The term ‘quantum leap’ is generally taken to mean a huge advancement. In fact, such leaps take place at a microscopic level. Individual electrons within atoms sometimes jump between an inner to an outer track in their orbit around the nucleus as they gain or lose energy.
A strange anomaly of quantum mechanics is that not everything reacts as we in the classical macroscopic world would expect; for example atoms can exist in two energy states at once.
For years such activity could only be theorised as single atomic particles are difficult to isolate and lose their quantum properties if they interact with the outside world. Strange phenomena predicted by quantum physics could not be directly observed, and researchers could only carry out ‘thought experiments’ that might in principle produce these effects.
The 2012 Nobel Prize for physics was shared by two scientists who, working independently, made great leaps forward in the field of quantum optics, studying interactions between light and matter through their "ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems".
In France, Serge Haroche and his team trapped photons of microwave light in a box and observed them using specialist atoms. In the US, David Wineland and his team kept ions (atoms with a net charge) inside a trap by surrounding them with electrical fields and manipulated their states with laser light at their laboratory in Boulder, Colorado.
The Boulder group isolated the particles by performing the experiments in vacuum and used laser beams to cool an individual ion, putting it in its lowest possible state of motion. In one experiment, they directed a carefully tuned laser pulse at the ion to push it into a quantum superposition state, halfway towards a higher energy level so that it is left in both levels simultaneously, with an equal probability of ending up in either of them when measured. In this way a quantum superposition of the ion’s energy states can be studied.
The team also used trapped ions to devise a clock that is more than ten times more accurate than current caesium-based atomic clocks. Caesium clocks operate in the microwave range whereas the Boulder group‘s ion clocks use ultraviolet light – hence their name: optical clocks. An optical clock can consist of just one ion or two ions in a trap. With two ions, one is used as the clock and the other is used to read out the state of the clock ion when measured. If one had started to measure time at the beginning of the universe in the Big Bang about 14 billion years ago, the optical clock would only have been off by about five seconds today.
When we navigate with the GPS we rely on time signals from satellites that contain atomic clocks. Einstein showed us that time can be affected by speed and gravity. With an optical clock it is possible to measure a difference in the passage of time when the clock‘s speed is changed by less than 10 metres per second, or when gravity is altered as a consequence of a difference in height of only 30 centimetres. The effects of speed and gravity on Satellite clocks is enormous by comparison and must be carefully accounted for.
The Boulder group was the first to demonstrate a quantum logic operation between two individual quantum bits. If this could be expanded, it could lead to the construction of a superfast computer for certain problems. In our normal computers, the smallest unit of information is a bit that takes the value of either 1 or 0. In a quantum computer, the basic unit of information – a quantum bit or qubit – can be 1 and 0 at the same time and each additional qubit doubles the amount of possible states. Therefore, a quantum computer of only 300 qubits could hold more values simultaneously than the number of atoms in the universe. However, to build such a quantum computer the qubits need to be isolated to preserve their quantum properties, yet they must also be able to communicate with the outside world in order to pass on the results of their calculations. This is the technical challenge faced by the many groups around the world that are trying to construct such a computer.
David Jeffery Wineland was born in Milwaukee, Wisconsin, in February 1944. The family moved to California where he attended Encina High School in Sacramento before gaining his BA at UC Berkeley in 1965. He earned his PhD under Norman Foster Ramsey Jr (who won the 1989 Nobel physics prize for his work on atomic clocks) at Harvard. Wineland then worked on electron traps with Hans Dehmelt (a co-recipient of the 1989 prize, for his work on ion and electron traps) at the University of Washington. In 1975 Wineland joined the National Bureau of Standards (now NIST) where he started the ion storage group. He is also on the physics faculty at the University of Colorado.
Wineland is married to Sedna Quimby-Wineland, daughter of George Quimby, who was professor of anthropology at Washington. They have two sons.
By Volker Steger
Wineland takes up the drawing challenge without showing any surprise and sketches with a very light stroke. „Is this a trap?“ I ask. Yes it is. For ions. They are kept prisoner in these setups, laser cooled and forced to carry out quantum computations. But it's all for a ggod cause: Science!