Quarantine
by Greg Egan
Legend, 1992
Quarantine is a transhumanist (maybe) science fiction novel dealing with quantum mechanics. It is also Greg Egan's first novel, and is very much in line with his later novels. It is sometimes lumped with Permutation City and Distress in a loose series (the "Subjective Cosmology Series"), but these books are only related in that they deal with, you guessed it, subjective cosmologies.
Theoretically, this book is about that time when aliens came around and constructed a 12 billion km sphere around the solar system without asking. But actually, that happened decades ago, and most people aren't too upset about it anymore -- it's not like we had any missions to Alpha Centauri on the planning board or anything.
So actually, this is the story of a private detective who is hired to investigate a mysterious kidnapping, and accidentally stumbles on an international conspiracy to hack quantum mechanics. This is a hard book to review without spoilers, as the first half is fast-moving, full of interesting technology, and a bit twisty, but the second half is actually the main point of the story. The second half is about the physical potential and psychological problems that go along with advanced quantum technology, which makes it a little bit less fast-moving, a little bit more twisty, and easy to spoil.
All in all, this is a pretty good book set in an interesting future. In 2066 apps are installed directly into your neural implants, security and counter-security are serious business, and nations are just starting to look redundant. It's not quite cyberpunk, but it's heading in that direction. The hero is smart, the author is smarter, and the science is basically good. It is probably worth reading for this alone.
And you might read it for this alone; the quantum theory is interesting, but perhaps not as interesting as Egan thinks. While it is a good introduction to some of the basics of quantum theory, it is also somewhat repetitive. While in 1992 it was reasonable to assume that a reader of popular science fiction didn't necessarily understand or know how to relate to quantum weirdness, this is less true today. In particular, the character's emotional response to the possible existence of alternate universes seems a bit overwrought, although Egan makes it work better than it should. Somewhat related to this, Egan has a habit of avoiding happy endings, and not simply happy in the sense of making the good guys win. He prefers nihilism (in both senses) to any sense of fulfilment or completion.
Overall, this is a good work of hard science fiction and a non-standard but also good work of transhumanist science fiction, and is worth reading if those interest you. It is also a good entry point into Egan's works, highlighting his intelligence, inventiveness, and ontological cynicism.