(published on 10/22/2007)
(published on 10/22/2007)
(published on 10/22/2007)
(published on 10/22/2007)
If the 'two' light waves are really propagating in the same direction, then actually they're one light wave. Whatever the polarization pattern happens to be, it will have 1/2 electric and 1/2 magnetic energy.
In a Michelson interferometer, if the phase is just right there will be perfect destructive interference in one output direction and perfect constructive interference in the other, at right angles. Thus the one beam really does have zero energy. All the energy goes into the other.
Mike W.
(published on 08/01/2009)
(published on 09/29/2010)
Shaun- Try drawing the picture. Say that we have an upward bump coming in from the left and a downward bump coming in from the right. If they're both the same symmetrical shape and the same size, when they exactly overlap the displacements cancel.
Now look at the leading (right) edge of the right-going wave. The transverse velocity there is obviously upward. Look at the trailing (right) edge of the left-going wave. The transverse velocity there is also upward. So when these overlap the net upward velocity is doubled.
Mike W.
(published on 03/29/2011)
(published on 12/26/2011)
(published on 11/11/2012)
Hi!
I was at the conference when this paper was first presented, and I really enjoyed the ensuing chaos and confusion. A lot of smart people were thoroughly confused; the results of that experiment are indeed very counterintuitive.
The author's interpretation of his experiment is that photons travel on discontinuous trajectories; that they can appear inside a region of space without ever entering or leaving that region.
Your interpretation is that destructive interference can be undone at a later time or position.
Both of these interpretations seem to be supported by the experimental evidence, but they are radical departures from standard classical or even quantum theory. As such, they should only be accepted if there is no simpler explanation within our conventional framework.
It turns out that this experiment can be understood completely using basic quantum mechanics. In fact, it can even be understood using completely classical electromagnetism! So the two interpretations above are unjustified and unnecessary.
Here's a sketch of the proper understanding in quantum mechanics. The reason this understanding wasn't immediately obvious is that the experiment cleverly wrapped several separate tricks into one cool and sneaky demonstration.
The experiment uses a small interferometer inside a larger interferometer. The inner interferometer has the cool physics, an effect called "weak value amplification." Basically, a clever arrangement of interference effects allows for any small changes made at certain mirrors to be amplified, while small changes made at other mirrors are not amplified. Specifically, the vibrations at A and B were designed to be amplified, while those at E and F were not. This effect is well understood even at a classical level; e.g. http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.66.1107
or http://arxiv.org/abs/0906.4832
Meanwhile, the outer interferometer is simply a "local oscillator"; basically, it is a strong field which interferes with any small fields coming from the inner interferometer, amplifying them until they are easy to measure. This too is a well-understood interference effect.
To put the entire picture in terms of interfering waves, it is important to realize that small amplitudes of waves are leaking through the interferometers, even when they are aligned for ALMOST destructive interference. These small bits of amplitude pick up tiny vibrations from all of the mirrors. The tiny vibrations from A and B are amplified by weak interference, and then the tiny vibrations from A, B, E, and F are all amplified by interference with the strong wave from the outer interferometer. Because vibrations from A and B get amplified twice, they are visible on the detector; E and F remain below the experimental noise.
The sneakiest part of this experiment is that the authors claim no vibrations from mirrors E and F were observed. In fact, such vibrations should have been detected, albeit at a much smaller level than those from mirrors A and B. Once you realize this, it is clear that tiny amplitudes of the wave ARE in fact interfering constructively, and it is those amplitudes that later are registered on your detector in an amplified fashion. There is NOT any "undoing of the destructive interference", nor are the photons traveling in discontinuous paths.
All of these statements agree with quantitative calculations and are equally true in quantum and classical wave mechanics. As beautiful as the experiment is, it doesn't force one to drastically change one's worldview, and it certainly doesn't challenge standard quantum mechanics.
Hope that helps!
David Schmid
(published on 12/03/2015)
(published on 10/22/2007)