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Related Concept Videos

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
Distribution and Dispersion00:54

Distribution and Dispersion

Ecology is the study of how organisms interact with their environment and with one another. An important aspect of ecology is understanding where species are found and how individuals are distributed within those areas. The geographic range of a species refers to the total area where its members are located, while dispersion describes the pattern of spacing of individuals within that range.Geographic Range and Dispersion PatternsWithin a species’ geographic range, individuals may be distributed...
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
Van der Waals Interactions01:24

Van der Waals Interactions

Atoms and molecules interact with each other through intermolecular forces. These electrostatic forces arise from attractive or repulsive interactions between particles with permanent, partial, or temporary charges. The intermolecular forces between neutral atoms and molecules are ion–dipole, dipole–dipole, and dispersion forces, collectively known as van der Waals forces.Polar molecules have a partial positive charge on one end and a partial negative charge on the other end of the molecule,...
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Hybridization of Atomic Orbitals II

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Related Experiment Video

Updated: Jun 4, 2026

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
07:56

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

Published on: September 5, 2019

Long-distance practical quantum key distribution by entanglement swapping.

Artur Scherer1, Barry C Sanders, Wolfgang Tittel

  • 1Institute for Quantum Information Science, University of Calgary, Calgary, AB, Canada T2N 1N4. ascherer@ucalgary.ca

Optics Express
|March 4, 2011
PubMed
Summary

We present a model for practical, long-distance quantum key distribution using entanglement swapping and off-the-shelf technology to maximize secret key rates over lossy channels.

Related Experiment Videos

Last Updated: Jun 4, 2026

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
07:56

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

Published on: September 5, 2019

Area of Science:

  • Quantum Information Science
  • Quantum Cryptography
  • Quantum Communication

Background:

  • Entanglement-based quantum key distribution (QKD) offers enhanced security.
  • Practical implementation faces challenges with lossy channels and detector imperfections.
  • Entanglement swapping is a key technique for extending QKD distances.

Purpose of the Study:

  • To develop a practical model for long-distance entanglement-based QKD.
  • To optimize resource allocation for maximizing secret key distribution rates.
  • To analyze the impact of realistic device imperfections on QKD performance.

Main Methods:

  • Utilizing entanglement swapping as a core component.
  • Modeling lossy transmission links (optical fibers, free space).
  • Incorporating imperfect threshold detectors with inefficiency and dark counts.
  • Optimizing source brightness and detector parameters.

Main Results:

  • Demonstrated a method to maximize secret key rates using existing technology.
  • Identified the optimal trade-off between detector efficiency and dark counts.
  • Determined the optimal source brightness for given distances and channel losses.

Conclusions:

  • Practical, long-distance QKD is achievable with current technology.
  • Resource optimization is crucial for maximizing secret key rates in realistic scenarios.
  • The model provides a framework for designing high-performance QKD systems.