47 research outputs found
Modeling of an efficient singlet-triplet spin qubit to photon interface assisted by a photonic crystal cavity
Efficient interconnection between distant semiconductor spin qubits with the
help of photonic qubits would offer exciting new prospects for future quantum
communication applications. In this paper, we optimize the extraction
efficiency of a novel interface between a singlet-triplet spin qubit and a
photonic qubit. The interface is based on a 220 nm thick GaAs/AlGaAs
heterostructure membrane and consists of a gate-defined double quantum dot
(GDQD) supporting a singlet-triplet qubit, an optically active quantum dot
(OAQD) consisting of a gate-defined exciton trap, a photonic crystal cavity
providing in-plane optical confinement and efficient out-coupling to an ideal
free space Gaussian beam while accommodating the gate wiring of the GDQD and
OAQD, and a bottom gold reflector to recycle photons and increase the optical
extraction efficiency. All essential components can be lithographically defined
and deterministically fabricated on the GaAs/AlGaAs heterostructure membrane,
which greatly increases the scalability of on-chip integration. According to
our simulations, the interface provides an overall coupling efficiency of 28.7%
into a free space Gaussian beam, assuming an SiO2 interlayer filling the space
between the reflector and the membrane. The performance can be further
increased by undercutting this SiO2 interlayer below the photonic crystal. In
this case, the overall efficiency is calculated to be 48.5%
Semiconductor membranes for electrostatic exciton trapping in optically addressable quantum transport devices
Combining the capabilities of gate defined quantum transport devices in
GaAs-based heterostructures and of optically addressed self-assembled quantum
dots could open broad perspectives for new devices and functionalities. For
example, interfacing stationary solid-state qubits with photonic quantum states
would open a new pathway towards the realization of a quantum network with
extended quantum processing capacity in each node. While gated devices allow
very flexible confinement of electrons or holes, the confinement of excitons
without some element of self-assembly is much harder. To address this
limitation, we introduce a technique to realize exciton traps in quantum wells
via local electric fields by thinning a heterostructure down to a 220 nm thick
membrane. We show that mobilities over
cmVs can be retained and that quantum point contacts and
Coulomb oscillations can be observed on this structure, which implies that the
thinning does not compromise the heterostructure quality. Furthermore, the
local lowering of the exciton energy via the quantum-confined Stark effect is
confirmed, thus forming exciton traps. These results lay the technological
foundations for devices like single photon sources, spin photon interfaces and
eventually quantum network nodes in GaAs quantum wells, realized entirely with
a top-down fabrication process.Comment: v2: added missing acknowledgement. v3: fixed typos in acknolwedgemen
A review of the scientific knowledge of the seascape off Dronning Maud Land, Antarctica
Despite the exclusion of the Southern Ocean from assessments of progress towards achieving the Convention on Biological Diversity (CBD) Strategic Plan, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has taken on the mantle of progressing efforts to achieve it. Within the CBD, Aichi Target 11 represents an agreed commitment to protect 10% of the global coastal and marine environment. Adopting an ethos of presenting the best available scientific evidence to support policy makers, CCAMLR has progressed this by designating two Marine Protected Areas in the Southern Ocean, with three others under consideration. The region of Antarctica known as Dronning Maud Land (DML; 20 degrees W to 40 degrees E) and the Atlantic sector of the Southern Ocean that abuts it conveniently spans one region under consideration for spatial protection. To facilitate both an open and transparent process to provide the vest available scientific evidence for policy makers to formulate management options, we review the body of physical, geochemical and biological knowledge of the marine environment of this region. The level of scientific knowledge throughout the seascape abutting DML is polarized, with a clear lack of data in its eastern part which is presumably related to differing levels of research effort dedicated by national Antarctic programmes in the region. The lack of basic data on fundamental aspects of the physical, geological and biological nature of eastern DML make predictions of future trends difficult to impossible, with implications for the provision of management advice including spatial management. Finally, by highlighting key knowledge gaps across the scientific disciplines our review also serves to provide guidance to future research across this important region.Peer reviewe
