Noise transfer of pump field noise with analysis frequency in a broadband parametric downconversion process

Our previous work had proved pump field noise coupling in the seed field injected optical parametric amplifier(OPA) at a certain analysis frequency. Inspired by this noise coupling mechanism, the frequency dependent squeezing factor due to excess pump noise was experimentally demonstrated. Apart from a reduced squeezing level with an increased noise, the results also prove that a broadband squeezing noise spectrum is not frequency dependent on the amplitude modulated pump field, but limited by the bandwidth of the amplitude modulator and OPA resonator, and the effective measurement is carried out in the frequency range of 2–10 MHz. It provides a guidance to design a broader-bandwidth, higher-level bright squeezed light.     

Theory of noise in a kilo-Hz cascaded high-energy Yb-doped nanosecond pulsed fiber amplifier

A theoretical analysis of noise in a high-power cascaded fiber amplifier is presented. Unlike the noise theory in low power communication, the noise of a high power system is redefined as the leaked output energy between pulses with coherent beat noise uncounted. This definition is more appropriate for high power usage in which the pulse energy receives more attention than the pulse shape integrity. Then the low power pre-amplifying stages are considered as linear amplification and analyzed by linear theory. In the high-power amplification stages, the inversion is assumed to recover linearly in the time interval between pulses. The time shape of the output pulse is different from that of the input signal because of different gains at the front and back ends of the pulse. Then, a criterion is provided to distinguish the nonlinear and linear amplifications based on the signal-to-noise ratio （SNR） analysis. Then, an experiment that shows that the output SNR actually drops off in nonlinear amplification is performed. The change in the noise factor can be well evaluated by pulse shape distortion.     

Unusual electronic structure of Dirac material BaMnSb_2 revealed by angle-resolved photoemission spectroscopy

High resolution angle resolved photoemission measurements and band structure calculations are carried out to study the electronic structure of BaMnSb_2. All the observed bands are nearly linear that extend to a wide energy range. The measured Fermi surface mainly consists of one hole pocket around Γ and a strong spot at Y which are formed from the crossing points of the linear bands. The measured electronic structure of BaMnSb_2 is unusual and deviates strongly from the band structure calculations. These results will stimulate further efforts to theoretically understand the electronic structure of BaMnSb_2 and search for novel properties in this Dirac material.     

Generation of a squeezed state at 1.55 μm with periodically poled LiNbO3

We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO 3.Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm,the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained.This system is compatible with standard telecommunication optical fibers,and will be useful for continuous variable long-distance quantum communication and distributed quantum computing.     

Frequency synthesis of forced opto-electronic oscillators at the X-band

Ultra-low phase noise performance is required for frequency agile local oscillators, which are the core for high resolution imagers, spectrum analyzers, and high speed data communications. A forced opto-electronic oscillator(OEO) benefits from frequency stabilization techniques for realizing a clean and low phase noise source at microwave and millimeter wave frequencies. Forced oscillation techniques of self-injection locking and self-phase lock loop are combined to provide an ultra-low oscillator phase noise both close-in and far-away from the carrier frequency, while a tunable yttrium iron garnet microwave filter combined with a wavelength tuned transversal filter are employed to implement both coarse and fine frequency tuning for a tunable X-band OEO. A phase noise of-137 dBc∕Hz at an offset frequency of 10 kHz is achieved covering the frequencies of 9 to 11 GHz with a fine frequency tuning resolution of 44 Hz/pm and coarse tuning of 25 MHz/m A. Moreover, the long term stability of the output signal is tested, and a maximum frequency drift of 2 kHz is measured within 60 min for the X-band synthesizer.     

Generation of a squeezed state at 1.55 μm with periodically poled LiNbO₃

We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO 3.Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm,the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained.This system is compatible with standard telecommunication optical fibers,and will be useful for continuous variable long-distance quantum communication and distributed quantum computing.     

Generating EPR-entangled mechanical state via feeding finite-bandwidth squeezed light

Einstein–Podolski–Rosen(EPR) entanglement state is achievable by combining two single-mode position and momentum squeezed states at a 50:50 beam-splitter(BS). We investigate the generation of the EPR entangled state of two vibrating membranes in a ring resonator, where clockwise(CW) and counter-clockwise(CCW) travelling-wave modes are driven by lasers and finite-bandwidth squeezed lights. Since the optomechanical coupling depends on the location of the membranes, CW and CCW can couple to the symmetric and antisymmetric combination of mechanical modes for a suitable arrangement, which corresponds to a 50:50 BS mixing. Moreover, by employing the red-detuned driving laser and tuning the central frequency of squeezing field blue detuned from the driving laser with a mechanical frequency, the squeezing property of squeezed light can be perfectly transferred to the mechanical motion in the weak coupling regime. Thus, the BS mixing modes can be position and momentum squeezed by feeding the appropriate squeezed lights respectively, and the EPR entangled mechanical state is obtained. Moreover, cavity-induced mechanical cooling can further suppress the influence of thermal noise on the entangled state.     

