arXiv subjects

Shuang Wang

Publications and source records attributed to Shuang Wang.

At least 163 records · Page 9Linked to original sources

arXiv2016

Hong-Ou-Mandel interference between two independent all fiber photon sources

Guided-wave platforms such as fiber and silicon-on-insulator waveguide show great advances over traditional free space implementations in quantum information technology for significant advantages of low transmission loss, low cost, integrability and compatible with mature fiber communication systems. Interference between independent photon sources is the key to realize complex quantum systems for more sophisticated applications such as multi-photon entanglement generation and quantum teleportation. In this work, we report Hong-Ou-Mandel interference between two independent all fiber photon pair sources over two 100GHz dense wave division multiplexing channels, the visibility reaches 53.2(8.4)% (82.9(5.3)%) without (with) back ground counts subtracted. In addition, we give a general theoretical description of the purity of the photon pair generation in dispersion shifted fiber and obtain the optimized condition for high purity photon pair generation. We also obtain a maximum coincidence to back ground ratio of 131 by cooling the fiber in liquid nitrogen. Our study shows great promising of integrated optical elements for future scalable quantum information promising.

quant-ph↗

arXiv2016

Non-Markovian property of afterpulsing effect in single-photon avalanche detector

The single-photon avalanche photodiode(SPAD) has been widely used in research on quantum optics. The afterpulsing effect, which is an intrinsic character of SPAD, affects the system performance in most experiments and needs to be carefully handled. For a long time, afterpulsing has been presumed to be determined by the pre-ignition avalanche. We studied the afterpulsing effect of a commercial InGaAs/InP SPAD (The avalanche photodiode model is: Princeton Lightwave PGA-300) and demonstrated that its afterpulsing is non-Markovian, with a memory effect in the avalanching history. Theoretical analysis and experimental results clearly indicate that the embodiment of this memory effect is the afterpulsing probability, which increases as the number of ignition-avalanche pulses increase. This conclusion makes the principle of the afterpulsing effect clearer and is instructive to the manufacturing processes and afterpulsing evaluation of high-count-rate SPADs. It can also be regarded as a fundamental premise to handle the afterpulsing signals in many applications, such as quantum communication and quantum random number generation.

physics.ins-det↗

arXiv2016

Impacts of different SNLS3 light-curve fitters on cosmological consequences of interacting dark energy models

We explore the cosmological consequences of interacting dark energy (IDE) models using the SNLS3 supernova samples. In particular, we focus on the impacts of different SNLS3 light-curve fitters (LCF) (corresponding to "SALT2", "SiFTO", and "Combined" sample). Firstly, making use of the three SNLS3 data sets, as well as the Planck distance priors data and the galaxy clustering data, we constrain the parameter spaces of three IDE models. Then, we study the cosmic evolutions of Hubble parameter $H(z)$, deceleration diagram $q(z)$, statefinder hierarchy $S^{(1)}_3(z)$ and $S^{(1)}_4(z)$, and check whether or not these dark energy diagnosis can distinguish the differences among the results of different SNLS3 LCF. At last, we perform high redshift cosmic age test using three old high redshift objects (OHRO), and explore the fate of the Universe. We find that, the impacts of different SNLS3 LCF are rather small, and can not be distinguished by using $H(z)$, $q(z)$, $S^{(1)}_3(z)$, $S^{(1)}_4(z)$, and the age data of OHRO. In addition, we infer, from the current observations, how far we are from a cosmic doomsday in the worst case, and find that the "Combined" sample always gives the largest 2$σ$ lower limit of the time interval between "big rip" and today, while the results given by the "SALT2" and the "SiFTO" sample are close to each other. These conclusions are insensitive to a specific form of dark sector interaction. Our method can be used to distinguish the differences among various cosmological observations.

astro-ph.CO↗

arXiv2016

More Evidence for the Redshift Dependence of Color from the JLA Supernova Sample Using Redshift Tomography

