Bounds on the entanglability of thermal states in liquid-state nuclear magnetic resonance

The role of mixed state entanglement in liquid-state nuclear magnetic resonance (NMR) quantum computation is not yet well-understood. In particular, despite the success of quantum information processing with NMR, recent work has shown that quantum states used in most of those experiments were not entangled. This is because these states, derived by unitary transforms from the thermal equilibrium state, were too close to the maximally mixed state. We are thus motivated to determine whether a given NMR state is entanglable - that is, does there exist a unitary transform that entangles the state? The boundary between entanglable and nonentanglable thermal states is a function of the spin system size $N$ and its temperature $T$. We provide new bounds on the location of this boundary using analytical and numerical methods; our tightest bound scales as $N \sim T$, giving a lower bound requiring at least $N \sim 22,000$ proton spins to realize an entanglable thermal state at typical laboratory NMR magnetic fields. These bounds are tighter than known bounds on the entanglability of effective pure states.Comment: REVTeX4, 15 pages, 4 figures (one large figure: 414 K

Mixed state geometric phases, entangled systems, and local unitary transformations

The geometric phase for a pure quantal state undergoing an arbitrary evolution is a ``memory'' of the geometry of the path in the projective Hilbert space of the system. We find that Uhlmann's geometric phase for a mixed quantal state undergoing unitary evolution not only depends on the geometry of the path of the system alone but also on a constrained bi-local unitary evolution of the purified entangled state. We analyze this in general, illustrate it for the qubit case, and propose an experiment to test this effect. We also show that the mixed state geometric phase proposed recently in the context of interferometry requires uni-local transformations and is therefore essentially a property of the system alone.Comment: minor changes, journal reference adde

A simple operational interpretation of the fidelity

This note presents a corollary to Uhlmann's theorem which provides a simple operational interpretation for the fidelity of mixed states.Comment: 1 pag

Probability distributions consistent with a mixed state

A density matrix $\rho$ may be represented in many different ways as a mixture of pure states, \rho = \sum_i p_i |\psi_i\ra \la \psi_i|. This paper characterizes the class of probability distributions $(p_i)$ that may appear in such a decomposition, for a fixed density matrix $\rho$. Several illustrative applications of this result to quantum mechanics and quantum information theory are given.Comment: 6 pages, submitted to Physical Review

Effect of fluctuations on the superfluid-supersolid phase transition on the lattice

We derive a controlled expansion into mean field plus fluctuations for the extended Bose-Hubbard model, involving interactions with many neighbors on an arbitrary periodic lattice, and study the superfluid-supersolid phase transition. Near the critical point, the impact of (thermal and quantum) fluctuations on top of the mean field grows, which entails striking effects, such as negative superfluid densities and thermodynamical instability of the superfluid phase -- earlier as expected from mean-field dynamics. We also predict the existence of long-lived "supercooled" states with anomalously large quantum fluctuations.Comment: 5 pages of RevTex4; as published in Physical Review

Rights of passage: law and the biopolitics of dying

Deleuze and Law: Forensic Futures explores the relation between law and life and the advent of a politics of 'life'. How have recent events focused social, political and cultural attention on the living body and its maintenance and management? The central concept, through which the embodiment of the subject will be examined will be that of 'bio-power'. Articulated by Michel Foucault, but brought to attention more recently in the work of Giorgio Agamben, this concept recognises that the relation between life and law is both historical and necessary: the law must operate on bodies but can only do so by establishing a border between the body of the polity, and the mere life excepted from political concern. The contemporary advent of bio-politics occurs when the polity increasingly and invasively operates on this 'mere' life, and the body or organism – rather than the self – becomes the object of political management. The manner in which the body becomes the focus of contemporary power has led legal theory to explore new questions of the threshold between life and death and has led social theory to question the new extensions of the law and the polity into embodied life. The contributors explore the forensic shift in contemporary social theory and cultural sensibility from a number of perspectives. Description of book from publisher website at: http://www.palgrave.com

Geopedologia e a sua influência sobre espécies arbóreas em florestas fluviais.

A recuperação de florestas fluviais compreende uma série de ações, sendo a primeira identificar a unidade fitogeográfica em que se está trabalhando. Na seqüência, a bacia hidrográfica deve ser compartimentada geopedologicamente, buscando identificar suas características hidrodinâmicas e, sobretudo, relacionar essas com os diversos padrões de leitos de rio, os quais possuem feições geomórficas distintas, ocupadas por diferentes tipos de solos. Em seguida, há a necessidade de se reconhecer como as espécies vegetais estão inseridas nesse contexto ambiental. Isso pode ser feito valendo-se de estudos que relacionem a fitossociologia às classes de solos, identificando a distribuição das espécies vegetais aos tipos de solos. Após a obtenção dessas informações e, com uma noção mais precisa do número necessário de indivíduos a ser produzido, além das informações fenológicas das mesmas, pode ser procedida a coleta de sementes. Essas ações irão garantir uma maior racionalização da operação. O procedimento de compartimentação geopedológica aqui proposto foi usado para segmentar a bacia hidrográfica do rio Itajaí em seis segmentos, havendo a indicação de espécies de acordo com o grau de saturação hídrica dos solos identificados na planície deste rio. Três categorias distintas de espécies (mesófilas, higrófilas e hidrófilas) são apontadas neste trabalho como potenciais para a recuperação de ambientes fluviais, todas em concordância com os padrões de solos identificados ao longo da Bacia.bitstream/CNPF-2009-09/40966/1/doc135.pd

Geometric observation for the Bures fidelity between two states of a qubit

In this Brief Report, we present a geometric observation for the Bures fidelity between two states of a qubit.Comment: 4 pages, 1 figure, RevTex, Accepted by Phys. Rev.