Phase Noise Quenching in a Four-Level Laser

In the presence of usual transmission losses, it is shown that phase noise in a four-level laser can be reduced below the Schawlow-Townes limit when lasing levels are coupled to a squeezed vacuum reservoir. The squeezed vacuum coupled to the lasing mode modifies the phase diffusion rate and dominates the contribution from transmission losses. It is predicted to obtain phase stability in the system and phase noise vanishes for larger squeezing. Gain of the laser remains positive under these conditions.     

PITCH DISCRIMINATION OF NARROW-BAND NOISE IN GUINEA PIGS

Frequency modulation of a narrow band noise evokes slow cortical responses(SCR)in guinea pigs just asfrequency modulation of pure tone does.Pitch difference limen of the narrow band noise can thus beeasily obtained by measuring the SCR threshold in terms of modulation depth.In guinea pigs values arefound to be noise hand-width(B) and central frequency(f)dependent and the f-B correlation can beexpressed as f=AB"where A is the key value of ffor a given fat B=1 Hzand,for f's of 1 kHz and 4 kHz,napproximates to 1/3.The f/f ratio is essentially a constan for all test f's ranging from 125 Hz to 8 kHz,provided Bis set sccording to a fixed B/frate.This is a very good demonstration of the Weber's law in respectto pitch discrimintion.For expressing the overall f-f-B relationship in guinea pigs a simple empiricalformula,f=0.1 f~(2/3)B~(1/3),is proposed,with which the calculated f values are quite close to theexperimentally obtained data.     

Stochastic Resonance in a Single - Mode Laser Driven by Pump Noise and Quantum Noise with Cross-Correlated Real and Imaginary Parts

We present an analytic investigation of the signal-to-noise ratio (SNR) by studying a signal modulated model of a single-mode laser system driven by pump noise and quantum noise with correlated real and imaginary parts,and find there is a maximum in the curve of the dependence of SNR upon the cross-correlation coefficient λq between the real part and the imaginary part, i.e., stochastic resonance appears in the SNR vs. λq curve. Moreover, when the SNR is at the maximum, the cross-correlation coefficient λq = 0, which is coincidentally at the minimum of the mean normalized intensity fluctuation. The influences on stochastic resonance by the intensities of the pump and the quantum noise, the amplitude of the modulation signal, and the net gain of the laser are also studied. Furthermore, in order to ensure that the results obtained in this paper is reliable, the valid range for the linear approximation method is discussed.     

Bias phase and light power dependence of the random walk coefficient of fiber optic gyroscope

Taking account of shot noise, thermal noise, dark current noise, and intensity noise that come from broad band light source, the dependence of the random walk coefficient of fiber optic gyroscope (FOG) on bias phase and light power is studied theoretically and experimentally. It is shown that with different optical and electronic parameters, the optimal bias phase is different and should be adjusted accordingly to improve the FOG precision. By choosing appropriate bias phase, the random walk coefficient of the aim FOG is reduced from 0.0026 to 0.0019 deg./h1/2.     

INVESTIGATION ON THE VALEN CE STATE OF Ce ATOM IN BULK AND nANOCRYSTAL CeO2 BY X—RAY ABSORPTION AND PHOTOEMISSION

Valence band photoemission spectra(PES) for both bulk and nanocrystal CeO2 have been masured on and off resonance of Ce 4d-4f absorption edge.The PES show that the bulk and nanocrystal CeO2 of diameter ranging from 8nm to 50nm exhibit a peak near Fermi edge with binding energy of abiyt 1.8eV peak shows a strong dependence on excitation energy,although it looks like the contribution of Ce^3 ion following the data reported in literatures.However,According to the results of resonance photoemission and X-ray absorption spectra at O 1s edge,this electronic structure may be associated to the intermediate state charge transfer effcets.     

Bias phase and light power dependence of the random walk coefficient of fiber optic gyroscope

Taking account of shot noise, thermal noise, dark current noise, and intensity noise that come from broad band light source, the dependence of the random walk coefficient of fiber optic gyroscope (FOG) on bias phase and light power is studied theoretically and experimentally. It is shown that with different optical and electronic parameters, the optimal bias phase is different and should be adjusted accordingly to improve the FOG precision. By choosing appropriate bias phase, the random walk coefficient of the aim FOG is reduced from 0.0026 to 0.0019 deg./h~(1/2).     

The power spectrum and correlation of flow noise for an axisymmetric body in water

Understanding the physical features of the flow noise for an axisymmetric body is important for improving the performance of a sonar mounted on an underwater platform. Analytical calculation and numerical analysis of the physical features of the flow noise for an axisymmetric body are presented and a simulation scheme for the noise correlation on the hydrophones is given. It is shown that the numerical values of the flow noise coincide well with the analytical values. The main physical features of flow noise are obtained. The flow noises of two different models are compared and a model with a rather optimal fore-body shape is given. The flow noise in horizontal symmetry profile of the axisymmetric body is non-uniform, but it is omni-directional and has little difference in the cross section of the body. The loss of noise diffraction has a great effect on the flow noise from boundary layer transition. Meanwhile, based on the simulation, the noise power level increases with velocity to approximately the fifth power at high frequencies, which is consistent with the experiment data reported in the literature. Furthermore, the flow noise received by the acoustic array has lower correlation at a designed central frequency, which is important for sonar system design.     

