Non--destructive quantum state measurements and Quantum noise squeezing – Niels Bohr Institute - University of Copenhagen

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Non--destructive quantum state measurements and Quantum noise squeezing

A method for non-destructive probing of the clock state population
of laser-cooled, dipole trapped Cs atoms at the standard quantum
limit is presented.

The non-destructive probing allows us to follow the evolution of the
population difference of the Cs-atom clock states when subjected to
microwave fields in real time. This way, Rabi oscillations on the
clock transition can be observed non-destructively over an extended
period of time. We apply microwave spectroscopy techniques to
characterize the evolution of the quantum state in the trap and
especially focus on the effect of probe induced inhomogeneous
dephasing and of probe induced spontaneous photon scattering on the
atomic ensemble.

We push the population readout precision to the quantum mechanical
limits and demonstrate that the measurement precision is limited by
quantum noise. We demonstrate that the correlations between two
consecutive, non--destructive measurements are non--classical and
that therefore an entangled state of atoms has been created in the
ensemble. The correlations allow us to infer a quantum noise
reduction of 72%, i.e., -5.4dB of remaining noise and
-3.5dB of spectroscopically relevant quantum noise squeezing.