253 research outputs found
Single-bit Feedback and Quantum Dynamical Decoupling
Synthesizing an effective identity evolution in a target system subjected to
unwanted unitary or non-unitary dynamics is a fundamental task for both quantum
control and quantum information processing applications. Here, we investigate
how single-bit, discrete-time feedback capabilities may be exploited to enact
or to enhance quantum procedures for effectively suppressing unwanted dynamics
in a finite-dimensional open quantum system. An explicit characterization of
the joint unitary propagators correctable by a single-bit feedback strategy for
arbitrary evolution time is obtained. For a two-dimensional target system, we
show how by appropriately combining quantum feedback with dynamical decoupling
methods, concatenated feedback-decoupling schemes may be built, which can
operate under relaxed control assumptions and can outperform purely closed-loop
and open-loop protocols.Comment: 12 pages, 2 figure
Generation and propagation of entanglement in driven coupled-qubit systems
In a bipartite system subject to decoherence from two separate reservoirs,
the entanglement is typically destroyed faster than for single reservoirs.
Surprisingly however, the existence of separate reservoirs can also have a
beneficial entangling effect: if the qubits are coupled and driven externally
by a classical field, the system ends up in a stationary state characterized by
a finite degree of entanglement. This phenomenon occurs only in a certain
region of the parameter space and the structure of the stationary state has a
universal form which does not depend on the initial state or on the specific
physical realization of the qubits. We show that the entanglement thus
generated can be propagated within a quantum network using simple local unitary
operations. We suggest the use of such systems as "batteries of entanglement"
in quantum circuits.Comment: 14 pages, 7 figure
Cooling atoms into entangled states
We discuss the possibility of preparing highly entangled states by simply
cooling atoms into the ground state of an applied interaction Hamiltonian. As
in laser sideband cooling, we take advantage of a relatively large detuning of
the desired state, while all other qubit states experience resonant laser
driving. Once spontaneous emission from excited atomic states prepares the
system in its ground state, it remains there with a very high fidelity for a
wide range of experimental parameters and all possible initial states. After
presenting the general theory, we discuss concrete applications with one and
two qubits.Comment: 16 pages, 6 figures, typos correcte
Discrete-time classical and quantum Markovian evolutions: Maximum entropy problems on path space
The theory of Schroedinger bridges for diffusion processes is extended to
classical and quantum discrete-time Markovian evolutions. The solution of the
path space maximum entropy problems is obtained from the a priori model in both
cases via a suitable multiplicative functional transformation. In the quantum
case, nonequilibrium time reversal of quantum channels is discussed and
space-time harmonic processes are introduced.Comment: 34 page
Human Polyomaviruses in the Cerebrospinal Fluid of Neurological Patients.
BACKGROUND:
Central nervous system (CNS) infections by human polyomaviruses (HPyVs), with the exception of JC (JCPyV), have been poorly studied.
METHODS:
In total, 234 cerebrospinal fluid (CSF) samples were collected from patients affected with neurological disorders. DNA was isolated and subjected to quantitative real-time PCR (Q-PCR) for the detection of six HPyVs: JCPyV, BKPyV, Merkel cell PyV (MCPyV), HPyV6, HPyV7, and HPyV9. Where possible, the molecular characterization of the viral strains was carried out by nested PCR and automated sequencing.
RESULTS:
JCPyV was detected in 3/234 (1.3%), BKPyV in 15/234 (6.4%), MCPyV in 22/234 (9.4%), and HPyV6 in 1/234 (0.4%) CSF samples. JCPyV was detected at the highest (p < 0.05) mean load (3.7
7 107 copies/mL), followed by BKPyV (1.9
7 106 copies/mL), MCPyV (1.9
7 105 copies/mL), and HPyV6 (3.3
7 104 copies/mL). The noncoding control regions (NCCRs) of the sequenced viral strains were rearranged.
CONCLUSIONS:
HPyVs other than JCPyV were found in the CSF of patients affected with different neurological diseases, probably as bystanders, rather than etiological agents of the disease. However, the fact that they can be latent in the CNS should be considered, especially in immunosuppressed patients
A novel nonsense ATP7A pathogenic variant in a family exhibiting a variable occipital horn syndrome phenotype
We report on a family with occipital horn syndrome (OHS) diagnosed in the proband's late fifties. A novel ATP7A pathogenic variant (c.4222A > T, p.(Lys1408*)), representing the first nonsense variant and the second late truncation causing OHS rather than classic Menkes disease, was found to segregate in the family. The predicted maintenance of transmembrane domains is consistent with a residual protein activity, which may explain the mild clinical presentation
Novel mutations support a role for Profilin 1 in the pathogenesis of ALS
AbstractMutations in the gene encoding profilin 1 (PFN1) have recently been shown to cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder. We sequenced the PFN1 gene in a cohort of ALS patients (n = 485) and detected 2 novel variants (A20T and Q139L), as well as 4 cases with the previously identified E117G rare variant (⌠1.2%). A case-control meta-analysis of all published E117G ALS+/â frontotemporal dementia cases including those identified in this report was significant p = 0.001, odds ratio = 3.26 (95% confidence interval, 1.6â6.7), demonstrating this variant to be a susceptibility allele. Postmortem tissue from available patients displayed classic TAR DNA-binding protein 43 pathology. In both transient transfections and in fibroblasts from a patient with the A20T change, we showed that this novel PFN1 mutation causes protein aggregation and the formation of insoluble high molecular weight species which is a hallmark of ALS pathology. Our findings show that PFN1 is a rare cause of ALS and adds further weight to the underlying genetic heterogeneity of this disease
Brain-Computer Interface for Clinical Purposes : Cognitive Assessment and Rehabilitation
Alongside the best-known applications of brain-computer interface (BCI) technology for restoring communication abilities and controlling external devices, we present the state of the art of BCI use for cognitive assessment and training purposes. We first describe some preliminary attempts to develop verbal-motor free BCI-based tests for evaluating specific or multiple cognitive domains in patients with Amyotrophic Lateral Sclerosis, disorders of consciousness, and other neurological diseases. Then we present the more heterogeneous and advanced field of BCI-based cognitive training, which has its roots in the context of neurofeedback therapy and addresses patients with neurological developmental disorders (autism spectrum disorder and attention-deficit/hyperactivity disorder), stroke patients, and elderly subjects. We discuss some advantages of BCI for both assessment and training purposes, the former concerning the possibility of longitudinally and reliably evaluating cognitive functions in patients with severe motor disabilities, the latter regarding the possibility of enhancing patients' motivation and engagement for improving neural plasticity. Finally, we discuss some present and future challenges in the BCI use for the described purposes
Quantum Feedback Control: How to use Verification Theorems and Viscosity Solutions to Find Optimal Protocols
While feedback control has many applications in quantum systems, finding
optimal control protocols for this task is generally challenging. So-called
"verification theorems" and "viscosity solutions" provide two useful tools for
this purpose: together they give a simple method to check whether any given
protocol is optimal, and provide a numerical method for finding optimal
protocols. While treatments of verification theorems usually use sophisticated
mathematical language, this is not necessary. In this article we give a simple
introduction to feedback control in quantum systems, and then describe
verification theorems and viscosity solutions in simple language. We also
illustrate their use with a concrete example of current interest.Comment: 12 pages, revtex
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