quantum optics

Light passing by a tiny structure changes direction. If the structure is smaller than the wavelength of the light, it acts like a lens and focuses the light into a spot smaller than the wave itself.

The laser beam in an optical tweezer is not just a spot of light but a force bag. A particle caught in it usually rolls toward the brightest point, like a ball into a dimple.

A laser hits an atom, and tears out an electron. The brighter the light, the stronger the kick, and the faster the electron flies away. That's how the familiar picture works, where light is a smooth wave. But what if the light isn't smooth but 'squeezed,' with quantum fluctuations, like the trembling of a string?

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 light beam usually travels in a straight line, but you can make it spin around its axis, like water swirling into a vortex as it drains. This 'twisted' light carries more information and is needed for ultra-fast communication and quantum computing.

When a heavy atomic nucleus splits into two fragments, an invisible quantum thread remains between them. This thread is entanglement: the state of one fragment is instantly linked to the state of the other, as if they were still a single whole. For the first time, physicists have precisely calculated how long and strong such a thread can be, tracing the fission process step by step.

A short flash of light is like a musical phrase: you can distinguish individual notes if you listen very carefully. But in the quantum world, these 'notes'—temporal modes — are squeezed down to picoseconds, and ordinary optics can barely tell them apart.

A drop of ink in a glass of water spreads in intricate swirls. Similarly, a quantum particle exchanging energy with its environment changes its state in a complex and entangled manner. Describing this dance between particle and environment has long baffled scientists.

Two pebbles drop into water at a distance. The waves from them run toward each other and at certain spots they cancel out — the water becomes smooth, even though each stone alone would create ripples. Much the same happens with a pair of photons (light particles) born in a single crystal and flying off in different directions.

A stone drops into a pond, and ripples spread across the water. In the same way, massive bodies generate gravitational waves, except it's space itself that ripples. So far, these waves have been caught by giant detectors that barely flinch as a wave passes through. But what happens on the microscopic scale, inside a tiny piece of matter?

A camera looks at two distant sparks. They're so close together that they merge into a single fuzzy blob. It seems impossible to tell them apart — the classic limit of optical microscopy has been reached. But quantum mechanics hints that the light field still holds a secret about where each spark sits.

The quantum world never stands still. Even in the most perfect resonator, a trap for particles of light, energy gradually leaks away, and information is erased. Physicists call this process decay, and it has its own rhythm: some 'notes' fade quickly, while others linger.

In a pot of boiling water, steam bubbles appear and disappear — a similar struggle takes place in two-dimensional materials. Here, electrons both create magnetism and try to extinguish it.

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.

On the wall: light and dark fringes. That’s what light looks like when it cancels itself out. Way back in the 17th century, Christiaan Huygens suggested that light is a wave.

A thrown stone sends ripples across water. A gravitational wave is the same kind of ripple, but in spacetime. It is produced, for example, by the merger of two black holes. In classical physics, this ripple is eternal: once created, it travels through the Universe without fading.

General relativity, which describes the structure of the universe, does not forbid closed timelike curves. But Stephen Hawking put forward the 'chronology protection' conjecture: quantum effects should destroy such curves, making time travel to the past impossible.

Three laser beams intertwine into a triangle. Each is linked to the other two: this is the structure of the new scheme that physicists call "fully connected three-mode squeezed vacuum." This is not just three independent light sources: inside a special crystal, triples of entangled photons are born, and the connection between them resembles a complete graph of…

A delicate watermark on wet paper, and a fogged-up glass before your eyes. That's roughly what reading quantum states of light looks like: fragile photon patterns get distorted by losses, and detectors catch only a small fraction of the signal.

A spotlight blazes straight into your eyes, and a few steps away a tiny firefly flickers. That's roughly what it's like hunting for an Earth-like planet around a neighboring star: the planet is a hundred million to ten billion times fainter than its star, and in the sky they almost merge into a single point.

