Single-Shot Readout and Weak Measurement of a Tin-Vacancy Qubit in Diamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2024-03-19 |
| Journal | arXiv (Cornell University) |
| Authors | Eric I. Rosenthal, Souvik Biswas, Giovanni Scuri, Hope Lee, Abigail Stein |
| Institutions | University of Illinois Urbana-Champaign, Stanford University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”- High-Fidelity Readout: Demonstrated single-shot electronic spin readout of a tin-vacancy (SnV-) qubit in diamond with a fidelity of 87.4%.
- Conditional Performance: Achieved a conditional readout fidelity of 98.5% by post-selecting on the outcome of two consecutive measurements.
- Compatibility Established: Confirmed that high-fidelity readout is compatible with rapid microwave spin control, demonstrating a favorable parameter regime for SnV- as a spin-photon interface.
- Rapid Spin Control: Demonstrated coherent spin manipulation with a microwave π-pulse time of 80 ns at 3.677 GHz.
- Efficiency Benchmark: Used weak quantum measurement to characterize the measurement apparatus, determining an overall measurement efficiency (η) of approximately 0.1%.
- Qubit Robustness: SnV- utilizes a large ground state splitting (minimum 820 GHz), making it robust to thermal decoherence and enabling coherent control at temperatures greater than 1 Kelvin.
- Fundamental Metrology: Developed a universal method using measurement-induced dephasing to characterize the efficiency of solid-state color center spin readout.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Qubit Type | SnV- | N/A | Negatively charged tin-vacancy center in diamond. |
| Operating Temperature | 1.7 | K | Used for T2 and T1 measurements. |
| Single-Shot Readout Fidelity (Fr) | 87.4 | % | 50 µs integration window. |
| Conditional Readout Fidelity (Fc) | 98.5 | % | Conditioning on two readouts. |
| Measurement Efficiency (η) | 0.1 | % | Overall loss between qubit and detector. |
| Cyclicity (Λ) | 2244 ± 108 | N/A | Ratio of spin-preserving to spin-flipping decay. |
| Polarization Rate (Γp) | 49.02 ± 0.72 | kHz | Rate of spin polarization at maximum cyclicity. |
| Microwave π-Pulse Time | 80 | ns | Rapid spin control demonstration. |
| Qubit Frequency (ωq/2π) | 3.677 | GHz | Used for 80 ns π-pulse. |
| Ground State Splitting (GSS) | 903 | GHz | Measured GSS for this moderately strained center. |
| Minimum GSS (SnV-) | 820 | GHz | Inherent property, allows higher temperature operation. |
| Coherence Time (T2CPMG-2) | 270 ± 30 | µs | Measured at 1.7 K, |
| Optical Decay Rate (γ) | 2π x (35 ± 1.6) | MHz | SnV- intrinsic property. |
| Magnetic Field Amplitude ( | B | ) | 125 |
| Readout Integration Window (τ) | 50 | µs | Used for single-shot fidelity calculation. |
| Saturation Power (Psat) | 313 ± 8 | nW | Optical drive power specified at cryostat input (Fig. 4). |
Key Methodologies
Section titled “Key Methodologies”The experiment utilizes a combination of optical, microwave, and magnetic field control techniques within a cryogenic confocal microscopy setup:
- Qubit Platform and Environment:
- The SnV- center is located in a diamond mesa structure (1 µm height, 2.5 µm width) on a (100) diamond chip.
- The system is cooled to 1.7 K using a cryostat.
- Spin State Preparation and Readout:
- Spin Initialization: Achieved via resonant optical pumping using the A1 transition (spin-preserving) or B2 transition.
- Optical Drive: Resonant laser light (619 nm range) is modulated by Acousto-Optic Modulators (AOMs) and an Electro-Optic Modulator (EOM) to drive the first sideband.
