  We measure tunnelling currents through electrostatically defined quantum dots
in a GaAs/AlGaAs heterostructure connected to two leads. For certain tunnelling
barrier configurations and high sample bias we find a pronounced resonance
associated with a Fermi edge singularity. This many-body scattering effect
appears when the electrochemical potential of the quantum dot is aligned with
the Fermi level of the lead less coupled to the dot. By changing the relative
tunnelling barrier strength we are able to tune the interaction of the
localised electron with the Fermi sea.
