Hyperfine-phonon spin relaxation in a single-electron GaAs quantum dot

Area of Science:

• Quantum Computing
• Condensed Matter Physics
• Semiconductor Nanostructures

Background:

• Spin relaxation time (T1) is crucial for qubit performance, with longer T1 improving coherence and readout fidelity.
• In GaAs quantum dots, spin relaxation at high magnetic fields is governed by phonon emission and spin-orbit coupling, showing T1 ∝ B⁻⁵ dependence.
• Theoretical predictions suggest a shift to nuclear spin coupling at lower fields, leading to isotropic relaxation and T1 ∝ B⁻³ scaling.

Purpose of the Study:

• To experimentally verify the predicted transition in spin relaxation mechanisms at low magnetic fields in GaAs quantum dots.
• To investigate the scaling of spin relaxation time (T1) with magnetic field (B) in an extended range, including previously unexplored low-field regimes.
• To achieve and report a significantly extended electron spin lifetime in a nanostructure.

Main Methods:

• Experimental measurement of spin relaxation time (T1) in GaAs quantum dots.
• Utilized a wider range of magnetic fields, enabled by lower operating temperatures.
• Characterized the magnetic field dependence and anisotropy of T1.

Main Results:

• Experimental confirmation of the predicted T1 ∝ B⁻³ scaling at low magnetic fields, attributed to nuclear spin coupling.
• Observed isotropic spin relaxation at low fields, contrasting with anisotropic behavior at high fields.
• Achieved a record maximum spin relaxation time (T1) of 57 ± 15 seconds at the lowest measured magnetic fields.

Conclusions:

• The study experimentally validates theoretical predictions regarding spin relaxation mechanisms in GaAs quantum dots at low magnetic fields.
• The demonstrated record electron spin lifetime provides a significant advancement for the development of robust spin-based qubits.
• Understanding and controlling T1 via magnetic field manipulation is key to improving qubit coherence and readout fidelity in quantum technologies.