Phase Fluctuations Research Articles

Comparison of modified Woo’s solar phase scintillation model with ESA’s BepiColombo superior solar conjunction measurement data for X-band and Ka-band

Solar phase scintillation is of major interest in deep space mission operations for designing a communications system capable of transmitting signals when the path is close to the Sun, but also for improving the navigation under these conditions. The basis of this work is Woo’s solar phase scintillation theory which reported a useful model for the spectral power density of phase scintillations of a signal traveling through a medium close to the Sun. In this paper, Woo’s solar phase scintillation formula is used for the simulation of the spectral density of phase fluctuations induced by the Sun on coherent signals (uplink and downlink carriers are coherently related by a fractional ratio implemented by the spacecraft’s transponder), for the two downlink frequency bands supported by the ESA deep space mission BepiColombo. In particular, the model has been compared to measurement data collected at low Sun Earth Probe (SEP) angles during the superior solar conjunction campaign in March 2021 (in its cruise phase to Mercury). The comparison shows a good match between the phase noise spectral densities of the modified formula and measurement data, therefore, confirming that the formula can be used for the planning and verification of the future near Sun measurements.

Se77 -NMR evidence for spin-singlet superconductivity with exotic superconducting fluctuations in FeSe

Although the nature of the superconducting state has been intensively studied in FeSe, many fundamental issues including the pairing symmetry and superconducting fluctuations are still highly controversial. Here, we report a revised $^{77}\mathrm{Se}$-nuclear magnetic resonance (NMR) study on the superconducting state of $^{77}\mathrm{Se}$-enriched bulk FeSe. Below the superconducting temperature (${T}_{c}$), by carefully avoiding the rf heating effect, a remarkable linewidth broadening and obvious reduction of the Knight shift are observed under external magnetic field along both in-plane and out-of-plane directions, suggesting an intrinsic superconducting nature. These exotic results unambiguously rule out the possibility of chiral $p$-wave pairing, and favor a pairing scenario with the mixing of ${s}^{\ifmmode\pm\else\textpm\fi{}}$ and $d$ wave. A slight decrease of the Knight shift well above ${T}_{c}$ is also revealed under a moderated external magnetic field, suggesting exotic superconducting fluctuations beyond phase fluctuations in the two-dimensional limit. These renewed NMR results provide valuable constraints for the theoretical models on the exotic superconductivity in FeSe.

Emerging Long‐Range Order from a Freeform Disordered Metasurface

Recently, disordered metasurfaces have attracted considerable interest due to their potential applications in imaging, holography, and wavefront shaping. However, how to emerge long-range ordered phase distribution in disordered metasurfaces remains an outstanding problem. Here, a general framework is proposed to generate a spatially homogeneous in-plane phase distribution from a disordered metasurface, by engineering disorder parameters together with topology optimization. As a proof-of-concept demonstration, an all-dielectric disordered supercell metasurface with relatively homogeneous in-plane phase fluctuation is designed by disorder parameter engineering, manifesting as polarization conversion-dependent random scattering or unidirectional transmission. Then, a topology optimization approach is utilized to overcome the lattice coupling effect and to further improve the homogeneity of complex electric field fluctuation. In comparison with the initial supercell metasurface, both the phase fluctuation range and the relative efficiency of the topology-optimized freeform metasurface are significantly improved, leading to a long-range ordered electric field distribution. Moreover, three experimental realizations are performed, all of which agree well with the theoretical results. This methodology may inspire more exotic optical phenomena and find more promising applications in disordered metasurfaces and disorderedoptics.

