High-Precision Fiber Noise Detection and Comparison over a 260 km Field Fiber Link.

In this paper, we present a high-precision optical frequency noise detection and comparison technique using a two-way transfer method over a 260 km field fiber link. This method allows for the comparison of optical frequencies between remote optical references without the need for data transfer through communication. We extend a previously established two-way comparison technique to obtain all data at the local site. Two optical carrier signals are injected into the bidirectional fiber from both ends, and one carrier is reflected back from the remote end. This enables the phase comparison of the two carrier signals at a single site without the need to transmit experimental data. The common-mode frequency noise induced by the bidirectional fiber link is detected and effectively suppressed without the need for sophisticated active fiber noise control. Our demonstration system, which uses a 260 km field fiber link and a common laser source, achieves a fractional instability of 2.5×10-17 at 1 s averaging time and scales down to 3.5×10-21 at 8000 s. This scheme offers the distinct advantage of completing the comparison at a single site, eliminating the need for remote data transfer via communication. This method is expected to enhance reliability for high-precision frequency comparisons between remote optical clocks and advanced atomic clocks.

Effective disinfecting of negative pressure pipelines of DCUs reduces the risk of cross infection in dental care.

Objectives: Microbial contamination of various accessory parts of the dental chair units (DCUs) is an essential source of cross infection, while the accessories of the crucial suction function are usually overlooked. In this study, we aim to find an effective disinfectant and a cost-effective method to remove bacterioplankton and bacterial biofilm deposited in the negative pressure suction pipelines to control cross infection during dental treatment. Methods: Double-chain quaternary ammonium salt disinfectant (Orotol Plus®), 3% hydrogen peroxide solution plus multi-enzyme cleaning agent and chlorine disinfectant are used to clean and disinfect the negative pressure pipelines of DCUs. Microbiological examinations, air condition detection, corrosion tests and gene sequencing are performed. Results: Little bacteria grow in the pipelines disinfected with double-chain quaternary ammonium salt disinfectants, destruction of biofilms in these pipelines appears, and multi-resistant bacteria cannot be detected. Minimal damage to metal sheets and fittings is caused by double-chain quaternary ammonium salt disinfectants. Conclusion: Double-chain quaternary ammonium salt disinfectant has excellent bactericidal ability and anti-biofilm effect, and it is less corrosive to the fittings of the pipelines. Thus, the double-chain quaternary ammonium salt disinfectant is a potential novel disinfectant for negative pressure suction pipelines of DCUs to control cross infection during dental treatment. Clinical significance: It is essential to add all these data to our dental practice to control cross infection with a broader landscape.

High-dynamic-range microwave sensing using atomic Rabi resonances.

Detection of the microwave (MW) field with high accuracy is very important in the physical science and engineering fields. Herein, an atomic Rabi resonance-based MW magnetic field sensor with a high-dynamic-range is reported, where α and ß Rabi resonances are used to measure MW fields. In MW measurement experiments, the sensor successfully measured a magnetic field of about 10 nT at 9.2 GHz using the α Rabi resonance line on the cesium clock transition and continuously detected the MW magnetic field in the X-band over a high dynamic power range of >60 dB from the ß Rabi resonance. Finally, the MW power frequency shift and power broadening are investigated to support more sensitive field measurements. The proposed MW detection method can be extended to cover a higher dynamic range and a wider frequency band by applying stronger excitations and exploring non-clock atomic transitions, respectively. In addition to MW magnetic field sensing, other potential application of the proposed method can be explored, including SI-traceable MW calibration and atomic communication.

Optomechanics and quantum phase of the Bose-Einstein condensate with the cavity mediated spin-orbit coupling.

We investigated the optomechanical dynamics and explored the quantum phase of a Bose-Einstein condensate in a ring cavity. The interaction between the atoms and the cavity field in the running wave mode induces a semiquantized spin-orbit coupling (SOC) for the atoms. We found that the evolution of the magnetic excitations of the matter field resembles that of an optomechanical oscillator moving in a viscous optical medium, with very good integrability and traceability, regardless of the atomic interaction. Moreover, the light-atom coupling induces a sign-changeable long-range interatomic interaction, which reshapes the typical energy spectrum of the system in a drastic manner. As a result, a new quantum phase featuring a high quantum degeneracy was found in the transitional area for SOC. Our scheme is immediately realizable and the results are measurable in experiments.

