Two-dimensional materials have emerged as a promising platform for quantum sensors due to their unique electronic, optical, and spin properties. Quantum sensors based on 2D materials exploit quantum mechanical phenomena such as spin coherence, exciton dynamics, and valley polarization to achieve unprecedented sensitivity in detecting magnetic fields, strain, and other physical quantities. Unlike classical sensors, these devices operate at the quantum limit, where their performance is governed by quantum coherence and entanglement.

Graphene, with its long spin relaxation times and high carrier mobility, serves as an excellent candidate for spin-based quantum sensors. Spin qubits in graphene can detect minute magnetic fields by leveraging the Zeeman effect, where external magnetic fields split the spin energy levels. The sensitivity of graphene-based spin magnetometers is determined by the spin coherence time (T₂), which can exceed microseconds in high-quality encapsulated graphene at low temperatures. At room temperature, however, spin dephasing due to phonon scattering and impurity interactions reduces T₂ to nanoseconds, limiting sensitivity. Despite this, graphene’s compatibility with ambient conditions and its tunable Fermi level via gating make it attractive for practical applications.

Transition metal dichalcogenides (TMDCs), such as MoS₂ and WSe₂, offer another pathway for quantum sensing through excitonic effects. Excitons in TMDCs are highly sensitive to strain and electric fields due to their large binding energies and strong spin-valley coupling. A monolayer TMDC can exhibit exciton energy shifts on the order of 10 meV per percent of uniaxial strain, enabling ultra-sensitive strain mapping. Additionally, the valley-selective optical transitions in TMDCs allow for all-optical readout of local strain and magnetic fields. The sensitivity of exciton-based sensors is fundamentally limited by the exciton lifetime, typically in the picosecond to nanosecond range, which sets a trade-off between temporal resolution and detection limits.

One of the key challenges in deploying 2D material quantum sensors is maintaining quantum coherence under ambient conditions. Decoherence sources include thermal fluctuations, charge noise, and substrate-induced disorder. Encapsulation techniques using hexagonal boron nitride (hBN) have proven effective in preserving spin and exciton coherence by reducing charge impurities and phonon scattering. For example, hBN-encapsulated graphene devices have demonstrated spin coherence times of up to 12 ns at room temperature, a significant improvement over bare graphene on SiO₂ substrates. Similarly, TMDCs sandwiched between hBN layers show enhanced exciton lifetimes due to suppressed defect-mediated non-radiative recombination.

In biomedical applications, 2D material quantum sensors offer non-invasive detection of neural activity and biomagnetic signals. Graphene spin qubits can theoretically achieve magnetic field sensitivities below 1 pT/√Hz, enabling the detection of weak biomagnetic fields generated by cardiac or neural activity. However, practical implementation requires shielding from environmental noise and integration with signal processing electronics. TMDC-based strain sensors, on the other hand, can monitor mechanical vibrations from cellular motion or arterial pulses with nanometer-scale displacement resolution. The atomic thickness of these materials allows for conformal contact with biological tissues, minimizing signal attenuation.

Industrial applications of 2D quantum sensors include precision metrology and defect detection in materials. Graphene magnetometers can map stray fields in superconducting circuits or magnetic storage media with sub-micron spatial resolution. In semiconductor manufacturing, TMDC exciton sensors provide non-destructive strain characterization in integrated circuits, identifying stress-induced failures before device packaging. The high sensitivity of these sensors also benefits geophysical exploration, where they can detect subtle variations in Earth’s magnetic field for mineral prospecting.

The performance limits of 2D material quantum sensors are dictated by fundamental quantum noise and material imperfections. For spin-based sensors, the sensitivity scales with the square root of the number of spins and their coherence time. In graphene, increasing the spin density via doping or proximity effects can enhance signal strength but may also introduce additional scattering. Excitonic sensors face intrinsic limits from radiative recombination rates, which determine the minimum detectable signal. Engineering dark exciton states or leveraging biexcitons in TMDCs could further improve sensitivity by prolonging the effective sensing window.

Future advancements in 2D quantum sensors will likely focus on hybrid architectures combining multiple quantum systems. For instance, integrating graphene spin qubits with TMDC excitons could enable multimodal sensing of magnetic and strain fields simultaneously. Another direction involves coupling 2D materials with photonic or plasmonic structures to enhance optical readout efficiency. The development of scalable fabrication methods, such as wafer-scale transfer and heterostructure assembly, will be critical for transitioning these sensors from laboratory prototypes to commercial devices.

In summary, 2D material quantum sensors represent a transformative approach to high-precision sensing by exploiting quantum mechanical phenomena. While challenges remain in coherence preservation and ambient operation, ongoing improvements in material quality and device engineering are steadily overcoming these barriers. Biomedical diagnostics, industrial inspection, and fundamental research stand to benefit significantly from the unparalleled sensitivity and miniaturization potential of these quantum-enabled technologies.