A review of the scientific knowledge of the seascape off Dronning Maud Land, Antarctica
Despite the exclusion of the Southern Ocean from assessments of progress towards achieving the Convention on Biological Diversity (CBD) Strategic Plan, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has taken on the mantle of progressing efforts to achieve it. Within the CBD, Aichi Target 11 represents an agreed commitment to protect 10% of the global coastal and marine environment. Adopting an ethos of presenting the best available scientific evidence to support policy makers, CCAMLR has progressed this by designating two Marine Protected Areas in the Southern Ocean, with three others under consideration. The region of Antarctica known as Dronning Maud Land (DML; 20°W to 40°E) and the Atlantic sector of the Southern Ocean that abuts it conveniently spans one region under consideration for spatial protection. To facilitate both an open and transparent process to provide the vest available scientific evidence for policy makers to formulate management options, we review the body of physical, geochemical and biological knowledge of the marine environment of this region. The level of scientific knowledge throughout the seascape abutting DML is polarized, with a clear lack of data in its eastern part which is presumably related to differing levels of research effort dedicated by national Antarctic programmes in the region. The lack of basic data on fundamental aspects of the physical, geological and biological nature of eastern DML make predictions of future trends difficult to impossible, with implications for the provision of management advice including spatial management. Finally, by highlighting key knowledge gaps across the scientific disciplines our review also serves to provide guidance to future research across this important region.publishedVersio
The Speed of Sound in Methane under Conditions of the Thermal Boundary Layer of Uranus
We present the first direct observations of acoustic waves in warm dense
matter. We analyze wavenumber- and energy-resolved X-ray spectra taken from
warm dense methane created by laser-heating a cryogenic liquid jet. X-ray
diffraction and inelastic free electron scattering yield sample conditions of
0.30.1 eV and 0.80.1 g/cm, corresponding to a pressure of
13 GPa and matching the conditions predicted in the thermal boundary
layer between the inner and outer envelope of Uranus. Inelastic X-ray
scattering was used to observe the collective oscillations of the ions. With a
highly improved energy resolution of 50 meV, we could clearly distinguish
the Brillouin peaks from the quasi-elastic Rayleigh feature. Data at different
wavenumbers were used to obtain a sound speed of 5.90.5 km/s, which
enabled us to validate the use of Birch's law in this new parameter regime.Comment: 7 pages, 4 figures with supplementary informatio
First results from the L3+C experiment at CERN
The L3+C experiment combines the high-precision spectrometer of the L3 detector at LEP, CERN, with a small air shower array. The momenta of cosmic ray induced muons can be measured from 20 to 2000 GeV/c. During the 1999 data taking period 5 billion muon events were recorded in the spectrometer. From April until mid Summer 2000 an additional 3 billion muon events have been recorded as well as 25 million air shower events. Here the first results on the muon momentum spectrum and charge ratio will be presented
The IceCube Data Acquisition System: Signal Capture, Digitization, and Timestamping
IceCube is a km-scale neutrino observatory under construction at the South
Pole with sensors both in the deep ice (InIce) and on the surface (IceTop). The
sensors, called Digital Optical Modules (DOMs), detect, digitize and timestamp
the signals from optical Cherenkov-radiation photons. The DOM Main Board (MB)
data acquisition subsystem is connected to the central DAQ in the IceCube
Laboratory (ICL) by a single twisted copper wire-pair and transmits packetized
data on demand. Time calibration is maintained throughout the array by regular
transmission to the DOMs of precisely timed analog signals, synchronized to a
central GPS-disciplined clock. The design goals and consequent features,
functional capabilities, and initial performance of the DOM MB, and the
operation of a combined array of DOMs as a system, are described here.
Experience with the first InIce strings and the IceTop stations indicates that
the system design and performance goals have been achieved.Comment: 42 pages, 20 figures, submitted to Nuclear Instruments and Methods
Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at âs=0.9 and 2.36 TeV
Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at root s = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN(ch)/d eta vertical bar(vertical bar eta vertical bar and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date
Enumerative Geometry
The central topics of this volume are enumerative geometry and intersection theory. The contributions are original (refereed) research papers