Phase Diffusion Rate Research Articles

Individual versus simultaneous estimation of two parameters in a correlated noisy environment

Recently, the phase parametric estimation for a single qubit system driven by a phase noisy laser under non-Markovian dynamics has been reported [Annals of Physics 351, 952 (2014)]. We here generalize the single-parameter estimation to the two-parameter scenario where a two-qubit system is influenced by the classical correlated noisy laser, and compare the performances of two-parameter estimation in both individual and simultaneous strategies by using the quantum Fisher information and the quantum Fisher information matrix, respectively. Our results show the phase parametric estimation precision can be significantly improved due to the memory effect arising from successive applications of the noisy laser. With the memory coefficient μ increasing, the precision of parameter estimation becomes more accurate. Besides, the phase parameter estimation precision can be drastically enhanced by engineering the ratios of classical phase diffusion rate and system-environment coupling strength in both Markovian and non-Markovian regions. Remarkably, we find the simultaneous estimation of two-phase parameters is not always advantageous over the individual strategy.

Promoting Effect of Microwave Field on Gas Phase Diffusion Limited Magnetite Reduction in Carbon Monoxide

To investigate the effect of microwave irradiation on the rate of magnetite reduction while increasing the gas phase diffusion rate limit, the microstructure and kinetics of CO reduction of magnetite powder were studied. The investigation was conducted through microwave irradiation and conventional heating at 900~1100 °C. Under the two heating methods, the iron crystal is selectively reduced and gradually expanded along the direction normal to the length of the ore powder, forming a strip of iron crystal that penetrates the powder and expands outward across the width. The microwave field can effectively improve the sintering of minerals. The changes in Avrami exponents m and k in the reduction process were determined by combining the Johnson–Mehl–Avrami (JMA) model with the lnln method. The microwave field did not change the limiting step. Microwave irradiation proves to be the most effective means to enhance both the initial reduction rate and the rate during the primary iron crystal precipitation phase. The morphology of the iron crystal takes on a dense punctate shape, influenced by the rate of diffusion control.

Effects of rare earth Sc2O3 doping on the phase composition, diffusion rate and conductivity of CaHf1−xScxO3−δproton conductor

To explain the electrochemical performance of Sc2O3 doped orthogonal CaHfO3, in the temperature range of 973 to 1473 K, the conductivity of this series of electrolyte samples in oxygen rich atmosphere and hydrogen rich atmosphere was measured by using the two terminal AC method. The conductivity first increases and then decreases with the increases of Sc2O3 doping amount; it reaches a maximum at the Sc3+ concentration of x = 0.18. Furthermore, doping with Sc3+ improves the conductivity of the electrolyte CaHf1−xScxO3−δ and reduces its conductivity activation energy. By examining the H / D isotope effect and the electromotive force of electrolyte samples, it is found that CaHf1−xScxO3−δ is a pure proton conductor between 973 and 1273 K. Furthermore, the chemical diffusion coefficients of the CaHf1−xScxO3−δ are about 1.25 × 10−6 to 1.61 × 10−5 cm2 s−1 in the temperatures range of 973 to 1473 K, that is to say, the response speed of the CaHf1−xScxO3−δ is very sensitive. Study found that proton is the major carrier in this electrolyte in both a hydrogen rich atmosphere and an oxygen rich atmosphere. Moreover, at higher temperatures of 1373 to 1473 K, positive holes are the primary carriers in an oxygen rich atmosphere.

Effects of external pressure on phase stability and diffusion rate in lithium-ion cells

Lithium-ion battery systems have dynamic diffusivity properties that continuously change as a function of state of charge due to lithium concentration gradients and material phase changes in both electrodes. Additionally, external factors such as pressure and temperature can further influence the ion-diffusion-rate profile with respect to the open-circuit potential resulting in different performance characteristics in different environments. Therefore it is critical to understand the impact of the external enviornment on diffusivity in order to optimize battery performance during usage in extreme conditions, particularly in the case of thin film batteries which are especially susceptible to changes in external pressure. This work investigates the combined effect of low to ambient external pressures and open-circuit potential on electrode diffusion-rate properties. Commercial thin film batteries were subjected to tests in a low-pressure chamber and in a dynamic materials analyzer simulating hydrostatic pressures between 0 and 115 KPa. Under each hydrostatic pressure condition, galvanostatic intermittent titration technique (GITT) was performed to measure the lithium diffusion rate at various states of charge and a method to extract the pressure-dependent component of the diffusivity measurements was developed and evaluated for statistical significance. The results show that the relationship between pressure and the aggregate cell diffusivity does not remain constant throughout the battery’s operating voltage limits. Three regions were found in the open ciricut voltage range in which diffusion displays a positive relation to pressure, no relation to pressure, and an inverse relation to pressure. It’s theorized that the pressure/diffusivity relationship is governed by individual electrode diffusivity and that depending on the state of charge, the effects of either the anode or cathode become more pronouced in the over-all aggregate diffusion rate measurement.

