Improved decoy-state quantum key distribution with uncharacterized heralded single-photon sources

Encoding system plays a significant role in quantum key distribution(QKD).However,the security and performance of QKD systems can be compromised by encoding misalignment due to the inevitable defects in realistic devices.To alleviate the influence of misalignments,a method exploiting statistics from mismatched basis is proposed to enable uncharacterized sources to generate secure keys in QKD.In this work,we propose a scheme on four-intensity decoy-state quantum key distribution with uncharacterized heralded single-photon sources.It only requires the source states are prepared in a two-dimensional Hilbert space,and can thus reduce the complexity of practical realizations.Moreover,we carry out corresponding numerical simulations and demonstrate that our present four-intensity decoy-state scheme can achieve a much higher key rate compared than a three-intensity decoy-state method,and meantime it can obtain a longer transmission distance compared than the one using weak coherent sources.

Heralding a New Era

China-Myanmar relations forge ahead six decades on The year 2010 marks the 60th anniversary of the establishment of diplomatic relations between China and Myanmar.

An autopsy case of a primary aortoenteric fistula: A pitfall of the endoscopic diagnosis

A primary aortoenteric fistula (PAEF), defined as a communication between the native aorta and the gastrointestinal tract, is a rare cause of gastrointes-tinal bleeding. The preoperative diagnosis of PAEF is extremely difficult. Consequently, PAEF may cause sudden and unexpected death. We present an autopsy case of a 68-year-old man who died of massive gastro-intestinal bleeding due to a PAEF. Autopsy revealed a pinhole rupture located on the third part of the duode-nal mucosa and fistulized into the adjacent abdominal aortic aneurysm (AAA). Our case indicates that the aortoenteric fistula can result in fatal gastrointestinal bleeding. Consequently, a PAEF should be included in the differential diagnosis of gastrointestinal bleeding.

Practical non-orthogonal decoy state quantum key distribution with heralded single photon source

Recently the performance of the quantum key distribution （QKD） is substantially improved by the decoy state method and the non-orthogonal encoding protocol, separately. In this paper, a practical non-orthogonal decoy state protocol with a heralded single photon source （HSPS） for QKD is presented. The protocol is based on 4 states with different intensities. i.e. one signal state and three decoy states. The signal state is for generating keys; the decoy states are for detecting the eavesdropping and estimating the fraction of single-photon and two-photon pulses. We have discussed three cases of this protocol, i.e. the general case, the optimal case and the special case. Moreover, the final key rate over transmission distance is simulated. For the low dark count of the HSPS and the utilization of the two-photon pulses, our protocol has a higher key rate and a longer transmission distance than any other decoy state protocol.

Clinical variants of pityriasis rosea

Pityriasis rosea(PR) is a common erythemato-squamous dermatosis which almost always, is easily diagnosed. Mostly the disease presents in its classical form. However, clinical dermatology is all about variations and PR is not an exception. Variants of the disease in some cases may be troublesome to diagnose and confuse clinicians. Prompt diagnosis and treatment of the condition becomes necessary to avoid unnecessary investigations. We hereby review and illustrate atypical presentations of the disease, including diverse forms of location and morphology of the lesions, the course of the eruption, and its differential diagnoses.

Round-Robin Differential Phase Shift with Heralded Single-Photon Source

Round-robin differential phase shift （RRDPS） is a novel quantum key distribution protocol which can bound information leakage without monitoring signal disturbance. In this work, to decrease the effect of the vacuum component in a weak coherent pulses source, we employ a practical decoy-state scheme with heralded singlephoton source for the RRDPS protocol and analyze the performance of this method. In this scheme, only two decoy states are needed and the yields of single-photon state and multi-photon states, as well as the bit error rates of each photon states, can be estimated. The final key rate of this scheme is bounded and simulated over transmission distance. The results show that the two-decoy-state method with heralded single-photon source performs better than the two-decoy-state method with weak coherent pulses.

Generation of Gaussian-Shape Single Photons for High Efficiency Quantum Storage

We report the generation of heralded single photons with Gaussian-shape temporal waveforms through the spatial light modulation technique in an atomic ensemble. Both the full width at half maximum and the peak position of the Gaussian waveform can be controlled while the single photon nature holds well. We also analyze the bandwidth of the generated single photons in frequency domain and show how the sidebands of the frequency spectrum are modified by the shape of the temporal waveform. The generated single photons are especially suited for the realization of high efficiency quantum storage based on electromagnetically induced transparency.

