Author: Chris Lee

Very occasionally, my imagination gets the better of me. When I encountered a paper entitled "How to Recover a Qubit That Has Fallen into a Black Hole," I envisioned a typical lab experiment. One student, having been given a precious quantum state, accidentally drops it into a black hole—"accidentally" in the same way that you accidentally break into the chemistry supplies cupboard and mix everything together under a fume hood just to see what will happen. Never mind, says the clearly annoyed lab instructor, who then performs some arcane maneuvers and recovers the carelessly handled qubit.

Reality has fewer students dropping quantum states into black holes but makes up for it with an excess of equally amusing theoretical physicists. The idea behind studying how to recover a qubit from a black hole is not to help future students avert a lab disaster but to understand the quantum state of a black hole.

Black holes are rather coy about what they have under their event horizons. Nothing that we send into a black hole is coming back, so the only information that comes directly from a black hole is the Hawking radiation it emits.

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"Oh, bugger, we're out of madness."

This is the sanitized version of an oft-heard new phrase in our house. Variations include "I've gone mad" and "you need more madness in your deck!" All of these are often combined with the phrase "we've lost."