6,496 research outputs found
Single photon absorption and dynamic control of a coupled quantum dot-cavity system
We theoretically investigate the dynamic interaction of a quantum dot in a
nanocavity with timesymmetric single photon pulses. The simulations, based on a
wavefunction approach, reveal that almost perfect single photon absorption
occurs for quantum dot-cavity systems operating on the edge between strong and
weak coupling regime. The computed maximum absorptions probability is close to
unity for pulses with a typical length comparable to the half of the Rabi
period. Furthermore, the dynamic control of the quantum dot energy via electric
fields allows the freezing of the light-matter interaction leaving the quantum
dot in its excited state. Shaping of single photon wavepackets by the electric
field control is limited by the occurrence of chirping of the single photon
pulse. This understanding of the interaction of single photon pulses with the
quantum dot-cavity system provides the basis for the development of advanced
protocols for quantum information processing in the solid state.Comment: 7 pages, 4 figure
Scalable photonic quantum computation through cavity-assisted interaction
We propose a scheme for scalable photonic quantum computation based on cavity
assisted interaction between single-photon pulses. The prototypical quantum
controlled phase-flip gate between the single-photon pulses is achieved by
successively reflecting them from an optical cavity with a single-trapped atom.
Our proposed protocol is shown to be robust to practical nose and experimental
imperfections in current cavity-QED setups.Comment: 5 pages, 2 figure
Measurements of the short-term stability of quartz crystal resonators: A window on future developments in crystal oscillators
Recent measurements of the inherent short-term stability of quartz crystal resonators are presented. These measurements show that quartz resonators are much more stable for times less than 1s than the best available commercial quartz oscillators. A simple model appears to explain the noise mechanism in crystal controlled oscillators and points the way to design changes which should permit more than 2 orders of magnitude improvement in their short-term stability. Calculations show that a reference signal at 1 THz, derived from frequency multiplying a 5 MHz source with the above measured crystal stability, should have an instantaneous or fast linewidth of order 1 Hz. These calculations explicitly include the noise contribution of our present multiplier chains and are briefly outlined
Parametric Oscillation with Squeezed Vacuum Reservoirs
Employing the quantum Hamiltonian describing the interaction of two-mode
light (signal-idler modes) generated by a nondegenerate parametric oscillator
(NDPO) with two uncorrelated squeezed vacuum reservoirs (USVR), we derive the
master equation. The corresponding Fokker-Planck equation for the Q-function is
then solved employing a propagator method developed in Ref. \cite{1}. Making
use of this Q-function, we calculate the quadrature fluctuations of the optical
system. From these results we infer that the signal-idler modes are in squeezed
states and the squeezing occurs in the first quadrature. When the NDPO operates
below threshold we show that, for a large squeezing parameter, a squeezing
amounting to a noise suppression approaching 100% below the vacuum level in the
first quadrature can be achieved.Comment: 16 page
The relationship between dental status, food selection, nutrient intake, nutritional status, and body mass index in older people
This paper reviewed the findings from a national survey in Great Britain which assessed whether dental status affected older people's food selection, nutrient intake, and nutritional status. The survey analyzed national random samples of free-living and institution subjects for dental examination, interview, and four-day food diary as well as blood and urine tests In the free-living sample, intakes of non-starch polysaccharides, protein, calcium, non-heme iron, niacin, and vitamin C were significantly lower in edentulous as compared to dentate subjects. People with 21 or more teeth consumed more of most nutrients, particularly non-starch polysaccharides. This relationship in intake was not apparent in the hematological analysis. Plasma ascorbate and retinol were the only analytes significantly associated with dental status. Having 21 or more teeth increased the likelihood of having an acceptable body mass index (BMI). Thus, maintaining a natural and functional dentition defined as having more than twenty teeth into old age plays an important role in having a healthy diet rich in fruits and vegetables, a satisfactory nutritional status, and an acceptable BMI
Climate Policyâs Uncertain Outcomes for Households: The Role of Complex Allocation Schemes in Cap and Trade
