Saikat Guha, Raytheon-BBN Technologies
Abstract:
For sending classical data over a lossy optical channel,
laser-light modulation (coherent states) is known to achieve the
ultimate (Holevo) limit to the channel capacity, albeit with an optimal
error correcting code and a joint-detection receiver that must make
collective measurements over long optical codeword blocks. Recent
advances in quantum information theory gives us several distinct
mathematical specifications of measurements that could achieve this
capacity limit. However, these specifications do not readily turn into
physical designs of how such a receiver might be explicitly built using
known optical components. All standard optical receivers perform below
the Holevo limit, particularly so, in the low-power regime. I will
present an overview of recent results and insights on explicit codes and
joint-detection receivers that could attain the Holevo capacity. I will
discuss the role different linear and non-linear optical elements might
play in such receiver realizations, and will point to theoretical and
experimental challenges that remain open in achieving the quantum limits
to the rate of reliable classical communication.