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Related Concept Videos

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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Atomic Nuclei: Nuclear Spin State Overview01:03

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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...
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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

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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.
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Atomic Nuclei: Nuclear Spin01:08

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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.
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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.
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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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Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving
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Feedback cooling of an atomic spin ensemble.

N Behbood1, G Colangelo1, F Martin Ciurana1

  • 1ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain.

Physical Review Letters
|August 29, 2014
PubMed
Summary

We demonstrate a novel quantum control technique to reduce spin noise in cold atomic ensembles. This method achieves significant noise reduction, paving the way for generating exotic entangled states.

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Area of Science:

  • Atomic physics
  • Quantum optics
  • Quantum information science

Background:

  • Cold atomic ensembles are crucial for quantum information processing.
  • Controlling quantum noise is essential for advancing quantum technologies.

Purpose of the Study:

  • To apply entropy removal via measurement and feedback to a cold atomic spin ensemble.
  • To reduce collective spin noise and generate novel quantum states.

Main Methods:

  • Utilized quantum nondemolition probing (Faraday rotation measurement).
  • Implemented feedback control using weak optical pumping.
  • Developed input-output relations and ensemble quantum noise models for analysis.

Main Results:

  • Achieved 12 dB spin noise reduction.
  • Reduced phase-space volume by a factor of 63.
  • Demonstrated a nonthermal route for generating entangled states.

Conclusions:

  • Entropy removal by measurement and feedback is an effective quantum control strategy.
  • The technique enables the creation of exotic entangled states like macroscopic singlet states.
  • This method has implications for quantum simulation and advanced quantum gas research.