Spatial emergence of off-diagonal long-range order throughout the BCS-BEC crossover

In a superfluid system, Off-Diagonal Long-Range Order (ODLRO) is expected to be exhibited in the appropriate reduced density matrices when the relevant particles (either bosons or fermion pairs) are considered to recede sufficiently far apart from each other. This concept is usually exploited to identify the value of the condensate density, without explicit concern, however, on the spatial range over which this asymptotic condition can effectively be achieved. Here, based on a diagrammatic approach that includes beyond-mean-field pairing fluctuations in the broken-symmetry phase at the level of the $t$-matrix also with the inclusion of the Gorkov-Melik-Barkhudarov (GMB) correction, we present a systematic study of the two-particle reduced density matrix for a superfluid fermionic system undergoing the BCS-BEC crossover, when the entities to recede far apart from each other evolve with continuity from largely overlapping Cooper pairs in the BCS limit to dilute composite bosons in the BEC limit. By this approach, we not only provide the coupling and temperature dependence of the condensate density at the level of our diagrammatic approach which includes the GMB correction, but we also obtain the evolution of the spatial dependence of the two-particle reduced density matrix, from a power-law at low temperature to an exponential dependence at high temperature in the superfluid phase, when the inter-particle coupling spans the BCS-BEC crossover. Our results put limitations on the minimum spatial extent of a finite-size system for which superfluid correlations can effectively be established.

Coherent fibre link for synchronization of delocalized atomic clocks.

Challenging experiments for tests in fundamental physics require highly coherent optical frequency references with suppressed phase noise from hundreds of kHz down to μHz of Fourier frequencies. It can be achieved by remote synchronization of many frequency references interconnected by stabilized optical fibre links. Here we describe the path to realize a delocalized optical frequency reference for spectroscopy of the isomeric state of the nucleus of Thorium-229 atom. This is a prerequisite for the realization of the next generation of an optical clock - the nuclear clock. We present the established 235 km long phase-coherent stabilized cross-border fibre link connecting two delocalized metrology laboratories in Brno and Vienna operating highly-coherent lasers disciplined by active Hydrogen masers through optical frequency combs. A significant part (up to tens of km) of the optical fibre is passing urban combined collectors with a non-negligible level of acoustic interference and temperature changes, which results in a power spectral density of phase noise over 105 rad2· Hz-1. Therefore, we deploy a digital signal processing technique to suppress the fibre phase noise over a wide dynamic range of phase fluctuations. To demonstrate the functionality of the link, we measured the phase noise power spectral density of a remote beat note between two independent lasers, locked to high-finesse stable resonators. Using optical frequency combs at both ends of the link, a long-term fractional frequency stability in the order of 10-15 between local active Hydrogen masers was measured as well. Thanks to this technique, we have achieved reliable operation of the phase-coherent fibre link with fractional stability of 7 × 10-18 in 103 s.

Abstract TP262: Effect Of Prehospital Blood Pressure Fluctuations On Early Neurological Changes In Acute Ischemic Stroke Patients With Large Vessel Occlusion

Introduction: Blood pressure fluctuations in the acute phase of large vessel occlusion (LVO) ischemic stroke are associated with infarct progression and poor outcomes. We evaluated the association of prehospital blood pressure variations on a Mobile Stroke Unit (MSU) with early neurological change. Methods: Prospectively-derived data were analyzed from tPA-eligible LVO patients treated and transported on the MSU, identified by hyperdense artery on CT or arterial occlusion on CTA. Patients were categorized by change in mean arterial pressure (ΔMAP) of > 10 mm Hg vs Δ MAP < 10 mmHg from arrival of MSU on-scene to arrival to the emergency department (ED). A sub-analysis of patients with ΔMAP > 10 mm Hg compared those whose MAP decreased by > 10 mm Hg vs those whose MAP increased by > 10 mm Hg. The primary outcome was 24-hour change in NIHSS. Groups were compared using Chi-square/Fisher’s exact test for categorical variables and Wilcoxon rank sum test for continuous variables. Results: A total of 39 tPA-eligible LVO patients were identified, 19 with ΔMAP < 10mm Hg and 20 with ΔMAP > 10mm Hg. Baseline characteristics were comparable between groups including NIHSS (18.0 [11.0, 21.0] vs 20.0 [16.8, 25.8]) (Table 1). A similar percentage from each group received tPA and thrombectomy. Upon presentation to ED, 7/19 (37%) patients with ΔMAP < 10mm Hg had a 30% improvement in NIHSS, compared to 4/20 (20%) patients with ΔMAP >10mm Hg (p=0.417). The 24-hour change in NIHSS was also similar (ΔMAP < 10mm Hg = 7.0 [3.5, 12.0] vs ΔMAP > 10 mm Hg 10.0 [4.0, 16.0], p=0.517). Among patients with ΔMAP of 10mm Hg group, those with MAP decrease by > 10 mm Hg had a 10 point [7.0, 16.0] improvement in NIHSS vs 6.0 [2.5, 15.0] point improvement in those whose MAP increased by > 10 mm Hg (p=0.169). Conclusion: Though limited by a small sample size, prehospital blood pressure fluctuations in LVO stroke patients on a MSU were not associated with early clinical changes.

