I'd thought it was theoretically impossible to do this, not just impractical.
Amplify’d from www.newscientist.com
IT MAY soon be possible to extract information from a quantum object - and even manipulate it - without simultaneously destroying its delicate quantum state. The result would be a boon for quantum computing, which requires control over such states. It would also defy a thought experiment dreamed up by physicist Erwin Schrödinger: in principle it is now possible to peek inside his box without endangering the life of the precarious pussycat inside.
In 2010, physicists put the largest system yet into a superposition: a 40-micrometre-long strip of piezoelectric material, which expands and contracts in response to voltage changes. They put it into a superposition of both minimal and more vigorous oscillation, but the method they used to observe the system caused it to lose this dual state.
Another team now proposes going a step further, putting a wire of about the same size in a superposition and offering a scheme to observe, and even manipulate it, without destroying the weird quantum state. Kurt Jacobs at the University of Massachusetts, Boston, and his team describe their idea in a study to appear in Physical Review A.
The first step is to put the wire into a superposition in which vibrations simultaneously displace it by equal amounts in opposite directions, like a guitar string that gets plucked in two directions at once. Next, an electric charge can be added to the wire, creating an electromagnetic field that can be detected by a sensor (see diagram).
Even though the sensor cannot pinpoint the position of the charge - and therefore the wire - it can detect how far the charge is from a neutral, "unplucked" position. That reveals some information about the system - essentially providing a glimpse inside the box containing Schrödinger's cat. The key is that it avoids opening the box completely, which would destroy the superposition, says Jacobs: "I extract information, but in a way that I don't learn too much."
Carrying out this experiment is still a few years awayRead more at www.newscientist.com
See this Amp at http://bit.ly/lbLJ7i