Wanted: Quantum physicist, prepared to talk to person insane

[compilerbitch]

If I entangle two particles A and B in such a way that they are in the same quantum state, then entangle them such that they are in different quantum states, what happens?

1. The universe ends with the biggest core dump in the history of the multiverse

2. Both particles cease to exist in some kind of impressive explosively thrown exception

3. Both particles end up entangled to be in the same state

4. Both particles end up entangled to be in different states

5. Both particles end up entangled, but are randomly entangled as in 4. or 5. above

6. Entanglement is broken, with both particles left in random states

7. Doing what I said is impossible for some clever but not immediately obvious reason

8. I am asking a stupid question (though I'd argue that knowing exactly why it is stupid would be valuable)

(note that 5 and 6 are not equivalent if either particle ends up further entangled)

The same problem, from a quantum computing point of view, could be restated a bit more simply. Given N classical bits, the number of possible combinations of values is 2^N. With N qubits in a mutually entagled state, the number of possible combinations is strictly less than 2^N, such that if an observation (and collapse to a classical, non-superposed state) is forced, the resulting classical value is constrained by the original entangled state. My question is, what happens if the entangled state allows exactly zero possible classical values?

Comments

[ashley-y.livejournal.com]

OK, you create two particles entangled in the same state. What exactly do you do next?

[compilerbitch.livejournal.com]

I don't know. I am assuming that there is an after-particle-creation mechanism that can impose entanglement. If there isn't, this is something worth knowing too.

[compilerbitch.livejournal.com]

(thinks further)

People have built gate-like quantum devices which presumably require interaction between already-entangled particles, so operations with this kind of flavour are at least generally feasible. If this specific thing isn't possible, then knowing exactly why would be useful, and possibly very important indeed if some of the consequences of this idea pan out.

[ashley-y.livejournal.com]

Entanglement is when two particles have the same state function. If you observe the particles, you'll collapse the state function. If you do something to one particle, you'll give it another state function. So the answer is 4.

[compilerbitch.livejournal.com]

I care more about entanglement where N>2.

[fluffymark]

Where N=2 the 2 particles can be entangled post-creation in theory (although in practice is hard, but possible). For N > 2 I don't think has been achieved in practice, as the act of entangling the 3rd particle tends to "measure" and break the entanglement of the first 2, although in theory a multi-particle entanglement is perfectly acceptable.