In this work, by applying the redshift tomography method to Joint Light-curve Analysis (JLA) supernova sample, we explore the possible redshift-dependence of stretch-luminosity parameter $α$ and color-luminosity parameter $β$. The basic idea is to divide the JLA sample into different redshift bins, assuming that $α$ and $β$ are piecewise constants. Then, by constraining the $Λ$CDM model, we check the consistency of cosmology-fit results given by the SN sample of each redshift bin. We also adopt the same technique to explore the possible evolution of $β$ in various subsamples of JLA. Using the full JLA data, we find that $α$ is always consistent with a constant. In contrast, at high redshift $β$ has a significant trend of decreasing, at $\sim 3.5σ$ confidence level (CL). Moreover, we find that low-$z$ subsample favors a constant $β$; in contrast, SDSS and SNLS subsamples favor a decreasing $β$ at 2$σ$ and $3.3σ$ CL, respectively. Besides, by using a binned parameterization of $β$, we study the impacts of $β$'s evolution on parameter estimation. We find that compared with a constant $β$, a varying $β$ yields a larger best-fit value of fractional matter density $Ω_{m0}$, which slightly deviates from the best-fit result given by other cosmological observations. However, for both the varying $β$ and the constant $β$ cases, the $1σ$ regions of $Ω_{m0}$ are still consistent with the result given by other observations.

astro-ph.CO↗

arXiv2016

A comprehensive investigation on the slowing down of cosmic acceleration

Shafieloo ea al. firstly proposed the possibility that the current cosmic acceleration (CA) is slowing down. However, this is rather counterintuitive because a slowing down CA cannot be accommodated in most mainstream cosmological models. In this work, by exploring the evolutionary trajectories of dark energy equation of state $w(z)$ and deceleration parameter $q(z)$, we present a comprehensive investigation on the slowing down of CA from both the theoretical and the observational sides. For the theoretical side, we study the impact of different $w(z)$ by using six parametrization models, and then discuss the effects of spatial curvature. For the observational side, we investigate the effects of different type Ia supernovae (SNe Ia), different baryon acoustic oscillation (BAO), and different cosmic microwave background (CMB) data, respectively. We find that (1) The evolution of CA are insensitive to the specific form of $w(z)$; in contrast, a non-flat Universe more favors a slowing down CA than a flat Universe. (2) SNLS3 SNe Ia datasets favor a slowing down CA at 1$σ$ confidence level, while JLA SNe Ia samples prefer an eternal CA; in contrast, the effects of different BAO data are negligible. (3) Compared with CMB distance prior data, full CMB data more favor a slowing down CA. (4) Due to the low significance, the slowing down of CA is still a theoretical possibility that cannot be confirmed by the current observations.

astro-ph.CO↗

arXiv2016

A New Result on Packing Unit Squares into a Large Square

In their 2009 note: \emph{Packing equal squares into a large square}, Chung and Graham proved that the uncovered area of a large square of side length $x$ is $O\left(x^{(3+\sqrt{2})/7}\log x\right)$ after maximum number of non-overlapping unit squares are packed into it, which improved the earlier results of Erdős-Graham, Roth-Vaughan, and Karabash-Soifer. Here we further improve the result to $O(x^{5/8})$ that also helps to improve the bound for the dual problem: finding the minimum number of unit squares needed for covering the large square, from $x^2+O\left(x^{(3+\sqrt{2})/7}\log x\right)$ to $x^2+O(x^{5/8})$.

math.CO↗

arXiv2016

Non-Markov property of afterpulsing effect in single-photon avalanche detector

Single-photon avalanche photodiode(SPAD) has been widely used in researching of quantum optics. Afterpulsing effect, which is an intrinsic character of SPAD, affects the system performance in most of the experiments and needs to be carefully handled. For a long time, afterpulsing has been presumed to be determined by the pre-ignition avalanche. We studied the afterpulsing effect of a commercial InGaAs/InP SPAD (APD: Princeton Lightwave PGA-300) and demonstrated that its afterpulsing is non-Markov, which has memory effect of the avalanching history. Theoretical analysis and the experimental results clearly indicate that the embodiment of this memory effect is the afterpulsing probability, which increases as the number of ignition-avalanche pulses increase. The conclusion makes the principle of afterpulsing effect clearer and is instructive to the manufacturing processes and afterpulsing evaluation of high-count-rate SPADs. It can also be regarded as an fundamental premise to handle the afterpulsing signals in many applications, such as quantum communication and quantum random number generator.