Heralded entanglement purification protocol using high-fidelity parity-check gate based on nitrogen-vacancy center in optical cavity

The decoherence of entangled states caused by the noisy channel is a salient problem for reducing the fidelity of quantum communication.Here we present a heralded two-photon entanglement purification protocol(EPP)using heralded high-fidelity parity-check gate(HH-PCG),which can increase the entanglement of nonlocal two-photon polarization mixed state.The HH-PCG is constructed by the input-output process of nitrogen-vacancy(NV)center in diamond embedded in a single-sided optical cavity,where the errors caused by the imperfect interaction between the NV center-cavity system and the photon can be heralded by the photon detector.As the unwanted components can be filtrated due to the heralded function,the fidelity of the EPP scheme can be enhanced considerably,which will increase the fidelity of quantum communication processing.

Quantum interference between heralded single photon state and coherent state

Balanced homodyne detection has been introduced as a reliable technique of reconstructing the quantum state of a single photon Fock state, which is based on coupling the single photon state and a strong coherent local oscillator in a beam splitter and detecting the field quadrature at the output ports separately. The main challenge associated with a tomographic characterization of the single photon state is mode matching between the single photon state and the local oscillator. Utilizing the heralded single photon generated by the spontaneous parametric process, the multi-mode theoretical model of quantum interference between the single photon state and the coherent state in the fiber beam splitter is established.Moreover, the analytical expressions of the temporal-mode matching coefficient and interference visibility and relationship between the two parameters are shown. In the experimental scheme, the interference visibility under various temporalmode matching coefficients is demonstrated, which is almost accordant with the theoretical value. Our work explores the principle of temporal-mode matching between the single photon state and the coherent photon state, originated from a local oscillator, and could provide guidance for designing the high-performance balanced homodyne detection system.

Measurement Device Independent Quantum Key Distribution Based on Orbital Angular Momentum under Parametric Light Source

On the one hand,existing measurement device independent quantum key distribution(MDI-QKD)protocols have usually adopted single photon source(SPS)and weak coherent photon(WCP),however,these protocols have suffered from multi-photon problem brought from photon splitter number attacks.On the other hand,the orbital angular momentum(OAM)-MDI-QKD protocol does not need to compare and adjust the reference frame,solving the dependency of the base in the MDI-QKD protocol.Given that,we propose the OAM-MDI-QKD protocol based on the parametric light sources which mainly include single-photon-added-coherent(SPACS)and heralded single-photon sources(HSPS).Due to the stability of OAM and the participation of parametric light sources,the performance of MDI-QKD protocol gradually approaches the ideal situation.Numerical simulation shows that compared with WCP scheme,HSPS and SPACS schemes have increased the maximum secure transmission distance by 30 km and 40 km respectively.

Passive Decoy-State Reference-Frame-Independent Quantum Key Distribution with Heralded Single-Photon Source

Reference-frame-independent（RFI）quantum key distribution（QKD）is a protocol which can share unconditional secret keys between two remote users without the alignment of slowly varying reference frames.We propose a passive decoy-state RFI-QKD protocol with heralded single-photon source（HSPS）and present its security analysis.Compared with RFI QKD using a weak coherent pulse source（WCPS）,numerical simulations show that the passive decoy-state RFI QKD with HSPS performs better not only in secret key rate but also in secure transmission distance.Moreover,our protocol is robust against the relative motion of the reference frames as well as RFI QKD with the WCPS.In addition,we also exploit Hoeffding＇s inequality to investigate the finite-key effect on the security of the protocol.

Propping up Propaganda？ Exploring the Role of The Herald Newspaper in Strengthening ZANU-PF＇s Political Position

This paper examines The Herald newspaper＇s role in safeguarding the seemingly unparalleled longevity of Zimbabwe＇s ruling Zimbabwe African National Union-Patriotic Front （ZANU-PF） party. Through an analysis of a sample of stories from both the paper＇s print and online editions, the study traces the origins of the broadsheet＇s ostensibly unflagging pro-ZANU-PF editorial positions, turning to article analysis to critically probe not only the motive but also the impact of the newspaper＇s assumed open allegiance to the revolutionary party. In a nation believed battered by perceived state brutality and widening political differences, The Herald has been accused of significantly influencing the pace of dictatorship while guardedly manipulating information to prop up President Robert Mugabe＇s party. So important has the paper become over the years that its often uncompromising, one-sided style of reporting has earned it praise among militant ZANU-PF hardliners while bitterly attracting widespread criticism from critics of the long-serving party.

