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� magnitude-time plot of quakes in the model. at the time of the arrow an
instantaneous perturbation is applied. note the resulting increase in activity.
(assumed to be the occurrence of seismic waves), it is observed
that the seismic activity in the system has a sharp increase following
the perturbation, well after it has vanished.
The origin of a temporarily delayed effect in the model is
tightly related to the existence of relaxation processes, as
the effect does not exist in the case in which relaxation is
absent. In this respect delayed dynamically triggered earthquakes
are in some sense similar to aftershocks: the latter
are delayed events triggered by a permanent perturbation
(the change in the stress field caused by the main shock)
while the former are delayed events triggered by a transient
perturbation (the passage of seismic waves), once the perturbation
has vanished.
The present investigation suggests that both aftershocks and
delayed dynamically triggered quakes originate in the same
kind of physical mechanism, namely internal relaxation
mechanisms within the faults, that the present model appropriately
captures. ■
III e.a. Jagla,
‘Delayed dynamic triggering of earthquakes: Evidence from a
statistical model of seismicity’, EPL 93 19001 (2011)
QUANTUM PHYSICS
Observing different quantum
trajectories in cavity QED
Quantum systems, as isolated as they can be, always interact
with their surrounding environment. This interaction can lead
to correlations between system and environment and, when
the states of the reservoir are inaccessible to observation, to
an irreversible loss of information on the system. This deleterious
decoherence effect is at the heart of the quantum theory
of measurement and plays an essential role in explaining the
emergence of classical behaviour in quantum systems.
08 EPN 42/5
However, this system-reservoir interaction can be exploited in
a completely different way when the environment can be
monitored. In this case, extracting information from the environment
causes the state of the system to change
stochastically, conditioned on the measurement record. This
can then be used to manipulate the system dynamics, being
an important strategy in quantum dynamical control.
While it is well known that there are infinitely many possible ways
of unravelling the decoherence process in terms of stochastic trajectories,
it is not always clear how to interpret these trajectories
in terms of concrete physical measurements on the environment.
In this paper we show how to produce, in a controllable manner,
a variety of quantum trajectories in realistic cavity quantum electrodynamics
setups. In the microwave regime, we show how the
detection of atoms that have crossed a cavity can induce a jump in
the field proportional to its quadrature. In this case, the field
dynamics is quite different from the usual photodetection monitoring
and can be used to produce conditional four-component
cat-like states. Alternatively, in the optical domain, the detection of
photons can be used to protect entangled states of atoms that
have interacted with the cavity field.
This proposal for the implementation of new stochastic trajectories
in terms of continuous measurements in realistic
systems certainly expands the possibility of engineering quantum
states of lights and atoms. ■
III m.f. santos and a.r.r. carvalho,
‘Observing different quantum trajectories in cavity QED‘,
EPL 94, 64003 (2011)
MATERIAL SCIENCE
Injection coupling
in quantum-cascade lasers
High-performance quantum-cascade lasers (QCLs) emitting at
terahertz frequencies are highly expected for some practical
applications, such as imaging and sensing.
� (a) Typical conduction band structure of terahertz QCls investigated here. The
injection coupling (Δ 1’4) varies from 1.6 to 10 mev. The light grey regions represent
doping layers. (b) Calculated J ndr, J peak gain and ΔJ as a function of injection
coupling. (c) Peak gain for different injection coupling structures.