Proposal for a hybrid clock system consisting of passive and active optical clocks and a fully stabilized microcomb.

Optical atomic clocks produce highly stable frequency standards and frequency combs bridge clock frequencies with hundreds of terahertz difference. In this paper, we propose a hybrid clock scheme, where a light source pumps an active optical clock through a microresonator-based nonlinear third harmonic process, serves as a passive optical clock via indirectly locking its frequency to an atomic transition, and drives a chip-scale microcomb whose mode spacing is stabilized using the active optical clock. The operation of the whole hybrid system is investigated through simulation analysis. The numerical results show: (i) The short-term frequency stability of the passive optical clock follows an Allan deviation of σy(τ) = 9.3 × 10-14τ-1/2 with the averaging time τ, limited by the population fluctuations of interrogated atoms. (ii) The frequency stability of the active optical clock reaches σy(τ) = 6.2 × 10-15τ-1/2, which is close to the quantum noise limit. (iii) The mode spacing of the stabilized microcomb has a shot-noise-limited Allan deviation of σy(τ) = 1.9 × 10-11τ-1/2. Our hybrid scheme may be realized using recently developed technologies in (micro)photonics and atomic physics, paving the way towards on-chip optical frequency comparison, synthesis, and synchronization.

Comparison of disinfection quality in nurseries of Nanjing during 2019-2021 / 中国学校卫生

Objective@#To analyze the disinfection quality and influencing factors of nurseries in Nanjing during 2019-2021, so as to provide a scientific basis for optimizing preventive disinfection strategies and measures in nurseries.@*Methods@#Environmental samples from 389 nurseries in Nanjing from January 2019 to December 2021 were tested, and the change of disinfection quality qualification rate was compared.@*Results@#The overall disinfection qualification rate of nurseries of year 2019-2021 were 96.32%, 95.85% and 94.60%, respectively, showing a downward trend ( χ 2 trend =8.67, P <0.05). Specifically, disinfection qualification rate of object surfaces, staff hands and tableware showed a downward trend, while the disinfection qualification rate of dynamic air showed an upward trend, and the differences were statistically significant ( χ 2 trend =23.17, 12.32, 5.37, 21.48, P <0.05). The total qualification rate of disinfection in Jiangning and Liuhe districts increased during 2019-2021( χ 2 trend =21.46, 24.05, P <0.05).@*Conclusion@#Disinfection quality of nurseries in Nanjing has declined by year during 2019-2021, especially the object surfaces and staff hands. It is urgent to optimize and refine the strategies and measures for preventive disinfection in nurseries, strengthen the training of personnel on disinfection knowledge, and ensure the quality of disinfection in nurseries.

Widely flexible and finely adjustable nonlocal dispersion cancellation with wavelength tuning.

In fiber-based quantum information processing with energy-time entangled photon pairs, optimized dispersion compensation is vital to preserve the strong temporal correlation of the photon pairs. We propose and experimentally verify that, by simply tuning the wavelength of the entangled photon pairs, nonlocal dispersion cancellation (NDC) can provide a widely flexible and finely adjustable solution for optimizing the dispersion compensation, which cannot be reached with the traditional local dispersion cancellation (LDC) instead. By way of example, when a 50 km-long single-mode fiber (SMF) is dispersion compensated by a 6.2-km-long commercial dispersion compensating fiber (DCF) based on the LDC configuration, it will lead to an almost invariant over-compensation in the wavelength range of 1500-1600 nm which restricts the observed temporal coincidence width of the self-developed energy-time entangled photon-pairs source to a minimum of ∼110 ps. While in the NDC configuration, the dispersion compensation can be readily optimized by tuning the signal wavelength to 1565.7 nm and a minimum coincidence width of 86.1 ± 0.7 ps is observed, which is mainly limited by the jitter of the single-photon detection system. Furthermore, such optimized dispersion compensation can also be achieved as the fiber length varies from 48 km to 60 km demonstrating the wide flexibility of NDC. Thanks to these capabilities, elaborate dispersion compensation modules are no longer required, which makes NDC a more versatile tool in fiber-based quantum information and metrology applications.

Single-photon microwave photonics.

