This PDF file contains the front matter associated with SPIE Proceedings Volume 11905, including the Title Page, Copyright information, and Table of Contents.

Wigner negativity, as a well-known indicator of nonclassicality, plays an essential role in quantum computing and simulation using continuous-variable systems. Recently, it has been proven that Einstein-Podolsky-Rosen steering is a prerequisite to generate Wigner negativity between two remote modes. Motivated by the demand of real-world quantum network, here we investigate the shareability of generated Wigner negativity in the multipartite scenario from a quantitative perspective. By establishing a monogamy relation akin to the generalized Coffman-Kundu-Wootters inequality, we show that the amount of Wigner negativity cannot be freely distributed among different modes. Moreover, for photon subtraction -- one of the main experimentally realized non-Gaussian operation -- we provide a general method to quantify the remotely generated Wigner negativity. With this method, we find that there is no direct quantitative relation between the Gaussian steerability and the amount of generated Wigner negativity. Our results pave the way for exploiting Wigner negativity as a valuable resource for numerous quantum information protocols based on non-Gaussian scenario.

This Conference Presentation, “Effect of molecular orbital angular momentum on spatial distribution of fluorescence during femtosecond laser filamentation in air,” was recorded for Photonics Asia 2021, held in Nantong, China.

The Fourier transform treatment on random quasi-phase matching (RQPM) problems in nonlinear polycrystalline materials is proposed to simplify the simulation process. The spatial frequency spectrum information of the polycrystalline material is obtained directly by Fourier transform analysis in the space domain, which is closely related to wave number and coherence length. Using this method to simulate the second harmonic generation (SHG), the results are consistent with the previous studies, which verifies the feasibility of this method.

A high-efficiency, high-peak-power, widely tunable optical parametric generator (OPG) based on a MgO-doped periodically poled lithium niobate (PPMgLN) crystal is reported. Pumped by a microchip passively Q-switched laser (duration: 330 ps, repetition rate:1 kHz) with the power output of 880 mW, the OPG could be continuously tuned from 1399 nm to 4443 nm by changing the grating period and working temperature. The OPG generated an output power of 591 mW for the signal (1758 nm) and the idler (2695 nm) waves, achieving the internal conversion efficiency of 67.16%, slope efficiency of 89.6% and peak power above 1 MW at 1758 nm. The evolution of linewidth of the signal wave during wavelength tuning were also studied and the theoretical models were proposed. The linewidth was narrowed from 100 GHz to GHz level using a continuous-wave (CW) tunable seeder. The linewidth reached 1.72 GHz at 1626 nm, close to the Fourier transform limit of the sub-nanosecond signal wave.

In many applications using light for practical purposes, the accuracy of optical experiment is limited most fundamentally by the finite amount of light utilized in the measurements. Special emphasis should be put on interferometry aimed at measuring the parameters of simple fringe patterns due to the following reasons. First, fringe parameter measurement provides a relatively well defined and tractable example of application of the theory. The desired parameters are easily defined, and methods for their measurement are readily devised based on common sense. Second, fringe parameter measurement is central to all problems involving coherence. The fundamental descriptors of light waves utilized in coherence theory are in fact measurable parameters of fringes. By examining the limitations to fringe parameter measurement, we are actually examining the limitations to the measurability of coherence itself. In this paper, fundamental limitations of estimating the amplitudes and phases of polar-interferograms recorded at low light levels are investigated. By modeling the receiver as a spatial array of photon-counting detectors, results are obtained that permit specification of the minimum number of photoevents required for estimation of fringe parameters to a given accuracy. Both a discrete Fourier-transform estimator and an optimum joint maximum-likelihood estimator are considered to specify the limiting performance of all unbiased estimators in terms of the collected light flux.

