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What Is the Triple Slit Experiment?

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.

The double-slit experiment is a key component of quantum mechanics understanding, paving the way for many of the features as described by it. By exploiting measuring prowess, I can demonstrate the wave and particle nature of objects traveling through the apparatus.

But often I wondered what would happen if you scaled this up? What happens when you bring in more slits? Turns out, the consequences are not so straightforward as you may think but then again when has quantum mechanics ever been straightforward?


Urbasi Sinha first developed the idea for a triple-slit experiment when thinking about Ψ, or the wave probability function, and how it pertains to the double-slit experiment. Each slit would have its own wave function, Ψ­A­­ and Ψ­­B, and so long as only one slit is open then the particle travelling through the slit would have either ΨA or ΨB as its wave function. When both are open, then many assume the wave function is ΨA + ΨB, for this is how the interference pattern of superimposed states can arise based on how you measure the system (Sinha 58-9).

But something sneaky has gone awry. Each of those was for when one gate was open and the other closed, therefore a lack of interaction between the two. The simple combination of wave functions doesn’t take the new interaction between the two into play. Our particle may start towards a slit but then suddenly change course and go to one of the others. It's much more complicated than the simple double-slit makes it appear to be (Ibid).

The possible path?

The possible path?


To resolve this, a missing term is needed. In 1994, Rafael Sorkin (Syracuse University) developed the Sorkin parameter to account for it. So why haven’t we heard of it often? Because many felt the term “would be so small as to be negligible.” Which is partially true. It has to be a small number otherwise it would have shown up in the data and made itself apparent by now. But if you upgrade to a triple-slit version, it should be easier to spot (59).

Sinha and the team at the Quantum Information and Computing Laboratory at the Raman Research Institute in Bangalore, India developed a microwave version of a triple-slit experiment. It was ironically done near a cornfield in the open which seems to have too many variables but actually, the reversal is true. The corn absorbs microwaves very well and with no walls around it removes reflective interference. Two horn antennae were used, one to emit the microwaves and one to absorb them. Between these was a plate with 3 slits of 10 centimeters width each and separated by 13 centimeters. Therefore, we have three wavefunctions: ΨA, ΨB, and ΨC (59-60).

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The results clearly showed that the total wave function Ψ did not equal ΨA + ΨB, + ΨC. But if you added the Sorkin parameter then it did work out. New insights into superposition, interference, and possible quantum computing upgrades can be had from these results, for we can get a fuller picture as to what is really going on (58, 60).

Looped Paths

That interference the Sorkin parameter is attempting to account for may include looped paths of particles, or where something takes a crazy path to the detector. This whole fascination with the triple slit was because of the slits interfering with the wave function of the other, but not many people imagined something going through slit A, backtracking through slit B, and then finally exiting slit C. Surely, that cannot happen…can it?

It does depend on expanding normal circumstances in order to tease out the effect but Omar S. Magana-Loaiza and Israel De Leon were able to demonstrate it using plasmons, or “strongly confined electromagnetic fields that can exist at the surface of metals,” and electrically charged slit openings. It is these two factors, when done in tandem with the triple-slit experiment, that increase the probability of these exotic paths (Zyga).

The interference pattern seen with this variation doesn’t follow the standard assumptions of traditional slit experiments but does follow a loop-trajectory pattern of weaving particles interfering with the straight pathed ones. Normally such a scenario is quite negligible which is why a ramped-up version of the experiment was required to see the effect (Ibid).

Works Cited

Sinha, Urbasi. “The Triple Slit Experiment.” Scientific American. Jan. 2020. Print. 58-60.

Zyga, Lisa. “Physicists detect exotic looped trajectories of light in three-slit experiment.” Science X Network, 06 Jan. 2017. Web. 03 Feb. 2021.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Leonard Kelley

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