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quantumlib / OpenFermion

The electronic structure package for quantum computers.
Apache License 2.0
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Create Hubbard model with more than 2 spins #456

Open kevinsung opened 6 years ago

kevinsung commented 6 years ago

From discussing with Joseph Carlson, people want to study a Hubbard model where each site splits up into not only 2 spins, but more. For instance, 3 represents some quark model, 4 some nuclei maybe. We should implement these too. This would be very helpful for the nuclear physics community.

babbush commented 6 years ago

I suggest they implement this!

bryano commented 6 years ago

I'm happy to take a stab at this. Would it be better to generalize the existing single-band Hubbard class or create a new one?

babbush commented 6 years ago

I'm open to you doing it either way.

bryano commented 6 years ago

After rereading Kevin's initial comment, I think I may have misinterpreted what was wanted here. In #465, I implemented a Hubbard model with multiple degrees of freedom per site, but still assuming either no spin or spin 1/2. In any case, what I wrote can easily be extended to the case of larger-spin particles.

bryano commented 6 years ago

@kevinsung Could you provide some links to the types of Hamiltonians you had in mind?

kevinsung commented 6 years ago

I actually don't know anything about this, but I asked Joe, who said that he would provide us with some.

kevinsung commented 6 years ago

@bryano Joe provided me with these notes: multi.pdf

bryano commented 6 years ago

Thanks. #465 allows those types of Hamiltonians to be expressed, with two exceptions: it's just fermionic as is, and is limited to 1- and 2-body interactions. These are straightforward extensions.

bryano commented 6 years ago

Can we close this now?

kevinsung commented 6 years ago

We should wait until the extensions you mentioned are implemented.