With the rapid development of microwave photonics technology, high-speed processing and ultra-weak signal detection capability have become the main bottlenecks in many applications. Thanks to the ultra-weak signal detection capability and the extremely low timing jitter properties of single-photon detectors, the combination of single-photon detection and classical microwave photonics technology may provide a solution to break the above bottlenecks. In this paper, we first report a novel concept of single-photon microwave photonics (SP-MWP), a SP-MWP signal processing system with phase shifting and frequency filtering functionalities is demonstrated based on a superconducting nanowire single photon detector (SNSPD) and a successive time-correlated single photon counting (TCSPC) module. Experimental results show that an ultrahigh optical sensitivity down to -100 dBm has been achieved, and the signal processing bandwidth is only limited by the timing jitter of single-photon detectors. In the meantime, the proposed system demonstrates an ultrahigh anti-interference capability, only the signal which is phase locked by the trigger signal in TCSPC can be extracted from the detected signals combining with noise and strong interference. The proposed SP-MWP concept paves a way to a novel interdisciplinary field of microwave photonics and quantum mechanism, named by quantum microwave photonics.

Implementation of field two-way quantum synchronization of distant clocks across a 7†km deployed fiber link.

The two-way quantum clock synchronization has been shown to provide femtosecond-level synchronization capability and security against symmetric delay attacks, thus becoming a prospective method to compare and synchronize distant clocks with enhanced precision and safety. In this letter, a field test of two-way quantum synchronization between a H-maser and a Rb clock linked by a 7 km-long deployed fiber is implemented by using time-energy entangled photon-pair sources. Limited by the intrinsic frequency stability of the Rb clock, the achieved time stability at 30 s is measured as 32 ps. By applying a fiber-optic microwave frequency transfer technology to build frequency syntonization between the separated clocks, the limit set by the intrinsic frequency stability of the Rb clock is overcome. A significantly improved time stability of 1.9 ps at 30 s is achieved, which is mainly restrained by the low number of acquired photon pairs due to the low sampling rate of the utilized coincidence measurement system. Such implementation demonstrates the high practicability of the two-way quantum clock synchronization method for promoting field applications.

Development and tuning of the microwave resonant cavity of a cryogenic cesium atomic fountain clock.

A cryogenic cesium atomic fountain clock is a novel clock with the microwave cavity and atomic free flight region placed in liquid nitrogen. On the one hand, the blackbody radiation shift is reduced at cryogenic temperature. On the other hand, the vacuum in the atomic free flight region is optimized, and the background gas collision shift reduced. The microwave resonant cavity is the most important unit in a cryogenic cesium atomic fountain clock. Through theoretical and simulative investigation, this study designs the configuration and dimensions for an optimized microwave cavity. Concurrently, experiments reveal the effects of temperature, pressure, humidity, and other factors on the resonant frequency of the microwave cavity. Combining the theoretical and experimental study, we obtain the resonant frequency difference between the microwave cavity in a cryogenic vacuum and at room temperature and ambient pressure. By subtracting this frequency difference, we adjust the microwave cavity for room temperature and ambient pressure, then vacuumize and immerse it in liquid nitrogen for verification and fine tuning. Finally, we determine that the microwave cavity resonant frequency deviation from the clock transition frequency is 10 kHz with an unloaded quality factor of 25 000, which meets the application requirements of the cryogenic cesium atomic fountain clock.

A Compact Laser System for the Pulsed Optically Pumped Rubidium Cell Atomic Clock.

We describe the design and implementation of a compact laser system for the pulsed optically pumped (POP) rubidium (Rb) cell atomic clock. The laser system includes packaged optics for sub-Doppler absorption, acousto-optic modulation and light beam expansion, and dedicated electronics for laser diode reliable single-mode operation and laser frequency stabilization. With beat measurements between two identical laser systems, the laser frequency stability was found to be 3.0×10-12 for averaging times from 1 to 60 s and it reached 3.5×10-12 at 10 000 s averaging time. Based on the compact laser system, the short-term stability of the Rb cell atomic clock in pulsed regime was approximately [Formula: see text], which is in reasonable agreement with the estimated [Formula: see text]. The compact laser system is significant in terms of the development of transportable and high-performance Rb atomic clock prototypes.

