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

Subspace confinement : how good is your qubit?

The basic operating element of standard quantum computation is the qubit, an isolated two-level system that can be accurately controlled, initialized and measured. However, the majority of proposed physical architectures for quantum computation are built from systems that contain much more complicated Hilbert space structures. Hence, defining a qubit requires the identification of an appropriate controllable two-dimensional sub-system. This prompts the obvious question of how well a qubit, thus defined, is confined to this subspace, and whether we can experimentally quantify the potential leakage into states outside the qubit subspace. We demonstrate how subspace leakage can be characterized using minimal theoretical assumptions by examining the Fourier spectrum of the oscillation experiment

How can we best chart children’s growth in the paperless age? The UK experience

Growth charts have played an integral part in the monitoring and assessment of children’s health for the past 50 years, but their use is now under threat as paperless electronic systems become more widely used. While the obvious solution is to adopt electronic charting systems, this can prove challenging in practice. This article describes the key issues to consider in planning this transition and the charting options available, ranging from bespoke local systems to commercial packages and a new initiative by the Royal College of Paediatrics and Child Health

The small FNR regulon of Neisseria gonorrhoeae: comparison with the larger Escherichia coli FNR regulon and interaction with the NarQ-NarP regulon

BACKGROUND: Neisseria gonorrhoeae can survive during oxygen starvation by reducing nitrite to nitrous oxide catalysed by the nitrite and nitric oxide reductases, AniA and NorB. The oxygen-sensing transcription factor, FNR, is essential for transcription activation at the aniA promoter, and full activation also requires the two-component regulatory system, NarQ-NarP, and the presence of nitrite. The only other gene known to be activated by the gonococcal FNR is ccp encoding a cytochrome c peroxidase, and no FNR-repressed genes have been reported in the gonococcus. In contrast, FNR acts as both an activator and repressor involved in the control of more than 100 operons in E. coli regulating major changes in the adaptation from aerobic to anaerobic conditions. In this study we have performed a microarray-led investigation of the FNR-mediated responses in N. gonorrhoeae to determine the physiological similarities and differences in the role of FNR in cellular regulation in this species. RESULTS: Microarray experiments show that N. gonorrhoeae FNR controls a much smaller regulon than its E. coli counterpart; it activates transcription of aniA and thirteen other genes, and represses transcription of six genes that include dnrN and norB. Having previously shown that a single amino acid substitution is sufficient to enable the gonococcal FNR to complement an E. coli fnr mutation, we investigated whether the gonococcal NarQ-NarP can substitute for E. coli NarX-NarL or NarQ-NarP. A plasmid expressing gonococcal narQ-narP was unable to complement E. coli narQP or narXL mutants, and was insensitive to nitrate or nitrite. Mutations that progressively changed the periplasmic nitrate sensing region, the P box, of E. coli NarQ to the sequence of the corresponding region of gonococcal NarQ resulted in loss of transcription activation in response to the availability of either nitrate or nitrite. However, the previously reported ligand-insensitive ability of gonococcal NarQ, the "locked on" phenotype, to activate either E. coli NarL or NarP was confirmed. CONCLUSION: Despite the sequence similarities between transcription activators of E. coli and N. gonorrhoeae, these results emphasise the fundamental differences in transcription regulation between these two types of pathogenic bacteria

Admissibility Compared: The Reception of Incriminating Expert Evidence (i.e., Forensic Science) in Four Adversarial Jurisdictions

