Public Quantum Communication and Superactivation

Superactivation of quantum nonlocality.

In this Letter we show that quantum nonlocality can be superactivated. That is, one can obtain violations of Bell inequalities by tensorizing a local state with itself. In the second part of this work we study how large these violations can be. In particular, we show the existence of quantum states with very low Bell violation but such that five copies of them give very large violations. In fac...

Quantum Communication Cannot Simulate a Public Coin

We study the simultaneous message passing model of communication complexity. Building on the quantum fingerprinting protocol of Buhrman et al., Yao recently showed that a large class of efficient classical public-coin protocols can be turned into efficient quantum protocols without public coin. This raises the question whether this can be done always, i.e. whether quantum communication can alwa...

Quasi-Superactivation of Classical Capacity of Zero-Capacity Quantum Channels

One of the most surprising recent results in quantum Shannon theory is the superactivation of the quantum capacity of a quantum channel. This phenomenon has its roots in the extreme violation of additivity of the channel capacity and enables to reliably transmit quantum information over zerocapacity quantum channels. In this work we demonstrate a similar effect for the classical capacity of a q...

On superactivation of one-shot zero-error quantum capacity and the related property of quantum measurements

We begin with a detailed description of a low dimensional quantum channel (dA = 4, dE = 3) demonstrating the symmetric form of superactivation of one-shot zero-error quantum capacity. This means appearance of a noiseless (perfectly reversible) subchannel in the tensor square of a channel having no noiseless subchannels. Then we describe a quantum channel Φ such that Q̄0(Φ) = 0 and Q̄0(Φ⊗ Φ) ≥ log...

A Secure Quantum Communication Protocol Using Insecure Public Channels