orbital angular momentum

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 regular laser beam travels straight, like the light from a flashlight. But light can be twisted into a spiral, like the thread of a corkscrew. Such a beam carries orbital angular momentum: it doesn't just illuminate, it also spins anything it encounters.

Imagine a string stretched between two tuning pegs. The slightest touch makes it vibrate, and from the pitch you can guess exactly how it was plucked. Physicists at the University of Arizona have stretched a similar string — not on a musical instrument, but on a silicon membrane just a hundred nanometers thick.

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.

In a ring accelerator, a beam of electrons circles millions of times. If the electrons are twisted like strands in a rope, their vortex motion should persist. But along the way, random jolts from imperfect magnets can disturb them. Scientists have described how vortex motion changes under such perturbations.

Two stars circle each other, gradually drawing closer. Their dance loses energy, and that energy escapes into space — in the form of gravitational waves, and sometimes other fields.

An electron is not just a point. It is a probability cloud, smeared out in space. When such a cloud collides with a powerful laser pulse, it can emit a high-energy photon — a gamma quantum. And this photon can be not just ordinary but twisted, like a corkscrew, carrying orbital angular momentum.

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.

The vacuum is not as empty as it seems. If an observer moves with acceleration, the vacuum around them heats up: this was predicted by William Unruh back in the 1970s. The effect is akin to black hole radiation, but in flat space.

In a small Petri dish sits a droplet of liquid the size of a pinhead. An ordinary scanner wouldn't even notice it: the signal is too weak. But bring a tiny magnetic field sensor close to the droplet, and the picture changes.

A light carousel spins not people but electrons. Instead of wooden horses, there are invisible blades of light. This is exactly the kind of 'carousel' physicists built to give electrons a spin. Usually, to twist an electron beam into a vortex, you need a tiny mask — a stencil with slits carved on the atomic scale. Fabricating it is extremely challenging.

Light isn't just straight rays; it's electromagnetic waves that can twist through space like a pair waltzing. Physicists call their total twist orbital angular momentum, and for a long time it was thought to obey the conservation law — a fundamental principle that follows from the symmetries of nature discovered by Emmy Noether.

An ordinary camera captures light reflected from objects and builds a picture from it. But if the object is hidden behind an obstacle or does not reflect light, radio waves come to the rescue: they pass through walls and fog, and a computer reconstructs the image from scattered signals.

Light usually pushes an atom straight ahead, like wind pushing a sail. But if the beam is twisted into a corkscrew, the picture changes: the atom can fly off to the side, as if caught by a spinning wheel. In the new work, physicists calculated that such a vortex photon can transfer almost all of its rotation to the atom — up to 100 percent.

Think of a stack of paper: when the sheets lie perfectly aligned, light passes through them uniformly. But turn one sheet by a few degrees, and the picture changes. Something similar happens with layers in certain materials: rotate them relative to each other, and their properties change — sometimes dramatically. Spectroscopy isn't the key here, or rather, it's not the method used.

Light is a stream of photons, and ordinarily a photon has no magnetic moment: it doesn't deflect in a magnetic field like iron filings.

A magnetic material can be compared to a crowd of tiny compasses. In an ordinary magnet, all the needles point in the same direction, and turning them all at once is no easy feat. Physicists have found a way to do this with an electric current.

A football kicked with spin doesn't fly straight: it bends to the side. A tightly focused beam of light does something similar: it starts pushing an atom not just forward but also sideways. Physicists measured this shift on a single calcium ion trapped in a light trap. The beam was aimed at the atom like a spotlight on a grain of sand.

Light doesn't always travel in a straight line. Its wave can be twisted into a spiral, like a stream of water from a rapidly rotating hose. This twist is called orbital angular momentum, and it can hide information: each turn acts as a separate communication channel. The problem was that only bulky setups of lenses and mirrors could recognize these twists.

When a top quark is born in a particle detector, it immediately decays into a shower of other particles. Catching a hint of new physics in that shower is like hearing a whisper at a rock concert. You need not just a good microphone, but the ability to subtract the roar of the amplifiers and the hum of the crowd.

Open systems exchange energy with their surroundings, like a guitar string fading into the air. Scientists built such a system out of light, twisting the beams into corkscrews and forming an artificial lattice — a maze where losses can be controlled at every step. Light in this maze always moves at the maximum possible speed, but its energy can fade or grow.

Two great theories describe reality: one — how massive bodies cause curvature of space, the other — the Standard Model — governs elementary particles. Reconciling them remains elusive, like trying to describe an ocean storm in the language of a diamond lattice.

A century ago, quantum mechanics gave the world a neat picture: a particle rotating around a point can only have certain discrete amounts of angular momentum, integer multiples of Planck's constant. This rule seemed as solid as the law of gravity, and it followed from simple algebraic arguments.

A century ago, quantum mechanics gave the world a neat picture: a particle rotating around a point can only have certain discrete amounts of angular momentum, integer multiples of Planck's constant. This rule seemed as solid as the law of gravity, and it followed from simple algebraic arguments.