  Photonic quantum computing is one of the leading approaches to universal
quantum computation. However, large-scale implementation of photonic quantum
computing has been hindered by its intrinsic difficulties, such as
probabilistic entangling gates for photonic qubits and lack of scalable ways to
build photonic circuits. Here we discuss how to overcome these limitations by
taking advantage of two key ideas which have recently emerged. One is a hybrid
qubit-continuous variable approach for realizing a deterministic universal gate
set for photonic qubits. The other is time-domain multiplexing technique to
perform arbitrarily large-scale quantum computing without changing the
configuration of photonic circuits. These ideas together will enable scalable
implementation of universal photonic quantum computers in which
hardware-efficient error correcting codes can be incorporated. Furthermore,
all-optical implementation of such systems can increase the operational
bandwidth beyond THz in principle, utimately enabling large-scale
fault-tolerant universal quantum computers with ultra-high operation frequency.
