Overcoming the rate-distance limit of quantum key distribution without quantum repeaters.

Quantum key distribution (QKD)1,2 allows two distant parties to share encryption keys with security based on physical laws. Experimentally, QKD has been implemented via optical means, achieving key rates of 1.26 megabits per second over 50 kilometres of standard optical fibre 3 and of 1.16 bits per hour over 404 kilometres of ultralow-loss fibre in a measurement-device-independent configuration 4 . Increasing the bit rate and range of QKD is a formidable, but important, challenge. A related target, which is currently considered to be unfeasible without quantum repeaters5-7, is overcoming the fundamental rate-distance limit of QKD 8 . This limit defines the maximum possible secret key rate that two parties can distil at a given distance using QKD and is quantified by the secret-key capacity of the quantum channel 9 that connects the parties. Here we introduce an alternative scheme for QKD whereby pairs of phase-randomized optical fields are first generated at two distant locations and then combined at a central measuring station. Fields imparted with the same random phase are 'twins' and can be used to distil a quantum key. The key rate of this twin-field QKD exhibits the same dependence on distance as does a quantum repeater, scaling with the square-root of the channel transmittance, irrespective of who (malicious or otherwise) is in control of the measuring station. However, unlike schemes that involve quantum repeaters, ours is feasible with current technology and presents manageable levels of noise even on 550 kilometres of standard optical fibre. This scheme is a promising step towards overcoming the rate-distance limit of QKD and greatly extending the range of secure quantum communications.

[Analysis of the effect of spread through air spaces on postoperative recurrence-free survival in patients with stage pT1N0M0 lung adenocarcinoma of different tumor size].

Objective: To investigate the effect of spread through air spaces (STAS) on the postoperative prognosis of patients with stage pT1N0M0 lung adenocarcinoma according to different tumor sizes. Methods: The clinicopathological and follow-up data of 511 patients with pT1N0M0 lung adenocarcinoma treated surgically in the Department of Thoracic Surgery, Cancer Hospital, Chinese Academy of Medical Sciences from January 2014 to June 2018 were retrospectively analyzed. There were 285 males and 226 females, aged 60 (53, 66) years. Those patients were divided into two groups according to STAS status, including STAS (-) group (342 cases) and STAS (+) group (169 cases). And the stratified analysis was performed according to the American Cancer Consortium (AJCC) 8th edition postoperative pathological tumor size T-stage (pT) of lung cancer, which was divided into pT1a (pT≤1 cm, 93 cases), pT1b (1 cm0.05]. Before and after IPTW adjustment, statistically significant differences were found in RFS between STAS (+) group and STAS (-) group [(72.50±2.23) vs (85.12±0.72) months, (77.74±1.12) vs (84.59±0.64) months, all P<0.001]. In addition, the risks of both local and distant recurrence were higher in STAS (+) group compared to STAS (-) group (6.7% vs 1.2% and 8.2% vs 3.6%, respectively; both P<0.05). Conclusion: For lung adenocarcinoma patients with pT1bN0M0 and pT1cN0M0, those patients with STAS (+) had a higher incidence of both local and distant recurrence and with poor RFS.

Testing the photon-number statistics of a quantum key distribution light source.

A commonly held tenet is that lasers well above threshold emit photons in a coherent state, which follow Poissonian statistics when measured in photon number. This feature is often exploited to build quantum-based random number generators or to derive the secure key rate of quantum key distribution systems. Hence the photon number distribution of the light source can directly impact the randomness and the security distilled from such devices. Here, we propose a method based on measuring correlation functions to experimentally characterize a light source's photon statistics and use it in the estimation of a quantum key distribution system's key rate. This promises to be a useful tool for the certification of quantum-related technologies.

Patterning-effect mitigating intensity modulator for secure decoy-state quantum key distribution.

