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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 Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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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: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
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The quadrupole mass analyzer consists of four cylindrical metal rods arranged in a diamond carrying a DC voltage and a radio-frequency AC voltage. The motion of ions through the quadrupole depends on the field strength, causing only ions of a certain m/z to resonate successfully and strike the detector at a given field strength. Though the transmission rate for these analyzers is high, the exact elemental composition of the sample is not determined because of low resolution; however, they are...
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Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

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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 Magnetic Moment00:59

Atomic Nuclei: Nuclear Magnetic Moment

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All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
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Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving
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Collisions between Ultracold Molecules and Atoms in a Magnetic Trap.

S Jurgilas1, A Chakraborty1, C J H Rich1

  • 1Centre for Cold Matter, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, United Kingdom.

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Ultracold molecules and atoms collide inelastically. Rotationally excited molecules show significant loss, while ground-state molecules exhibit minimal loss, suggesting different collision dynamics.

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Area of Science:

  • Ultracold atom-molecule collisions
  • Quantum defect theory
  • Molecular spectroscopy

Background:

  • Investigating inelastic collisions between ultracold molecules and atoms is crucial for understanding quantum phenomena.
  • Calcium fluoride (CaF) molecules and rubidium (Rb) atoms are ideal systems for studying these interactions due to their tunable properties.

Purpose of the Study:

  • To measure the inelastic collision rate coefficients between ultracold CaF molecules and Rb atoms.
  • To investigate the role of molecular rotation and spin states in collision dynamics.
  • To compare experimental results with theoretical predictions from quantum defect theory.

Main Methods:

  • Preparation of ultracold CaF molecules and Rb atoms in a magnetic trap.
  • Controlled preparation of molecules in specific rotational and spin states.
  • Measurement of inelastic collision rates via loss spectroscopy.
  • Application of a single-channel loss model based on quantum defect theory.

Main Results:

  • Inelastic collision rate coefficient for spin-stretched molecules in the first rotationally excited state and spin-stretched atoms is (6.6±1.5)×10⁻¹¹ cm³/s at ~100 μK.
  • No significant inelastic loss observed for molecules in the ground rotational state.
  • Upper bound for spin-relaxation rate coefficient set at <5.8×10⁻¹² cm³/s (95% confidence).
  • Quantum defect theory suggests a short-range loss parameter near unity for excited molecules and below 0.04 for ground-state molecules.

Conclusions:

  • Molecular rotational state significantly impacts inelastic collision dynamics with atoms.
  • Ground-state CaF molecules exhibit suppressed inelastic loss, indicating strong control over collision outcomes.
  • Experimental findings align with quantum defect theory predictions, validating its applicability to ultracold atom-molecule systems.