Watching Schrodinger's Cat Die: A Famous Example of the Wierdness of Quantum Mechanics

Watching Schrodinger's Cat Die: "Gently recording the cat's paw prints both makes it die, or come to life"

In the world of quantum physics, a system can be in two superposed states at the same time, as long as no one is observing. An observation perturbs the system and forces it into one or the other. Physicists say that the original entangled wave functions collapsed into a classical state.

Continuous monitoring of a qantum system can direct the quantum state along a random path. This three-dimensional map shows how scientists tracked the transition between two qubit states many times to determine the optimal path. Irfan Siddiqi image.

In the past 10 years, theorists such as Andrew N. Jordan, professor of physics at the University of Rochester and coauthor of the Nature paper, have developed theories predicting the most likely way in which a quantum system will collapse.

"The Rochester team developed new mathematics to predict the most likely path with high accuracy, in the same way one would use Newtown's equations to predict the least cumbersome path of a ball rolling down a mountain," Siddiqi said. "The implications are significant, as now we can design control sequences to steer a system along a certain trajectory. For example, in chemistry one could use this to prefer certain products of a reaction over others."

Lead researcher Steve Weber, a graduate student in Siddiqi's group, and Siddiqi's former postdoctoral fellow Kater Murch, now an assistant professor of physics at Washington University in St. Louis, proved Jordan correct. They measured the trajectory of the wave function of a quantum circuit — a qubit, analogous to the bit in a normal computer — as it changed. The circuit, a superconducting pendulum called a transmon, could be in two different energy states and was coupled to a second circuit to read out the final voltage, corresponding to the pendulum's frequency.

"If you did this experiment many, many times, measuring the road the system took each time and the states it went through, we could determine what the most likely path is," Siddiqi said. "Then we could design a control sequence to take the road we want to take for a given quantum evolution."

If you probed a chemical reaction in detail, for example, you could find the most likely path the reaction would take and design a way to steer the reaction to the products you want, not the most likely, Siddiqi said.

"The experiment demonstrates that, for any choice of final quantum state, the most likely or 'optimal path' connecting them in a given time can be found and predicted," Jordan said. "This verifies the theory and opens the way for active quantum control techniques."

The work was supported in part by the Office of Naval Research and the Office of the Director of National Intelligence (ODNI) of the Intelligence Advanced Research Projects Activity (IARPA), through the Army Research Office.

RELATED INFORMATION

Irfan Siddiqi’s Quantum Nanoelectronics Laboratory
Kater Murch’s website
Andrew Jordan’s website
Mapping the optimal route between two quantum states (7/31/14 Nature)

Pages: 1 · 2

Health and Science, Learning, Senior Women Web, Articles, Sightings, What's New Add comments

Watching Schrodinger's Cat Die: "Gently recording the cat's paw prints both makes it die, or come to life"

More Articles