#Bispectrum

[sklogw]

happy pride to everyone on the bispectrum!

[starkcontrasts]

erasing a bisexual character's romantic relationship with a member/s of the opposite sex in favor of blindly pushing for a gay one does not make you the ally you think you are

[synteltelecom]

Syntel Telecom presents S Neos Fever Detection Solutions http://bit.ly/sneos   https://www.dropbox.com/s/cmdsmij4m5zdexi/Fever%20Detection%20Syntel-Product%20details%2023052020.pdf?dl=0

[didanawisgi]

The Healing Connection: EEG Harmonics, Entrainment, and Schumann's Resonances. Luke Hendricks, William F. Bengston, Jay Gunkelman, Published 2010.

This study looks at interpersonal coupling or connectivity between healer and subject pairs using advanced signal processing approaches and instantaneous EEG phase coupling. Paired recordings of the healer and subject were done both with the subject at a distance and in the proximity of the healer. The EEG data were analyzed for cross-spectral coupling using the bispectrum, as well as the more traditional Fourier-based spectral analysis and EEG waveform analysis looking at phase. The healer's EEG data showed harmonic frequency coupling across the spectra, followed by between-individual EEG frequency entrainment effects, and then by instantaneous EEG phase locking. These results suggest the presence of a connection between the healer and subject. We observed the healer producing a pattern of harmonics, consistent with Schumann Resonances, with an entrainment of the subject's EEG by the healer's resonance standing waves, and with eventual phase coupling seen between the healer and subject-paired EEGs. We speculate that Schumann's resonance-based standing potential effect might serve as a connectivity mechanism underlying healing.

[arxt1]

Non-Gaussianity constraints from Planck spectral distortion cross-correlations. (arXiv:2205.15971v1 [astro-ph.CO])

Primordial non-Gaussianity can source $\mu$-distortion anisotropies that are correlated with the large-scale temperature and polarization signals of the cosmic microwave background (CMB). A measurement of $\mu T$ and $\mu E$ correlations can therefore be used to constrain it on wavelengths of perturbations not directly probed by the standard CMB anisotropies. In this work, we carry out a first rigorous search for $\mu$-type spectral distortion anisotropies with \Planck data, applying the well-tested constrained ILC component-separation method combined with the needlet framework. We reconstruct a $\mu$ map from \Planck data, which we then correlate with the CMB anisotropies to derive constraints on the amplitude $\fNL$ of the local form bispectrum, specifically on the highly squeezed configurations with effective wavenumbers $k_s \simeq \SI{740}{Mpc^{-1}}$ and $k_L \simeq \SI{0.05}{Mpc^{-1}}$. We improve previously estimated constraints by more than an order of magnitude. This enhancement is owing to the fact that for the first time we are able to use the full multipole information by carefully controlling biases and systematic effects in the final analysis. We also for the first time incorporate constraints from measurements of $\mu E$ correlations, which further tighten the limits. A combination of the derived \Planck $\mu T$ and $\mu E$ power spectra yields $|\fNL| \lesssim 6800$ (95\% c.l.) on this highly squeezed bispectrum. This is only $\simeq 3$ times weaker than the anticipated constraint from \LiteBIRD alone. We show that a combination of \LiteBIRD with \Planck will improve the expected future constraint by $\simeq 20\%$ over \LiteBIRD alone. These limits can be used to constrain multi-field inflation models and primordial black hole formation scenarios, thus providing a promising novel avenue forward in CMB cosmology.

from gr-qc updates on arXiv.org https://ift.tt/PH3IQWS

[thepotterpapers]

Harry Potter and the CMB bispectrum in the squeezed limit

Harry Potter and the CMB bispectrum in the squeezed limit

— Potter Papers (@PotterPapers) November 1, 2018

[dorcasrempel]

Uncovering the hidden “noise” that can kill qubits

MIT and Dartmouth College researchers have demonstrated, for the first time, a tool that detects new characteristics of environmental “noise” that can destroy the fragile quantum state of qubits, the fundamental components of quantum computers. The advance may provide insights into microscopic noise mechanisms to help engineer new ways of protecting qubits.  

Qubits can represent the two states corresponding to the classic binary bits, a 0 or 1. But, they can also maintain a “quantum superposition” of both states simultaneously, enabling quantum computers to solve complex problems that are practically impossible for classical computers.

But a qubit’s quantum “coherence” — meaning  its ability to maintain the superposition state — can fall apart due to noise coming from environment around the qubit. Noise can arise from control electronics, heat, or impurities in the qubit material itself, and can also cause serious computing errors that may be difficult to correct.

