Since Michelson and Morley’s famous experiment to detect the “luminiferous aether,” optical interferometry has offered valuable tools for studying fundamental physics. Nowadays, cutting-edge applications of the technique include its use as a high-precision ruler for detecting gravitational waves (see Focus: The Moon as a Gravitational-Wave Detector) and as a platform for quantum computing (see Viewpoint: Quantum Leap for Quantum Primacy). But as methods for cooling and controlling atoms have advanced, a new kind of interferometer has become available, in which light waves are replaced by matter waves [1]. Such devices can measure inertial forces with a sensitivity even greater than that of optical interferometers [2] and could reveal new physics beyond the standard model. In a new experiment, Jason Hogan and his colleagues at Stanford University have addressed one of the obstacles that have limited the potential of matter-wave interferometers until now: inefficient coupling between the atoms that constitute the matter waves and the light pulses used to manipulate them [3]. Their technique could lead to matter-wave interferometers sensitive enough to detect fluctuations in Earth’s rotation rate or manifestations of general relativistic effects such as the space-time “torsion” predicted by some alternative theories of gravity.

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