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SUMMARY:Macroscopic Quantum Tunneling in Bose-Einstein Condensates - Prof.
  Lincoln D. Carr\, Department of Physics\, Colorado School of Mines\, Gold
 en\, Colorado\, U.S.A.
DTSTART:20130705T110000Z
DTEND:20130705T120000Z
UID:TALK44176@talks.cam.ac.uk
CONTACT:Dr. Judith B. Rommel
DESCRIPTION:I present three studies on macroscopic quantum tunneling of Bo
 se-Einstein condensates.  First\, I show how even at the simplest mean fie
 ld level already the problem of escape through a barrier has new features 
 compared to single particle physics: the tunneling time is not the inverse
  of the rate and interactions allow one to tune from bound to quasi-bound 
 to unbound states freely [1].  Second\, I show how tunneling in a double-w
 ell system leads to Josephson junction and Schrodinger cat (NOON state) ph
 ysics.  I demonstrate that although a very small bias or tilt in the poten
 tial can destroy Cat-like states\, by intentional use of bias the many bod
 y wavefunction can be used to protect such states from destruction (or int
 ernal decoherence) [2].  Third\, I present a full many-body calculation of
  entangled quantum dynamics of the escape problem [3]\, exploring entangle
 ment\, number correlations\, and other features not accessible by instanto
 n or other methods.  I show that the tunneling process is non-smooth\, and
  actually occurs in bursts.  When approximately half the particles have tu
 nneled out of the well\, the particles remaining are maximally entangled w
 ith the escaped portion.  Number fluctuations greatly modify the escape ti
 me beyond mean field predictions.  Preliminary indications are that the ti
 me derivative of number fluctuations serves as a witness to the spatial en
 tropy of entanglement.  In summary\, these three views on macroscopic quan
 tum tunneling show that even a weakly interacting many body system already
  has significantly different features on all levels as compared to the sin
 gle particle problem.\n\n[1]  L. D. Carr\, M. J. Holland\, and B. A. Malom
 ed\, ``Macroscopic quantum tunnelling of Bose-Einstein condensates in a po
 tential well of finite depth\,'' J. Phys. B: At. Mol. Opt. Phys.\, v. 38\,
  p. 3217 (2005).\n\n[2] D. R. Dounas-Frazer\, A. M. Hermundstad\, and L. D
 . Carr\, ``Ultracold bosons in a tilted multilevel double-well potential\,
 '' Phys. Rev. Lett.\, v. 99 p. 200402 (2007).\n\n[3] J. A. Glick and Linco
 ln D. Carr\, ``Macroscopic Quantum Tunneling of Solitons in Bose-Einstein 
 Condensates\,'' arXiv:1105.5164 (2011).
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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