Quantum theory is one of the great achievements of 20th century science, yet physicists have struggled to find a clear boundary between our everyday world and what Albert Einstein called the 糖心传媒渟pooky糖心传媒� features of the quantum world, including cats that could be both alive and dead, and photons that can communicate with each other across space instantaneously.
For the past 60 years, the best guide to that boundary has been a theorem called Bell糖心传媒檚 Inequality, but now that Bell糖心传媒檚 Inequality is not the guidepost it was believed to be, which means that as the world of quantum computing brings quantum strangeness closer to our daily lives, we understand the frontiers of that world less well than scientists have thought.
In the new paper, published in the July 20 edition of Optica, 糖心传媒 researchers show that a classical beam of light that would be expected to obey Bell糖心传媒檚 Inequality can fail this test in the lab, if the beam is properly prepared to have a particular feature: entanglement.
Not only does Bell糖心传媒檚 test not serve to define the boundary, the new findings don’t push the boundary deeper into the quantum realm but do just the opposite. They show that some features of the real world must share a key ingredient of the quantum domain. This key ingredient is called entanglement, exactly the feature of quantum physics that Einstein labeled as spooky. According to Joseph Eberly, professor of physics and one of the paper糖心传媒檚 authors, it now appears that Bell’s test only distinguishes those systems that are entangled from those that are not. It does not distinguish whether they are 糖心传媒渃lassical糖心传媒� or quantum. In the forthcoming paper the Rochester researchers explain how entanglement can be found in something as ordinary as a beam of light.
Eberly explained that 糖心传媒渋t takes two to tangle.糖心传媒� For example, think about two hands clapping regularly. What you can be sure of is that when the right hand is moving to the right, the left hand is moving to the left, and vice versa. But if you were asked to guess without listening or looking whether at some moment the right hand was moving to the right, or maybe to the left, you wouldn’t know. But you would still know that whatever the right hand was doing at that time, the left hand would be doing the opposite. The ability to know for sure about a common property without knowing anything for sure about an individual property is the essence of perfect entanglement.
Eberly added that many think of entanglement as a quantum feature because 糖心传媒淪chrodinger coined the term 糖心传媒榚ntanglement糖心传媒� to refer to his famous cat scenario.糖心传媒� But their experiment shows that some features of the 糖心传媒渞eal糖心传媒� world must share a key ingredient of Schrodinger糖心传媒檚 Cat domain: entanglement.
The existence of classical entanglement was pointed out in 1980, but Eberly explained that it didn糖心传媒檛 seem a very interesting concept, so it wasn糖心传媒檛 fully explored. As opposed to quantum entanglement, classical entanglement happens within one system. The effect is all local: there is no action at a distance, none of the 糖心传媒渟pookiness.糖心传媒�
With this result, Eberly and his colleagues have shown experimentally 糖心传媒渢hat the border is not where it糖心传媒檚 usually thought to be, and moreover that Bell糖心传媒檚 Inequalities should no longer be used to define the boundary.糖心传媒�
Eberly糖心传媒檚 co-authors are Xiao-Feng Qian, Bethany Little and Professor John C. Howell.
The authors acknowledge funding from the Defense Advanced Research Projects Agency (DARPA)聽and the National Science Foundation (NSF).