physics.ins-det↗

arXiv2016

Diagnosing $Λ$HDE model with statefinder hierarchy and fractional growth parameter

Recently, a new dark energy model called $Λ$HDE was proposed. In this model, dark energy consists of two parts: cosmological constant $Λ$ and holographic dark energy (HDE). Two key parameters of this model are the fractional density of cosmological constant $Ω_{\Lambda0}$, and the dimensionless HDE parameter $c$. Since these two parameters determine the dynamical properties of DE and the destiny of universe, it is important to study the impacts of different values of $Ω_{\Lambda0}$ and $c$ on the $Λ$HDE model. In this paper, we apply various DE diagnostic tools to diagnose $Λ$HDE models with different values of $Ω_{\Lambda0}$ and $c$; these tools include statefinder hierarchy \{$S_3^{(1)}, S_4^{(1)}$\}, fractional growth parameter $ε$, and composite null diagnostic (CND), which is a combination of \{$S_3^{(1)}, S_4^{(1)}$\} and $ε$. We find that: (1) adopting different values of $Ω_{\Lambda0}$ only has quantitative impacts on the evolution of the $Λ$HDE model, while adopting different $c$ has qualitative impacts; (2) compared with $S_3^{(1)}$, $S_4^{(1)}$ can give larger differences among the cosmic evolutions of the $Λ$HDE model associated with different $Ω_{\Lambda0}$ or different $c$; (3) compared with the case of using a single diagnostic, adopting a CND pair has much stronger ability to diagnose the $Λ$HDE model.

astro-ph.CO↗

arXiv2015

Measurement-Device-Independent Quantum Coin Tossing

Quantum coin tossing (QCT) is an important primitive of quantum cryptography and has received continuous interest. However, in practical QCT, Bob's detectors can be subjected to detector-side channel attacks launched by dishonest Alice, which will possibly make the protocol completely insecure. Here, we report a simple strategy of a detector-blinding attack based on a recent experiment. To remove all the detector side channels, we present a solution of measurement-device-independent QCT (MDI-QCT). This method is similar to the idea of MDI quantum key distribution (QKD). MDI-QCT is loss tolerant with single-photon sources and has the same bias as the original loss-tolerant QCT under a coherent attack. Moreover, it provides the potential advantage of doubling the secure distance for some special cases. Finally, MDI-QCT can also be modified to fit the weak coherent-state sources. Thus, based on the rapid development of practical MDI-QKD, our proposal can be implemented easily.

quant-ph↗

arXiv2015

Storage of multiple single-photon pulses emitted from a quantum dot in a solid-state quantum memory

Quantum repeaters are critical components for distributing entanglement over long distances in presence of unavoidable optical losses during transmission. Stimulated by Duan-Lukin-Cirac-Zoller protocol, many improved quantum-repeater protocols based on quantum memories have been proposed, which commonly focus on the entanglement-distribution rate. Among these protocols, the elimination of multi-photons (multi-photon-pairs) and the use of multimode quantum memory are demonstrated to have the ability to greatly improve the entanglement-distribution rate. Here, we demonstrate the storage of deterministic single photons emitted from a quantum dot in a polarization-maintaining solid-state quantum memory; in addition, multi-temporal-mode memory with $1$, $20$ and $100$ narrow single-photon pulses is also demonstrated. Multi-photons are eliminated, and only one photon at most is contained in each pulse. Moreover, the solid-state properties of both sub-systems make this configuration more stable and easier to be scalable. Our work will be helpful in the construction of efficient quantum repeaters based on all-solid-state devices