Stochastic Resonance in a Single-Mode Laser Driven by Pump Noise and Quantum Noise with Cross-Correlated Real and Imaginary Parts

We present an analytic investigation of the signal-to-noise ratio (SNR) by studying a signal modulated model of a single-mode laser system driven by pump noise and quantum noise with correlated real and imaginary parts,and find there is a maximum in the curve of the dependence of SNR upon the cross-correlation coefficient λq between the real part and the imaginary part, i.e., stochastic resonance appears in the SNR vs. λq curve. Moreover, when the SNR is at the maximum, the cross-correlation coefficient λq = O, which is coincidentally at the minimum of the mean normalized intensity fluctuation. The influences on stochastic resonance by the intensities of the pump and the quantum noise, the amplitude of the modulation signal, and the net gain of the laser are also studied. Furthermore, in order to ensure that the results obtained in this paper is reliable, the valid range for the linear approximation method is discussed.     

Generation of a squeezed state at 1.55 μ with periodically poled LiNbO3

We report on the generation of a squeezing vacuum at 1.55 μm using an optical parametric amplifier based on periodically poled LiNbO₃. Using three specifically designed narrow linewidth mode cleaners as the spatial mode and noise filter of the laser at 1.55 μm and 775 nm, the squeezed vacuum of up to 3.0 dB below the shot noise level at 1.55 μm is experimentally obtained. This system is compatible with standard telecommunication optical fibers, and will be useful for continuous variable long-distance quantum communication and distributed quantum computing.     

Entanglement Manipulation for a Two-Mode Squeezed Vacuum State

By numerically analysing the entropy of entanglement of the output state from a Mach-Zehnder interferometer for the two-mode squeezed vacuum state input, it is found that if the internal phase shift of the interferometer is adjusted to the value of 0 or 7r, the entangling characteristic of the input state is efficiently preserved at the output. If the internal phase shift is tuned to the value of Tr/2, the two-mode squeezed vacuum state is completely disentangled at the output of the setup. If the internal phase shift deviates from the above values, the input state is degraded into a partially entangled output state. Based on these results, a method for optically realizing the entanglement preservation, entanglement degradation, and disentanglement via the interferometer is obtained.     

Electronic and transport properties of V-shaped defect zigzag MoS_2 nanoribbons

Based on the nonequilibrium Green＇s function （NEGF） in combination with density functional theory （DFT） calcu- lations, we study the electronic structures and transport properties of zigzag MoS2 nanoribbons （ZMNRs） with V-shaped vacancy defects on the edge. The vacancy formation energy results show that the zigzag vacancy is easier to create on the edge of ZMNR than the armchair vacancy. Both of the defects can make the electronic band structures of ZMNRs change from metal to semiconductor. The calculations of electronic transport properties depict that the currents drop off clearly and rectification ratios increase in the defected systems. These effects would open up possibilities for their applications in novel nanoelectronic devices.     

Stochastic resonance in a bistable system with coloured correlation between additive and multiplicative noise

The phenomenon of stochastic resonance (SR) in a bistable nonlinear system with coupling between additive and multiplicative noises is investigated when the correlation between two noise terms is coloured. It is found that the signal-to-noise ratio (SNR) of the system is affected not only by the coupling strength λ between two noise terms, but also by the noise correlation time τ. The SNR is changed from a single peak, to two peaks with a dip, and then to a monotonically decreasing function with noise strength. The dependence of the SR on the initial conditions is entirely caused by the coupling strength λ between two noise terms.     

Terahertz superconducting kinetic inductance detectors demonstrating photon-noise-limited performance and intrinsic generation-recombination noise

The development of large-format detector arrays with background-limited performance is of particular interest at the terahertz(THz) band, which is a unique band in search of our cosmic origins. With high sensitivity and being more promising in the pixel number and multiplexing technology, superconducting kinetic inductance detectors(KID) are emerging as a major choice of detectors of this type. Here we fabricate three-THz-band(0.35/0.85/1.4 THz) KIDs on a single chip from a 120-nm-thick aluminum(Al) superconducting film and measure photon-noise-limited performance and intrinsic generation-recombination noise at high(>1 p W) and low(<1 f W) optical radiation power, respectively. Their responses to blackbody(optical) radiation are proven to be purely from photons compared with the responses of two dark KIDs intentionally arranged on the same detector chip. The lowest optical noise equivalent power(NEP) reaches 6×10^-18W/Hz^0.5and the optical coupling efficiency is in the range of 49%-56% for the three KIDs, which are in good agreement with the simulation results.