Quantum sensing is a creative application of quantum technology which is opening new horizons in order to make sensitive measurements even below the Standard Quantum Limit (SQL). In order to achieve this, an exclusive phenomenon of Quantum Entanglement is widely used for various tasks such as target detection, providing high resolution of the target, encryption of data and quantum teleportation which may seem to be impracticable. Moreover, the field of quantum technology has witnessed appreciable progress by using microwaves than optical photons. Microwave photons as efficient they are can also be used in a system for obtaining quantum information about the surroundings. \nIn this work, an idea is proposed to make use of microwaves as a source for the photonic sensor network. Squeezed microwave states are used for the generation of microwave photons which are used in their entangled state distributed among sensors and thereafter detected by the homodyne detector. Here, the use of hybrid coupler is also made to act as beam splitters forming the Continuous Variable multipartite entanglement of the microwave photons for further detection. Another idea is proposed to use a system for generation and detection of microwave photons in order to have application in quantum sensing field. In this for the generation part Nitrogen Vacancy (NV) centers defect is used as these NV centers with electrons can be used to manipulate microwaves in order to emit photons which carry quantum information about the environment. Then these emitted photons can be detected using a system formed by qubits and resonators which are coupled in a peculiar way using the dissipation engineering to detect itinerant photons.
Quantum sensing is a creative application of quantum technology which is opening new horizons in order to make sensitive measurements even below the Standard Quantum Limit (SQL). In order to achieve this, an exclusive phenomenon of Quantum Entanglement is widely used for various tasks such as target detection, providing high resolution of the target, encryption of data and quantum teleportation which may seem to be impracticable. Moreover, the field of quantum technology has witnessed appreciable progress by using microwaves than optical photons. Microwave photons as efficient they are can also be used in a system for obtaining quantum information about the surroundings. \nIn this work, an idea is proposed to make use of microwaves as a source for the photonic sensor network. Squeezed microwave states are used for the generation of microwave photons which are used in their entangled state distributed among sensors and thereafter detected by the homodyne detector. Here, the use of hybrid coupler is also made to act as beam splitters forming the Continuous Variable multipartite entanglement of the microwave photons for further detection. Another idea is proposed to use a system for generation and detection of microwave photons in order to have application in quantum sensing field. In this for the generation part Nitrogen Vacancy (NV) centers defect is used as these NV centers with electrons can be used to manipulate microwaves in order to emit photons which carry quantum information about the environment. Then these emitted photons can be detected using a system formed by qubits and resonators which are coupled in a peculiar way using the dissipation engineering to detect itinerant photons.
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.
Background: High-precision sensing is vital for modern technology, yet conventional sensors are fundamentally constrained by classical noise limits. Quantum sensing leverages principles of quantum mechanics, such as superposition and entanglement, to overcome these barriers, offering unprecedented sensitivity. This review comprehensively analyzes the current state of quantum sensor technology, focusing on its underlying physical principles, emerging applications, and the pathway toward industrial maturation.Methods: We synthesize findings from key research areas, detailing the foundational quantum systems like Nitrogen-Vacancy (NV) centers in diamond and advanced optical techniques. The paper reviews the theoretical methods used to achieve sub-shot-noise performance and discusses the system-level engineering challenges necessary for practical deployment, particularly concerning microwave control and optical readout. We also assess the current landscape of standardization efforts for quantum technologies.Results: Significant breakthroughs are highlighted in both biomedical and environmental sensing. Applications range from tracking cellular redox-status using electron-paramagnetic resonance to ultra-sensitive salinity measurements. The analysis confirms that quantum sensing provides superior resolution compared to classical counterparts, unlocking new capabilities in in-vivo and real-time monitoring.Discussion: While offering transformative potential, widespread adoption faces hurdles, including the maintenance of quantum coherence in ambient environments and the high cost and complexity of current instrumentation. Future efforts must focus on miniaturization, integration with classical systems, and standardized fabrication protocols. Quantum sensing represents the next-generation technological paradigm for metrology.
Quantum sensors emerged among quantum technologies as the ones with promising potential applications in the near future. This perspective reviews two leading quantum sensing platforms and their advancements toward biological applications: quantum light sources and color centers in diamonds. Quantum light, including squeezed states and N00N states, allows enhanced phase measurements by surpassing the classical shot noise limits. This advantage can be exploited in several contexts, enabling improved resolution and sensitivity, which are particularly valuable in biological contexts where traditional high-intensity illumination could damage or alter delicate samples. In parallel, color centers in diamonds, specifically nitrogen-vacancy and silicon-vacancy centers, also emerged as promising for sensing applications due to their high sensitivity and biocompatibility. These sensors enable detailed intracellular measurements, such as temperature detection, and show potential for measuring magnetic fields of biological origin. Despite these advancements, significant challenges remain in translating these technologies from a controlled laboratory environment to practical, widely applicable devices for diverse biological applications. Overcoming these challenges is crucial for unlocking the full potential of quantum sensors in the biological field.
Quantum communication is a holy grail to achieve secure communication among a set of partners, since it is provably unbreakable by physical laws. Quantum sensing employs quantum entanglement as an extra resource to determine parameters by either using less resources or attaining a precision unachievable in classical protocols. A paradigmatic example is the quantum radar, which allows one to detect an object without being detected oneself, by making use of the additional asset provided by quantum entanglement to reduce the intensity of the signal. In the optical regime, impressive technological advances have been reached in the last years, such as the first quantum communication between ground and satellites, as well as the first proof-of-principle experiments in quantum sensing. The development of microwave quantum technologies turned out, nonetheless, to be more challenging. Here, we will discuss the challenges regarding the use of microwaves for quantum communication and sensing. Based on this analysis, we propose a roadmap to achieve real-life applications in these fields.
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.
By combing photonics and radiofrequency (RF) engineering, microwave photonics has been widely studied in the past few decades for the generation, processing, control and distribution of microwave and RF signals using photonic techniques. In parallel with the continuous hot research on classic microwave photonic systems, cross research between microwave photonics and other disciplines is also a promising research spot for scientists in this area. Here we review emerging advances in recent years in cross research between microwave photonics and quantum technology, i.e., quantum microwave photonics that harnessing quantum technology to achieve features or functions that are very complex or even not possible using traditional microwave photonic technology and vice versa. Key motivations of quantum microwave photonics are discussed. The basic operation principle of the quantum single-photon detection scheme, which is the main building block of current quantum microwave photonic systems, is provided. Selected recent advances, including weak microwave signal detection, microwave photonic phase shifting and filtering, nonlocal frequency-to-time mapping, RF compressed sensing, and quantum key distribution, are summarized. Challenges and future prospects of quantum microwave photonics are also discussed.