19 research outputs found
Continuous quantum error correction for non-Markovian decoherence
We study the effect of continuous quantum error correction in the case where
each qubit in a codeword is subject to a general Hamiltonian interaction with
an independent bath. We first consider the scheme in the case of a trivial
single-qubit code, which provides useful insights into the workings of
continuous error correction and the difference between Markovian and
non-Markovian decoherence. We then study the model of a bit-flip code with each
qubit coupled to an independent bath qubit and subject to continuous
correction, and find its solution. We show that for sufficiently large
error-correction rates, the encoded state approximately follows an evolution of
the type of a single decohering qubit, but with an effectively decreased
coupling constant. The factor by which the coupling constant is decreased
scales quadratically with the error-correction rate. This is compared to the
case of Markovian noise, where the decoherence rate is effectively decreased by
a factor which scales only linearly with the rate of error correction. The
quadratic enhancement depends on the existence of a Zeno regime in the
Hamiltonian evolution which is absent in purely Markovian dynamics. We analyze
the range of validity of this result and identify two relevant time scales.
Finally, we extend the result to more general codes and argue that the
performance of continuous error correction will exhibit the same qualitative
characteristics.Comment: 16 pages, 4 figures, minor typos corrected, references update
Non-Markovian dynamics of a qubit coupled to an Ising spin bath
We study the analytically solvable Ising model of a single qubit system
coupled to a spin bath. The purpose of this study is to analyze and elucidate
the performance of Markovian and non-Markovian master equations describing the
dynamics of the system qubit, in comparison to the exact solution. We find that
the time-convolutionless master equation performs particularly well up to
fourth order in the system-bath coupling constant, in comparison to the
Nakajima-Zwanzig master equation. Markovian approaches fare poorly due to the
infinite bath correlation time in this model. A recently proposed
post-Markovian master equation performs comparably to the time-convolutionless
master equation for a properly chosen memory kernel, and outperforms all the
approximation methods considered here at long times. Our findings shed light on
the applicability of master equations to the description of reduced system
dynamics in the presence of spin-baths.Comment: 17 pages, 16 figure
Optimal signal states for quantum detectors
Quantum detectors provide information about quantum systems by establishing
correlations between certain properties of those systems and a set of
macroscopically distinct states of the corresponding measurement devices. A
natural question of fundamental significance is how much information a quantum
detector can extract from the quantum system it is applied to. In the present
paper we address this question within a precise framework: given a quantum
detector implementing a specific generalized quantum measurement, what is the
optimal performance achievable with it for a concrete information readout task,
and what is the optimal way to encode information in the quantum system in
order to achieve this performance? We consider some of the most common
information transmission tasks - the Bayes cost problem (of which minimal error
discrimination is a special case), unambiguous message discrimination, and the
maximal mutual information. We provide general solutions to the Bayesian and
unambiguous discrimination problems. We also show that the maximal mutual
information has an interpretation of a capacity of the measurement, and derive
various properties that it satisfies, including its relation to the accessible
information of an ensemble of states, and its form in the case of a
group-covariant measurement. We illustrate our results with the example of a
noisy two-level symmetric informationally complete measurement, for whose
capacity we give analytical proofs of optimality. The framework presented here
provides a natural way to characterize generalized quantum measurements in
terms of their information readout capabilities.Comment: 13 pages, 1 figure, example section extende
Experiences with workflows for automating data-intensive bioinformatics
High-throughput technologies, such as next-generation sequencing, have turned molecular biology into a
data-intensive discipline, requiring bioinformaticians to use high-performance computing resources and carry out
data management and analysis tasks on large scale. Workflow systems can be useful to simplify construction of
analysis pipelines that automate tasks, support reproducibility and provide measures for fault-tolerance. However,
workflow systems can incur significant development and administration overhead so bioinformatics pipelines are
often still built without them. We present the experiences with workflows and workflow systems within the
bioinformatics community participating in a series of hackathons and workshops of the EU COST action SeqAhead.
The organizations are working on similar problems, but we have addressed them with different strategies and
solutions. This fragmentation of efforts is inefficient and leads to redundant and incompatible solutions. Based on our
experiences we define a set of recommendations for future systems to enable efficient yet simple bioinformatics
workflow construction and execution.Pubblicat
QSPR Models for Predictions and Data Qualit\ue0 assurances: Melting Point and Boiling Point of Perfluorinated Chemicals,
10noneBhhatarai B.; Teetz W.; Ăberg T.; Liu T.; Jeliazkova N.; Kochev N. ; Ognyan P.; Tetko I.; Kovarich S.; Gramatica P.Bhhatarai, Barun; Teetz, W.; Ăberg, T.; Liu, T.; Jeliazkova, N.; Kochev, N.; Ognyan, P.; Tetko, I.; Kovarich, Simona; Gramatica, Paol
Synthesis of 4-acetyl-2(3<i>H</i>)-benzothiazolone: Sulfur bioisostere of benzoxazolone allelochemicals
<p></p> <p>A multi-step methodology for the synthesis of 4-acetyl-2(3<i>H</i>)-benzothiazolone was developed in order to prepare a new biomimetic analogue of benzoxazolone allelochemicals. The compound was prepared from commercially available <i>o</i>-toluidine in 23% overall yield. The structure of 4-acethyl-2(3<i>H</i>)-benzothiazolone was confirmed by NMR spectroscopy and X-ray crystallography.</p
Local Deuteration Enables NMR Observation of Methyl Groups in Proteins from Eukaryotic and CellâFree Expression Systems
Therapeutically relevant proteins such as GPCRs, antibodies and kinases face clear limitations in NMR studies due to the challenges in site-specific isotope labeling and deuteration in eukaryotic expression systems. Here we describe an efficient and simple method to observe the methyl groups of leucine residues in proteins expressed in bacterial, eukaryotic or cell-free expression systems without modification of the expression protocol. The method relies on simple stereo-selective 13C-labeling and deuteration of leucine that alleviates the need for additional deuteration of the protein. The spectroscopic benefits of âlocalâ deuteration are examined in detail through Forbidden Coherence Transfer (FCT) experiments and simulations. The utility of this labeling method is demonstrated in the cell-free synthesis of bacteriorhodopsin and in the insect-cell expression of the RRM2 domain of human RBM39