Define Ampere precision by one electron at a time

This is a new way of defining the standard ampere, unit of current, more precisely, built by physicists in Finland and the United States. The team led by Jukka Pekola of the Helsinki University of Technology created a single-electron transistor to convert the ac voltage into an extremely accurate current.

Ampere, volt and ohm are the three basic quantities of electricity. Although physicists have invented modern methods for defining volt and ohm in a microscopic way (methods of measuring Josephson voltage and quantum Hall effect), so far, experiments The most accurate ampere measurement is just a repeat of the measurement technique that has been introduced since the 19th century.

"This compact single-door device is easily used for many different components through parallel channels to create a larger output current," Pekola said. "The level of small current intensity has been an obstacle in creating single-electron flow intensity pumps, and our study hopes to solve this difficult problem."

Today, ampere is still defined as the current intensity running in two long parallel conductors, 1 meter apart, when the interaction force between them has a defined value. This definition is based on macroscopic measurements, so the geometry of the conductors will limit the accuracy of the measurement.

Measuring extremely small currents

Instead, physicists now want to define the ampere by creating an extremely accurate power source: only one electron is released at a time. Although previously, researchers have tried to create such a device to define ampere, but no one has succeeded, because it has been proved that the work of measuring such a tiny electric current is very difficult.

Now, Pekola and colleagues have solved this problem by creating a single-electron, single-electron transistor transistor (the article was published in Nature Physics). Their device consists of a small conducting island, which is connected to the outside via two tunneling layers. The electron can penetrate the tunnel through this contact layer, running along the conductor and then tunneling through the contact layer again. The device also includes a gate electrode (gate electrode), which is used to regulate the flow of electrons through the conductor, by applying a voltage.

The tunnel exposure layer is actually a very thin insulating layer that electrons can pass through thanks to the quantum tunnel effect. The contact layer is designed so small that the repulsion between electrons will be enough to eliminate the possibility of having more than one electron crossing this tunnel, at a time.

Model of components

Cooling below 0.1 K:

This device is cooled below 0.1 K to avoid thermal disturbance, its two ends maintaining a constant 1-way voltage, while the gate electrode is controlled by an alternating voltage. . The exact number of electrons passing through the device during an electric oscillation cycle is determined by the amplitude and the mean value (mean value) of the voltage applied to the electrode gate.

The current flowing through the device is the number of electrons passing through the tunnel each cycle times the charge of each electron and the source's frequency of oscillation. The oscillation frequency of the source and the number of electrons passing through the device per cycle can be determined, the charge of the electron is also known, so the device can be considered to be an infinite source exactly.

Although the researchers still need to improve the accuracy of the device, Pekola believes that this transistor is one of the brightest candidates to create an " amperage pump logic combination ", aimed at ampere definition. Answering Physicsworld.com , he said the problem could be solved by paralleling 10 such devices together, then the current would be about 10 pA large - large enough to be measured.

Simulate the operation of an electronic transistor