5,995 research outputs found
A new species of Dialeurodes Cockerell (Hemiptera: Aleyrodidae) on Schefflera Forst and Forst in Florida
Descriptions of pupal cases of Dialeurodes schefflerae, new species, as well as distribution records are presented. This species is known to occur in Florida, Hawaii and Puerto Rico appearing to feed only on species of Schefflera Forst and Forst. This restriction to plant hosts in the Asian genus Schefflera, along with its affinities with Dialeurodes agalmae Takahashi, Dialeurodes citri (Ashmead) and Dialeurodes kirkaldyi (Kotinsky), suggests it is an invasive species, probably endemic to the Asian region
Extending Quantum Coherence in Diamond
We experimentally demonstrate over two orders of magnitude increase in the
coherence time of nitrogen vacancy centres in diamond by implementing
decoupling techniques. We show that equal pulse spacing decoupling performs
just as well as non-periodic Uhrig decoupling and has the additional benefit
that it allows us to take advantage of "revivals" in the echo (due to the
coherent nature of the bath) to explore the longest coherence times. At short
times, we can extend the coherence of particular quantum states out from
T_2*=2.7 us out to an effective T_2 > 340 us. For preserving arbitrary states
we show the experimental importance of using pulse sequences, that through
judicious choice of the phase of the pulses, compensate the imperfections of
individual pulses for all input states. At longer times we use these
compensated sequences to enhance the echo revivals and show a coherence time of
over 1.6 ms in ultra-pure natural abundance 13C diamond.Comment: 7 pages, 7 figures; minor syntax/typo. changes and updated reference
Universal Control of Nuclear Spins Via Anisotropic Hyperfine Interactions
We show that nuclear spin subsystems can be completely controlled via
microwave irradiation of resolved anisotropic hyperfine interactions with a
nearby electron spin. Such indirect addressing of the nuclear spins via
coupling to an electron allows us to create nuclear spin gates whose
operational time is significantly faster than conventional direct addressing
methods. We experimentally demonstrate the feasibility of this method on a
solid-state ensemble system consisting of one electron and one nuclear spin.Comment: RevTeX4, 8 pages, 8 figure
Two-stage fan. 3: Data and performance with rotor tip casing treatment, uniform and distorted inlet flows
A two stage fan with a 1st-stage rotor design tip speed of 1450 ft/sec, a design pressure ratio of 2.8, and corrected flow of 184.2 lbm/sec was tested with axial skewed slots in the casings over the tips of both rotors. The variable stagger stators were set in the nominal positions. Casing treatment improved stall margin by nine percentage points at 70 percent speed but decreased stall margin, efficiency, and flow by small amounts at design speed. Treatment improved first stage performance at low speed only and decreased second stage performance at all operating conditions. Casing treatment did not affect the stall line with tip radially distorted flow but improved stall margin with circumferentially distorted flow. Casing treatment increased the attenuation for both types of inlet flow distortion
Recommended from our members
Storyline description of Southern Hemisphere midlatitude circulation and precipitation response to greenhouse gas forcing
As evidence of climate change strengthens, knowledge of its regional implications becomes an urgent need for decision making. Current understanding of regional precipitation changes is substantially limited by our understanding of the atmospheric circulation response to climate change, which to a high degree remains uncertain. This uncertainty is reflected in the wide spread in atmospheric circulation changes projected in multimodel ensembles, which cannot be directly interpreted in a probabilistic sense. The uncertainty can instead be represented by studying a discrete set of physically plausible storylines of atmospheric circulation changes. By mining CMIP5 model output, here we take this broader perspective and develop storylines for Southern Hemisphere (SH) midlatitude circulation changes, conditioned on the degree of global-mean warming, based on the climate responses of two remote drivers: the enhanced warming of the tropical upper troposphere and the strengthening of the stratospheric polar vortex. For the three continental domains in the SH, we analyse the precipitation changes under each storyline. To allow comparison with previous studies, we also link both circulation and precipitation changes with those of the Southern Annular Mode. Our results show that the response to tropical warming leads to a strengthening of the midlatitude westerly winds, whilst the response to a delayed breakdown (for DJF) or strengthening (for JJA) of the stratospheric vortex leads to a poleward shift of the westerly winds and the storm tracks. However, the circulation response is not zonally symmetric and the regional precipitation storylines for South America, South Africa, South Australia and New Zealand exhibit quite specific dependencies on the two remote drivers, which are not well represented by changes in the Southern Annular Mode
