Group IV color centers in diamond are among the most promising optically active electron-spin systems with strong optical transitions and long spin coherences. The orbital ground-state splitting of the center is particularly important to suppress the interaction with coherence-limiting phonons. A higher orbital ground-state splitting improves the spin-coherence properties and sets the upper limit for the operating temperature. Negatively charged silicon-vacancy centers have an ordinary ground-state splitting from spin-orbit coupling of only 48 G Hz , resulting in required temperatures below 1 K, which can only be achieved by dilution refrigerators. Here, we increase the orbital ground-state splitting by up to an order of magnitude by induced strain in a single-crystal diamond membrane. The characterized orbital ground-state splitting in highly strained regions could allow for electron-spin-coherence times of milliseconds at 1.5 K . We demonstrate cavity-assisted spectroscopy enabled by coupling the emitter ensemble with a selectable strain to the mode of a Fabry-Perot microcavity. Calculation of the absorption cross section yields σ abs ens ≈ 4.9 ⋅ 10 − 11 cm 2 . Furthermore, temperature-dependent lifetime measurements reveal a Purcell enhanced twofold reduction in emitter lifetime below 1 ns at 4 K .
Group IV color centers in diamond are among the most promising optically active electron-spin systems with strong optical transitions and long spin coherences. The orbital ground-state splitting of the center is particularly important to suppress the interaction with coherence-limiting phonons. A higher orbital ground-state splitting improves the spin-coherence properties and sets the upper limit for the operating temperature. Negatively charged silicon-vacancy centers have an ordinary ground-state splitting from spin-orbit coupling of only 48 G Hz , resulting in required temperatures below 1 K, which can only be achieved by dilution refrigerators. Here, we increase the orbital ground-state splitting by up to an order of magnitude by induced strain in a single-crystal diamond membrane. The characterized orbital ground-state splitting in highly strained regions could allow for electron-spin-coherence times of milliseconds at 1.5 K . We demonstrate cavity-assisted spectroscopy enabled by coupling the emitter ensemble with a selectable strain to the mode of a Fabry-Perot microcavity. Calculation of the absorption cross section yields σ abs ens ≈ 4.9 ⋅ 10 − 11 cm 2 . Furthermore, temperature-dependent lifetime measurements reveal a Purcell enhanced twofold reduction in emitter lifetime below 1 ns at 4 K .
Group-IV color centers in diamond are promising candidates for quantum networks due to their dominant zero-phonon line and symmetry-protected optical transitions that connect to coherent spin levels. The negatively charged tin-vacancy (SnV) center possesses long electron spin lifetimes due to its large spin-orbit splitting. However, the magnetic dipole transitions required for microwave spin control are suppressed, and strain is necessary to enable these transitions. Recent work has shown spin control of strained emitters using microwave lines that suffer from Ohmic losses, restricting coherence through heating. We utilize a superconducting coplanar waveguide to measure SnV centers subjected to strain, observing substantial improvement. A detailed analysis of the SnV center electron spin Hamiltonian based on the angle-dependent splitting of the ground and excited states is performed. We demonstrate coherent spin manipulation and obtain a Hahn echo coherence time of up to T 2 = 430 μ s . With dynamical decoupling, we can prolong coherence to T 2 = 10 ms , about a sixfold improvement compared to earlier works. We also observe a nearby coupling C 13 spin, which may serve as a quantum memory, thus substantiating the potential of SnV centers in diamond and demonstrates the benefit of superconducting microwave structures. Published by the American Physical Society 2024
Efficient coupling between quantum emitters and optical cavities is essential for scalable quantum photonic technologies. Group-IV vacancy centers in diamond, particularly the negatively charged tin-vacancy center, have emerged as promising candidates due to their spectral stability, high Debye-Waller factor, and large orbital splitting in ground states. Here, we demonstrate controlled coupling of a single negatively charged tin-vacancy center hosted in a nanodiamond to a fully tunable Fabry-Pérot microcavity. At cryogenic temperatures, we access the weak-coupling regime and observe a transition from the bad-emitter regime to the bad-cavity regime as the optical transition of the color center narrows. At 4 K, a Purcell factor exceeding 1.7 is measured, confirming cavity-enhanced emission. The obtained results demonstrate the potential of Sn − V − centers in nanodiamonds as a coherent single-photon source for quantum networks.
A key requirement for many applications in solid-state quantum sciences is a high fluence of indistinguishable photons. The spontaneous emission of these photons is governed by the coupling of an excited quantum system to electromagnetic vacuum fluctuations. In our experiment, we enhance this coupling by engineering a tunable Fabry-Perot microcavity. The quantum system we study is the nitrogen-vacancy (NV) center in diamond, a workhorse for quantum science and engineering, due to its optical transitions and the coherent electron spin system it hosts. Our device consists of a high-quality, nano-fabricated, single-crystalline diamond membrane bonded to a planar mirror; the cavity is completed by a second, concave mirror. Using piezo positioners, we achieve full spectral and spatial tunability and freedom in selecting NVs with favorable emission properties in our low-temperature (4 Kelvin) experiments. Upon tuning of the cavity into resonance, we find significant enhancement of the 637 nm zero phonon line for several individual NVs which is accompanied by a strong reduction of the overall photoluminescence (PL) lifetime. We infer a 30-fold enhancement of the zero-phonon transition rate at best. The fraction of the PL emission associated to this resonant transition is thereby increased from 3% to 46%. Our results constitute a significant leap on the route towards the implementation of fast long-distance quantum networks, which are currently limited by the photon emission rate in their nodes. Furthermore, our versatile design is readily applicable to other solid-state quantum emitters like color centers in silicon carbide.