Investigating the impact of the latitudinal velocity profile on nonlinear gradient drift instability development in the subauroral ionosphere

Subauroral polarization streams (SAPS) are regions in the subauroral ionosphere with lower plasma density and large westward flow driven by a poleward electric field. Density irregularities have been observed in the SAPS region; these irregularities can negatively impact radio signals by causing phase and amplitude fluctuations. Previous work identified the gradient drift instability (GDI) as a generation mechanism of such ionospheric irregularities in SAPS and investigated the impact of the velocity profile on the GDI development. The turbulence spectra of the GDI are important to understand as they can provide insight into spatial scales associated with the turbulent evolution that may impact radio propagation. We hypothesize that the background electric field, through the neutral wind, and the nature of the velocity shear have an impact on the power laws from the turbulence spectra. A 2D fluid model is used to investigate the turbulence spectra of GDI in SAPS with a fixed background density profile and different latitudinal velocity profiles. Data from Super Dual Auroral Radar Network (SuperDARN) radar and Global Positioning System (GPS) provide the background ionospheric conditions. The neutral wind direction is chosen to be in the equatorward direction, which is in line with typical observations; however, this can be used to modify the electric field to consider new possibilities in the SAPS region. The angle of the electric field is manifested through the combination of the background velocity profile ( drift) and the neutral wind. The turbulence spectra of cases with no velocity profile and with different neutral wind directions are analyzed. The impact of velocity shear is studied by translating the velocity shear location relative to the density gradient. Numerical spectral analysis results are presented and compared to recent experimental observations. Results of spectral slopes of GDI simulations with no background velocity ( drift) were found to be and for the normalized density and the perturbed electric potential, respectively. Spectral slopes for simulations with different velocity shear locations were found to follow power laws of and for the normalized density and perturbed electric potential (inside SAPS region), respectively.

Quantum-enhanced interferometry by entanglement-assisted rejection of environmental noise

Sensing and measurement tasks in severely adverse conditions such as loss, noise, and dephasing can be improved by illumination with quantum states of light. Previous results have shown a modest reduction in the number of measurements necessary to achieve a given precision. Here, we compare three illumination strategies for estimating the relative phase in a noisy, lossy interferometer. When including a common phase fluctuation in the noise processes, we show that using an entangled probe achieves an advantage in parameter estimation precision that scales with the number of entangled modes. This work provides a theoretical foundation for the use of highly multimode entangled states of light for practical measurement tasks in experimentally challenging conditions.

Elimination of abnormal phase fluctuation in digital holography

In digital holography, the phase is most important, and the quality of the reconstructed phase determines the final reconstructed image effect. However, noise is inevitably introduced in the process of recording the hologram. For regions without object light, the phase has a random distribution, which affects the final phase quality. This kind of noise is called abnormal phase fluctuations in this paper. The correlation between amplitude and phase in digital holography is used to judge whether there is useful phase information. Through structural similarity and the light-dark relationship, a credible probability mask is introduced to extract the phase that needs to be preserved. The simulation and experimental results show that abnormal phase fluctuations are successfully removed, and the useful phase information is retained.

