[Paper Review] Enhanced stability of defect-based qubits in quantum wells

Viktor Ivády, Joel Davidsson+6 more|arXiv (Cornell University)|May 28, 2019

Diamond and Carbon-based Materials Research44 references3 citations

TL;DR

This paper demonstrates that the quantum well formed by a stacking fault in silicon carbide stabilizes the charge state of the PL6 center—a divacancy defect—enabling robust optical cycling and high-fidelity spin initialization and readout at elevated temperatures. The defect's enhanced stability arises from electron confinement in the quantum well, offering a material-based solution to charge-state instability in color centers for scalable quantum technologies.

ABSTRACT

Optically addressable paramagnetic point defects in semiconductors are among the most promising systems for quantum-information technologies. However, the fidelities of spin initialization and readout rely on optical cycling, and charge-state instabilities during this cycle have proven to be an important unresolved problem. In this work, we demonstrate that the quantum well of an extended defect can stabilize the charge state of a point defect. In particular, we establish that the PL6 center in silicon carbide is a divacancy within a stacking fault, and that the quantum well deriving from this stacking fault stabilizes the defect's charge state, leading to its extraordinary performance at elevated temperatures and unusual robustness to optical cycling. The generalization of our results provides a material-based solution to the optical instability of color centers in semiconductors that may facilitate the development of a new class of robust single-photon sources and spin qubits.

Motivation & Objective

• To address the critical challenge of charge-state instability in optically addressable color centers in semiconductors.
• To understand the origin of the exceptional thermal and optical stability of the PL6 center in 4H-SiC.
• To establish a general design principle for stabilizing charge states in point defects using quantum well engineering.
• To enable high-fidelity spin initialization and readout at elevated temperatures through defect engineering.

Proposed method

• Identification of the PL6 center as a divacancy defect located within a stacking fault in 4H-SiC.
• Use of photoluminescence spectroscopy to probe the optical and electronic properties of the defect under varying temperature and excitation conditions.
• Theoretical modeling of the electronic structure and charge-state stability, including electron confinement in the quantum well formed by the stacking fault.
• Analysis of optical cycling performance to assess stability and fidelity of spin initialization and readout over repeated cycles.
• Comparison of charge-state dynamics in the defect with and without the quantum well structure to isolate its stabilizing effect.

Experimental results

Research questions

• RQ1 What is the atomic structure of the PL6 center in 4H-SiC, and how does it differ from isolated point defects?
• RQ2 How does the presence of a stacking fault and associated quantum well influence the charge-state stability of the defect?
• RQ3 To what extent does the quantum well enhance optical cycling fidelity and thermal robustness of the defect?
• RQ4 Can the quantum well effect be generalized to stabilize other color centers in semiconductors?

Key findings

• The PL6 center is identified as a divacancy defect embedded within a stacking fault in 4H-SiC.
• The quantum well formed by the stacking fault confines electrons, stabilizing the defect’s charge state against fluctuations.
• The defect exhibits robust optical cycling and high-fidelity spin initialization and readout at elevated temperatures, exceeding typical performance limits.
• The quantum well structure suppresses charge-state instabilities that otherwise limit the performance of color centers in semiconductors.
• The mechanism provides a generalizable design principle for engineering stable, optically addressable qubits in semiconductors.