Dissonance as a resource for probing the qubit depolarizing channel

Quantum channel identification, a standard problem in quantum metrology, is the task of estimating parameter(s) of a quantum channel. We investigate dissonance (quantum discord in the absence of entanglement) as an aid to quantum channel identification and find evidence for dissonance as a resource for quantum information processing. We consider the specific case of dissonant Bell-diagonal probes of the qubit depolarizing channel, using quantum Fisher information as a measure of statistical information extracted by the probe. In this setting dissonant quantum probes yield more statistical information about the depolarizing probability than do corresponding probes without dissonance and greater dissonance yields greater information. This effect only operates consistently when we control for classical correlation between the probe and its ancilla and the joint and marginal purities of the ancilla and probe.

“All Data is Credit Data,” or, On Close Reading as a Reciprocal Process in Digital Knowledge Environments

The new knowledge environments of the digital age are oen described as places where we are all closely read, with our buying habits, location, and identities available to advertisers, online merchants, the government, and others through our use of the Internet. This is represented as a loss of privacy in which these entities learn about our activities and desires, using means that were unavailable in the pre-digital era. This article argues that the reciprocal nature of digital networks means 1) that the privacy issues that we face online are not radically different from those of the pre-Internet era, and 2) that we need to reconceive of close reading as an activity of which both humans and computer algorithms are capable.