A Yale-led group of researchers has derived a formula for understanding where quantum objects land when they are transmitted. Credit: Illustration by Michael S. Helfenbein/Yale University
If objects in motion are like rainwater flowing through a gutter and landing in a puddle, then quantum objects in motion are like rainwater that might end up in a bunch of puddles, all at once. Figuring out where quantum objects actually go has frustrated scientists for years. Now a Yale-led group of researchers has derived a formula for understanding where quantum objects land when they are transmitted.This offers insight for controlling open quantum systems in a variety of situations.
“The formula we derive turns out to be very useful in operating a quantum computer,” said Victor Albert. “Our result says that, in principle, we can engineer ‘rain gutters’ and ‘gates’ in a system to manipulate quantum objects, either after they land or during their actual flow.” In this case, the gutters and gates represent the idea of dissipation, a process that is usually destructive to fragile quantum properties, but that can sometimes be engineered to control and protect those properties.
It is a fundamental principle of nature that objects will move until they reach a state of minimal energy, or grounding. But in quantum systems, there can be multiple groundings because quantum systems can exist in multiple states at the same time, ie superposition. That’s where the gutters and gates come in. Jiang, Albert, et al used these mechanisms to formulate the probability of quantum objects landing in 1 spot or the other. The formula also showed there was a situation in which superposition can never be sustained: when a quantum “droplet” in superposition has landed in one puddle already, but hasn’t yet arrived at the other puddle. “In other words, such a superposition state always loses some of its quantum properties as the ‘droplet’ flows completely into both puddles,” Albert said. “This is in some ways a negative result, but it is a bit surprising that it always holds.”
Both aspects of the formula will be helpful in building quantum computers. As the research community continues to develop technological platforms capable of supporting such systems, Albert said, it will need to know “what is and isn’t possible.” http://journals.aps.org/prx/abstract/10.1103/PhysRevX.6.041031
http://news.yale.edu/2016/11/17/tracking-flow-quantum-information
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