Nanophotonic quantum sensing with engineered spin-optic coupling
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2023-01-09 |
| Journal | Nanophotonics |
| Authors | Laura Kim, Hyeongrak Choi, Matthew E. Trusheim, Hanfeng Wang, Dirk Englund |
| Institutions | Cambridge Electronics (United States), DEVCOM Army Research Laboratory |
| Citations | 15 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled āExecutive SummaryāThis paper proposes a paradigm shift in Nitrogen-Vacancy (NV) diamond quantum sensing, focusing on engineered nanophotonic interfaces to achieve near-unity optical readout fidelity at room temperature.
- Core Challenge Addressed: Conventional NV ensemble sensing relies on visible fluorescence readout (532 nm pump), which suffers from low spin contrast and poor photon collection efficiency (<10%), resulting in suboptimal readout fidelity (uncertainty ĻR often ā 1000).
- Proposed Solution: Transitioning the readout mechanism to Infrared (IR) absorption (1042 nm probe) via the spin-selective singlet state transition (1A1). This method is non-destructive and allows for near-unity collection efficiency.
- Nanophotonic Enhancement: Resonant structures (cavities, metasurfaces, slow-light waveguides) are utilized to enhance the spin-optic coupling, compensating for the inherently small IR absorption cross-section (one order of magnitude smaller than visible transitions).
- Performance Goal: Achieving sensitivity near the spin projection noise limit (nT for 1-second integration) by dramatically improving the readout fidelity (ĻK = 1/F).
- Application Focus: The technology is particularly advantageous for applications requiring efficient use of a micro- to nanoscale sensing volume, where scaling up the NV number is not feasible.
- Key Advantage of IR Readout: Purcell enhancement of the singlet-state transition favorably improves measurement spin contrast, unlike enhancement of visible transitions, which dilutes the contrast.
Technical Specifications
Section titled āTechnical Specificationsā| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Ground State Splitting (ZFS) | 2.87 | GHz | Zero-Field Splitting (3A2) |
| Operating Temperature | Ambient | - | Room temperature operation |
| Fluorescence Pump Wavelength | 532 | nm | Conventional optical initialization/readout |
| IR Absorption Probe Wavelength | 1042 | nm | Spin-selective singlet state transition readout |
| Diamond Refractive Index | 2.4 | - | ndiamond |
| Conventional Readout Uncertainty (Ensemble) | ~1000 | ĻR | Typical fluorescence readout limitation [10-12] |
| Conventional Collection Efficiency | <10 | % | Planar diamond substrate, high NA objective |
| Target Magnetic Sensitivity (Projection Limit) | nT | s-1/2 | For 1-second integration (assuming T2 ā 1 Āµs) |
| IR Absorption Cross-Section | ~10 | - | Approximately one order of magnitude smaller than visible transitions [29, 30] |
| Singlet State Lifetime Ratio (1A1 vs 1E) | ~100 | - | 1A1 lifetime is two orders of magnitude shorter than 1E [28] |
| Cavity Enhancement Factor (Purcell) | Ī/Ī0 | - | Proportional to (Q / Veff) * (Field Intensity)2 |
Key Methodologies
Section titled āKey MethodologiesāThe proposed methodology centers on engineering the spin-optic coupling via resonant nanophotonic structures to maximize the absorption signal at 1042 nm.
- Readout Mechanism Transition: Shift from the conventional probabilistic fluorescence readout (relying on branching ratios) to a non-destructive, spin-selective IR absorption readout (1042 nm) targeting the singlet state (1A1).
- Cavity Design for Purcell Enhancement: Utilizing high Quality factor (Q) and low effective mode volume (Veff) cavities to maximize the Purcell factor (Ī/Ī0). This enhances the transition rate, overcoming the small intrinsic IR absorption cross-section (Ļs).
- Metasurface Field Concentration: Implementing plasmonic or dielectric metasurfaces to achieve significant electric field enhancement (|ER|2/|E0|2) over the NV sensing volume, ensuring sufficient optical path-length enhancement without increasing physical footprint.
- Slow-Light Waveguide (WG) Integration: Designing WGs to reduce the group velocity (vg) of the 1042 nm probe light. This increases the interaction time between the NV ensemble and the optical field, maximizing the spin-dependent extinction (FOM ā e-LĪ±NV(1 - e-LĪ±NV)2).
- Coherent Detection Adoption: Employing coherent detection methods (e.g., homodyne or heterodyne) to measure the absorption signal, which is beneficial for systems operating in environments with large electrical noise.
- NV Position Engineering: Mitigating spatial variability in NV dynamics and sensitivity (caused by inhomogeneous electric fields in nanostructures) by controlling NV placement with high spatial precision (e.g., 10 nm scale) using techniques like delta-doping or focused ion implantation.
Commercial Applications
Section titled āCommercial ApplicationsāThe enhanced sensitivity and spatial resolution enabled by nanophotonic IR absorption readout are critical for next-generation quantum technologies and high-resolution imaging.
- Nanoscale Magnetic Imaging: Detection of magnetic fields generated by single electron spins or nuclear magnetic resonance (NMR) on the scale of single molecules under ambient conditions.
- Quantum Diamond Microscopy (QDM): High-fidelity, volume-normalized sensing for micro- to nanoscale samples, outperforming current QDM methods in sensitivity per unit volume.
- Vector Magnetometry: Development of compact, high-sensitivity vector magnetometers utilizing the polarization dependence of the engineered spin-optic coupling.
- Biological Transduction/Sensing: Detection of weak magnetic or electric signals generated by biological processes (e.g., single-neuron action potentials).
- Computational Imaging Systems: Utilizing spin-dependent phase and amplitude changes of the optical signal, compatible with compressive sensing techniques for gaining multidimensional information.
- Solid-State Quantum Repeaters: The ability to achieve high-fidelity readout is fundamental for scalable integration of long-lived quantum memories into photonic circuits.
View Original Abstract
Abstract Nitrogen vacancy centers in diamond provide a spin-based qubit system with long coherence time even at room temperature, making them suitable ambient-condition quantum sensors for quantities including electromagnetic fields, temperature, and rotation. The optically addressable level structures of NV spins allow transduction of spin information onto light-field intensity. The sub-optimal readout fidelity of conventional fluorescence measurement remains a significant drawback for room-temperature ensemble sensing. Here, we discuss nanophotonic interfaces that provide opportunities to achieve near-unity readout fidelity based on IR absorption via resonantly enhanced spin-optic coupling. Spin-coupled resonant nanophotonic devices are projected to particularly benefit applications that utilize micro- to nanoscale sensing volume and to outperform present methods in their volume-normalized sensitivity.