single qubit operation

In a quiet room with no magnets anywhere, two electrons in a silicon trap still feel a faint trembling. It comes from the nuclei of silicon and germanium atoms, which spin randomly like the needles of broken compasses. This trembling was once considered noise, but now it has become a measuring instrument itself.

Graphene, a sheet of carbon just one atom thick, can change its magnetic properties the way water changes shape: sometimes flowing, sometimes freezing into ice. In a new study, physicists peered inside this process for the first time using a sensor the size of a needle tip.

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 quantum particle moves in a circle, passing through several stations. At each station, something happens to it — for example, its properties change slightly. After completing a full circle, the particle returns, but its state is no longer exactly what it was at the start.

The Josephson junction is a bridge made of superconductor, separated by an ultra-thin insulating layer. Current flows through it even without voltage. But when the current becomes too large, the bridge starts to oscillate, and even steps, Shapiro steps, appear on the voltage graph. Between these steps hide invisible gaps where the system behaves strangely.

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.

An eardrum at the very edge of a waterfall. Sound behaves strangely here: echoes don't multiply: they fade. That's exactly what gravitational waves look like at the horizon of a black hole — the boundary beyond which even light disappears.

Electrons in a solid usually either run freely (metal) or are locked in place (insulator). But sometimes strong mutual repulsion locks them into a halfway state: charges stand still, while spins, tiny magnetic arrows, continue to live their own life. This is called a Mott insulator.

Superconducting qubits are the beating heart of quantum computers, but their rhythm is disrupted by decoherence: quantumness dissolves into noise.

Quantum computing suffers from 'false notes' — errors that arise from the slightest inaccuracy. Now they are eliminated with the precision of tuning a concert grand piano. The idea traces back to the dreams of pioneers — David Deutsch and Peter Shor — of flawless operations.

A black hole resembles a safe that slowly gives up its contents, energy and information, through a faint glow known as Hawking radiation. But if the safe opens too quickly, a 'firewall' may flare up at its boundary — a region where the familiar laws of physics break down. In the new work, physicists complicated the model of this safe.

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 star contracts under its own gravity, and at some point its fate hangs on a razor-thin balance. Classical physics paints a grim picture: if the mass and the force of compression are tuned with terrifying precision, what emerges is not a black hole but a 'naked' singularity.

A lithium battery is like a tiny city: lithium ions are the residents who move between electrode neighborhoods, generating current. But to understand how much energy the city can deliver, you need to know not only the street layout (the material's structure) but also how residents interact with neighbors, transportation, and even the weather.

A quantum particle traveling around a closed ring leaves two distinct 'records' along its path. The first is like a fingerprint on a doorknob: it remains unchanged no matter how many times you turn the knob, and it only tells you about the shape and material.

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.

Even at absolute rest, atoms emit a faint noise — unavoidable quantum jitter. In the debates between Einstein and Bohr, this noise, like an unceasing whisper, blurs the interference fringes from an atomic slit. Overcoming this limit was considered impossible.

A typical photon source can be likened to a club entrance with a single bouncer. He tries to let people in one at a time, but occasionally couples sneak past. Physicists call this the purity problem: photons must arrive strictly solo, otherwise quantum computing breaks down.

Gravity is a cosmic net: massive bodies stretch it, and lighter objects roll along its curves. But in the world of atoms, this net begins to tremble chaotically, producing infinite values in the equations. Spacetime curvature ceases to be smooth. Usually, quantum corrections to gravity explode into infinities.

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.

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.

An ordinary pendulum swings at the same frequency as the push it receives. But in the quantum world, you can create a system that responds to a push two, three, or more times slower, as if it has its own rhythm. Such systems are called discrete time crystals.

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.

Modern detectors of gravitational waves confirm that black holes are real. Spacetime can be compared to a giant trampoline: massive stars make it sag.

The early universe resembled a rapidly inflating balloon: it expanded so fast that light couldn't keep up with its own edges. Then this frantic acceleration gave way to calm expansion. The balloon was no longer being blown up, and it began to slowly deflate. At the moment of the regime change, emptiness didn't stay empty: from it, as if from an overheated boiler, pairs of particles burst forth.

An orchestra where every musician plays their own part, and the conductor tries to catch the overall melody. That's roughly how physicists view electrons in cuprates — ceramic materials that conduct electricity without resistance at temperatures above liquid nitrogen.

Four musicians play in harmony only if they hold hands. In the quantum world, such a chain is formed by four electrons in four neighboring quantum dots — tiny traps for charge. This is the basis of the SAGE qubit (from "singlet-based always-on exchange").

The quantum vacuum is not emptiness, but a tautly stretched string, where particles constantly appear and vanish. Abruptly changing conditions, like shifting the mirrors of a microcavity, causes the 'string' to emit real photons.

A conventional antenna array is like a choir: many voices singing in unison, with the sound amplified in only one direction. To catch a signal from another side, you have to rearrange the whole choir. Now imagine a single voice that can change its timbre so that the sound itself focuses in the desired direction.

The biggest puzzle in physics is how to reconcile spacetime curvature with quantum mechanics. At the Planck length, billions of billions times smaller than an atom, the rules break down. This frontier was discovered by Max Planck.

Eighteen tiny cells line up in two rows on a piece of germanium. Each cell is a quantum dot — a trap for a single electron whose spin acts as a qubit. Previously, such systems could only be assembled in small numbers, but here we have an entire lattice working as a single ensemble.

Instead of millions of rigidly fixed particles — 10,000 atoms, working as beads on a quantum abacus. Each bead can be both zero and one at the same time. But the key is: if an error creeps into the calculation, the atoms can be physically moved: as if you could rearrange the abacus on the fly so that the glitch doesn't ruin the result.

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.

In everyday life, time flows on its own, like a river past its banks. But in quantum gravity, things are different: time does not flow; it emerges from relations between objects, like a pattern in a carpet that is only visible when viewed from a certain spot.

A three-seat swing never stops: one rider is always left hanging. That’s a frustrated magnet — a perpetual dance with no rest. To study it, physicists built a quantum simulator from 256 atoms, meticulously mimicking the crystal TmMgGaO₄.

An ion quantum computer is like a chandelier with a dozen pendants: pull one, and they all start swinging. Each ion is a qubit, but when there are many, their collective vibrations crowd the stage. Any operation on one pair disturbs the neighbors, and the computation goes awry.

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.

An ordinary door swings both ways, but the physicists rigged a one-way door for atoms — enter at will, but leaving is off-limits. The atoms were cooled nearly to absolute zero — in such deep cold, they merge into a single cloud. This cloud was placed in a neat lattice of laser beams, adding a tiny irregularity, like a step at the threshold.

Two people read the same book, but one turns the page first and then looks at the text, while the other does the opposite. It would seem the result is the same. But in the quantum world, the order of operations changes everything. This work examines models that output sequences of symbols, like a ticket machine.