Peering Deeply into the Hydrogen Atom for the First Time in History
A few decades ago, who would have imagined that we’d be able to photograph a hydrogen atom? Given what we know about quantum mechanics, the whole concept would have been dismissed as absurd.
But in that creative nexus where science and technology merge, miracles can happen. The seemingly impossible can become reality, and that is exactly what happened in 2013 when an international team of scientists successfully captured an image of the hydrogen atom, in all its simple yet sublime glory.
This amazing feat was announced in the May 24, 2013 edition of Physical Review Letters. It was achieved by a group of nine scientist connected with universities and physics institutes in Germany, the Netherlands, France, Greece and the United States. To accomplish this task, they developed a new type of observational device known as a ‘quantum microscope.’ This equipment and the experiments it enables allow physicists to peer all the way into the subatomic realm, without disturbing it or altering its nature.
Conventional microscopes magnify microorganisms or other objects too small to be seen with the naked eye. In general, the more powerful the microscope the smaller the object or life form that can be seen.
But beyond a certain point we can descend no further. Quantum physics prohibits the visual exploration of the extremely small, since the very act of trying to see into the subatomic realm shapes its reality.
Electrons have a dual nature, as both a particle and a wave. If you try to observe the wave function the electron will switch into particle mode, and vice versa. This indeterminacy gives electrons a fuzzy nature and puts them off limits from the probing of light particles (photons).
But there is a predictability to quantum processes that leaves the door cracked open, ever so slightly. We can’t be exactly sure where an electron will be or know how it will behave as it orbits around a nucleus, but we can identify locations where it won’t be. With respect to electrons, a node is a location where there’s a zero probability of an electron being found, and uncovering the nodal structure of an electron helps reveal where it actually is while it remains in a wave-like state.
The challenge has been to manipulate an electron’s behaviour in a way that can be used to create images. That is what the scientific team studying the hydrogen atom were striving to achieve, and eventually they figured out how to do it.
The specific technique they used to make their quantum microscope is known as photoionization microscopy. Scientists have known of the existence of this technology for more than 30 years, but it took quite a while to figure out how it could be used to create a realistic image of a hydrogen atom, as it actually existed at the time the image was completed.
A newly developed “quantum microscope” directly observes the electron orbitals of a hydrogen atom, using photoionization and an electrostatic magnifying lens
Hydrogen atoms were chosen for this experiment because they are the simplest of all atoms. They have only one electron orbiting around a nucleus that contains one proton. Approximately 75 percent of the matter we observe in the universe is hydrogen, and most of it is found in stars and in interstellar clouds and gas.
When we look inside the hydrogen atom, we’re literally gazing into the heart of the universe. Hydrogen is the stuff from which almost everything is made, which is all the more remarkable considering how simple the hydrogen atom appears to be.
When the Netherlands- and Germany-based team developed the first images of the hydrogen atom, there were no surprises—which itself is not surprising, since no surprises were expected. Quantum physics is in many ways mysterious and counter-intuitive, and it posits the existence of a world where matter and consciousness seem inextricably intertwined. But despite the Alice-in-Wonderland aura of quantum physics, and the fuzziness it builds into the very core of reality, it is still the most experimentally-confirmed theory in all of science.
Consequently, when the researchers revealed the first-ever image of a hydrogen atom, what was seen was exactly what was expected. The electron wave function (the electron’s orbit), and its nodal structure, manifested as a pair of rings circling around the core of the atom (its proton nucleus). They were displayed on the screen of the detector as a result of interference patterns created when the atom was excited by a laser. These interference patterns separate the locations where the electron could be from the locations where it couldn’t be (the nodes), allowing for the reproduction of the wave function in the form of a visual image.
There is some trickery involved here. Looking at the hydrogen atom directly remains impossible. But the image derived from interference patterns is a perfect representation of reality, and its precise accuracy is what makes the “photographing” of the hydrogen atom a remarkable achievement.
“What you see on the detector is what exists in the atom,” says Marc Vrakking from the Max Born Institute in Berlin, who was one of the lead scientists in this study. “If you look at the measured projections on the detector, you can easily recognize the nodes, and see their radial, ring-like structure.”
Next Stop: Helium
Helium is the second most common element in the universe. It makes up about 23 percent of existing matter. It is also the second simplest atom, with two electrons, two protons and either one or two neutrons. As the second element on the periodic table, it was a logical candidate for the next attempt to “photograph” an atom.
In 2014, the Amsterdam-Berlin team was able to recreate their initial experimental results with a helium atom. Once again, they produced images that corresponded with the appearance of an actual atom in real life.
When helium was manipulated with electric charges, it was observed to switch back and forth between two states. In one state, its two electrons exhibited correlated or coordinated behaviour, giving it an emergent property absent in the hydrogen atom.
“Although one of the helium electrons is very tightly bound to the nucleus, and the other one is very highly excited, we can see that the electrons know of each other’s existence and that they “talk” to each other,” Vrakking explains.
In the other, less excited state, electron orbits stay separate and atom functioning is similar to that of hydrogen.
Going Even Deeper?
As techniques continue to develop, more and more images of atoms and even molecules are likely to be produced. Farther in the future, perhaps scientists will develop a scheme to create accurate representations of quarks or leptons, the fundamental building blocks from which protons, electrons and all the elements of nature are formed.
This may sound like an impossible dream. But time and the scientific method often combine to stretch the boundaries of the possible far beyond what had been anticipated.
Top image: Illustration of an atom. Credit: Ezume Images / Adobe Stock
By Nathan Falde