Squeezing of a two-level system due to classical phase noisy laser

Based on the Heisenberg uncertainty relation and the entropy uncertainty relation, the nonclassical effects described by variance squeezing and entropy squeezing for a two-level system driven by a classical phase noisy laser are investigated. Analytical expressions of the variance squeezing and entropy squeezing subjected to the classical phase noisy laser are derived. Our results show that the nonclassical squeezed effects can be protected for a long time in both the Markovian and non-Markovian regions by controlling the ratios between the phase diffusion rate and the system-laser coupling strength. Besides, we also develop an effective strategy to enhance the nonclassical squeezed effects with the help of filtering operation. The underlying physical mechanism to enhance the squeezing is also analyzed.

In operando detection of lithium diffusion behaviors at low temperature in 18650 Li-ion battery anode

Lithium diffusion process in an 18650 cell was investigated in-operando using neutron diffraction. The graphite anode delithiation rate and the amount of discharge capacity during the discharging process were correlated with the temperature and current rate. At room temperature, the lithium diffusion rate in LiC6 phase at the high rate capability (C/5) is same as at low rate capability (C/20), which means that lithium diffusion in LiC6 crystal phase is independent of the current rate in this range during the discharge process. Lowering temperature to −20 °C decreases both the lithium diffusion and capacity, although the latter can be partially recovered by using lower C-rate.

Cell-based computational model of early ovarian development in mice.

Despite its importance to reproduction, certain mechanisms of early ovarian development remain a mystery. To improve our understanding, we constructed the first cell-based computational model of ovarian development in mice that is divided into two phases: Phase I spans embryonic day 5.5 (E5.5) to E12.5; and Phase II spans E12.5 to postnatal day 2. We used the model to investigate four mechanisms: in Phase I, (i) whether primordial germ cells (PGCs) undergo mitosis during migration; and (ii) if the mechanism for secretion of KIT ligand from the hindgut resembles inductive cell-cell signaling or is secreted in a static manner; and in Phase II, (iii) that changes in cellular adhesion produce germ cell nest breakdown; and (iv) whether localization of primordial follicles in the cortex of the ovary is due to proliferation of granulosa cells. We found that the combination of the first three hypotheses produced results that aligned with experimental images and PGC abundance data. Results from the fourth hypothesis did not match experimental images, which suggests that more detailed processes are involved in follicle localization. Phase I and Phase II of the model reproduce experimentally observed cell counts and morphology well. A sensitivity analysis identified contact energies, mitotic rates, KIT chemotaxis strength, and diffusion rate in Phase I and oocyte death rate in Phase II as parameters with the greatest impact on model predictions. The results demonstrate that the computational model can be used to understand unknown mechanisms, generate new hypotheses, and serve as an educational tool.

From Kardar-Parisi-Zhang scaling to explosive desynchronization in arrays of limit-cycle oscillators.

Phase oscillator lattices subject to noise are one of the most fundamental systems in nonequilibrium physics. We have discovered a dynamical transition which has a significant impact on the synchronization dynamics in such lattices, as it leads to an explosive increase of the phase diffusion rate by orders of magnitude. Our analysis is based on the widely applicable Kuramoto-Sakaguchi model, with local couplings between oscillators. For one-dimensional lattices, we observe the universal evolution of the phase spread that is suggested by a connection to the theory of surface growth, as described by the Kardar-Parisi-Zhang (KPZ) model. Moreover, we are able to explain the dynamical transition both in one and two dimensions by connecting it to an apparent finite-time singularity in a related KPZ lattice model. Our findings have direct consequences for the frequency stability of coupled oscillator lattices.

