报告题目：Quantum information processing with atoms trapped near an optical nanofiber: dispersive
response theory with applications to QND measurement and spin squeezing单 位：University of New Mexico
报 告 人：戚晓东
Abstract:While optical fibers have been used for primary quantum communications, atom-fiber and atom-
waveguide based quantum interfaces have been proposed as effective elements to implement necessary
quantum repeaters, quantum data buses and quantum chips to enable long-haul quantum communications
and broader quantum information processing applications. We study the strong coupling between photons
and atoms that can be achieved in an optical nanofiber geometry when the interaction is dispersive. While
the Purcell enhancement factor for spontaneous emission into the guided mode does not reach the strong-
coupling regime for individual atoms, one can obtain high cooperativity for ensembles of a few thousand
atoms due to the tight confinement of the guided modes and constructive interference over the entire chain
of trapped atoms. We studied the theory of the phase shift and polarization rotation induced on the guided
light by the trapped atoms using the dyadic Green's function method. The Green's function is related to a full
Heisenberg-Langevin treatment of the dispersive response of the quantized field to tensor polarizable atoms.
In this talk, I will illustrate how do we apply our formalism to quantum nondemolition (QND) measurement of
the atoms via polarimetry. We study shot-noise-limited detection of atom number for atoms in a completely
mixed spin state and the squeezing of projection noise for atoms in clock states. Compared with squeezing of
atomic ensembles in free space, we capitalize on unique features that arise in the nanofiber geometry including
anisotropy of both the intensity and polarization of the guided modes. We use a first principles stochastic master
equation to model the squeezing as function of time in the presence of decoherence due to optical pumping.
We find a peak metrological squeezing of ~5 dB is achievable with current technology for ~2500 atoms prepared
in clock states trapped 180 nm from the surface of a nanofiber with radius a=225 nm. The theory established can
be used to guide the design of nanofiber- or waveguide-based quantum interfaces.
 X. Qi, B. Q. Baragiola, P. S. Jessen, I. H. Deutsch, ArXiv:1509.02625 [quant-ph].
 S. T. Dawkins, R. Mitsch, D. Reitz, E. Vetsch, and A. Rauschenbeutel, Phys. Rev. Lett. 107, 243601 (2011).
 I. H. Deutsch and P. S. Jessen, Optics Communications 283, 681 (2010).