Cavity quantum electrodynamics with color centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-08-06 |
| Journal | Optica |
| Authors | Erika Janitz, Mihir K. Bhaskar, Lilian Childress |
| Institutions | McGill University, Harvard University Press |
| Citations | 124 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Objective: Realizing efficient, coherent interfaces between optical photons and long-lived solid-state matter qubits (color centers in diamond) using Cavity Quantum Electrodynamics (cQED).
- Performance Benchmark: State-of-the-art SiV-cQED systems have achieved ultra-high cooperativity (C > 100), enabling near-deterministic spin-photon interactions and memory-enhanced quantum communication.
- Platform Comparison (NV vs. SiV): Nitrogen-Vacancy (NV) centers offer superior spin coherence (T2 > 1 s in bulk) but suffer from poor optical coherence near surfaces. Silicon-Vacancy (SiV) centers offer superior optical coherence (lifetime-limited linewidths) but require deep cryogenic operation (T < 500 mK) for long spin T2.
- Methodologies: Two primary approaches are reviewed: 1) Open Fabry-Perot microcavities (compatible with bulk-like diamond membranes, ideal for NV centers), and 2) All-diamond nanophotonic cavities (PCCs/microdisks, maximizing Q/V, ideal for surface-insensitive SiV centers).
- Fabrication Challenges: Achieving high Q/V ratios requires nanoscale precision in emitter placement (sub-100 nm via implantation) and ultra-smooth surfaces (0.1 nm-rms roughness via ICP RIE etching) in resilient diamond material.
- Key Achievement: The first experimental demonstration of memory-enhanced quantum communication using a solid-state platform, leveraging high-fidelity spin readout (F > 0.9998) and spin-photon entanglement (F > 0.944).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV ZPL Wavelength | 637 | nm | Zero Phonon Line |
| SiV ZPL Wavelength | 737 | nm | Zero Phonon Line |
| GeV ZPL Wavelength | 602 | nm | Zero Phonon Line |
| SiV Debye-Waller Factor (ζ) | 0.7 | - | Fraction of emission into ZPL (high optical efficiency) |
| NV Excited State Lifetime (Ï) | 11-13 | ns | - |
| SiV Excited State Lifetime (Ï) | 1.6-1.7 | ns | Short lifetime, consistent with non-radiative processes |
| SiV Spin Coherence Time (T2) | > 10 | ms | Achieved at T < 500 mK |
| NV Spin Coherence Time (T2) | > 1 | s | Achieved in bulk diamond at 3.7 K (using decoupling) |
| SiV Orbital Splitting Temp (ħÎGS/kB) | 2.4 | K | Required temperature for exponential suppression of phonon dephasing |
| SiV-cQED Cooperativity (C) | > 100 | - | State-of-the-art nanophotonic device |
| SiV Spin Readout Fidelity (F) | 0.9998 ± 0.0002 | - | Single-shot, cavity-enhanced readout |
| Fabry-Perot Finesse (F) | 5,260 | - | Achieved in NV membrane coupling experiment |
| Fabry-Perot Cavity Linewidth | 60 | pm | Required stabilization precision for resonant coupling |
| Diamond Membrane Thickness | 100 nm - 1 | ”m | Used in Fabry-Perot membrane-in-cavity geometry |
| Diamond Surface Roughness | ~ 0.1 | nm-rms | Achieved via ICP RIE etching (ArCl2/O2 recipes) |
| Nanophotonic Q/V0 (Achieved) | > 104 | - | Freestanding 1D PCCs (V0 is cubic wavelength in diamond) |
Key Methodologies
Section titled âKey Methodologiesâ-
Emitter Incorporation and Localization:
- Ion Implantation: Used focused ion beam (FIB) or lithographically aligned masks (LAM) to achieve precise 3D localization of impurities (e.g., N, Si) followed by high-temperature annealing (up to 1200 °C) to form color centers.
- Delta-Doping/Overgrowth: Combining shallow masked implantation with subsequent pristine single crystal diamond overgrowth to limit implantation straggle and improve 3D localization.