With their ability to process and transfer quantum information, large-scale entanglement-based quantum networks could be at the heart of a new age of quantum information, enabling fundamentally new applications such as distributed quantum computation, quantum communication, and quantum enhanced sensing. Due to their long spin coherence, controllable local qubit registers and optically active spins, color centers in diamond are prime candidates for nodes of such a network, and have enabled some of the most advanced quantum network demonstrations to date. These demonstrations include the distribution of a 3-node GHZ state across a quantum network, entanglement swapping, entanglement distillation, and memory-enhanced quantum communication. To move beyond current proof-of-principle networks, a further increase of entanglement generation rates is crucial. This thesis presents theoretical and experimental work on enhancing the spin-photon interface of color centers in diamond to achieve this goal, making use of the Purcell effect. The discussed work follows two main directions: embedding of color centers in open, tuneable Fabry-Perot micro-cavities, and in all-diamond photonic crystal cavities. First, we describe theoretical and experimental progress towards cavity-enhanced quantum networks based on nitrogen-vacancy (NV) centers in diamond. Due to their first order sensitivity to electric fields, we choose to embed NV centers in microns-thin diamond membranes that can be integrated into open fiber-based micro-cavities. We develop analytical methods to optimize the design of such open cavity systems for maximum Purcell enhancement of embedded color centers. We demonstrate a method to fabricate optically coherent NV centers in microns-thin diamond membranes, and use such structures to demonstrate the resonant excitation and detection of coherent, Purcell enhanced NV emission. A theoretical model in excellent agreement with our results suggests our system can improve entanglement rates between distant NV centers by two orders of magnitude with near-term improvements to the setup. Second, we describe progress towards an efficient spin-photon interface of group-IV color centers in diamond by coupling them to photonic nanostructures, allowing for large-scale integration. Due to their first-order insensitivity to electric fields, group-IV color centers can be brought in close proximity to surfaces (~ 100 nm), allowing for sub-wavelength mode volumes and thus very high Purcell factors. We numerically optimize photonic crystal cavity designs to maximize the Purcell enhancement of embedded emitters, test the robustness of our designs to real-world fabrication imperfections, and devise a method to efficiently interface nanophotonic structures. We then proceed to fabricate all-diamond photonic crystal cavities, making use of a dry etching technique that is selective to different crystallographic directions, and characterize the resulting optical quality factors. Finally, we marry the developed fabrication methods to fabricate microns-sized diamond platelets that can be transferred from a holding frame in a controlled fashion. This capability could be crucial for the realization of hybrid photonic circuits that we expect to be at the heart of future large-scale quantum networks.
Robust spin-photon interfaces in solids are essential components in quantum networking and sensing technologies.Ideally, these interfaces combine a long-lived spin memory, coherent optical transitions, fast and high-fidelity spin manipulation, and straightforward device integration and scaling.The tinvacancy center (SnV) in diamond is a promising spin-photon interface with desirable optical and spin properties at 1.7 K.However, the SnV spin lacks efficient microwave control, and its spin coherence degrades with higher temperature.In this work, we introduce a new platform that overcomes these challenges-SnV centers in uniformly strained thin diamond membranes.The controlled generation of crystal strain introduces orbital mixing that allows microwave control of the spin state with 99.36(9)% gate fidelity and spin coherence protection beyond a millisecond.Moreover, the presence of crystal strain suppresses temperature-dependent dephasing processes, leading to a considerable improvement of the coherence time up to 223ð10Þ μs at 4 K, a widely accessible temperature in common cryogenic systems.Critically, the coherence of optical transitions is unaffected by the elevated temperature, exhibiting nearly lifetime-limited optical linewidths.Combined with the compatibility of diamond membranes with device integration, the demonstrated platform is an ideal spin-photon interface for future quantum technologies.
The tin-vacancy (SnV) center in diamond is a promising spin-photon interface for quantum networks, combining favorable optical properties with spin coherence above 1K. Unfolding the full potential requires cavity enhancement to increase photon-emitter coupling efficiency. Here, we demonstrate cavity-enhanced light-matter coupling of SnV centers in a fully tunable Fabry-Pérot microcavity operating at temperatures down to 1K with in-situ magnetic field control. We access the diamond-like regime of hybrid cavity modes through integration of low-roughness diamond membranes, where the field is concentrated inside the diamond and Purcell enhancement is maximized. Diamond-like modes deliver a more than two-fold increase in the effective Purcell factor over air-like modes, reaching C0=4.1(1) compared to C0=1.85(5) in the air-like case, while simultaneously relaxing mechanical stability requirements. Resonant probing reveals coherent cavity-emitter coupling with 96% extinction contrast and a coherent cooperativity of C=4.0(14). By applying a magnetic field, we further achieve spin-resolved cavity extinction, observing spin-selective optical transitions with a contrast of Cspin=0.91. These results establish SnV centers in diamond coupled to open Fabry-Pérot microcavities as a promising platform for efficient spin-photon interfaces.