Search for axions from nearby star Betelgeuse comes up empty

The elusive axion particle is many times lighter than an electron, with properties that barely make an impression on ordinary matter. As such, the ghost-like particle is a leading contender as a component of dark matter—a ...

Using drones to create local quantum networks

A team of researchers affiliated with several institutions in China has used drones to create a prototype of a small airborne quantum network. In their paper published in the journal Physical Review Letters, the researchers ...

High-flux table-top source for femtosecond hard X-ray pulses

Femtosecond hard X-ray pulses are an important tool for unraveling structure changes of condensed matter on atomic length and time scales. A novel laser-driven X-ray source provides femtosecond copper Kα pulses at a 1 kHz ...

Metasurface enabled quantum edge detection

Metasurfaces provide unique platforms to realize exotic phenomena including negative refraction, achromatic focusing, and electromagnetic cloaking due to the engineered dielectric or metallic architectures. The intersection ...

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In physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, because the photon has no rest mass; this allows for interactions at long distances. Like all elementary particles, photons are governed by quantum mechanics and will exhibit wave-particle duality – they exhibit properties of both waves and particles. For example, a single photon may be refracted by a lens or exhibit wave interference, but also act as a particle giving a definite result when its location is measured.

The modern concept of the photon was developed gradually by Albert Einstein to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light's energy, and explained the ability of matter and radiation to be in thermal equilibrium. It also accounted for anomalous observations, including the properties of black body radiation, that other physicists, most notably Max Planck, had sought to explain using semiclassical models, in which light is still described by Maxwell's equations, but the material objects that emit and absorb light are quantized. Although these semiclassical models contributed to the development of quantum mechanics, further experiments proved Einstein's hypothesis that light itself is quantized; the quanta of light are photons.

In the modern Standard Model of particle physics, photons are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of photons, such as charge, mass and spin, are determined by the properties of this gauge symmetry.

The photon concept has led to momentous advances in experimental and theoretical physics, such as lasers, Bose–Einstein condensation, quantum field theory, and the probabilistic interpretation of quantum mechanics. It has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers and for sophisticated applications in optical communication such as quantum cryptography.

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