Long-Term Spin State Storage Using Ancilla Charge Memories
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-12-01 |
| Journal | Physical Review Letters |
| Authors | Harishankar Jayakumar, Artur Lozovoi, Damon Daw, Carlos A. Meriles |
| Institutions | City College of New York, The Graduate Center, CUNY |
| Citations | 13 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details a novel method for long-term storage and readout of Nitrogen-Vacancy (NV) center spin states in diamond using neighboring defects as classical charge memories, termed Ancilla-Aided Integrated Detection (AID).
- Core Innovation: The NV qubit spin state is converted into a classical charge state (NV- or NV0) in surrounding ancilla defects (Silicon-Vacancy or other NVs) via Spin-to-Charge Conversion (SCC).
- Mechanism: Spin-selective ionization of the NV qubit generates free carriers (electrons/holes) that diffuse and are captured by the ancilla ensemble, altering the ancillaâs photoluminescence (PL).
- Storage Capability: The trapped charge states in the ancilla defects act as virtually unlimited long-term classical memories for the qubit spin state, particularly in the dark.
- Readout Strategy: The spin signal is read out by measuring the integrated fluorescence of the ancilla ensemble, separating the qubit manipulation and readout processes for independent optimization.
- Demonstrated Control: The technique successfully implemented basic building blocks of NV spin control, including time-resolved Rabi oscillations and Hahn-echo sequences, using the ancilla charge readout.
- Sensitivity Potential: Modeling suggests that AID can potentially boost sensitivity beyond existing standard optical sensing (SOS) techniques, especially if ancilla traps feature high photon emission rates or long ionization/recombination times.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Concentration (Sample 1) | 10-2 | ppm | Type 1b diamond (SiV present) |
| SiV Concentration (Sample 1) | 10-1 | ppm | Type 1b diamond (Ancilla trap) |
| Nitrogen Concentration (Sample 1) | 1 | ppm | Type 1b diamond |
| Green Laser Wavelength (L1) | 520 | nm | SCC/Initialization |
| Red Laser Wavelength (L2) | 632 | nm | SCC/Readout/Initialization |
| Green Laser Power (L1) | 3 | mW | Initialization/SCC |
| Red Laser Power (L2) | 21 | mW | SCC (High power) |
| MW Frequency (NV Resonance) | 2.87 | GHz | NV ground state crystal-field splitting |
| MW Pulse Duration | 100 | ns | Spin manipulation (Rabi/Echo) |
| SCC Pulse Duration | 100 | ns | Simultaneous Green/Red pulses |
| Electron Mobility (”n) | 2.4 · 1011 | ”m2/(V·s) | Ambient conditions (T=293 K) |
| Hole Mobility (”p) | 2.1 · 1011 | ”m2/(V·s) | Ambient conditions (T=293 K) |
| Electron Diffusion Coefficient (Dn) | 6.1 · 109 | ”m2/s | Ambient conditions (T=293 K) |
| Hole Diffusion Coefficient (Dp) | 5.3 · 109 | ”m2/s | Ambient conditions (T=293 K) |
| Optimal SiV-AID Ring Width (w) | 5 | ”m | For maximum SNR (Fig. S4d) |
| Ancilla Readout Filter | 650 to 800 | nm | Passband filter for NV/SiV fluorescence |
Key Methodologies
Section titled âKey MethodologiesâThe experimental methodology combines magnetic resonance and multi-color confocal microscopy to implement the Ancilla-Aided Integrated Detection (AID) protocol:
- Confocal Setup and Illumination: Experiments utilize a home-built confocal microscope with an air objective (NA=0.7). Illumination spots (~1 ”m diameter) are generated using 520 nm (green) and 632 nm (red) diode lasers.
- Microwave (MW) Control: MW pulses (2.87 GHz) are applied via an omega-shaped stripline supporting the diamond sample, enabling precise control over the NV qubit spin state (ms = 0 and ms = ±1).
- Charge Initialization: The experimental area (e.g., 40x40 ”m2) is initialized via multiple red (632 nm) or green (520 nm) laser scans to prepare the NV and ancilla defects into a specific non-fluorescent (dark) charge state (e.g., NV- or SiV0).
- Spin-to-Charge Conversion (SCC): The NV qubit is subjected to simultaneous, high-power green (3 mW) and red (21 mW) laser pulses (100 ns duration). This process selectively ionizes the NV based on its spin state (ms = 0 state is more likely to ionize).
- Carrier Generation and Diffusion: SCC generates free electrons and holes that diffuse away from the central qubit illumination spot.
- Ancilla Trapping and Activation: Diffusing carriers are captured by neighboring ancilla traps (SiV or NV), converting the ancilla into a fluorescent (bright) charge state (e.g., SiV- or NV0). This charge state change acts as the spin memory.
- Time-Resolved Measurement: The protocol is adapted for time-resolved measurements (e.g., Rabi and Hahn-echo sequences) by varying the MW pulse duration or the spin evolution time (te) between SCC cycles.
- AID Readout: The integrated fluorescence (PL) of the activated ancilla ensemble is measured over a broad time interval (50 ms to 2 s). The spin signal is extracted by calculating the differential fluorescence between MW on-resonance and off-resonance conditions.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of spin state storage via ancilla charge memories has significant implications for several high-technology sectors:
- Quantum Computing and Memory: Provides a pathway for long-lived quantum memories by converting fragile spin states into robust, classical charge states, potentially overcoming limitations imposed by short spin coherence times.
- Quantum Sensing and Metrology: Offers a platform for enhanced sensitivity in NV-based sensors (e.g., magnetometers, thermometers) by integrating the signal over long periods, potentially boosting the Signal-to-Noise Ratio (SNR) beyond standard optical readout limits.
- Diamond Defect Engineering: Establishes a framework for optimizing the spatial distribution, concentration, and type of defects (qubits and ancillae) in diamond materials to maximize charge capture efficiency and readout fidelity.
- Spintronics: Enables spin-polarized carrier injection into wide-bandgap semiconductors without relying on ferromagnetic electrodes, opening new routes for spin transport applications.
- Quantum Communication: Explores the use of charge carriers (electrons/holes) as âflying qubitsâ to transport quantum information between remote spin registers, crucial for building quantum networks.
View Original Abstract
We articulate confocal microscopy and electron spin resonance to implement spin-to-charge conversion in a small ensemble of nitrogen-vacancy (NV) centers in bulk diamond and demonstrate charge conversion of neighboring defects conditional on the NV spin state. We build on this observation to show time-resolved NV spin manipulation and ancilla-charge-aided NV spin state detection via integrated measurements. Our results hint at intriguing opportunities in the development of novel measurement strategies in fundamental science and quantum spintronics as well as in the search for enhanced forms of color-center-based metrology down to the limit of individual point defects.