Perfect Transfer of Arbitrary States in Quantum Spin Networks

We propose a class of qubit networks that admit perfect state transfer of any two-dimensional quantum state in a fixed period of time. We further show that such networks can distribute arbitrary entangled states between two distant parties, and can, by using such systems in parallel, transmit the higher dimensional systems states across the network. Unlike many other schemes for quantum computation and communication, these networks do not require qubit couplings to be switched on and off. When restricted to $N$-qubit spin networks of identical qubit couplings, we show that $2\log_3 N$ is the maximal perfect communication distance for hypercube geometries. Moreover, if one allows fixed but different couplings between the qubits then perfect state transfer can be achieved over arbitrarily long distances in a linear chain. This paper expands and extends the work done in PRL 92, 187902.Comment: 12 pages, 3 figures with updated reference

Chinua Achebe and the Possibility of Modern Tragedy

It is often said that the conditions for the creation of tragedy in art do not exist in the twentieth century. Modern man has lost a universal acquiescence in the existence of God. We all aspire to be materially prosperous members of a small nuclear family, neglecting or even unaware of our extended family. Modern government and taxation encourages self-interest rather than a sense of community. The lines which Calphurnia, Caesar\u27s wife, speaks on the morning of the fatal Ides of March - \u27When beggars die there are no comets seen;/ The heavens themselves blaze forth the death of princes\u27 - reverberate less persuasively in an era of republicanism. It was not the heavens which blazed forth the death of President Kennedy or the fall of Nikolai Ceauscescu but the television cameras and the newspapers. Can tragedy possibly exist in a world where the innermost sexual secrets of our leaders are frequently made public knowledge or where atomic devastation and environmental pollution threaten the annihilation of our species

The Africa Centre in London

By the early 1960\u27s it was obvious that all of Africa would shortly be free of colonial domination. The British and the French had withdrawn; the Spanish seemed hardly aware of their small territories; and cracks were already showing in the Portuguese regime, which was having to contend with an increasingly severe independence struggle in Angola and Mozambique. A few thorns remained to be plucked from the colonial flesh, Rhodesia being the most awkward, and only the ingenuous would claim that all vestiges of European authority vanished with the lowering of flags. A new Africa had emerged, however. Were the former imperial capitals to forget about it all, retaining only statues and anthems as relics of their domain, or would a practical means be found of continuing the associations with Africa by educational and cultural contact

J.N Jeffares

We have all experienced it. Someone we hugely admire because of their inexhaustible energy or their creative talent dies, and it is as though night had fallen in the afternoon. It is simply not possible that this person has gone. Yes, they were nearly 85, but they seemed so young, so positive, and they still had so much to give

Book reviews

Chinua Achebe, Anthills of the Savannah., Yasmine Gooneratne, Relative Merits: A Personal Memoir of the Bandaranaike Family. David Maughan-Brown, Land, Freedom and Fiction: history and ideology in Kenya