Hexagonal boron nitride (hBN) has emerged as a critical material in quantum information science due to its unique properties, including an atomically smooth surface, wide bandgap, and low defect density. Its role spans multiple domains, from hosting spin qubits and quantum emitters to serving as an ideal dielectric in superconducting circuits. The material’s compatibility with other two-dimensional systems further enables hybrid quantum devices with enhanced functionality. Below, we explore these applications in detail, focusing on coherence times, spin-photon interfaces, and integration with other materials.

One of the most promising applications of hBN is as a host for spin qubits. The material’s intrinsic properties, such as its weak spin-orbit coupling and nuclear spin-free lattice, make it an excellent candidate for maintaining long coherence times. Studies have demonstrated that defects in hBN, particularly the negatively charged boron vacancy (V_B^-), exhibit spin coherence times exceeding microseconds at room temperature. These defects can be optically addressed and manipulated, making them suitable for quantum memory and sensing applications. The ability to initialize, control, and read out spins in hBN defects provides a pathway toward scalable quantum networks.

Quantum emitters in hBN, often associated with point defects or strain-induced localized states, have shown remarkable brightness and stability. These emitters operate at room temperature with narrow linewidths, a rare feature among solid-state quantum systems. The emission wavelengths typically fall within the visible to near-infrared spectrum, making them compatible with existing optical fiber technologies. The deterministic placement of these emitters remains an active area of research, with techniques such as electron irradiation and strain engineering showing promise. The integration of hBN emitters with photonic cavities has further enhanced their performance, achieving Purcell factors that significantly improve photon extraction efficiency.

In superconducting quantum circuits, hBN serves as a high-performance dielectric. Its low dielectric loss and high breakdown voltage make it ideal for reducing noise in qubit architectures. For example, hBN has been used as a gate dielectric in graphene-based superconducting qubits, where it minimizes charge noise and improves coherence times. The material’s layered structure allows for precise thickness control, enabling optimal capacitance and reduced parasitic effects. Superconducting resonators incorporating hBN dielectrics have demonstrated quality factors exceeding one million, a critical metric for minimizing energy loss in quantum systems.

The spin-photon interface in hBN is another area of significant interest. Defect centers in hBN can couple to photons, enabling the transfer of quantum information between spins and flying qubits. This interface is essential for quantum communication and distributed quantum computing. Recent experiments have shown that hBN defects can emit photons entangled with their spin states, a prerequisite for quantum repeaters. The ability to tune the emission wavelength via strain or electric fields adds further versatility to these systems. Coupling hBN emitters to nanophotonic structures, such as waveguides or photonic crystals, enhances light-matter interaction, paving the way for on-chip quantum networks.

Hybrid systems combining hBN with other two-dimensional materials offer additional functionalities. For instance, hBN-graphene heterostructures leverage the strengths of both materials: graphene’s high electron mobility and hBN’s insulating properties. These heterostructures have been used to create ultra-clean quantum dots with well-defined spin states. Similarly, hBN-MoS2 hybrids exploit the strong light-matter interaction in transition metal dichalcogenides while benefiting from hBN’s dielectric screening. Such systems enable novel quantum devices, including single-photon detectors and valleytronic circuits.

The coherence times of spin qubits in hBN are influenced by several factors, including temperature, magnetic field, and material purity. At cryogenic temperatures, spin coherence times can extend into the millisecond range, limited primarily by phonon interactions and spectral diffusion. Dynamic decoupling techniques have been employed to mitigate these effects, further prolonging coherence. The isotopic purity of hBN also plays a role; isotopically enriched samples with reduced nuclear spin noise exhibit superior spin properties. These advances are critical for realizing fault-tolerant quantum computation.

Despite its advantages, challenges remain in the large-scale integration of hBN into quantum devices. The deterministic creation of defect centers with uniform properties is still under development. Additionally, the transfer and stacking of hBN layers without introducing contaminants or strain inhomogeneities require refined fabrication techniques. Progress in these areas will determine the scalability of hBN-based quantum technologies.

In summary, hexagonal boron nitride is a versatile material that addresses several key challenges in quantum information science. Its ability to host spin qubits and quantum emitters, combined with its exceptional dielectric properties, positions it as a cornerstone for future quantum devices. The development of hybrid systems and spin-photon interfaces further expands its potential, offering a pathway toward practical quantum networks and sensors. Continued research into material quality and device integration will be essential for unlocking the full capabilities of hBN in quantum applications.