One of the striking features of a qubit is that, unlike a classical bit, it can be in two states at the same time. That is, until a measurement is made on the qubit, causing it to collapse into a single state. This measurement process and the resulting collapse may at first seem irreversible. (Once you open the box to find a dead cat, there's no going back, right?) But recently physicists have been investigating the possibility of "uncollapsing," or recovering the state of, a qubit that has been partially collapsed due to a weak measurement. The results could be used for implementing quality control in quantum systems.
In a new paper published in Physical Review Letters, physicists J. A. Sherman, et al., at the University of Oxford, have experimentally demonstrated a recovery method that can restore the state of a single qubit, in principle perfectly, after it has partially collapsed.