Bose 2.2 User Manual Page 39

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Refs. [51, 118]),
E
(2)
inter
(d
lat
) =
g
dd
N
2
(2π)
3/2
σ
3
ρ
1
Z
0
du
(1 3u
2
)(1 u
2
(η + L
2
))
(1 ηu
2
)
5/2
exp
L
2
u
2
2(1 ηu
2
)
!
, (2.33)
where
L
def
= d
lat
ρ
is the normalized distance between the samples, and
η
def
=
1
κ
2
. The
remaining integral in Eq. (2.33) must be computed numerically.
We show the value of the inter-site energy per particle,
E
(2)
inter
/N
, versus the normalized
distance
L
for the cases of spherical clouds (
κ
= 1) and pancake-shaped clouds (
κ
= 10)
in Fig. 2.5. Furthermore, we show the overlap of the wave functions
N
12
/
(2
N
)
def
=
R
Ψ
1
(
r
2
(
r
)
d
3
r
. This value corresponds to the number of atoms in the region where
the clouds overlap, normalized by the total atom number 2
N
in the system. For the
calculations, we use typical chromium parameters:
N
= 3000,
µ
m
= 6
µ
B
, and
σ
ρ
= 3
m
.
0.010.1 1 10 100
200
1
0
-2
-4
-6
100
0
0.1 1 10 100
(a) (b)
Fig. 2.5, Inter-site energy of two Gaussian shaped dipolar clouds:
The figures
show the inter-site energy per particle (solid blue lines) and the overlap of the
wave functions
N
12
/
(2
N
) (dashed black lines) versus the normalized distance
L
=
d
lat
ρ
. (a) Case of two spherical clouds (
κ
= 1) and (b) case of two
pancake-shaped clouds with
κ
= 10. We use typical chromium parameters
specified in the text.
We first consider the case of two spherical dipolar clouds, displayed in Fig. 2.5(a). At
large distances
L
1 the inter-site interaction energy is practically zero. When the clouds
approach each other, the energy becomes more and more negative until the clouds show a
significant overlap of
N
12
/
(2
N
)
0
.
5. The minimum value
Min
n
E
(2)
inter
/N
o
h ·
6
Hz
close to
L
= 2 is small compared to the total energy per particle in the system for our
parameters
23
,
E/N h ·
1
kHz
. In the limit
L
0 the clouds entirely overlap and the
23
For weak interactions, i.e.
N a/a
ho
.
10, the typical energy per particle is
E/N '
2
~¯ω
[89, Ch.6.2].
Inserting a typical mean trapping frequency
¯ω
= 2
π ·
500
Hz
, we obtain the value
E/N ' h ·
1
kHz
given in the text.
39
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