Lower bound for the quantum capacity of a discrete memoryless quantum channel

We generalize the random coding argument of stabilizer codes and derive a lower bound on the quantum capacity of an arbitrary discrete memoryless quantum channel. For the depolarizing channel, our lower bound coincides with that obtained by Bennett et al. We also slightly improve the quantum Gilbert-Varshamov bound for general stabilizer codes, and establish an analogue of the quantum Gilbert-Varshamov bound for linear stabilizer codes. Our proof is restricted to the binary quantum channels, but its extension of to l-adic channels is straightforward.Comment: 16 pages, REVTeX4. To appear in J. Math. Phys. A critical error in fidelity calculation was corrected by using Hamada's result (quant-ph/0112103). In the third version, we simplified formula and derivation of the lower bound by proving p(Gamma)+q(Gamma)=1. In the second version, we added an analogue of the quantum Gilbert-Varshamov bound for linear stabilizer code

Tomography increases key rates of quantum-key-distribution protocols

We construct a practically implementable classical processing for the BB84 protocol and the six-state protocol that fully utilizes the accurate channel estimation method, which is also known as the quantum tomography. Our proposed processing yields at least as high key rate as the standard processing by Shor and Preskill. We show two examples of quantum channels over which the key rate of our proposed processing is strictly higher than the standard processing. In the second example, the BB84 protocol with our proposed processing yields a positive key rate even though the so-called error rate is higher than the 25% limit.Comment: 13 pages, 1 figure, REVTeX4. To be published in PRA. Version 2 adds many references, a closed form key rate formula for unital channels, and a procedure for the maximum likelihood channel estimatio

Being Asian American

The interplay between individualist and collectivist orientations, ethnic identity, and beliefs about stereotypes was explored among Asian Americans. The authors proposed four components of Asian American Identity: feelings of interdependence with family, a sense of connectedness to heritage and tradition, a belief that achievement would reflect well on one's family and group generally, and an awareness of structural barriers and racism. A sample of 162 Asian American university students perceived stereotypes about Asian Americans as focusing primarily on school achievement and secondarily on social attributes. Although rarely engaging in strategies to avoid being academically labeled, students engaged in strategies to avoid labeling in other domains. Students varied in their valuation of the model minority label, with those high in Asian American Identity, collectivism, and work ethic more likely to view the label positively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67527/2/10.1177_0021886397334002.pd