Quantum key distribution (QKD) is a technology that allows two users to exchange cryptographic keys securely. The decoy state technique enhances the technology, ensuring keys can be shared at high bit rates over long distances with information theoretic security. However, imperfections in the implementation, known as side-channels, threaten the perfect security of practical QKD protocols. Intensity modulators are required for high-rate decoy-state QKD systems, although these are unstable and can display a side channel where the intensity of a pulse is dependent on the previous pulse. Here we demonstrate the superior practicality of a tunable extinction ratio Sagnac-based intensity modulator (IM) for practical QKD systems. The ability to select low extinction ratios, alongside the immunity of Sagnac interferometers to DC drifts, ensures that random decoy state QKD patterns can be faithfully reproduced with the patterning effects mitigated. The inherent stability of Sagnac interferometers also ensures that the modulator output does not wander over time.

Near perfect mode overlap between independently seeded, gain-switched lasers.

We drastically improve the mode overlap between independently seeded, gain-switched laser diodes operating at gigahertz repetition rates by implementing a pulsed light seeding technique. Injecting pulsed light reduces the emission time jitter and enables frequency chirp synchronization while maintaining random optical phases of the emitted laser pulses. We measure interference of these pulsed sources both in the macroscopic regime, where we demonstrate near perfect mode overlap, and in the single photon regime, where we achieve a Hong-Ou-Mandel dip visibility of 0.499 ± 0.004, thus saturating the theoretical limit of 0.5. The measurement results are reproduced by Monte-Carlo simulations with no free parameters. Our light source is an ideal solution for generation of high rate, indistinguishable coherent pulses for quantum information applications.

Quantum key distribution over multicore fiber.

We present the first quantum key distribution (QKD) experiment over multicore fiber. With space division multiplexing, we demonstrate that weak QKD signals can coexist with classical data signals launched at full power in a 53 km 7-core fiber, while showing negligible degradation in performance. Based on a characterization of intercore crosstalk, we perform additional simulations highlighting that classical data bandwidths beyond 1Tb/s can be supported with high speed QKD on the same fiber.

High speed prototype quantum key distribution system and long term field trial.

Securing information in communication networks is an important challenge in today's world. Quantum Key Distribution (QKD) can provide unique capabilities towards achieving this security, allowing intrusions to be detected and information leakage avoided. We report here a record high bit rate prototype QKD system providing a total of 878 Gbit of secure key data over a 34 day period corresponding to a sustained key rate of around 300 kbit/s. The system was deployed over a standard 45 km link of an installed metropolitan telecommunication fibre network in central Tokyo. The prototype QKD system is compact, robust and automatically stabilised, enabling key distribution during diverse weather conditions. The security analysis includes an efficient protocol, finite key size effects and decoy states, with a quantified key failure probability of ε = 10⁻¹°.

Efficient decoy-state quantum key distribution with quantified security.

We analyse the finite-size security of the efficient Bennett-Brassard 1984 protocol implemented with decoy states and apply the results to a gigahertz-clocked quantum key distribution system. Despite the enhanced security level, the obtained secure key rates are the highest reported so far at all fibre distances.

First Report of Leaf Spot Caused by Alternaria longipes on Atractylodes macrocephala in China.

