Quantum weirdness helps design better accelerometers

“BUILD A BETTERMM accelerometer and the world will make a beaten path to your door.” Not, perhaps, as snappy as Ralph Waldo Emerson’s original aphorism about a mousetrap. But it is the hope of Graeme Malcolm, a physicist at the University of Strathclyde, in Glasgow. Dr Malcolm’s speciality is high-purity lasers. These can be used to make instruments of great precision. And those, in turn, can be employed to build devices which can detect the tiniest of forces—as tiny, for example, as the gravitational pull of a passing lorry.Laser light is famously pure. The way lasers work means that the beams which emerge from them are monochromatic. But there is purity, and then there is purity. In a truly monochromatic beam, all light would be of exactly the same frequency. In practice, this never happens. Wobbles caused by small temperature changes and vibrations, and by imperfections in the mirrored cavity in which the beam is generated and amplified, mean no laser beam is perfectly pure. The light from a cheap laser pointer might have a frequency range—known as its line width—of 500 megahertz (Hz), while the line width of a specialised scientific laser would be nearer 1Hz. Dr Malcolm’s latest offering, by contrast, has a line width of a mere 20Hz.