A team of University of Toronto physicists have demonstrated a newtechnique to squeeze light to the fundamental quantum limit, afinding that has potential applications for high-precisionmeasurement, next-generation atomic clocks, novel quantum computingand our most fundamental understanding of the universe.
Krister Shalm, Rob Adamson and Aephraim Steinberg of U of T´sDepartment of Physics and Centre for Quantum Information and QuantumControl, publish their findings in the January 1 issue of the prestigiousinternational journal Nature.
"Precise measurement lies at the heart of all experimental science:the more accurately we can measure something the more information we canobtain. In the quantum world, where things get ever-smaller, accuracy ofmeasurement becomes more and more elusive," explains PhD graduate studentKrister Shalm.
Light is one of the most precise measuring tools in physics and hasbeen used to probe fundamental questions in science ranging fromspecial relativity to questions concerning quantum gravity.. Butlight has its limits in the world of modern quantum technology.
The smallest particle of light is a photon and it is so small that anordinary light bulb emits billions of photons in a trillionth of asecond.. "Despite the unimaginably effervescent nature of these tinyparticles, modern quantum technologies rely on single photons to store andmanipulate information. But uncertainty, also known as quantum noise, getsin the way of the information," explains Professor Aephraim Steinberg.
Squeezing is a way to increase certainty in one quantity such asposition or speed but it does so at a cost. "If you squeeze thecertainty of one property that is of particular interest, theuncertainty of another complementary property invevitably grows," he says.
In the U of T experiment, the physicists combined three separatephotons of light together inside an optical fibre, to create atriphoton. "A strange feature of quantum physics is that when severalidentical photons are combined, as they are in optical fibres such asthose used to carry the internet to our homes, they undergo an "identitycrisis" and one can no longer tell what an individual photon is doing,"Steinberg says. The authors then squeezed the triphotonic state to gleanthe quantum information that was encoded in the triphoton´s polarization.(Polarization is a property of light which is at the basis of 3D movies,glare-reducing sunglasses, and a coming wave of advanced technologies suchas quantum cryptography.)
In all previous work, it was assumed that one could squeezeindefinitely, simply tolerating the growth of uncertainty in theuninteresting direction. "But the world of polarization, like theEarth, is not flat," says Steinberg.
"A state of polarization can be thought of as a small continentfloating on a sphere. When we squeezed our triphoton continent, atfirst all proceeded as in earlier experiments. But when we squeezedsufficiently hard, the continent lengthened so much that it began to "wraparound" the surface of the sphere," he says.
"To take the metaphor further, all previous experiments were confined tosuch small areas that the sphere, like your home town, looked as though itwas flat. This work needed to map the triphoton on a globe, which werepresented on a sphere providing an intuitive and easily applicablevisualization. In so doing, we showed for the first time that thespherical nature of polarization creates qualitatively different statesand places a limit on how much squeezing is possible," says Steinberg.
"Creating this special combined state allows the limits to squeezing to beproperly studied," says Rob Adamson. "For the firsttime, we have demonstrated a technique for generating any desiredtriphoton state and shown that the spherical nature of polarization statesof light has unavoidable consequences. Simply put: to properly visualizequantum states of light, one should draw them on a sphere."
Source: University of Toronto