The existence of fractional charges carrying the current is experimentally demonstrated. Using a 2-D electron system in high perpendicular magnetic field we measure the shot noise associated with tunneling in the fractional quantum Hall regime at Landau level filling factor 1/3. The noise gives a direct determination of the quasiparticle charge, which is found to be e * = e/3 as predicted by Laughlin. The existence of e/3 Laughlin quasiparticles is unambiguously confirmed by the shot noise to Johnson-Nyquist noise cross-over found for temperature Θ = e * V ds /2kB. Can fractional charges carry the current in a conductor? Up to now, there was no evidence of such phenomenon. Usual metals are known to form Fermi liquids with quasiparticles of charge e. Low dimensional systems are believed to offer a richer spectrum of excitations. Indeed, fractional charges have been predicted for commensurate charge density waves in one dimensional systems [1], and for two-dimensional electron systems (2DES) [2] in high perpendicular magnetic field when the fractional quantum Hall effect occurs [3]. In this letter, we report experimental evidence of charges e/3 carrying the current. The observation is done in the Fractional Quantum Hall (FQH) regime at Landau level filling factor ν = 1/3.2-D electrons in high magnetic field give rise to degenerate Landau Levels (LL) with one state per flux quantum φ 0 = h/e in the plane. For integer LL filling factor ν = n s /n φ , the cyclotron or the enhanced Zeeman gap gives rise to the integer quantum Hall effect [4] IQHE (n s and n φ = eB/h are the electron and quantum flux density) [5]. The simplest elementary excitation is an electron removed from the highest occupied LL, leaving a hole having the size of a flux quantum and a unit charge e. At fractional filling factor ν = 1/q, q odd, a gap ∆ ≃ e 2 /ǫl c also opens resulting from the interactions [6] (l c = (h/eB) 1/2 ). This is the FQH effect. Laughlin has proposed [2] that an elementary excitation can be realized by introducing a flux quantum φ 0 in the collective wavefunction. As there is one electron for q flux quanta, the so-called Laughlin quasiparticle has fractional charge e * = e/q. Extensions of the Laughlin approach to higher rational fractions ν = p/q[7] explain many bulk transport properties but so far no direct experimental evidence for the bulk Laughlin quasiparticles have been found. The quasiparticles in the bulk have been mostly probed using thermal activation. The prefactor of the activated conductivity has shown a striking [8] relation to the quasiparticle charge but is not fully understood [9]. Comparison of the chemical potential jump at fractional ν obtained from capacitance measurements with the activation energy may also determine e *

We show experimentally that even when no bias voltage is applied to a quantum conductor, the electronic quantum partition noise can be investigated with GHz radio frequency excitation. Using a quantum point contact configuration as the ballistic conductor we are able to make an accurate determination of the partition noise Fano factor resulting from the photon-assisted shot noise. Applying both voltage bias and rf irradiation we are able to make a definitive quantitative test of the scattering theory of photon-assisted shot noise.

We report on the results obtained from specially designed high electron mobility transistors at 4.2 K: the gate leakage current can be limited lower than 1 aA, and the equivalent input noise-voltage and noise-current at 1 Hz can reach 6.3 nV/Hz1∕2 and 20 aA/Hz1∕2, respectively. These results open the way to realize high performance low-frequency readout electronics under very low-temperature conditions.