1,073 research outputs found
The Deflationary Bias of the ZLB and the FED’s Strategic Response
The paper shows, in a simple analytical framework, the existence of a deflationary bias in an
economy with a low natural rate of interest, a Zero Lower Bound (ZLB) constraint on
nominal interest rates and a discretionary Central Bank with an inflation mandate. The
presence of the ZLB prevents the central bank from offsetting negative shocks to inflation
whereas it can offset positive shocks. This asymmetry pushes average inflation below the
target which in turn drags down inflation expectations and reinforces the likelihood of hitting
the ZLB. We show that this deflationary bias is particularly relevant for a Central Bank with
a symmetric dual mandate (i.e. minimizing deviations from inflation and employment),
especially when facing demand shocks. But a strict inflation targeter cannot escape the suboptimal deflationary equilibrium either. The deflationary bias can be mitigated by targeting
“shortfalls” instead of “deviations” from maximum employment and/or using flexible
average inflation targeting. However, changing monetary policy strategy risks inflation
expectations becoming entrenched above the target if the natural interest rate increases
Realistic continuous-variable quantum teleportation with non-Gaussian resources
We present a comprehensive investigation of nonideal continuous-variable
quantum teleportation implemented with entangled non-Gaussian resources. We
discuss in a unified framework the main decoherence mechanisms, including
imperfect Bell measurements and propagation of optical fields in lossy fibers,
applying the formalism of the characteristic function. By exploiting
appropriate displacement strategies, we compute analytically the success
probability of teleportation for input coherent states, and two classes of
non-Gaussian entangled resources: Two-mode squeezed Bell-like states (that
include as particular cases photon-added and photon-subtracted de-Gaussified
states), and two-mode squeezed cat-like states. We discuss the optimization
procedure on the free parameters of the non-Gaussian resources at fixed values
of the squeezing and of the experimental quantities determining the
inefficiencies of the non-ideal protocol. It is found that non-Gaussian
resources enhance significantly the efficiency of teleportation and are more
robust against decoherence than the corresponding Gaussian ones. Partial
information on the alphabet of input states allows further significant
improvement in the performance of the non-ideal teleportation protocol.Comment: 14 pages, 6 figure
Quasideterministic generation of maximally entangled states of two mesoscopic atomic ensembles by adiabatic quantum feedback
We introduce an efficient, quasideterministic scheme to generate maximally
entangled states of two atomic ensembles. The scheme is based on quantum
nondemolition measurements of total atomic populations and on adiabatic quantum
feedback conditioned by the measurements outputs. The high efficiency of the
scheme is tested and confirmed numerically for ideal photodetection as well as
in the presence of losses.Comment: 7 pages, 6 figures, title changed, revised version published on Phys.
Rev
Tunable non-Gaussian resources for continuous-variable quantum technologies
We introduce and discuss a set of tunable two-mode states of
continuous-variable systems, as well as an efficient scheme for their
experimental generation. This novel class of tunable entangled resources is
defined by a general ansatz depending on two experimentally adjustable
parameters. It is very ample and flexible as it encompasses Gaussian as well as
non-Gaussian states. The latter include, among others, known states such as
squeezed number states and de-Gaussified photon-added and photon-subtracted
squeezed states, the latter being the most efficient non-Gaussian resources
currently available in the laboratory. Moreover, it contains the classes of
squeezed Bell states and even more general non-Gaussian resources that can be
optimized according to the specific quantum technological task that needs to be
realized. The proposed experimental scheme exploits linear optical operations
and photon detections performed on a pair of uncorrelated two--mode Gaussian
squeezed states. The desired non-Gaussian state is then realized via ancillary
squeezing and conditioning. Two independent, freely tunable experimental
parameters can be exploited to generate different states and to optimize the
performance in implementing a given quantum protocol. As a concrete instance,
we analyze in detail the performance of different states considered as
resources for the realization of quantum teleportation in realistic conditions.