Atractylodes macrocephala Koidz. is a perennial herb that has been used in Chinese herbal medicine for centuries. During the summer of 2011, leaf spots were observed on leaves of A. macrocephala in Panan County of Zhejiang Province, China. Approximately 40% of the plants surveyed showed severe symptoms of leaf spot. At the initial stage of the infection, small, light brown spots appeared on the leaves that gradually became semicircular, oval, or irregular-shaped with dark brown or black centers surrounded by brown or light brown margins. The lesions enlarged and coalesced to form large areas of necrosis on leaves until entire leaves died. Eight fungal isolates were obtained from diseased A. macrocephala leaves by a tissue isolation method (1). Isolates were cultured on potato dextrose agar (PDA) plates at 25°C in darkness. Colonies on PDA were initially white and became grayish brown over time. Conidiophores were light brown with one or a few regular septa, mostly unbranched. Conidia were obclavate, dark brown, with three to eight transverse and zero to two longitudinal or oblique septa, and on average measured 35.1 (20 to 53) × 9.8 (5.8 to 13.3) µm (n = 20). The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS1F/ITS4 and sequenced (GenBank Accession No. JQ004404). The ITS sequence had 99% identity over 545 bp with Alternaria longipes (Ellis & Everh.) E. W. Mason (GenBank Accession No. AY278835), a fungal pathogen reported to cause leaf spot on Smilax china in China (3). To further identify the fungus, we chose the Alternaria allergen gene (Alt a 1 gene), which aids in identifying species of Alternaria (2). Amplification of the Alt a 1 gene was conducted using primers Alt-for/Alt-rev and sequenced (GenBank Accession No. JQ004405). Sequence comparisons showed there was 97% sequence identity with Alternaria longipes (GenBank Accession No. AY563304). Pathogenicity tests were performed on detached healthy A. macrocephala leaves. Nine leaves were inoculated by placing a PDA plug (0.5 cm2) of mycelia on upper surfaces of the leaves. Another nine leaves treated with sterile PDA plugs served as a control. Leaves were incubated in three petri dishes with a 12-h photoperiod at 25°C and 95% relative humidity. After 7 days, the symptoms described above were observed on all inoculated leaves, whereas no symptoms developed on control leaves. Reisolation of the fungus from symptomatic leaf tissues on PDA confirmed that the causal agent was Alternaria longipes. This pathogenicity test was performed three times. The genus Alternaria is ubiquitous and includes both plant pathogenic and saprophytic species that may cause leaf spot and blight on numerous plants (3,4), but to our knowledge, our research demonstrated this is the first report of leaf spot on A. macrocephalae caused by Alternaria longipes in China. References: (1) O. D. Dhingra and J. B. Sinclair. Basic Plant Pathology Methods. CRC Press, Boca Raton, FL, 1995. (2) S. G. Hong et al. Fungal Genet. Biol. 42:119, 2005. (3) Y. Long et al. Plant Pathol. 58:800, 2009. (4) S. X. Zang et al. J. Hebei Normal Univ. Sci. Tech. 19:46, 2005.

Inhibition of extracellular signal-regulated kinase downregulates endoplasmic reticulum stress-induced apoptosis and decreases brain injury in a cardiac arrest rat model.

Cerebral ischemia-reperfusion injury (CIRI) is the predominant cause of neurological disability after cardiac arrest/cardiopulmonary resuscitation (CA/CPR). The endoplasmic reticulum stress (ERs)-induced apoptosis plays an important role in neuronal survival/death in CIRI. Our previous studies reported that the extracellular signal-regulated kinase (ERK) inhibitor, PD98059, alleviates CIRI after CA/CPR. Whether ERs-induced apoptosis is involved in the neuroprotection of PD98059 remains unknown. This study aims to investigate the effects of ERK inhibition by PD98059 on ERs-induced apoptosis after CIRI in the CA/CPR rat model. The baseline characteristics of male adult Sprague-Dawley (SD) rats in all groups were evaluated before CA/CPR. The SD rats that survived from CA/CPR were randomly divided into 3 groups (n=12/group): normal saline group (1 ml/kg), dimethylsulfoxide (DMSO, the solvent of PD98059, 1 ml/kg) group, PD98059 group (0.3 mg/kg). Another 12 SD rats were randomly selected as the Sham group. Twenty-four hours after resuscitation, neural injury was assessed by survival rate, neurological deficit scores (NDS) and Nissl staining; apoptosis of brain cells was detected using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining; mRNA expression and protein levels of ERs-related protein BIP, PERK, ATF4 and CHOP were checked with RT-PCR and Western Blot. The results showed that there were no significant differences in baseline characteristics before CA/CPR among all groups. PD98059 significantly improved survival rate and NDS, increased the Nissl bodies in neurons, reduced apoptosis, downregulated the mRNA transcription and expression levels of BIP, PERK, ATF4 and CHOP at 24 h after CA/CPR. Our results demonstrate that inhibition of ERK by PD98059 alleviates ERs-induced apoptosis via BIP-PERK-ATF4-CHOP signaling pathway and mitigates CIRI in the CA/CPR rat model.

Probing higher order correlations of the photon field with photon number resolving avalanche photodiodes.

