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Optically Addressable Spin Pairs in Hexagonal Boron Nitride Across a Wide Wavelength Range


Core Concepts
Hexagonal boron nitride (hBN) universally contains optically addressable spin pairs that can be coherently controlled across a wide range of emission wavelengths from violet to near-infrared.
Abstract

The authors demonstrate that hBN samples from various sources, including bulk crystals, nanopowders, and epitaxial films, all contain optically addressable spin pairs that can be detected via optically detected magnetic resonance (ODMR) spectroscopy. These spin pairs exhibit emission wavelengths spanning a continuous range from violet (420 nm) to near-infrared (1000 nm).

The ODMR contrast is relatively consistent across the different emission wavelengths and sample types, suggesting a universal underlying mechanism for the spin pair formation. The authors further show that the spin pairs can be coherently controlled through Rabi oscillations, regardless of the emission wavelength.

Additionally, the authors investigate the co-existence of the spin pairs with boron vacancy (V-B) defects in electron-irradiated hBN samples. They identify that 785 nm laser excitation selectively addresses the spin pairs without exciting the V-B defects, while 532 nm excitation is optimal for V-B readout. This demonstrates the ability to independently address multiple spin species in hBN, which could be useful for quantum technologies.

Overall, the results establish hBN as a uniquely versatile platform for spin-based quantum applications, as the desired optical readout wavelength can be chosen to suit the specific requirements.

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Stats
The ODMR contrast reaches up to 0.6% in the bulk crystal and 1.0% in the nanopowder sample. The Rabi oscillations show clear coherent control of the spin pairs across the different emission wavelengths.
Quotes
"Hexagonal boron nitride (hBN) universally contains optically addressable spin pairs that can be coherently controlled across a wide range of emission wavelengths from violet to near-infrared." "The ODMR contrast is relatively consistent across the different emission wavelengths and sample types, suggesting a universal underlying mechanism for the spin pair formation." "The authors further show that the spin pairs can be coherently controlled through Rabi oscillations, regardless of the emission wavelength."

Deeper Inquiries

How can the atomic structure and electronic properties of the spin pair defects in hBN be further elucidated to enable targeted engineering and optimization for quantum applications?

To further elucidate the atomic structure and electronic properties of spin pair defects in hexagonal boron nitride (hBN), advanced characterization techniques such as electron paramagnetic resonance (EPR), atomic force microscopy (AFM), and scanning tunneling microscopy (STM) can be employed. These methods can provide insights into the local environment of the defects, their spatial distribution, and their interactions with surrounding atoms. Additionally, first-principles computational methods, including density functional theory (DFT), can be utilized to model the electronic structure of these defects. By simulating various configurations and charge states, researchers can identify the most stable configurations and predict their optical and magnetic properties. This theoretical framework can guide experimental efforts to synthesize specific defect types with desired characteristics. Targeted engineering can also be achieved through controlled doping and irradiation techniques. For instance, varying the concentration of carbon or other impurities during the growth of hBN can lead to the formation of specific spin-active defects. By systematically studying the resulting defects and their properties, researchers can optimize the spin coherence times and optical readout efficiencies, which are crucial for quantum applications such as quantum computing and quantum sensing.

What other spin-active defects or impurities may co-exist with the spin pairs in hBN, and how can their interactions be leveraged for multi-modal sensing or quantum information processing?

In addition to the spin pairs, other spin-active defects in hBN include boron vacancy (V_B) defects, nitrogen vacancy (V_N) centers, and various carbon-related defects. The V_B defect, in particular, has been identified as a paramagnetic spin-triplet center, which can be optically initialized and read out, making it a candidate for quantum information processing. The interactions between these different spin-active defects can be leveraged for multi-modal sensing by utilizing their distinct optical signatures and spin dynamics. For example, by employing different laser wavelengths to selectively excite and read out the spin states of V_B defects and spin pairs, researchers can create a multiplexed sensing platform. This approach allows for simultaneous monitoring of multiple spin species, enhancing the sensitivity and specificity of the sensing application. Furthermore, the coupling between different spin defects can enable the implementation of quantum gates and entanglement protocols, which are essential for quantum information processing. By carefully controlling the interactions between these defects through external magnetic fields or optical pumping, it may be possible to create entangled states that can be used for quantum communication and computation.

Given the broad wavelength range of the spin pairs, how could they be integrated with other quantum emitters or photonic structures to enable novel hybrid quantum devices?

The broad wavelength range of spin pairs in hBN presents unique opportunities for integration with other quantum emitters and photonic structures. One potential approach is to couple these spin pairs with single-photon emitters, such as quantum dots or color centers in diamond, to create hybrid quantum devices that leverage the strengths of both systems. For instance, by integrating hBN with photonic crystal structures, it is possible to enhance the emission properties of the spin pairs through Purcell effect, thereby increasing their brightness and coherence times. This integration can facilitate the development of on-chip quantum light sources that operate across a wide spectral range, suitable for various quantum applications. Moreover, the ability to selectively address different spin pairs using specific laser wavelengths allows for the creation of multi-channel quantum networks. By combining these spin pairs with waveguide structures, researchers can develop devices capable of routing quantum information through different channels, enhancing the scalability of quantum networks. Additionally, the versatility of hBN as a substrate for various two-dimensional materials enables the construction of complex heterostructures. These heterostructures can host multiple quantum emitters and spin defects, allowing for the exploration of many-body quantum phenomena and the development of novel quantum algorithms. In summary, the integration of spin pairs in hBN with other quantum emitters and photonic structures can lead to the realization of advanced hybrid quantum devices, paving the way for new applications in quantum communication, sensing, and computation.
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