Weak Pulse Research Articles

Single-pulse Emission Variation of Two Pulsars Discovered by FAST

We investigate the single-pulse emission variations of two pulsars, PSRs J0211+4235 and J0553+4111, observed with the Five-hundred-meter Aperture Spherical radio Telescope at the 1.25 GHz central frequency. The observation sessions span from 2020 December to 2021 July, with 21 and 22 observations for them respectively. The integrated pulse profile of PSR J0211+4235 shows that there is a weak pulse component following the main component, and PSR J0553+4111 displays a bimodal profile with a bridge component in the middle. PSR J0211+4235 presents significant nulling phenomenon with nulling duration lasting from 2 to 115 pulses and burst duration lasting from 2 to 113 pulses. The NF of each observation is determined to be 45%–55%. No emission greater than three σ is found in the mean integrated profile of all nulling pulses. In most cases, the pulse energy changes abruptly during the transition from null to burst, while in the transition from burst to null there are two trends: abrupt and gradual. We find that the nulling phenomenon of PSR J0211+4235 is periodic by the Fourier transform of the null and burst state. In addition, the single-pulse modulation characteristics of these two pulsars are investigated, and the distributions of modulation index, LRFS and 2DFS are analyzed with PSRSALSA. The left peak of PSR J0553+4111 has intensity modulation. Finally, the polarization properties of these two pulsars are obtained through polarization calibration, and their characteristics are analyzed. The possible physical mechanisms of these phenomena are discussed.

Overcoming Fundamental Bounds on Quantum Conference Key Agreement

Twin-Field Quantum Key Distribution (TF-QKD) enables two distant parties to establish a shared secret key, by interfering weak coherent pulses (WCPs) in an intermediate measuring station. This allows TF-QKD to reach greater distances than traditional QKD schemes and makes it the only scheme capable of beating the repeaterless bound on the bipartite private capacity. Here, we generalize TF-QKD to the multipartite scenario. Specifically, we propose a practical conference key agreement (CKA) protocol that only uses WCPs and linear optics and prove its security with a multiparty decoy-state method. Our protocol allows an arbitrary number of parties to establish a secret conference key by single-photon interference, enabling it to overcome recent bounds on the rate at which conference keys can be established in quantum networks without a repeater.

High-altitude Magnetospheric Emissions from Two Pulsars

We discover three new weak pulse components in two known pulsars, one in PSR J0304+1932 and two in PSR J1518+4904. These components are emitted about halfway between the main emission beam and the interpulse beam (beam from the opposite pole). They are separated from their main pulse peak by 99° ± 3° for J0304+1932 and 123.°6 ± 0.°7 (leading) and 93° ± 0.°4 (trailing) for J1518+4904. Their peak-intensity ratios to main pulses are ∼ 0.06% for J0304+1932 and ∼0.17% and ∼0.83% for J1518+4904. We also analyzed the flux fluctuations and profile variations of the emissions for the two pulsars. The results show correlations between the weak pulses and their main pulses, indicating that these emissions come from the same pole. We estimated the emission altitude of these weak pulses and derived a height of about half of the pulsar’s light-cylinder radius. These pulse components are a unique sample of high-altitude emissions from pulsars, and challenge the current pulsar emission models.

Discussion of Acute Deficiency Syndrome Theory and its Clinical Application

Discussion of Acute Deficiency Syndrome Theory and its Clinical Application

(Invited) Two-color soliton meta-atoms and molecules

We present a detailed overview of the physics of two-color soliton molecules in nonlinear waveguides, i.e. bound states of localized optical pulses which are held together due to an incoherent interaction mechanism. The mutual confinement, or trapping, of the subpulses, which leads to a stable propagation of the pulse compound, is enabled by the nonlinear Kerr effect. Special attention is paid to the description of the binding mechanism in terms of attractive potential wells, induced by the refractive index changes of the subpulses, exerted on one another through cross-phase modulation. Specifically, we discuss nonlinear-photonics meta atoms, given by pulse compounds consisting of a strong trapping pulse and a weak trapped pulse, for which trapped states of low intensity are determined by a Schr\"odinger-type eigenproblem. We discuss the rich dynamical behavior of such meta-atoms, demonstrating that an increase of the group-velocity mismatch of both subpulses leads to an ionization-like trapping-to-escape transition. We further demonstrate that if both constituent pulses are of similar amplitude, molecule-like bound-states are formed. We show that z-periodic amplitude variations permit a coupling of these pulse compound to dispersive waves, resulting in the resonant emission of Kushi-comb-like multi-frequency radiation.

