Researchers at Stockholm University have been able to demonstrate how measuring a quantum system causes it to change.
Despite the importance of the measurement process within the theory, it still holds unanswered questions: Does a quantum state collapse instantly during a measurement? If not, how much time does the measurement process take and what is the quantum state of the system at any intermediate step?
The scientists have answered these questions using a single strontium ion trapped in an electric field. The measurement on the ion lasts only a millionth of a second. By producing a “film” consisting of pictures taken at different times of the measurement they showed that the change of the state happens gradually under the measurement influence.
The “film” displays the evolution during the measurement process. The individual pictures show tomography data where the height of the bars reveal the degree of superposition that is still preserved. During the measurement some of the superpositions are lost—and this loss happens gradually—while others are preserved as they should be for an ideal quantum measurement.
The results are published in the scientific journal Physical Review Letters. (Phys.org)