A newly-discovered fundamental property of electrical currents in extremely small metal circuits demonstrates how negatively-charged particles can wash over said circuit like waves, generating interference in parts of the circuit where no current is delivered.
This characteristic, discovered by researchers at the University of Twente’s MESA+ institute and detailed in a recent Scientific Reports paper, is due largely to the circuit’s geometry as well as the quantum mechanical wave character of electrons, according to the study authors.
As part of their research, the MESA+ team demonstrated electron interference—a phenomenon in which propagating waves interact coherently—in a gold ring with a 500 nanometer diameter. One side of the ring was connected to a tiny wire through which an electrical current could be driven, while the other side was connected to a different wire attached to a voltmeter.
When they applied the current, sending a varying magnetic field through the ring, they detected electron interference on the other side of the ring, even though no net current passed through the ring. Their experiment revealed that electrons can bleed into the ring, thus altering the electrical properties in parts of circuit not expected to be affected by the current.
Findings could help shape future quantum computers
Despite the fact that the gold ring was diffusive (its electron mean free path was much smaller than the ring itself), the authors said that the effect was surprisingly pronounced. It shows that electrons must be considered waves in nanoscale circuits at extremely low temperatures, since this behavior is said to be a prime example of quantum mechanical wave-particle duality.
Specifically, the MESA+ team explained, the outcome of their research is directly due to the fact that quantum equations of motion are nonlocal. Their work helps explain one specific type of nonlocality known as dynamical nonlocality, which is a large part of all experiments that involve quantum interference.
Quantum interference, they said, is affected by a phenomenon known as decoherence, in which the physical environment causes loss of phase memory, as well as by performing a “which-path-measurement,” which removes dynamical nonlocality and terminates the interference pattern. In their experiments, the University of Twente researchers discovered that the geometry of a circuit can also affect dynamical nonlocality, which could help shape future quantum computers.
“We have thus shown a new aspect of the dynamical nonlocality of electrons in a quantum nanoscale circuit that is solely governed by geometric aspects and not by external measurement. Understanding this geometrical constraint is essential for the optimal design of any quantum circuit based on the dynamical nonlocality of the electron,” the authors wrote.
“Moreover, as deduced from our model, the specific link found between geometry and nonlocality is not limited by the diffusive transport regime of our experiment, nor by the specific quantum wave-particle used (in our case electrons) but, as other important geometrical constrains4, is a universal property of quantum dynamics,” they added. “We believe that these results will trigger further investigation of the fundamental properties of quantum dynamics and of its application in nanoscale quantum circuits.”
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Feature Image: University of Twente
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