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Chinese Physics Letters

Generation of Nitrogen-Vacancy Center Pairs in Bulk Diamond by Molecular Nitrogen Implantation

Gong Zhao-Jun, Xiang-Dong Chen, Li Congcong, Shen Li, Zhao Bo-Wen, Fang‐Wen Sun

Published Feb 1, 2016• 2 citations
Publisher

Abstract

The coupled negatively charged nitrogen-vacancy (NV − ) center system is a promising candidate for scalable quantum information techniques. In this work, ionized nitrogen molecules are implanted into bulk diamond to generate coupled NV − center pairs. The two-photon autocorrelation measurement and optically detected magnetic resonance measurement are carried out to confirm the production of the NV − center pair. Also, both 1.3 μs decoherence time and 4.9 kHz magnetic coupling strength of the NV − center pair are measured by controlling and detecting the spin states. Along with nanoscale manipulation and detection methods, such coupled NV − centers through short distance dipole-dipole interaction would show high potential in scalable quantum information processes.

DOI
10.1088/0256-307x/33/2/026105

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The coupled negatively charged nitrogen-vacancy (NV − ) center system is a promising candidate for scalable quantum information techniques. In this work, ionized nitrogen molecules are implanted into bulk diamond to generate coupled NV − center pairs. The two-photon autocorrelation measurement and optically detected magnetic resonance measurement are carried out to confirm the production of the NV − center pair. Also, both 1.3 μs decoherence time and 4.9 kHz magnetic coupling strength of the NV − center pair are measured by controlling and detecting the spin states. Along with nanoscale manipulation and detection methods, such coupled NV − centers through short distance dipole-dipole interaction would show high potential in scalable quantum information processes.
A nitrogen vacancy (NV) center in diamond is known as a solid-state spin quantum bit (qubit) at room temperature. The fabrication of scalable quantum registers based on NV centers is a long-standing issue. In 2005, spin-spin interaction between NV-N pairs, which were fabricated by N2 ion implantation, was reported. An entanglement between two electron-spin qubits becomes an excellent quantum information processing component, as accomplished by an NV-NV pair with a nanometer-scale distance in 2010 and 2013. More recently,strongly dipolar coupled NV-NV pairs were realized by 14N 30 keV implantationvia nanoholes in PMMA resist mask. The creation yields of NV-NV pairs dramatically improved, and the nanohole implantation had been thought to be the most promising technique to integrate NV centers. However, the problem of the technique is the finite size of nanoholes. The distribution of nitrogen atoms is determined by both ion straggling and nanohole diameter. The scaling of NV centers is stagnant up to two for several years. To overcome the barrier of triple NV centers, our previous research gave a ground-breaking idea of a highly populated NV center complex by introducing a molecular ion implantation technique in 2019. Since the molecular ion is regarded as an idea point source, the distribution of nitrogen atoms is determined by only ion straggling. Therefore, our proposed method is more effective than other implantation techniques including nanohole implantation. Instead of a pure nitrogen cluster which is commonly unstable, the stable organic molecular ions (adenine; C5N5H5) were utilized as the ion source. We successfully implanted C5N4Hn ions into single crystalline diamonds. Three NV centers were integrated, and the dipolar interactions among them were successfully observed. In 2022, we succeeded in creating more than 5 NV centers by phthalocyanine (C32H18N8) ion implantation. The next challenge is the implantation of isotopically enriched molecular ions. The isotopically enriched ion contains 13C and 15N. The implantation of isotopically enriched molecular ions is able to create 15NV-13C hybrid quantum registers. In this presentation, we will show the development of the isotopically enriched molecular ion beam and the characterization of created NV centers by laboratory-built confocal microscopy (CFM) and optically detected magnetic resonance (ODMR).
