Squeezing and entanglement in a Bose–Einstein condensate

The standard quantum limit defines the performance of the best available measurement devices for quantities such as time or position. Many of these sensors are interferometers in which the standard quantum limit can be overcome by using quantum-entangled states (in particular, spin squeezed states) at the two input ports. A team from the University of Heidelberg's Kirchhoff Institute for Physics now demonstrates spin squeezed states suitable for atomic interferometry by splitting a Bose–Einstein condensate into a few parts using an optical lattice potential. The measurements imply entanglement between the particles, a resource that would allow a precision gain of 3.8 dB over the standard quantum limit for interferometric measurements.