8,933 research outputs found
myCopter: Enabling Technologies for Personal Aerial Transportation Systems: Project status after 2.5 years
Current means of transportation for daily commuting are reaching their limits during peak travel times, which results in waste of fuel and loss of time and money. A recent study commissioned by the European Union considers a personal aerial transportation system (PATS) as a viable alternative for transportation to and from work. It also acknowledges that developing such a transportation system should not focus on designing a new flying vehicle for personal use, but instead on investigating issues surrounding the implementation of the transportation system itself. This is the aim of European project myCopter: to determine the social and technological aspects needed to set up a transportation system based on personal aerial vehicles (PAVs). The project focuses on three research areas: human-machine interfaces and training, automation technologies, and social acceptance. Our extended abstract for inclusion in the conference proceedings and our presentation will focus on the achievements during the first 2.5 years of the 4-year project. These include the development of an augmented dynamic model of a PAV with excellent handling qualities that are suitable for training purposes. The training requirements for novice pilots are currently under development. Experimental evaluations on haptic guidance and human-in-the-loop control tasks have allowed us to start implementing a haptic Highway-in-the-Sky display to support novice pilots and to investigate metrics for objectively determining workload using psychophysiological measurements. Within the project, developments for automation technologies have focused on vision-based algorithms. We have integrated such algorithms in the control and navigation architecture of unmanned aerial vehicles (UAVs). Detecting suitable landing spots from monocular camera images recorded in flight has proven to reliably work off-line, but further work is required to be able to use this approach in real time. Furthermore, we have built multiple low-cost UAVs and equipped them with radar sensors to test collision avoidance strategies in real flight. Such algorithms are currently under development and will take inspiration from crowd simulations. Finally, using technology assessment methodologies, we have assessed potential markets for PAVs and challenges for its integration into the current transportation system. This will lead to structured discussions on expectations and requirements of potential PAV users
Deterministic and cascadable conditional phase gate for photonic qubits
Previous analyses of conditional \phi-phase gates for photonic qubits that
treat cross-phase modulation (XPM) in a causal, multimode, quantum field
setting suggest that a large (~\pi rad) nonlinear phase shift is always
accompanied by fidelity-degrading noise [J. H. Shapiro, Phys. Rev. A 73, 062305
(2006); J. Gea-Banacloche, Phys. Rev. A 81, 043823 (2010)]. Using an atomic
V-system to model an XPM medium, we present a conditional phase gate that, for
sufficiently small nonzero \phi, has high fidelity. The gate is made cascadable
by using using a special measurement, principal mode projection, to exploit the
quantum Zeno effect and preclude the accumulation of fidelity-degrading
departures from the principal-mode Hilbert space when both control and target
photons illuminate the gate
Quantum Computers, Factoring, and Decoherence
In a quantum computer any superposition of inputs evolves unitarily into the
corresponding superposition of outputs. It has been recently demonstrated that
such computers can dramatically speed up the task of finding factors of large
numbers -- a problem of great practical significance because of its
cryptographic applications. Instead of the nearly exponential (, for a number with digits) time required by the fastest classical
algorithm, the quantum algorithm gives factors in a time polynomial in
(). This enormous speed-up is possible in principle because quantum
computation can simultaneously follow all of the paths corresponding to the
distinct classical inputs, obtaining the solution as a result of coherent
quantum interference between the alternatives. Hence, a quantum computer is
sophisticated interference device, and it is essential for its quantum state to
remain coherent in the course of the operation. In this report we investigate
the effect of decoherence on the quantum factorization algorithm and establish
an upper bound on a ``quantum factorizable'' based on the decoherence
suffered per operational step.Comment: 7 pages,LaTex + 2 postcript figures in a uuencoded fil
Qudit-Basis Universal Quantum Computation using Interactions
We prove that universal quantum computation can be realized---using only
linear optics and (three-wave mixing) interactions---in any
-dimensional qudit basis of the -pump-photon subspace. First, we
exhibit a strictly universal gate set for the qubit basis in the
one-pump-photon subspace. Next, we demonstrate qutrit-basis universality by
proving that Hamiltonians and photon-number operators generate the
full Lie algebra in the two-pump-photon subspace, and showing
how the qutrit controlled- gate can be implemented with only linear optics
and interactions. We then use proof by induction to obtain our
general qudit result. Our induction proof relies on coherent photon
injection/subtraction, a technique enabled by interaction between
the encoding modes and ancillary modes. Finally, we show that coherent photon
injection is more than a conceptual tool in that it offers a route to preparing
high-photon-number Fock states from single-photon Fock states.Comment: 9 pages, 3 figure
Scheme for direct measurement of a general two-qubit Hamiltonian
The construction of two-qubit gates appropriate for universal quantum
computation is of enormous importance to quantum information processing.
