Southwest Quantum Information and Technology

Eleventh Annual Meeting, February 19-22, 2009
Seattle, Washington

Full Program | Thursday | Friday | Saturday | Sunday

SESSION 12: Quantum Communication
Session Chair:
10:45-11:15	Jon Yard, Los Alamos National Laboratory
	Quantum communication with zero-capacity channels
	Abstract. A quantum channel models a physical process in which noise is added to a quantum system via interaction with its environment. Protecting quantum systems from such noise can be viewed as an extension of the classical communication problem introduced by Shannon sixty years ago. A fundamental quantity of interest is the quantum capacity of a given channel, which measures the amount of quantum information which can be protected, in the limit of many transmissions over the channel. In this talk, I will show that certain pairs of channels, each with a capacity of zero, can have a strictly positive capacity when used together, implying that the quantum capacity does not completely characterize a channel's ability to transmit quantum information. As a corollary, I will show that a commonly used lower bound on the quantum capacity - the coherent information, or hashing bound - is an overly pessimistic benchmark against which to measure the performance of quantum error correction because the gap between this bound and the capacity can be arbitrarily large. This is joint work with Graeme Smith (IBM), published in the Sept. 26 issue of Science.
11:15-11:45	Patrick Rice, Los Alamos National Lab
	Comparison between continuous wave and pulsed laser EQKD
	Abstract. Entangled quantum key distribution (EQKD) is a secure protocol that is based on fundamental quantum mechanics and is not vulnerable to these threats. The primary figure of merit for QKD systems is the ability to generate secret bits. However, to date, methods that have been developed to simulate the secret bit rate generation for EQKD systems have been limited by techniques that do not provide a complete description of the quantum state produced by the source. In this talk, I show a complete description and comparison of the secret bit rate for continuous-wave and pulsed laser EQKD systems. In particular, I highlight the relevant Poissonian and thermal photon statistics that affect the EQKD secret bit rate and use practical system parameters and configurations to show regimes where one expects optimal performance for each case.
11:45-12:15	Min-Hsiu Hsieh, Quantum Computation and Information Project, Solution Oriented Research for Science and Technology
	The Classically-Enhanced Father Protocol
	Abstract. The classically-enhanced father protocol is an optimal protocol for a sender to transmit both classical and quantum information to a receiver by exploiting preshared entanglement and a large number of independent uses of a noisy quantum channel. We detail the proof of a quantum Shannon theorem that gives the three-dimensional capacity region containing all achievable rates that the classically-enhanced father protocol obtains. Points in the capacity region are rate triples consisting of the classical communication rate, the quantum communication rate, and the entanglement consumption rate of a particular coding scheme. The classically-enhanced father protocol is more general than any other protocol in the family tree of quantum Shannon theoretic protocols. Several previously known quantum protocols are now child protocols of the classically-enhanced father protocol. Interestingly, the classically-enhanced father protocol gives insight for constructing optimal classically-enhanced entanglement-assisted quantum error-correcting codes.