Boosting up quantum key distribution by learning statistics of practical single photon sources

We propose a simple quantum-key-distribution (QKD) scheme for practical single photon sources (SPSs), which works even with a moderate suppression of the second-order correlation $g^{(2)}$ of the source. The scheme utilizes a passive preparation of a decoy state by monitoring a fraction of the signal via an additional beam splitter and a detector at the sender's side to monitor photon number splitting attacks. We show that the achievable distance increases with the precision with which the sub-Poissonian tendency is confirmed in higher photon number distribution of the source, rather than with actual suppression of the multi-photon emission events. We present an example of the secure key generation rate in the case of a poor SPS with $g^{(2)} = 0.19$, in which no secure key is produced with the conventional QKD scheme, and show that learning the photon-number distribution up to several numbers is sufficient for achieving almost the same achievable distance as that of an ideal SPS.Comment: 11 pages, 3 figures; published version in New J. Phy

Pathogenomic analyses of Mycobacterium microti, an ESX-1-deleted member of the Mycobacterium tuberculosis complex causing disease in various hosts.

Mycobacterium microti is an animal-adapted member of the Mycobacterium tuberculosis complex (MTBC), which was originally isolated from voles, but has more recently also been isolated from other selected mammalian hosts, including occasionally from humans. Here, we have generated and analysed the complete genome sequences of five representative vole and clinical M. microti isolates using PacBio- and Illumina-based technologies, and have tested their virulence and vaccine potential in SCID (severe combined immune deficient) mouse and/or guinea pig infection models. We show that the clinical isolates studied here cluster separately in the phylogenetic tree from vole isolates and other clades from publicly available M. microti genome sequences. These data also confirm that the vole and clinical M. microti isolates were all lacking the specific RD1mic region, which in other tubercle bacilli encodes the ESX-1 type VII secretion system. Biochemical analysis further revealed marked phenotypic differences between isolates in type VII-mediated secretion of selected PE and PPE proteins, which in part were attributed to specific genetic polymorphisms. Infection experiments in the highly susceptible SCID mouse model showed that the clinical isolates were significantly more virulent than the tested vole isolates, but still much less virulent than the M. tuberculosis H37Rv control strain. The strong attenuation of the ATCC 35872 vole isolate in immunocompromised mice, even compared to the attenuated BCG (bacillus Calmette-Guérin) vaccine, and its historic use in human vaccine trials encouraged us to test this strain's vaccine potential in a guinea pig model, where it demonstrated similar protective efficacy as a BCG control, making it a strong candidate for vaccination of immunocompromised individuals in whom BCG vaccination is contra-indicated. Overall, we provide new insights into the genomic and phenotypic variabilities and particularities of members of an understudied clade of the MTBC, which all share a recent common ancestor that is characterized by the deletion of the RD1mic region

Non-equilibrium universality in the dynamics of dissipative cold atomic gases

The theory of continuous phase transitions predicts the universal collective properties of a physical system near a critical point, which for instance manifest in characteristic power-law behaviours of physical observables. The well-established concept at or near equilibrium, universality, can also characterize the physics of systems out of equilibrium. The most fundamental instance of a genuine non-equilibrium phase transition is the directed percolation universality class, where a system switches from an absorbing inactive to a fluctuating active phase. Despite being known for several decades it has been challenging to find experimental systems that manifest this transition. Here we show theoretically that signatures of the directed percolation universality class can be observed in an atomic system with long range interactions. Moreover, we demonstrate that even mesoscopic ensembles — which are currently studied experimentally — are sufficient to observe traces of this non-equilibrium phase transition in one, two and three dimensions

On-demand semiconductor single-photon source with near-unity indistinguishability

Single photon sources based on semiconductor quantum dots offer distinct advantages for quantum information, including a scalable solid-state platform, ultrabrightness, and interconnectivity with matter qubits. A key prerequisite for their use in optical quantum computing and solid-state networks is a high level of efficiency and indistinguishability. Pulsed resonance fluorescence (RF) has been anticipated as the optimum condition for the deterministic generation of high-quality photons with vanishing effects of dephasing. Here, we generate pulsed RF single photons on demand from a single, microcavity-embedded quantum dot under s-shell excitation with 3-ps laser pulses. The pi-pulse excited RF photons have less than 0.3% background contributions and a vanishing two-photon emission probability. Non-postselective Hong-Ou-Mandel interference between two successively emitted photons is observed with a visibility of 0.97(2), comparable to trapped atoms and ions. Two single photons are further used to implement a high-fidelity quantum controlled-NOT gate.Comment: 11 pages, 11 figure

Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering: Determined by the OLYMPUS Experiment

The OLYMPUS collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, $R_{2\gamma}$, a direct measure of the contribution of hard two-photon exchange to the elastic cross section. In the OLYMPUS measurement, 2.01~GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of $\approx 20\degree$ to $80\degree$. The relative luminosity between the two beam species was monitored using tracking telescopes of interleaved GEM and MWPC detectors at $12\degree$, as well as symmetric M{\o}ller/Bhabha calorimeters at $1.29\degree$. A total integrated luminosity of 4.5~fb$^{-1}$ was collected. In the extraction of $R_{2\gamma}$, radiative effects were taken into account using a Monte Carlo generator to simulate the convolutions of internal bremsstrahlung with experiment-specific conditions such as detector acceptance and reconstruction efficiency. The resulting values of $R_{2\gamma}$, presented here for a wide range of virtual photon polarization $0.456<\epsilon<0.978$, are smaller than some hadronic two-photon exchange calculations predict, but are in reasonable agreement with a subtracted dispersion model and a phenomenological fit to the form factor data.Comment: 5 pages, 3 figures, 2 table

Deficiency in the endocytic adaptor proteins PHETA1/2 impairs renal and craniofacial development

A critical barrier in the treatment of endosomal and lysosomal diseases is the lack of understanding of the in vivo functions of the putative causative genes. We addressed this by investigating a key pair of endocytic adaptor proteins, PH domain-containing endocytic trafficking adaptor 1 and 2 (PHETA1/2; also known as FAM109A/B, Ses1/2, IPIP27A/B), which interact with the protein product of OCRL, the causative gene for Lowe syndrome. Here, we conducted the first study of PHETA1/2 in vivo, utilizing the zebrafish system. We found that impairment of both zebrafish orthologs, pheta1 and pheta2, disrupted endocytosis and ciliogenesis in renal tissues. In addition, pheta1/2 mutant animals exhibited reduced jaw size and delayed chondrocyte differentiation, indicating a role in craniofacial development. Deficiency of pheta1/2 resulted in dysregulation of cathepsin K, which led to an increased abundance of type II collagen in craniofacial cartilages, a marker of immature cartilage extracellular matrix. Cathepsin K inhibition rescued the craniofacial phenotypes in the pheta1/2 double mutants. The abnormal renal and craniofacial phenotypes in the pheta1/2 mutant animals were consistent with the clinical presentation of a patient with a de novo arginine (R) to cysteine (C) variant (R6C) of PHETA1. Expressing the patient-specific variant in zebrafish exacerbated craniofacial deficits, suggesting that the R6C allele acts in a dominant-negative manner. Together, these results provide insights into the in vivo roles of PHETA1/2 and suggest that the R6C variant is contributory to the pathogenesis of disease in the patient

Laparoscopic correction of perforated peptic ulcer: first choice? A review of literature

Background Perforated peptic ulcer (PPU), despite antiulcer medication and Helicobacter eradication, is still the most common indication for emergency gastric surgery associated with high morbidity and mortality. Outcome might be improved by performing this procedure laparoscopically, but there is no consensus on whether the benefits of laparoscopic closure of perforated peptic ulcer outweigh the disadvantages such as prolonged surgery time and greater expense. Methods An electronic literature search was done by using PubMed and EMBASE databases. Relevant papers written between January 1989 and May 2009 were selected and scored according to Effective Public Health Practice Project guidelines. Results Data were extracted from 56 papers, as summarized in Tables 1-7. The overall conversion rate for laparoscopic correction of perforated peptic ulcer was 12.4%, with main reason for conversion being the diameter of perforation. Patients presenting with PPU were predominantly men (79%), with an average age of 48 years. Onethird had a history of peptic ulcer disease, and one-fifth took nonsteroidal anti-inflammatory drugs (NSAIDs). Only 7% presented with shock at admission. There seems to be no consensus on the perfect setup for surgery and/or operating technique. In the laparoscopic groups, operating time was significant longer and incidence of recurrent leakage at the repair site was higher. Nonetheless there was significant less postoperative pain, lower morbidity, less mortality, and shorter hospital stay. Conclusion There are good arguments that laparoscopic correction of PPU should be first treatment of choice. A Boey score of 3, age over 70 years, and symptoms persisting longer than 24 h are associated with higher morbidity and mortality and should be considered contraindications for laparoscopic intervention