Quasiparticle Pair-Production and Quantum Entanglement

Chris Doran, Anthony Norden Lasenby

Cheng-An Chen, Sergei Khlebnikov, Chen-Lung Hung

We report observations of quasiparticle pair production by a modulational instability in an atomic superfluid and present a measurement technique that enables direct characterization of quasiparticle quantum entanglement. By quenching the atomic interaction to attractive and then back to weakly repulsive, we produce correlated quasiparticles and monitor their evolution in a superfluid through evaluating the in situ density noise power spectrum, which essentially measures a "homodyne" interference between ground-state atoms and quasiparticles of opposite momenta. We observe large amplitude growth in the power spectrum and subsequent coherent oscillations in a wide spatial frequency band within our resolution limit, demonstrating coherent quasiparticle generation and evolution. The spectrum is observed to oscillate below a quantum limit set by the Peres-Horodecki separability criterion of continuous-variable states, thereby confirming quantum entanglement between interaction quench-induced quasiparticles.

Jan Petter Morten, Daniel Huertas‐Hernando, Wolfgang Belzig +1 more

We study the production of spatially separated entangled electrons in ferromagnetic leads from Cooper pairs in a superconducting lead. We give a complete description of the elementary charge transfer processes, i) transfer of Cooper pairs out of the superconductor by Andreev reflection and ii) distribution of the entangled quasiparticles among the ferromagnetic leads, in terms of their statistics. The probabilities that entangled electrons flow into spatially separated leads are completely determined by experimentally measurable tunnel conductances and polarizations. Finally, we investigate how currents, noise and cross-correlations are affected by transport of entangled electrons.

Petar Jurcevic, B. P. Lanyon, Philipp Hauke +4 more

Maciej Pylak, Paweł Zin

We perform a simulation of the experiment [J. C. Jaskula et al., Phys. Rev. Lett. 109, 220401 (2012)] where the temporal modification of the effective one-dimensional interaction constant was used to create pairs of atoms with opposite velocities. The simulations clearly demonstrate the huge impact of the interaction between quasiparticles due to finite temperature on the pair production process, explaining the relatively small atomic pair production and the absence of number squeezing in the experiment.

Fabio Benatti