bell states

A layered cake of molybdenum disulfide MoS2 sits on the lab bench. It is prepared in the usual way: adhesive tape peels off the top layers to obtain a thin sample. But beneath the tape remains an invisible cavity where the atomic floors are no longer pressed together. It is there that electrons begin to behave differently than in the crystal bulk.

Quantum communication is like sending a secret letter that tears apart at any attempt to peek. So far, such a letter can only be sent along one road, and that's slow. Scientists have figured out how to send 16 couriers along 16 parallel roads, different frequencies of light, and verified that the letters arrive intact.

Quantum systems made of many particles are the basis of future computers and secure networks. But the more particles there are, the harder it is to understand how they are arranged: the number of possible states grows like an avalanche. The usual approach, measuring everything, takes an incredibly long time.

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 quantum computer isn't just a bunch of qubits: it's a whole city, where each resident is one of the machine's possible states. Residents get to know each other through weak interactions between qubits: if one state can transition to another, a thread of acquaintance is drawn between them.

In a hall with a thousand spectators, applause blends into a general noise, but if someone falls out of rhythm — a ripple runs through the crowd. The quantum world works similarly: atoms in a trap can behave as a single whole, or they can fall apart into independent individuals.

Imagine a huge puzzle where each piece is a quantum particle. To complete the picture, you don't just fit the pieces together: you need to entangle them in a special way. Usually, this is done by carefully applying operations one after another, like assembling the puzzle strictly by the instructions, row by row.

Hot water sometimes freezes faster than warm water: this odd fact is known as the Mpemba effect. Now something similar has been found in the quantum world: a state with weak entanglement (a special quantum connection between particles) can beat a more entangled one to the finish line.

A thin silver thread nearly as long as a hair's width, and inside it, pristine quantum laws hold sway. Physicists built a conductor where electrons can only move forward or backward, like on a perfectly straight single-lane road with no shoulders. On such a road, any pothole or pebble would normally destroy the fragile quantum state.

Seven dancers step onto the stage. They join hands so that any trio or quartet moves in perfect harmony with the rest — no group falls out of the overall rhythm. In the quantum world, this is called an absolutely maximally entangled state (AME for short). It's a perfect knot where every part knows everything about the whole.

The quantum vacuum is not empty: it is permeated by entanglement linking distant regions. But when physicists tried to compute this entanglement, it turned out to be infinite. The culprit: particles with very low energy that can smear out over arbitrarily large volumes. They are like waves with no shores to contain them.

The quantum networks of the future resemble the Tower of Babel: each node speaks its own dialect. Some store information in the polarization of a photon — the direction of oscillation of the light wave. Others use time bins: that is, when exactly the pulse arrives.

A polar molecule is like a tiny dumbbell with opposite charges at its ends. Normally, such particles quickly stick together or fly apart when they meet — electric forces are too strong. But the authors of the work found a way to turn this aggressiveness into a controlled game.

Cut a spin chain, and particles without an energy gap appear at the edges. They are called zero modes, and they live only at the boundary. Previously, they were counted using complex topological invariants, but now there is a simpler way.

If you accelerate an observer to near-light speed, the emptiness around them stops being cold. A thermal glow emerges — an effect predicted in 1976 and named after William Unruh. For earthly accelerations, this glow is vanishingly faint, like a whisper at a rock concert.

Neurochips work differently from conventional computers, which are built according to the blueprints of von Neumann with separate memory and processor. At the core of these chips is a network of simple cells, similar to neurons, and, like water that evenly fills containers of any shape, they easily find a solution without unnecessary steps.

A quantum computer relies on two forces: entanglement (particles behaving as a single whole) and "magic"—a measure of how far a state is from familiar classical physics. But how these two resources relate as a many-particle system evolves in time has remained a puzzle. The authors approached the problem through time.

Quantum entanglement — a phenomenon where the states of two or more particles become interconnected regardless of the distance between them — usually links intrinsic properties such as spin or polarization. However, a new experiment has for the first time realized entanglement of the positions of two atoms in space.

Crystals fascinate us with their perfect spatial order: atoms frozen at lattice points, like beads on an invisible string. But what if the same symmetry unfolds in time? Time crystals are systems that, without any external cue, start repeating their states cyclically — clocks wound by nature itself. Inside this tireless rhythm, disorder seems to have no place.

