Séminaire « fluides quantiques » : Guilia Ferrini



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Macroscopic superpositions in the presence of phase noise in a Bose Josephson junction

Guilia Ferrini, LKB (CNRS – Université P. et M. Curie)

A Bose Josephson Junction is a system composed of bosons which can occupy two modes which can be coupled. This system models either an ultracold bosonic gas trapped in a double-well potential, either a gas of ultracold bosons in two different hyperfine states, trapped in the same harmonic potential. Both configurations have been experimentally realized, and found interesting applications, e.g. in high-precision interferometry [1]. If the system is initially prepared in a coherent state and evolves after suppressing the coupling of the two modes, at short time the state undergoes squeezing [2], and at larger time macroscopic superpositions of coherent states are formed [3]. One of the most relevant sources of noise in such a system, together with particle losses, is phase noise, resulting from stochastic fluctuations of the energies of the two modes. We address the question how the presence of phase noise affects the formation of squeezed states and macroscopic superpositions, showing in particular how these latter display an unexpected robustness against decoherence induced by the noise considered [4].

[1] M. Albiez et al, Phys. Rev. Lett. 95, 010402 (2005); J. Esteve et al, Nature 455, 1216 (2008).
[2] C. Gross et al, Nature 464, 1165 (2010). M. Kitagawa and M. Ueda, Phys. Rev. A 47, 5138 (1993).
[3] F. Piazza, L. Pezze and A. Smerzi, Phys. Rev. A 78, 051601 (2008); G. Ferrini, A. Minguzzi and F.W.J. Hekking, Phys. Rev. A 78, 023606 (2008).
[4] G. Ferrini et al, Phys. Rev. A 82, 033621 (2010); Phys. Rev. A 84, 043628 (2011).

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