Bright Sub-Poissonian Light through Intrinsic Feedback and External Control.

Balancing nonlinear gain and loss automatically generates sub-Poissonian light, through negative feedback, when the gain is significantly reduced (increased) by the addition (subtraction) of a single photon. We show that micromaser trapping states can provide the necessary feedback in the presence of photon loss and, with the addition of external parametric control, realize a photon number on the order of 100 and a Mandel Q parameter of -0.998, i.e., number squeezing of 27 dB.

To catch and reverse a quantum jump mid-flight.

In quantum physics, measurements can fundamentally yield discrete and random results. Emblematic of this feature is Bohr's 1913 proposal of quantum jumps between two discrete energy levels of an atom1. Experimentally, quantum jumps were first observed in an atomic ion driven by a weak deterministic force while under strong continuous energy measurement2-4. The times at which the discontinuous jump transitions occur are reputed to be fundamentally unpredictable. Despite the non-deterministic character of quantum physics, is it possible to know if a quantum jump is about to occur? Here we answer this question affirmatively: we experimentally demonstrate that the jump from the ground state to an excited state of a superconducting artificial three-level atom can be tracked as it follows a predictable 'flight', by monitoring the population of an auxiliary energy level coupled to the ground state. The experimental results demonstrate that the evolution of each completed jump is continuous, coherent and deterministic. We exploit these features, using real-time monitoring and feedback, to catch and reverse quantum jumps mid-flight-thus deterministically preventing their completion. Our findings, which agree with theoretical predictions essentially without adjustable parameters, support the modern quantum trajectory theory5-9 and should provide new ground for the exploration of real-time intervention techniques in the control of quantum systems, such as the early detection of error syndromes in quantum error correction.

Radical Chain Reduction of CCl4 Initiated by Illumination of SPEEK Solutions.

Efficient reduction of CCl4 took place upon exposure to 350-nm photons of aqueous solutions containing sulfonated poly(ether etherketone) (SPEEK) as a sensitizer and either poly(vinyl alcohol) (PVA) or HCO2H/HCO2- buffer. The photoreaction formed chloride ions whose concentration increased linearly with time in solutions free of O2, whereas slower reductions occurred in the presence of air. Utilization of formate buffer as the H-atom donor yielded photoreactions at least 10 times faster than those in the presence of PVA and generated CHCl3 as another reaction product. The quantum yield of chloride ion formation, ø(Cl-), was found to be a function of both the SPEEK concentration and concentration of formate buffer. Whereas the quantum efficiency increased steadily with decreasing solution acidity, a drastic surge in the reaction rate occurred in neutral solutions. ø(Cl-) first increased rapidly to a maximum value exceeding 1 at pH 7.3 and then decreased thereafter. The dependence of r(Cl-) on (I0)1/2, where I0 is the light intensity, and the occurrence of postirradiation formation of Cl- through the reduction of CCl4 in the dark are further evidence that the photoreaction proceeded by a chain process. Several of the kinetic features were rationalized by means of a mechanism involving the α-hydroxy radicals of SPEEK and •CCl3 as chain carriers.

PSINET: Assisting HIV Prevention Amongst Homeless Youth by Planning Ahead.

Homeless youth are prone to Human Immunodeficiency Virus (HIV) due to their engagement in high risk behavior such as unprotected sex, sex under influence of drugs, etc. Many non-profit agencies conduct interventions to educate and train a select group of homeless youth about HIV prevention and treatment practices and rely on word-of-mouth spread of information through their social network. Previous work in strategic selection of intervention participants does not handle uncertainties in the social network's structure and evolving network state, potentially causing significant shortcomings in spread of information. Thus, we developed PSINET, a decision support system to aid the agencies in this task. PSINET includes the following key novelties: (i) it handles uncertainties in network structure and evolving network state; (ii) it addresses these uncertainties by using POMDPs in influence maximization; and (iii) it provides algorithmic advances to allow high quality approximate solutions for such POMDPs. Simulations show that PSINET achieves ~60% more information spread over the current state-of-the-art. PSINET was developed in collaboration with My Friend's Place (a drop-in agency serving homeless youth in Los Angeles) and is currently being reviewed by their officials.

