Nobel Prize physics winners one step closer to achieving quantum computer


Two quantum physicists, David J. Wineland from the University of Colorado in Boulder and Serge Haroche from the Collège de France in Paris, have won the Nobel Prize in Physics this year, "for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems", and their research has taken us one step closer to achieving the next stage in computing power — the quantum computer.

The quantum world that atomic particles exist in is a strange place. If we could shrink down and enter that world, we could perform feats that would amaze those that were in a world bound by classical physics (like we are now). Concepts such as 'time' and 'place', 'awake' and 'asleep', or even 'alive' and 'dead', as the example of Schrödinger's famous thought experiment demonstrates, would become meaningless. We could switch back and forth between these states at will, and we could even exist in more than one state — here and there, awake and asleep, alive and dead — at the same time.

This condition of being in more than one state at the same time is known as 'superposition'. It is their independent discovery of methods to not only accurately measure particles, but also to place them into a state of superposition, that earned Wineland and Haroche the Nobel Prize and has brought us closer to quantum computing.

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'Classical' computing is based on bits, and each bit can have one of two states, one or zero, used similar to a light switch being on or off. Two bits can be used to represent one of four different states — 00, or 01, or 10, or 11. Add more bits, and you can represent more states, equal to 2 to the nth power (where n is the number of bits). In the case of quantum computing, 'qubits' are used, each of which is capable of having a state of one, or zero, or both one and zero at the same time. Two qubits together can represent the same states as bits can — 00, 01, 10 and 11 — but they can represent all of those states simultaneously. This represents a vast, quantum leap (if you'll excuse the pun) in the amount of information that can be stored and processed at the same time.

The problem with achieving quantum computing has been a fairly basic one — at least for quantum physics — that you could not accurately measure the quantum state of a particle (such as a photon) without altering the state of the particle. The very act of measuring the particle imparts energy to it, which alters it sufficiently that it can no longer be considered the same particle. You have effectively changed it into a different particle and the original is considered 'destroyed'. In order for quantum computing to work, individual quantum particles must remain intact, with only their specific quantum state changing to reflect a state of being a one, zero, or both. The two Nobel laureates approached this problem from two opposite directions.

Wineland's group trapped charged atoms (ions) of beryllium using the electric fields from an electrode 'cage', which suspended the ions in a vacuum and isolated them from everything else around them. They then used a laser beam to reduce the natural thermal motion of the ions, putting them into their lowest energy state (near absolute zero Kelvin, or minus 273.15 degrees C), and by using carefully tuned laser pulses, they were able to change the energy state of the ions, and even put them into superposition states.

Haroche and his team bounced microwave photons between two mirrors, set about 3 cm apart, that were made of superconducting material cooled to near absolute zero. These mirrors were pretty close to perfect reflectors, and the photons were able to bounce back and forth between them for about a tenth of a second before being lost or absorbed. To a photon, that is an extremely long life-time, and since they are moving at the speed of light they travel about 40,000 kilometres in that time, which is a little less than the equatorial circumference of the Earth. The team sent individual 'Rydberg atoms' — which are about 1000 times larger than typical atoms — through the gap between the mirrors at a very specific speed, where they interacted with the microwave photons and then exited out the other side. If a shift was detected in the quantum state the Rydberg atom as it exited the gap, it indicated the presence of the microwave photon in the gap and the quantum state of the photon. If no shift was detected, it meant that the photon had been lost or absorbed before the Rydberg atom passed through the gap. Thus, Haroche and his team were able to measure the presence and state of a photon without destroying it, and by altering the experiment slightly, they were able to accomplish the extremely difficult task of counting the photons as well.

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Winning the Nobel Prize these days comes with an award of 8 million Swedish kronor (about $1.17 million Canadian dollars). This is down from 10 million kronor in previous years. With the worldwide financial crisis, the Nobel foundation cut the value of the prize this year, due to strained resources.

The efforts of Wineland's and Haroche's teams have put quantum computing within reach, however there are still some obstacles to overcome. Further testing will determine whether systems using more qubits together can be adequately controlled, and if they can (there's nothing to say they can't), the next stage would be making such a computer practical and easy to build.

Current predictions are that we'll have a working, practical quantum computer by the end of this century. Given how much the world has changed due to invention of the classical computer, I'm sure that any speculation now about what life will be like after we achieve quantum computing will seem as quaint to the people then, as the predictions from people in the 1800's and 1900's about how life would be like now seem to us. At the same time, I think I'm safe in saying that it will be an incredible time to live in.

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