quant-ph↗

arXiv2015

Randomness determines practical security of BB84 quantum key distribution

Unconditional security of the BB84 quantum key distribution protocol has been proved by exploiting the fundamental laws of quantum mechanics, but the practical quantum key distribution system maybe hacked by considering the imperfect state preparation and measurement respectively. Until now, different attacking schemes have been proposed by utilizing imperfect devices, but the general security analysis model against all of the practical attacking schemes has not been proposed. Here, we demonstrate that the general practical attacking schemes can be divided into the Trojan horse attack, strong randomness attack and weak randomness attack respectively. We prove security of BB84 protocol under randomness attacking models, and these results can be applied to guarantee the security of the practical quantum key distribution system.

quant-ph↗

arXiv2015

Robust quantum random number generator based on avalanche photodiodes

We propose and demonstrate a scheme to realize a high-efficiency truly quantum random number generator (RNG) at room temperature (RT). Using an effective extractor with simple time bin encoding method, the avalanche pulses of avalanche photodiode (APD) are converted into high-quality random numbers (RNs) that are robust to slow varying noise such as fluctuations of pulse intensity and temperature. A light source is compatible but not necessary in this scheme. Therefor the robustness of the system is effective enhanced. The random bits generation rate of this proof-of-principle system is 0.69 Mbps with double APDs and 0.34 Mbps with single APD. The results indicate that a high-speed RNG chip based on the scheme is potentially available with an integrable APD array.

quant-ph↗

arXiv2015

Experimental demonstration of quantum key distribution without monitoring of the signal disturbance

Quantum key distribution (QKD) enables two distant users, Alice and Bob, to share secret keys. In existing QKD protocols, an eavesdropper's intervention will inevitably disturb the quantum signals; thus, Alice and Bob must monitor the signal disturbance to place a bound on the potential information leakage. However, T. Sasaki et al. proposed a quite different protocol, named round-robin differential phase shift (RRDPS), in which the amount of eavesdropped information is bounded without monitoring the signal disturbance. Here, we present the first active implementation of the RRDPS protocol. In our experiment, Alice prepares packets of pulses, with each packet being a train with 65 pulses, and the global phase of each packet is randomized. Bob uses a 1-GHz, 1-64-bit actively controlled variable-delay interferometer to realize random switching of the different delays. Benefiting from the large pulse number of each packet, the high stability and low insertion loss of the interferometer, the system can distribute secret key over a distance of 90 km. Our results confirm the feasibility of performing practical QKD with this novel protocol.

quant-ph↗

arXiv2015

A simple implementation of quantum key distribution based on single-photon Bell state measurement

Recently some alternatives of the measurement device independent quantum key distribution(MDI-QKD) based on the single-photon Bell state measurement (SBSM) have been proposed. Although these alternatives are not precisely as secure as MDI-QKD, they possess the advantage of high key rate of traditional BB84-like protocol and avoid the technical complexity of two-photon interference required in the MDI-QKD. However, the setups of these proposed schemes are rather complicated compared to commonly used BB84 systems. Here we propose a simple implementation of SBSM-based QKD which is directly built on the existing realization of BB84 QKD. Our proposal exhibits the hidden connection between SBSM-based QKD and traditional phase-coding QKD protocols. This finding discloses the physics behind these two different types of QKD protocols. In addition, we experimentally demonstrate the feasibility of our protocol.

quant-ph↗

arXiv2014

Revisit of constraints on holographic dark energy: SNLS3 dataset with the effects of time-varying $β$ and different light-curve fitters

