How Quantum Mechanics Went From Baffling Theory to Revolutionizing Modern Technology

Once a baffling theory, quantum mechanics has evolved into a driving force behind modern technology and frontier research.

A century ago, quantum mechanics was a bold and puzzling idea that challenged even leading scientists. Today, it underpins many everyday technologies, including lasers, microchips, quantum computers, and secure communication systems.

In a new perspective published in Science, Dr. Marlan Scully, a University Distinguished Professor at Texas A&M University, reviews how quantum mechanics has progressed from an unusual theory to a tool for tackling some of science’s most difficult problems.

“Quantum mechanics started as a way to explain the behavior of tiny particles,” said Scully, who is also affiliated with Princeton University. “Now it’s driving innovations that were unimaginable just a generation ago.”

Scully has played a major role in advancing the field. He co-authored the influential textbook “Quantum Optics,” widely used by physicists. His research in coherent nanoscale laser spectroscopy has enabled scientists to study molecules with atomic-level precision. He has also developed new concepts in quantum heat engines that challenge traditional thermodynamic limits and point to possible future energy technologies.

Thought experiment to real-world impact

In 1935, Erwin Schrödinger introduced his well-known cat paradox, proposing that a cat could exist as both alive and dead until observed. The idea was meant to highlight the unusual nature of quantum theory. “That ‘quantum weirdness’ is no longer just a philosophical puzzle,” said Scully. “It’s the foundation of quantum computing, quantum cryptography, and even gravitational wave detection.”

Early pioneers such as Schrödinger and Werner Heisenberg developed wave mechanics and matrix mechanics, two competing approaches to describing quantum systems. These frameworks were later unified into quantum field theory, which explains how particles interact through electromagnetic and nuclear forces.

Their work built on Niels Bohr’s early atomic model, which pictured electrons orbiting the nucleus like planets around the sun, helping lay the groundwork for modern quantum theory.

The power of coherence

One of the most significant ideas in quantum physics is quantum coherence, which describes how particles such as atoms and photons can remain linked and behave in a coordinated way, even across large distances.

This concept led to the development of the laser, once considered impractical. Today, lasers are widely used in barcode scanners, medical procedures, and advanced scientific research.

Quantum coherence also enables quantum entanglement, which Albert Einstein famously described as “spooky action at a distance.” Through entanglement, particles can share information in ways that support quantum encryption and improve the sensitivity of instruments like LIGO, which detects ripples in spacetime.

Beyond the Carnot Limit

Perhaps the most mind-bending application is the quantum heat engine. Traditional engines are limited by the Carnot Limit, the maximum efficiency allowed by thermodynamics. By using quantum coherence, researchers can design engines that exceed this classical boundary.

“It’s a striking example of how quantum principles can rewrite the rules of classical physics,” Scully said.

Biology and black holes

Quantum mechanics is increasingly influencing other areas of science. In biology, methods such as coherent Raman spectroscopy allow researchers to study viruses at the nanoscale.

It is also shaping our understanding of the universe. Theories such as string theory and quantum gravity attempt to connect quantum mechanics with Einstein’s theory of relativity, a long-standing challenge in physics.

Another long-standing problem is turbulence, the complex motion of fluids like air and water that affects aviation, weather, and climate. By studying superfluid helium, which exhibits unusual quantum behavior, scientists are identifying patterns that could improve weather prediction, climate models, and flight safety.

The next century of quantum

Despite its successes, quantum mechanics still raises major questions. Can gravity be described within a quantum framework? How might quantum computers transform medicine and materials science? What new insights into the universe could emerge from quantum technologies?

Scully believes continued research will be key. “At the start of the 20th century, many thought physics was complete,” he said. “Now, in the 21st century, we know the adventure is just beginning.”

Reference: “One hundred years of quantum mechanics” by Marlan O. Scully and William G. Unruh, 4 December 2025, Science.
DOI: 10.1126/science.ady6092

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