Nonlocal Nuclear Spin Quieting in Quantum Dot Molecules: Optically Induced Extended Two-Electron Spin Coherence Time

Area of Science:

• Quantum Information Science
• Condensed Matter Physics
• Materials Science

Background:

• Quantum dot molecules (QDMs) are promising for quantum computing due to their tunable electronic properties.
• Maintaining spin coherence in quantum systems is crucial for reliable quantum information processing.
• Nuclear spin fluctuations in semiconductor quantum dots can limit qubit coherence times.

Purpose of the Study:

• To extend coherence times between all four two-electron spin ground states in an InAs quantum dot molecule (QDM).
• To investigate the mechanism of nuclear spin suppression and its effect on coherence.
• To establish a method for measuring the reduction of nuclear spin fluctuations.

Main Methods:

• Utilizing nonlocal suppression of nuclear spin fluctuations in vertically stacked quantum dots (QDs).
• Optically addressing only the top QD transitions for control and measurement.
• Employing dark-state spectroscopy to reveal long coherence times.
• Performing line shape analysis to quantify the Overhauser field distribution.

Main Results:

• Demonstrated extended coherence between all four two-electron spin ground states of the InAs QDM.
• Identified nuclear spin locking, mediated by exchange interaction, as the source of long coherence.
• Provided the first measurement of Overhauser field distribution quieting, correlating with reduced nuclear spin fluctuations.

Conclusions:

• Nonlocal suppression of nuclear spin fluctuations is an effective strategy for enhancing qubit coherence in QDMs.
• Nuclear spin locking offers a robust mechanism for preserving quantum information.
• The developed line shape analysis provides a valuable tool for characterizing and improving qubit performance.