[Paper Review] Quantum well stabilized point defect spin qubits

Ivády, Joel Davidsson+11 more|arXiv (Cornell University)|May 28, 2019

Diamond and Carbon-based Materials Research64 references17 citations

TL;DR

This paper proposes a quantum well engineered in silicon carbide to stabilize the charge state of point defect spin qubits, overcoming issues of charge instability and phonon interference. Using density-functional theory and synchrotron x-ray diffraction, the authors identify a near-stacking fault axial divacancy as the source of robust, room-temperature spin qubits with high optical stability and resistance to photoionization.

ABSTRACT

Defect-based quantum systems in in wide bandgap semiconductors are strong candidates for scalable quantum-information technologies. However, these systems are often complicated by charge-state instabilities and interference by phonons, which can diminish spin-initialization fidelities and limit room-temperature operation. Here, we identify a pathway around these drawbacks by showing that an engineered quantum well can stabilize the charge state of a qubit. Using density-functional theory and experimental synchrotron x-ray diffraction studies, we construct a model for previously unattributed point defect centers in silicon carbide (SiC) as a near-stacking fault axial divacancy and show how this model explains these defect's robustness against photoionization and room temperature stability. These results provide a materials-based solution to the optical instability of color centers in semiconductors, paving the way for the development of robust single-photon sources and spin qubits.

Motivation & Objective

• Address charge-state instabilities and phonon interference that limit the performance of defect-based spin qubits in wide bandgap semiconductors.
• Overcome the challenge of optical instability in color centers, which hinders reliable spin initialization and single-photon source operation.
• Develop a materials-based solution to enhance the robustness and scalability of spin qubits in silicon carbide.
• Identify and characterize previously unattributed point defect centers in SiC as axial divacancies with unique electronic and structural properties.
• Enable room-temperature operation of spin qubits by stabilizing their charge state through engineered quantum well structures.

Proposed method

• Employ density-functional theory (DFT) to model the electronic structure and charge-state stability of point defects in 4H-SiC.
• Use synchrotron x-ray diffraction to experimentally probe the local crystal structure and confirm the presence of stacking faults.
• Engineer a quantum well structure in SiC to confine electrons and stabilize the charge state of the defect center.
• Analyze the defect's response to photoionization and phonon coupling to assess optical and thermal stability.
• Correlate theoretical predictions with experimental data to validate the model of the axial divacancy as a robust spin qubit candidate.
• Investigate the role of the near-stacking fault in modifying the electronic potential and suppressing charge-state transitions.

Experimental results

Research questions

• RQ1 What is the atomic-scale structure of previously unattributed point defect centers in 4H-SiC that exhibit robust optical and spin properties?
• RQ2 How does the presence of a quantum well structure influence the charge-state stability of point defects in SiC?
• RQ3 To what extent does the axial divacancy defect resist photoionization and maintain its spin state at room temperature?
• RQ4 What is the role of the near-stacking fault in stabilizing the electronic environment of the defect center?
• RQ5 Can engineered quantum well structures in SiC enable scalable, room-temperature spin qubits with high initialization fidelity?

Key findings

• The previously unattributed point defect centers in 4H-SiC are identified as axial divacancies with a near-stacking fault configuration.
• The quantum well structure effectively stabilizes the charge state of the defect, reducing charge-state fluctuations and enhancing spin initialization fidelity.
• The axial divacancy exhibits strong resistance to photoionization, enabling stable optical cycling at room temperature.
• Synchrotron x-ray diffraction confirms the presence of a stacking fault near the defect, which is critical for electronic stabilization.
• The defect maintains a robust spin ground state with long coherence times, suitable for quantum information applications.
• The combination of DFT modeling and experimental validation demonstrates that quantum well engineering is a viable pathway to stabilize spin qubits in wide bandgap semiconductors.