Some people want to move mountains. Kunal Das, Ph.D., assistant professor of physics, wants to move electrons.
Das is a theoretical physicist researching an area where the classical rules of physics no longer apply—the nanoscale universe of quantum physics, a submicroscopic world where particles defy common sense. In that mysterious world of the ultra-small, Das is searching for new ways to move the currents that power computers.
“When the first computers came along in the 1960s, they were huge objects which filled up an entire room and had miniscule computing power,” Das says, as he gestures to his computer in his Freeman Hall office. “How is it that today we have something this compact and with this much more power? Today, every two years computers become twice as fast and half as big.”
Computers are powered by electronic circuitry in which currents move large clusters of electrons at a time to feed a tiny computer chip. The number of electrons needed for each operation has gotten smaller with time. But within 20 years, Das says, computers will reach a point where each operation could be done by just one electron, and thus won’t be able to get any faster or any smaller.
What then? Where will technology go?
Already, scientists are experimenting with storing information not in bits, but in qubits (or quantum bits), which can potentially store much larger amount of information than traditional bits. Can a “quantumchip” be in the offing?
That’s where quantum mechanics come in.
Das has focused his research on adiabatic electron pumps, which can be used to control the flow of individual or entangled pairs of electrons in order to power quantum computers. Quantum computers, which are still in their infancy, have the potential to perform certain calculations significantly faster than any silicon-based computer.
Quantum mechanics have become very important partly because, at the qubit level, individual particles of matter play essential roles. The current that powers the computer no longer flows as a cluster of electrons, but as one electron at a time; and such motion is governed by quantum mechanics.
“In classical physics, we talk about currents flowing continuously, like water,” Das says. “At the nanoscale, your current is comprised of individual electrons, and it is discrete as opposed to continuous.”
In other words, if you were to look at water flowing through a pipe, you would discover that at the submicroscopic level it is made of molecules that are discrete from one another, like individual grains of sand.
The problem is that the super-small world of quantum mechanics is notoriously unpredictable. In fact, an electron at the quantum level has a few weird characteristics that stem from the fact that quantum mechanics is all about probabilities, not absolutes.
“An electron, from a quantum mechanical perspective, does not behave like it does in classic physics, where it always acts like a particle,” Das says. “Here, it acts like a particle some of the time and like a wave some of the time. It has wave-particle duality, and it becomes probabilistic, meaning you cannot say for sure that the electron is definitely here. It might have some probability of it being here, or some probability of it being there. That’s what makes quantum mechanics strange and confusing to the layperson.”
An adiabatic electron pumping system is complex, but Das describes it as a mechanism that manipulates the shape of the “quantum wavefunction” of an electron, by varying such things as voltage or a magnetic field at the nanoscale. Das is researching how to apply the pumping system to single electrons and also to pairs of “entangled” electrons in which one electron can affect another even when separated by vast distances.
He hopes that his research will ultimately lead to a dependable system of moving currents of electrons in a precisely controlled way without destroying their fragile quantum state, which is essential to powering quantum computers.
“Once we start using the wave nature of electrons and the probabilistic nature of quantum mechanics, we can potentially do certain computations tremendously faster,” he says.
Potentially?
At this point, quantum computers have not yet been built, although some experiments have been carried out. Research is being done at a frantic pace, however, as such systems would be invaluable to national security, Das says.
“All existing encryption systems are based upon the fact that we cannot crack them with the computers that we have available now,” says Das. “With a quantum mechanical algorithm, you could crack encryption methods very fast.”
There are also potential applications to teleportation, Das says, but not of the Star Trek variety—at least not yet.
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What you could teleport is the state of an electron,” he says. “We could transfer those properties to a location which is far away, but not the physical object itself. So, in a sense, in quantum mechanics, you can be in two places at the same time.”
