85 research outputs found
Holonomic quantum computation in the presence of decoherence
We present a scheme to study non-abelian adiabatic holonomies for open
Markovian systems. As an application of our framework, we analyze the
robustness of holonomic quantum computation against decoherence. We pinpoint
the sources of error that must be corrected to achieve a geometric
implementation of quantum computation completely resilient to Markovian
decoherence.Comment: I. F-G. Now publishes under name I. Fuentes-Schuller Published
versio
Universal quantum computation by holonomic and nonlocal gates with imperfections
We present a nonlocal construction of universal gates by means of holonomic
(geometric) quantum teleportation. The effect of the errors from imperfect
control of the classical parameters, the looping variation of which builds up
holonomic gates, is investigated. Additionally, the influence of quantum
decoherence on holonomic teleportation used as a computational primitive is
studied. Advantages of the holonomic implementation with respect to control
errors and dissipation are presented.Comment: 5 pages, 2 figures, REVTEX, title changed, typos correcte
Topological Features in Ion Trap Holonomic Computation
Topological features in quantum computing provide controllability and noise
error avoidance in the performance of logical gates. While such resilience is
favored in the manipulation of quantum systems, it is very hard to identify
topological features in nature. This paper proposes a scheme where holonomic
quantum gates have intrinsic topological features. An ion trap is employed
where the vibrational modes of the ions are coherently manipulated with lasers
in an adiabatic cyclic way producing geometrical holonomic gates. A crucial
ingredient of the manipulation procedures is squeezing of the vibrational
modes, which effectively suppresses exponentially any undesired fluctuations of
the laser amplitudes, thus making the gates resilient to control errors.Comment: 9 pages, 4 figures, REVTE
Dynamics and Berry phase of two-species Bose-Einstein condensates
In terms of exact solutions of the time-dependent Schrodinger equation for an
effective giant spin modeled from a coupled two-mode Bose-Einstein condensate
(BEC) with adiabatic and cyclic time-varying Raman coupling between two
hyperfine states of the BEC, we obtain analytic time-evolution formulas of the
population imbalance and relative phase between two components with various
initial states, especially the SU(2)coherent state. We find the Berry phase
depending on the number parity of atoms, and particle number dependence of the
collapse revival of population-imbalance oscillation. It is shown that
self-trapping and phase locking can be achieved from initial SU(2) coherent
states with proper parameters.Comment: 18 pages,5 figure
Semiconductor-based Geometrical Quantum Gates
We propose an implementation scheme for holonomic, i.e., geometrical, quantum
information processing based on semiconductor nanostructures. Our quantum
hardware consists of coupled semiconductor macroatoms addressed/controlled by
ultrafast multicolor laser-pulse sequences. More specifically, logical qubits
are encoded in excitonic states with different spin polarizations and
manipulated by adiabatic time-control of the laser amplitudes . The two-qubit
gate is realized in a geometric fashion by exploiting dipole-dipole coupling
between excitons in neighboring quantum dots.Comment: 4 Pages LaTeX, 3 Figures included. To appear in PRB (Rapid Comm.
Efficient and robust entanglement generation in a many-particle system with resonant dipole-dipole interactions
We propose and discuss a scheme for robust and efficient generation of
many-particle entanglement in an ensemble of Rydberg atoms with resonant
dipole-dipole interactions. It is shown that in the limit of complete dipole
blocking, the system is isomorphic to a multimode Jaynes-Cummings model. While
dark-state population transfer is not capable of creating entanglement, other
adiabatic processes are identified that lead to complex, maximally entangled
states, such as the N-particle analog of the GHZ state in a few steps. The
process is robust, works for even and odd particle numbers and the
characteristic time for entanglement generation scales with N^a, with a being
less than unity.Comment: 4 figure
Geometric phases of mesoscopic spin in Bose-Einstein condensates
We propose a possible scheme for generating spin-J geometric phases using a
coupled two-mode Bose-Einstein condensate (BEC). First we show how to observe
the standard Berry phase using Raman coupling between two hyperfine states of
the BEC. We find that the presence of intrinsic interatomic collisions creates
degeneracy in energy that allows implementation of the non-Abelian geometric
phases as well. The evolutions produced can be used to produce interference
between different atomic species with high numbers of atoms or to fine control
the difference in atoms between the two species. Finally, we show that errors
in the standard Berry phase due to elastic collisions may be corrected by
controlling inelastic collisions between atoms.Comment: 6 pages, 2 figure
Slow oscillatory activity and levodopa-induced dyskinesias in Parkinson’s disease
The pathophysiology of levodopa-induced dyskinesias (LID) in Parkinson’s disease is not well understood.