Building such gates is dependent on accurate knowledge of the interaction
dynamics between two qubit systems. This letter will present a systematic
method for reconstructing the full two-qubit interaction Hamiltonian through
experimental measures of concurrence. This not only gives a convenient method
for constructing two qubit quantum gates, but can also be used to
experimentally determine various Hamiltonian parameters in physical systems. We
show explicitly how this method can be employed to determine the first and
second order spin-orbit corrections to the exchange coupling in quantum dots.Comment: 4 Pages, 1 Figur
Electronic bandstructure and optical gain of lattice matched III-V dilute nitride bismide quantum wells for 1.55 m optical communication systems
Dilute nitride bismide GaNBiAs is a potential semiconductor alloy for near-
and mid-infrared applications, particularly in 1.55 m optical
communication systems. Incorporating dilute amounts of Bismuth (Bi) into GaAs
reduces the effective bandgap rapidly, while significantly increasing the
spin-orbit-splitting energy. Additional incorporation of dilute amounts of
Nitrogen (N) helps to attain lattice matching with GaAs, while providing a
route for flexible bandgap tuning. Here we present a study of the electronic
bandstructure and optical gain of the lattice matched
GaNBiAs/GaAs quaternary alloy quantum well (QW) based on the
16-band kp model. We have taken into consideration the interactions
between the N and Bi impurity states with the host material based on the band
anticrossing (BAC) and valence band anticrossing (VBAC) model. The optical gain
calculation is based on the density matrix theory. We have considered different
lattice matched GaNBiAs QW cases and studied their energy dispersion curves,
optical gain spectrum, maximum optical gain and differential gain; and compared
their performances based on these factors. The thickness and composition of
these QWs were varied in order to keep the emission peak fixed at 1.55 m.
The well thickness has an effect on the spectral width of the gain curves. On
the other hand, a variation in the injection carrier density has different
effects on the maximum gain and differential gain of QWs of varying
thicknesses. Among the cases studied, we found that the 6.3 nm thick
GaNBiAs lattice matched QW was most suited for 1.55
m (0.8 eV) GaAs-based photonic applications.Comment: Accepted in AIP Journal of Applied Physic
Electronic and optical properties of quantum wells embedded in wrinkled nanomembranes
The authors theoretically investigate quantum confinement and transition
energies in quantum wells (QWs) asymmetrically positioned in wrinkled
nanomembranes. Calculations reveal that the wrinkle profile induces both blue-
and redshifts depending on the lateral position of the QW probed. Relevant
radiative transistions include the ground state of the electron (hole) and
excited states of the hole (electron). Energy shifts as well as stretchability
of the structure are studied as a function of wrinkle amplitude and period.
Large tunable bandwidths of up to 70 nm are predicted for highly asymmetric
wrinkled QWs.Comment: 3 pages, 4 figures. The following article has been submitted to
Applied Physics Letters. After it is published, it will be found at
http://apl.aip.or
Non-thermal nuclear magnetic resonance quantum computing using hyperpolarized Xenon
Current experiments in liquid-state nuclear magnetic resonance quantum
computing are limited by low initial polarization. To address this problem, we
have investigated the use of optical pumping techniques to enhance the
polarization of a 2-qubit NMR quantum computer (13C and 1H in 13CHCl3). To
efficiently use the increased polarization, we have generalized the procedure
for effective pure state preparation. With this new, more flexible scheme, an
effective pure state was prepared with polarization-enhancement of a factor of
10 compared to the thermal state. An implementation of Grover's quantum search
algorithm was demonstrated using this new technique.Comment: 4 pages, 3 figures. Submitted for publicatio
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