There is an increasing demand for multiplexing of quantum key distribution with optical communications in a single fiber in consideration of high costs and practical applications in the metropolitan optical network. Here, we realize the integration of quantum key distribution and Optical Transport Network of 80 Gbps classical data at 15 dBm launch power over 50 km of the widely used standard (G.652 Recommendation of the International Telecom Union Telecom Standardization Sector) telecom fiber. A secure key rate of 11 kbps over 20 km is obtained. By tolerating a high classical optical power up to 18 dBm of 160 Gbps classical data on single mode fiber our result shows the potential and tolerance of quantum key distribution being used in future large capacity transmission systems, such as metropolitan area networks and data center. The quantum key distribution system is stable and practical which is insensitive to the polarization disturbance of channels by using phase coding system based on Faraday-Michelson interferometer. We also discuss the fundamental limit for quantum key distribution performance in the multiplexing environment.

We investigate a quantum random number generation (QRNG) based on backward spontaneous Raman scattering (SpRS) in standard single-mode fiber, where the randomness of photon wavelength superposition and arrival time are simultaneously utilized. The experiment uses four avalanche photodiodes working in gated Geiger mode to detect backward Raman scattering photons from four different wavelength channels and a time-to-digital converter placed behind the detectors to record their arrival time.

Lights carrying orbital angular momentum (OAM) have potential applications in precise rotation measurement, especially in remote sensing. Interferometers, especially nonlinear quantum interferometers, have also been proven to greatly improve the measurement accuracy in quantum metrology. By combining these two techniques, we theoretically propose a new atom-light hybrid Sagnac interferometer with OAM lights to advance the precision of the rotation measurement. A rotation sensitivity below standard quantum limit is achieved due to the enhancement of the quantum correlation of the interferometer even with 96% photon losses. This makes our protocol robustness to the photon loss. Furthermore, combining the slow light effect brings us at least four orders of magnitude of sensitivity better than the earth rotation rate. This new type interferometer has potential applications in high precision rotation sensing.

Recently, a source-independent quantum random number generator (SI-QRNG), which can generate secure random numbers with untrusted sources, has been realized. However, the measurement loopholes of the trusted but imperfect devices used in SI-QRNGs have not yet been fully explored. Here, we point out and evaluate the security loopholes of practical imperfect measurement devices in SI-QRNGs. We also provide corresponding countermeasures to prevent these information leakages by recalculating the conditional minimum entropy and adding a monitor. Furthermore, by taking into account the finite-size effect, we show that the influence of the afterpulse can exceed that of the finite-size effect with the large number of sampled rounds. Our protocol is simple and effective, and it promotes the security of SI-QRNG in practice as well as the compatibility with high-speed measurement evices, thus paving the way for constructing ultrafast and security-certified commercial SI-QRNG systems.

The decoy-state method substantially improves the performance of quantum key distribution (QKD) and perfectly solves crucial issues caused by multiphoton pulses. In recent years, the decoy-state method has occupied a key position in practicality, and almost all the QKD systems have employed the decoy-state method. However, the imperfections of traditional intensity modulators limit the performance of the decoy-state method and bring side-channels. In this work, a special intensity modulator and its accompanying modulation method are designed and experimentally verified for the secure, stable and high-performance decoy-state QKDs. The experimental result indicates that its stable and adjustable intensities, convenient two-level modulation, inherently high speed, and compact structure is extremely fit the future trends and will help the decoy-state method to be perfectly applied to QKD systems.

A widely tunable eye-safe noncollinear phase-matched (PM) KTP optical parametric oscillator (OPO) with fixed output direction was proposed. Based on a novel confocal optics system, the input pump beam from a pulsed 1064 nm Nd:YAG laser could be deflected into the OPO with a tunable and agile noncollinear angle while maintaining the resonator unaffected. As a result, stable OPO operation with a wide tuning range of 124 nm was achieved easily with a beam scanner. The pump threshold, output energy, linewidth and temporal pulse shapes during wavelength tuning were also measured and discussed.

