Biomedical Engineering Reference
In-Depth Information
800
800
600
600
400
400
σ = 0.5 meV
V = -1 meV
200
200
0
40 80 120
temperature [K]
0
40 80 120
temperature [K]
Fig. 9.27 The de ca y time of the photoluminescence from an ensemble of DQDs with the average
energy mismatch
Δ =
0. Left : the standard deviation of
Δ
is equal to
σ =
0
.
5 meV and the values
of the coupling V are the same as in Fig. 9.26 . Right : V
=
1meV,
σ =
1meV( red solid line ),
3meV( blue dashed line ), and 10 meV ( green dash-dotted line )[ 52 ]
The resulting temperature dependence is very similar to that observed for a single
dot (Fig. 9.26 ). In the right panel of Fig. 9.27 , the results for larger values of
the standard deviation
are shown. Now, the shape of temperature dependence
changes significantly. When
σ
, the ensemble is dominated by DQDs that are
composed of very different dots. This is the situation when
σ |
V
|
for which the
collective effects are negligible. Hence, one does not observe a decrease of the PL
decay time at low temperatures for such ensembles.
Δ |
V
|
9.5.2
Entanglement Decay
In Sect. 9.3.4 , we discussed the evolution of entanglement in the DQD system in
the case of a restricted Hamiltonian which can be diagonalized exactly. In the
following, the full model will be taken into account, including both the phonon
reservoir and coupling to the radiation vacuum, and we will discuss the role of
radiative recombination for long-time entanglement decay, as well as the effects on
the evolution of entanglement induced by the phonon-assisted excitation transfer,
and the results of the interplay between the interactions of the DQD system with the
phonon and photon environments [ 62 ].
The extended model is much more complicated and presents many new features,
on which we wish to focus. To this end, we will restrict the discussion to one of
the previously discussed, fully entangled initial states, namely the “singlet” state
of Eq. ( 9.29 ). As discussed previously, the zero-temperature approximation may
be used for the radiation reservoir at any reasonable temperature, so there is no
interaction in the system which can lead to the creation of the biexcitonic state and
the state space is restricted to the three lower-energy DQD states,
|
00
,
|
01
,and
|
. In this case, the problem of calculating the concurrence and subsequently
the EOF is greatly reduced since the concurrence is always proportional to the
10
 
Search WWH ::




Custom Search