Phase Noise Reduction in an MEMS Oscillator Using a Nonlinearly Enhanced Synchronization Domain

We investigate the phase dynamics of a closed-loop MEMS-based oscillator and demonstrate how one can exploit nonlinear behavior to improve oscillator phase noise characteristics by synchronizing the oscillator with a weak harmonic drive. Analytical predictions are based on an oscillator model that incorporates a resonator element with a weak cubic (i.e., Duffing type) nonlinearity, weak coupling to a clean external harmonic drive, and both thermal and frequency noise terms. The method of stochastic averaging is used to derive an expression for the rate of phase diffusion induced by the noises, and the results predict a remarkable phase noise reduction of three order of magnitude when the oscillator is synchronized to the weak external field. The predictions are experimentally demonstrated using a closed-loop oscillator with a double-anchored double-ended-tuning-fork MEMS resonator with coupling to a small external sinusoidal signal from a signal generator, demonstrating a 30 dB/Hz drop in phase noise. The results show how one can generate a clean high-power signal from a relative noisy oscillator by synchronizing it with a low-power external signal. The results also confirm recent studies showing that the parameter range of synchronization is significantly expanded when the resonator operates in its nonlinear regime. [2016-0067]

Understanding the Synthetic Pathway of a Single-Phase Quarternary Semiconductor Using Surface-Enhanced Raman Scattering: A Case of Wurtzite Cu2ZnSnS4 Nanoparticles

Single-phase Cu2ZnSnS4 (CZTS) is an essential prerequisite toward a high-efficiency thin-film solar cell device. Herein, the selective phase formation of single-phase CZTS nanoparticles by ligand control is reported. Surface-enhanced Raman scattering (SERS) spectroscopy is demonstrated for the first time as a characterization tool for nanoparticles to differentiate the mixed compositional phase (e.g., CZTS, CTS, and ZnS), which cannot be distinguished by X-ray diffraction. Due to the superior selectivity and sensitivity of SERS, the growth mechanism of CZTS nanoparticle formation by hot injection is revealed to involve three growth steps. First, it starts with nucleation of Cu(2-x)S nanoparticles, followed by diffusion of Sn(4+) into Cu(2-x)S nanoparticles to form the Cu3SnS4 (CTS) phase and diffusion of Zn(2+) into CTS nanoparticles to form the CZTS phase. In addition, it is revealed that single-phase CZTS nanoparticles can be obtained via balancing the rate of CTS phase formation and diffusion of Zn(2+) into the CTS phase. We demonstrate that this balance can be achieved by 1 mL of thiol with Cu(OAc)2, Sn(OAc)4, and Zn(acac)2 metal salts to synthesize the CZTS phase without the presence of a detectable binary/ternary phase with SERS.

Spectral properties of a resonator driven by a superconducting single-electron transistor

We analyze the spectral properties of a resonator coupled to a superconducting single electron transistor (SSET) close to the Josephson quasiparticle resonance. Focussing on the regime where the resonator is driven into a limit-cycle state by the SSET, we investigate the behavior of the resonator linewidth and the energy relaxation rate which control the widths of the main features in the resonator spectra. We find that the linewidth becomes very narrow in the limit-cycle regime, where it is dominated by a slow phase diffusion process, as in a laser. The overall phase diffusion rate is determined by a combination of direct phase diffusion and the effect of amplitude fluctuations which affect the phase because the resonator frequency is amplitude dependent. For sufficiently strong couplings we find that a regime emerges where the phase diffusion is no longer minimized when the average resonator energy is maximized. Finally we show that the current noise of the SSET provides a way of measuring both the linewidth and energy relaxation rate.

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.

Phase Diffusion of a q-Deformed Oscillator

We examine the problem of phase diffusion rate in a U(1) global phase symmetry broken system, from the perspective of q-deformed oscillators where the deformation parameter represents the anharmonicity. It is shown that broken phase symmetry states, described by deformed coherent states, suffer phase diffusion at a rate determined by the deformation parameter. Analytical discussions are given for the case of weak deformations, while detailed numerical results are presented when strong anharmonicity is present in the system.

