Quantum computers will be able to perform tasks that silicon-based computers wouldn’t be able to do, like cracking the codes that protect bank transactions. Several research teams have revealed solid evidence that quantum physics does embody a level of complexity that classical computers could never match. The new devices these groups have built are much simpler to build than quantum computers but could some day perform some of the same tasks.
The scientists published their findings in the journal Science¹ ² and in pre-prints in arXiv³ ⁴. It’s been theorized previously that there are many obstacles to quantum computing, such as the fact that certain quantum particles, like photons, have behaviors that are impossible to predict using ordinary computers.
In the most recent studies, researchers have injected four identical photons into a network of beam splitters on a chip¹. Thanks to quantum interference, which happens when photons strike a beam splitter simultaneously, the photons take a different path through the optical maze each time the experiment is run. Detectors spot the particles at the end of the run, revealing the probabilities of arriving at all possible destinations.
Without the device that the researchers constructed, calculating these probabilities would be mathematically difficult, yet not impossible. Every added particle doubles the computational difficulty. If 100 photons were put in such a device, the most powerful supercomputer on the planet wouldn’t be able to crunch the numbers.
The experiment could be scaled up to that size, but generating large numbers of identical photons will require getting the timing just right and this won’t be easy. Thankfully other teams are working on similar projects as well. A team in Australia unveiled their own prototype² and two more groups, in Austria and Italy, describe similar experiments³ ⁴.
These machines are proofs of principle, and their construction has only been recently possible thanks to the ability to produce simultaneous batches of identical photons with high reliability.
- Spring, J. B. et al. Science http://dx.doi.org/10.1126/science.1231692 (2012).
- Broome, M. et al. Science http://dx.doi.org/10.1126/science.1231440 (2012).
- Crespi, A. et al. http://arXiv.org/abs/1212.2783 (2012).
- Tillmann, M. et al. http://arXiv.org/abs/1212.2240 (2012).