



Quantum cats are hard to see
December 19, 2011
International team of researchers explain the difficulty of detecting quantum effects Are there parallel universes? And how will we know? This is one of many fascinations people hold about quantum physics. Researchers from the universities of Calgary and Waterloo in Canada and the University of Geneva in Switzerland have published a paper this week in Physical Review Letters explaining why we don't usually see the physical effects of quantum mechanics. "Quantum physics works fantastically well on small scales but when it comes to larger scales, it is nearly impossible to count photons very well. We have demonstrated that this makes it hard to see these effects in our daily life," says Dr. Christoph Simon, who teaches in the Department of Physics and Astronomy at the University of Calgary and is one of the lead authors of the paper entitled: Coarsegraining makes it hard to see micromacro entanglement. It's well known that quantum systems are fragile. When a photon interacts with its environment, even just a tiny bit, the superposition is destroyed. Superposition is a fundamental principle of quantum physics that says that systems can exist in all their possible states simultaneously. But when measured, only the result of one of the states is given. This effect is known as decoherence, and it has been studied intensively over the last few decades. The idea of decoherence as a thought experiment was raised by Erwin Schrödinger, one of the founding fathers of quantum physics, in his famous cat paradox: a cat in a box can be both dead and alive at the same time. But, according to the authors of this study, it turns out that decoherence is not the only reason why quantum effects are hard to see. Seeing quantum effects requires extremely precise measurements. Simon and his team studied a concrete example for such a "cat" by using a particular quantum state involving a large number of photons. "We show that in order to see the quantum nature of this state, one has to be able to count the number of photons in it perfectly," says Simon. "This becomes more and more difficult as the total number of photons is increased. Distinguishing one photon from two photons is within reach of current technology, but distinguishing a million photons from a million plus one is not." University of Calgary Related Quantum Physics Current Events and Quantum Physics News ArticlesMathematicians prove the Umbral Moonshine ConjectureMonstrous moonshine, a quirky pattern of the monster group in theoretical math, has a shadow  umbral moonshine. Mathematicians have now proved this insight, known as the Umbral Moonshine Conjecture, offering a formula with potential applications for everything from number theory to geometry to quantum physics. Researchers use real data rather than theory to measure the cosmosFor the first time researchers have measured large distances in the Universe using data, rather than calculations related to general relativity. Fraudproof credit cards possible with quantum physicsCredit card fraud and identify theft are serious problems for consumers and industries. Though corporations and individuals work to improve safeguards, it has become increasingly difficult to protect financial data and personal information from criminal activity. 45year physics mystery shows a path to quantum transistorsAn odd, iridescent material that's puzzled physicists for decades turns out to be an exotic state of matter that could open a new path to quantum computers and other nextgeneration electronics. The mysterious 'action at a distance' between liquid containersFor several years, it has been known that superfluid helium housed in reservoirs located next to each other acts collectively, even when the channels connecting the reservoirs are too narrow and too long to allow for substantial flow. University of Minnesota engineers make sound loud enough to bend light on a computer chipDuring a thunderstorm, we all know that it is common to hear thunder after we see the lightning. That's because sound travels much slower (768 miles per hour) than light (670,000,000 miles per hour). Cooling with the coldest matter in the worldPhysicists at the University of Basel have developed a new cooling technique for mechanical quantum systems. Using an ultracold atomic gas, the vibrations of a membrane were cooled down to less than 1 degree above absolute zero. Hiding in plain sight: Elusive dark matter may be detected with GPS satellitesThe everyday use of a GPS device might be to find your way around town or even navigate a hiking trail, but for two physicists, the Global Positioning System might be a tool in directly detecting and measuring dark matter, so far an elusive but ubiquitous form of matter responsible for the formation of galaxies. Heat transfer sets the noise floor for ultrasensitive electronicsA team of engineers and scientists has identified a source of electronic noise that could affect the functioning of instruments operating at very low temperatures, such as devices used in radio telescopes and advanced physics experiments. Entanglement made tangibleQuantum entanglement refers to the "pairing" of two subatomic particles in such a way that they form a whole quantum system. More Quantum Physics Current Events and Quantum Physics News Articles

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