THE ROAD MOST TAKEN
Background: This week we published a paper that defines the optimal path through quantum space. In short: classical systems are unmoved when a measurement is performed. Not so quantum systems, where continuous monitoring can direct the quantum state along a random path. The authors have tracked the quantum trajectories in a qubit, consisting of two aluminum paddles connected by a tunable Josephson junction deposited on silicon.
The team managed to determine which of the possible paths between an initial and a final quantum state is the most probable and show that these ‘optimal paths’ are in agreement with the route predicted by theory, a quantum relative of the principle of least action that defines the correct path linking two points in space and time in classical mechanics.
As well as giving insights into the interplay between measurement dynamics and evolution of a system, this work opens up new possibilities for first-principles synthesis of control sequences for complex quantum systems and in information processing.
Design challenge: This striking visualisation was created by Kater Murch, one of the authors of the paper. It shows individual quantum trajectories, with the whole showing ‘optimal paths.’ The starkness of the many white trajectory lines on a black background immediately drew our attention, and we asked the team to work with us on a cover.
Specifically, we asked Murch if he wouldn’t mind experimenting with various colour patterns, to see how it might affect the ability to see the optimal paths (see bottom image) but in the end we decided that the random colours actually made it more difficult to see the overall result, and stayed with the original black and white.