The impact of higher-order dispersion coefficients on the correlation function is a significant topic in quantum technology, particularly for transmission over dispersion-compensated optical fibres. This study focuses on using the standard deviation of the correlation function as a metric to assess the influence of higher-order dispersion coefficients. It demonstrates that the second and third orders of dispersion coefficients play a crucial role in this investigation. When the amplitude of the probability function of a single photon is broad, it should be considered within the context of the dispersive structure, such as in the case of Bragg grating. The concept behind dispersion management is to effectively correlate the entangled photons while filtering out the broad amplitude of the probability function of a single photon. Within the framework of this study, we find that the third-order dispersion coefficient in a Bragg grating, serving as a biphoton transmission medium, significantly affects the standard deviation of the correlation of entangled photons, leading to a decline in its value. Notably, whether the third-order dispersion coefficient is positive or negative contributes to this effect.
The impact of higher-order dispersion coefficients on the correlation function is a significant topic in quantum technology, particularly for transmission over dispersion-compensated optical fibres. This study focuses on using the standard deviation of the correlation function as a metric to assess the influence of higher-order dispersion coefficients. It demonstrates that the second and third orders of dispersion coefficients play a crucial role in this investigation. When the amplitude of the probability function of a single photon is broad, it should be considered within the context of the dispersive structure, such as in the case of Bragg grating. The concept behind dispersion management is to effectively correlate the entangled photons while filtering out the broad amplitude of the probability function of a single photon. Within the framework of this study, we find that the third-order dispersion coefficient in a Bragg grating, serving as a biphoton transmission medium, significantly affects the standard deviation of the correlation of entangled photons, leading to a decline in its value. Notably, whether the third-order dispersion coefficient is positive or negative contributes to this effect.
Abstract In the realm of quantum information processing and precision measurements, a range of non-classical effects based on entangled photon pairs are employed. Non-local dispersion cancellation is one of these properties, in which the second photon (idler) can be manipulated to cancel the effects of dispersion on the first photon (signal). In the present study, a thorough investigation is conducted into non-local dispersion cancellation by using excitation modes within a Bragg grating slab waveguide. We present a complete theoretical analysis of non-local dispersion cancellation for frequency-limited entangled photon pairs. For the analysis of the effect of dispersion cancellation, we use a spontaneous parametric down-conversion (SPDC) photon pair source with frequency correlation and anti-correlation as the entangled source. To evaluate the dispersion cancellation effect for information processing applications, the second correlation function is used and calculated as a practical and tangible metric. Considering different cases for Bragg Grating waveguide the results on both photons are extracted and discussed. Moreover, we will show that the physical parameters of the waveguide that the second photon is propagated inside will be effective in minimizing the width of the temporal correlation function. Hence, this study underscores the feasibility of achieving non-local dispersion cancellation through strategic optimization of optical and geometric parameters in the Bragg Grating waveguide, with potential implications for quantum information processing and high-resolution sensing endeavors.
Quantum optical integrated circuits have heralded a paradigm shift in the realm of quantum information processing. Integrated photonics technology now empowers the creation of intricate optical circuits on single chips. While optical integrated circuits used to pose formidable challenges for numerous quantum applications, they have, in recent times, evolved to satisfy stringent requirements across a spectrum of research and industrial domains. Today, it is imperative to delve into research aimed at both crafting and preserving quantum properties within photonic substrates. Superimposed Bragg grating structures have emerged as valuable components within optical applications, poised to play pivotal roles in the development of integrated circuits. Nevertheless, these structures exhibit an inherent drawback in the form of dispersion, which can potentially compromise the preservation of quantum states. In this study, we meticulously scrutinize the physical attributes of these structures to elucidate the factors contributing to undesirable dispersion effects. We also investigate the correlation between two photons at the termination point of the structure. The superimposed Bragg grating structure under scrutiny boasts periods of both 1 and 3 micrometers, an overall length of 100 micrometers, and radiates at a wavelength of 1.55 micrometers. By subjecting photons to this medium individually or in tandem and analyzing their correlation function, we aim to pinpoint elements that effectively safeguard the quantum properties inherent in the system. This research endeavor is poised to yield valuable insights that will substantially influence the design of quantum integrated circuits, enhancing their efficacy in computational tasks and quantum information processing.
