Figure: Schematic
representation of the nonlocal electron interference experiment.
A dc current is
driven from the upper left to the lower left contact. A nonlocal, oscillating
voltage is
measured between the upper and lower right contacts due the magnetic-field
induced
single-electron interference in the 500 nanometer ring in the middle.
(January 6, 2015) Nanotechnologists
at the University of Twente research institute MESA+ have discovered a new
fundamental property of electrical currents in very small metal circuits. They
show how electrons can spread out over the circuit like waves and cause
interference effects at places where no electrical current is driven. The
geometry of the circuit plays a key role in this so called nonlocal effect. The
interference is a direct consequence of the quantum mechanical wave character
of electrons and the specific geometry of the circuit. For designers of quantum
computers it is an effect to take account of. The results are published in the
British journal Scientific Reports.
Interference is a common phenomenon in nature and occurs
when one or more propagating waves interact coherently. Interference of sound,
light or water waves is well known, but also the carriers of electrical current
– electrons – can interfere. It shows that electrons need to be considered as
waves as well, at least in nanoscale circuits at extremely low temperatures: a
canonical example of the quantum mechanical wave-particle duality.
GOLD RING
The researchers from the University of Twente have
demonstrated electron interference in a gold ring with a diameter of only 500
nanometers (a nanometer is a million times smaller than a millimeter). One side
of the ring was connected to a miniature wire through which an electrical
current can be driven. On the other side, the ring was connected to a wire with
a voltmeter attached to it. When a current was applied, and a varying magnetic
field was sent through the ring, the researchers detected electron interference
at the other side of the ring, even though no net current flowed through the
ring.