mxx1's avatar

Entanglement

Entanglement gets treated like the weird party trick of quantum computing, but it is not limited to qubits. Any “thingy” that can hold a quantum state can be entangled – electrons, photons, atoms, superconducting circuits, ions, even large molecules.

Coherence refers to the phase relationships in the quantum states of a quantum thingy, or between multiple such thingys. In almost every system where coherence survives, it lives in electronic wavefunctions. Electrons carry coherent spin or orbital states, photons carry coherent electromagnetic field modes, atoms and ions use superpositions of internal electronic levels, superconducting circuits rely on collective quantum states of billions of electrons, and defects in crystals store coherence in the spin of a trapped electron. Even in large molecules or mechanical oscillators, the coherent part ultimately traces back to controlled superpositions in their electronic or vibrational states.

The whole circus of “superposition”, “interference”, “coherence” and “entanglement” boils down to one simple fact: quantum behaviour is just the persistence of well-defined relative phases across whatever parts of a system you are looking at.

Up close, two quantum thingys can interact. “Close” simply means physically close enough for their innards to overlap so a joint state can form. When you entangle them you give them a shared state, NOT matching individual states. Separate them by any distance and that shared state stays intact.

But here’s the magic bit. When you measure one, the shared quantum state collapses. What had been a spread of possibilities (say in superposition of electronic states) is forced into a single definite configuration. The second thingy ends up in the only value that fits that now fixed configuration. Nothing travels across space, nothing updates remotely. You didn’t change the distant particle. You just “collapsed” the shared rule that linked them.

The smart people just get used to the maths being right and deny there is any spooky action at a distance. Some of them even start believing that the maths is God.

They did come up with the concept of state space (Hilbert Space). In this maths, the whole universe is represented in a way that has no physical dimensions or time at all so the waveforms can interact to their heart’s content. Its the physicist’s equivalent of atomic metadata extended to its own dimension. They solved their intuitive problem by removing dimensionality from their mathematical representation of the universe.

It still doesn’t explain why things have to be physically “close” to cohere. The answer to that is more complex bullshit that makes as much sense as the rest of it – things can maintain coherence at infinite separation because the correlation is already built, but they cannot form coherence at a distance because nothing physical is creating it in the first place. Which is to say the explanation is the observation. The closest analogue I can think of is love and I can’t explain that either. Moving on…

It would seem however that entanglement and superposition are related in the timeless and dimensionless universe. Superposition is what a single quantum thingy can do on its own. Entanglement is what happens when a superposition refuses to split into independent parts for two or more such thingys. You can have superposition without entanglement, but you can only have entanglement when superposition is shared between multiple systems.

We built our intuition in a world where space and distance are the main organising principles, but in fact we are also living in a timeless probability matrix. It would seem that we have been tricked into thinking that timeless probability space is “timeful” dimensional space. I am guessing this is due to limitations of 20W molecular computer system that comprises our cranial innards; it was far more efficient to operate in the limiting case than to model the full circus that lies underneath.

So we know there is a “metadata” state which is where quantum behaviour lives, a probability-driven dimensionless layer with superposition, coherence and entanglement baked in. Below that maybe there is a meta-metadata state in which the constraints live that force those rules to behave consistently and give rise to the symmetries and conservation laws.

Whether that’s an ontological hierarchy or just the only way our maths can represent things, well, I will leave that as an exercise for some nerd that cares.