992 research outputs found
Optomechanics
We review recent progress in the field of optomechanics, where one studies
the effects of radiation on mechanical motion. The paradigmatic example is an
optical cavity with a movable mirror, where the radiation pressure can induce
cooling, amplification and nonlinear dynamics of the mirror.Comment: 12 pages, 4 figures, submitted to the proceedings of the NATO
Advanced Research Workshop 'Recent Advances in Nonlinear Dynamics and Complex
System Physics', Tashkent, Uzbekistan, 200
Pension reform, capital markets, and the rate of return
This paper discusses the consequences of population aging and a fundamental pension reform – that is, a shift towards more pre-funding – for capital markets in Germany. We use a stylized closed-economy, overlapping-generations model to compare the effects of the recent German pension reform with those of a more decisive reform that would freeze the current pay-as-you-go contribution rate and thus result in a larger funded component of the pension system. We predict rates of return to capital under both reform scenarios over a long horizon, taking demographic projections as given. Our main finding is that the future decrease in the rate of return is much smaller than often claimed in the public debate. Our simulations show that the capital stock will decrease once the baby boom generations enter retirement even if there were no fundamental pension reform. The corresponding decrease in the rate of return, the direct effect of population aging, is around 0.7 percentage points. While the capital market effects of the recent German pension reform are marginal, the rate of return to capital would decrease by an additional 0.5 percentage points under the more decisive reform proposal.
On the nature of Thermal Diffusion in binary Lennard-Jones liquids
The aim of this study is to understand deeper the thermal diffusion transport
process (Ludwig-Soret effect) at the microscopic level. For that purpose, the
recently developed reverse nonequilibrium molecular dynamics method was used to
calculate Soret coefficients of various systems in a systematic fashion. We
studied binary Lennard-Jones (LJ) fluids near the triple point (of one of the
components) in which we separately changed the ratio of one of the LJ
parameters mass, atomic diameter and interaction strength while keeping all
other parameters fixed and identical. We observed that the magnitude of the
Soret coefficient depends on all three ratios. Concerning its sign we found
that heavier species, smaller species and species with higher interaction
strengths tend to accumulate in the cold region whereas the other ones
(lighter, bigger or weaker bound) migrate to the hot region of our simulation
cell. Additionally, the superposition of the influence of the various
parameters was investigated as well as more realistic mixtures. We found that
in the experimentally relevant parameter range the contributions are nearly
additive and that the mass ratio often is the dominating factor.Comment: 27 pages, 9 figures, submitted to J. Chem. Phy
Entanglement of mechanical oscillators coupled to a non-equilibrium environment
Recent experiments aim at cooling nanomechanical resonators to the ground
state by coupling them to non-equilibrium environments in order to observe
quantum effects such as entanglement. This raises the general question of how
such environments affect entanglement. Here we show that there is an optimal
dissipation strength for which the entanglement between two coupled oscillators
is maximized. Our results are established with the help of a general framework
of exact quantum Langevin equations valid for arbitrary bath spectra, in and
out of equilibrium. We point out why the commonly employed Lindblad approach
fails to give even a qualitatively correct picture
Multistability and spin diffusion enhanced lifetimes in dynamic nuclear polarization in a double quantum dot
The control of nuclear spins in quantum dots is essential to explore their
many-body dynamics and exploit their prospects for quantum information
processing. We present a unique combination of dynamic nuclear spin
polarization and electric-dipole-induced spin resonance in an electrostatically
defined double quantum dot (DQD) exposed to the strongly inhomogeneous field of
two on-chip nanomagnets. Our experiments provide direct and unrivaled access to
the nuclear spin polarization distribution and allow us to establish and
characterize multiple fixed points. Further, we demonstrate polarization of the
DQD environment by nuclear spin diffusion which significantly stabilizes the
nuclear spins inside the DQD
Full photon statistics of a light beam transmitted through an optomechanical system
In this paper, we study the full statistics of photons transmitted through an
optical cavity coupled to nanomechanical motion. We analyze the entire temporal
evolution of the photon correlations, the Fano factor, and the effects of
strong laser driving, all of which show pronounced features connected to the
mechanical backaction. In the regime of single-photon strong coupling, this
allows us to predict a transition from sub-Poissonian to super-Poissonian
statistics for larger observation time intervals. Furthermore, we predict
cascades of transmitted photons triggered by multi-photon transitions. In this
regime, we observe Fano factors that are drastically enhanced due to the
mechanical motion.Comment: 8 pages, 7 figure
Enhanced quantum nonlinearities in a two mode optomechanical system
In cavity optomechanics, nanomechanical motion couples to a localized optical
mode. The regime of single-photon strong coupling is reached when the optical
shift induced by a single phonon becomes comparable to the cavity linewidth. We
consider a setup in this regime comprising two optical modes and one mechanical
mode. For mechanical frequencies nearly resonant to the optical level
splitting, we find the photon-phonon and the photon-photon interactions to be
significantly enhanced. In addition to dispersive phonon detection in a novel
regime, this offers the prospect of optomechanical photon measurement. We study
these QND detection processes using both analytical and numerical approaches
The optomechanical instability in the quantum regime
We consider a generic optomechanical system, consisting of a driven optical
cavity and a movable mirror attached to a cantilever. Systems of this kind (and
analogues) have been realized in many recent experiments. It is well known that
those systems can exhibit an instability towards a regime where the cantilever
settles into self-sustained oscillations. In this paper, we briefly review the
classical theory of the optomechanical instability, and then discuss the
features arising in the quantum regime. We solve numerically a full quantum
master equation for the coupled system, and use it to analyze the photon
number, the cantilever's mechanical energy, the phonon probability distribution
and the mechanical Wigner density, as a function of experimentally accessible
control parameters. We observe and discuss the quantum-to-classical transition
as a function of a suitable dimensionless quantum parameter.Comment: 23 pages, 6 figures, subm. to focus issue of New Journal of Physics
on "Mechanical Systems at the Quantum Limit
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