I just released two new papers onto the arXiv, Noise thresholds for entanglement purification and Practical effects in cat state breeding.

Noise thresholds for entanglement purification

In this paper we consider the effects of noisy quantum gates on the operation of the entanglement purification protocol proposed by Bennett et al. We consider two figures of merit, the maximum achievable fidelity of an output state, and the minimum fidelity of an input state for purification to be possible. Both of these measures are a function of gate noise rates. When plotted against gate noise rate, these two measures converge for a particular value of gate noise. At this point purification is no longer possible, defining a noise threshold on gates. For the protocol in question this noise threshold is roughly 0.092, which is achievable in many present-day experimental architectures.

Practical effects in cat state breeding

In this paper (joint work with Austin Lund) we discuss two significant practical effects in the preparation of so-called cat states, which are defined as superpositions of distinct coherent states. Specifically, we consider the effects of loss and mode-mismatch. We find that the size of the cat states that may be prepared is upper bounded as a function of these two parameters. For experimentally realistic parameters we anticipate that cat state magnitudes will be limited to an average photon number of less than 5.