Submission + - Quantum Zeno Effect Allows Interaction-free Switch (technologyreview.com)
KentuckyFC writes: The quantum zeno effect is one of the more fascinating consequences of quantum mechanics. It applies to quantum systems that are evolving from one state to another, say from a state representing 0 to one representing a 1. If the quantum system starts in the 0 state, it evolves into a superposition of 0 and 1 states. A measurement can then cause it to collapse into one state or the other. But a measurement very soon after this evolution begins is much more likely to produce a 0 than a 1 and repeating this measurement rapidly enough ensures the chances of a 1 occurring approach zero. In effect, the process of repeated measurement prevents the 0 state evolving into a 1. Now a group of physicists have shown how this can be used to make a switch. The basic idea is to take a signal wave in state 0 which will evolve into a 1 when it passes it through a nonlinear waveguide. But measuring this wave will prevent this evolution. This can be done by making the signal wave interact with another "control" wave. The presence of the control wave maintains the signal wave in a 0 state while the absence of the control waves causes the signal wave to switch to a 1. The result is an all-optical switch that is interaction-free because it is the absence of the control wave that causes the switch. Such a device offers a number of important advantages over conventional all-optical switches. First, this type of switch should operate at extremely low power since there is no signal loss associated with the switching process. Second, the quantum state of the signal wave is preserved. That's a biggie. It means this kind of switch could become the heart of quantum routers that will make a kind of quantum internet possible.
