The first rule of quantum mechanics is that you do not talk about quantum mechanics.
No, wait — that’s Fight Club.
The first rule of quantum mechanics — or one of its foundational laws, anyway — is that you cannot observe a quantum system without changing it. It’s a bit like how you can’t open the oven door to look at a souffle while it’s baking, lest the souffle collapse into a doughy glop (note: in a different, more accurate sense, it’s not really like that at all).
Basically, quantumness happens when you’re not looking at it. By peeking, you bully your system into a mundanely unquantum state. But IQC postdoc Krister Shalm and colleagues at the University of Toronto recently figured out a clever way to peek without ruining the souffle, so to speak, and just published their results in Science. They used a technique called “weak measurement” to track the paths that photons (particles of light) traveled through an experiment, providing an unprecedented glimpse inside the black box of the quantum world.
And thankfully, unlike Fight Club, Krister is allowed — and eager — to talk about it.
In an interview with the Waterloo Region Record, Krister used the analogy of a child (or overzealous grown-up) shaking a wrapped Christmas present in an effort to discern the contents. In a sense, Krister and his colleagues discerned the hidden goings-on within their “double-slit” experiment (in which light is beamed through a pair of narrow slits and quantumness ensues) without actually looking inside the experiment.
“This is our equivalent of shaking the box,” Krister said.
The result was a never-before-seen snapshot of the paths that quantum particles blazed while zipping through the double-slit experiment — a snapshot that physics textbooks have long declared unsnappable.
The ingenuity and success of the experiment has already garnered a lot of attention since yesterday’s publication of the Science paper.
Tomorrow at noon, Krister will be interviewed on the CBC Radio science show Quirks and Quarks (the interview was actually recorded a couple of days ago and was a big thrill for Krister, a long-time listener of the show, who blogged about it here).
We here at the Quantum Factory congratulate Krister and his colleagues for shaking the quantum box so successfully, giving us a look at its contents (thankfully, the gift inside is way cooler than a Christmas sweater or socks).