control signal

In 1996, physicists asked: how much noise can a quantum channel withstand before it stops transmitting information? A phone call where every third word is replaced by random noise is still understandable. Up to what level of interference can the listener still grasp the meaning?

A handful of coins drops onto a table — heads and tails land wherever they please. The same goes for an instantaneous snapshot of a quantum chain: in some places a particle is present, in others it is not. But behind the disorder lurks a precise angle. In this work, a chain of particles closed into a ring was considered. It was divided into four arcs: two were measured, two were left untouched.

A lone erbium atom sits on a silver substrate, and its spin, the electron's internal rotation, stores quantum information. Previously, flipping this spin required a magnetic pulse: a blunt tool that disturbs neighbors and works slowly. Now physicists from Germany and Korea have shown that a single electric voltage suffices.

A drop of water on glass trembles and shimmers: it seems to have a life of its own. Similar behavior can now be observed in the world of colloids: tiny particles suspended in a liquid. Researchers simulated particles that emit chemical signals. These signals, like scents in the air, spread around and cause neighbors to either draw closer or move apart.

A cup of hot coffee sometimes freezes faster than cold tap water. This paradox, known as the Mpemba effect, has long been considered a curiosity of classical physics. Now its quantum counterpart has helped test and tune quantum processors — devices that may one day power supercomputers.

A superconducting qubit is like a finicky musical instrument: until you tune it, you won't get a clean note. But even after tuning, the pitch drifts. The culprits are tiny defects in the material that physicists call two-level systems. They're like invisible cracks that appear and disappear, throwing off the processor's rhythm.

Two dancers on stage must move in perfect sync, but if one hesitates, the whole routine is ruined. That's roughly how quantum computers with neutral atoms work: two atoms are entangled by putting them into a Rydberg state (as huge as a balloon compared to an ordinary atom), and then you wait for them to 'dance' their part.

You're standing in the shower: you turn the tap, and the water is either freezing or scalding. The pipes have a mind of their own — the pressure jumps unpredictably. The new controller learns on the go: it doesn't know the plumbing layout, but within minutes it adapts and gently guides the temperature to comfort, without breaching safety limits.

Ordinary atomic clocks are like a tuning fork that must be kept in perfect silence and stillness. The slightest movement, and the note goes flat. The same goes for atoms: their thermal motion shifts the frequency of radiation, so ultra-precise clocks require almost complete immobilization of the particles.

A living cell constantly emits faint magnetic signals, as if whispering. Scientists eavesdrop on this whisper with two microscopic 'microphones'—magnetic field sensors.

Building a quantum network node is like teaching a dancer to balance on a carbon thread over an abyss. One leg must spring lightly from the wire, hurling photon-messengers into the external world. The other must grip the rope tightly, guarding precious quantum information.

Tuning a quantum processor is monotonous work: you need to calibrate each qubit — a quantum cell — much like a watchmaker adjusting dozens of tiny gears. Humans get tired and make mistakes.

A quantum computer is like an orchestra where each musician, a qubit, must play their part accurately and on time. Usually, musicians are seated in fixed positions and connected by conductors' consoles. But what if we let them move freely across the stage and turn the movement itself into part of the music?

A pendulum that swings on its own, without any winding — in the quantum world, such 'pendulums' are called time crystals. In them, rhythmic motion arises spontaneously and does not decay. But until now, controlling this rhythm was nearly impossible: any intervention threatened to destroy the fragile order.

Three guitar strings on the same instrument, but each tuning peg turns with a different resistance: one gives way immediately, another is stiff, and the third is completely stuck.

Light loves symmetry: in an open channel, it flows equally both ways. To steer it one way, physicists often use magnets. A new approach does without, using rotation — just the speed of a vinyl record — and interference from two atoms. Rotation changes the “pitch” of light for different directions, just as a siren’s tone shifts when a car approaches or recedes.

Energy transfer in photosynthesis is like a children's slide: it bends under the weight of one, reshaping the path for the next. That's what happens in a leaf: an excited molecule instantly reshapes the 'landscape' of its neighbors. Physicists reproduce this effect using ions suspended in a vacuum trap.

Quantum bits (qubits) are like delicate music in a noisy factory. Ambient magnetic fields constantly 'drown out' their quantum state, turning a coherent signal into cacophony. Usually, this destructive process is slowed by retuning the qubits themselves to different frequencies, but that doesn't always work.

The atom is like a conductor, and the light in the resonator is the orchestra. Their energy exchange, known as the Jaynes–Cummings interaction (part of the Standard Model), lets the atom use “baton” strokes to change the rhythm and timbre of the oscillations.

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.