Dielectric modulation strategy of carbon nanotube field effect transistors based pressure sensor: towards precise monitoring of human pulse

Continuous monitoring of arterial pulse has great significance for detecting the early onset of cardiovascular disease and assessing health status, while needs pressure sensors with high sensitivity and signal-to-noise ratio (SNR) to accurately capture more health information concealed in pulse waves. Field effect transistors (FETs) combined with the piezoelectric film is an ultrahigh sensitive pressure sensor category, especially when the FET works in the subthreshold regime, where the signal enhancement effect on the piezoelectric response is the most effective. However, controlling the work regime of FET needs extra external bias assistance which will interfere with the piezoelectric response signal and complicate the test system thus making the scheme difficult to implement. Here, we described a gate dielectric modulation strategy to match the subthreshold region of the FET with the piezoelectric output voltage without external gate bias, finally enhancing the sensitivity of the pressure sensor. A carbon nanotube field effect transistor and polyvinylidene fluoride (PVDF) together form the pressure sensor with a high sensitivity of 7 × 10−1 kPa−1 for a pressure range of 0.038–0.467 kPa and 6.86 × 10−2 kPa−1 for a pressure range of 0.467–15.5 kPa, SNR, and the ability to continuously monitor pulse in real-time. Additionally, the sensor enables high-resolution detection of weak pulse signals under large static pressure.

Undiagnosed Takayasu Arteritis in Pregnancy

Takayasu arteritis is a chronic inflammation involving large vessels and it often occurs in young women of childbearing age. We described a case of a 29- year- old lady with previous history of proliferative ischemic retinopathy was noted to have low upper limbs blood pressure and weak upper limb pulses postpartumly. An urgent CT angiogram of thorax revealed features suggestive of large vessel vasculitis with involvement of ascending arch, descending aorta and its main branches, corresponding to type II TA . She was diagnosed to have Takayasu arteritis post delivery, and she underwent a successful pregnancy without intrapartum and postpartum complications. High index of suspicion must be given for pregnant patient who have persistent low blood pressure and weak pulse for early detection to avoid severe complications.

Stabilization of modulation instability by control field in semiconductor quantum wells

This article explores the modulation instability of a continuous or quasi-continuous weak probe pulse in a three-level asymmetric double quantum wells under an electromagnetically induced transparency regime, controlled by a strong laser beam. The dynamics of modulation instability reveals that the instability gain as well as its bandwidth is greatly influenced by control field Rabi frequency. The probe pulse is found to be almost stable against modulation instability for higher values of control field Rabi frequency. The results of this investigation may potentially apply for oscillation free generation of supercontinuum in quantum well nanostructures.

Aperiodic stochastic resonance in a biased monostable system excited by different weak aperiodic pulse signals and strong noise

Aperiodic stochastic resonance in a biased monostable system excited by different weak aperiodic pulse signals and strong noise

Model of a New Peripheral Near-Surface Magmanic Chamber of the Elbrus Volcanic Center

Intracrustal magmatic structures have pronounced resonant properties, due to which these structures are able to generate secondary seismic waves at their own frequencies. Based on strain data obtained with a 75-meter laser interferometer ‒ strainmeter, resonance modes are identified and parameters of magmatic structures of the Elbrus volcanic center are estimated. Such resonant modes are unique for each magmatic formation and determine the size and physical-mechanical properties of this magmatic structure. This paper analyzes the local formation, which manifested itself as a some compact area of numerous weak seismic pulses registered in the Elbrus region by the seismometers of the Geophysical Service of the Russian Academy of Sciences in 2011. The results of studies based on seismic and strain data, as well as the results of microseismic sounding, showed the presence of a new peripheral near-surface magmatic chamber in the Elbrus volcanic center. The characteristic size of this new magmatic chamber is 2.5‒3 km.