The phase compensation with high accuracy is one of the key technologies in continuous variable quantum key distribution (CVQKD) system, which directly influences the secure key rate and transmission distance. However, traditional phase compensation method cannot accurately estimate the phase drift due to the additive noise introduced by coherent detector. In this paper, we propose a new phase compensation method based on mean denoising, where a training sequence is designed for estimating phase drift in the transmitter (Alice) and an average of the multi-points in the training sequence is estimated to remove the influence of additive noise. Simulation results show that the compensation accuracy of the proposed method can reach 0.9932, which is 20% better than that based on traditional method. Our method can significantly reduce the influence of additive noise, and improve the system performance by controlling excess noise in phase compensation process.

Based on the three-energy level exciton model of the quantum dot lasers (QDLs), the nonlinear dynamics of the sole ground-state emitting QDL (GS-QDL) under external optical injection is numerically studied. The results show that the GS-QDL can generate period-one, period-two, multi-period, chaotic pulse and injection locking states under suitable injection parameters. By analyzing the distribution of these dynamic states in the injection parameter space, it is found that the period-one state and injection locking state occupy a large area, but the region of the complex dynamics is relatively small. Moreover, the complexity of the chaotic signals generated by the GS-QDL is quantified by the permutation entropy calculation. The results show that the complexity of the chaotic signals is less than 0.90, which indicates that the GS-QDL is low sensitivity to external optical injection. The GS-QDL can be used in isolator-free photonic integrated circuits.

Levitated microspheres have enabled a wide variety of precision sensing applications which have caught great attentions in recent years. Optical tweezers technology is one of the most important methods of microspheres levitation. The stability of laser power directly affects the microspheres levitation and the precision of the measurement. This paper discusses the major factors of power stabilization in semiconductor laser. A PID-controlled model is used to control the feedback on the laser. The system mode is established after the analyzing of the characteristic of the model parameters. The experiment is demonstrated with a commercial semiconductor laser. With the external power stabilization module a 16dB laser power stability control is achieved at the relaxation oscillation, and the long-term stability is improved from 3% to 0.4%.

In this paper, a frequency-shifted-assisted continuous variable quantum key distribution with local local oscillator (LLOCVQKD) scheme is proposed based on Gaussian modulated coherent state. In the proposed scheme, the quantum signal and pilot tone can be completely isolated in frequency domain by frequency-shifting quantum optical carrier, so that the crosstalk from strong pilot tone to weak quantum signal can be effectively eliminated compared with our former pilottone scheme based on CS-DSB modulation. Moreover, an improved phase noise compensation scheme based on pilottone- assisted phase calibration and adaptive phase rotation is proposed for eliminating the dominate phase noise without the help of any training sequences, which promotes the blocks of the quantum key. Besides, a low level of excess noise is experimentally obtained for supporting the secure key rate of 7.15 Mbps over secure transmission distance of 25 km, verifying the simple and high-rate LLO-CVQKD.

In this paper, a high-rate Gaussian-modulated coherent-state (GMCS) continuous-variable quantum key distribution (CV-QKD) scheme with a local local oscillator is experimentally demonstrated. The transmission of quantum signal and pilot tone in optical fiber adopts frequency and polarization multiplexing technology. By optimizing frequency bandwidth, modulation variance and intensity of the pilot tone, the CVQKD system is demonstrated at different metropolitan distance, and the secure key rate of 13.53Mbps, 8.24Mbps, 5.39Mbps 3.66Mbps and 2.55Mbps over transmission distance of 5km, 10km, 15km, 20km and 25km are obtained, respectively.

In continuous-variable quantum key distribution system with a true local oscillator (LLO CV-QKD), part of the phase noise associated with the coherent detector and the phase-reference intensity can be considered as trusted because which can be locally calibrated at the receiver’s side. The trusted phase noise model can significantly improve the noise tolerance of the system since the phase noise is the major excess noise. However, the transmission of the phase-reference pulse through the insecure quantum channel in the LLO CV-QKD system may leave rooms for the eavesdropper to mount attacks. Here, we propose a practical and flexible phase-reference intensity attack scheme using a phaseinsensitive amplifier to amplify the intensity of the phase-reference pulse. In this case, the eavesdropper can compromise the security of the LLO CV-QKD system severely by lowering the trusted part of the phase noise to compensate her increased attack on the signal pulse while the total excess noise is unchanged. We simulate the secure key rate with respect to the transmission distance to show that precisely monitoring the instantaneous intensity of the phase-reference pulse in real time is of great importance to guarantee the security of the LLO CV-QKD system.