Laser phase noise quenching via squeezed vacuum reservoir

It is shown by Gea-Banacloche [Phys. Rev Lett. 59, 543 (1987)] that the Laser Phase diffusion rate may be reduced by as much as one-half when laser is coupled out through a partially transmitting mirror to ``squeezed vacuum'' as opposed to ordinary vacuum. This happens for a particular choice of the phase of the squeezed field. However, phase stability is not achieved for this choice of phase. In this paper, this analysis is extended by including a separate squeezed vacuum reservoir which couples the spontaneous decay between the lasing levels. The results show that, it is possible to obtain the phase stability as well as phase noise quenching in this system.

Micromaser spectrum and phase diffusion dynamics

We discuss a scheme to relate the phase diffusion dynamics of the micromaser field to the measured atomic population statistics. This can allow us to measure the linewidth of the micromaser spectrum and to solve a relevant decoherence problem in cavity quantum electrodynamics. The main steps are (i) a suitable preparation of the cavity field state to generate coherences, (ii) the transfer of information on the dynamics of field coherences to probe atoms by the action of an external resonant coherent field and (iii) the derivation of the phase diffusion rate, hence the micromaser linewidth, from the measured population statistics of the probe atoms. The method can be applied even in the presence of trapping states, wher ep eculiar linewidth oscillations are expected for increasing pump rate, due to the quantum nature of the micromaser field.

Quantum theory of an exciton condensate subject to radiative decay

Semiconductor excitons obey Bose-Einstein statistics in the low-density limit. In this paper, a two-level quantum model for an exciton condensate subject to radiative decay is presented. The condensate state has a well-defined exciton number and a slow phase diffusion rate analogous to a coherent state created by a (photon) laser. Since excitons recombine radiatively, the statistics of the device can be observed by photodetection. Our analytical and numerical results at steady state reveal that the change in population statistics of the ground state is gradual across the threshold region, above which a condensate forms. When radiative losses are present, the condensate mode is ``quasicoherent;'' in the limit of no losses a coherent state is approached. Far below threshold the ground state is well described by a thermal distribution. The higher level, that is the ``pump,'' remains thermally distributed at all times.

Coherent population trapping of Bose-Einstein condensates: Detection of phase diffusion

Two Bose-Einstein condensates in different Zeeman sublevels can be decoupled from driving light fields in coherent population trapping. A condensate pair with a deterministic entanglement and a controllable value of the relative phase may be prepared by selecting the phase difference between the coherent light fields. The rate of the condensate phase diffusion may be determined from the two-photon resonant absorption of radiation.

Relaxation and 1/f noise in phonon systems

This paper examines the relationships that exist between low-frequency fluctuations of the rate of dissipation in nonequilibrium thermodynamic systems and higher-order multitime statistical moments of equilibrium noise. In particular, it studies the relationships between internal friction fluctuations in the phonon system being excited and low-frequency fluctuations of Raman scattering of light in an equilibrium phonon system. We show that both processes are related to strong fluctuations in the phase diffusion rate and the relaxation of phonon modes generated, in turn, by the exponential instability of the dynamical paths of the system.

Micromaser linewidth

In earlier papers, the linewidth of a micromaser was approximated by a phase diffusion rate that was obtained using a single decay rate assumption to model the decay of the electric field in the micromaser cavity. These methods gave analytic but approximate answers. Exact methods calculated the spectrum via the two-time correlation function, but required extensive numerical calculations. In this paper, we present an approximate analytic derivation of the micromaser spectrum via the two-time correlation function that is more accurate than other approximate analytic methods yet requires much less numerical calculation than the exact methods. We also review the other methods, both analytical and exact, and present numerical comparisons.

An atom laser based on evaporative cooling

An atom laser is a device which would ideally produce a coherent excitation of a single mode of the Bose-atom field. That is to say, an atom laser field would have a well defined number of atoms, and a slow rate of phase diffusion. Here we consider an atom laser model recently proposed by Holland et al, based on evaporative cooling of atoms. We extend their model, and give approximate analytical results for the time-dependent intensity and phase statistics of the atom laser in different regimes. Although the intensity fluctuations may be relatively small, the laser linewidth is always in excess of the bare linewidth of the laser mode. Nevertheless, in one regime (weak collisions), the laser linewidth may be less than the output flux of atoms, which is a minimum requirement for considering the output to be coherent.