89 research outputs found
Can quantum regression theorem be reconciled with quantum fluctuation dissipation theorem ?
In the attempt to derive the regression theorem from the fluctuation
dissipation theorem several authors claim the violation of the former theorem
in the quantum case. Here we pose the question: does it exists a quantum
fluctuation dissipation theorem (QFDT) in its conventional interpretation? It
is shown that the relation usually called as the QFDT is the condition of
detailed macroscopic energetic balance. Following this interpretation the
existing conflict between the two theorems in the quantum case is removed.Comment: 13 pages, 3rd Int. Conf. on Unsolved Problems on Noise (will be
published in Proceedings
Voltage controlled terahertz transmission through GaN quantum wells
We report measurements of radiation transmission in the 0.220--0.325 THz
frequency domain through GaN quantum wells grown on sapphire substrates at room
and low temperatures. A significant enhancement of the transmitted beam
intensity with the applied voltage on the devices under test is found. For a
deeper understanding of the physical phenomena involved, these results are
compared with a phenomenological theory of light transmission under electric
bias relating the transmission enhancement to changes in the differential
mobility of the two-dimensional electron gas
Noise influence on electron dynamics in semiconductors driven by a periodic electric field
Studies about the constructive aspects of noise and fluctuations in different
non-linear systems have shown that the addition of external noise to systems
with an intrinsic noise may result in a less noisy response. Recently, the
possibility to reduce the diffusion noise in semiconductor bulk materials by
adding a random fluctuating contribution to the driving static electric field
has been tested. The present work extends the previous theories by considering
the noise-induced effects on the electron transport dynamics in low-doped
n-type GaAs samples driven by a high-frequency periodic electric field
(cyclostationary conditions). By means of Monte Carlo simulations, we calculate
the changes in the spectral density of the electron velocity fluctuations
caused by the addition of an external correlated noise source. The results
reported in this paper confirm that, under specific conditions, the presence of
a fluctuating component added to an oscillating electric field can reduce the
total noise power. Furthermore, we find a nonlinear behaviour of the spectral
density with the noise intensity. Our study reveals that, critically depending
on the external noise correlation time, the dynamical response of electrons
driven by a periodic electric field receives a benefit by the constructive
interplay between the fluctuating field and the intrinsic noise of the system.Comment: 9 pages, 4 figures, to appear in J. Stat. Mechanics: Theory and
Experim., 200
Modelling of small-signal response and electronic noise in semiconductor high-field transport
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