Two synchronized swimmers dive into the sea. One hits calm water, the other a whirlpool. Their movements, perfectly coordinated at the start, diverge. Something similar happens to two quantum particles when one moves in flat space and the other in curved space.

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

An electron and its antiparticle — the positron, predicted by Дираком, — upon meeting, momentarily form позитроний: a tiny pair circling each other, like in an atom but without a nucleus. Almost instantly it decays, emitting two photons that turn out to be mysteriously linked.

Quantum entanglement often behaves like a synchronized dance visible from only one angle. Change the way you observe it, and the particles appear disconnected. This limits secure communications. Now physicists have created a pair of photons whose 'dance' is flawless from all perspectives.

Light or sound can be confined in a tiny region of a crystal, like a pearl in a shell. Usually, two methods are used. The first is like a heavy ball in a pit: a particle with large mass simply cannot roll out. The second is a perfect cage of mirrors, where waves cancel each other everywhere except in the trap itself.

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.

Neutrinos are the true ghosts of the microcosm. Nearly massless and chargeless, they pass through planets as if through empty space. But inside each neutrino hides not one particle but three — three 'flavors' (electron, muon, and tau) that constantly morph into one another. This dance is called oscillation.

A cloud of rubidium atoms falls into a trap made of light. Lasers and magnetic fields arrange it like a crystal lattice, but the cells here are not fractions of a millimeter: they are fractions of a micrometer.

Three dancers move as one: each feels all the others, and the overall harmony cannot be reduced to individual interactions. This is roughly how three particles behave, born from an electron and positron collision at the speed of light. They are a top quark, its antiparticle, and a Z boson.

Two particles separated by kilometers change their states in concert, as if there were no distance between them. This is called quantum entanglement, and since its discovery it has baffled physicists: no known carrier can travel faster than light, yet correlations appear instantaneously.

Two dice lie in different rooms. If they are 'entangled,' a roll of one instantly determines the outcome of the other — even at a distance. In the quantum world, such a link is called steering: one party, by performing measurements on their side, seems to dictate the state of the partner.

Hot water sometimes freezes before cold: this is the Mpemba effect. In the quantum realm, a similar paradox appears: the more the equilibrium is disrupted, the faster it recovers. It's like fleeing from disorder (entropy) in reverse: the system rushes toward order, and a large initial imbalance only helps.

Any measuring device is spoiled by quantum noise — the chaotic jitters of elementary particles. To tame it, physicists used a trick on calcium fluoride molecules, much like squeezing a balloon: press in one spot, and it bulges in another.

Imagine an orchestra where every musician plays their own part without listening to the others. Suddenly, without any visible command, neighboring musicians begin to sync perfectly, yet there is still no overall melody.

Imagine a library where instead of books, you have every conceivable combination of a few dozen quantum particles. The number of combinations grows like a snowball: add one particle, and the volume doubles. For fifty particles, there are more shelves than atoms in the visible universe.

Ordinary water freezes as expected. But sometimes hot water turns to ice faster than cold — the Mpemba effect. Recently, a similar rule-breaking was found in quantum entanglement — the invisible link between particles discovered by Erwin Schrödinger.

Two entangled photons fly apart in opposite directions but continue to behave as a single whole: measuring one instantly determines the state of the other. That's quantum entanglement. But sometimes it resembles a seasoned spy — leaving no traces detectable by ordinary checks.

Before assembling a huge puzzle, you need to stamp out the pieces — otherwise the picture won't come together. In fusion-based quantum computers, the role of such pieces is played by tiny clumps of light — photonic resource states. They are collided and measured to gradually grow the computational fabric.

Four tiny puddles, and in them ripple droplets of a superfluid. These droplets are atoms cooled to near absolute zero and paired up like little magnets. When the whole setup rotates, the fluid flows between the puddles. Simply counting how many droplets end up in each reveals the angle and angular velocity.

A quantum computer is like an orchestra where each musician plays their part, but if one hits a wrong note, the melody falls apart. Errors arise constantly: from thermal jitter, from imperfect instruments. To keep the symphony going, you need a "conductor" who hears the off-key notes and corrects them on the fly.

On the surface of a tiny sphere live two invisible fields, like two kinds of ripples on a soap bubble. These fields don't just oscillate on their own: they constantly influence each other, like musicians playing in unison. In a new study, physicists derived exact equations that describe how this ripple changes over time, heats up, and descends into chaos.