Unconventional spectral signature of Tc in a pure d-wave superconductor.

In conventional superconductors, the phase transition into a zero-resistance and perfectly diamagnetic state is accompanied by a jump in the specific heat and the opening of a spectral gap1. In the high-transition-temperature (high-Tc) cuprates, although the transport, magnetic and thermodynamic signatures of Tc have been known since the 1980s2, the spectroscopic singularity associated with the transition remains unknown. Here we resolve this long-standing puzzle with a high-precision angle-resolved photoemission spectroscopy (ARPES) study on overdoped (Bi,Pb)2Sr2CaCu2O8+δ (Bi2212). We first probe the momentum-resolved electronic specific heat via spectroscopy and reproduce the specific heat peak at Tc, completing the missing link for a holistic description of superconductivity. Then, by studying the full momentum, energy and temperature evolution of the spectra, we reveal that this thermodynamic anomaly arises from the singular growth of in-gap spectral intensity across Tc. Furthermore, we observe that the temperature evolution of in-gap intensity is highly anisotropic in the momentum space, and the gap itself obeys both the d-wave functional form and particle-hole symmetry. These findings support the scenario that the superconducting transition is driven by phase fluctuations. They also serve as an anchor point for understanding the Fermi arc and pseudogap phenomena in underdoped cuprates.

Instantaneous harmonic detection based on composite observer for distort grid with DC bias and variable frequency

This paper presents a real-time detection method for harmonic extraction, which can deal with sudden fluctuation of amplitude, phase, and frequency of the fundamental wave, and has advantages of rapid speed and high accuracy. First, using the Least Squares method with forgetting factor to extract phase and frequency of the fundamental wave, then the phase information is used to design a linear time-varying observer, which is based on a state space model constructed from the grid signal and harmonic components, to estimate state variables and realize the extraction of DC bias and harmonics. Taking Lyapunov function and Lasalle invariant set principle to prove stability and convergence of the proposed observer. Additionally, the input observer method and the definition method are given for DC bias. Simulation and experimental results show that even if the power grid signal is distorted, the method can quickly and accurately extract harmonic components, and it is still robust in the case of white noise, inter-harmonics or high-order harmonics.

Nonmagnetic scattering induced suppression of superfluid density in Bi-2212

Nonlinear current-voltage (IV) characteristics of Bi-2212 observed in the presence of the nonmagnetic impurity have been explained incorporating the idea of Berezinskii-Kosterlitz - Thouless (BKT). An exponent (η) is extracted as a function of temperature (T) for several Bi2−x Sr2 CaCu2−x Zn x O8+δ (Bi-2212) superconducting samples. Within the framework of the Ambegaokar-Halperin-Nelson-Siggia (AHNS) theory we have extracted the superfluid phase stiffness (SPS) as a function of T. A scaling between the SPS and critical temperature is observed. Strong suppression by the nonmagnetic impurity has been explained using the idea of localized phase fluctuations in the superconducting planes.

Demonstration of an optical phase conjugation based dual‐hop PDM‐QPSK free‐space optical communication link

The dual-hop free-space optical (FSO) communication link for polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK) signals is proposed and experimentally demonstrated in an atmospheric chamber with the optical phase conjugation (OPC) compensating the turbulence-induced signal distortions. The phase fluctuations can be effectively reduced by the OPC, as the error vector magnitudes are 10.03% and 8.28% decreased for x- and y-polarization. At the bit error rate of 1 × 10–3, the power penalty of the dual-hop link with OPC is 2.85 or 2.34 dB lower than that of each polarization without OPC.

