By Ibtisam AbbasiReviewed by Louis CastelJan 3 2025

The principles of quantum mechanics have played a key role in modern applications, and in improving our understanding of modern concepts of physics, leading to much more reliable, robust, and effective systems in all industries.¹ In recent years, several researchers have demonstrated experimental proof of quantum tunneling, showcasing the ability of particles to pass through impassable barriers like waves, which was deemed impossible by classical physicists. Recent scientific advancements have been possible due to our understanding of the non-deterministic nature of sub-atomic particles by quantum mechanics concepts, enhancing our knowledge of the phenomena taking place in the universe.

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What is Quantum Tunneling?

Quantum tunneling has given us the key to understanding the process of allowing micro-sized particles to move through barriers considered forbidden by classical physics. The main idea behind the process is that particles can also act like waves, allowing them to pass through energy states, and positions that are very difficult to predict, and not allowed using classical computational techniques.

The Heisenberg Uncertainty principle and wave-particle duality - the major differences between classical and quantum physics - are at the core of quantum tunneling. These concepts do not allow for pre-defined estimation of energy, position, and momentum of micro-particles.

The Concept of Energy Barrier in Quantum Tunneling

In quantum tunneling, the concept of energy barriers plays a crucial role. It is the parameter that helps us understand the spatial and temporal location of a quantum particle within a specific region of interest.

The Importance of Wave Function

The behavior of particles is explained using the Schrodinger equation, which unveils a particle’s wave function and allows us to calculate it. Knowing the energy, mass, and wave function of a quantum particle, all other critical parameters can be calculated, and the probability of finding a quantum particle within different regions of interest in space can be accurately estimated.

The solution of Schrodinger’s equation yields 2 different results, and solving the equation for n number of regions leads to 2n possibilities. Experts then meticulously decide the boundary conditions and implement accurate constraints, ensuring no discontinuities exist in the wave function.²

Conditions for Tunneling

Classically, if the kinetic energy of a particle is less than an energy barrier, it was thought to be impossible for the particle to pass through said barrier. However, in quantum mechanics, a particle can pass through a thin barrier even at lower energy states.

Quantum tunneling has been observed when particles are able to pass through a barrier with finite height, and very thin thickness. Furthermore, quantum tunneling processes have been demonstrated only when the potential energy of the barrier is higher than the kinetic energy of the particle. The microscopic size of the particle enables it to have a wave-function, and easily penetrate the barrier.³ When these conditions are met, we can expect to see the quantum particle on the other side of the barrier by quantum tunneling.

Key Concepts

Heisenberg’s Uncertainty Principle

Heisenberg’s Uncertainty principle postulates that we cannot be certain about a particle’s position and momentum at a precisely defined time.⁴ If the momentum of a particle is accurately known, we can’t be sure about its location. So, we can’t be sure of both attributes simultaneously, which makes it possible for the particles to exhibit quantum tunneling.

When a particle reaches an energy barrier, we are certain about its position; however, by the uncertainty principle, the momentum can’t be calculated exactly. The momentum drives the particle to tunnel through the energy barrier and reach the other side despite the huge difference in their potential energy states.

Quantum Tunneling and the Potential Barrier

The existence of a particle beyond a barrier which has much higher potential energy by tunneling was deemed impossible in classical physics. When the potential barrier has an infinite height, the wave packet of the particle can’t tunnel through it and is reflected. For a potential barrier with a finite thickness and infinite width, the particle can filter through the boundary of the barrier, but eventually, it decays out.

However, in the case of a potential barrier with finite width, and thickness, the quantum particle penetrates the barrier, and tunnels through it to the next side.⁵ The existence of a potential barrier defines the quantum tunneling process, and by varying the barrier attributes, we can precisely control the process of quantum tunneling and regulate it for different applications.

Role of Quantum Tunneling in Alpha/Radioactive Decay

G. Gamow explained that the complex process of radioactive alpha decay was possible due to quantum tunneling. An alpha particle is composed of 2 protons and neutrons. Gamow’s theory states that although the Coulomb force between particles existing in the nucleus of radioactive material is much higher, alpha particle decay is possible due to quantum tunneling. The alpha particle tunnels through the potential barriers despite having lower energy, and is released from the nuclei of radioactive material. Gamow performed extensive quantum mechanics calculations, and the experimental results proved that quantum tunneling was responsible for the alpha particle being released from the parent nuclei.⁶ The release of alpha particles by tunneling through the barriers, changes the nature of the radioactive element making it more stable.

Real-World Applications of Quantum Tunneling

Electronics and Semiconductors

Quantum tunneling is at the center of condensed-matter physics and is used for fabricating high-efficiency metal-oxide-semiconductor field-effect transistors (MOSFETs), quantum dots, and reaction tunneling diodes (RTDs).⁷

Terahertz communication (THz) systems are highly efficient within the ultra-wide THz band and are becoming a key system for modern 6g systems. For modern THz devices, Quantum-tunneling metal-insulator-metal (MIM) diodes are becoming a key technology for fast, and rapid data transfer.

