2 research outputs found
Spin squeezing, entanglement and quantum metrology with Bose-Einstein condensates
Squeezed states, a special kind of entangled states, are known as a useful
resource for quantum metrology. In interferometric sensors they allow to
overcome the "classical" projection noise limit stemming from the independent
nature of the individual photons or atoms within the interferometer. Motivated
by the potential impact on metrology as wells as by fundamental questions in
the context of entanglement, a lot of theoretical and experimental effort has
been made to study squeezed states. The first squeezed states useful for
quantum enhanced metrology have been proposed and generated in quantum optics,
where the squeezed variables are the coherences of the light field. In this
tutorial we focus on spin squeezing in atomic systems. We give an introduction
to its concepts and discuss its generation in Bose-Einstein condensates. We
discuss in detail the experimental requirements necessary for the generation
and direct detection of coherent spin squeezing. Two exemplary experiments
demonstrating adiabatically prepared spin squeezing based on motional degrees
of freedom and diabatically realized spin squeezing based on internal hyperfine
degrees of freedom are discussed.Comment: Phd tutorial, 23 pages, 17 figure
Squeezing and entanglement in a Bose-Einstein condensate
Entanglement, a key feature of quantum mechanics, is a resource that allows
the improvement of precision measurements beyond the conventional bound
reachable by classical means. This is known as the standard quantum limit,
already defining the accuracy of the best available sensors for various
quantities such as time or position. Many of these sensors are interferometers
in which the standard quantum limit can be overcome by feeding their two input
ports with quantum-entangled states, in particular spin squeezed states. For
atomic interferometers, Bose-Einstein condensates of ultracold atoms are
considered good candidates to provide such states involving a large number of
particles. In this letter, we demonstrate their experimental realization by
splitting a condensate in a few parts using a lattice potential. Site resolved
detection of the atoms allows the measurement of the conjugated variables atom
number difference and relative phase. The observed fluctuations 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