From memory devices to the heart of stars
Consider the operation of a flash memory card, such as an SSD or USB drive, which is capable of data retention even when powered off; the immense energy output from the sun and stars; or research indicating the occurrence of enzyme catalysis and DNA mutation [1]. These diverse applications are unified by the quantum mechanical phenomenon known as quantum tunneling.
Quantum tunneling refers to the capacity of particles to penetrate energy barriers despite lacking the requisite energy to surpass these obstacles according to classical mechanics. This effect arises from superposition, which imparts wave-like characteristics to quantum-scale particles and permits probabilistic presence across multiple locations. The transmission coefficient, which quantifies the likelihood of tunneling, is determined by the barrier’s height and width, in addition to the particle’s mass and energy [2].
Application of the time-independent Schrödinger equation allows the decomposition of the particle’s wave function into components situated within and outside the barrier. By ensuring continuity of the wave functions at the boundaries, the transmission coefficient can be derived. This theoretical framework has been effectively utilized in various fields, including the development of scanning tunneling microscopes and quantum dots.
Running your digital world
Modern electronics exist in a delicate balance with quantum tunneling. At the heart of today’s microprocessors are advanced transistors, which depend on the quantum ability of electrons to traverse ultra-thin insulating barriers. This tunneling enables transistors to switch on and off at remarkable speeds while using minimal energy, supporting the drive for faster, more energy-efficient devices. As technology advances and the insulating layers within transistors are made thinner to fit more components onto a single chip, the probability of electrons tunneling through these barriers inevitably increases. This leads to unwanted leakage currents, which can generate excess heat and disrupt circuit performance. Such leakage is a major challenge, setting hard physical boundaries on how much further Moore’s law—the trend of doubling transistor density— can be extended.
Yet, the same quantum effect that poses challenges in mainstream electronics is ingeniously exploited in specialized components. Tunnel diodes, for example, are engineered with extremely thin junctions that encourage electrons to quantum tunnel from one side to the other. This property allows tunnel diodes to switch at incredibly high speeds, making them invaluable for high-frequency circuits and telecommunications technologies where rapid response times are essential.
Quantum tunneling is also fundamental to how data is stored in non-volatile memory devices such as flash drives and solid-state drives (SSDs). In these devices, information is retained by manipulating electrons onto or off a “floating gate,” separated from the rest of the circuit by a thin oxide barrier. When writing or erasing data, electrons tunnel through this barrier, and once in place, they remain trapped, even if the device is disconnected from power. This is why your photos, documents, and other files remain safely stored on a USB stick or SSD long after you unplug them.
In summary, quantum tunneling is both a challenge and a tool in modern electronics. Engineers must constantly innovate to suppress unwanted tunneling in ever-smaller transistors, while simultaneously designing components that rely on controlled tunneling for speed, efficiency, and reliable data storage. This duality underscores how quantum mechanics is not merely an abstract scientific theory, but a practical force shaping the infrastructure of everyday digital life.
Powering stars, chips, and qubits
On a cosmic scale, quantum tunneling is fundamental to the process by which stars, including the Sun, emit light. It facilitates the fusion of protons within stellar cores by enabling them to overcome their mutual electrostatic repulsion, thus allowing nuclear fusion to occur at temperatures lower than those required in a strictly classical context. The existence of life on Earth relies on this mechanism, as it powers the energy output of stars that sustain our planet. Insights into tunneling continue to inform research efforts aimed at developing fusion reactors, where analogous physical principles must be managed under controlled conditions rather than governed by stellar gravity.
In superconducting circuits, which comprise materials capable of conducting electric current without resistance, pairs of electrons known as Cooper pairs tunnel through thin insulating barriers called Josephson junctions. When cooled to near absolute zero, these systems enable billions of paired electrons to behave collectively as a single quantum entity. This phenomenon has resulted in devices with exceptional sensitivity for measuring voltage and magnetic fields. Additionally, Josephson junctions play a central role in the architecture of superconducting qubits, where precision control of tunneling between quantum states enables reliable quantum logic operations.
The Nobel Prize in Physics 2025 was awarded to John Clarke, Michael H. Devoret, and John M. Martinis for their pioneering work in designing a macroscopic system utilizing a Josephson junction. The system was composed of two superconductors separated by an ultra-thin oxide layer, only a few nanometers thick. This layer permitted electron tunneling, and the observed discrete energy levels were in complete conformity with quantum mechanical predictions, a notable accomplishment from both experimental and theoretical standpoints [3].
A feature, a bug, and a design principle
Imagine a world where the chemical foundations of life and technology remain a mystery. Without quantum mechanics, our understanding of chemical bonds would be impossibly incomplete, the very medicines that save lives daily could never be designed, and the machines and electronics we rely on in our daily lives would not be possible.
Quantum tunneling stands as a striking testament that quantum phenomena are not mere scientific oddities; they are the bedrock of modern innovation. The same quantum effect that challenges engineers by causing troublesome current leaks in ever-smaller transistors is deliberately harnessed for breakthroughs: non-volatile memory, lightning-fast diodes, atomic-resolution microscopes, and the frontier of quantum computing all depend on it.
Every second, billions of electrons tunnel invisibly within the technology that surrounds you, their quantum behaviour silently orchestrating our digital universe. Far from being an abstract theory, quantum mechanics is the invisible engine driving your phone, your computer, your lasers, and LEDs—the essential infrastructure of twenty-first century life. Our entire technological existence pivots on the strange but real phenomena of the quantum world, challenging us to see science not as distant or esoteric, but as the very substance of our everyday reality.