Light waves are never perfectly smooth — they are constantly jittered by quantum ripples. These almost invisible nudges were studied by Nobel laureate Roy Glauber, who laid the foundations of quantum optics. Now physicists have learned to freeze these ripples.

A false vacuum is not just a supercooled liquid, but a quantum hologram, ready to spring to life under the right projection. Its decay is described by the tunneling of a quantum field from a metastable minimum, and the classic calculation via Euclidean instantons is as elegant as a still life under spotlights.

A beam of light enters frosted glass and fades — nothing unusual. But physicists have long known how to make light pass through without losing a single photon. This trick is called electromagnetically induced transparency: two light waves cancel each other at the right point, and absorption disappears. Now a similar feat has been pulled off with atoms.

Light flows like an invisible river. If you place an obstacle in the stream, the water whirls into eddies. Likewise, specially designed surfaces create light 'whirlpools' that catch nanoparticles like wood chips.

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.

In the depths of a diamond crystal, studded with NV centers, a symphony slumbers. Each defect is like a tuning fork, ready to respond to a passing acoustic wave. But alone, their voices are barely audible: the spin-phonon coupling is weaker than a whisper. A maestro is needed, one who can turn timid vibrations into a resounding choir.

Quantum computers of the future will likely communicate via light. An atom stores information, and a photon carries it across the network. But an atom doesn't hang still: it jitters and oscillates, and this motion can corrupt the signal. Previously, engineers could only calculate for a stationary atom.

Data on the internet travels at the speed of light through fiber optics. In classical networks, delays aren't critical, but for quantum communication, perfect synchronization is essential: particles of light with encoded information must converge at the detector in the same instant.

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.

Quantum electrodynamics, or QED, describes how light interacts with charged particles — for example, electrons. It is one of the most precise theories in history: its predictions match experiment to the eleventh decimal place.

A surfer glides across the ocean surface until a big wave comes, and then they're flying forward. Similarly, a free electron interacts with light: usually the energy exchange is barely noticeable, but if the surrounding medium begins to oscillate rhythmically, each wave crest pushes the particle harder and harder.

Light gets trapped in a crystal lattice, but not an ordinary one: it's turned inside out, like a honeycomb where instead of wax there's emptiness, and the edges are made of material. That's how an inverted opal is built: a three-dimensional photonic crystal that blocks light of certain colors.

Toss a handful of phosphorus into silicon, and at a certain impurity concentration the material suddenly starts conducting electricity. This is a metal-insulator phase transition, and it happens abruptly. But what exactly changes in the electron wave functions when an insulator becomes a metal?

A thrown stone follows a smooth arc: its path is easy to predict. But if the stone skips across water, the trajectory becomes jagged and far more interesting. Quantum particles behave much the same way when their state is not a calm wave with fixed energy but a turbulent mix of several waves at once.

A single camera shot stores both a normal picture and a hidden map of how light rippled through the scene. Quantum entanglement makes this possible. Pairs of linked photons are generated: one visits the object, its twin takes a detour. Later, measuring the twin one way pulls out the brightness information.

When an electric charge moves with acceleration, it emits electromagnetic radiation, i.e., light — a familiar phenomenon in physics. However, researchers have found that when moving along a specially chosen trajectory, the radiation acquires unusual properties.

A quantum computer is like an orchestra: each musician plays their own part, but the slightest noise from the audience can throw off the whole ensemble. The particles that store information easily lose their coherence from thermal jolts or stray magnetic fields.

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.

A swing can rock strongly or barely move. Usually, if left alone, it stays in its chosen mode. But in the microworld, things are different: a tiny membrane, oscillating under the action of a laser beam, can spontaneously jump from one amplitude to another.

Physicists have proposed an experiment: a laser beam acts as a quantum detector and splits into two beam-ears. Each ear is directed through a tiny cloud of ultracold atoms — in this state, atoms merge into a single wave.