Uncertainty is a fundamental characteristic of climate change. This paper focuses on uncertainty in the implementation of climate policy, especially as it affects the level and distribution of the burden on households that results from the allocation of emissions allowances. We examine the WaxmanâMarkey bill (H.R. 2454), introduced in the U.S. House of Representatives in 2009, with bookend scenarios labeled optimistic and pessimistic. The scenarios illustrate varied outcomes associated with allocations to electricity local distribution companies, investments in energy efficiency, and technology development. We introduce a third scenario for comparison, which allocates a substantial portion of allowance value directly to households as lump-sum payments. We find the average net household burden in 2016 in the optimistic scenario to be 13.19. In the pessimistic scenario, the net household burden rises to 23.41. While the burden varies by income group, the relative impacts stay roughly the same in the optimistic and pessimistic cases, thus the uncertainty in average burdens does not carry over to uncertainty in the distribution of those burdens. Both scenarios impose the greatest burden as a percentage of income on middle-income households. Allocation of allowance value directly back to households as a lump-sum payment imposes an average net household burden of $206 with much less uncertainty in outcome; the distributional impacts are highly progressive.cap and trade, allocation, distributional effects, cost burden, equity, regulation,local distribution companies
Quantum tunneling through vacuum-multiparticle induced potentials
The vacuum cavity mode induces a potential barrier and a well when an
ultra-slow excited atom enters the interaction region so that it can be
reflected or transmitted with a certain probability. We demonstrate here that a
slow-velocity excited particle tunnels freely through a vacuum electromagnetic
field mode filled with ground state atoms. The reason for this is the
trapping of the moving atom into its upper state due to multiparticle
influences and the corresponding decoupling from the interaction with the
environment such that the emitter does not {\it see} the induced potentials.Comment: Multiparticle samples, quantum tunneling, vacuum induced potential
Collapse-revival dynamics and atom-field entanglement in the non-resonant Dicke model
We consider the dynamics of atomic and field coherent states in the
non-resonant Dicke model. At weak coupling an initial product state evolves
into a superposition of multiple field coherent states that are correlated with
the atomic configuration. This process is accompanied by the buildup and decay
of atom-field entanglement and leads to the periodic collapse and revival of
Rabi oscillations. We provide a perturbative derivation of the underlying
dynamical mechanism that complements the rotating wave approximation at
resonance. The identification of two different time scales explains how the
dynamical signatures depend on the sign of detuning between the atomic and
field frequency, and predicts the generation of either atomic or field cat
states in the two opposite cases. We finally discuss the restrictions that the
buildup of atom-field entanglement during the collapse of Rabi oscillations
imposes on the validity of semi-classical approximations that neglect
entanglement.Comment: 9 pages, 10 figures. Published versio
General linewidth formula for steady-state multimode lasing in arbitrary cavities
A formula for the laser linewidth of arbitrary cavities in the multimode
non-linear regime is derived from a scattering analysis of the solutions to
semiclassical laser theory. The theory generalizes previous treatments of the
effects of gain and openness described by the Petermann factor. The linewidth
is expressed using quantities based on the non-linear scattering matrix, which
can be computed from steady-state ab initio laser theory; unlike previous
treatments, no passive cavity or phenomenological parameters are involved. We
find that low cavity quality factor, combined with significant dielectric
dispersion, can cause substantial deviations from the Schawlow-Townes-Petermann
theory.Comment: 5 pages, 2 figure
The Trade-off between Private Lots and Public Open Space in Subdivisions at the Urban-Rural Fringe
In many communities on the urbanârural fringe, subdivisions are subject to âclusteringâ rules, in which houses must be located on a portion of the total land area and the remainder of the land is left as open space. This open space may be undisturbed forest or pastureland, or it may include recreation facilities and trails. In some communities, the open space may remain in agricultural use as pasture or cropland. Although the open space may provide benefits to subdivision residents, it means that those residents are living in a higher-density setting than people living in conventional subdivisions. It is unclear whether the benefits offset the loss experienced by smaller lots and higher density. This trade-off is the focus of our study. We use data on subdivision house sales occurring between 1981 and 2001 in a county on the fringe of the Washington, DC, metropolitan area to estimate a hedonic price model. We examine how households value being adjacent to open space and having more open space in the subdivision, and how they may be willing to trade off those amenities with their own private lot space. We find that private acreage matters to householdsâa 10 percent larger lot leads to about a 0.6 percent higher house price, all else being equal. Subdivision open space is also valuable to households, but the marginal effect is much smaller than the marginal effect of private lot space. We also find that subdivision open space does substitute for private land, but the extent of the trade-off is small. We use the results of the estimated hedonic model to simulate the effects on prices of jointly increasing open space and reducing average lot size, holding the size of the subdivision constant. We find that average house prices are lower with clustering, particularly for interior lots that are not adjacent to open space.subdivisions, clustering, hedonic property values, open space
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