The experiment is an extension of the double slit experiment. It seems that the photon "knows in advance" whether the second slit is open or closed. (http://www.hotquanta.com/wpd.html#BM2Slit)
It seems clear that there is some sort of feedback loop between the sensor of the wave/particle and the single/double slits.
In normal experience, we see both waves and particles as moving in one direction, and as time passes, the wave/particle moves along. I would like to theorize an additional dimension besides the four common (three space dimensions and one time dimension). This fifth dimension is outside of time or has no connection to time. So the wave/particle exists in the fifth dimension in a way that is different than the way it exists in the other four dimensions. In the fifth dimension, the wave/particle is the same object both at the single/double slit and at the sensor.
Let me provide a metaphor for this fifth dimension. Let's say I have a box with a dial on the box. I can turn the dial to zero thru nine. I put the box on the table, and turn the dial to zero. I take a photograph of the dial. I put the box on the chair and turn the dial to five. I look at the photograph, and it shows the dial at five.
Let me do a thought experiment. Consider the classic double slit experiment. Only this time, the source of the photon is a galaxy one billion light years away from the single/double slit. Then the sensor is another one billion light years away from the single/double slit. Assume that the wave/particle that exists in this fifth dimension uses the fifth dimension as a feedback. The wave/particle travels from the source galaxy to the single/double slit where a scientist is standing, and then travels to the sensor. When the scientist standing at the single/double slit opens the second slit, the scientist at the sensor sees a wave. When the scientist at the slit closes the second slit, the scientist at the sensor sees a particle. Because the fifth dimension is outside of time, the effect is immediate. It is as if the wave/particle at the sensor is in the same position, fifth dimensionally speaking, as the wave/particle at the sensor, even though the two are separated by a billion light years in the normal three dimensions.
Ok, that's the hypothesis. Now you do the math.
Here is the original article.
A new thought experiment makes it clearer than ever that photons aren’t simply particles or waves.
Proposal for a Quantum Delayed-Choice Experiment
Radu Ionicioiu and Daniel R. Terno
Phys. Rev. Lett. 107, 230406 (2011)
Published December 2, 2011
C. Orzel/Union College
Which way did it go? In a Mach-Zehnder interferometer, photons can appear to go along either of two paths (particle behavior) or along both paths (wave behavior), depending on whether the second beam splitter is in place. A new thought experiment would allow both behaviors simultaneously.
Quantum physics tells us that a photon isn’t strictly a particle or strictly a wave. And yet most of us will revert back—whenever we can—to familiar concepts of billiard balls or vibrating strings when picturing photons in our heads. A new thought experiment, proposed in Physical Review Letters, hopes to break us of these old habits. The authors imagine a type of quantum switch that controls whether a simple optical measurement tests for particlelike or wavelike behavior in a single photon. This slight reworking of a famous experiment demonstrates with logical precision the futility of trying to label the photon as a particle or a wave.
The wave-particle duality is often illustrated by splitting a light beam so that it travels along two separate paths that later merge to form an interference pattern from the combined beams. For a dim beam delivering photons one-at-a-time, this interference suggests that each photon is a wave that travels down both paths simultaneously. But if the paths are observed individually, then the photon will behave like a particle, traveling down only one path or the other and generating no interference. The fact that no experiment can measure both the wave and the particle behaviors simultaneously is called the principle of complementarity.