Principles of Control for Decoherence-Free Subsystems
Decoherence-Free Subsystems (DFS) are a powerful means of protecting quantum
information against noise with known symmetry properties. Although Hamiltonians
theoretically exist that can implement a universal set of logic gates on DFS
encoded qubits without ever leaving the protected subsystem, the natural
Hamiltonians that are available in specific implementations do not necessarily
have this property. Here we describe some of the principles that can be used in
such cases to operate on encoded qubits without losing the protection offered
by the DFS. In particular, we show how dynamical decoupling can be used to
control decoherence during the unavoidable excursions outside of the DFS. By
means of cumulant expansions, we show how the fidelity of quantum gates
implemented by this method on a simple two-physical-qubit DFS depends on the
correlation time of the noise responsible for decoherence. We further show by
means of numerical simulations how our previously introduced "strongly
modulating pulses" for NMR quantum information processing can permit
high-fidelity operations on multiple DFS encoded qubits in practice, provided
that the rate at which the system can be modulated is fast compared to the
correlation time of the noise. The principles thereby illustrated are expected
to be broadly applicable to many implementations of quantum information
processors based on DFS encoded qubits.Comment: 12 pages, 7 figure
Subsystem Pseudo-pure States
A critical step in experimental quantum information processing (QIP) is to
implement control of quantum systems protected against decoherence via
informational encodings, such as quantum error correcting codes, noiseless
subsystems and decoherence free subspaces. These encodings lead to the promise
of fault tolerant QIP, but they come at the expense of resource overheads.
Part of the challenge in studying control over multiple logical qubits, is
that QIP test-beds have not had sufficient resources to analyze encodings
beyond the simplest ones. The most relevant resources are the number of
available qubits and the cost to initialize and control them. Here we
demonstrate an encoding of logical information that permits the control over
multiple logical qubits without full initialization, an issue that is
particularly challenging in liquid state NMR. The method of subsystem
pseudo-pure state will allow the study of decoherence control schemes on up to
6 logical qubits using liquid state NMR implementations.Comment: 9 pages, 1 Figur
Environment Assisted Metrology with Spin Qubit
We investigate the sensitivity of a recently proposed method for precision
measurement [Phys. Rev. Lett. 106, 140502 (2011)], focusing on an
implementation based on solid-state spin systems. The scheme amplifies a
quantum sensor response to weak external fields by exploiting its coupling to
spin impurities in the environment. We analyze the limits to the sensitivity
due to decoherence and propose dynamical decoupling schemes to increase the
spin coherence time. The sensitivity is also limited by the environment spin
polarization; therefore we discuss strategies to polarize the environment spins
and present a method to extend the scheme to the case of zero polarization. The
coherence time and polarization determine a figure of merit for the
environment's ability to enhance the sensitivity compared to echo-based sensing
schemes. This figure of merit can be used to engineer optimized samples for
high-sensitivity nanoscale magnetic sensing, such as diamond nanocrystals with
controlled impurity density.Comment: 9 pages, 6 figure
Environment Assisted Precision Measurement
We describe a method to enhance the sensitivity of precision measurements
that takes advantage of a quantum sensor's environment to amplify its response
to weak external perturbations. An individual qubit is used to sense the
dynamics of surrounding ancillary qubits, which are in turn affected by the
external field to be measured. The resulting sensitivity enhancement is
determined by the number of ancillas that are coupled strongly to the sensor
qubit; it does not depend on the exact values of the coupling strengths and is
resilient to many forms of decoherence. The method achieves nearly
Heisenberg-limited precision measurement, using a novel class of entangled
states. We discuss specific applications to improve clock sensitivity using
trapped ions and magnetic sensing based on electronic spins in diamond.Comment: 4 pages, 3 figure
- …