  Phase insensitive optical amplification of an unknown quantum state is known
to be a fundamentally noisy operation that inevitably adds noise to the
amplified state [1 - 5]. However, this fundamental noise penalty in
amplification can be circumvented by resorting to a probabilistic scheme as
recently proposed and demonstrated in refs [6 - 8]. These amplifiers are based
on highly non-classical resources in a complex interferometer. Here we
demonstrate a probabilistic quantum amplifier beating the fundamental quantum
limit utilizing a thermal noise source and a photon number subtraction scheme
[9]. The experiment shows, surprisingly, that the addition of incoherent noise
leads to a noiselessly amplified output state with a phase uncertainty below
the uncertainty of the state prior to amplification. This amplifier might
become a valuable quantum tool in future quantum metrological schemes and
quantum communication protocols.