The Application of Low-Frequency Transition in the Assessment of the Second-Order Zeeman Frequency Shift.

Second-order Zeeman frequency shift is one of the major systematic factors affecting the frequency uncertainty performance of cesium atomic fountain clock. Second-order Zeeman frequency shift is calculated by experimentally measuring the central frequency of the (1,1) or (-1,-1) magnetically sensitive Ramsey transition. The low-frequency transition method can be used to measure the magnetic field strength and to predict the central fringe of (1,1) or (-1,-1) magnetically sensitive Ramsey transition. In this paper, we deduce the formula for magnetic field measurement using the low-frequency transition method and measured the magnetic field distribution of 4 cm inside the Ramsey cavity and 32 cm along the flight region experimentally. The result shows that the magnetic field fluctuation is less than 1 nT. The influence of low-frequency pulse signal duration on the accuracy of magnetic field measurement is studied and the optimal low-frequency pulse signal duration is determined. The central fringe of (-1,-1) magnetically sensitive Ramsey transition can be predicted by using a numerical integrating of the magnetic field "map". Comparing the predicted central fringe with that identified by Ramsey method, the frequency difference between these two is, at most, a fringe width of 0.3. We apply the experimentally measured central frequency of the (-1,-1) Ramsey transition to the Breit-Rabi formula, and the second-order Zeeman frequency shift is calculated as 131.03 × 10-15, with the uncertainty of 0.10 × 10-15.

Pulsed vapor cell atomic clock with a differential Faraday rotation angle detection.

Laser intensity noise is one of the main limiting factors in pulsed vapor cell clocks. To reduce the contribution of the laser intensity noise to detection signal in the pulsed optically pumped atomic clock, a scheme based on the differential Faraday rotation angle is proposed. Theoretically, the Ramsey fringes, the sensitivity of clock frequency to laser intensity fluctuation and the signal to noise ratio for absorption, differential, and Faraday rotation angle methods are calculated and compared. Using a Wollaston prism rotated 45°relative to the incident polarization, and two photodetectors, Ramsey fringes of three detection methods are obtained simultaneously. In the proposed scheme, the long-term Faraday rotation angle fluctuation is 0.66% at 30000s, which is much smaller than fluctuation of traditional absorption signal 3.9% at 30000s. And the contribution of laser intensity noise to clock instability is also reduced. Using optimized photodetector with high common mode rejection ratio, a better performance should be expected. This proposed scheme is attractive for the development of high performance vapor clock based on pulsed optically pumped.

Phase gradient protection of stored spatially multimode perfect optical vortex beams in a diffused rubidium vapor.

We experimentally investigate the optical storage of perfect optical vortex (POV) and spatially multimode perfect optical vortex (MPOV) beams via electromagnetically induced transparency (EIT) in a hot vapor cell. In particular, we study the role that phase gradients and phase singularities play in reducing the blurring of the retrieved images due to atomic diffusion. Three kinds of manifestations are enumerated to demonstrate such effect. Firstly, the suppression of the ring width broadening is more prominent for POVs with larger orbital angular momentum (OAM). Secondly, the retrieved double-ring MPOV beams' profiles present regular dark singularity distributions that are related to their vortex charge difference. Thirdly, the storage fidelities of the triple-ring MPOVs are substantially improved by designing line phase singularities between multi-ring MPOVs with the same OAM number but π offset phases between adjacent rings. Our experimental demonstration of MPOV storage opens new opportunities for increasing data capacity in quantum memories by spatial multiplexing, as well as the generation and manipulation of complex optical vortex arrays.

High-precision nonlocal temporal correlation identification of entangled photon pairs for quantum clock synchronization.

High-precision nonlocal temporal correlation identification in entangled photon pairs is critical to measure the time offset between remote independent time scales for many quantum information applications. The first nonlocal correlation identification was reported in 2009, which extracts the time offset via the algorithm of iterative fast Fourier transformations and their inverse. The best identification resolution is restricted by the peak identification threshold of the algorithm, and thus the time offset calculation precision is limited. In this paper, an improvement for the identification is presented both in resolution and precision via a modified algorithm of direct cross correlation extraction. A flexible resolution down to 1 ps is realized, which is only dependent on the least significant bit resolution of the time-tagging device. The attainable precision is shown to be mainly determined by the inherent timing jitter of single photon detectors, the acquired pair rate, and acquisition time, and a sub-picosecond precision (0.72 ps) has been achieved at an acquisition time of 4.5 s. This high-precision nonlocal measurement realization provides a solid foundation for the field applications of entanglement-based quantum clock synchronization, ranging, and communications.