Previous studies have shown that for the Supernova Legacy Survey three-year (SNLS3) data there is strong evidence for the redshift-evolution of color-luminosity parameter $β$ of type Ia supernovae (SN Ia). In this paper, we explore the effects of varying $β$ on the cosmological constraints of holographic dark energy (HDE) model. In addition to the SNLS3 data, we also use Planck distance prior data of cosmic microwave background (CMB), as well as galaxy clustering (GC) data extracted from Sloan Digital Sky Survey (SDSS) data release 7 and Baryon Oscillation Spectroscopic Survey (BOSS). We find that, for the both cases of using SN data alone and using SN+CMB+GC data, involving an additional parameter of $β$ can reduce $χ^2$ by $\sim$ 36; this shows that $β$ deviates from a constant at 6$σ$ confidence levels. Adopting SN+CMB+GC data, we find that compared to the constant $β$ case, varying $β$ yields a larger fractional matter density $Ω_{m0}$ and a smaller reduced Hubble constant $h$; moreover, varying $β$ significantly increases the value of HDE model parameter $c$, leading to $c\approx 0.8$, consistent with the constraint results obtained before Planck. These results indicate that the evolution of $β$ should be taken into account seriously in the cosmological fits. In addition, we find that relative to the differences between the constant $β$ and varying $β(z)$ cases, the effects of different light-curve fitters on parameter estimation are very small.

astro-ph.CO↗

arXiv2014

Mismatched-basis statistics enable quantum key distribution with uncharacterized qubit sources

In the postprocessing of quantum key distribution, the raw key bits from the mismatched-basis measurements, where two parties use different bases, are normally discarded. Here, we propose a postprocessing method that exploits measurement statistics from mismatched-basis cases, and prove that incorporating these statistics enables uncharacterized qubit sources to be used in the measurement-device-independent quantum key distribution protocol and the Bennett-Brassard 1984 protocol, a case which is otherwise impossible.

quant-ph↗

arXiv2014

Effects of time-varying $β$ in SNLS3 on constraining interacting dark energy models

It has been found that, for the Supernova Legacy Survey three-year (SNLS3) data, there is strong evidence for the redshift-evolution of color-luminosity parameter $β$. In this paper, adopting the $w$-cold-dark-matter ($w$CDM) model and considering its interacting extensions (with three kinds of interaction between dark sectors), we explore the evolution of $β$ and its effects on parameter estimation. In addition to the SNLS3 data, we also take into account the Planck distance priors data of the cosmic microwave background (CMB), the galaxy clustering (GC) data extracted from SDSS DR7 and BOSS, as well as the direct measurement of Hubble constant from the Hubble Space Telescope (HST) observation. We find that, for all the interacting dark energy (IDE) models, adding a parameter of $β$ can reduce $χ^2$ by $\sim$ 34, indicating that $β_1 = 0$ is ruled out at 5.8$σ$ confidence level (CL). Furthermore, it is found that varying $β$ can significantly change the fitting results of various cosmological parameters: for all the dark energy models considered in this paper, varying $β$ yields a larger $Ω_{c0}$ and a larger $w$; on the other side, varying $β$ yields a smaller $h$ for the $w$CDM model, but has no impact on $h$ for the three IDE models. This implies that there is a degeneracy between $h$ and $γ$. Our work shows that the evolution of $β$ is insensitive to the interaction between dark sectors, and then highlights the importance of considering $β$'s evolution in the cosmology fits.

astro-ph.CO↗

arXiv2014

Decoy state measurement-device-independent quantum key distribution based on the Clauser-Horne-Shimony-Holt inequality

The measurement-device-independent quantum key distribution (MDI-QKD) protocol is proposed to remove the detector side channel attacks, while its security relies on the assumption that the encoding systems are perfectly characterized. In contrast, the MDI-QKD protocol based on the Clauser-Horne-Shimony-Holt inequality (CHSH-MDI-QKD) weakens this assumption, which only requires the quantum state to be prepared in the two-dimensional Hilbert space and the devices are independent. In experimental realizations, the weak coherent state, which is always used in QKD systems due to the lack of an ideal single photon source, may be prepared in the high-dimensional space. In this paper, we investigate the decoy-state CHSH-MDI-QKD protocol with $s(3 \le s \le 5)$ intensities, including one signal state and $s-1$ decoy states, and we also consider the finite-size effect on the decoy-state CHSH-MDI-QKD protocol with five intensities. Simulation results show that this scheme is very practical.

quant-ph↗