We demonstrate the use of two high speed avalanche photodiodes in exploring higher order photon correlations. By employing the photon number resolving capability of the photodiodes the response to higher order photon coincidences can be measured. As an example we show experimentally the sensitivity to higher order correlations for three types of photon sources with distinct photon statistics. This higher order correlation technique could be used as a low cost and compact tool for quantifying the degree of correlation of photon sources employed in quantum information science.

Field test of quantum key distribution in the Tokyo QKD Network.

A secure communication network with quantum key distribution in a metropolitan area is reported. Six different QKD systems are integrated into a mesh-type network. GHz-clocked QKD links enable us to demonstrate the world-first secure TV conferencing over a distance of 45km. The network includes a commercial QKD product for long-term stable operation, and application interface to secure mobile phones. Detection of an eavesdropper, rerouting into a secure path, and key relay via trusted nodes are demonstrated in this network.

Biogas feedstock potentials and related water footprints from residues in China and the European Union.

China encounters heavy air pollution caused by coal consumption. China and the EU aim to decrease greenhouse gas emissions. Shifting to biogas from residues contributes to solving both problems. This study assesses China's biogas potentials and related water footprints (WFs) and compares results with potentials and WFs for the EU. Starting from a literature review on EU biogas potentials, it analyzes information resulting in a calculation methodology, its validation and application to China. Finally, it estimates WFs and makes a comparative assessment of biogas potentials of the EU and China. In the EU, biogas from agricultural, forestry and other residues might contribute 8% (5300 PJ) to primary energy consumption, in China 10% (13,275 PJ.) In the EU, agriculture contributes 41%, forestry 26%, other residues 23%, and manure 10%. The corresponding results for China are agriculture (67%), forestry (23%), manure (7%) and other residues (3%). In the EU, biogas might contribute 45% to total gas demand; in China more biogas can be produced than consumed in 2018 (185% of demand). The EU results fall in the range of residue potentials from earlier studies. Maize, wheat, barley and rapeseed contribute 78% to the EU agricultural biogas potential. In China, dominant crops are maize (49%), rice (18%), wheat (12%) and seed cotton (6%). For water, there are large differences among WFs of specific crop residues, but also between WFs for EU and Chinese crop residues. Most Chinese crop residues have larger WFs than the EU residues. Biogas from sugar beet residues has the smallest WFs, biogas from tobacco residues the largest. Although using residues for energy does not change total national WFs, it reallocates WFs over main products and residues. The comparative assessment supports better use of biogas potentials from residues with lower WFs and is also applicable for other regions and countries.

[Epidemiological characteristics of imported malaria in Zhengzhou City from 2016 to 2020].