Based on a four-level rate equation model, we numerically simulated the nonlinear dynamics of a diode-pumped solidstate passively Q-switched laser. A Nd:YAG and a Cr⁴⁺:YAG is used as the gain medium and the saturable absorber in this system, respectively. Through setting the pumping rate or the round-trip optical loss at different values, the diodepumped solid-state passively Q-switched Nd:YAG/Cr⁴⁺:YAG laser may operate at the period-one, period-two, multiperiod or chaotic states. For a certain specific state, the time series, the power spectra and the Poincaré maps are represented. Moreover, the route for the diode-pumped solid-state passively Q-switched Nd:YAG/Cr⁴⁺:YAG laser entering into chaos is revealed by mapping the bifurcation.

A two-qubit quantum swap gate scheme based on coherent state qubit is proposed in cavity quantum electrodynamics system. Our scheme adopt the interaction between the Λ-type atomic ensemble and the two-mode optical cavity, and the swap gate can be realized directly only one step, so as to save a lot of quantum resources and reduce the number of single qubit rotation operations in the actual quantum information processing. It is found that under the condition of large detuning limit, the excited states of atoms are adiabatically eliminated, and the decoherence caused by the spontaneous emission of atoms is effectively suppressed. All atoms in the optical cavity are universally addressed, which reduces the experimental operation difficulty of the scheme. The fidelity of the quantum logic gate is maintained at a very high level when the photon loss of the cavity field is considered. Compared with the single-atom scheme, it is found that the atom-cavity interaction time required by the atomic ensemble scheme is inversely proportional to the number of atoms, so that the speed of the quantum logic gate can be increased by N times. Therefore, in principle, as long as enough atoms interacting with the optical field, an effective coupling of any atom-cavity field can be generated, which is conducive to selecting the appropriate quantum gate operation time in practical operation and effectively avoiding decoherence.

Femtosecond laser direct writing (FLDW) technique has been widely applied for fabrications of various photonic quantum chips in glass, such as chips for quantum computation, quantum walk, quantum simulation and quantum metrology. Photonic quantum logic gates are the building blocks for the realization of linear optical universal quantum computation. Up to now, several photonic quantum logic gates have been fabricated by FLDW, such as polarization encoded Hadamard (H) gate, Controlled NOT (CNOT) gate, herald CNOT gate and path encoded herald Controlled phase (CZ) gate and CNOT gate. By combining several single-qubit and two-qubit gates together, the constructed quantum circuits can realize some special functions, such as generating entangled states and perform quantum computation algorithms. Based on the successful fabrication of path encoded CNOT gate by FLDW, we further realized the fabrication of photonic quantum chips by cascading one H gate and one CNOT gate at the control qubit to generate path encoded Bell states, whose fidelity of truth table can reach 97.60.3%. Further, we cascaded one H gate and two parallel CNOT gates at the same control qubit to generate path encoded GHZ states, but which need three photons. Both Bell states and GHZ states are important entangled photon resources, which are widely used in quantum communication and quantum computation, and both combinations of logic gates above can be applied in many quantum circuits, so this work is of great importance and lays the technical foundation for the FLDW of more complex and powerful photonic quantum computation chips.

The field-orthogonal temporal modes (TM) of electromagnetic fields form a new framework for quantum information. A lot of efforts have been made to develop the tools for photonic quantum information processing in TM framework. However, the distribution of temporally multiplexed quantum states over long distance optical fibers has not been realized yet. As a first step toward long distance distribution of TMs, we study fourth-order interference and show how the dispersion influence the field spectrum by launching a pulsed field in different temporal modes into a M-Z interferometer with unbalanced dispersion induced by transmission fibers in two arms. The investigation is useful for further investigating the distribution of temporally multiplexed quantum states in fiber network.

