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.
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.
The precision measurements provided by quantum sensing plays a significant role in fields of science. However, the sensitivity is limited by the standard quantum limit (SQL). Quantum entangled state have a potential to beat the SQL and to approach the Heisenberg limit (HL). In particular, entanglement sensors based on Nitrogen-Vacancy (NV) centers provide high spatial resolution at room temperature. In 2021, it was reported that the multi-spin sensor constituted by the NV electron spin (S=1), the 14N nuclear spin (I=1), and proximate 13C nuclear spin (I=1/2) beat the SQL1 . However, since the nuclear gyromagnetic ratio is ~MHz/T, it does not lead to a dramatic improvement of sensitivity. For enhancement of quantum sensing, it is required to utilize the entangled state among dipole coupled NV centers.
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).
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.
Quantum sensing has witnessed rapid development and transition from laboratories to practical applications in the past decade. Applications of quantum sensors, ranging from nanotechnologies to biosensing, are expected to benefit from quantum sensors' unprecedented spatial resolution and sensitivity. Solid-state spin systems are particularly attractive platforms for quantum sensing technologies because room temperature operation is viable while reaching the quantum limits of sensitivity. Among various solid-state spin systems, nitrogen-vacancy (NV) centers in diamond demonstrated high-fidelity initialization, coherent control, and high contrast readout of the electron spin state. However, electron spin coherence due to noise from the surrounding spin bath and this environment effect limits the sensitivity of NV centers. Thus, a critical task in NV center-based quantum sensing is sensitivity enhancement through coherence protection. Several strategies, such as dynamical decoupling techniques, feedback control, and nuclear spin-assisted sensing protocols, have been developed and realized for this task. Among these strategies, nuclear spin-assisted protocols have demonstrated greater enhancement of electron spin coherence. In addition, the electron and nuclear spin pair of an NV center in diamond naturally allows the application of the nuclear spin-assisted sensitivity enhancement protocol. Owing to long nuclear coherence times, further enhancement of sensitivity can be achieved by exploiting active nuclear spins (e.g., 14N, 13C) in the proximity of an NV center as memory ancillas when coupled with the NV center. Here, we review the spin properties of NV centers, mechanisms of the nuclear spin-assisted protocol and its gate variation, and the status of quantum sensing applications in high-resolution nuclear spin spectroscopy, atomic imaging, and magnetic field sensing. We discuss the potential for commercialization, current challenges in sensitivity enhancement, and conclude with future research directions for promoting the development of nuclear spin-assisted protocol and its integration into industrial applications.
A nitrogen vacancy (NV) center in diamond is known as a qubit with excellent magneto-optical properties at room temperature. Not only is NV center used for Quantum Information Processing (QIP), it is utilized for quantum sensing. The integrated NV centers in nanometer range have the potential of further improvement of sensitivity, etc. Ion implantation into diamond is known as one of the most popular methods for creating multiple qubits. In 2019, we have reported that the creation of three qubits was realized by implantation of the organic molecular (C5N4Hn) ion containing four nitrogen atoms1). In this study, we successfully developed Phthalocyanine (C32N8H18) ion beam for further integration of NV centers. After implantation and annealing, we succeeded to observe the fluorescence spots from NV centers. Fig. 1. shows schematic diagram of 284 keV-C32N8H18 ion implantation into diamond. Red, black, blue, and gray circles indicate nitrogen, carbon, hydrogen, and vacancy, respectively. Dashed circles indicate the NV centers. The average distance between nitrogen atoms is calculated to be 9±4 nm by SRIM (Stopping and Range In Matter) code. After annealing at 1000 oC for 2 hours in vacuum, the fluorescent image is observed by using home-build confocal laser scanning fluorescent microcopy.
Nitrogen Vacancy (NV) centers are point defects in diamond that allow magnetic field sensing based on Optically Detected Magnetic Resonance (ODMR). They are processed in ultrapure single-domain CVD grown diamond crystals and can be operated at room temperature. This results in solid-state sensors with a wide variety of applications. Ensemble of NV centers can be used to perform wide-field magnetic imaging with sensitivity in the nT range. Single NV centers can also be processed, which allows sensing at the atomic scale. This possibility, combined with its unique coherence properties, make NV center an ideal candidate for quantum sensing.