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Demonstration of magic dressing of $^3$He

Raymond Tat

TL;DR

The paper addresses magnetic-field stability in time-varying dressing-field scenarios for high-precision nEDM experiments. It introduces and demonstrates magic dressing, a method that renders spin precession insensitive to small variations in the dressing amplitude by operating near extremal points of the Bessel function $J_0$ (or zeros of $J_1$) for a single species. Experimental results with SEOP-polarized $^3$He show a substantial increase in $T_2$ under AC gradients when magic dressing is applied, validating the approach to mitigate gradient-induced decoherence. The authors extend the concept to two-species systems by proposing a modulated dressing sequence that achieves both magic and critical dressing, enabling robust two-species nEDM measurements (e.g., neutron and $^3$He) without stringent amplitude stability. Together, these results offer a practical route to improved magnetic-field control and longer coherence times in nEDM experiments like nEDMSF.

Abstract

A common concern in high-precision neutron electric dipole moment (nEDM) experiments is that of magnetic field stability. For static fields, this problem can be mitigated through the use of a superconducting holding field coil, which when operated in persistent current mode serves to stabilize the magnetic field. However, such a solution is not viable when time-varying magnetic fields are present, as is the case for the spin dressing mode of the proposed nEDMSF (nEDM super-fluid) experiment. This experiment features an oscillating magnetic field to dress the gyromagnetic ratios of $^3$He and neutrons to the same value, a condition known as critical dressing. Fluctuations in the dressing field amplitude have the potential to disrupt this condition. Here, we investigate a modification to spin dressing, termed ``magic dressing,'' which renders the system insensitive to small variations in dressing field amplitude. We further demonstrate the utility of this method for the single spin-species case using a sample of polarized $^3$He. We find a dramatic increase in transverse relaxation time in the presence of magnetic field gradients.

Demonstration of magic dressing of $^3$He

TL;DR

The paper addresses magnetic-field stability in time-varying dressing-field scenarios for high-precision nEDM experiments. It introduces and demonstrates magic dressing, a method that renders spin precession insensitive to small variations in the dressing amplitude by operating near extremal points of the Bessel function (or zeros of ) for a single species. Experimental results with SEOP-polarized He show a substantial increase in under AC gradients when magic dressing is applied, validating the approach to mitigate gradient-induced decoherence. The authors extend the concept to two-species systems by proposing a modulated dressing sequence that achieves both magic and critical dressing, enabling robust two-species nEDM measurements (e.g., neutron and He) without stringent amplitude stability. Together, these results offer a practical route to improved magnetic-field control and longer coherence times in nEDM experiments like nEDMSF.

Abstract

A common concern in high-precision neutron electric dipole moment (nEDM) experiments is that of magnetic field stability. For static fields, this problem can be mitigated through the use of a superconducting holding field coil, which when operated in persistent current mode serves to stabilize the magnetic field. However, such a solution is not viable when time-varying magnetic fields are present, as is the case for the spin dressing mode of the proposed nEDMSF (nEDM super-fluid) experiment. This experiment features an oscillating magnetic field to dress the gyromagnetic ratios of He and neutrons to the same value, a condition known as critical dressing. Fluctuations in the dressing field amplitude have the potential to disrupt this condition. Here, we investigate a modification to spin dressing, termed ``magic dressing,'' which renders the system insensitive to small variations in dressing field amplitude. We further demonstrate the utility of this method for the single spin-species case using a sample of polarized He. We find a dramatic increase in transverse relaxation time in the presence of magnetic field gradients.

Paper Structure

This paper contains 16 sections, 13 equations, 12 figures, 3 tables.

Table of Contents

  1. Spin Dressing and nEDM Measurement
  2. Magic Dressing
  3. Magic Dressing for a Single Species
  4. SEOP Apparatus
  5. Laser Optics
  6. Magnetic Field System
  7. Dressing Coil Design
  8. SEOP and NMR Electronics
  9. Demonstration of Magic Dressing
  10. Dressed Tipping
  11. Measurement Scheme
  12. Analysis of Magic Dressing Data
  13. Discussion of Results
  14. Magic Dressing for Two Species
  15. Conclusion
  16. ...and 1 more sections

Figures (12)

  • Figure 1: Optics elements to produce two beams of circularly polarized light to optically pump the rubidium vapor.
  • Figure 2: Schematic of optics used for the SEOP system. Having two beam paths that converge at the cell allows us to utilize all 60W of laser power.
  • Figure 3: Side view of magnetic field components used for in-situ NMR with the SEOP system, with the oven shown in the center. The outer red coils are the $B_0$ coils, the circular black coils are shim coils, and the square coils mounted in black frames around the oven are the dressing field coils.
  • Figure 4: Front view of the SEOP oven, showing the four square dressing coils around in the oven.
  • Figure 5: Simplified diagram of electronics used for NMR in the SEOP Lab
  • ...and 7 more figures