- #1
Fightfish
- 954
- 118
So, I was examining the ground state of a Bose-Hubbard dimer in the negligible interaction limit, which essentially amounts to constructing and diagonalizing a two-site hopping matrix that has the form
[tex]
H_{i,i+1}^{(n)} = H_{i+1,i}^{(n)} = - \sqrt{i}\sqrt{n-i+1},
[/tex]
with all other elements zero. The superscript [itex]n[/itex] refers to the fixed number of particles present on the dimer, and the dimension of the matrix is given by [itex]n+1[/itex].
Essentially this gives rise to a hollow centrosymmetric tridiagonal matrix. Explicitly, we have:
[tex]
H^{(2)} =
\left(
\begin{array}{ccc}
0 & -\sqrt{2} & 0 \\
-\sqrt{2} & 0 & -\sqrt{2} \\
0 & -\sqrt{2} & 0 \\
\end{array}
\right)
[/tex][tex]
H^{(3)} =
\left(
\begin{array}{cccc}
0 & -\sqrt{3} & 0 & 0 \\
-\sqrt{3} & 0 & -2 & 0 \\
0 & -2 & 0 & -\sqrt{3} \\
0 & 0 & -\sqrt{3} & 0 \\
\end{array}
\right)
[/tex][tex]
H^{(4)} =
\left(
\begin{array}{ccccc}
0 & -2 & 0 & 0 & 0 \\
-2 & 0 & -\sqrt{6} & 0 & 0 \\
0 & -\sqrt{6} & 0 & -\sqrt{6} & 0 \\
0 & 0 & -\sqrt{6} & 0 & -2 \\
0 & 0 & 0 & -2 & 0 \\
\end{array}
\right)
[/tex] and so on.
In examining the unnormalized eigenstate with the lowest (most negative) eigenvalue, there seems to exist a Pascal-triangle-like sequence:
[tex]|\psi_{g}^{(1)}\rangle= [1,1][/tex][tex]|\psi_{g}^{(2)}\rangle= [1,\sqrt{2},1][/tex][tex]|\psi_{g}^{(2)}\rangle= [1,\sqrt{3},\sqrt{3},1][/tex][tex]|\psi_{g}^{(3)}\rangle= [1,\sqrt{4},\sqrt{6},\sqrt{4},1][/tex][tex]|\psi_{g}^{(4)}\rangle= [1,\sqrt{5},\sqrt{10},\sqrt{10},\sqrt{5},1][/tex]
This is highly suggestive that some sort of recurrence relation or mapping to binomial expansion exists; however thus far I have not been successful in trying to extract it. Might some one be able to shed some light on this?
[tex]
H_{i,i+1}^{(n)} = H_{i+1,i}^{(n)} = - \sqrt{i}\sqrt{n-i+1},
[/tex]
with all other elements zero. The superscript [itex]n[/itex] refers to the fixed number of particles present on the dimer, and the dimension of the matrix is given by [itex]n+1[/itex].
Essentially this gives rise to a hollow centrosymmetric tridiagonal matrix. Explicitly, we have:
[tex]
H^{(2)} =
\left(
\begin{array}{ccc}
0 & -\sqrt{2} & 0 \\
-\sqrt{2} & 0 & -\sqrt{2} \\
0 & -\sqrt{2} & 0 \\
\end{array}
\right)
[/tex][tex]
H^{(3)} =
\left(
\begin{array}{cccc}
0 & -\sqrt{3} & 0 & 0 \\
-\sqrt{3} & 0 & -2 & 0 \\
0 & -2 & 0 & -\sqrt{3} \\
0 & 0 & -\sqrt{3} & 0 \\
\end{array}
\right)
[/tex][tex]
H^{(4)} =
\left(
\begin{array}{ccccc}
0 & -2 & 0 & 0 & 0 \\
-2 & 0 & -\sqrt{6} & 0 & 0 \\
0 & -\sqrt{6} & 0 & -\sqrt{6} & 0 \\
0 & 0 & -\sqrt{6} & 0 & -2 \\
0 & 0 & 0 & -2 & 0 \\
\end{array}
\right)
[/tex] and so on.
In examining the unnormalized eigenstate with the lowest (most negative) eigenvalue, there seems to exist a Pascal-triangle-like sequence:
[tex]|\psi_{g}^{(1)}\rangle= [1,1][/tex][tex]|\psi_{g}^{(2)}\rangle= [1,\sqrt{2},1][/tex][tex]|\psi_{g}^{(2)}\rangle= [1,\sqrt{3},\sqrt{3},1][/tex][tex]|\psi_{g}^{(3)}\rangle= [1,\sqrt{4},\sqrt{6},\sqrt{4},1][/tex][tex]|\psi_{g}^{(4)}\rangle= [1,\sqrt{5},\sqrt{10},\sqrt{10},\sqrt{5},1][/tex]
This is highly suggestive that some sort of recurrence relation or mapping to binomial expansion exists; however thus far I have not been successful in trying to extract it. Might some one be able to shed some light on this?