The smallest unit of information in a computer is the bit—either on or off, 1 or 0. Modern computing power is built entirely on the combination and interconnection of countless ones and zeros. Quantum computers, however, have their own version of the bit: the qubit. Like a classical bit, a qubit has two basic states. The key difference is that quantum effects enable superposition, allowing a qubit to exist as both 0 and 1 simultaneously, in varying proportions. This means a qubit can theoretically represent an infinite number of states.
This ambiguity is what gives quantum computers their theoretical “superpowers.” In principle, quantum computers can solve problems in mere fractions of a second—problems that would take today’s most powerful supercomputers an impractical amount of time. However, quantum computing is still in its early stages. One of the biggest challenges is connecting qubits, as a single qubit alone cannot function as a computer.
One way to represent the 0 and 1 of a qubit is through the alignment of electron spin, a fundamental quantum mechanical property of electrons and other particles. Simply put, spin can be thought of as a kind of torque, pointing either “up” (1) or “down” (0). When two or more spins are quantum-mechanically entangled, they influence each other’s states—changing the orientation of one affects all the others. This makes spin interactions a promising way to enable qubits to “communicate.”
However, as with much of quantum physics, this “language”—the interaction between spins—is extraordinarily complex. While it can be described mathematically, solving the equations exactly is nearly impossible, even for relatively simple chains of just a few spins. Not exactly ideal conditions for turning theory into reality…
A model becomes reality
Researchers at Empa’s nanotech@surfaces laboratory have now developed a method that allows many spins to “talk” to each other in a controlled manner – and that also enables the researchers to “listen” to them, i.e. to understand their interactions. Together with scientists from the International Iberian Nanotechnology Laboratory and the Technical University of Dresden, they were able to precisely create an archetypal chain of electron spins and measure its properties in detail. Their results have now been published in the renowned journal Nature Nanotechnology.
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