  The Winter Colloquium on the Physics of Quantum Electronics (PQE) has been a
seminal force in quantum optics and related areas since 1971. It is rather
mindboggling to recognize how the concepts presented at these conferences have
transformed scientific understanding and human society. In January, 2017, the
participants of PQE were asked to consider the equally important prospects for
the future, and to formulate a set of questions representing some of the
greatest aspirations in this broad field. The result is this multi-authored
paper, in which many of the world's leading experts address the following
fundamental questions: (1) What is the future of gravitational wave astronomy?
(2) Are there new quantum phases of matter away from equilibrium that can be
found and exploited - such as the time crystal? (3) Quantum theory in uncharted
territory: What can we learn? (4) What are the ultimate limits for laser photon
energies? (5) What are the ultimate limits to temporal, spatial, and optical
resolution? (6) What novel roles will atoms play in technology? (7) What
applications lie ahead for nitrogen-vacancy centers in diamond? (8) What is the
future of quantum coherence, squeezing, and entanglement for enhanced
superresolution and sensing? (9) How can we solve (some of) humanity's biggest
problems through new quantum technologies? (10) What new understanding of
materials and biological molecules will result from their dynamical
characterization with free electron lasers? (11) What new technologies and
fundamental discoveries might quantum optics achieve by the end of this
century? (12) What novel topological structures can be created and employed in
quantum optics?