Whole exome sequencing in a patient with uniparental disomy of chromosome 2 and a complex phenotype.

Whole exome sequencing and chromosomal microarrays are two powerful technologies that have transformed the ability of researchers to search for potentially causal variants in human disease. This study combines these tools to search for causal variants in a patient found to have maternal uniparental isodisomy of chromosome 2. This subject has a complex phenotype including skeletal and renal dysplasia, immune deficiencies, growth failure, retinal degeneration and ovarian insufficiency. Eighteen non-synonymous, rare homozygous variants were identified on chromosome 2. Additionally, five genes with compound heterozygous mutations were detected on other chromosomes that could lead to a disease phenotype independent of the uniparental disomy found in this case. Several candidate genes with potential connection to the phenotype are described but none are definitively proven to be causal. This study highlights the potential for detection of a large number of candidate genes using whole exome sequencing complicating interpretation in both the research and clinical settings. Forums must be created for publication and sharing of detailed phenotypic and genotypic reports to facilitate further biological discoveries and clinical counseling.

Stationary inversion of a two level system coupled to an off-resonant cavity with strong dissipation.

We present an off-resonant excitation scheme that realizes pronounced stationary inversion in a two level system. The created inversion exploits a cavity-assisted two-photon resonance to enhance the multiphoton regime of nonlinear cavity QED and survives even in a semiconductor environment, where the cavity decay rate is comparable to the cavity-dot coupling rate. Exciton populations of greater than 0.75 are obtained in the presence of realistic decays and pure dephasing. Quantum trajectory simulations and master equation calculations help elucidate the underlying physics and delineate the limitations of a simplified rate equation model. Experimental signatures of inversion and multiphoton cavity QED are predicted in the fluorescence intensity and second-order correlation function measured as a function of drive power.

A new approach to scoring systems to improve identification of acute medical admissions that will require critical care.

Removal of the intensive care unit (ICU) at the Vale of Leven Hospital mandated the identification and transfer out of those acute medical admissions with a high risk of requiring ICU. The aim of the study was to develop triaging tools that identified such patients and compare them with other scoring systems. The methodology included a retrospective analysis of physiological and arterial gas measurements from 1976 acute medical admissions produced PREEMPT-1 (PRE-critical Emergency Medical Patient Triage). A simpler one for ambulance use (PREAMBLE-1 [PRE-Admission Medical Blue-Light Emergency]) was produced by the addition of peripheral oxygen saturation to a modification of MEWS (Modified Early Warning Score). Prospective application of these tools produced a larger database of 4447 acute admissions from which logistic regression models produced PREEMPT-2 and PREAMBLE-2, which were then compared with the original systems and seven other early warning scoring systems. Results showed that in patients with arterial gases, the area under the receiver operator characteristic curve was significantly higher in PREEMPT-2 (89·1%) and PREAMBLE-2 (84.4%) than all other scoring systems. Similarly, in all patients, it was higher in PREAMBLE-2 (92·4%) than PREAMBLE-1 (88·1%) and the other scoring systems. In conclusion, risk of requiring ICU can be more accurately predicted using PREEMPT-2 and PREAMBLE-2, as described here, than by other early warning scoring systems developed over recent years.

Onset of a quantum phase transition with a trapped ion quantum simulator.

A quantum simulator is a well-controlled quantum system that can follow the evolution of a prescribed model whose behaviour may be difficult to determine. A good example is the simulation of a set of interacting spins, where phase transitions between various spin orders can underlie poorly understood concepts such as spin liquids. Here we simulate the emergence of magnetism by implementing a fully connected non-uniform ferromagnetic quantum Ising model using up to 9 trapped (171)Yb(+) ions. By increasing the Ising coupling strengths compared with the transverse field, the crossover from paramagnetism to ferromagnetic order sharpens as the system is scaled up, prefacing the expected quantum phase transition in the thermodynamic limit. We measure scalable order parameters appropriate for large systems, such as various moments of the magnetization. As the results are theoretically tractable, this work provides a critical benchmark for the simulation of intractable arbitrary fully connected Ising models in larger systems.

