30 research outputs found
Magnetic-film atom chip with 10 m period lattices of microtraps for quantum information science with Rydberg atoms
We describe the fabrication and construction of a setup for creating lattices
of magnetic microtraps for ultracold atoms on an atom chip. The lattice is
defined by lithographic patterning of a permanent magnetic film. Patterned
magnetic-film atom chips enable a large variety of trapping geometries over a
wide range of length scales. We demonstrate an atom chip with a lattice
constant of 10 m, suitable for experiments in quantum information science
employing the interaction between atoms in highly-excited Rydberg energy
levels. The active trapping region contains lattice regions with square and
hexagonal symmetry, with the two regions joined at an interface. A structure of
macroscopic wires, cut out of a silver foil, was mounted under the atom chip in
order to load ultracold Rb atoms into the microtraps. We demonstrate
loading of atoms into the square and hexagonal lattice sections simultaneously
and show resolved imaging of individual lattice sites. Magnetic-film lattices
on atom chips provide a versatile platform for experiments with ultracold
atoms, in particular for quantum information science and quantum simulation.Comment: 7 pages, 7 figure
Comparative study of nonlinear properties of EEG signals of a normal person and an epileptic patient
Background: Investigation of the functioning of the brain in living systems
has been a major effort amongst scientists and medical practitioners. Amongst
the various disorder of the brain, epilepsy has drawn the most attention
because this disorder can affect the quality of life of a person. In this paper
we have reinvestigated the EEGs for normal and epileptic patients using
surrogate analysis, probability distribution function and Hurst exponent.
Results: Using random shuffled surrogate analysis, we have obtained some of
the nonlinear features that was obtained by Andrzejak \textit{et al.} [Phys Rev
E 2001, 64:061907], for the epileptic patients during seizure. Probability
distribution function shows that the activity of an epileptic brain is
nongaussian in nature. Hurst exponent has been shown to be useful to
characterize a normal and an epileptic brain and it shows that the epileptic
brain is long term anticorrelated whereas, the normal brain is more or less
stochastic. Among all the techniques, used here, Hurst exponent is found very
useful for characterization different cases.
Conclusions: In this article, differences in characteristics for normal
subjects with eyes open and closed, epileptic subjects during seizure and
seizure free intervals have been shown mainly using Hurst exponent. The H shows
that the brain activity of a normal man is uncorrelated in nature whereas,
epileptic brain activity shows long range anticorrelation.Comment: Keywords:EEG, epilepsy, Correlation dimension, Surrogate analysis,
Hurst exponent. 9 page
Quantitative analysis by renormalized entropy of invasive electroencephalograph recordings in focal epilepsy
Invasive electroencephalograph (EEG) recordings of ten patients suffering
from focal epilepsy were analyzed using the method of renormalized entropy.
Introduced as a complexity measure for the different regimes of a dynamical
system, the feature was tested here for its spatio-temporal behavior in
epileptic seizures. In all patients a decrease of renormalized entropy within
the ictal phase of seizure was found. Furthermore, the strength of this
decrease is monotonically related to the distance of the recording location to
the focus. The results suggest that the method of renormalized entropy is a
useful procedure for clinical applications like seizure detection and
localization of epileptic foci.Comment: 10 pages, 5 figure
Network inference - with confidence - from multivariate time series
Networks - collections of interacting elements or nodes - abound in the
natural and manmade worlds. For many networks, complex spatiotemporal dynamics
stem from patterns of physical interactions unknown to us. To infer these
interactions, it is common to include edges between those nodes whose time
series exhibit sufficient functional connectivity, typically defined as a
measure of coupling exceeding a pre-determined threshold. However, when
uncertainty exists in the original network measurements, uncertainty in the
inferred network is likely, and hence a statistical propagation-of-error is
needed. In this manuscript, we describe a principled and systematic procedure
for the inference of functional connectivity networks from multivariate time
series data. Our procedure yields as output both the inferred network and a
quantification of uncertainty of the most fundamental interest: uncertainty in
the number of edges. To illustrate this approach, we apply our procedure to
simulated data and electrocorticogram data recorded from a human subject during
an epileptic seizure. We demonstrate that the procedure is accurate and robust