If you carry a cup of coffee slowly and steadily around a room and then return to the same spot, nothing happens to the drink. But in the quantum world, things are different: a particle that makes such a loop comes back not quite the same. It picks up an elusive 'extra'—the geometric phase, which physicists call the Berry phase.

Quantum computers in the cloud are like a post office: you send a letter, and someone else reads the address and the contents. In ordinary computing, the server sees your data and algorithm. Blind quantum computing is an unopenable envelope: the server does the work but doesn't know what it's doing.

A radio picks up a broadcast through crackle and hiss. That's roughly how modern quantum computers work: the useful signal drowns in noise. The longer the computation runs, the more the interference distorts the result.

The rows of wires stretching from the warm room into the fridge holding the quantum chip look like a tangled telephone exchange from the last century. Each qubit needed its own analog channel for precise tuning, and the cables carried extra heat and got underfoot. Now researchers have placed a digital-to-analog converter right in the cold zone, next to the qubits.

Tiny magnets inside atoms, nuclear spins, can 'freeze' for long minutes in a cold crystal. This hinders the quick tuning of quantum sensors: everything takes too long to reach the desired state. Physicists have found a way to nudge them with light.

Quantum entanglement is like an invisible web that connects particles even when they are far apart. In large systems (say, a piece of material) this web can either quickly weave through all the atoms or tangle into a knot and stay put. The first case is called quantum chaos, the second localization.

A quantum computer is like an orchestra where every musician must play their part perfectly, or the melody falls apart. Previously, controlling qubits — the quantum 'musicians'—required a room full of equipment, and every extra wire added noise.

A judge walks into the courtroom but doesn't look at the evidence: he immediately delivers the verdict. That's how the new quantum sensor works: it doesn't measure the signal but directly decides which class it belongs to. In conventional quantum sensing, it's all like a detective story: first you gather clues (measure the signal), then you analyze them.

At Fermilab's accelerator, a particle beam strikes a target of frozen ammonia. The hydrogen nuclei inside are like tiny tops, and physicists need them all spinning the same way. Then the collisions reveal how the proton's spin is put together.

Quantum computers promise to solve problems that are beyond the reach of ordinary computers. But their components, quantum bits, are very sensitive. One type of quantum bit is an oscillating circuit that can exist in two states, like a pendulum swinging left or right. These states store information.

A modern hospital sensor is like a sensitive microphone in a noisy hall. It picks up a weak signal from the heart or brain, but along with it comes the hum of machines, footsteps, the breathing of neighbors. Separating the desired sound from the interference is a science in itself.

A quantum computer is like an orchestra where each musician plays their part, but if the conductor waves the baton a bit too hard, the delicate instruments go out of tune from excess heat. Controlling qubits at 10 mK (300 times colder than your freezer) is like conducting an orchestra in an ice-cold hall where even a breath can ruin everything.

A quantum magnetometer based on hydrogen nuclei works like noise-canceling headphones. It alternately "listens" to the field in two different ways: the noise is the same for both, but the desired signal is different. By subtracting one from the other, the device extracts the signal, reducing interference by more than 1000 times.

A quantum bit (qubit) is like a barely discernible whisper in a hum of voices. A regular amplifier makes the whisper louder, but along with it, the hum as well, making it harder to hear the essence. Physicists have created a clever device that generates two identical signal-whispers at different frequencies — the original and its echo.

An AI has learned to conduct the quantum orchestra. Its instruments: superconducting circuits — artificial atoms kept colder than interstellar space. This AI-conductor designs and runs entire experimental scores, not just playing notes but creating them on the fly.

A quantum computer based on electron spins is like a row of tiny spinning tops. Each top spins either clockwise or counterclockwise: that's a qubit. To find out the result of a computation, you typically stop the top and see which way it fell. But if you have many tops, each one needs its own "eye"—an extra helper qubit.

A quantum computer in the lab resembles an orchestra: lasers play the role of bows, and ions are the strings. To play the desired melody, powerful radio signals are sent to the lasers: they set the rhythm and pitch. But part of this "music" escapes the stage.

A fridge magnet attracts a paperclip: we can feel that field with our hands. Now shrink that field by a billion times. Atoms inside our bodies emit such weak signals, and they are very hard to catch. Scientists built the sensor from special molecules that themselves behave like tiny magnets.

A tiny diamond hangs in the air, held by an electric field like a speck of dust in a beam of light. Hidden inside are defects — places where a carbon atom is replaced by nitrogen, with a vacancy nearby. These defects behave like little magnets that can be flipped with laser and microwaves.

Light enters a tiny cavity with mirrored walls and hits an erbium atom hidden in a crystal. The atom absorbs the light and flips its nucleus into another state, like a toggle switch that clicks when pressed. But this switch is not ordinary: it obeys the laws of the quantum world and can be in two positions at once.