Phase diffusion model of a one-dimensional superradiance lattice and its application as a controllable high-frequency light reflector

We study the effect of quantum phase fluctuation (QPF) on a one-dimensional superradiance lattice (1DSL) and its application as a controllable high-frequency light reflector. In electromagnetically induced transparency (EIT)-based 1DSL [Phys. Rev. Lett. 114, 043602 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.043602], counter-propagating control laser fields are responsible for the hopping of electrons from the i th to the j th atom, where n 1 and n 2 coupling photons are required for forward and backward modes, respectively. In the limit of n 1 , n 2 ≫ 1 , the role of QPF becomes significant, and, therefore, the phase diffusion model of 1DSL needs to be considered. We show that in the presence of QPF a perfect 1DSL can be realized due to the fact that EIT vanishes at the resonance condition when probe detuning is zero. It leads to a reasonably high (around 60%) reflectivity of the incident probe field at resonance condition. For the off resonant case, the reflectivity reduces due to the phase diffusion; however, it can be overcome via manipulation of the control fields.

Analysis of coherent laser echo characteristics back scattered from rough Gaussian target

The surface property of rough target can cause the decoherence and depolarization effects, which is among the main limiting factors in heterodyne detection. In the decoherence analyses, the phase fluctuation model of laser echo from rough target is established based on the spectral density method, and the phase fluctuations under typical roughness conditions are obtained by Monte Carlo method. The distribution properties of heterodyne signal amplitudes are analyzed under different surface height fluctuation σ and correlation length T. Then the corresponding experiments are carried out, which show that the phase fluctuations of laser echo satisfy the Gaussian distribution, and the decoherence effect induces the reductions and fluctuations of heterodyne signal amplitudes, especially with larger roughness surface. For typical rough metal targets, the depolarization characteristics of laser echoes from different scattering positions are obtained, which suggest that the depolarization effect increases with the rise of roughness. The positive correlation between the decoherence and depolarization effects provides a reference for the design of heterodyne lidar system, and the statistics can also be adopted for target roughness inference and target type identification.

Ferroelectric to incommensurate fluctuations crossover in PbHfO3−PbSnO3

Perovskite solid solutions PbHfO3-PbSnO3 offer valuable opportunities for studying the formation mechsnisms of incommensurate phases, owing to the presence of an intermediate (between cubic and incommensurate) phase, which is stabilized in PbHfO3 upon PbSnO3 admixture. Here, x-ray diffuse scattering signal is used to quantify the evolution of susceptibilities related to different modes of distortion (ferroelectric, incommensurate, antiferrodistortive) as a function of temperature and the results are critically compared to the predictions of a minimal symmetry-based Landau-like model with two coupled order parameters (ferroelectric and antiferrodistortive) and incommensurate order parameter being interpreted as inhomogeneous polarization. Experimentally, we observe a Curie-Weiss-like linear dependence of ferroelectric stiffness (inverse of susceptibility related to homogeneous polarization fluctuations) in the cubic phase down to about 50 K above the transition to the intermediate phase, where this dependence nearly saturates. Upon cooling down to the intermediate phase, the maximum of susceptibility shifts gradually to the non-zero wavevector, where another Curie-Weiss-like linear stiffness trend is established, but with respect to the incommensurate order parameter. Symmetry of diffuse scattering distributions indicates an orthorhombic symmetry of the intermediate phase. A notable temperature dependence of the constant that describes the energy of polarization inhomogeneities is observed experimentally, which is in disagreement with the model expectations. Specifics of this dependence suggest the presence of a nearly temperature-independent characteristic length scale for inhomogeneities across several phases. Other differences with the model suggest that the incommensurate order parameter cannot be straightforwardly identified with weakly-inhomogeneous ferroelectric polarization.

