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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: Types of Nuclear Relaxation01:28

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Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
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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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Atomic Nuclei: Magnetic Resonance01:05

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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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Storing quantum coherence in a quantum dot nuclear spin ensemble for over 100 milliseconds.

Harry E Dyte1, Santanu Manna2,3, Saimon F Covre da Silva2,4

  • 1School of Mathematical and Physical Sciences, University of Sheffield, Sheffield, United Kingdom.

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|December 4, 2025
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Nuclear spins in quantum dots achieve over 100 ms coherence times. This breakthrough in solid-state quantum memory is vital for quantum communication networks.

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Area of Science:

  • Quantum Information Science
  • Solid-State Physics
  • Materials Science

Background:

  • Long coherence times are essential for quantum computing and quantum memory.
  • Nuclear spins in epitaxial GaAs/AlGaAs quantum dots show promise due to isolation and optical coupling.
  • Current coherence times (~1 ms) are limited by nuclear spin interactions and crystal strain.

Purpose of the Study:

  • To significantly extend nuclear spin coherence times in quantum dots.
  • To engineer a more robust solid-state quantum memory.
  • To enable practical quantum repeaters for optical quantum communication.

Main Methods:

  • Strain engineering of the nuclear spin ensemble.
  • Application of tailored dynamical decoupling sequences.
  • Utilizing epitaxial GaAs/AlGaAs quantum dots as the quantum system.

Main Results:

  • Achieved nuclear spin coherence times exceeding 100 ms.
  • Overcame limitations imposed by dipole-dipole interactions and nuclear quadrupolar coupling.
  • Demonstrated a significant enhancement over previous coherence limits.

Conclusions:

  • The study presents a viable method for extending quantum memory coherence times.
  • This advancement paves the way for functional solid-state quantum memories.
  • The results are crucial for developing quantum repeaters in quantum communication networks.