One of the barriers to using quantum states for information processing is the unexpected effects of observation. Trying to figure out how to put these counter intuitive processes to work often seems insurmountable, as is the case when contemplating how to preserve the usual superposed states of qbits when the goal is to send them over a network. That superposition, the simultaneous holding of multiple states, is the biggest difference from how information is represented in classical computing. Observation ends superposition, or more properly causes it to decohere.
Technology Review explains some new research Yu-Ping Huang and colleagues at Northwestern that may make switching and routing of quantum information possible.
First a little more about the effect itself. Imagine a photon in state 0 which has a certain probability of decaying into state 1. Now carry out a series of periodic measurements on the photon. Between the measurements, the photon evolves into a superposition 0 and 1 states and a measurement will cause it collapse into one or other of these.
However, if the time between the measurements is small, the chances of it collapsing to form a 1 are smaller than the chances of it becoming a 0. And if the periodic measurements are made rapidly enough, the probability of a measurement producing a 1 tends to zero.
In effect, the process of repeated measurement prevents the photon decaying from a 0 to a 1. That’s the quantum zeno effect, sometimes also called the watched-pot-never-boils effect.
Now Huang and co have come up with a scheme that exploits this effect to create a switch. The basic idea is to take a signal wave in state 0 which will decay or evolve into a 1 when it passes it through a nonlinear waveguide.
Not only is the quantum state, the superposition, of the information carrying bit preserved with this scheme but it could offer power savings to boot. The research is still very much in the theoretical stage but is part of a larger project at DARPA. By the time quantum computers are ready to be networked together, we may just be able to do so practically.