Information encoded in high-dimensional quantum states can achieve ultrahigh rates over metropolitan distances.

No abstract

Quantum key distribution (QKD) allows two remote users to establish a secret key in the presence of an eavesdropper. The users share quantum states prepared in two mutually-unbiased bases: one to generate the key while the other monitors the presence of the eavesdropper. Here, we show that a general d-dimension QKD system can be secured by transmitting only a subset of the monitoring states. In particular, we find that there is no loss in the secure key rate when dropping one of the monitoring states. Furthermore, it is possible to use only a single monitoring state if the quantum bit error rates are low enough. We apply our formalism to an experimental d = 4 timephase QKD system, where only one monitoring state is transmitted, and obtain a secret key rate of 17.4 ± 2.8 Mbits/s at a 4 dB channel loss and with a quantum bit error rate of 0.045 ± 0.001 and 0.037 ± 0.001 in time and phase bases, respectively, which is 58.4% of the secret key rate that can be achieved with the full setup. This ratio can be increased, potentially up to 100%, if the error rates in time and phase basis are reduced. Our results demonstrate that it is possible to substantially simplify the design of high-dimensional QKD systems, including those that use the spatial or temporal degrees-of-freedom of the photon, and still outperform qubit-based (d = 2) protocols.

We investigate experimentally a cascade of temperature-compensated unequal-path interferometers that can be used to measure frequency states in a high-dimensional quantum distribution system. In particular, we demonstrate that commercially-available interferometers have sufficient environmental isolation so that they maintain an interference visibility greater than 98.5% at a wavelength of 1550 nm over extended periods with only moderate passive control of the interferometer temperature (< ±0.50 • C). Specifically, we characterize two interferometers that have matched delays: one with a free-spectral range of 2.5 GHz, and the other with 1.25 GHz. We find that the relative path of these interferometers drifts less than 3 nm over a period of one hour during which the temperature fluctuates by < ±0.10 • C. The error in our measurement is largely dominated by the small drift in the frequency and power of the stabilized laser used to perform the measurement. When we purposely heat the interferometers over a temperature range of 20-50 • C, we find that the temperature sensitivity is different for each interferometer, likely due to slight manufacturing errors during the temperature compensation procedure. Over this range, we measure a path-length shift of 26 ± 9 nm/ • C for the 2.5 GHz interferometer. For the 1.25 GHz interferometer, the path-length shift is nonlinear and is locally equal to zero at a temperature of 37.1 • C and is 50 ± 17 nm/ • C at 22 • C. With these devices, we realize a cascade of 1.25 GHz and 2.5 GHz interferometers to measure four-dimensional classical frequency states created by modulating a stable and continuous-wave laser. We observe a visibility > 99% over an hour, which is mainly limited by our ability to precisely generate these states. Overall, our results indicate that these interferometers are well suited for realistic time-frequency quantum distribution protocols. arXiv:1610.04947v1 [quant-ph]

Two low-lying neutron-unbound excited states of 24 O, populated by proton-knockout reactions on 26 F, have been measured using the MoNA and LISA arrays in combination with the Sweeper Magnet at the Coupled Cyclotron Facility at the NSCL using invariant mass spectroscopy. The current measurement confirms for the first time the separate identity of two states with decay energies 0.51(5) MeV and 1.20(7) MeV, and provides support for theoretical model calculations, which predict a 2 + first excited state and a 1 + higher energy state. The measured excitation energies for these states, 4.70(15) MeV for the 2 + level and 5.39(16) MeV for the (1 + ) level, are consistent with previous lower-resolution measurements, and are compared with five recent model predictions.

BackgroundVisceral leishmaniasis (VL), caused by an intracellular parasite Leishmania donovani in the Indian subcontinent, is considered to be anthroponotic. The role of domestic animals in its transmission is still unclear. Although cattle are the preferred blood host for Phlebotomus argentipes, the sandfly vector of VL in the Indian subcontinent, very little information is available for their role in the disease transmission. In this study, we examined domestic cattle for serological and molecular evidence of Leishmania infection in a VL-endemic area in Bangladesh. Blood samples from 138 domestic cattle were collected from houses with active or recently-treated VL and post-kala-azar dermal leishmaniasis patients. The presence of anti-leishmanial antibodies in serum was investigated using enzyme-linked immunosorbent assay (ELISA) and then with direct agglutination tests (DAT). Nested PCR (Ln PCR) was performed to amplify the ssu-rRNA gene using the DNA extracted from Buffy coat. Recently-developed molecular assay loop-mediated isothermal amplification (LAMP) was also performed for further sensitive detection of parasite DNA.ResultsIn this study, 9.4% (n = 13) of the cattle were found to be positive by ELISA. Of the 13 ELISA-positive cattle, only four (30.8%) were positive in DAT. Parasite DNA was not detected in either of the molecular assays (Ln PCR and LAMP).ConclusionsThe study confirmed the presence of antibodies against Leishmania parasite in cattle. However, the absence of Leishmania DNA in the cattle indicates clearly that the cattle do not play a role as reservoir host. Similar study needs to be undertaken in the Indian subcontinent to determine the role of other domestic animals on which sandflies feed.

