| Metadata | Details |
|---|
| Publication Date | 2020-11-19 |
| Journal | American Journal of Physics |
| Authors | Vikas K. Sewani, Hyma H. Vallabhapurapu, Yang Yang, Hannes R. Firgau, Chris Adambukulam |
| Institutions | UNSW Sydney, Centre for Quantum Computation and Communication Technology |
| Citations | 32 |
| Analysis | Full AI Review Included |
- Low-Cost Quantum Platform: A cost-effective experimental setup (less than USD 20k) was developed for demonstrating coherent spin control using Nitrogen-Vacancy (NV-) centers in diamond, specifically designed for undergraduate teaching laboratories.
- Room-Temperature Operation: The system operates robustly at room temperature in ambient atmosphere, eliminating the need for complex cryogenic or high-vacuum environments typical of advanced quantum research.
- Coherent Control Demonstrated: The setup successfully implemented key quantum control protocols, including Optically Detected Magnetic Resonance (ODMR), Rabi oscillations (ΩR = 2.69 MHz), and dynamical decoupling sequences (Hahn echo, CPMG).
- Key Coherence Metrics: Measured longitudinal relaxation time (T1) was 1.64 ± 0.25 ms, while the free precession coherence time (T2) via Hahn echo was 1.2 ± 0.2 µs.
- Pulsed Sequence Engineering: The system uses a Pulse Blaster and I/Q modulation to generate precise nanosecond-scale microwave (MW) pulses (e.g., π/2 pulse = 72 ns) necessary for two-axis control on the Bloch sphere.
- High-Density Sample Use: Utilizing a high-density NV- diamond sample ensures a large signal-to-noise ratio, making the measurements insensitive to minor misalignment and high ambient light levels.
| Parameter | Value | Unit | Context |
|---|
| Total Setup Cost | less than 20k | USD | Excluding PC and standard lab equipment |
| Operating Temperature | Room Temperature | °C | Ambient atmosphere |
| NV Zero-Field Splitting (D) | 2.87 | GHz | Ground state |
| Excitation Wavelength | 520 | nm | Green laser diode |
| Zero-Phonon Line (ZPL) | 637 | nm | NV- emission wavelength |
| Objective Numerical Aperture | 0.80 | NA | Olympus MS Plan 50x |
| Laser Focal Spot Size | ~1 | µm | Excitation volume |
| MW Antenna Resonance (Measured) | ~2.49 | GHz | PCB loop-gap resonator |
| Maximum MW Power | +24 (251) | dBm (mW) | Input to antenna |
| Maximum B1 Field (Simulated) | 306 | µT | Oscillating magnetic field at NV center |
| Rabi Frequency (ΩR) | 2.69 ± 0.02 | MHz | Coherent spin rotation rate |
| Rabi Coherence Time (TRabi) | 1.12 ± 0.14 | µs | Driven coherence time |
| Longitudinal Relaxation Time (T1) | 1.64 ± 0.25 | ms | Spin decay time |
| Hahn Echo Coherence Time (T2) | 1.2 ± 0.2 | µs | Free precession coherence time |
| π/2 Pulse Length | 72 | ns | Calibrated pulse duration |
| π Pulse Length | 144 | ns | Calibrated pulse duration |
| Electron Irradiation Density | 1018 | electrons/cm2 | HPHT diamond processing |
| Annealing Temperature | 900 | °C | Post-irradiation treatment (in vacuum) |
- Diamond Sample Preparation:
- Used a Type 1b (111)-oriented high-pressure, high-temperature (HPHT) diamond.
- Irradiated the diamond with 1018 electrons/cm2 density.
- Annealed the sample in vacuum at 900 °C for 2 hours to activate the NV- centers.
- Optical Setup and Alignment:
- A 520 nm fiber-coupled green laser diode was focused onto the diamond sample using a 50x/0.80NA objective lens, achieving a ~1 µm focal spot.
- Photoluminescence (PL) emission was collected through the same objective, filtered (600 nm long pass, 900 nm short pass) to isolate the NV- signal, and directed to a photodiode via a multi-mode fiber.
- Spin Initialization and Readout:
- Continuous 520 nm laser excitation initialized the NV spins into the 0>g state.
- Readout relied on the spin-dependent PL contrast, where the 0>g state emits approximately 30% more photons than the ±1>g states.
- Microwave (MW) Control System:
- A SignalCore SC800 MW source fed into a Texas Instruments I/Q modulator, controlled by TTL pulses from a Pulse Blaster.
- The modulated MW signal was amplified to +24 dBm and delivered to the NV centers via a custom PCB loop-gap resonator antenna (resonant at ~2.49 GHz).
- Pulsed Sequence Generation:
- A SpinCore Pulse Blaster ESR Pro 250 was programmed via Matlab to generate precise TTL sequences (down to nanosecond resolution) for controlling the laser (CH1) and the I/Q modulator (CH2, CH3).
- I/Q modulation allowed for phase control (e.g., 0°, 90°, 45°) necessary for X- and Y-axis rotations on the Bloch sphere.
- Signal Acquisition:
- A dual-phase lock-in amplifier (Ametek 5210) was used for phase-sensitive detection of the photodiode signal, synchronized to a reference frequency (CH0) provided by the Pulse Blaster, enabling high signal-to-noise ratio extraction of the low-contrast spin signal.
- Quantum Sensing and Metrology: NV- centers are leading solid-state quantum sensors used for high-resolution magnetic field detection, electric field sensing, and temperature measurement at the nanoscale.
- Biomedical Imaging: Applications in magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy, particularly for nanoscale sensing in biological systems (e.g., measuring spin dynamics in single cells).
- Quantum Information Processing: The NV spin system serves as a robust, room-temperature solid-state qubit, foundational for developing quantum computing architectures and quantum communication technologies.
- Materials Characterization: The ODMR and coherence measurement techniques are critical for benchmarking and characterizing the quality and noise environment of other emerging quantum materials, such as silicon qubits and superconducting qubits.
- Advanced Educational Tools: The setup itself is a commercializable platform for university-level quantum engineering education, providing hands-on experience with fundamental quantum control concepts.
View Original Abstract
The room temperature compatibility of the negatively charged nitrogen-vacancy (NV−) center in diamond makes it the ideal quantum system for a university teaching lab. Here, we describe a low-cost experimental setup for coherent control experiments on the electronic spin state of the NV− center. We implement spin-relaxation measurements, optically detected magnetic resonance, Rabi oscillations, and dynamical decoupling sequences on an ensemble of NV− centers. The relatively short times required to perform each of these experiments (<10 min) demonstrate the feasibility of the setup in a teaching lab. Learning outcomes include basic understanding of quantum spin systems, magnetic resonance, the rotating frame, Bloch spheres, and pulse sequence development.
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- 2019 - Quantum computing circuits and devices [Crossref]
- 2018 - Silicon qubits [Crossref]
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