  In an unseeded SU(1,1) interferometer composed of two cascaded degenerate
parametric amplifiers, with direct detection at the output, we demonstrate a
phase sensitivity overcoming the shot noise limit by 2.3 dB. The interferometer
is strongly unbalanced, with the parametric gain of the second amplifier
exceeding the gain of the first one by a factor of 2, which makes the scheme
extremely tolerant to detection losses. We show that by increasing the gain of
the second amplifier, the phase supersensitivity of the interferometer can be
preserved even with detection losses as high as 80%. This finding can
considerably improve the state-of-the-art interferometry, enable sub-shot-noise
phase sensitivity in spectral ranges with inefficient detection, and allow
extension to quantum imaging.
