Laser-written coherent nitrogen-vacancy centers as building block for efficient quantum photonic devices (Conference Presentation)
Viktoria Yurgens, Josh A. Zuber, Sigurd Flågan, Marta De Luca, Brendan Shields, Tomasz Jakubczyk, Ilaria Zardo, Patrick Maletinsky, Richard John Warburton
We report on pulsed-laser induced and solid-immersion lens (SIL) assisted generation of nitrogen-vacancy centers (NVs) in diamond. The NVs are characterized by a narrow distribution of the optical transition linewidth peaked around 50 MHz. This includes the effect of long-term spectral diffusion caused by a necessary repump green laser. Such high-quality NVs are excellent candidates for practical implementations employing two-photon quantum interference with separate NV centers. The perspective of implementation of these NVs in open microcavities will be discussed.
We report on pulsed-laser induced and solid-immersion lens (SIL) assisted generation of nitrogen-vacancy centers (NVs) in diamond. The NVs are characterized by a narrow distribution of the optical transition linewidth peaked around 50 MHz. This includes the effect of long-term spectral diffusion caused by a necessary repump green laser. Such high-quality NVs are excellent candidates for practical implementations employing two-photon quantum interference with separate NV centers. The perspective of implementation of these NVs in open microcavities will be discussed.
High Resolution Image Download MS PowerPoint Slide We report on pulsed-laser-induced generation of nitrogen-vacancy (NV) centers in diamond facilitated by a solid-immersion lens (SIL). The SIL enables laser writing at energies as low as 5.8 nJ per pulse and allows vacancies to be formed close to a diamond surface without inducing surface graphitization. We operate in the previously unexplored regime, where lattice vacancies are created following tunneling breakdown rather than multiphoton ionization. We present three samples in which NV center arrays were laser-written at distances between ∼1 and 40 μm from a diamond surface, all presenting narrow distributions of optical linewidths with means between 62.1 and 74.5 MHz. The linewidths include the effect of long-term spectral diffusion induced by a 532 nm repump laser for charge-state stabilization, thereby emphasizing the particularly low-charge-noise environment of the created color centers. Such high-quality NV centers are excellent candidates for practical applications employing two-photon quantum interference with separate NV centers. Finally, we propose a model for disentangling power broadening from inhomogeneous broadening in the NV center optical linewidth.
The negatively charged nitrogen-vacancy (NV) center in diamond is among the most promising solid-state systems implementations of a quantum bit. However, integration of the NV center into any efficient photonic environment requires microstructuring the diamond at below-micrometer scale. Preserving the low NV zero-phonon line inhomogeneous broadening during this process is a major challenge with standard NV creation methods. This issue severely limits practical applications of NV centers. Initial studies on pulsed-laser assisted creation of NVs yielded promising results by creating NVs with low inhomogeneous broadening at desired spatial locations in diamond [1]. Crucially, the lattice damage resulting from implantation of energetic ions was avoided. However, the method relied on a narrow window of parameters for successful writing. We widen this window by using a solid immersion lens (SIL), which facilitates laser writing over a broad range of pulse energies and allows for vacancy formation close to a diamond surface without inducing surface graphitization. We operate in the previously unexplored regime where lattice vacancies are created following tunneling breakdown rather than multiphoton ionization [2]. We present NV arrays that have been created between 1 and 40 µm from a diamond surface, all presenting optical linewidth distributions with means as low as 61.0±22.8 MHz [2], including spectral diffusion induced by off-resonant repump for charge stabilization. This emphasizes the exceptionally low charge-noise environment of laser-written NVs. Such high-quality NV centers are excellent candidates for practical applications employing two-photon quantum interference with separate NV centers. Finally, we propose a model for disentangling power broadening from inhomogeneous broadening in the NV zero-phonon line optical linewidth [2]. [1] Y.-C. Chen, P. S. Salter, S. Knauer, … and J. M. Smith, Nat. Photonics 11, 77 (2017). [2] V. Yurgens, J.A Zuber, S. Flågan, M. De Luca, B.J. Shields, I. Zardo, P. Maletinsky, R.J. Warburton, and T. Jakubczyk, ACS Photonics 8, 1726–1734 (2021)
The nitrogen-vacancy center (NV) in diamond, with its exceptional spin coherence and convenience in optical spin initialization and readout, is increasingly used both as a quantum sensor and as a building block for quantum networks. Employing photonic structures for maximizing the photon collection efficiency in these applications typically leads to broadened optical linewidths for the emitters, which are commonly created via nitrogen ion implantation. With studies showing that only native nitrogen atoms contribute to optically coherent NVs, a natural conclusion is to either avoid implantation completely or substitute nitrogen implantation by an alternative approach to vacancy creation. Here, we demonstrate that implantation of carbon ions yields a comparable density of NVs as implantation of nitrogen ions and that it results in NV populations with narrow optical linewidths and low charge-noise levels even in thin diamond microstructures. We measure a median NV linewidth of 150 MHz for structures thinner than 5 μm, with no trend of increasing linewidths down to the thinnest measured structure of 1.9 μm. We propose a modified NV creation procedure in which the implantation is carried out after instead of before the diamond fabrication processes and confirm our results in multiple samples implanted with different ion energies and fluences.
