and others have even created “cat states”.
Wineland and Haroche’s techniques are neatly complementary: While Wineland traps electrically charged atoms using laser light, Haroche measures trapped photons by sending atoms through a trap.
Haroche, who noticed the 46 Sweden code when the Nobel call came this morning, said in an interview on the Nobel Prize website that the ability to work with single atoms and photons means that quantum properties that are “veiled” due to statistical effects, come out in the open. “If you were to ask me what was the application,” he said, “I would tell you I don't know. And I would just tell you that I think there will be some applications.”
This story was corrected on 10 October.