Researchers have developed statistics-based models to estimate the impact of unwanted noise sources surrounding qubits to create new ways to protect them, and to gain insights into the noise mechanisms themselves. But, those tools generally capture simplistic “Gaussian noise,” essentially the collection of random disruptions from a large number of sources. In short, it’s like white noise coming from the murmuring of a large crowd, where there’s no specific disruptive pattern that stands out, so the qubit isn’t particularly affected by any one particular source. In this type of model, the probability distribution of the noise would form a standard symmetrical bell curve, regardless of the statistical significance of individual contributors.

In a paper published today in the journal Nature Communications, the researchers describe a new tool that, for the first time, measures “non-Gaussian noise” affecting a qubit. This noise features distinctive patterns that generally stem from a few particularly strong noise sources.

The researchers designed techniques to separate that noise from the background Gaussian noise, and then used signal-processing techniques to reconstruct highly detailed information about those noise signals. Those reconstructions can help researchers build more realistic noise models, which may enable more robust methods to protect qubits from specific noise types. There is now a need for such tools, the researchers say: Qubits are being fabricated with fewer and fewer defects, which could increase the presence of non-Gaussian noise.

“It’s like being in a crowded room. If everyone speaks with the same volume, there is a lot of background noise, but I can still maintain my own conversation. However, if a few people are talking particularly loudly, I can’t help but lock on to their conversation. It can be very distracting,” says William Oliver, an associate professor of electrical engineering and computer science, professor of the practice of physics, MIT Lincoln Laboratory Fellow, and associate director of the Research Laboratory for Electronics (RLE). “For qubits with many defects, there is noise that decoheres, but we generally know how to handle that type of aggregate, usually Gaussian noise. However, as qubits improve and there are fewer defects, the individuals start to stand out, and the noise may no longer be simply of a Gaussian nature. We can find ways to handle that, too, but we first need to know the specific type of non-Gaussian noise and its statistics.”

“It is not common for theoretical physicists to be able to conceive of an idea and also find an experimental platform and experimental colleagues willing to invest in seeing it through,” says co-author Lorenza Viola, a professor of physics at Dartmouth. “It was great to be able to come to such an important result with the MIT team.”

Joining Oliver and Viola on the paper are: first author Youngkyu Sung, Fei Yan, Jack Y. Qiu, Uwe von Lüpke, Terry P. Orlando, and Simon Gustavsson, all of RLE; David K. Kim and Jonilyn L. Yoder of the Lincoln Laboratory; and Félix Beaudoin and Leigh M. Norris of Dartmouth.

Pulse filters

For their work, the researchers leveraged the fact that superconducting qubits are good sensors for detecting their own noise. Specifically, they use a “flux” qubit, which consists of a superconducting loop that is capable of detecting a particular type of disruptive noise, called magnetic flux, from its surrounding environment.

In the experiments, they induced non-Gaussian “dephasing” noise by injecting engineered flux noise that disturbs the qubit and makes it lose coherence, which in turn is then used as a measuring tool. “Usually, we want to avoid decoherence, but in this case, how the qubit decoheres tells us something about the noise in its environment,” Oliver says.

Specifically, they shot 110 “pi-pulses” — which are used to flip the states of qubits — in specific sequences over tens of microseconds. Each pulse sequence effectively created a narrow frequency “filter” which masks out much of the noise, except in a particular band of frequency. By measuring the response of a qubit sensor to the bandpass-filtered noise, they extracted the noise power in that frequency band.

By modifying the pulse sequences, they could move filters up and down to sample the noise at different frequencies. Notably, in doing so, they tracked how the non-Gaussian noise distinctly causes the qubit to decohere, which provided a high-dimensional spectrum of the non-Gaussian noise.

Error suppression and correction

The key innovation behind the work is carefully engineering the pulses to act as specific filters that extract properties of the “bispectrum,” a two-dimension representation that gives information about distinctive time correlations of non-Gaussian noise.

Essentially, by reconstructing the bispectrum, they could find properties of non-Gaussian noise signals impinging on the qubit over time — ones that don’t exist in Gaussian noise signals. The general idea is that, for Gaussian noise, there will be only correlation between two points in time, which is referred to as a “second-order time correlation.” But, for non-Gaussian noise, the properties at one point in time will directly correlate to properties at multiple future points. Such “higher-order” correlations are the hallmark of non-Gaussian noise. In this work, the authors were able to extract noise with correlations between three points in time.