High-order photon correlations of light fields are important for characterizing the quantum nature. Since Hanbury Brown and Twiss conducted the pioneering experiments in the 1950s, the HBT effect has inspired extensive research on high-order photon correlation in quantum optics, quantum information, and quantum imaging. The Single-photon counting module is one of the most widely used single-photon detectors. Due to its high detection efficiency and low dark counts in the visible and near-infrared region, it is reasonably chosen for basic research on quantum mechanics. Many researches have demonstrated that the maximum value of second-order photon correlation g(2)(τ) at zero delay (τ = 0) can be used to distinguish different light fields. Therefore, the HBT scheme containing two single photon detectors have been widely used in many advanced studies, such as space interference, ghost imaging, single photon detection with high efficiency, etc. However, higher-order photon correlations g(n) (n > 2) can reveal more measurable characteristics of light fields, such as information about the non-Gaussian scattering process, the skewness and kurtosis of photon number distribution, etc. When the extended HBT scheme is used to measure higher-order photon correlations, the experimental conditions including quantum efficiency and background noise greatly affect the photon correlation measurement. The influences of the counting rate and resolution time of the detection system on the measurements are also very important and cannot be ignored. Therefore, the comprehensive considering of various influence factors is necessary for accurately measuring the high-order photon correlations and also a challenge. In this paper, we present a method based on double Hanbury Brown-Twiss scheme for the accurate measuring of high-order photon correlations g(n) (n > 2). The system consists of four single photon counting modules and is used to detect and analyze the joint distribution probability of temporal photon correlation. Considering the effects of the background noise and overall efficiency, theoretically, we analyze the correlations of the third- and fourth-order photon with the incident light intensity, squeezing parameter and photon number respectively for thermal state, coherent state, squeezed vacuum state, and Fock state. Meanwhile, experimentally we study the influences of resolution time and counting rate on correlations of the coherent state and thermal state with third- and fourth-order photon. On condition that the resolution time is 210 ns and the counting rate is 80 kc/s, the correlations of third and fourth-order photon with the thermal state at zero time delay are accurately measured, and the relative statistical deviations of the measured vales from the theoretical values are 0.3% and 0.8%, respectively. In addition, the third- and fourth-order photon correlations of the thermal state at different delay times are also observed. It is demonstrated that the high-order photon correlations of light fields are measured accurately by comprehensively analyzing various influencing factors. This technique provides a promising and useful tool to investigate quantum correlated imaging and quantum coherence of light fields.
Dispersive optics quantum key distribution (DO-QKD) based on energy-time entangled photon pairs is an important QKD scheme. In DO-QKD, the arrival time of photons is used in key generation and security analysis, which would be greatly affected by fiber dispersion. In this work, we established a theoretical model of the entanglement-based DO-QKD system, considering the protocol, physical processes (such as fiber transmission and single-photon detection), and the analysis of security tests. Based on this theoretical model, we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD. By analyzing the benefits and costs of dispersion compensation, the system performance under G.652 and G.655 optical fibers are shown, respectively. The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks. Whereas, it is still required in DO-QKD systems with longer fiber transmission distances.
In the experiment presented in the paper, HBT (Hanbury-Brown and Twiss) interferometer is used to measure the second-order correlation function (G2) for two entangled photons, denoted as signal and idle ones, generated by the spontaneous parametric down-conversion process. When an extra optical fiber is inserted in the signal's path, the arrival times of these two photons are different, so that the length of the fiber can be estimated by measuring the time offset in the G2 function.#br#As the laser light we used is not monochromatic, the experimental result is affected by the group velocity dispersion (GVD). Light of different wavelength has different velocity and leads to different travelling time in the fiber. Through calculation, we find that the G2 function of each wavelength has the same shape but different center time offset. Thus, the final G2 function, as a superimposition of the functions with different wavelengths, is broadened in a long-distance measurement, which seriously reduces the estimation accuracy. We analyze this phenomenon in both theory and experiment, and the experimental results fit our theoretical simulations quite well.#br#In the theoretical analysis, we find that the group velocity dispersion introduces an additional time offset to the final G2 function which is proportional to the total time offset. In our experiment, this additional time offset is about 1% of the total time offset. In particular, this effect results in a 63600 ps extra time offset, which can be compensated in post process, with a time accuracy of about 1 ps.#br#This paper focuses on the G2 function affected by the group velocity dispersion, and also calculates the additional time offset produced by group velocity dispersion, and thus gives a method to compensate the additional time offset through calculation.
Abstract In this study, we investigate the effects of chromatic dispersion on single-photon temporal wave functions (TWFs) in the context of quantum communications. Departing from classical beam analysis, we focus on the temporal shape of single photons, specifically exploring generalized Gaussian modes. From this foundation, we introduce chirped and unchirped Gaussian TWFs, demonstrating the impact of the chirp parameter in mitigating chromatic dispersion effects. Furthermore, we extend our investigation to time-bin qubits, a topic of ongoing research relevance. By exploring the interplay of dispersion effects on qubit interference patterns, we contribute essential insights to quantum information processing. This comprehensive analysis considers various parameters, introducing a level of complexity not previously explored in the context of dispersion management. We demonstrate the relationships between different quantities and their impact on the spreading of TWFs. Our results not only deepen the theoretical understanding of single-photon TWFs but also offer practical guidelines for system designers to optimize symbol rates in quantum communications.