The Bridge of Chinese and Western Information Exchange in the 19th Century—The Translation of Peking Gazette from North-China Herald Office

The publication of the translation of Peking Gazette by North-China Herald Office began in 1850 when “TheNorth-China Herald” was first published and finally ended at the end of the 19th century. Peking Gazette is alsoknown and used by more Western readers through the great influence of English newspapers under the jurisdictionof North-China Herald Office. These translations provided western readers with rich knowledge about China in thelate Qing Dynasty, enhanced their understanding and understanding of the events from the court to the socialcustoms in the late Qing Dynasty, and on this basis, exerted an important influence on the historical process ofSino-Western relations in the middle and late 19th century.

Heralded entanglement concentration for photon systems with linear-optical elements

We present two nonlocal entanglement concentration protocols(ECPs)to distill a subset of N-photon systems in a GreenbergerHorne-Zeilinger(GHZ)state or a W state from a set of photon systems in a partially entangled GHZ-like pure state or a lessentangled W-like state with known parameters,respectively.Our ECPs have some advantages.First,our ECPs work in a heralded way with linear-optical elements only,without the postselection based on nonlinear optics,far different from the previous ECPs.Second,they require only a copy of the less-entangled photon system in each round of the entanglement concentration process,not two copies,which decreases the difficulty of their implementation in experiment largely.Third,our ECPs avoid checking the photon number in the output modes of linear-optical elements with the sophisticated single-photon detectors.Moreover,all parties can operate the process for concentration simultaneously and independently,which leads to flexible operations and improves the performance greatly in experiment.These advantages make our ECPs useful in practical applications in long-distance quantum communication network.

Micro/nano-fiber-based source of heralded single photons at the telecom band

We experimentally demonstrate a heralded single photon source at 1290 nm by exploiting the spontaneous four wave mixing in a taper-drawn micro/nano-fiber（MNF）. Because the frequency detuning between the pump and heralded single photons is ~58 THz, the contamination by Raman scattering is significantly reduced at room temperature. Since the MNF is naturally connected to standard single mode fibers via fiber tapers, the source would be compatible with the existing fiber networks. When the emission rate of heralded signal photons is about 4.6 kHz, the measured second-order intensity correlation function g（2）（0） is 0.017 ± 0.002, which is suppressed by a factor of more than 55, relative to the classical limit.

Storage of telecom-C-band heralded single photons with orbital-angular-momentum encoding in a crystal

A memory-based quantum repeater architecture provides a solution to distribute quantum information to an arbitrary long distance.Practical quantum repeaters are likely to be built in optical-fiber networks which take advantage of the low-loss transmission between quantum memory nodes.Most quantum memory platforms have characteristic atomic transitions away from the telecommunication band.A nondegenerate photon pair source is therefore useful for connection of a quantum memory to optical fibers.Here,we report a high-brightness narrowband photon-pair source which is compatible with a rare-earth-ion-doped crystal Pr^3+:Y2SiO5.The photon-pair source is generated through a cavityenhanced spontaneous parametric down-conversion process with the signal photon at 606 nm and the idler photon at 1540 nm.Moreover,using the telecom C-band idler photons for heralding,we demonstrate the reversible transfer of orbital-angular-momentum qubit between the signal photon and the quantum memory based on Pr3^+:Y2SiO5.

Performance of passive decoy-state quantum key distribution with mismatched local detectors

In quantum key distribution(QKD),the passive decoy-state method can simplify the intensity modulation and reduce some of side-channel information leakage and modulation errors.It is usually implemented with a heralded single-photon source.In Wang et al 2016(Phys.Rev.A 96032312),a novel passive decoy-state method is proposed by Wang et al,which uses two local detectors to generate more detection events for tightly estimating channel parameters.However,in the original scheme,the two local detectors are assumed to be identical,including the same detection efficiency and dark count rate,which is often not satisfied in the realistic experiment.In this paper,we construct a model for this passive decoy-state QKD scheme with two mismatched detectors and explore the effect on QKD performance with certain parameters.We also take the finite-size effect into consideration,showing the performance with statistical fluctuations.The results show that the efficiencies of local detectors affect the key rate more obviously than dark count rates.