When we want to show quantum behavior (like tunneling or double slit)

[Lapidus]

When we want to show quantum behavior (like tunneling or double slit) of a large object like a buckyball molecule, what do we need to watch out for in an experiment?

Is it the following?

a, that all constituents of the object (the single atoms of the buckyball) are described by one coherent state, i.e. by one pure wavefunction (how do we achieve it??)

b, slowing it down, since Broglie wavelength, which relates the momentum of the object with wave behaviour of the object

c, isolating the object and cooling the temperature, so reducing environmental decoherence

Is that partly true?

Additional question:
If we shut down entanglement with the environment, why is the object not automatically in a pure state? Why would the object with all its constituents not be described by one coherent wave function then?

thanks

 

[Bill_K]

The key to quantum behavior is isolation. Let's be clear that the kind of quantum behavior you're talking about involves a number of buckyballs, not just one. Regarding the first and last questions, a single isolated buckyball *is* described by one coherent state.

Recall a benzene molecule, whose carbon atoms are held together by three single bonds and three double ones. The ground state of the benzene molecule is a superposition of two configurations. Chemists like to say it 'resonates' between the configurations. In a buckyball each carbon atom has three nearest neighbors and is joined to them by two single bonds and one double bond. Again the ground state is a superposition of a number of states (12,500 of them in this case!) I'd say that qualifies as quantum behavior.

To get large molecules like buckyballs to interfere with each other, you have to get them in a coherent state to begin with (there's the rub) and then insure they are sufficiently isolated from the environment to remain coherent.

 

[Lapidus]

thanks Bill_k!

To get large molecules like buckyballs to interfere with each other, you have to get them in a coherent state to begin with (there's the rub) and then insure they are sufficiently isolated from the environment to remain coherent.

But how to get them in a coherent state to begin with?

 

[Bill_K]

This is an interesting point. Reading what they did with buckyballs, it was a double slit experiment, in which you get a single buckyball to interfere with itself. Apparently there are two issues to overcome.

One is to get the coherence length of a buckyball large enough to span the distance between the two slits. It sounds like how they arranged this was by shooting them through a tiny pinhole. The second issue is to make sure the buckyball is initially in its ground state. Because if it emitted a photon halfway through the experiment, that would tell you which slit it went through, thus destroying the interference pattern!