Science Made Simple: What is Quantum Mechanics?

This landmark theory originated in the early 20th century and has been widely used in the real world in the 21st century. Argonne scientist Harmon and many other scientists apply quantum mechanics in the laboratory and are developing technologies that may one day transform society and our understanding of the universe. Quantum sensors can detect previously undetectable cancer cells. A quantum internet could ensure that information and data communications are hacker-proof. Quantum computers can solve complex problems that classical computers cannot. Quantum theory will also continue to advance our understanding of the universe, from the intricate dynamics deep within atoms to the grand cosmic events of the birth of the universe.

In the early 20th century, scientists began to develop quantum mechanics to explain a series of experimental results that could not be explained by any other explanation. Today, scientists are using this theory to create powerful technologies—unbreakable messaging, faster drug discovery, and higher-quality images on cell phone and television screens.

So, what is quantum? In a broader sense, the word "quantum" can refer to the smallest possible amount of something. The field of quantum mechanics studies the most fundamental matter, energy and light, and the way they interact to make up the world.

Unlike the way we usually think about the world, where we imagine things individually having the properties of particles or waves (such as baseballs and ocean waves), this concept doesn't work in quantum mechanics. Depending on the circumstances, scientists may observe that the same quantum object has the properties of a particle or a wave. For example, light cannot be considered to be just photons (a type of light particle) or just light waves, because we may observe both behaviors in different experiments.

On ordinary days, we see things in only one "state" at a time: here or there, moving or stationary, right side up or tail up. In quantum mechanics, the state of an object is not always straightforward. For example, before we determine the location of a set of quantum objects, they may exist in a superposition (or a special combination) of one or more locations. Different possible states combine and interfere with each other like waves in a pond, and an object only has a definite position after we observe it. Superposition is one of the main features that makes quantum computers possible, as it allows us to represent information in new and useful ways.

Another interesting quantum behavior is tunneling, where quantum objects (such as electrons) can sometimes pass through otherwise impenetrable obstacles. This happens because superposition allows an electron to have a small chance of appearing on the other side of the barrier. Quantum tunneling technology has applications in areas such as flash memory devices, powerful microscopes and quantum computers.

When quantum objects interact, they are connected to each other through a connection called entanglement. This connection is maintained even when objects are far apart. Einstein called it the "ghost of distance." Scientists are using it for ultra-secure communications, and it's also an essential feature of quantum computing.

At the U.S. Department of Energy's (DOE) Argonne National Laboratory, scientists use world-class expertise and research facilities to develop quantum technologies for storing, transmitting, and protecting information, and to study our universe, from the complex dynamics deep inside atoms to events as grand as the birth of the universe. Argonne also leads Q-NEXT (the U.S. Department of Energy's National Quantum Information Science Research Center), which develops quantum materials and devices and applies the power of quantum technology to communications.