On Delay of the Delayed Choice Experiment

Anthony J. Leggett

Jeffrey H. Boyd

Kim et al published an article, ``A delayed choice quantum eraser,'' in 1999 that appeared to show many remarkable things, including that the choice of observable erases the interference fringes that were previously recorded in a double slit experiment. However, the solidity of those conclusions hinges on whether or not quantum mechanics provides the only available explanation of that experiment. By thinking outside the box we have a different way of viewing that experiment. We find there is no delayed choice in the Kim experiment of 1999. There is no quantum eraser. What appears to be a delayed choice and a quantum eraser involve a different understanding of Kim's experiment than the one we favor. We also show how the double slit experiment can be understood with local cause and effect, and without complementarity.

Ke Liu, Yuan Xu, Weiting Wang +9 more

Wave-particle complementarity lies at the heart of quantum mechanics. To illustrate this mysterious feature, Wheeler proposed the delayed-choice experiment, where a quantum system manifests the wave- or particle-like attribute, depending on the experimental arrangement, which is made after the system has entered the interferometer. In recent quantum delayed-choice experiments, these two complementary behaviors were simultaneously observed with a quantum interferometer in a superposition of being closed and open. We suggest and implement a conceptually different quantum delayed-choice experiment by introducing a which-path detector (WPD) that can simultaneously record and neglect the system's path information, but where the interferometer itself is classical. Our experiment is realized with a superconducting circuit, where a cavity acts as the WPD for an interfering qubit. Using this setup, we implement the first twofold delayed-choice experiment, which demonstrates that the system's behavior depends not only on the measuring device's configuration that can be chosen even after the system has been detected but also on whether we a posteriori erase or mark the which-path information, the latter of which cannot be revealed by previous quantum delayed-choice experiments. Our results represent the first demonstration of both counterintuitive features with the same experimental setup, significantly extending the concept of quantum delayed-choice experiment.

T. Hellmuth, Arthur Zajonc, HERBERT WALTHER

Bram Gaasbeek

The delayed choice experiments are a collection of experiments where the counterintuitive laws of quantum mechanics are manifested in a very striking way. Although the delayed choice experiments can be very accurately described with the standard framework of quantum optics, a more didactical and intuitive explanation seems not to have been given so far. In this note, we fill that gap.

M. Bahrami, Afshin Shafiee