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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.4K
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...
2.4K
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

870
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
870
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.5K
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...
1.5K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

1.3K
Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the...
1.3K
¹H NMR Signal Multiplicity: Splitting Patterns01:13

¹H NMR Signal Multiplicity: Splitting Patterns

7.0K
When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
7.0K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

3.4K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
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Related Experiment Video

Updated: May 3, 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

9.8K

High efficiency coupling of photon pairs in practice.

T Guerreiro, A Martin, B Sanguinetti

    Optics Express
    |February 12, 2014
    PubMed
    Summary

    Researchers developed a quantum model for designing efficient entangled photon sources. This model achieves over 80% coupling efficiency, crucial for quantum communication experiments like Bell tests.

    Area of Science:

    • Quantum optics
    • Quantum information science

    Background:

    • Entangled photon sources are vital for advanced quantum experiments, including loophole-free Bell tests and device-independent quantum key distribution.
    • High coupling efficiency in these sources is a critical requirement for experimental success.

    Purpose of the Study:

    • To present a simple quantum theoretical model for designing entangled photon sources with high pair coupling efficiency.
    • To demonstrate the model's effectiveness in achieving high coupling efficiency in challenging configurations.

    Main Methods:

    • Development of a quantum theoretical model for optimizing entangled photon source design.
    • Application of the model to a highly frequency non-degenerate configuration.
    • Experimental validation across continuous wave and pulsed pump regimes, and with different nonlinear crystals.

    More Related Videos

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    Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source

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    Generation and Coherent Control of Pulsed Quantum Frequency Combs

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    Related Experiment Videos

    Last Updated: May 3, 2026

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

    Published on: September 5, 2019

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    Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source
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    Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source

    Published on: April 4, 2017

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    Generation and Coherent Control of Pulsed Quantum Frequency Combs
    06:42

    Generation and Coherent Control of Pulsed Quantum Frequency Combs

    Published on: June 8, 2018

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    Main Results:

    • Demonstrated a symmetric coupling efficiency exceeding 80% in a highly frequency non-degenerate configuration.
    • Successfully applied the technique in both continuous wave and pulsed pump regimes.
    • Validated the approach with various nonlinear crystals, showcasing broad applicability.

    Conclusions:

    • The proposed quantum theoretical model provides a practical method for designing high-efficiency entangled photon sources.
    • This work significantly advances the development of sources required for sophisticated quantum communication protocols.
    • The demonstrated high coupling efficiency opens new possibilities for experimental quantum information science.