14,408 research outputs found
Two-particle dark state cooling of a nanomechanical resonator
The steady-state cooling of a nanomechanical resonator interacting with three
coupled quantum dots is studied. General conditions for the cooling to the
ground state with single and two-electron dark states are obtained. The results
show that in the case of the interaction of the resonator with a
single-electron dark state, no cooling of the resonator occurs unless the
quantum dots are not identical. The steady-state cooling is possible only if
the energy state of the quantum dot coupled to the drain electrode is detuned
from the energy states of the dots coupled to the electron source electrode.
The detuning has the effect of unequal shifting of the effective dressed states
of the system that the cooling and heating processes occur at different
frequencies. For the case of two electrons injected to the quantum dot system,
the creation of a two-particle dark state is established to be possible with
spin-antiparallel electrons. The results predict that with the two-particle
dark state, an effective cooling can be achieved even with identical quantum
dots subject of an asymmetry only in the charging potential energies coupling
the injected electrons. It is found that similar to the case of the
single-electron dark state, the asymmetries result in the cooling and heating
processes to occur at different frequencies. However, an important difference
between the single and two-particle dark state cases is that the cooling
process occurs at significantly different frequencies. This indicates that the
frequency at which the resonator could be cooled to its ground state can be
changed by switching from the one-electron to the two-electron Coulomb blockade
process.Comment: Published versio
Spectral properties of a thresholdless dressed-atom laser
We investigate spectral properties of the atomic fluorescence and the output
field of the cavity-mode of a single-atom dressed-state laser in a photonic
crystal. We pay a particular attention to the behavior of the spectra in the
presence of the frequency dependent reservoir and search for signatures of the
thresholdless lasing. Although the thresholdless behavior has been predicted by
analyzing the photon statistics of the cavity field, we find that the threshold
behavior still exists in the spectrum of the cavity field. We find that the
structure of cavity field spectrum depends strongly on the strange of the
pumping rate. For low pumping rates, the spectrum is not monochromatic, it is
composed of a set of discrete lines reveling the discrete (quantum) structure
of the combined dressed-atom plus the cavity field system. We find that for a
certain value of the pumping rate, the multi-peak structure converts into a
single very narrow line centered at the cavity field frequency. A physical
explanation of the behavior of the spectra is provided in terms of dressed
states of the system.Comment: Special Issue of Journal Modern Optics - Fetschrift in honour of
Lorenzo Narducc
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Epidemiologic studies of particulate matter and lung cancer
Particulate matter (PM) plays an important role in air pollution, especially in China. European and American researchers conducted several cohort-based studies to examine the potential relationship between PM and lung cancer and found a positive association between PM and lung cancer mortality. In contrast, the results regarding PM and lung cancer risk remain inconsistent. Most of the previous studies had limitations such as misclassification of PM exposure and residual confounders, diminishing the impact of their findings. In addition, prospective studies on this topic are very limited in Chinese populations. This is an important problem because China has one of the highest concentrations of PM in the world and has had an increased mortality risk due to lung cancer. In this context, more prospective studies in Chinese populations are warranted to investigate the relationship between PM and lung cancer
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