How ultracold, superdense atoms become invisible

An atom's electrons are arranged in energy shells. Like concertgoers in an arena, each electron occupies a single chair and cannot drop to a lower tier if all its chairs are occupied. This fundamental property of atomic physics ...

Energizer atoms: Physicists find new way to keep atoms excited

JILA researchers have tricked nature by tuning a dense quantum gas of atoms to make a congested "Fermi sea," thus keeping atoms in a high-energy state, or excited, for about 10% longer than usual by delaying their normal ...

New material could be two superconductors in one

MIT physicists and colleagues have demonstrated an exotic form of superconductivity in a new material the team synthesized only about a year ago. Although predicted in the 1960s, until now this type of superconductivity has ...

Coal creation mechanism uncovered

The mechanism behind one of the first stages of coal creation may not be what we thought it was, according to a team of researchers who found that microbes were responsible for coal formation and production of methane in ...

Shrinking qubits for quantum computing with atom-thin materials

For quantum computers to surpass their classical counterparts in speed and capacity, their qubits—which are superconducting circuits that can exist in an infinite combination of binary states—need to be on the same wavelength. ...

New microscopy technique for quantum simulation

Researchers from the Institute of Laser Physics at Universität Hamburg have developed a new technique for quantum gas microscopy that now allows imaging of three-dimensional quantum systems. In the journal Nature, they report ...

Researchers propose a simpler design for quantum computers

Today's quantum computers are complicated to build, difficult to scale up, and require temperatures colder than interstellar space to operate. These challenges have led researchers to explore the possibility of building quantum ...

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Atom

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determine the isotope of the element.

The name atom comes from the Greek ἄτομος/átomos, α-τεμνω, which means uncuttable, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was divisible. The principles of quantum mechanics were used to successfully model the atom.

Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom's mass is concentrated in the nucleus, with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus. Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties.

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