Coaxial pump-probe measurement using color-selective double pulses generated by a spatial-light-modulator-based optical pulse shaper

Coaxial time-resolved spectroscopy (TRS) based on a pump–probe technique using a color-selective double pulse (CSDP) is proposed. The CSDP, generated using an optical pulse shaper (OPS), was composed of different spectral components. Coaxially propagating CSDPs were used for pump and weak probe pulses. As a proof of concept, we evaluated the transient absorption of a ZnTe crystal from the difference between the temporal waveforms of the output chirped probe pulse with and without pump pulse using the OPS. Upon changing the pulse width of the probe pulse, the measured temporal width of the reaction was 0.2 ps, which agreed with that measured via conventional TRS.

Forearm compartment syndrome after a trans-ulnar coronary intervention in a patient with ST segment elevation myocardial infarction

Compartment syndrome is a very rare but possibly devastating complication of coronary angiography when a trans-radial approach is used. The trans-ulnar approach is an attractive option in cases with anatomic variations of the radial artery or weak radial pulses. Even though it is expected that the trans-ulnar approach has a similar risk of developing compartment syndrome like trans-radial approach, the literature does not have many case reports describing this complication. Here we report a case of a woman who developed forearm compartment syndrome after trans-ulnar coronary intervention in the setting of ST-segment elevation myocardial infarction.

Receiver sensitivity of type-I return-to-zero signals having finite extinction ratios.

In this two-part paper, we develop expressions describing the receiver sensitivity of return-to-zero (RZ) signals having finite extinction ratios (ERs) and arbitrary duty cycles. Between the two known ways of modeling RZ signals, this work focuses on the RZ signal composed of strong and weak pulses, which represent marks and spaces, respectively (hereinafter referred to as Type I). Using our derived expressions, we show that the receiver sensitivity of a Type-I RZ signal is independent of the duty cycle if the system performance is limited by signal-dependent noise. Otherwise, there exists an optimum duty cycle for receiver sensitivity. We also quantitatively discuss the varying impact of finite ER on the receiver sensitivity for different duty cycles. We present the experimental results supporting our theoretical analysis.

Generation of a time–bin Greenberger–Horne–Zeilinger state with an optical switch

Multipartite entanglement is a critical resource in quantum information processing that exhibits much richer phenomenon and stronger correlations than in bipartite systems. This advantage is also reflected in its multi-user applications. Although many demonstrations have used photonic polarization qubits, polarization-mode dispersion confines the transmission of photonic polarization qubits through an optical fiber. Consequently, time–bin qubits have a particularly important role to play in quantum communication systems. Here, we generate a three-photon time–bin Greenberger–Horne–Zeilinger (GHZ) state using a 2 × 2 optical switch as a time-dependent beam splitter to entangle time–bin Bell states from a spontaneous parametric down-conversion source and a weak coherent pulse. To characterize the three-photon time–bin GHZ state, we performed measurement estimation, showed a violation of the Mermin inequality, and used quantum state tomography to fully reconstruct a density matrix, which shows a state fidelity exceeding 70%. We expect that our three-photon time–bin GHZ state can be used for long-distance multi-user quantum communication.

Neuronal Dynamics: from Complexity to Simplicity

An analytical study is performed to obtain the phase description of a network of Leaky Integrate-and-Fire (LIF) neurons. We start by discussing the behaviour of single LIF neuron in the presence of a constant current and then derive the corresponding phase oscillator model for some parameters setup. In the case of two identical LIF neurons where the interactions are ruled by the weak pulse input, we determine the analytical expression for the phase response curve. Next, we extend the phase reduction principles to a generic case of N networks of identical LIF neurons. The final model of so-called phase oscillators is widely used to study synchronization in many natural systems. Through numerical simulations, we find an agreement between the LIF neurons and the phase oscillators model.