We have recorded local field potentials (LFP) from macroelectrodes implanted in the subthalamic nucleus
(STN) of 14 patients with Parkinson’s disease following surgical treatment with deep brain stimulation. Patients
were studied in the ‘Off’ medication state and in the ‘On’ motor state after administration of levodopa–
carbidopa (po) or apomorphine (sc) that elicited dyskinesias in 11 patients. The logarithm of the power
spectrum of the LFP in selected frequency bands (4–10, 11–30 and 60–80 Hz) was compared between the
‘Off’ and ‘On’ medication states. A peak in the 11–30 Hz band was recorded in the ‘Off’ medication state
and reduced by 45.2% (P < 0.001) in the ‘On’ state. The ‘On’ was also associated with an increment of 77. 6%
(P < 0.001) in the 4–10 Hz band in all patients who showed dyskinesias and of 17.8% (P < 0.001) in the 60–80 Hz
band in the majority of patients. When dyskinesias were only present in one limb (n = 2), the 4–10 Hz peak was
only recorded in the contralateralSTN. These findings suggest that the 4–10 Hz oscillation is associated with the
expression of LID in Parkinson’s disease
Benchmarking the performance of a low-cost Magnetic Resonance Control System at multiple sites in the open MaRCoS community
Purpose: To describe the current properties and capabilities of an
open-source hardware and software package that is being developed by many sites
internationally with the aim of providing an inexpensive yet flexible platform
for low-cost MRI. Methods: This paper describes three different setups from 50
to 360 mT in different settings, all of which used the MaRCoS console for
acquiring data, and different types of software interfaces (custom-built GUI or
PulSeq overlay) to acquire the data. Results: Images are presented from both
phantoms and in vivo from healthy volunteers to demonstrate the image quality
that can be obtained from the MaRCoS hardware/software interfaced to different
low-field magnets. Conclusions: The results presented here show that a number
of different sequences commonly used in the clinic can be programmed into an
open-source system relatively quickly and easily, and can produce good quality
images even at this early stage of development. Both the hardware and software
will continue to develop, and it is an aim of this paper to encourage other
groups to join this international consortium.Comment: 9 pages, 10 figures, comments welcom
VEHICLE CLASSIFICATION IN URBAN REGIONS OF THE GLOBAL SOUTH FROM AERIAL IMAGERY
Land transport is a major contributor to the human-caused climate change; knowing the total number and composition of the vehicle fleet is key for estimating its emissions. Especially for countries of the Global South, emission inventories are associated with high uncertainties because fleet data are often unknown or outdated – classifying vehicles on remote sensing has the potential to change this. We present the XWHEEL dataset based on annotated vehicles in aerial images with six classes depending on the number of wheels, size and motorization. The dataset consists of 73 annotated aerial images of the city of Dar es Salaam (Tanzania) with 15,973 vehicles. To analyze the performance of the dataset, a convolutional neural network, ReDet, and a transformer-based neural network, DINOOBB, are trained with different configurations and validated on the validation and test split, but also on aerial images from other regions. The transformer-based DINO architecture has been adapted to the remote sensing domain and modified to predict Oriented Bounding Boxes. Results show a good performance on the test split from Dar es Salaam, when the two-wheeled classes are merged and the non-motorized three-wheeled vehicles are excluded due to their rare occurrence. The best performing algorithm configurations with four classes were then tested on aerial images of Kathmandu (Nepal) and Kampala (Uganda). The performance drops for cycles and three-wheeled vehicles, as their appearance varies between countries. A main finding is that we can reliably detect the different vehicle classes in Dar es Salaam. When algorithms trained on XWHEEL are generalized to other regions of the Global South, performance decreases for the more difficult classes (bicycles and tricycles). To obtain results that are comparable across the board, we therefore recommend expanding the dataset with additional annotations from other regions of the Global South
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