These modern diodes are fabricated by creating an insulating layer between two metal contacts, and use quantum tunneling technology for electron transport, allowing for high-frequency signal amplification, and rectification. The modern applications of these diodes operating on quantum tunneling principles include infrared detectors and wireless power transmission systems.⁸

Additionally, in modern optical communication systems, quantum tunneling is used for the development of ultra-fast optical switches, which allow for the efficient generation of ultrashort pulses of light. These optical switches are used in modern optical long-distance fiber optics systems allowing data transfer in the Giga-Hz range.⁹

Nuclear Fusion Reactions

Quantum tunneling lies at the core of nuclear fusion technology. In nuclear physics, heavy-ion fusion reactions at energies below the Coulomb barrier are possible due to quantum tunneling.¹⁰

The fusion reactions occurring in the sun take place using quantum tunneling. The fusion reaction at the sun’s core involves the combining of Hydrogen nuclei (light particles) to form Helium particles (heavy particles), with the release of 28 MeV of energy.

Although the repulsive forces between the particles are difficult to overcome, particles present at the core of the sun behave as waves. The particles acting like waves, undergo quantum tunneling and pass through the repulsive electric field barrier. This leads to the fusion of the particles and the release of massive amounts of energy.¹¹ Hence, quantum tunneling has been powering our sun and other stars by allowing fusion reactions to take place for thousands of years. Recreating nuclear fusion on Earth will require having a clearer understanding of quantum tunneling.

What is a Scanning Tunneling Microscope (STM)?

Scanning Tunneling Microscope (STM), introduced in 1981 by IBM physicists has been essential for the advancement of nanotechnology, and modern electronics.¹² This modern microscopy technique, utilizing quantum tunneling of electrons, is being used in various domains such as semiconductor manufacturing, and modern electronics. The system employs a sharp metallic tip positioned within a few angstroms of a conducting surface, facilitated by a 3D piezoelectric scanner for precise spatial control.

When a voltage V is applied between the tip and the sample, electrons tunnel through the potential barrier that separates them. This tunneling phenomenon forms the basis for capturing high-resolution images. The method is particularly effective for studying advanced materials, such as 2D nanoparticles with superior resolution and sensitivity.¹³

Despite quantum tunneling accelerating scientific progress in recent years, much more research is needed to unearth the complexities of the quantum realm. Recently, researchers have also started to utilize quantum tunneling to boost memory storage and data transmission. With the advancement in material technology, and quantum tunneling allowing particles to pass the speed of light, it is expected to play a critical role in advancing crucial domains like material sciences.

Explore the role of quantum tunneling in nature

Further Reading

1. Mermin, N. (2018). Making better sense of quantum mechanics. Reports on Progress in Physics, 82(1), 012002. Available at: https://www.doi.org/10.1088/1361-6633/aae2c6
2. University of Colorado Boulder. (2014). Quantum Tunneling Overview. [Online]. Available at: https://spot.colorado.edu/~rehnd/heuristics/pdf/tunnelingSummary.pdf [Accessed on: December 18, 2024].
3. LibreTexts Chemistry (2020). Quantum Mechanics: Tunneling. Supported by: Department of Education Open Textbook Pilot Project. [Online]. Available at: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/02._Fundamental_Concepts_of_Quantum_Mechanics/Tunneling#:~:text=For%20a%20quantum%20particle%20to,particle%20(E%3CV). [Accessed on: December 18, 2024].
4. Parker, M. (2014). Basic Quantum Concepts for Engineering Undergraduates: Making More Effective Use of Heisenberg’s Uncertainty Principle. 2014 ASEE Southeast Section Conference. Available at: https://papers.asee-se.org/proceedings/ASEE2014/Papers2014/13.pdf
5. Ling, S. et. al. The Quantum Tunneling of Particles through Potential Barriers. Quantum Mechanics. University Physics Volume 3. University of Central Florida. Available at: https://pressbooks.online.ucf.edu/osuniversityphysics3/chapter/the-quantum-tunneling-of-particles-through-potential-barriers/ [Accessed on: December 19, 2024].
6. Krori, K. et. al. (2021). Gamows alpha decay theory revisited. arXiv preprint arXiv:2112.09578. Available at: https://doi.org/10.48550/arXiv.2112.09578
7. Martín-Palma, R. (2020). Quantum tunneling in low-dimensional semiconductors mediated by virtual photons. AIP Advances, 10(1). Available at: https://doi.org/10.1063/1.5133039
8. Ozyigit, D. et al. (2023). Manufacturing of quantum-tunneling MIM nanodiodes via rapid atmospheric CVD in terahertz band. Sci Rep 13, 20733. Available at: https://doi.org/10.1038/s41598-023-47775-5
9. Quantum News (2024). Exploring Quantum Tunneling: Applications and Implications. Quantum Zeitgeist. [Online]. Available at: https://quantumzeitgeist.com/exploring-quantum-tunneling-applications-and-implications/ [Accessed on: December 19, 2024].
10. Hagino, K., & Takigawa, N. (2012). Subbarrier fusion reactions and many-particle quantum tunneling. Progress of theoretical physics, 128(6), 1061-1106. Available at: https://doi.org/10.1143/PTP.128.1061
11. Siegel, E. (2015). It's The Power Of Quantum Mechanics That Allows The Sun To Shine. Forbes. [Online]. Available at: https://www.forbes.com/sites/ethansiegel/2015/06/22/its-the-power-of-quantum-mechanics-that-allow-the-sun-to-shine/ [Accessed on: December 20, 2024].
12. IBM. (2024). The Scanning Tunneling Microscope. [Online]. Available at: https://www.ibm.com/history/scanning-tunneling-microscope [Accessed on: December 20, 2024].
13. Zeljkovic Lab. (2024). Boston College, Department of Physics. [Online]. Available at: https://www.bc.edu/bc-web/schools/morrissey/departments/physics/labs/Zeljkovic-Lab/research/facilities.html [Accessed on: December 20, 2024].

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