noise reduction spectroscopy

Fatty liver disease often goes unnoticed, but over time it can lead to serious problems. To avoid taking a tissue sample, doctors use ultrasound: sound waves pass through the tissue and attenuate differently depending on fat content. This parameter, the attenuation coefficient, shows how "fat" the liver is. But the method has a flaw.

An array of radio telescopes is like a camera missing several lenses. Ever since Karl Jansky picked up the radio hiss of the Milky Way, astronomers have been trying to piece together a whole picture from fragmentary signals. But the antennas are spaced apart, and the mathematically “developed” image — the dirty map — ends up smeared.

A single-pixel camera works like an artist creating a picture through a stencil with many holes. In each frame, only a portion of the light, modulated by a mask, a spatial light modulator, reaches the single sensor, and then the computer reconstructs the full image by assembling this mosaic with computational algorithms.

Traditional hearing aids resemble a chef who cooks from a recipe blindly. They analyze the sound chaos from the microphone and amplify speech based on it. In a noisy café, this approach often errs. The new system behaves like an experienced cook: first processes the signal, then samples the result.

Look into the night sky — before you is not a scattering of lights, but a multi-layered manuscript. Under the bright ink of stars and galaxies appears a faded, almost erased text.

The gamma sky, captured by the Fermi telescope, is a grand symphony of thousands of sources. Here, the rhythmic pulsations of pulsars, the powerful chords of active galactic nuclei, but most of all — unidentified objects, whose part remains a mystery.

An ultra-sensitive microphone listens not to sound, but to the trembling of space itself. That's how gravitational wave detectors work — LIGO, Virgo, KAGRA.

After a merger, the newborn black hole emits a fading tremble — gravitational waves, similar to a ringing bell. By analyzing the overtones of this signal, spectroscopy can determine its mass and spin rate.

In 1948, engineer Claude Shannon laid the foundations of information theory. The Nyquist–Shannon theorem gave the first answer: to avoid losing a signal, you need at least twice as many measurements as the fastest feature in the signal. In 2006, the method of compressed sensing relaxed this requirement.

Any light measurement runs into a fundamental limit: photons hit the camera sensor unevenly. This natural ripple (shot noise) blurs fine details, like trying to pick out a quiet instrument in an orchestra through the noise of the hall.

Gravitational wave detectors are microphones listening to the trembling of space. But their own noise drowns out weak signals. To hear more, physicists add special "squeezed" light to the instrument: it reduces quantum noise, like noise cancellation in headphones.

A quantum memory node is a tiny diamond with a defect that can store and emit single photons. But its light has a wavelength of 637 nanometers, the same red as a ruby, and is almost completely absorbed after just a few meters of standard optical fiber.

A laser beam passes through a cell, and the cell responds to the touch, like a taut string plucked by a finger. The frequency of this 'ring' reveals how stiff or soft the material is. That's how Brillouin microscopy works, named after the French physicist Leon Brillouin.

Hunting for a single glowing spot in a dark sample is like trying to find a needle in a haystack: the microscope beam crawls line by line, wasting time and light. Physicists replaced this slow sweep with random light patterns. The sample is illuminated with a broad field, but each time with a new pattern of bright and dark patches, as if random shadows from a grid were projected onto it.

A metal needle descends onto a piece of superconductor. All of this happens inside a refrigerator that cools the sample to 30 thousandths of a degree above absolute zero — a hundred times colder than outer space. A weak current is passed through the needle, and by how electrons travel through the tiny contact point, physicists read what is happening inside the material.

A detector that hunts for rare particles is like an ear trying to catch a whisper in a noisy room. The quieter the signal, the harder it is to tell apart from random noise. In the NUCLEUS experiment, such detectors, cryogenic calorimeters, are cooled to near absolute zero so they can pick up even a faint pulse of heat from a single particle.

In a lab, you measure a very weak signal — say, a tiny change in a magnetic field. The instrument trembles from passing cars, from the experimenter's breathing, from wires heating up. This technical noise can't be fully eliminated, and it sets a limit on precision. An ordinary sensor works like a scale that sways with any draft.

A radio receiver hunting for dark matter is like a bell: it responds to only one note. The trouble is, nobody knows what note dark matter plays, so the bell needs to be retunable. Usually, a metal rod is inserted inside, but it creates extra noise.

A charged particle spiraling in a magnetic field doesn't stay silent: it emits light. This light is called synchrotron radiation, and it shows up everywhere — from distant galaxies to laboratory accelerators.

A quantum processor is like an orchestra where each musician (qubit) must play their part precisely in time. But in reality, the instruments go out of tune: qubits lose energy, and their interactions get distorted. To tune this orchestra, you first need to record how it sounds right now: that is, measure the noise parameters and couplings.

Radio telescopes are like ears listening to space. Usually, there's just one ear: it picks up a signal from a single tiny spot in the sky. That's slow. The Parkes telescope in Australia now has 72 ears working at once.

Terahertz radiation sits between microwaves and infrared light. It passes through clothing, paper, and plastic but is blocked by water and metal. That's why these waves are used in security scanners and for quality control of materials.

A speck of glass floats in a laser beam. Air molecules, photons, even Earth's gravity give it little pushes, and by watching its jitter, you can tell what pushed it. But every measurement has a limit: the particle's own noise hides weak signals. Quantum mechanics sets that limit, but it can be bypassed.

Light in a microscope doesn't arrive as a steady stream but like buckshot from a bag: sometimes more photons, sometimes fewer. This random scatter is the shot noise. It sets a limit: faint signals from tiny objects get lost in the ripple. Scientists have found a way to calm this buckshot.

A tuning fork rings at a single note, but soft overtones, multiples of the frequency that mix with the fundamental, are always present.

Even a laser beam has an invisible tremor — quantum noise. Physicists have learned to 'squeeze' it, like a balloon pinched at the waist: the noise quiets in one direction but amplifies in another. Scientists hid the excess noise where it doesn't interfere with precise light measurements.

Ordinary light always jitters a bit: its brightness and color fluctuate, like the air in a balloon after a tap. In 'squeezed' light, these fluctuations are redistributed — as if you squeeze the balloon from one side, making it thinner here and thicker there, but the total volume stays the same.

Ice clouds can masquerade as water clouds. A satellite lidar sends a short laser pulse downward and catches the reflection. If flat ice plates hang horizontally in the cloud, they act like tiny mirrors: light bounces back almost without loss. To the instrument, such a flash looks just like a reflection from water droplets.

A gravitational-wave detector catches not only the roar of mergers but also the quiet splash when a star or gas cloud dives into a supermassive black hole. Such a dive, like a stone falling into a well, generates waves at all frequencies at once—and in that spectrum lies encoded the nature of the well itself.

A laser beam is trapped between two mirrors, one of which trembles under an invisible force. Each vibration of the mirror changes the phase of the light, and from these changes you can infer the force. But the light itself pushes on the mirror, which is quantum backaction, and it imposes a fundamental limit on measurement accuracy.

Detecting a single quantum emitter is like tuning a piano on a factory floor full of screaming machines: the pure tone drowns in noise. But the tuner doesn’t try to outshout the racket — he picks up a tuning fork and listens for beatings. That’s how even a barely audible echo becomes clear.

Earth's climate resembles a choir, where each member sings their own part at their own pitch. Some voices hold low notes, like multi-year ocean temperature oscillations, while others produce rapid trills, like short atmospheric waves. The conductor needs to hear each one, but the voices overlap and the notes blend into a mush.