For stronger field more astonishing phases appear where the Hall conductance becomes a fraction of the unit of conductance (inverse of resistance) [3]. In this regime called "fractional quantum Hall effect", the current can be carried by quasi particles carrying a fractional charge e * = e/m, m = 3 or 5 ... , function of the experimental conditions. Like quarks, the fractional charges e/m cannot be separated in vacuum and must remain confined in the two-dimensional electronic fluid. But unlike quarks, which are fermions, these objects are anyons, presenting the statistical angle π/m. Finding a way to manipulate these anyons to try to highlight their fractional statistics is an experimental challenge, and a first step in that way has just been successfully completed by SPEC researchers. Beyond this advance, it should also be noted that anyons are not only a theoretical curiosity, but also brings a new potential path for quantum computing, based on their manipulation.

Experimental setup and principle of measurement:

In its principle, the carried out experiment consists of analyzing the electrical noise of a very weak electric current. This current must be low enough for the charges individually pass through the conductor, so generating a shot noise which amplitude is characteristic of the charge of an elementary transport event.

For this, a AsGa/As(Al)Ga semiconductor heterojunction with high electronic mobility was carried out at Cavendish Laboratory in Cambridge (UK) by epitaxial growth. The two-dimensional electron layer is located at the interface, buried by 100 nanometers. With the nanofabrication facilities of SPEC, a conductor a few tens of microns wide is obtained by etching. Electric contacts are added to apply the bias voltage and inject and measure the current, as well as a pair of electrostatic grids whose polarization allows adjusting the width of a conductive constriction in the center of the sample, thus forming a Quantum Point Contact (QPC).

To overcome the thermal noise, the sample is cooled to 20 mK in a dilution refrigerator and subjected to a strong perpendicular magnetic field of about 11 T. The applied strong magnetic field imposes that the current is propagated only in channels along the edges of the sample, with a direction imposed by the sign of the field. The conductor's core, which is not traversed by any net macroscopic current, forms a Hall topological insulator. A bias voltage V injects an incident current that splits at the level of QCP into a non-deflected (transmitted) current and a "reflected" current between the channels facing each other. In the case of a very weak reflection of the current, the reflected current results from the rare and uncorrelated transfer of charges e*. Since the statistic is Poissonian, the ratio of the shot noise to the average current gives a direct measurement of the charge of the exchanged quasi-particles .

The first measures have consisted in reproducing the results obtained by the same team twenty years ago [4], when the fractional loads (e/3) were observed for the very first time. The new device then allows extending the observation to even smaller fractions of charges: e/5 [5].

Manipulation of fractional electric charges:

But it is the proof of the emission and absorption of photons by the anyons that is the fundamental discovery of the present study. This interaction provides a second measurement method confirming the reality of the fractional excitations. It also opens the way to controlled time resolved manipulation of anyon . For this, a periodic voltage of microwave frequency f (a few tens of GHz) is superimposed to the DC bias voltage V injecting some current in the conductor. At the working temperature (20 mK), the quantum of energy hf is much higher than the thermal energy. An additional electrical noise, called photo-assisted, is observed, attesting that the quasi-particles are sensitive to photons. This photo-assisted noise appears when the applied  bias voltage is beyond a threshold VJ such that e*V_J = ± hf [5]. Checking this fractional Josephson relationship attests that accelerated e* charge in a bias potential V can effectively absorb or emit hf quanta .