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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)

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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...
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¹H NMR Signal Multiplicity: Splitting Patterns01:13

¹H NMR Signal Multiplicity: Splitting Patterns

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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...
6.5K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.6K
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...
2.6K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

3.0K
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...
3.0K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

1.5K
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 involved orbitals. The...
1.5K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.4K
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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Strong coupling between a single-photon and a two-photon Fock state.

Shuai-Peng Wang1,2,3, Alberto Mercurio4,5, Alessandro Ridolfo6

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Researchers achieved strong coupling between single photons and two-photon states in circuit quantum electrodynamics (cQED). This breakthrough enables deterministic photon-photon interactions for quantum nonlinear optics, paving the way for advanced quantum technologies.

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Area of Science:

  • Quantum Optics
  • Quantum Information Science
  • Circuit Quantum Electrodynamics (cQED)

Background:

  • Strong nonlinear coupling between single photons is crucial for quantum information processing.
  • Existing methods struggle to achieve deterministic, coherent photon-photon interactions.

Purpose of the Study:

  • To experimentally demonstrate strong coupling between single-photon and two-photon Fock states.
  • To explore a new regime of quantum nonlinear optics with individual photons.

Main Methods:

  • Utilized an ultrastrongly-coupled circuit-QED system with a detuned flux qubit as a coupler.
  • Exploited ultrastrong light-matter interaction and external flux bias to break conservation laws.

Main Results:

  • Observed strong one-two-photon coupling by breaking excitation number and parity conservation.
  • Resolved Quantum Rabi-like avoided crossing between photon states.
  • Demonstrated thresholdless second harmonic generation for sub-unity mean photon numbers.

Conclusions:

  • The study establishes a new regime for quantum nonlinear optics.
  • Enables deterministic and coherent interaction of individual photons without external fields.
  • Paves the way for all-optical deterministic quantum logic and single-photon frequency conversion.