Photon bound state dynamics from a single artificial atom

The interaction between photons and a single two-level atom constitutes a fundamental paradigm in quantum physics. The nonlinearity provided by the atom leads to a strong dependence of the light–matter interface on the number of photons interacting with the two-level system within its emission lifetime. This nonlinearity unveils strongly correlated quasiparticles known as photon bound states, giving rise to key physical processes such as stimulated emission and soliton propagation. Although signatures consistent with the existence of photon bound states have been measured in strongly interacting Rydberg gases, their hallmark excitation-number-dependent dispersion and propagation velocity have not yet been observed. Here we report the direct observation of a photon-number-dependent time delay in the scattering off a single artificial atom—a semiconductor quantum dot coupled to an optical cavity. By scattering a weak coherent pulse off the cavity–quantum electrodynamics system and measuring the time-dependent output power and correlation functions, we show that single photons and two- and three-photon bound states incur different time delays, becoming shorter for higher photon numbers. This reduced time delay is a fingerprint of stimulated emission, where the arrival of two photons within the lifetime of an emitter causes one photon to stimulate the emission of another.

Multiphoton Ionization Reduction of Atoms in Two-Color Femtosecond Laser Fields.

We report the ionization reduction of atoms in two-color femtosecond laser fields in this joint theoretical-experimental study. For the multiphoton ionization of atoms using a 400nm laser pulse, the ionization probability is reduced if another relatively weak 800nm laser pulse is overlapped. Such ionization reduction consistently occurs regardless of the relative phase between the two pulses. The time-dependent Schrödinger equation simulation results indicate that with the assisted 800nm photons the electron can be launched to Rydberg states with large angular quantum numbers, which stand off the nuclei and thus are hard to be freed in the multiphoton regime. This mechanism works for hydrogen, helium, and probably some other atoms if two-color laser fields are properly tuned.

Revealing Local Temporal Profile of Laser Pulses of Intensity above 1014 W/cm2

We demonstrated a method for in situ temporal characterization of an intense femtosecond laser pulse around its focus where the laser intensity exceeds 1014 W/cm2. Our method is based on the second harmonic generation (SHG) by a relatively weak femtosecond probe pulse and the intense femtosecond pulses under analysis in the gas plasma. With the increase in the gas pressure, it was found that the incident pulse evolves from a Gaussian profile to a more complicated structure featured by multiple peaks in the temporal domain. Numerical simulations of filamentation propagation support the experimental observations of temporal evolution. This simple method can be applied to many situations involving femtosecond laser-gas interaction, when the temporal profile of the femtosecond pump laser pulse with an intensity above 1014 W/cm2 cannot be measured in traditional ways.

PSR-LSTM model for weak pulse signal detection

PSR-LSTM model for weak pulse signal detection

Performance Evaluation of an A Band Differential Absorption LIDAR Model and Inversion for the Ocean Surface Pressure from Low-Earth Orbit

Remote sensing of ocean surface pressure from space is very important, and differential absorption LIDAR and differential absorption radar are only two kinds of remote sensing instruments with this potential. The differential absorption LIDAR works with the integral path mode from the spacecraft in the 400 km low-Earth orbit. The differential optical depth of the oxygen A-band is measured, and then the ocean surface pressure is obtained using a circle-iterative calculation. Performance evaluation of the differential absorption LIDAR model was based on feasibility to the advanced system parameters of the space instrument, whilst weak echo pulse energy at ocean surface yielded random errors in the surface pressure measurement. On the other hand, uncertain atmospheric temperature profiles and water vapor mixture profiles resulted in a primary systematic error in the surface pressure. The error of the surface pressure is sensitive to the jitter of the central frequency of laser emission. Under a strict implementation of the error budget, the time resolution is 6.25 s and the along-orbit distance resolution is 44 km, 625 echoes from ocean surface was cumulatively averaged. Consequently, if the jitter of the central frequency of laser emission exceeded 10 MHz, controlling the error of the surface pressure below 0.1% proved almost hopeless; further, the error could be expected to within 0.1–0.2%; however, the error limited within 0.2–0.3% is an achievable indicator.