If you’ve seen any of the recent movies in the Marvel Cinematic Universe, you’ve probably spent at least a brief moment pondering the word “quantum.” Like a lot of scientific words used in movies, quantum sounds important, difficult, and powerful. And it gets thrown around a lot to explain difficult plot necessities. As Scott Lang says in Ant-Man and The Wasp:
“Do you guys just put the word quantum in front of everything?”
Quantum physics has been around for more than a century. Whether you realize it or not, quantum physics underlies most things in the modern world from fridge magnets and computer memory to cell phones, MRI machines, and drug design. In fact, you can’t really separate quantum science from science in general anymore. You may not notice it, and you may not need to use its difficult math to describe the everyday world, but the quantum revolution in science established that the quantum mechanical explanation of the world is the one that is most correct at the most levels so far.
In short, Isaac Newton’s equations don’t always work at the very smallest physical scale.
Quantum mechanics, which physicists developed at the beginning of the 20th century, describes how light and matter behave at the miniscule atomic scale. You probably recognize at least some of the founders’ names: Max Planck, Albert Einstein, Niels Bohr, Werner Heisenberg, Erwin Schrödinger, Louis de Broglie, Paul Dirac, Max Born, and many others. They developed quantum mechanics to explain several observations that classical physics could not, such as the nature of light.
Wave or Particle?
Newton suggested light was a stream of particles, but experiments by scientists in the 19th century revealed that light acted like a wave of water. In his famous “double-slit” experiment in 1805, Thomas Young showed that when light passes through two slits in a barrier, it moves through like water. The waves of light pass through the openings and interfere with each other. These waves of light form a pattern with peak intensities.
About a century later, Einstein found that light was only absorbed and radiated in defined chunks, called quanta of energy. Was light a wave or a bunch of particles?
This apparent contradiction came to a head when scientists recreated Young’s experiment by shooting single particles, like electrons, through the slits. Something very puzzling happened. The clumps of electrons would land at distinct points. However, after several rounds had been fired at the detection screen, the clumps of electrons resembled the wave interference pattern that occurs when light passes through the slits, but only if the electrons were detected on the screen and not before. It was like the individual particles were interfering with themselves. Resolving this discrepancy, called “wave-particle duality,” has plagued physicists ever since.
After Einstein realized that light waves also move as individual photons, Louis de Broglie suggested that electrons, and all matter, actually, must also move like waves somehow. A few years later, Schrödinger developed a wave equation that described the “quantum state” of a particle or group of particles. This equation was known immediately to be correct mathematically. But puzzlingly, it also described strange realities. For example, it states a particle could be in two places at the same time. When you measure it, though, it would only be found in one place. No one could explain what this meant in the everyday world.
In fact, to this day, no one completely agrees. Some physicists, like Hugh Everett, have suggested that the multiple possibilities dictated by Schrödinger’s equation actually predict multiple actualities—that is, many worlds, or the “multiverse” if you’re in the Marvel Cinematic Universe. The particle really is in both places, just in different universes, and they interfere with each other, but you can only directly measure one of them in your own reality.
Certain or Uncertain?
The way the single particles acted when fired at the two slits has flummoxed scientists. They could point the “electron gun” right at one slit, and some electrons would apparently go through the other slit. Although scientists could accurately predict a football’s trajectory, they could never tell you exactly where an electron would go. Further, it turned out that Schrödinger’s wave function predicted accurately that if you changed one particle in a system, it would almost magically change a separate, entangled particle, even if that particle was across the universe! But even measuring basic properties of these particles was more challenging than scientists expected. The Uncertainty Principle states that there’s a limit to our ability to measure certain pairs of physical properties at any one time. For instance, you can measure an electron’s position, but you are then limited in how well you can measure its momentum. And it’s true for a particle’s energy and time. The more you know one, the less you know the other.
One unexpected, mind-bending feature of this principle is the observed and verified fact that pairs of particles can suddenly appear and disappear literally out of nowhere, as long as it happens in a very short amount of time. These quantum fluctuations in spacetime mean the fabric of the universe, like the ocean, will never be completely still. In fact, the whole universe is entangled in groups and pairs that affect each other.
Given the incredible consequences of quantum mechanics, head-scratchers in the Marvel Cinematic Universe don’t seem quite as far-fetched.
So, what do these strange consequences mean for us now? As Jonathan Dowling, LSU Department of Physics & Astronomy professor and Hearne Chair of Theoretical Physics, sees it, quite a lot.
“We are currently in the midst of a second quantum revolution,” he said. “The first quantum revolution gave us new rules that govern physical reality. The second quantum revolution will take these rules and use them to develop new technologies.”
All of the quantum technology research conducted at LSU fall into three general categories: quantum sensing and imaging, quantum cryptography and communications, and quantum computing. These broad areas are each based on fundamental quantum properties.
Of all quantum technologies, it’s quantum computing that is getting the most attention, and for good reason. In normal computing, information is transmitted through bytes, which are brief messages written in a Morse-like code of eight bits, each of which are either 0 or 1. But in the quantum realm, a particle can be in a superposition of both here and there, or both 0 and 1. Thus, you can use quantum bits, or qubits, to compute on more possibilities at once. And when entangled particles are used for those qubits, algorithms could compute tasks that are practically impossible now at speeds far outstripping current capabilities. What would take a modern computer years and years to compute, a quantum computer could handle in seconds.
LSU Department of Physics & Astronomy Professor Illya Vekhter, one of the many scientists conducting quantum research at LSU, provides the following perspective:
“Everything fundamental science needed to know about silicon we knew by the late 1960s, and only after that, scientists have still developed devices that continue to improve over half a century later. Everything fundamental about cell phones we knew by the 1980s. So, when I do my research, I have some ideas of what it may be used for, but the job of a condensed matter physicist or quantum technologies person is to study what can be turned into a device 10, 20, or 50 years later. That is the only way we can bring about new developments.”
In all the uncertainty of quantum physics, one thing is certain. Quantum technology is going to be world altering---and it may come about quite quickly. Earlier this year, the White House organized a meeting with leading research universities, including LSU, as part of the National Quantum Initiative, a $1.2 billion federal investment to establish a coordinated effort to advance quantum information science and technology.
“This dialogue was the beginning of a national effort potentially on the scale of the Manhattan Project or the Space Race, leading to new technologies we cannot even imagine now,” said Samuel J. Bentley, LSU vice president of research and economic development.
Administrators directing five federal agencies attended the meeting and facilitated discussions on key topics such as basic research, educational strategies, workforce development, and technology commercialization. At this meeting with fellow flagship universities and the Ivy League, Bentley represented LSU and the quantum faculty, who are at the forefront in developing theory and materials important to quantum information science. No word on whether Dr. Pym or Mr. Lang were present.
This story was one of the cover features of the 2019-2020 print issue of LSU Research magazine, on the theme of convergence. Also, check out our Louisiana Quantum Initiative website for more information as well as a complete listing of quantum researchers around the state.
Kristopher Mecholsky, Ph.D.
LSU Office of Research & Economic Development
LSU Office of Research & Economic Development