OBJECTIVE: To analyze the epidemiological characteristics of reported imported malaria cases in Zhengzhou City from 2016 to 2020, so as to provide insights into the management of imported malaria in the city. METHODS: All data pertaining to cases with definitive diagnosis of malaria in Zhengzhou City from 2016 to 2020 were captured from the National Notifiable Disease Report System and the Information Management System for Parasitic Disease Control in China, including individual demographic data, and malaria onset, initial diagnosis and definitive diagnosis data. All data were descriptively analyzed. The duration from malaria onset to initial diagnosis, from initial diagnosis to definitive diagnosis and from onset to definitive diagnosis was compared among cases. In addition, the diagnoses of imported malaria cases in which definitive diagnosis was made were compared with the reexaminations by Zhengzhou Municipal Malaria Diagnosis Reference Laboratory. RESULTS: A total of 302 cases with definitive diagnosis of malaria were reported in Zhengzhou City from 2016 to 2020, and all were imported cases, with Plasmodium falciparum malaria as the predominant type (230 cases, 76.2%). There were 293 malaria cases imported from Africa (293 cases, 97.0%), which mainly included Nigeria (48 cases, 15.9%), Angola (40 cases, 13.2%), and the Democratic Republic of the Congo (29 cases, 9.6%). There was no obvious seasonality found in the date of malaria onset and time of reporting malaria. The ratio of male to female malaria cases was 49.3:1, and there were 103 cases (34.1%) with the current residency address in Zhengzhou City, 193 cases (63.9%) with the current residency address in other cities of Henan Province and 6 cases (2.0%) in other provinces of China. There were 271 cases (89.7%) seeking initial diagnosis in medical institutions, and the diagnostic accuracy of malaria was 56.6% (171/302) at initial diagnosis institutions. A total of 122 cases (40.4%) sought medical care on the day of malaria onset, and 252 cases (86.4%) within 3 days; however, only 22 cases (7.3%) were definitively diagnosed on the day of onset, and 162 cases (53.6%) diagnosed within 3 days. There were no significant differences between malaria cases seeking initial diagnosis at medical institutions and disease control and prevention institutions in terms of the duration from malaria onset to initial diagnosis (Z = -1.663, P > 0.05), from initial diagnosis to definitive diagnosis (Z = -0.413, P > 0.05) or from malaria onset to definitive diagnosis (Z = -0.838, P > 0.05). The median duration (interquartile range) from initial diagnosis to definitive diagnosis of malaria was 3.00 (2.00), 3.00 (6.00), 2.00 (4.00) d and 1.00 (1.00) d among cases seeking medical care at township-level and lower, county-, city- and province-level medical institutions, and the median duration from initial diagnosis to definitive diagnosis of malaria was significantly longer among cases seeking medical care at township-level and lower medical institutions than at city (Z = -3.286, P < 0.008 33) and province-level medical institutions (Z = -9.119, P < 0.008 33), while the median duration from initial diagnosis to definitive diagnosis [1.00 (3.00) d vs. 2.00 (4.00) d; Z = -4.099, P < 0.016] and from malaria onset to definitive diagnosis [3.00 (4.00) d vs. 4.00 (5.00) d; Z = -2.868, P < 0.016] among malaria cases with the current residency address in Zhengzhou City was both shorter than in other cities of Henan Province. The diagnostic accuracy was 89.1% (269/302) among malaria cases in which definitive diagnosis was made, and the accuracy of malaria reexaminations was 94.0% (284/302) in Zhengzhou Municipal Malaria Diagnosis Reference Laboratory. CONCLUSIONS: P. falciparum malaria was predominant among reported imported malaria cases in Zhengzhou City from 2016 to 2020, and these imported malaria cases were predominantly diagnosed at medical institutions; however, the diagnostic capability of malaria is poor in township-level and lower medical institutions. Strengthening the collaboration between medical institutions and disease control and prevention institutions and improving the diagnostic capability building at medical institutions are recommended to consolidate malaria elimination achivements.

Efficient entanglement distribution over 200 kilometers.

Here we report the first demonstration of entanglement distribution over a record distance of 200 km which is of sufficient fidelity to realize secure communication. In contrast to previous entanglement distribution schemes, we use detection elements based on practical avalanche photodiodes (APDs) operating in a self-differencing mode. These APDs are low-cost, compact and easy to operate requiring only electrical cooling to achieve high single photon detection efficiency. The self-differencing APDs in combination with a reliable parametric down-conversion source demonstrate that entanglement distribution over ultra-long distances has become both possible and practical. Consequently the outlook is extremely promising for real world entanglement-based communication between distantly separated parties.

Gigahertz decoy quantum key distribution with 1 Mbit/s secure key rate.

We report the first gigahertz clocked decoy-protocol quantum key distribution (QKD). Record key rates have been achieved thanks to the use of self-differencing InGaAs avalanche photodiodes designed specifically for high speed single photon detection. The system is characterized with a secure key rate of 1.02 Mbit/s for a fiber distance of 20 km and 10.1 kbit/s for 100 km. As the present advance relies upon compact non-cryogenic detectors, it opens the door towards practical and low cost QKD systems to secure broadband communication in future.

LncRNA-NEF inhibits proliferation, migration and invasion of esophageal squamous-cell carcinoma cells by inactivating wnt/ß-catenin pathway.

