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--></style><title>MIT Quantum Information Processing Seminar
Announcement</title></head><body>
<div>Next week's MIT QIP seminar will take place on Monday, Oct. 4 at
16:00 in 4-237, and features:</div>
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<div align="center"><font size="+2"><b>Capacity of Bosonic
Communications</b></font></div>
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<div align="center"><font size="+1"><i>by</i> Jeff Shapiro (MIT
Research Laboratory of Electronics)</font></div>
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<div align="center"><u>ABSTRACT</u></div>
<div><br></div>
<blockquote>The capacity C for transmitting classical information is
investigated for Bosonic channels with isotropic Gaussian
noise. For the pure-loss channel -- in which signal photons may
be lost in propagation -- the exact value of C is derived. The
Holevo information of this channel is shown to be additive, and a
"classical'" encoding procedure employing coherent states is
shown to achieve capacity. For active channel models -- in which
noise photons are injected from an external environment or the signal
is amplified with unavoidable quantum noise -- upper and lower bounds
are obtained for the capacity. These bounds are asymptotically
tight at low and high noise levels. Exact capacity results --
given by the lower bounds -- would follow from proving the conjecture
that a coherent-state input minimizes the output entropy from such
channels.</blockquote>
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