Postscript to the second quantum revolution.

In 2003 Jon Dowling and I published,  “Quantum Technology: The Second Quantum Revolution”. While we covered (somewhat naively) the main elements that have since emerged as significant --- metrology, communication and computation --- we missed what will perhaps be the most significant of all: quantum machine learning.  I will discuss my collaborations with Jon, spanning more that 25 years, with a particular focus on our converging views of the importance of optical quantum computing. I will then outline some new ideas for quantum machine learning based on irreversible quantum features, such as tunnelling and spontaneous emission, with a curious connection to quantum limited clocks.  This could lead to more energy efficient machine learning