  The optical microresonator-based frequency comb (microcomb) provides a
versatile platform for nonlinear physics studies and has wide applications
ranging from metrology to spectroscopy. Deterministic quantum regime is an
unexplored aspect of microcombs, in which unconditional entanglements among
hundreds of equidistant frequency modes can serve as critical ingredients to
scalable universal quantum computing and quantum networking. Here, we
demonstrate a deterministic quantum microcomb in a silica microresonator on a
silicon chip. 40 continuous-variable quantum modes, in the form of 20
simultaneously two-mode squeezed comb pairs, are observed within 1 THz optical
span at telecommunication wavelengths. A maximum raw squeezing of 1.6 dB is
attained. A high-resolution spectroscopy measurement is developed to
characterize the frequency equidistance of quantum microcombs. Our
demonstration offers the possibility to leverage deterministically generated,
frequency multiplexed quantum states and integrated photonics to open up new
avenues in fields of spectroscopy, quantum metrology, and scalable quantum
information processing.