Effect of cooling rate on the size fluctuation of V-containing phases in Al-V master alloys

To investigate the relationship between the solidification cooling rate and the size fluctuation of different V-containing phases, Al-4 wt. % V master alloys with various V-containing constituents were prepared at different cooling rates carried out by a wedge-shaped water-cooled copper mold, a graphite mold and a refractory mold at 1050°C, respectively. The variance of lognormal density function was used to characterize the size fluctuation of V-containing phases quantitatively. The results show that the largest size difference of both Al10V phases and Al3V phases is simultaneously present in the ingot prepared by the average solidification cooling rate of 2°C·s-1, while the smallest difference of Al10V phases in size is present in the ingot prepared by the average solidification cooling rate of 271°C·s-1. The size fluctuation of the Al3V phases first increases slightly and then decreases with increasing average solidification cooling rate in the range of 30~195°C·s-1.

Waveform Distortion of Gaussian Beam in Atmospheric Turbulence Simulated by Phase Screen Method

The atmospheric turbulence phase screen is generated based on the power spectrum inversion method, and the multiple transmission processes are statistically averaged. The waveform distortion of the Gaussian beam in the atmospheric turbulence is analyzed; the simulation results show that the property of Gaussian beam has been destroyed after its passing through the atmospheric turbulence. When the beam waist radius is close to a certain radius, the degree of change becomes larger. When it approaches the critical value, the wave surface no longer changes sharply, and as the turbulence intensity increases, the phase fluctuation becomes more and more severe, the coherence of the beam is destroyed, and the spot may be split into several pieces. Finally, the relationship of intensity fluctuation, amplitude fluctuation, and bit error rate with distance is analyzed.

СТАБИЛЬНОСТЬ ЧАСТОТЫ ГЕНЕРАТОРОВ И ВЕРОЯТНОСТЬ БИТОВОЙ ОШИБКИ В СИСТЕМАХ РАДИОСВЯЗИ С М-КАМ СИГНАЛАМИ

Introduction. The issues of the development of digital communication technologies, their implementation and the development of new high-speed data transmission standards, which entail finding more efficient ways to use the allocated frequency band, which allows for the transmission of more data in a narrower frequency band, are considered. Reducing the required frequency band at a given data transfer rate is achieved by sending more bits using a single character. Methods: The main directions for improving modern digital communication technologies are the search for ways to use allocated frequency bands, which will be more efficient, i.e. will increase the amount of transmitted data while reducing the allocated bandwidth. The use of signal multiplexing techniques such as QAM and OFDM signal shaping reduces the occupied bandwidth to approximately the symbol rate. Bit error probability is one of the most important indicators of the efficiency of a communication system. Issues related to the analysis of the bit error probability depending on the signal-to-noise ratio in the communication channel received fundamental and comprehensive consideration. At the same time, the relationship between bit error probability and frequency stability is less explored. Research results: The solution of this problem is possible by changing the amplitude and phase of the carrier between many discrete states of a large number of carrier frequencies with a low channel speed. Based on this, the article discusses issues related to the representation of the signal in the communication channel, taking into account the occurrence of fluctuations in amplitude, frequency and phase from nominal values. The conditions for the influence of constant and random components of the signal frequency deviation from the nominal value on the probability of a bit error are formulated. To implement the formed conditions, the results of mathematical modeling are presented, confirming the correctness of the theoretical results obtained and the main patterns noted.

Diffuse scattering from lamellar structures.

Lamellar structures are formed in a variety of soft materials including lipids, surfactants, block polymers, clays, colloids, semicrystalline polymers and others. Lamellar phases are characterized by scattering patterns containing pseudo-Bragg peaks from the layer ordering. However, fluctuations of the lamellae give rise to diffuse scattering in addition. This diffuse scattering can provide valuable information on the elastic properties of lamellae which control their fluctuations. A number of models to account for this are described in this Tutorial Review, along with examples from the literature. In addition, diffuse scattering from in-plane fluctuations or structures such as perforations or patterned nanoparticles is considered. This type of diffuse scattering can give unique information on the nature of, and positional (and bond orientational) ordering within, correlated structures within the lamellar plane. Anisotropic diffuse scattering features from thermotropic smectic phases is also briefly discussed.