  Shot noise measurements were recently exploited to measure the charge of the
quasiparticles in the Fractional Quantum Hall (FQH) regime. For fractional
filling factors nu=1/3 and 2/5 of the first Landau level, fractional charges
q=e/3 and e/5, respectively, were measured. We investigate here the interaction
of e/3 quasiparticles with a strong backscatterer and find unexpected results.
When a weak backscatterer is introduced in the path of an otherwise noiseless
current of quasiparticles, stochastic partitioning of the quasiparticles takes
place and shot noise proportional to their charge appears. Specifically, at
nu=1/3, noise corresponding to q=e/3 appears. However, the measured charge
increases monotonically as backscattering becomes stronger, approaching
asymptotically q=e. In other words, only electrons, or alternatively, three
bunched quasiparticles, tunnel through high potential barriers when impinged by
a noiseless current of quasiparticles. Here we show that such bunching of
quasiparticles by a strong backscatterer depends on the average occupation
(dilution) of the impinging quasiparticle current. For a very dilute impinging
current, bunching ceases altogether and the transferred charge approaches
q=e/3. These surprising results prove that a sparse beam of quasiparticles,
each with charge e/3, tunnel through high potential barriers, originally
thought to be opaque for them.
