Quantum key distribution based on a Sagnac loop interferometer and polarization-insensitive phase modulators

We present a design for a quantum key distribution(QKD) system in a Sagnac loop configuration, employing a novel phase modulation scheme based on frequency shift, and demonstrate stable BB84 QKD operation with high interference visibility and low quantum bit error rate (QBER). The phase modulation is achieved by sending two light pulses with a fixed time delay (or a fixed optical path delay) through a frequency shift element and by modulating the amount of frequency shift. The relative phase between two light pulses upon leaving the frequency-shift element is determined by both the time delay (or the optical path delay) and the frequency shift, and can therefore be controlled by varying the amount of frequency shift. To demonstrate its operation, we used an acousto-optic modulator (AOM) as the frequency-shift element, and vary the driving frequency of the AOM to encode phase information.The interference visibility for a 40km and a 10km fiber loop is 96% and 99%, respectively, at single photon level. We ran BB84 protocol in a 40-km Sagnac loop setup continuously for one hour and the measured QBER remained within the 2%~5% range. A further advantage of our scheme is that both phase and amplitude modulation can be achieved simultaneously by frequency and amplitude modulation of the AOM's driving signal, allowing our QKD system the capability of implementing other protocols, such as the decoy-state QKD and the continuous- variable QKD. We also briefly discuss a new type of Eavesdropping strategy ("phaseremapping" attack) in bidirectional QKD system.Comment: 4 page

Time Dependent Saddle Node Bifurcation: Breaking Time and the Point of No Return in a Non-Autonomous Model of Critical Transitions

There is a growing awareness that catastrophic phenomena in biology and medicine can be mathematically represented in terms of saddle-node bifurcations. In particular, the term `tipping', or critical transition has in recent years entered the discourse of the general public in relation to ecology, medicine, and public health. The saddle-node bifurcation and its associated theory of catastrophe as put forth by Thom and Zeeman has seen applications in a wide range of fields including molecular biophysics, mesoscopic physics, and climate science. In this paper, we investigate a simple model of a non-autonomous system with a time-dependent parameter $p(\tau)$ and its corresponding `dynamic' (time-dependent) saddle-node bifurcation by the modern theory of non-autonomous dynamical systems. We show that the actual point of no return for a system undergoing tipping can be significantly delayed in comparison to the {\em breaking time} $\hat{\tau}$ at which the corresponding autonomous system with a time-independent parameter $p_{a}= p(\hat{\tau})$ undergoes a bifurcation. A dimensionless parameter $\alpha=\lambda p_0^3V^{-2}$ is introduced, in which $\lambda$ is the curvature of the autonomous saddle-node bifurcation according to parameter $p(\tau)$, which has an initial value of $p_{0}$ and a constant rate of change $V$. We find that the breaking time $\hat{\tau}$ is always less than the actual point of no return $\tau^*$ after which the critical transition is irreversible; specifically, the relation $\tau^*-\hat{\tau}\simeq 2.338(\lambda V)^{-\frac{1}{3}}$ is analytically obtained. For a system with a small $\lambda V$, there exists a significant window of opportunity $(\hat{\tau},\tau^*)$ during which rapid reversal of the environment can save the system from catastrophe

Measurement of Absorption Cross Section of a Lossy Object in Reverberation Chamber Without the Need for Calibration

A reliable and simple procedure is proposed to measure the averaged absorption cross section (ACS) of a lossy object in a reverberation chamber (RC). This procedure is based on the time-domain measurement of the ACS in an RC. In the time-domain, to obtain the ACS, the chamber decay time needs to be known. Conventionally, the ACS is normally measured in the frequency domain, and a full two-port calibration must be carried out before collecting the S-parameters, which is tedious and time-consuming. In reality, the chamber decay time depends on the diffused loss of the RC, not the insertion loss of the cables. In this paper, by making use of this fact, the ACS can be measured accurately without calibration, which will simplify the measurement process and shorten the measurement time at the same time

Control of Long Pulse Pumped Supercontinuum Generation Using Weak Trigger Signal

This work was supported by National Natural Science Foundation of China under Grants 61675008, and Shenzhen Science and Technology Innovation Commission under Grant GJHZ20180411185015272.Peer reviewedPostprin

Integrating Li-Fi Wireless Communication and Energy Harvesting Wireless Sensor for Next Generation Building Management

Wireless sensors have been increasingly utilized in the design of next generation high performance buildings. When deploying wireless sensors, energy supply and data communication are the major concerns. Although energy harvest wireless sensors could automatically feed themselves by harvesting ambient energy, the presence of reliable energy sources to support dependable wireless transmission is a great challenge. The emerging Li-Fi technology is promising to fundamentally solve this problem. Li-Fi stands for Light-Fidelity, which is a new kind of wireless communication systems using light as a medium instead of traditional radio-frequency electromagnetic radiation. Li-Fi technology provides harvested energy to power wireless sensors with a unique advantage of power generation from the lighting system being controlled. The combination of Li-Fi and energy harvesting wireless sensor technologies could enable attractive features and bring in great benefits in the design of next generation high performance buildings because: (i) energy harvest sensors do not face the short-of-energy problem; (ii) Li-Fi enables much higher transmission speed compared to the existing RF electromagnetic technologies, thus, energy harvest sensors could easily deliver environmental parameters quickly for control purposes; (iii) energy harvest sensors could assist the building management team to understand the coverage area of the lighting system; (iv) the communication of sensor aggregated information can be naturally encrypted due to the combination of both technologies

Cross-Channel Integration and Customer Retention in Omnichannel Retailing: The Role of Retailer Image and Alternative Attractiveness

Cross-channel integration (CCI) is increasingly considered as an important driver of customer retention in omnichannel retailing. However, the existing findings about the relationship between CCI and customer retention are contradictory, wherein both positive and non-significant findings exist. This study aims to explore the contingency role of retailer image and alternative attractiveness for the above relationship. Specifically, both two-way and three-way interaction effects of retailer image and alternative attractiveness were tested. Our survey finding confirmed the positive relationship between CCI and customer retention. We also found that the positive relationship was negatively moderated by retailer image, while positively moderated by alternative attractiveness. This study further uncovered that alternative attractiveness can weaken the negative moderating effect of retailer image. Implications and limitations of the study are discussed