There is an epistemic crisis in many areas of forensic science. This crisis emerged largely in response both to the mobilization of a range of academic commentators and critics and the rise and influence of DNA typing. It gained popular and authoritative support through the influence of the National Academy of Science (NAS) and a surprisingly critical report produced under its auspices by a committee of the National Research Council (NRC). Interestingly, as this article endeavors to explain, the courts themselves seem to have played a rather indirect, inconsistent and ultimately ineffective role in the supervision and evaluation of forensic science evidence. Indeed, in the aftermath of recent criticism of the forensic sciences, this essay considers the effect of the dominant admissibility standards that operate in four common law jurisdictions. The revealing result seems to be that although admissibility standards vary across these jurisdictions, actual admissibility practices are remarkably consistent. In this article we will question the extent to which courts (and legal personnel) are able to meaningfully invigilate the use of forensic science evidence in criminal proceedings and consider some of the ideological commitments and institutional pressures that might lead judges in all jurisdictions to prefer inclusive approaches to incriminating expert opinions. In the first part of the article, we compare rules, jurisprudence and practices, across four jurisdictions: the United States, England and Wales, Canada, and Australia. All profoundly shaped by the English common law, these jurisdictions (and their sub- jurisdictions) tend to use a mixture of common law (e.g. England and Wales and Canada), judge-made rules (e.g. the U.S. Federal Rules of Evidence) and statutory schemes (e.g. the Australian Evidence Act 1995 Cth and many states in the United States) to regulate the admission of evidence, including expert opinion. These jurisdictions tend to maintain criminal trial processes that remain reasonably similar and facilitate broad brush comparisons. Our findings suggest that admissibility standards, including the first generation of reliability-based standards, seem to make little, if any, difference to (traditional) admissibility decision-making and practice. Allowing for some variation, the same sorts of forensic science evidence are admitted across all jurisdictions, even where the techniques are not demonstrably reliable and the jurisdiction in question has explicit reliability standards and other rules regulating the admission of expert opinion evidence. Moreover, it is our contention that the legal accommodation of the techniques considered in this article exemplifies a more general response to admissibility and the regulation of forensic science and medicine evidence. In the second part of the article we will consider possible explanations and some of the implications of our findings

Life, Death and Preferential Attachment

Scientific communities are characterized by strong stratification. The highly skewed frequency distribution of citations of published scientific papers suggests a relatively small number of active, cited papers embedded in a sea of inactive and uncited papers. We propose an analytically soluble model which allows for the death of nodes. This model provides an excellent description of the citation distributions for live and dead papers in the SPIRES database. Further, this model suggests a novel and general mechanism for the generation of power law distributions in networks whenever the fraction of active nodes is small.Comment: 5 pages, 2 figure

Constraining the X-ray heating and reionization using 21-cm power spectra with Marginal Neural Ratio Estimation

Cosmic Dawn (CD) and Epoch of Reionization (EoR) are epochs of the Universe which host invaluable information about the cosmology and astrophysics of X-ray heating and hydrogen reionization. Radio interferometric observations of the 21-cm line at high redshifts have the potential to revolutionize our understanding of the universe during this time. However, modeling the evolution of these epochs is particularly challenging due to the complex interplay of many physical processes. This makes it difficult to perform the conventional statistical analysis using the likelihood-based Markov-Chain Monte Carlo (MCMC) methods, which scales poorly with the dimensionality of the parameter space. In this paper, we show how the Simulation-Based Inference (SBI) through Marginal Neural Ratio Estimation (MNRE) provides a step towards evading these issues. We use 21cmFAST to model the 21-cm power spectrum during CD-EoR with a six-dimensional parameter space. With the expected thermal noise from the Square Kilometre Array (SKA), we are able to accurately recover the posterior distribution for the parameters of our model at a significantly lower computational cost than the conventional likelihood-based methods. We further show how the same training dataset can be utilized to investigate the sensitivity of the model parameters over different redshifts. Our results support that such efficient and scalable inference techniques enable us to significantly extend the modeling complexity beyond what is currently achievable with conventional MCMC methods.Comment: 15 pages, 9 figures. Accepted for publication in MNRA

High-Resolution Measurements of the Dark Matter Halo of NGC 2976: Evidence for a Shallow Density Profile