OBJECTIVE: Our study aimed to investigate the role of lncRNA-Neighboring Enhancer of FOXA2 (NEF) in esophageal squamous-cell carcinoma. PATIENTS AND METHODS: Tumor tissues and adjacent tissues were obtained from esophageal squamous-cell carcinoma patients, and blood samples were extracted from both patients with esophageal squamous-cell carcinoma and healthy volunteers. The expression of NEF was detected by quantitative Real-Time Polymerase Chain Reaction (qRT-PCR). All patients were followed-up for 5 years and ROC curve analysis and survival analysis were performed to evaluate the diagnostic and prognostic values of serum NEF for esophageal squamous-cell carcinoma. NEF expression vector was transfected into cells of esophageal squamous-cell carcinoma cell lines. Cell proliferation, migration and invasion were detected by CCK-8 assay, transwell migration assay, and transwell invasion assay, respectively. The interaction between NEF and wnt/ß-catenin pathway were explored by Western blot and qRT-PCR. RESULTS: Expression of NEF was significantly downregulated in tumor tissues than in adjacent tissues in most patients. Serum level of NEF was higher in esophageal squamous-cell carcinoma patients than in healthy controls, and was significantly correlated with tumor size and tumor distant tumor metastasis. Serum NEF is a promising diagnostic and prognostic marker for esophageal squamous-cell carcinoma. NEF overexpression inhibited cancer cell proliferation, migration and invasion. NEF overexpression decreased the expression levels of wnt/ß-catenin pathway-related proteins, while Wnt activator showed no significant effects on NEF. However, Wnt inhibitor reduced the effects of NEF overexpression on cell proliferation, migration and invasion. CONCLUSIONS: LncRNA NEF may inhibit the proliferation, migration and invasion of esophageal squamous-cell carcinoma cells by inactivating with wnt/ß-catenin pathway.

Practical quantum key distribution over 60 hours at an optical fiber distance of 20km using weak and vacuum decoy pulses for enhanced security.

Experimental one-way decoy pulse quantum key distribution running continuously for 60 hours is demonstrated over a fiber distance of 20km. We employ a decoy protocol which involves one weak decoy pulse and a vacuum pulse. The obtained secret key rate is on average over 10kbps. This is the highest rate reported using this decoy protocol over this fiber distance and duration.

Effects of epoxyeicosatrienoic acids (EETs) on retinal macular degeneration in rat models.

OBJECTIVE: Here we use a rat model to investigate the effects of epoxyeicosatrienoic acids (EETs) on retinal macular degeneration along with pathological and physiological mechanisms of the disease. MATERIALS AND METHODS: Six choroidal neovascularization (CNV) rats were created with a 532 nm laser and received intravitreal injections of EETs in both eyes. On day 1, 3, 7 and 14 after photocoagulation, the thickness and area of CNV were measured with HE staining and choroidal flat mounts. COX-2 and VEGF levels in CNV were detected by immunohistochemistry method. Protein and mRNA expression were studied by Western blotting and RT-PCR. RESULTS: 14 days after photocoagulation, CNV thickness and area were significantly reduced (p<0.01) in the treatment group compared with the control group. COX-2 and VEGF had high expression in vascular endothelial cells and stromal cells of CNV. Peak expression of COX-2 and VEGF was significantly higher (p<0.01) in the treatment group than in the control group. 7 days after photocoagulation, VEGF protein and mRNA expression were significantly lower (p<0.05) in the treatment group than in the control group, whereas COX-2 mRNA showed no significant difference (p>0.05). FFA found that CNV fluorescein leakage area was significantly reduced (p<0.05) in the treatment group than in the control group. 14 days after photocoagulation, neovascularization area was significantly smaller (p<0.05) in the treatment group than in the control group. Vitreous EETs levels in the treatment group were significantly higher than in the control group. Compared with the control group, the celecoxib treatment group had significantly increased vitreous EETs (p<0.05). CONCLUSIONS: Intravitreal injection of celecoxib could suppress the thickness and area of laser-induced macular degeneration CNV. It also improved the vitreous EETs levels in CNV model rats. COX-2 expression was upregulated in the early generation of laser-induced CNV, which may play an important role in regulating expression of VEGF.