# About the tutorial of Fermions and Jordan-Wigner String

+1 vote
asked Sep 30, 2017

Hi,

On the page of http://itensor.org/docs.cgi?page=tutorials/fermions
, it shows the anticommutation relation of spinless case can be derived by treating it for i < j.
However, I think the derivation doesn't work for i = j.
Is there anything I missed?
Thank you very much!

Victor.

+1 vote
answered Oct 11, 2017 by (760 points)
edited Oct 11, 2017

Hello Victor,

For i = j,
$$ci ci^\dagger + ci^\dagger ci = ai ai^\dagger + ai^\dagger ai = 1.$$
Maybe you missed the fact that for Hard Core bosons, it's
$$\{a, a^\dagger\} = 1,$$
not
$$[a, a^\dagger] = 1.$$

Hope this helps. Thanks.

commented Oct 11, 2017 by (350 points)
Hi,

You are right. Thanks for your help.
commented Oct 11, 2017 by (19,870 points)
Thanks for the answer hermit0308. I thought this was probably the correct answer but wanted to do some reading to make sure. Certainly it's consistent to define the hard core boson operators to anticommute on site (and commute when the sites are different of course).

A possibly clearer definition of the Jordan-Wigner transformation is to transform the fermion operators into spin operators attached to string instead of hard-core bosons attached to string. As you may know, in the spin interpretation, the string operators are the Pauli Z operators. Furthermore, the Pauli matrices X,Y,Z anticommute with each other so the on-site behavior is like fermions already.
commented Oct 13, 2017 by (760 points)
Hi Miles, thanks for the comment.
commented Oct 13, 2017 by (350 points)
Thanks for your help.