We have obtained two-dimensional velocity fields of the dwarf spiral galaxy NGC 2976 in Halpha and CO. The high spatial (~75 pc) and spectral (13 km/s and 2 km/s, respectively) resolution of these observations, along with our multicolor optical and near-infrared imaging, allow us to measure the shape of the density profile of the dark matter halo with good precision. We find that the total (baryonic plus dark matter) mass distribution of NGC 2976 follows a rho_tot ~ r^(-0.27 +/- 0.09) power law out to a radius of 1.8 kpc, assuming that the observed radial motions provide no support. The density profile attributed to the dark halo is even shallower, consistent with a nearly constant density of dark matter over the entire observed region. A maximal disk fit yields an upper limit to the K-band stellar mass-to-light ratio (M*/L_K) of 0.09^{+0.15}_{-0.08} M_sun/L_sun,K (including systematic uncertainties), with the caveat that for M*/L_K > 0.19 M_sun/L_sun,K the dark matter density increases with radius, which is unphysical. Assuming 0.10 M_sun/L_sun,K < M*/L_K < 0.19 M_sun/L_sun,K, the dark matter density profile lies between rho_dm ~ r^-0.17 and rho_dm ~ r^-0.01. Therefore, independent of any assumptions about the stellar disk or the functional form of the density profile, NGC 2976 does not contain a cuspy dark matter halo. We also investigate some of the systematic effects that can hamper rotation curve studies, and show that 1) longslit rotation curves are far more vulnerable to systematic errors than two-dimensional velocity fields, 2) NGC 2976 contains large radial motions at small radii, and 3) the Halpha and CO velocity fields of NGC 2976 agree within their uncertainties. [slightly abridged]Comment: 30 pages, 4 tables, 13 figures (7 in color; Figures 1 and 3 are low-resolution to save space). Accepted for publication in ApJ. Version with full-resolution figures available at http://astro.berkeley.edu/~bolatto/ngc2976rotation.ps (46 MB

Precision characterisation of two-qubit Hamiltonians via entanglement mapping

We show that the general Heisenberg Hamiltonian with non-uniform couplings can be characterised by mapping the entanglement it generates as a function of time. Identification of the Hamiltonian in this way is possible as the coefficients of each operator control the oscillation frequencies of the entanglement function. The number of measurements required to achieve a given precision in the Hamiltonian parameters is determined and an efficient measurement strategy designed. We derive the relationship between the number of measurements, the resulting precision and the ultimate discrete error probability generated by a systematic mis-characterisation, when implementing two-qubit gates for quantum computing.Comment: 6 Pages, 3 figure

Fitness of INTERGROWTH-21st birth weight standards for Chinese-ethnicity babies

OBJECTIVE: To determine the fitness of the INTERGROWTH-21st birth weight standards (INTERGROWTH21) for ethnic Chinese babies compared with a local reference (FOK2003). DESIGN: Population-based analysis of territory-wide birth data. SETTING: All public hospitals in Hong Kong. PARTICIPANTS: Live births between 24 and 42 complete weeks' gestation during 2006-2017. MAIN OUTCOME MEASURES: Babies' birth weight Z-scores were calculated using published methods. The two references were compared in three aspects: (1) the proportions of large-for-gestational-age (LGA) or small-for-gestational-age (SGA) infants, (2) the gestation-specific and sex-specific mean birth weight Z-scores and (3) the predictive power for SGA-related complications. RESULTS: 488 896 infants were included. Using INTERGROWTH21, among neonates born <33 weeks' gestation, the mean birth weight Z-scores per week were closer to zero (-0.2 to 0.05), while most of them were further from zero (0.06 to 0.34) after excluding infants with a high risk of abnormal intrauterine growth. Compared with FOK2003, INTERGROWTH21 classified smaller proportions of infants as SGA (8.3% vs 9.6%) and LGA (6.6% vs 7.9%), especially SGA among preterm infants (13.1% vs 17.0%). The area under the receiver operating characteristic curve for predicting SGA-related complications was greater with FOK2003 (0.674, 95% CI 0.670 to 0.677) than INTERGROWTH21 (0.658, 95% CI 0.655 to 0.661) (p<0.001). CONCLUSIONS: INTERGROWTH21 performed less well than FOK2003, a local reference for ethnic Chinese babies, especially in infants born <33 weeks' gestation. Although the differences are clinically small, both these references performed poorly for extremely preterm infants, and thus a more robust chart based on a larger sample of appropriately selected infants is needed