For the fidelity of teleportation of an unknown coherent state, we show that
the resources associated to the optimized parameters outperform, in a
significant range of experimental values, both Gaussian twin beams and
photon-subtracted squeezed states.Comment: 13 pages, 7 figure
Can Fiscal Budget-Neutral Reforms Stimulate Growth? Model-Based Results
This paper focuses on growth enhancing budget-neutral fiscal reforms, i.e. changes in the
composition of government revenues and spending that stimulate GDP growth while keeping the
ratio of the fiscal budget to GDP constant. To this aim, we present simulation results using a
multi-country DSGE model with three large economic regions, the US, the euro area and the rest
of the world. The model features constrained and unconstrained non-Ricardian households and a
detailed government sector; its multi-country nature allows investigating cross-country
spillovers. The paper focuses on the most growth-friendly budget-neutral fiscal measures: (i) an
incomplete fiscal devaluation (ii) a rise in government investment compensated by a fall in
government consumption and (iii) a rise in government investment compensated by a rise in
consumption and labor taxes. Dampening or amplifying effects due to coordination across
policies (monetary and fiscal) and across economic regions are also considered. Three main
results stand out. First, an increase in government investment financed by rising less
distortionary taxes appears to be an effective growth-friendly budget-neutral reform in the sense
that it generates both short- and long-run GDP growth and improves fiscal sustainability. Second,
benefits and costs of budget-neutral reforms are not equally distributed across agents, giving rise
to a policy trade-off between growth and distributional consequences. Third, budget-neutral
reforms do not have large cross-border trade spillovers; however, reforms coordinated across all
countries in periods of accommodative monetary policy do have amplified domestic effects
Geometric Effects and Computation in Spin Networks
When initially introduced, a Hamiltonian that realises perfect transfer of a
quantum state was found to be analogous to an x-rotation of a large spin. In
this paper we extend the analogy further to demonstrate geometric effects by
performing rotations on the spin. Such effects can be used to determine
properties of the chain, such as its length, in a robust manner. Alternatively,
they can form the basis of a spin network quantum computer. We demonstrate a
universal set of gates in such a system by both dynamical and geometrical
means
The Interconnected Magmatic Plumbing System of the Natron Rift
Understanding the magmatic plumbing system of rift volcanoes is essential when examining the
interplay between magmatic and tectonic forces. Recent seismicity, volcanic activity, magma emplacement,
and volatile release make the Natron basin the ideal location to study these processes in the East African
Rift System. Here, we present the first high-resolution tomographic imaging of Oldoinyo Lengai volcano
and surrounding volcanic systems using attenuation mapping. High scattering and absorption features reveal
fluid-filled fracture networks below regions of magmatic volatile release at the surface and a close spatial
association between carbonatite volcanism and deeply penetrating, fluid-filled faults. High-absorption features
appear sensitive to fluids and thermal gradients, revealing a central sill complex and connected plumbing
system down to the mid-crust, which links volcanoes and rift segments across the developing magmatic rift
Engineering massive quantum memories by topologically time-modulated spin rings
We introduce a general scheme to realize perfect storage of quantum
information in systems of interacting qubits. This novel approach is based on
{\it global} external controls of the Hamiltonian, that yield time-periodic
inversions in the dynamical evolution, allowing a perfect periodic quantum
state recontruction. We illustrate the method in the particularly interesting
and simple case of spin systems affected by XY residual interactions with or
without static imperfections. The global control is achieved by step
time-inversions of an overall topological phase of the Aharonov-Bohm type. Such
a scheme holds both at finite size and in the thermodynamic limit, thus
enabling the massive storage of arbitrarily large numbers of local states, and
is stable against several realistic sources of noise and imperfections.Comment: 12 pages, 9 figure
An Experimental Approach to a Rapid Propulsion and Aeronautics Concepts Testbed
Modern aircraft design tools have limitations for predicting complex propulsion-airframe interactions. The demand for new tools and methods addressing these limitations is high based on the many recent Distributed Electric Propulsion (DEP) Vertical Take-Off and Landing (VTOL) concepts being developed for Urban Air Mobility (UAM) markets. We propose that low cost electronics and additive manufacturing can support the conceptual design of advanced autonomy-enabled concepts, by facilitating rapid prototyping for experimentally driven design cycles. This approach has the potential to reduce complex aircraft concept development costs, minimize unique risks associated with the conceptual design, and shorten development schedule by enabling the determination of many "unknown unknowns" earlier in the design process and providing verification of the results from aircraft design tools. A modular testbed was designed and built to evaluate this rapid design-build-test approach and to support aeronautics and autonomy research targeting UAM applications utilizing a complex, transitioning-VTOL aircraft configuration. The testbed is a modular wind tunnel and flight model. The testbed airframe is approximately 80% printed, with labor required for assembly. This paper describes the design process, fabrication process, ground testing, and initial wind tunnel structural and thermal loading of a proof-of-concept aircraft, the Langley Aerodrome 8 (LA-8)
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