Schrödinger’s Web

Race to Build the Quantum Internet

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I very much enjoyed Jonathan Dowling's previous book about quantum technology, Schrödinger's Killer App. So picking this up (via Interlibrary Loan) was a no-brainer.

Unfortunately, it's posthumous. Dowling's colleague at Louisiana State, Mark Wilde, provides a moving foreword to the book describing Dowling's unusual approach to his lifelong research interest.

Like the previous book, this one is full of opinions, anecdotes, jokes, inside-baseball stories of how the game of physics is played. No math, unless you count Bra-Ket notation, which Dowling relies on heavily. I'm not sure how easy this is to follow; I (admittedly) did not.

The previous book described quantum computing; this book takes that as a given, and goes on (eventually) to describe current and upcoming networking technologies based on quantum behavior. But first, there's a lengthy (but interesting) discussion of the history of physicist's conceptions of light. Particles or waves? Well, both. But also, neither. The quantum internet depends on communication via photons, the inherently quantized clumps of light that (nevertheless) obey Maxwell's famous wave equations.

The quantum internet also depends on the three quantum weirdness features that Einstein famously despised (repeating from my previous report): uncertainty (you don't know an experimental result until you measure); unreality (the measure doesn't really exist until you measure); and nonlocality (measuring at point A can affect a measurement of an "entangled" property at point B. And B can be across the room from A, or light years away.)

How this applies: a photon's polarization doesn't exist until you measure it, and is inherently unknown until you do. And if you generate entangled photons, and send them off on their merry way, observing the polarization of one immediately collapses the other into a known state, even if it's miles, or light years, away. Weird. But also useful.

There is a lot of discussion of hardware (Photon guns, detectors, Bell-testers, interferometers, etc.). Dowling shows how things can be put together for all sorts of applications, most notably utterly secure point-to-point cryptography.

The state of play, Dowling notes, is interesting: specifically, the Chinese seem to be way ahead of the US in developing quantum internet technology. Specifically, see Quantum Experiments at Space Scale at Wikipedia. Aieee!

There's some bad news. The editing is sloppy. (Page 124: "A nanosecond is one-millionth of a second,…" Um, no.) Dowling refers to his colorful illustrations, but no matter how hard you stare, in the dead-trees versions of the book they remain sullenly monochrome. (The Kindle version, I checked, reproduces them in color. But, geez, CRC Press wants $42.95 for the paperback, and a cool $200 for the hardback! You can't do color at that price?)


Last Modified 2024-01-17 3:40 PM EDT