Towards feedback control of entanglement

We provide a model to investigate feedback control of entanglement. It consists of two distant (two-level) atoms which interact through a radiation field and becomes entangled. We then show the possibility to stabilize such entanglement against atomic decay by means of a feedback action.Comment: 6 pages, 4 figure

Developments in plant breeding for improved nutritional quality of soya beans I. Protein and amino acid content

Soya beans, like other legumes, contain low concentrations of the nutritionally essential sulphur amino acid, methionine. Cysteine, although not an essential amino acid because it can be synthesized from methionine, also influences the nutritional quality of soya bean products when it is only present in low levels. A low cysteine content will also aggravate a methionine deficiency. Soya bean lines deficient in 7S protein subunits have been identified. The 7S proteins contain substantially less methionine and cysteine than the 11S proteins. With the myriad of genetic null alleles for these subunits it may be possible to tailor the 7S/11S storage protein ratio and their total composition in seeds to include only those subunits with the richest sulphur amino acid composition. Cotyledon feeding experiments, using isolated soya bean cotyledons, demonstrated that addition of methionine to the culture media caused increased synthesis of both proteins and free amino acids but the mechanism by which this takes place is not clear

Developments in plant breeding for improved nutritional quality of soya beans II. Anti-nutritional factors

Nutritional value of most plant materials is limited by the presence of numerous naturally occurring compounds which interfere with nutrient digestion and absorption. Although processing is employed widely in removal of these factors, selection of cultivars of soya beans with inherently low levels would have a considerable impact on efficiency of non-ruminant livestock production. The review considers the role of plant breeding in achieving this objective. The most abundant trypsin inhibitors are the Kunitz and the Bowman Birk inhibitors, containing 181 and 71 amino acids respectively. The Kunitz inhibitor is present at a concentration of 1.4g/kg of total seed contents and the Bowman Birk inhibitor 1.6g/kg. A large number of isoforms of the Bowman Birk inhibitor have been described in soya bean cultivars and it has been shown that the general properties of the inhibitor are, in fact, attributable to different isoforms. Nulls for both Bowman-Birk and Kunitz trypsin inhibitors have been identified, allowing new low trypsin inhibitor cultivars to be produced. However, research into breeding for low trypsin inhibitor cultivars currently has limited application as trypsin inhibitors contribute a major proportion of the methionine content of soya beans. Trypsin inhibitors are thought to be involved in the regulation of and protection against unwanted proteolysis in plant tissues and also act as a defense mechanism against attack from diseases, insects and animals. Hence, in breeding programes for low trypsin inhibitor cultivars, alternative protection for growing plants must be considered. Use of soya beans in non-ruminant animal feeds is limited by the flatulence associated with their consumption

Non-Markovian homodyne-mediated feedback on a two-level atom: a quantum trajectory treatment

Quantum feedback can stabilize a two-level atom against decoherence (spontaneous emission), putting it into an arbitrary (specified) pure state. This requires perfect homodyne detection of the atomic emission, and instantaneous feedback. Inefficient detection was considered previously by two of us. Here we allow for a non-zero delay time $\tau$ in the feedback circuit. Because a two-level atom is a nonlinear optical system, an analytical solution is not possible. However, quantum trajectories allow a simple numerical simulation of the resulting non-Markovian process. We find the effect of the time delay to be qualitatively similar to that of inefficient detection. The solution of the non-Markovian quantum trajectory will not remain fixed, so that the time-averaged state will be mixed, not pure. In the case where one tries to stabilize the atom in the excited state, an approximate analytical solution to the quantum trajectory is possible. The result, that the purity ($P=2{\rm Tr}[\rho^{2}]-1$) of the average state is given by $P=1-4\gamma\tau$ (where $\gamma$ is the spontaneous emission rate) is found to agree very well with the numerical results.Comment: Changed content, Added references and Corrected typo

Constrained Regulatory Exit in Energy Law

In recent years, the federal government’s efforts to open up competitive electricity markets have transformed how we think about the regulation of energy. In many respects, the Federal Energy Regulatory Commission’s (FERC) broad “deregulatory” efforts, which commenced in the 1990s, might appear to be a case of paradigmatic regulatory exit as defined by J.B. Ruhl and Jim Salzman. But our case study of FERC’s restructuring of wholesale electricity markets reveals some important institutional features that make exit in federalism contexts, and under federal statutory duties, a rich and difficult problem. In the context of energy, exit from one regulatory sphere can create regulatory gaps. This has led FERC, which largely exited the regulation of wholesale electricity rates, to increase regulation in other spheres. It has also invited forms of intergovernmental exchange, as states have emulated or otherwise responded to FERC’s regulatory modifications in the areas in which states have jurisdiction. In this sense, the transition to competitive energy supply markets has involved constrained exit characterized by a hydraulic back-and-forth between regulators and institutions in an effort to ensure that statutory duties are fulfilled and other public needs are met. This assessment of regulatory exchange has a prescriptive implication: a federal regulator seeking to exit specific forms of conventional regulation needs to proactively develop strategies to facilitate regulatory exchange, while simultaneously preserving its authority over important substantive values related to its regulatory mission. Attention to “offsetting” regulations is often necessary to ensure that problematic regulatory gaps will not arise. In the energy context, these strategies might also include the use of mechanisms that give other institutions a voice in implementing exit strategies, as well as better ex ante regulatory planning for market enforcement that will continue after partial exit. We argue that it is not only a good strategy for federal regulators to recognize this hydraulic feature of exit, but that cooperative federalism statutes such as the Federal Power Act often require them to do so

