# Query on use of prism in delayed choice quantum eraser experiment

• I
• Steve4Physics
In summary, the Delayed Choice Quantum Eraser experiment involves various schematic diagrams, some of which include a prism to diverge the two idler photon paths. However, the way in which the prism is shown refracting the 'idler rays' in these diagrams contradicts Snell's law. It is unclear if this is a mistake or if there is a misunderstanding. One of the diagrams also has incorrect ray paths through the Glan-Thomson prism. A correct diagram has been found, but concerns about copyright have been raised.

#### Steve4Physics

Homework Helper
Gold Member
TL;DR Summary
Query on use of prism in delayed choice quantum eraser experiment
Hi. I’ve seen a number of schematic diagrams for the Delayed Choice Quantum Eraser experiment. Some include a prism to make the two idler photon paths diverge.

However, the prism is shown refracting the ‘idler rays’ in a way which contravenes Snell’s law. E.g. see prism marked ‘PS’ (not the Glan-Thompson prism) here:

(from https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser)

Is this a mistake or have I misunderstood something? Thanks.

Steve4Physics said:
However, the prism is shown refracting the ‘idler rays’ in a way which contravenes Snell’s law. E.g. see prism marked ‘PS’ (not the Glan-Thompson prism) here:
Hmmm. I doubt the prism in the diagram is supposed to show the actual path of light in the experiment.

Steve4Physics
Drakkith said:
Hmmm. I doubt the prism in the diagram is supposed to show the actual path of light in the experiment.
Yes. It seems that part of the diagram is a bit of a 'bodge'. But the rest of the diagram seems OK. But I've found similar diagrams showing the same thing, so it's very puzzling.

No one is worried about Snell's law when they're throwing shapes and lines into powerpoint.

tistemfnp, vanhees71, Steve4Physics and 1 other person
Drakkith said:
No one is worried about Snell's law when they're throwing shapes and lines into powerpoint.
I guess so. But it's much more than a minor misjudgement of angles.

And I noticed another mistake in the diagram. The ray paths through the Glan-Thomson prism (just after the SPDC non-linear crystal) are wrong.

Maybe I'm just being too picky!

With a bit of searching (using Google Images) I've now found a diagram which appears correct. I’m not sure about copyright so here's just the link:
https://www.researchgate.net/public...-delayed-choice-quantum-eraser-experiment.ppm

Drakkith and vanhees71