A polarization demultiplexing algorithm for continuous-variable quantum key distribution (CV-QKD) system based on Stokes space is proposed and experimentally demonstrated. In the CV-QKD system, the pilot tone and quantum signal is modulated on the two orthogonal states of polarization (SOP), respectively. Since the power of the pilot-tone is much higher than quantum signal, the received signals in Stokes space present a single cluster point. Therefore, the K-means algorithm is used to find the coordinate of the cluster point, and the polarization rotation angles can be obtained by the coordinate. The advantages of the proposed algorithm are fast convergence, simple computation and modulation format independence. Experimental results of 100 MHz pilot-tone-assisted Gaussian-modulated CV-QKD system with local local oscillator (LLO) are given, and the results show that the proposed algorithm split the pilot-tone and quantum signal effectively. Furthermore, experimental results show that the proposed algorithm can track SOP scrambling of ≥3141.59 rad/s without sacrificing the performance of excess noise, which is satisfying for most scenarios of the LLO CV-QKD system.

Based on Bohr-Sommerfeld quantum theory and the single and two-photon absorption selection rule of quantum mechanics, a new quantum impedance Lorentz oscillator model is proposed, which relates the electron transition process to the resonance absorption of the Lorentz oscillator. The natural frequency of the oscillator is unified with the intrinsic frequency of the electron transition. A formula for calculating the parameters of the oscillator, including the damping coefficient, is given in terms of the electron charge and mass, Bohr radius and effective quantum number. Based on the Boltzmann distribution of thermodynamics, an expression of vibrator intensity under the emission and absorption equilibria of light is presented. Based on this model and considering that "electron pair" is one of the molecular chemical bonds, the effective quantum number before and after the electronic transition of TPAT-AN-XF and ASPI is calculated by fitting the linear absorption spectra of TPAT-AN-XF and ASPI, and also the two-photon absorption cross sections of the two organic molecules are numerically simulated. The numerical results agree well with the experiment. The results show that the quantum impedance Lorentz oscillator can better describe the absorption properties of TPAT-An-XF and ASPI.

Bohr’s complementarity is one central tenet of quantum physics. The paradoxical wave-particle duality of quantum matters and photons has been tested in Young’s double-slit (double-path) interferometers. The object exclusively exhibits wave and particle nature, depending measurement apparatus that can be delayed chosen to rule out too-naive interpretations of quantum complementarity. All experiments to date have been implemented in the double-path framework, while it is of fundamental interests to study complementarity in multipath interferometric systems. Here we demonstrate generalised multipath wave-particle duality in a quantum delayed-choice experiment, implemented by large-scale silicon-integrated multipath interferometers. Single-photon displays sophisticated transitions between wave and particle characters, determined by the choice of quantum-controlled generalised Hadamard operations. We characterise particle-nature by multimode which-path information and wave-nature by multipath coherence of interference, and demonstrate the generalisation of Bohr’s multipath duality relation. Our work provides deep insights into multidimensional quantum physics and benchmarks controllability of integrated photonic quantum technology.

The principle approach, modeling, and error analysis are analyzed, and the system configuration based on freeform is advanced proposed in the algorithm analysis. In order to improve the resolution of the imaging system and reach the theoretical limit, the off-axis system optimization method is promoted from the perspective of theory to engineering. The simulation results show that the system can meet the application requirements of MTF, REA, RMS and other related criteria. Moreover, the system has reduced in volume and weight significantly.

We demonstrate a passively mode-locked and a passively Q-switched erbium-doped fiber laser respectively by utilizing a same saturable absorber fabricated with tungsten trioxide (WO₃). When the WO₃ saturable absorber is employed to provide the pulse narrowing effect, Q-switched pulses were observed with a repetition rate of 44.11 kHz and a pulse width of 3.42 μs. Moreover, the Q-switched laser could realize hybrid mode-locking after an in-line polarizer was inserted, which could introduce an additional pulse narrowing effect of nonlinear polarization rotation under a certain polarization state. The 3- dB spectral bandwidth and the repetition rate of mode-locked pulses are about 7.5 nm and 22.51 MHz respectively. The pulse train is stable with a signal to noise ratio of 70 dB.

