  We propose an all-optical approach to achieve optical nonreciprocity on a
chip by quantum squeezing one of two coupled resonator modes. By parametric
pumping a nonlinear resonator unidirectionally with a classical coherent field,
we squeeze the resonator mode in a selective direction due to the
phase-matching condition, and induce a chiral photon interaction between two
resonators. Based on this chiral interresonator coupling, we achieve an
all-optical diode and a three-port quasi-circulator. By applying a second
squeezed-vacuum field to the squeezed resonator mode, our nonreciprocal device
also works for single-photon pulses. We obtain an isolation ratio of >40 dB for
the diode and fidelity of $>98\%$ for the quasi-circulator, and insertion loss
of <1 dB for both. We also show that nonreciprocal transmission of strong light
can be switched on and off by a relative weak pump light. This achievement
implies a nonreciprocal optical transistor. Our protocol opens up a new route
to achieve integrable all-optical nonreciprocal devices permitting
chip-compatible optical isolation and nonreciporcal quantum information
processing.
