Deep in the basement of the McLennan Physical Laboratories at U of T, researchers believe they have made a major breakthrough that may lead to the construction of a powerful computer.
Jeff Lundeen and Kevin Resch, graduate students working under Dr. Aephraim Steinberg, have created a type of switch using powerful lasers and crystals that they hope may eventually be used in the building of a super-fast quantum computer.
A quantum computer is a machine that would exploit the principles of quantum mechanics. In particular, they use a principle called “superposition,” which involves particles that can be in two states at once provided they are not interfered with in any way.
An analogy of particles and states is that of a coin toss. The coin is considered the particle while the states will be “heads” or “tails.”
If the coin is flipped and then hidden, the principle of superposition makes a bizarre claim: that as long as the coin is not examined or interfered with at all, the coin will exist in both the heads-up and tails-up condition at the same time.
This analogy is only approximate, since the effects of quantum mechanics usually only become relevant on the sub-microscopic scale.
In a quantum computer, the traditional physical “bits” of information (which can be either 0 or 1) are replaced with particles in a superposition of both states—essentially ones that are both 0 and 1 at the same time.
The fact that each bit is both 0 and 1 at the same time greatly increases the potential processing power of the computer for certain tasks, like encryption.
One of the greatest challenges in building such a computer is how to get the mechanics of the computer to work while still maintaining the superposition of the particles. In order for this to happen, the particles cannot be measured or disturbed. Ironically, at the same time, the particles need to be directed and forced to perform calculations.
Resch and Lundeen believe they may have come up with a solution to part of this problem with their discovery of a “quantum switch” that will allow the superposed particles to be manipulated without destroying their superposition. To do this, they shone a high-powered laser through a special type of crystal lens.
The majority of the laser light continues through but a small fraction of the light gets split up into two identical beams at right angles to each other through a process called down conversion.
The superposed particles that the researchers used were photons, which are the particles that compose light. Photons are sturdier than other particles because it is harder to destroy their superposition. When these photons are shot through the down-converted beam, the researchers were able to mimic the behaviour of a computer switch without affecting the particles’ superposition.
Quantum computers have great potential for encryption and database searches, although Lundeen acknowledged that there is a “misconception that they will replace the desktop [computer].”
Although the invention of a quantum computer is still a long way in the future, this discovery may bring them one step closer to reality.
Photograph by Simon Turnbull
