Universal coherence protection in a solid-state spin qubit
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-08-13 |
| Journal | Science |
| Authors | Kevin C. Miao, Joseph P. Blanton, Christopher P. Anderson, Alexandre Bourassa, Alexander L. Crook |
| Institutions | National Institutes for Quantum and Radiological Science and Technology, University of Chicago |
| Citations | 110 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research presents a major advancement in solid-state quantum coherence by implementing a universal protection protocol for a silicon carbide (SiC) spin qubit.
- Core Achievement: Construction of a robust qubit embedded in a decoherence-protected subspace (DPS) using Hamiltonian engineering via a continuous microwave drive (dressed states).
- Material System: Ground-state electron spin of a basally oriented kh divacancy defect in 4H-SiC, operated at zero external magnetic field (B = 0 mT).
- Universal Protection: The dressed spin states exhibit high-order protection against magnetic, electric, and temperature fluctuations, which typically limit solid-state coherence.
- Inhomogeneous Dephasing Time (T2*): Increased by over four orders of magnitude, reaching 22.4(10) milliseconds (ms).
- Hahn-Echo Coherence Time (T2): Extended to 64(4) ms, representing a thousand-fold increase over the undriven B=0 state.
- Practical Advantages: The continuous drive protocol offers uninterrupted coherence protection, lower peak drive powers compared to pulsed dynamical decoupling, and is compatible with active feedback to mitigate slow frequency drifts.
- Scalability: The B=0 operation is highly advantageous for integration with low critical field superconducting quantum systems, paving the way for robust hybrid quantum architectures.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Protected T2 (Inhomogeneous)* | 22.4(10) | ms | Achieved in DPS with active feedback. |
| Protected T2 (Hahn-Echo) | 64(4) | ms | Achieved in DPS (among the longest measured for optically addressable electron spins). |
| T2 Improvement Factor* | >4 orders of magnitude | N/A | Compared to undriven state. |
| Undriven T2 (B=0)* | 163(8) | ”s | Typical value for kh divacancy without dressing. |
| Undriven T2 (B=0) | 18.16(12) | ”s | Typical value for kh divacancy without dressing. |
| Operating Magnetic Field (B) | 0 | mT | Zero external magnetic field operation (clock transition). |
| Operating Temperature | 5 | K | Cryogenic operating temperature. |
| Transverse ZFS (E/(2Ï)) | 18.353164(4) | MHz | Intrinsic property of the kh divacancy in 4H-SiC. |
| Dressing Drive Rabi Frequency (Ω/(2Ï)) | 350 | kHz | Used for measurements; chosen to mitigate higher-order dispersion. |
| Magnetic Noise Magnitude (Nuclear Bath) | 13 | ”T | Estimated isotropic fluctuation magnitude limiting residual coherence. |
| Feedback Correction Magnitude | ~30 | Hz | Measured and corrected drift in spin resonance frequency. |
| Drive Oscillator Stability | 100 | ppm/°C | Stability of the microwave dressing drive oscillator. |
Key Methodologies
Section titled âKey Methodologiesâ- Material and Environment: Isolated kh divacancy spin-1 system in naturally abundant, commercial 4H-SiC, maintained at 5 K.
- Spin Control Infrastructure: Used on-chip wires (for microwave magnetic fields) and capacitors (for microwave electric fields) for spin manipulation, alongside a three-axis electromagnet for vector control of the external magnetic field.
- Clock Transition Operation: The spin system was operated at B = 0 mT, leveraging the intrinsic transverse zero-field splitting (ZFS) to create clock transitions, minimizing first-order magnetic sensitivity.
- Hamiltonian Engineering (Dressing): A continuous microwave drive, resonant with the |+) â |-) transition (at frequency Ï = 2E), was applied to hybridize the spin and photon states.
- Decoherence-Protected Subspace (DPS) Formation: Sufficiently strong driving (Rabi frequency Ω) induced Autler-Townes splitting, forming dressed spin states (|±1>) which constitute the DPS.
- Coherent Manipulation: Quantum operations were performed within the DPS using resonant AC magnetic fields (for Îms = ±1 transitions) and AC electric fields (for Îms = ±2 transitions).
- Coherence Measurement: Ramsey free precession and Hahn-echo sequences were executed on the superposition state $|\psi_0\rangle = \frac{1}{\sqrt{2}}(|+1\rangle + |-1\rangle)$ to quantify T2* and T2.
- Active Feedback Protocol: An error signal derived from Ramsey free precession was used to measure and correct slow drifts (~30 Hz) in the dressed spin resonance frequency, mitigating inhomogeneity caused by dressing drive amplitude fluctuations.
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated universal coherence protection and long coherence times in a scalable semiconductor platform (SiC) are critical for next-generation quantum technologies:
- Quantum Computing: SiC divacancies serve as robust, optically addressable qubits. The extended T2 and T2* times increase the available timescale for complex quantum algorithms and error correction.
- Quantum Memory and Storage: The 64 ms T2 time allows the electron spin to function as a high-fidelity, long-lived quantum memory element, crucial for quantum repeaters and networks.
- Hybrid Quantum Systems: The ability to operate the qubit at B = 0 mT facilitates seamless integration with superconducting circuits (e.g., resonators), which typically require low or zero magnetic fields, enabling the creation of efficient quantum buses.
- Quantum Sensing: The spin system retains high sensitivity to resonant control fields while being robust against non-resonant environmental noise (magnetic, electric, thermal), making it ideal for high-precision, stable quantum sensors.
- Scalable Solid-State Architectures: SiC is a mature semiconductor platform, allowing for the integration of these high-coherence qubits into scalable, on-chip devices using existing semiconductor fabrication techniques.
View Original Abstract
Dressed for coherence Solid-state qubits based on the electron spin of defects in silicon carbide or diamond provide a robust and versatile architecture for developing quantum technologies. The longer the lifetime of a spin, the more manipulations and quantum calculations can be performed, making for a more powerful quantum computational platform. Miao et al. show that by dressing the spins associated with the divacancy in silicon carbide with microwave photons, the lifetime can be extended by several orders of magnitude into milliseconds (see the Perspective by Hemmer). The technique effectively creates a quiet space for the qubit, thereby protecting it from magnetic, electric, and temperature fluctuations. This approach could be applicable to other architectures and provide a universal route to protecting qubits. Science , this issue p. 1493 ; see also p. 1432