# I Does macro-object get entangled?

Tags:
1. Sep 4, 2016

### entropy1

Suppose we have a pair of entangled particles. Suppose the first particle of the pair interacts with a macro-object and decoheres. Does the macro object get entangled with the second particle?

2. Sep 4, 2016

Entanglement can only happen between quantum numbers.
One of the particles can interact with very limited part of the macro object, by that the information is lost because you cannot know which particle is the entangled one. If you do know which is the new entangled particle than you go back to the beginning of the question.

3. Sep 4, 2016

### StevieTNZ

I would say yes, as that follows from the Schrodinger equation.

4. Sep 4, 2016

### Staff: Mentor

Leonard Susskind gave a lecture entitled ER=EPR in which he posits creating pairs of black holes entirely out of entangled particle pairs, thus making the black holes fully entangled. I would say that a black hole is about as macro as you can get.

5. Sep 5, 2016

### vanhees71

Entanglement can in principle occur for any quantum mechanical system. E.g., you can have entanglement between phonon states of two diamonds (at room temperature!):

http://www.scientificamerican.com/article/room-temperature-entanglement/

K. C. Lee et al, Entangling Macroscopic Diamonds at Room Temperature, Science 334, 1253 (2011)

Last edited by a moderator: May 8, 2017
6. Sep 5, 2016

### entropy1

I am particulary interested in entanglement of a macro object with one of a pair of entangled particles.

If I understand correctly, decoherence of a particle in a macro object leaves the macro object in a single state, is that correct?

7. Sep 5, 2016

### Staff: Mentor

The entire quantum system consisting of two particles and the macroscopic object is always - before, during, and after the experiment - in a single state. At no time does it ever make sense to talk about anything not being in a single state.

8. Sep 5, 2016

### Staff: Mentor

Superposition of macroscopic objects (~50micrometer) has been demonstrated, and I think they used entanglement with something else (light?) to measure that superposition. You have to be very careful to avoid decoherence, however.

In MWI, you could see the objects as entangled even after decoherence, but it is an entanglement that you cannot use in any way.

9. Sep 5, 2016

### dlgoff

Does this count? I think so.

Last edited by a moderator: May 8, 2017
10. Sep 5, 2016

### StevieTNZ

That state being a superposition of possible outcomes?

11. Sep 5, 2016

### Staff: Mentor

In general no, it's a density matrix. It may be a pure state which can be represented as a ray in some Hilbert space, and if so we can choose a basis in which it will be a superposition of possible outcomes (and other bases in which it will not be such a superposition).

12. Sep 6, 2016

### entropy1

So, in all, I understand that it is possible to entangle particle B of an entangled pair A-B with macro-object O, in the case that particle A interacts and decoheres in object O, so that O and B become entangled? Is this dependent of the interpretation of QM used?

13. Sep 6, 2016

### Staff: Mentor

You're asking the English language to do more than it is capable of. The mathematical formalism is clear and properly describes entanglement and decoherence; natural language does not.