Towards the Quantum Standard of Electric Current
Researchers at Low Temperature Laboratory and Laboratory of Physics (TKK) and at University of Stony Brook (New York) have potentially solved the problem of accurately defining the ampere.
The group has developed a frequency to current converter, the accuracy of which is based on the known charge of an electron and the extreme accuracy in defining frequency. The nanodevice is essentially a single electron transistor which works as a simple single-electron turnstile. Its best performance is achieved at very low temperatures.
Previously, the electric current and its unit, the ampere, have been defined through the classical force induced to two parallel leads carrying the current. In the past years, many proposals and experiments have been put forward to achieve a relatively simple and accurate high-yield current source. No satisfying device has been implemented yet.
”The goal of our research has been to develop a reliable frequency to current converter since the frequency can be fixed with ultra high accuracy. It was interesting to observe that in this more than two decades old field, there is still room for simple inventions”, says professor Jukka Pekola, the leader of the PICO group at Low Temperature Laboratory.
In the experiments carried out at TKK in Micronova, the method was observed to work so well (see the figure) that the device can be regarded as one of the most potential candidates to realize a metrological current pump.
This device, which may revolutionize quantum metrology, works as follows: The turnstile is biased to a fixed dc voltage and its island is capacitively coupled to a sinusoidal gate voltage with frequency f. Thus the dc off-set and the amplitude of the gate drive determine exactly the number, n, of electrons passed through the device in each cycle, and hence the electric current. In this case, the current is defined to be nef, where e is the electron charge.
”At the moment, our work is focused on eliminating the remaining errors using advanced designs of the device and active error correction schemes”, tells Jukka Pekola with optimism.
The research is closely related to the so-called quantum metrological triangle experiment, in which the fundamental constants of nature e and h (Planck’s constant) are checked for consistency using the quantum standards of electric voltage, current, and resistance. These kinds of experiments are pursued in a couple of laboratories world wide, for example, at Otaniemi campus in the Center for Metrology and Accreditation in collaboration with Low Temperature Laboratory and VTT.
Professor Jukka Pekola | alfa
The most recent press releases about innovation >>>
Die letzten 5 Focus-News des innovations-reports im Überblick:
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
New technique promises tunable laser devices
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...