Background and AimAsian house shrew (Suncus murinus), a widely distributed small mammal in the South Asian region, can carry helminths of zoonotic importance. The aim of the study was to know the prevalence and diversity of gastrointestinal (GI) helminths in free-ranging Asian house shrew (S. murinus) in Bangladesh.Materials and MethodsA total of 86 Asian house shrews were captured from forest areas and other habitats of Bangladesh in 2015. Gross examination of the whole GI tract was performed for gross helminth detection, and coproscopy was done for identification of specific eggs or larvae.ResultsThe overall prevalence of GI helminth was 77.9% (67/86), with six species including nematodes (3), cestodes (2), and trematodes (1). Of the detected helminths, the dominant parasitic group was from the genus Hymenolepis spp.(59%), followed by Strongyloides spp.(17%), Capillaria spp. (10%), Physaloptera spp. (3%), and Echinostoma spp.(3%).ConclusionThe finding shows that the presence of potential zoonotic parasites (Hymenolepis spp. and Capillaria spp.) in Asian house shrew is ubiquitous in all types of habitat (forest land, cropland and dwelling) in Bangladesh. Therefore, further investigation is crucial to examine their role in the transmission of human helminthiasis.

We propose a new method for implementing mutually unbiased generation and measurement of time-bin qudits using a cascade of electro-optic phase modulator -coded fiber Bragg grating pairs. Our approach requires only a single spatial mode and can switch rapidly between basis choices. We obtain explicit solutions for dimensions d = 2, 3, 4 that realize all d + 1 possible mutually unbiased bases and analyze the performance of our approach in quantum key distribution. Given its practicality and compatibility with current technology, our approach provides a promising springboard for scalable processing of high-dimensional time-bin states.Mutually unbiased bases (MUBs) are of fundamental importance in quantum mechanics. A collection of bases is called mutually unbiased if any eigenstate from one basis overlaps equally with all states from the other bases. Since a measurement result in one basis provides no predictive information about the outcome of a subsequent measurement in one of its mutually unbiased partners, 1,2 MUBs represent optimal choices for quantum state tomography in noisy environments 1,3 and guarantee security against eavesdropping in quantum key distribution (QKD). 4,5 Implementing MUBs experimentally can be challenging, especially in high-dimensional Hilbert spaces (dimension d > 2). For example, in time-bin encoding, the best known method for measuring states mutuallyunbiased with respect to single-time-bin wavepackets is to use nested delay interferometers (DIs). 6-8 This approach requires the use of d detectors and is difficult to scale to high d in a practical setting. Furthermore, passive DIs produce satellite pulses that reduce the probability of successful measurement to 1/d. 9,10 Therefore, a critical objective is to develop an approach for synthesizing time-bin MUBs that preserves single-spatial-mode quantum information processing, is rapidly reconfigurable, and enables measurements with high success probability. Here we propose and analyze a novel configuration for generating and measuring quantum photonic states prepared in various time-bin MUBs using a cascade of electro-optic phase modulator (EOM) -coded fiber Bragg grating (FBG) pairs (see Fig. 1). We find explicit solutions of (d + 1)-element MUB families for d = 2, 3, 4 and simulate performance of a multibasis QKD system. Importantly, our approach can be implemented using current technology and offers the first truly single-mode paradigm for time-bin MUBs. a) Electronic mail: lukensjm@ornl.gov IN OUT FBG 1 EOM 1 FBG N EOM N Time-Bin Transformation W UNIT CELL UNIT CELL FIG. 1. Proposed system. The input state propagates through a series of N unit cells, each comprising an EOM and coded FBG. Ideally the input-to-output path produces a one-to-one mapping between states from different bases.In our design, we impose the requirement that a physical configuration must transform between all MUBs available in a d-dimensional space. This criterion is motivated by high-dimensional QKD, as both increasing the dimension d and employing (d + 1)-basi...