An ultra-stable 1.5 T permanent magnet assembly for qubit experiments at cryogenic temperatures

Area of Science:

• Physics
• Materials Science
• Quantum Computing

Background:

• Static magnetic fields are crucial for material characterization and spin polarization in Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR).
• A consistent, high-magnitude static magnetic field is often required for these applications.

Purpose of the Study:

• To design, simulate, and characterize a novel permanent magnet assembly for generating high magnetic field strengths.
• To assess the stability and suitability of this assembly for demanding applications like spin qubit experiments.

Main Methods:

• Utilized a Halbach array configuration of neodymium magnets.
• Incorporated Supermendur, a soft magnetic material, to enhance the magnetic field within the air gap.
• Performed detailed design, simulation, and experimental characterization of the magnet assembly.

Main Results:

• Achieved magnetic field strengths of up to 1.5 Tesla over a 7 mm air gap.
• Demonstrated outstanding magnetic field stability with a drift rate below 2.8 parts per billion per hour (|D| < 2.8 ppb/h).
• Successfully validated the assembly's performance in spin qubit experiments within a dilution refrigerator.

Conclusions:

• The developed permanent magnet assembly provides a stable, high-field magnetic environment.
• This technology serves as a viable, more compact, and cost-effective replacement for superconducting solenoids in applications such as spin qubit research.
• The high stability makes it suitable for sensitive quantum experiments requiring precise magnetic field control.