-
Open Fabry-Perot Microcavity Fabrication:
- Micromirror Creation: Laser ablation or FIB milling used to create shallow parabolic dimples (micron-scale radius of curvature, R) on optical fiber tips or planar substrates, followed by low-loss dielectric mirror coating.
- Membrane Preparation: Bulk diamond thinned via laser slicing/polishing or He-ion implantation/liftoff to create ultra-smooth, micron-thick membranes (100 nm to 1 ”m).
- Surface Smoothing: Inductively Coupled Plasma Reactive Ion Etching (ICP RIE) using alternating ArCl2 and O2 recipes to achieve surface roughness as low as 0.1 nm-rms.
-
All-Diamond Nanophotonic Cavity Fabrication:
- Patterning: Electron-beam lithography (EBL) used to define high-resolution patterns for Photonic Crystal Cavities (PCCs) and microdisks.
- Dry Etching: Plasma-based dry etching techniques (e.g., RIE) combined with sophisticated masks to etch high-aspect ratio structures in diamond.
- Underetching (Isolation): Structures isolated from the bulk substrate using either angled RIE (resulting in triangular cross-sections) or selective crystallographic etching (resulting in rectangular cross-sections and flat lower surfaces).
-
In-Situ Tuning and Stabilization:
- Cavity Resonance Tuning: Achieved by condensing gas (e.g., Xenon) onto the nanostructure at cryogenic temperatures to increase the local refractive index, followed by selective laser light boiling to precisely reverse the shift.
- Emitter Spectral Tuning (NV): DC Stark effect used to actively compensate for spectral diffusion and mismatch by applying electric fields.
- Emitter Spectral Tuning (SiV): Two-photon Raman transitions or dynamic strain control used for wavelength tuning, compensating for the SiVâs insensitivity to electric fields.
Commercial Applications
Section titled âCommercial Applicationsâ- Quantum Communication and Networking:
- Quantum Repeaters: Utilizing cavity-coupled spin-photon interfaces to efficiently distribute entanglement over long distances, overcoming photon loss limitations.
- Distributed Quantum Computing: Forming the fundamental nodes (memory and processing units) connected by photonic channels in a quantum internet architecture.
- Quantum Key Distribution (QKD): Enabling high-efficiency, quantum-secured communication protocols.
- Quantum Information Processing:
- Solid-State Quantum Memory: Using the long-lived spin states (NV, SiV) as robust quantum memories for light, critical for asynchronous quantum operations.
- Deterministic Single-Photon Sources: Creating bright, on-demand sources of indistinguishable photons required for linear optical quantum computing (LOQC).
- Quantum Sensing and Metrology:
- High-Fidelity Spin Readout: Leveraging cavity enhancement for rapid, high-fidelity single-shot spin readout, improving the performance of diamond-based quantum sensors.
- Quantum-Enhanced Interferometry: Utilizing quantum networks for improved precision in tasks like clock synchronization.
- Advanced Diamond Materials:
- Wafer-Scale Diamond Photonics: Development of scalable fabrication techniques for thin-film, single-crystal diamond (e.g., via implantation/liftoff) suitable for mass production of nanophotonic devices.
View Original Abstract
Coherent interfaces between optical photons and long-lived matter qubits form a key resource for a broad range of quantum technologies. Cavity quantum electrodynamics (cQED) offers a route to achieve such an interface by enhancing interactions between cavity-confined photons and individual emitters. Over the last two decades, a promising new class of emitters based on defect centers in diamond has emerged, combining long spin coherence times with atom-like optical transitions. More recently, advances in optical resonator technologies have made it feasible to realize cQED in diamond. This article reviews progress towards coupling color centers in diamond to optical resonators, focusing on approaches compatible with quantum networks. We consider the challenges for cQED with solid-state emitters and introduce the relevant properties of diamond defect centers before examining two qualitatively different resonator designs: micrometer-scale Fabry-Perot cavities and diamond nanophotonic cavities. For each approach, we examine the underlying theory and fabrication, discuss strengths and outstanding challenges, and highlight state-of-the-art experiments.