Nontrivial quantum effects in biology: A skeptical physicists' view

Invited contribution to "Quantum Aspects of Life", D. Abbott Ed. (World Scientific, Singapore, 2007).Comment: 15 pages, minor typographical errors correcte

The singer and the song: Nick Cave and the archetypal function of the cover version

Throughout his career, from The Boys Next Door, through The Birthday Party, and with The Bad Seeds, Australian singer / songwriter Nick Cave has balanced his own set of creative voices alongside those of others through his choice of cover versions. Cave’s 1986 album with The Bad Seeds, ‘Kicking Against the Pricks’, is a collection of cover versions that spans American folk idioms (‘Black Betty’, ‘Hey Joe’, ‘The Singer’), Tin-Pan-Alley balladeering (‘Something’s Gotten Hold of my Heart’, ‘By the Time I Get to Phoenix’) and left-field alt-rock (‘All Tomorrow’s Parties’, ‘The Hammer Song’). Cave’s first single as a solo artist beyond the confines of The Birthday Party was a cover of ‘In The Ghetto’, made famous by Elvis Presley, and the cover version has been a noticeable presence in Cave’s work both in his live and recorded output ever since. This chapter seeks to understand the uses of Cave’s choices of cover versions, both in terms of the idiosyncrasies of his own interpretations, and the context within which Cave places himself as part of a wider musical community. Cave’s relationship to a pantheon of elder statesmen figures (Johnny Cash, Bob Dylan or Leonard Cohen for example) is understood as not only one of recognising influences, but also of placing Cave within a specific tradition or lineage. Equally, certain song forms such as the folk ballad or the blues lament are utilised to give shape and form to Cave’s wider concerns outside of the specific cover version. Cave’s reimagining of John Lee Hooker’s ‘Tupelo’, or Dylan’s ‘Wanted Man’ from The Firstborn is Dead (1985) provide clues to the uses of the cover to both articulate the individual interpreting the song, thus placing it within a personalised lexicon, and to connect the singer to traditions, or archetypes of performance that resonate in specific ways. Cave’s covers are never wholly reproductions, at times they are reworking's that might be seen to reconnect a song to a potential ‘lost truth’, at others they may be seen as parodies or homages that have more transparent aims. However at all times, the connections between Cave the singer and the latent archetypes inherent in the song provide provocative and loaded connections and values. This paper seeks to understand how Cave’s choices of cover versions, and his approaches to interpretation, shape not only the musical moment, but also our perceptions of Cave as an artist in a broader sens

A Quantitative Analysis of IRAS Maps of Molecular Clouds

We present an analysis of IRAS maps of five molecular clouds: Orion, Ophiuchus, Perseus, Taurus, and Lupus. For the classification and description of these astrophysical maps, we use a newly developed technique which considers all maps of a given type to be elements of a pseudometric space. For each physical characteristic of interest, this formal system assigns a distance function (a pseudometric) to the space of all maps; this procedure allows us to measure quantitatively the difference between any two maps and to order the space of all maps. We thus obtain a quantitative classification scheme for molecular clouds. In this present study we use the IRAS continuum maps at 100$\mu$m and 60$\mu$m to produce column density (or optical depth) maps for the five molecular cloud regions given above. For this sample of clouds, we compute the ``output'' functions which measure the distribution of density, the distribution of topological components, the self-gravity, and the filamentary nature of the clouds. The results of this work provide a quantitative description of the structure in these molecular cloud regions. We then order the clouds according to the overall environmental ``complexity'' of these star forming regions. Finally, we compare our results with the observed populations of young stellar objects in these clouds and discuss the possible environmental effects on the star formation process. Our results are consistent with the recently stated conjecture that more massive stars tend to form in more ``complex'' environments.Comment: 27 pages Plain TeX, submitted to ApJ, UM-AC 93-15, 15 figures available upon reques

All-optical versus electro-optical quantum-limited feedback

All-optical feedback can be effected by putting the output of a source cavity through a Faraday isolator and into a second cavity which is coupled to the source cavity by a nonlinear crystal. If the driven cavity is heavily damped, then it can be adiabatically eliminated and a master equation or quantum Langevin equation derived for the first cavity alone. This is done for an input bath in an arbitrary state, and for an arbitrary nonlinear coupling. If the intercavity coupling involves only the intensity (or one quadrature) of the driven cavity, then the effect on the source cavity is identical to that which can be obtained from electro-optical feedback using direct (or homodyne) detection. If the coupling involves both quadratures, this equivalence no longer holds, and a coupling linear in the source amplitude can produce a nonclassical state in the source cavity. The analogous electro-optic scheme using heterodyne detection introduces extra noise which prevents the production of nonclassical light. Unlike the electro-optic case, the all-optical feedback loop has an output beam (reflected from the second cavity). We show that this may be squeezed, even if the source cavity remains in a classical state.Comment: 21 pages. This is an old (1994) paper, but one which I thought was worth posting because in addition to what is described in abstract it has: (1) the first formulation (to my knowledge) of quantum trajectories for an arbitrary (i.e. squeezed, thermal etc.) broadband bath; (2) the prediction of a periodic modification to the detuning and damping of an oscillator for the simplest sort of all-optical feedback (i.e. a mirror) as seen in the recent experiment "Forces between a Single Atom and Its Distant Mirror Image", P. Bushev et al, Phys. Rev. Lett. 92, 223602 (2004