This information can help programmers validate and tailor dynamical error suppression and error-correcting codes for qubits, which fixes noise-induced errors and ensures accurate computation.

Such protocols use information from the noise model to make implementations that are more efficient for practical quantum computers. But, because the details of noise aren’t yet well-understood, today’s error-correcting codes are designed with that standard bell curve in mind. With the researchers’ tool, programmers can either gauge how their code will work effectively in realistic scenarios or start to zero in on non-Gaussian noise.

Keeping with the crowded-room analogy, Oliver says: “If you know there’s only one loud person in the room, then you’ll design a code that effectively muffles that one person, rather than trying to address every possible scenario.”

Uncovering the hidden “noise” that can kill qubits syndicated from https://osmowaterfilters.blogspot.com/

[arxt1]

Non-Gaussianity in inflationary scenarios for primordial black holes. (arXiv:2110.08189v1 [astro-ph.CO])

Working in an idealised framework in which a series of phases of evolution defined by the second slow-roll parameter $\eta$ are matched together, we calculate the reduced bispectrum, $f_{\rm NL}$, for models of inflation with a large peak in their primordial power spectra. We find $f_{\rm NL}$ is typically approximately constant over scales at which the peak is located, and provide an analytic approximation for this value. This allows us to identify the conditions under which $f_{\rm NL}$ is large enough to have a significant impact on the resulting production of primordial black holes (PBHs) and scalar induced gravitational waves (SIGWs). Together with analytic formulae for the gradient of the rise and fall in the power spectrum, this provides a toolkit for designing or quickly analysing inflationary models that produce PBHs and SIGWs.

from gr-qc updates on arXiv.org https://ift.tt/3aIKZxs

[arxt1]

Multi-Scale Perturbation Theory II: Solutions and Leading-Order Bispectrum in the $\Lambda$CDM Universe. (arXiv:2104.04260v2 [gr-qc] UPDATED)

Two-parameter perturbation theory (2PPT) is a framework designed to include the relativistic gravitational effects of small-scale nonlinear structures on the large-scale properties of the Universe. In this paper we use the 2PPT framework to calculate and study the bispectrum of matter in a spatially-flat $\Lambda$CDM cosmology. This is achieved by deploying Newtonian perturbation theory to model the gravitational fields of quasi-nonlinear structures, and then subsequently using them as source terms for the large-scale cosmological perturbations. We find that our approach reproduces some of the expected relativistic effects from second-order cosmological perturbation theory, but not all. This work therefore provides a first step in deploying a formalism that can simultaneously model the weak gravitational fields of both linear and nonlinear structures in a realistic model of the Universe.

from gr-qc updates on arXiv.org https://ift.tt/3dSULye

[thepotterpapers]

Harry Potter and the CMB bispectrum in the squeezed limit

Harry Potter and the CMB bispectrum in the squeezed limit

— Potter Papers (@PotterPapers) February 14, 2017

[arxt1]

The parity-odd Intrinsic Bispectrum. (arXiv:2103.08614v1 [astro-ph.CO])

At linear order the only expected source of a curl-like, B mode, polarization pattern in the cosmic microwave background (CMB) is primordial gravitational waves. At second-order B modes are also produced from purely scalar, density, initial conditions. Unlike B modes from primordial gravitational waves, these B modes are expected to be non-Gaussian and not independent from the temperature and gradient-like polarization, E mode, CMB anisotropies. We find that the three point function between a second-order B mode and two first-order T/E modes is a powerful probe of second-order B modes and should be detectable by upcoming CMB experiments. We focus on the contribution to the three point function arising from non-linear evolution and scattering processes before the end of recombination as this provides new information on the universe at $z> 1000$. We find that this contribution can be separated from the other contributions and is measurable at $\sim 2.5 \sigma$ by CMB experiments with noise levels of $\sim 1 \mu$Karcmin and delensing efficiencies $\ge 90\%$, such as the proposed PICO satellite. We show that approximately half of the total signal arises from non-linearly induced vector and tensor metric perturbations, as evaluated in the Newtonian gauge. This bispectrum is a unique probe of these perturbations in the CMB, as their contribution to the power spectrum is suppressed. An important feature of this bispectrum is that the detectability will increase with decreasing experimental noise, in the absence of primordial B modes, provided that delensing efficiencies improve in parallel.

from gr-qc updates on arXiv.org https://ift.tt/3bT2cpe