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The Quantum-Mechanical Model of an Atom

The Quantum-Mechanical Model of an Atom

Shortly after de Broglie published his ideas that the electron in a hydrogen atom could be better thought of as being a circular standing wave instead of a particle moving in quantized circular orbits, Erwin Schrödinger extended de Broglie’s work by deriving what is now known as the Schrödinger equation. When Schrödinger applied his equation to hydrogen-like atoms, he was able to reproduce Bohr’s expression for the energy and, thus, the Rydberg formula governing hydrogen spectra.

Atomic Nuclei: Nuclear Spin State Population Distribution

Atomic Nuclei: Nuclear Spin State Population Distribution

Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.

The de Broglie Wavelength

The de Broglie Wavelength

In the macroscopic world, objects that are large enough to be seen by the naked eye follow the rules of classical physics. A billiard ball moving on a table will behave like a particle; it will continue traveling in a straight line unless it collides with another ball, or it is acted on by some other force, such as friction. The ball has a well-defined position and velocity or well-defined momentum, p = mv, which is defined by mass m and velocity v at any given moment. This is the typical...

The Bohr Model

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded by lighter and even tinier electrons continually moving about the nucleus was well established. This picture was called the planetary model since it pictured the atom as a miniature “solar system” with the electrons orbiting the nucleus like planets orbiting the sun. The simplest atom is hydrogen, consisting of a single proton as the...

Atomic Nuclei: Nuclear Relaxation Processes

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis.

Atomic Structure

Atomic Structure

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Updated: Feb 24, 2026

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference

Published on: September 5, 2019

Long-Distance Distribution of Atom-Photon Entanglement Based on a Cavity-Free Cold Atomic Ensemble.

Tian-Yu Wang^1,2,3, Ren-Hui Chen^1,2,3, Yan Li^1,2

¹University of Science and Technology of China, Laboratory of Quantum Information, Hefei 230026, China.

Physical Review Letters

|February 22, 2026

Summary

Researchers developed a quantum network node using cold atoms for long-distance quantum communication. This system achieves high entanglement fidelity over 20 km, paving the way for robust quantum networks.

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Area of Science:

Quantum Information Science
Quantum Networking
Atomic Physics

Background:

Quantum networks require reliable quantum memory nodes for distributed quantum applications.
Long-distance atom-photon distribution is crucial for scaling quantum technologies.

Purpose of the Study:

To demonstrate a cavity-free cold atomic ensemble as a quantum network node.
To achieve efficient atom-photon entanglement distribution over long distances.

Main Methods:

Utilized a cavity-free cold atomic ensemble for quantum memory.
Employed a high-efficiency, polarization-independent quantum frequency conversion (QFC) module.
Converted 780-nm photons to the telecom S band (1522 nm) for transmission.

Main Results:

Achieved an initial retrieval efficiency of ~55% and a memory lifetime of 160 μs for atomic qubits.
Observed entanglement fidelity >80% between atoms and telecom photons after 20 km fiber transmission.
Demonstrated a low-noise QFC with up to 48.5% external efficiency and a signal-to-noise ratio of 6.9 for 100 km transmission.

Conclusions:

The developed quantum node enables robust atom-photon entanglement distribution over long distances.
This platform is a significant step towards realizing kilometer-level quantum networks.
The results lay the foundation for future distributed quantum computing and secure communication.