We present an energy-efficient method for conversion of relatively long (nanosecond) optical pulses into an extraordinary light structure – a packet of ordered picosecond pulses which differs from the known types of ordered ultrashort pulse patterns (like soliton molecules). The method relies on revealed peculiarities of nonlinear evolution of an ultrashort dark pulse implanted in a nanosecond bright pulse when they propagate in an optical fiber. Under certain conditions, energy of the background nanosecond pulse, which initially contains a single ultrashort dark pulse, can be mostly converted into a structured burst of ultrashort bright pulses. This burst can feature relatively high (manifold of the initial value) peak power and ultrahigh (sub-THz) intraburst pulse repetition. This dark pulse evolution develops at prorogation distances of a few tens of nonlinear lengths in telecom fibers under conditions of anomalous dispersion. Thus, it can be considered on the one hand as an important limitation for fiber transmission of particular optical waveforms, and on the other hand as a promising method for ultrashort pulse bursts generation.

Properties of noise-like pulses are analysed from the viewpoint of their employment as radiation carriers with relatively high energy. The difference from the well-known method of chirped pulse amplification consists in that instead of temporal stretching of a pulse prior to amplification, this technology relies upon redistribution of the pulse energy among components of a relatively long structured pulse. The fundamental principles of these two approaches are similar and constitute reduction of radiation load (across a surface or volume) at a given moment in time. The prospects of the new method are discussed.

Numerical simulation of the fiber optic parametric oscillator aiming the goal to produce picosecond narrowband pulses for CARS has been performed in an extremely wide range of parameters, such as a pump pulse duration, parametric frequency shift, spectral bandwidth of the pump and the parametric pulses. It required extremely large calculation window both in time (3.5 ns) and spectral (from 433 nm to 3100 nm) domains. We managed to speed up simulation in fifty times by graphic processor unit, which allowed to define the areas of stability for different lengths of standard passive and photonic-crystal fibers used in the external linear cavity of oscillator. The cavity length reached a value of 100 meters that was resulted in parametric pulses with the energy up to 40 nJ and peak power up to 1 kW at a wavelength about 800 nm.

High energy pulse self-compression in a hollow core waveguide filled with noble gases has been under intensive study. Here, its dependence on the input pulse group delay dispersion (GDD) and third order dispersion (TOD) is studied experimentally. Pulses with energy of 3 mJ, at a repetition rate of 1 kHz, with Fourier transform limited FWHM pulse duration of 24 fs from a Ti:sapphire laser amplifier system are focused into a 2 cm long, 150 μm inner diameter hollow core waveguide filled with 10 mbar argon gas for self-compression. The input pulse GDD and TOD are tuned by an acousto-optic programmable dispersive filter in the laser amplifier system and the output pulses after the waveguide are measured. We found that the pulses are optimally compressed along a diagonal line in the GDD-TOD plane, where the output pulses are near Fourier transform limited. However, along the other diagonal line the pulses are poorly compressed due to pre-pulses appearing. We also compared the spectral phases and temporal profiles of the output pulses at selected points along the two diagonal lines. Along the optimal compression diagonal line, the spectral phases are flatter and the temporal profiles are better comparing to the other diagonal line where the strong pre-pulses occur. Therefore, the optimal input pulse shapes for self-compression are those without pre-pulses. These input pulses can be found easily along the diagonal line where the GDD is decreasing with the TOD in the GDD-TOD plane.

Synchronously pumped Raman oscillators provide efficient nonlinear spectral conversion of ultrashort pulses. Designing of Raman oscillators is a highly dimensional optimization task requiring extensive computations. Here, we implement novel numerical model of stimulated Raman scattering to design a specific laser system with embedded cavities of mode-locked fiber laser and Raman oscillator. Following system allows taking the advantages of high intracavity powers of mode-locked laser during Raman spectral conversion. We analyze the regions of stable coexistence of mode-locked and Raman pulses, their spectral-temporal and coherent properties.