in both the determination of edges and the reporting of uncertainty associated
with that determination.Comment: 12 pages, 7 figures (low resolution), submitte
Nonlinear analysis of EEG signals at different mental states
BACKGROUND: The EEG (Electroencephalogram) is a representative signal containing information about the condition of the brain. The shape of the wave may contain useful information about the state of the brain. However, the human observer can not directly monitor these subtle details. Besides, since bio-signals are highly subjective, the symptoms may appear at random in the time scale. Therefore, the EEG signal parameters, extracted and analyzed using computers, are highly useful in diagnostics. This work discusses the effect on the EEG signal due to music and reflexological stimulation. METHODS: In this work, nonlinear parameters like Correlation Dimension (CD), Largest Lyapunov Exponent (LLE), Hurst Exponent (H) and Approximate Entropy (ApEn) are evaluated from the EEG signals under different mental states. RESULTS: The results obtained show that EEG to become less complex relative to the normal state with a confidence level of more than 85% due to stimulation. CONCLUSIONS: It is found that the measures are significantly lower when the subjects are under sound or reflexologic stimulation as compared to the normal state. The dimension increases with the degree of the cognitive activity. This suggests that when the subjects are under sound or reflexologic stimuli, the number of parallel functional processes active in the brain is less and the brain goes to a more relaxed stat
Magnetic-film atom chip with 10 μm period lattices of microtraps for quantum information science with Rydberg atoms
Detecting directional coupling in the human epileptic brain: Limitations and potential pitfalls
Shuttling-based trapped-ion quantum information processing
Moving trapped-ion qubits in a microstructured array of radiofrequency traps offers a route toward realizing scalable quantum processing nodes. Establishing such nodes, providing sufficient functionality to represent a building block for emerging quantum technologies, e.g., a quantum computer or quantum repeater, remains a formidable technological challenge. In this review, the authors present a holistic view on such an architecture, including the relevant components, their characterization, and their impact on the overall system performance. The authors present a hardware architecture based on a uniform linear segmented multilayer trap, controlled by a custom-made fast multichannel arbitrary waveform generator. The latter allows for conducting a set of different ion shuttling operations at sufficient speed and quality. The authors describe the relevant parameters and performance specifications for microstructured ion traps, waveform generators, and additional circuitry, along with suitable measurement schemes to verify the system performance. Furthermore, a set of different basic shuttling operations for a dynamic qubit register reconfiguration is described and characterized in detai
Fault-Tolerant Parity Readout on a Shuttling-Based Trapped-Ion Quantum Computer
Quantum error correction requires the detection of errors via reliable measurements of multiqubit correlation operators. As these operations are inherently faulty, fault-tolerant schemes for realizing quantum error correction are required. Recently, a paradigm requiring only minimal resource overhead in the form of “flag” qubits to detect and correct errors has been proposed. We experimentally demonstrate a fault-tolerant weight-4 parity-check measurement scheme, where one additional flag qubit serves to detect errors, which would otherwise proliferate into uncorrectable weight-2 errors onto the qubit register. We achieve a parity measurement fidelity of 92.3(2)%, which increases to 93.2(2)% upon conditioning to the flag readout result, which shows that the measurement scheme intercepts intrinsic errors occurring throughout the sequence. We show that the protocol is capable of reliably intercepting faults by deliberately injecting bit- and phase-flip errors. For holistic benchmarking of the parity measurement scheme, we use an entanglement witnessing scheme requiring a minimal number of measurements to verify genuine six-qubit multipartite entanglement. The demonstrated fault-tolerant parity measurement scheme constitutes the key building block in a broad class of resource-efficient flag-based quantum error correction protocols including topological color codes. Our hardware platform is based on atomic ions stored in a microchip ion trap. The qubit register is dynamically reconfigured via shuttling operations enabling effective full connectivity without operational cross talk, thereby providing key prerequisites underlying fault-tolerant circuit design. These architectural features in combination with the demonstrated approach to flag-based fault-tolerant quantum error correction open up a route toward scalable fault-tolerant quantum computing