Article Curiouser and curiouser: delving into quantum Cheshire cats

[C C]

https://physicsworld.com/a/curiouser-and...hire-cats/

EXCERPTS: . . . quantum felines get their name from the Cheshire cat in Lewis Carroll’s Alice’s Adventures in Wonderland, which disappears leaving its grin behind. As Alice says: “I’ve often seen a cat without a grin, but a grin without a cat! It’s the most curious thing I ever saw in my life!”

Things are curiouser in the quantum world, where the property of a particle seems to be in a different place from the particle itself. A photon’s polarization, for example, may exist in a totally different location from the photon itself: that’s a quantum Cheshire cat.

While the prospect of disembodied properties might seem disturbing, it’s a way of interpreting the elegant predictions of quantum mechanics. That at least was the thinking when quantum Cheshire cats were first put forward by Yakir Aharonov, Sandu Popescu, Daniel Rohrlich and Paul Skrzypczyk in an article published in 2013 (New J. Phys. 15 113015).

To get to grips with the concept, remember that making a measurement on a quantum system will “collapse” it into one of its eigenstates – think of opening the box and finding Schrödinger’s cat either dead or alive. However, by playing on the trade-off between the strength of a measurement and the uncertainty of the result, one can gain a tiny bit of information while disturbing the system as little as possible. If such a measurement is done many times, or on an ensemble of particles, it is possible to average out the results, to obtain a precise value.

[...] To make sense of this in a quantum sense, we need an intuitive mental image, even a limited one. This is why quantum Cheshire cats are a powerful metaphor, but they are also more than that, guiding researchers into new directions. Indeed, since the initial discovery, Aharonov, Popescu and colleagues have stumbled  upon more surprises.

In 2021 they generalized the quantum Cheshire cat effect to a dynamical picture in which the “disembodied” property can propagate in space (Nature Comms 12 4770). For example, there could be a flow of angular momentum without anything carrying it (Phys. Rev. A 110 L030201). In another generalization, Aharonov imagined a massive particle with a mass that could be measured in one place with no momentum, while its momentum could be measured in another place without its mass (Quantum 8 1536). A gedankenexperiment to test this effect would involve a pair of nested Mach–Zehnder interferometers with moving mirrors and beam splitters... (MORE - missing details)

[confused2]

I'm not convinced that Heisenberg's cat is useful unless you have a problem with cats getting into your garden (tick). Better would be an infinite number of tins with coins in. You shake all the tins so you don't know whether the coin will show heads or tails. When you open one (any) tin the infinite number of other tins vanish instantaneously and that's how you get one result from the infinite number of tins.

If you put dollars or cents into the all the tins you can tell which (later) by the weighing any tin but until you actually open one you still have an infinite number of tins because you havn't found out which way up the coin is.

So you can weigh a tin in one place and still have an infinite number of tins to choose from in another place,

I get this kind of information from alien sources so I claim 30 points on the Crackpot scale.

[Magical Realist]

This to me is very interesting---that properties can unhook themselves from their objects and float about like disembodied ghosts. But what happens to our whole definition of objects as "bundles of properties" if those properties are not innately tied to those objects? Is an apple still an apple if detached from its redness, roundness, and sweetness? Is there no inherent substance to the apple making it an in-itself unity of its various properties? How could we refer to such an ineffable property--its very thingness? What could be predicable about it?