  Controlling femtosecond optical pulses with temporal precision better than
one cycle of the carrier field has a profound impact on measuring and
manipulating interactions between light and matter. We explore pulses that are
carved from a continuous-wave laser via electro-optic modulation and realize
the regime of sub-cycle optical control without a mode-locked resonator. Our
ultrafast source, with a repetition rate of 10 GHz, is derived from an
optical-cavity-stabilized laser and a microwave-cavity-stabilized electronic
oscillator. Sub-cycle timing jitter of the pulse train is achieved by
coherently linking the laser and oscillator through carrier-envelope phase
stabilization enabled by a photonic-chip supercontinuum that spans up to 1.9
octaves across the near infrared. Moreover, the techniques we report are
relevant for other ultrafast lasers with repetition rates up to 30 GHz and may
allow stable few-cycle pulses to be produced by a wider range of sources.
