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Logo: Institut für Quantenoptik/Leibniz Universität Hannover
Logo Leibniz Universität Hannover
Logo: Institut für Quantenoptik/Leibniz Universität Hannover
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Spin changing collisions lead to a pairwise transfer of atoms from the Zeeman levels mF = +1 and mF = -1. Hence, for a fixed total number of atoms N = N+1 + N-1, a so-called twin-Fock state with the exact same number of atoms N+1 = N-1 in the two Zeeman levels is created. This state, which is a particular Dicke state, can be depicted as a ring on the equator of the multi-particle Bloch sphere (a). Experimentally, it is best characterized by a measurement of the sub shot-noise fluctuations in the Jz component (c), i.e. the reduced fluctuations in the particle number difference, and the spin length (b). As an important difference to spin squeezed states, the spin length cannot be measured in terms of the expectation value of a single spin component. Hence, we introduced new criteria to correctly characterize the created Dicke state. In our measurements, we achieve a generalized spin squeezing of -11.4 dB (d) and an entanglement depth of at least 28 particles (e) by employing a newly developed criterion.

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