Quantification of nonlocal dispersion cancellation for finite frequency entanglement.

Benefiting from the unique quantum feature of nonlocal dispersion cancellation (NDC), the strong temporal correlation of frequency-entangled photon pair source can be maintained from the unavoidable dispersive propagation. It has thus played a major role in many fiber-based quantum information applications. However, the limit of NDC due to finite frequency entanglement has not been quantified. In this study, we provide a full theoretical analysis of the NDC characteristics for the photon pairs with finite frequency entanglement. Experimental examinations were conducted by using two spontaneous parametric down-conversion photon pair sources with frequency correlation and anticorrelation properties. The excellent agreement demonstrates the fundamental limit on the minimum temporal correlation width by the nonzero two-photon spectral correlation width of the paired photons, which introduces an inevitable broadening by interaction with the dispersion in the signal path. This study provides an easily accessible tool for assessing and optimizing the NDC in various quantum information applications.

Hybrid frequency-time spectrograph for the spectral measurement of the two-photon state.

In this Letter, a hybrid frequency-time spectrograph combining a tunable optical filter and a dispersive element is presented for measurement of the spectral properties of the two-photon state. In comparison with the previous single-photon spectrograph utilizing the dispersive Fourier transformation (DFT) technique, this method is advanced since it avoids the need for additional wavelength calibration and the electronic laser trigger for coincidence measurement; therefore, its application is extended to continuous wave (CW) pumped two-photon sources. The achievable precision of the spectrum measurement has also been discussed in theory and demonstrated experimentally with a CW pumped periodically poled lithium niobate (PPLN) waveguide-based spontaneous parametric down-conversion photon source. Such a device is expected to be a versatile tool for the characterization of the frequency entangled two-photon state.

Inherent resolution limit on nonlocal wavelength-to-time mapping with entangled photon pairs.

Nonlocal wavelength-to-time mapping between frequency-entangled photon pairs generated with the process of spontaneous parametric down-conversion is theoretically analyzed and experimentally demonstrated. The spectral filtering pattern experienced by one photon in the photon pair will be non-locally mapped into the time domain when the other photon propagates inside a dispersion-compensation fiber with large group velocity dispersion. Our work, for the first time, points out that the spectral bandwidth of the pump laser will become the dominated factor preventing the improvement of the spectral resolution when the involved group velocity dispersion is large enough, which provides an excellent tool for characterizing the resolution of a nonlocal wavelength-to-time mapping for further quantum information applications.

Larvicididal Activity of Natural Repellents Against the Dengue Vector, Aedes aegypti.

The present research aimed to evaluate the larvicidal activity of several recently discovered natural repellents formulated in lotions against larvae of Aedes aegypti. We used a modified larval bioassay method by the World Health Organization standards in evaluating larval mortality at 24-, 48-, and 72-h exposure. Among the test repellents, 2-undecanone showed 100% mortality of Ae. aegypti larvae, followed by catnip oil, capric acid, coconut oil fatty acids, methyl caprate, methyl laurate, and coconut oil methyl esters. The repellent, 2-undecanone showed median lethal concentration (LC50) values of 73.07, 26.45, and 15.68 ppm at 24-, 48-, and 72-h exposure, respectively. Larvicidal activity varied among the other repellents tested.

Microwave Pulse-Coherent Technique-Based Clock With a Novel Magnetron-Type Cavity.

We report a high-performance pulsed optically pumped (POP) Rb clock based on a novel magnetron-type microwave cavity. The cavity has a volume of 30 mL, enabling a highly homogenous microwave field distribution. With the laser frequency tuning to the ground-state hyperfine level F = 2 of the D2 line, we observe a Ramsey fringe contrast of 52% in terms of optical absorption detection. The resultant shot noise limit is estimated to be [Formula: see text]. The clock frequency stability is measured as [Formula: see text] (1-100 s), which is limited by the relative intensity noise of the light.