Ionized nitrogen molecules (15{}^{15}15N2+{}_{2}^{+}2+​) are used as efficient point sources for creating NV${}^{\ensuremath{-}}$ pairs in diamond with nanoscale spatial separation and up to 55 kHz magnetic coupling strength. Co-implantation of 12{}^{12}12C+{}^{+}+ increased the yield of pairs, and a 13{}^{13}13C-depleted diamond allowed 0.65 ms coherence times to be obtained. Further coupling to a third dark spin provided a strongly coupled three-spin register. These results mark an important step towards realization of multiqubit systems and scalable NV${}^{\ensuremath{-}}$ quantum registers.
Nitrogen-vacancy defect color centers are created in a high purity single crystal diamond by nitrogen-ion implantation. Both optical spectrum and optically detected magnetic resonance are measured for these artificial quantum emitters. Moreover, with a suitable mask, a lattice composed of nitrogen-vacancy centers is fabricated. Rabi oscillation driven by micro-waves is carried out to show the quality of the ion implantation and potential in quantum manipulation. Along with compatible standard lithography, such an implantation technique shows high potential in future to make structures with nitrogen-vacancy centers for diamond photonics and integrated photonic quantum chip.
Precise control over the spatial distribution and charge state of nitrogen-vacancy (NV) centers in diamond is a key requirement for further advancing this platform in quantum sensing and photonic applications. Here, we investigate nitrogen ion implantation as a scalable method to engineer NV centers in bulk single-crystalline (SC) and a 5 μ m -thick polycrystalline (PC) diamond membrane. Nitrogen-doped regions (1–80 ppm) were fabricated using a 0.7 MeV ion beam and high-temperature annealing, with NV center formation verified by confocal fluorescence imaging and spectral analysis. In SC bulk diamond, we estimate the NV concentration from spectral analysis and model the fluorescence response as a function of implantation dose, capturing both the initial increase at low concentrations and a saturation behavior at higher doses due to quenching mechanisms. In contrast, PC diamond membranes show a weaker dependence at low implantation fluences, consistent with pre-existing nitrogen impurities, thus making a statistical model significantly more complex. The activation yield is found to be of order of 1%, which is lower than in N-rich diamond samples, as implanted N is predominantly interstitial. Photoluminescence spectroscopy indicates that NV 0 is the dominant charge state in both materials, with a laser-power-dependent redistribution between neutral and negative charge states. Optically detected magnetic resonance (ODMR) measurements in SC bulk diamond resolve the hyperfine structure and allow extraction of the dephasing time ( T 2 ∗ ), while in PC diamond membranes, where NV centers tend do form near the grain boundaries, the ODMR signals are observed but spectral resolution is currently limited by impurities, grain-dependent NV orientations, and photoluminescence background.
Abstract A nitrogen vacancy (NV) center in diamond is known as a solid-state spin qubit at room temperature. NV centers coherently coupled by dipole–dipole interactions have a potential to accomplish quantum registers at room temperature. This study reports to develop a phthalocyanine ion implantation technique to fabricate multiple dipole-coupled NV centers. Photon counts and optically detected magnetic resonance spectra show that up to four NV centers were successfully created in a confocal spot. The histogram of photon counts is fitted by a Poisson distribution, and the ratio of multiple NV spots suggests the potential for a five NV centers creation.
The Nitrogen-Vacancy (NV) center in diamond is applied as quantum sensor for magnetic fields, temperature, electric field, etc. Quantum sensing based on an entangled state between dipole coupled NV center pair can overcome standard quantum limit to reach Heisenberg limit. It is expected to be more sensitive measurement than quantum sensing based on single NV center. Even though the generation of entangled state has been demonstrated by Double Electron-Electron Resonance (DEER)1,2, the utilization of entanglement state for enhancement of quantum sensing has not yet been studied. To realize the quantum sensing based on entangled state, we have developed organic compound ion implantation3,4 method to efficiently create dipole coupled NV centers. We reported the creation of NV center pair with dipole-dipole interaction strengths of about 100 kHz by using C5N4Hn ion implantation and pointed out the potential of entangled state with high fidelity (~0.9) at 5th IFQMS. In this study, we will report the generation of quantum entangled states between NV center pair and discuss the magnetic field sensing by using entangled state.