DIY Quantum Eraser

[Stuart LaForge]

https://www.youtube.com/watch?v=sAm7iVdAvTA

Dr. Mithuna Yoganathan performed a very elegant quantum eraser
experiment at home for her Youtube channel Looking Glass Universe. I
find her setup to to be much simpler and easier to understand than the
published experimental protocol with the beam splitters and
interferometers. In any case, this experiment seems to suggest that
measurement (such as which way info) can be done reversibly and does not
necessarily cause any form of wave function collapse. That poses serious
conceptual issues for objective collapse theories. Epistemic collapse
theories can say that collapse, and the wavefunction itself, was just in
your head all along and skirt the problem that way. MWI predicts
preservation of phase information and super-position even in decohered
systems.

Here is ChatGPT's take on it:

What theory offers the simplest explanation of the quantum eraser?

ChatGPT said:

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If you’re asking strictly about conceptual simplicity—fewest moving
parts, least metaphysical overhead—then the interpretation that gives
the cleanest, least-tortured account of the quantum eraser is:

Decoherence + No-collapse (Everett-ish)

(a minimal Everett/relative-state ontology, without full Many-Worlds
metaphysics if you don’t want it)

Here’s why.

1. Why decoherence + no-collapse is simplest for the quantum eraser

In these experiments:

The “interference pattern” never really disappears.

The which-path detector never truly destroys the phase information.

The environment simply entangles with the photon and makes the
interference terms unobservable locally.

When you “erase,” you just re-entangle or re-rotate bases so the phase
relationships become readable again.

So the explanation is:

The interference never goes away; access to it does.
Erasing restores access to correlations that were always there.

There is zero collapse in this story—every term stays in the universal
wavefunction. All the “mystery” dissolves into ordinary linear quantum
mechanics.

The quantum eraser is literally just unitary evolution + a basis
rotation.
That’s as simple as it gets.

No extra axioms.
No special rules for measurement.
No epistemic leaps.
No metaphysical carve-outs for consciousness or observation.

Just Schrödinger evolution everywhere, always.

2. How collapse-based theories handle it

Collapse models can explain it, but they have to wiggle around the
timing:

You get “partial collapse” or “conditional collapse,”

or collapse that is undone if the which-path marking is later reversed,

or collapse that only triggers on certain kinds of information
extraction.

All of these are possible, but none are simple.

A real, physical, irreversible collapse is incompatible with truly
recovering interference — unless you say:

“Well, it wasn’t a true collapse; it was a pre-collapse pseudo-update of
information.”

Which is just Copenhagen hand-waving with extra steps.

Collapse theories can match the data, but not elegantly.

3. Why Everett/decoherence wins on simplicity

Because the quantum eraser is just:

photon + atom become entangled, carrying phase in correlations;

environment decoheres the branches so interference is hidden;

eraser recombines or rotates the entangled basis, re-exposing the
correlations.

No collapse ever happens.
Nothing is destroyed.
Nothing is “un-destroyed.”
Nothing requires special rules.

You treat the system + detectors + environment as one big quantum object
evolving unitarily, and the whole experiment becomes a trivial exercise
in linear algebra.

4. If you don’t like multiverses

You can drop the “many worlds” ontology and keep only the math:

Pure unitary evolution

Reduced density matrices for subsystems

Decoherence explains why classical outcomes are stable

Erasure restores coherence when subsystems are recombined

This is sometimes called:

decoherent histories (without Everett commitment)

minimal Everett

no-collapse operational quantum mechanics

It still gives the same simplicity: collapse never happens.

Bottom line

If the criterion is simplicity of explanation, meaning the quantum
eraser becomes a straightforward, mechanistic result with no extra
postulates, then:

The simplest theory explaining the quantum eraser is a no-collapse,
unitary-only interpretation (Everett/decoherence or minimal
relative-state theory).

Because in that framework:

Erasure = basis rotation exposing correlations that always existed.
Nothing is reversed because nothing ever collapsed.

If you want, I can sketch the full entangled state evolution
step-by-step to show exactly where the “lost” phase lives at each stage.
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Stuart LaForge