As a quantum state collapses from a quantum superposition to a classical state or a different superposition, it will follow a path known as a quantum trajectory. For each start and end state there is an optimal or "most likely" path, but it is not as easy to predict the path or track it experimentally as a straight-line between two points would be in our everyday, classical world.
In a new paper featured on the July 30 cover of Nature, scientists from the Institute for Quantum Studies at Chapman University, the University of Rochester, University of California at Berkeley, and Washington University in St. Louis have shown that it is possible to track these quantum trajectories and compare them to a recently developed theory for predicting the most likely path a system will take between two states.
Andrew N. Jordan, professor of physics at the University of Rochester and member of Chapman's Institute for Quantum Studies, is one of the authors of the paper. His group had developed this new theory in an earlier paper. The results published this week show good agreement between theory and experiment.
For their experiment, the Berkeley and Washington University teams devised a superconducting qubit with exceptional coherence properties, permitting it to remain in a quantum superposition during the continuous monitoring. The experiment actually exploited the fact that any measurement will perturb a quantum system. This means that the optimal path will come about as a result of the continuous measurement and how the system is being driven from one quantum state to another.
Kater Murch, co-author and assistant professor at Washington University in St. Louis, explained that a key part of the experiment was being able to measure each of these trajectories while the system was changing, something that had not been possible until now. This was made possible by using a breakthrough called "weak measurements" introduced
|Contact: Sheri Ledbetter|