Introduction

This post is part of a series on the First and Second Quantum Revolutions, exploring their impact on modern technology and scientific advancements.

In recent years, quantum technologies have made the leap from theoretical physics to real-world applications. Among these advancements, quantum sensing stands out as one of the most transformative. But what exactly makes quantum sensing so special? The answer lies in fundamental quantum properties—superposition, entanglement, and quantum coherence—that allow sensors to achieve unprecedented levels of precision and sensitivity.

This blog post explores the principles that enable quantum sensors to surpass classical sensing technologies, highlighting their advantages and potential applications.

The Science Behind Quantum Sensing

Superposition and Quantum Coherence: The Path to Precision

Quantum systems can exist in multiple states simultaneously, a phenomenon known as superposition. This property enables quantum sensors to interact with external fields (such as magnetic or gravitational fields) in ways that classical systems cannot.

Additionally, quantum coherence—the ability of a quantum system to maintain its state over time—allows for highly stable and precise measurements. Coherence is particularly important in technologies like atomic clocks, where maintaining a stable frequency reference is crucial for accurate timekeeping. The coherence time T₂ determines how long a quantum state remains undisturbed and is crucial for sensor stability. Atomic clocks operate based on the transition frequency ν between two energy levels, given by:

ν = (E₂ – E₁) / h

where E₂ and E₁ are the energy levels and h is Planck’s constant. This precision enables applications such as GPS and high-resolution spectroscopy.

Entanglement: The Quantum Advantage

Quantum entanglement is a phenomenon where two or more particles become correlated in such a way that their states are instantly linked, regardless of distance. This allows quantum sensors to surpass classical limitations in measurement resolution.

For example, entangled atoms in an atomic interferometer can improve sensitivity beyond the standard quantum limit, achieving Heisenberg-limited precision, which is given by:

Δθ = 1 / (N)

where Δθ is the measurement uncertainty and N is the number of entangled particles. This level of precision is unattainable by classical measurement techniques, which suffer from noise and environmental interference.

Quantum Noise Reduction: Beating Classical Limits

Classical sensors are inherently limited by thermal and shot noise, which introduce uncertainty in measurements. Quantum sensors, on the other hand, can leverage squeezed states of light or atoms to reduce measurement uncertainty beyond classical limits.

A prime example is squeezed light interferometry, which is already being used to improve gravitational wave detection in experiments like LIGO. The sensitivity improvement follows the squeezing parameter ξ:

ΔX = e^(-r) ΔX₀

where ΔX is the reduced quantum noise, r is the squeezing factor, and ΔX₀ is the original uncertainty. This technique allows the detection of minute ripples in spacetime.

Key Advantages of Quantum Sensing

Quantum sensors provide unique benefits over classical sensors in various domains:

1. Unprecedented Sensitivity – Quantum sensors can detect extremely weak signals, such as minute magnetic fields, gravitational changes, and single-photon interactions.

2. Higher Precision – Quantum-enhanced interferometry enables measurements with precision levels unattainable by classical methods.

3. Reduced Noise and Improved Stability – Quantum systems are less affected by thermal fluctuations and environmental disturbances.

4. Non-Invasive and Passive Sensing – Quantum sensors can extract information from systems without disturbing them, which is critical for applications in biomedical imaging and remote sensing.

Real-World Applications of Quantum Sensing

Magnetometry and Biomedical Imaging

Quantum magnetometers, such as NV center-based diamond sensors, can detect weak magnetic fields at the nanoscale. These sensors have significant applications in biomedical imaging, such as non-invasive brain activity mapping (quantum-enabled MEG) and early disease detection.

Quantum Clocks for Navigation and Timing

Ultra-precise atomic clocks, based on quantum principles, are essential for applications such as GPS navigation, secure communications, and synchronization of financial transactions. The accuracy of these clocks allows positioning systems to function even in GPS-denied environments.

Gravitational and Geophysical Sensing

Quantum gravimeters use atom interferometry to detect variations in Earth’s gravitational field with extreme accuracy. The phase shift in a quantum gravimeter follows:

Δφ = (k g T²)

where k is the wavevector, g is gravitational acceleration, and T is the interrogation time. These sensors can be used for underground exploration, earthquake prediction, and even planetary science.

Defense and Security

Quantum sensors are playing a crucial role in security and defense, offering enhanced detection of submarines, underground bunkers, and stealth aircraft by sensing minute gravitational and magnetic anomalies.

Quantum Imaging and Spectroscopy

Quantum-enhanced imaging allows for ultra-sensitive spectroscopy, which can be used in applications ranging from environmental monitoring to materials science. Quantum-enhanced lidar systems, for example, provide superior imaging capabilities even in low-light or obscured conditions.

Conclusion

Quantum sensing represents a fundamental leap forward in measurement science. By exploiting the unique properties of quantum mechanics, these sensors achieve levels of precision and sensitivity that were previously thought impossible. Their applications span across industries, from healthcare to defense, space exploration, and beyond.

The author of this article is a quantum researcher at the Technion and also leads the advanced quantum lab course at the Technion.

As we continue to develop and refine quantum sensing technologies, IZAK Scientific is at the forefront of integrating these advancements into real-world applications. Stay tuned as we explore deeper insights into specific quantum sensors in upcoming posts.

IZAK Scientific will be exhibiting at the OASIS 2025 conference, and we invite you to join us to discuss quantum sensing, quantum technologies, and more.

References

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2. Pezzè, L., Smerzi, A., Oberthaler, M. K., Schmied, R., & Treutlein, P. (2018). Quantum metrology with nonclassical states of atomic ensembles. Reviews of Modern Physics, 90(3), 035005.

3. Giovannetti, V., Lloyd, S., & Maccone, L. (2011). Advances in quantum metrology. Nature Photonics, 5(4), 222-229.

4. Kitching, J., Knappe, S., & Donley, E. A. (2011). Atomic sensors—a review. IEEE Sensors Journal, 11(9), 1749-1758