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Videos de Conceptos Relacionados

Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

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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.
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Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

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In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
1.6K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.8K
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...
1.8K
Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

2.1K
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
2.1K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

3.3K
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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Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

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All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...
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Aceleración de una máquina de Ising coherente mediante transición de espín XY-Ising

Kyungduk Kim1, Yoshihisa Yamamoto2,3

  • 1Physics & Informatics Laboratories, NTT Research, Inc., Sunnyvale, CA, 94085, USA. kyungduk.kim@ntt-research.com.

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La introducción de la dinámica de espín XY en máquinas de Ising coherentes (CIM) utilizando ganancia insensible a la fase acelera significativamente la resolución de problemas. Este enfoque permite que los espines se volteen, escapen de mínimos locales y reduzcan el tiempo de computación por diez para tareas de optimización complejas.

Palabras clave:
máquinas de Ising coherentesdinámica de espín XYganancia insensible a la faseoptimización combinatoriacomputación cuánticafísica óptica

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Área de la Ciencia:

  • Computación cuántica
  • Física óptica
  • Complejidad computacional

Sus antecedentes:

  • Las máquinas de Ising coherentes (CIM) convencionales utilizan ganancia sensible a la fase, lo que limita los estados de espín a valores discretos de Ising.
  • Esta limitación puede atrapar a las CIM en mínimos locales, lo que dificulta la resolución eficiente de problemas.

Objetivo del estudio:

  • Demostrar numéricamente que la incorporación de la dinámica de espín XY mejora el rendimiento de CIM.
  • Explorar los beneficios de la ganancia paramétrica óptica insensible a la fase para permitir espines XY de fase continua.

Principales métodos:

  • Simulaciones numéricas de CIM que incorporan ganancia paramétrica óptica insensible a la fase.
  • Evaluación comparativa del rendimiento en instancias de problemas sembradas de Wishart.
  • Análisis del impacto de la transición entre la dinámica de espín XY e Ising.

Principales resultados:

  • La ganancia insensible a la fase permite espines XY de fase continua, facilitando el volteo de espines y el escape de mínimos locales.
  • Las transiciones graduales de la dinámica XY a la dinámica de Ising redujeron el tiempo de solución en aproximadamente un orden de magnitud.
  • Las transiciones adaptadas entre los regímenes similares a XY y similares a Ising ofrecieron mejoras adicionales en el rendimiento.

Conclusiones:

  • Se establece un marco novedoso para la ingeniería de la dinámica de CIM en todo el espacio de cuadratura de fase.
  • Los hallazgos sugieren el potencial de arquitecturas totalmente ópticas en la optimización combinatoria eficiente.
  • La dinámica de espín XY ofrece una ventaja significativa sobre la dinámica puramente de Ising para resolver problemas complejos.