Nitrogen vacancy centres in diamond have shown strong potential for use as qubits in quantum computing. However, nitrogen vacancy centres have a low percentage of overall emission emitted through the Zero Phonon Line (ZPL). In addition, the fabrication of NV centres with controlled positioning is limited. This thesis presents the ZPL linewidth characterisation of NV centres fabricated using laser writing and laser diffusion. Only one out of the six NV centres characterised showed a <100 MHz average single scan linewidth, which suggests that the laser diffusion process needs to improved. The low ZPL emission can be enhanced by cavity coupling to Fabry-Pérot microcavities. Fabry-Pérot microcavities are susceptible to vibrations, which will decouple the cavity from the NV centre and reduce the photon enhancement. A cavity stabilisation system based on cavity fringe stabilisation is implemented, and the results of the stability are presented. The Fabry-Pérot microcavity can be stabilised with 0.13 nm using fringe stabilisation. High collection efficiency of the emission is also desired for maximising the entanglement rate and is reduced by optical aberrations. For NV centres in bulk diamond, using Solid Immersion Lenses (SILs) removes the spherical aberration that is introduced when collecting NV emission through a planar interface. This thesis presents the results of modelling the aberrations for NV centres cavity coupled to a Fabry-Pérot microcavity and for hemispherical SILs on diamond. The wavefronts of the aberrations introduced by the planar mirror of the microcavity and the aberrations introduced by the positioning error of the SIL are modelled numerically. A deformable mirror is implemented into a confocal microscope to monitor the aberrations of the photonic devices and the results are compared with the numerical model. For Fabry-Pérot microcavities, the intensity loss caused by the aberrations introduced by the planar mirror was predicted to be less than 10 \% due to the thin mirror substrate and low numerical aperture of the cavity mode. This prediction was consistent with the experimental results where an effective 3 \% increase in light collection was observed with aberration correction. For the SILs, the model predicts that the collection efficiency is more sensitive to the lateral positioning of the SIL relative to the NV centre than the axial positioning error.
We report the observation of stable optical transitions in nitrogen-vacancy (NV) centers created by ion implantation. Using a combination of high temperature annealing and subsequent surface treatment, we reproducibly create NV centers with zero-phonon lines (ZPL) exhibiting spectral diffusion that is close to the lifetime-limited optical line width. The residual spectral diffusion is further reduced by using resonant optical pumping to maintain the NV(-) charge state. This approach allows for placement of NV centers with excellent optical coherence in a well-defined device layer, which is a crucial step in the development of diamond-based devices for quantum optics, nanophotonics, and quantum information science.
Abstract Diamond membrane devices containing optically coherent nitrogen-vacancy (NV) centers are key to enable novel cryogenic experiments such as optical ground-state cooling of hybrid spin-mechanical systems and efficient entanglement distribution in quantum networks. Here, we report on the fabrication of a (3.4 ± 0.2) μm thin, smooth (surface roughness rq < 0.4 nm over an area of 20 μm by 30 μm) diamond membrane containing individually resolvable, narrow linewidth (< 100 MHz) NV centers. We fabricate this sample via a combination of high-energy electron irradiation, high-temperature annealing, and an optimized etching sequence found via a systematic study of the diamond surface evolution on the microscopic level in different etch chemistries. Although our particular device dimensions are optimized for cavity-enhanced entanglement generation between distant NV centers in open, tunable microcavities, our results have implications for a broad range of quantum experiments that require the combination of narrow optical transitions and micrometer-scale device geometry.