- Readout: Spin-dependent photoluminescence (PL) is collected confocally, filtered to isolate the phonon sideband (PSB, using a 635 nm long pass filter), and detected by a single-photon counter.
- Fidelity Optimization: The magnetic field (B) is precisely aligned near the spin dipole axis (azimuthal angle ζ ≈ 147°, misalignment ≈ 10°) to maximize cyclicity (Λ).
- Microwave Spin Control:
- Microwaves are delivered via a wire bond draped over the diamond chip.
- Rabi oscillations are used to demonstrate rapid coherent control (80 ns π-pulse).
- Noise and Stability Management:
- Charge Resonance Checks (CRCs): Applied before and after readout steps. CRCs involve simultaneously driving both A1 and B2 transitions to ensure the qubit remains in the correct charge state and is not spectrally diffusing.
- Post-Selection: Data analysis is post-selected based on successful CRC passes (retaining ~7.5% of total cycles) to ensure high fidelity.
- Weak Quantum Measurement (Characterization):
- The qubit is prepared in a superposition state and subjected to a weak resonant laser pulse of variable power (p) and duration (τ).
- This pulse is placed within a dynamical decoupling sequence (CPMG-2) to measure the resulting measurement-induced dephasing rate (Γφ).
- Comparison of the dephasing rate (Γφ) and the collected photon signal (ñb - ñd) is used to calculate the measurement efficiency (η).
Commercial Applications
Section titled “Commercial Applications”The SnV- platform, validated by these high-fidelity readout and control results, is highly relevant for next-generation quantum technologies, particularly those requiring robust, high-rate spin-photon interfaces.
- Quantum Networking and Communication:
- Quantum Repeater Nodes: SnV- is a strong candidate for building quantum repeater nodes, offering advantages over SiV- due to its robustness at elevated temperatures (several Kelvin) and high quantum efficiency (80%-90%).
- High-Rate Entanglement Generation: The high cyclicity (Λ ≈ 2200) and strong zero-phonon line (ZPL) emission (Debye-Waller factor ~60%) promise significantly higher entanglement generation rates compared to NV- centers.
- Solid-State Quantum Computing:
- Quantum Memory: The long spin coherence time (T2CPMG-2 = 270 µs) enables the SnV- spin to serve as a robust quantum memory element.
- Integrated Qubit Registers: The compatibility of SnV- with nanophotonic structures (waveguides, cavities) supports the development of scalable, integrated quantum registers.
- Quantum Metrology and Sensing:
- Efficiency Benchmarking: The weak quantum measurement methodology developed provides a universal tool for characterizing the efficiency and performance of readout systems across various solid-state platforms (including SiV- and superconducting qubits).
- Diamond Material Requirements (Relevant to CVD):
- The work relies on high-quality diamond material containing implanted SnV- centers, typically requiring High-Purity CVD Diamond for low nitrogen and defect concentrations to maximize coherence.
View Original Abstract
The negatively charged tin-vacancy center in diamond (SnV$^-$) is an emerging platform for building the next generation of long-distance quantum networks. This is due to the SnV$^-$‘s favorable optical and spin properties including bright emission, insensitivity to electronic noise, and long spin coherence times at temperatures above 1 Kelvin. Here, we demonstrate measurement of a single SnV$^-$ electronic spin with a single-shot readout fidelity of $87.4%$, which can be further improved to $98.5%$ by conditioning on multiple readouts. We show this performance is compatible with rapid microwave spin control, demonstrating that the trade-off between optical readout and spin control inherent to group-IV centers in diamond can be overcome for the SnV$^-$. Finally, we use weak quantum measurement to study measurement induced dephasing; this illuminates the fundamental interplay between measurement and decoherence in quantum mechanics, and makes use of the qubit’s spin coherence as a metrological tool. Taken together, these results overcome an important hurdle in the development of the SnV$^-$ based quantum technologies, and in the process, develop techniques and understanding broadly applicable to the study of solid-state quantum emitters.