How do we maintain a system in a non-dertministic state?

[Grinkle]

@mfb From this thread -

https://www.physicsforums.com/threa...ract-with-the-particle-in-double-slit.949489/

Post #2 -

"It is not feasible to keep such a large and especially a biological object in a state without measurement"

How does one keep a multi-particle system in a state where no 'measurement' or interaction occur to cause the system to show to a deterministic state? What is practical limit and what is the bottleneck in being able to keep yet more complicated systems in a non-deterministic state?

I don't know how to word the question properly. I hope its clear what I am asking. I wanted to use the word collapse but I don't know how to use it properly so I avoided it.

 

[jedishrfu]

Some quantum entangled systems usually remain so for 90us or so. This limits the number of operations that can be performed before it decays and you lose your answer.

In this report of a few years ago they got to 10ms for two qubits:

https://phys.org/news/2015-09-entanglement-lifetime-magnitude-coupled-cavities.html

Im sure they've extended it beyond the 10ms but don't have a good reference for it.

Here's a Forbes article that may have more details on the lifetimes:

https://www.forbes.com/sites/chador...you-create-quantum-entanglement/#ef23c5e1732b

 

[Grinkle]

@jedishrfu Thanks for the articles. One thing I take away from these articles is that keeping particles in an entangled condition (I hope that is the right way to describe it) necessarily implies suspending or destroying any macro-level function the particles may have once had. So quantum bits are feasible because suspending their functionality (keeping them from being either 0 or 1) is the whole point. More complicated systems than a bit don't even have conceptual existence in a state of entanglement, because their macro-existence requires interaction of individual particles.

So its relevant to ask how many Q-bits can be entangled with each other and how long can that entanglement be sustained - these are valid engineering questions.

But beyond Q-bits and how many Q-bits, there really isn't anything meaningful to consider - is this a sound perspective? For example, the idea of a cat in a state of superposition between alive and dead is not at all meaningful, if a cats particles are all entangled, one no longer has a cat in the first place.

 

[mfb]

For example, the idea of a cat in a state of superposition between alive and dead is not at all meaningful, if a cats particles are all entangled, one no longer has a cat in the first place.

Yeah, basically.

The relevant concept here is decoherence. If you just let the wave function evolve you can get a superposition of things where there is no chance to ever bring them to interfere again. In that case the states are decoherent. Collapse interpretations then claim all but one part of this superposition magically vanish. MWI says they continue as independent "worlds". Other interpretations have other ways to look at this.