Abstracts

Experiments to observe the entangled particles inside macroscopic quantum states

Morgan Mitchell, ICFO - Institute of Photonic Sciences

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Macroscopic quantum phenomena, from the relatively familiar (squeezing) to the very exotic (high-Tc superconductivity) are thought to be produced by the collective actions of macroscopic numbers of entangled particles. Can we observe the microscopic, particulate entanglement underlying a macroscopic quantum state? I will describe two experiments, one with atoms and one with photons, that measure the entanglement of particles in a squeezed state. Using quantum non-demolition measurements on a spin ensemble, we produce a macroscopic spin singlet, an unpolarized squeezed state containing at least 500,000 entangled atoms. In another experiment, we extract photons from a polarization-squeezed beam and use quantum state tomography to directly observe pair-wise entanglement. We confirm the predicted large-scale entanglement: all photon pairs arriving within the squeezing coherence time are entangled.