Observation of ground-state quantum beats in atomic spontaneous emission.

We report ground-state quantum beats in spontaneous emission from a continuously driven atomic ensemble. Beats are visible only in an intensity autocorrelation and evidence spontaneously generated coherence in radiative decay. Our measurement realizes a quantum eraser where a first photon detection prepares a superposition and a second erases the "which path" information in the intermediate state.

Hb M Dothan [beta 25/26 (B7/B8)/(GGT/GAG-->GAG//Gly/Glu-->Glu]; a new mechanism of unstable methemoglobin variant and molecular characteristics.

A new unstable beta globin chain variant associated with methemoglobin (Met-Hb) phenotype was found in a Caucasian infant. Molecular analysis of the beta globin gene using polymerase chain reaction (PCR) amplification and sequencing led to the detection of a new in frame deletion in exon-1. Direct sequencing of the PCR product revealed a 3 bp deletion (-GTG) between codons 25/26, which resulted in the loss of a single amino acid (-Gly). We propose that this newly discovered unstable M-hemoglobin (M-Hb) variant, named Hb Dothan [GGT/GAG-->GAG//Gly/Glu-->Glu], is caused by a shift in the amino acid sequence and altered packing of the B and E helices during beta globin synthesis, and also changes the orientation of the critical proximal and distal histidine in the F and E helices respectively. Phenotype/Genotype features and molecular characteristics of this new beta chain are presented in this communication.

Quantum teleportation of the temporal fluctuations of light.

A scheme for the teleportation of a beam of light including its temporal fluctuations is proposed. Expressions for the teleported degrees of first- and second-order optical coherence are presented. Teleportation of an antibunched photon stream illustrates the proposal.

Intensity-field correlation of single-atom resonance fluorescence.

We report measurements of an intensity-field correlation function of the resonance fluorescence of a single trapped 138Ba+ ion. Detection of a photon prepares the atom in its ground state, and we observe its subsequent evolution under interaction with a laser field of well-defined phase. We record the regression of the resonance fluorescence source field. This provides a direct measurement of the field of the radiating dipole of a single atom and exhibits its strong nonclassical behavior. In the setup, an interference measurement is conditioned on the detection of a fluorescence photon.

Disentanglement of source and target and the laser quantum state.

Disentanglement of a laser source from its target qubit is proposed as a criterion establishing the laser quantum state as a coherent state. It is shown that the source-target density operator has a unique factorization in coherent states when the environmental record monitoring laser pump quanta is ignored. The source-target state conditioned upon the complete environmental record is entangled, though, as a state of known total quanta number (source plus target).

Entanglement within the quantum trajectory description of open quantum systems.

The degree of entanglement in an open quantum system varies according to how information in the environment is read. A measure of this contextual entanglement is introduced based on quantum trajectory unravelings of the open system dynamics. It is used to characterize the entanglement in a driven quantum system of dimension 2 x infinity where the entanglement is induced by the environmental interaction. A detailed mechanism for the environment-induced entanglement is given.

Proposed test of quantum nonlocality for continuous variables.

We propose a test of nonlocality for continuous variables using a two-mode squeezed state as the source of nonlocal correlations and a measurement scheme based on conditional homodyne detection. Both the Clauser-Horne-Shimony-Holt and the Clauser-Horne inequality are constructed from the conditional homodyne data and found to be violated for a squeezing parameter larger than r approximately 0.48.

Time-asymmetric fluctuations of light and the breakdown of detailed balance.

Temporal fluctuations of the light radiated by a photoemissive source are studied through the cross correlation of output fields. Whereas microscopic reversibility guarantees time-symmetric fluctuations in thermal equilibrium--where detailed balance holds--away from equilibrium time asymmetry is permitted. Examples of time asymmetry in cavity QED are reported.

Quenching of singlet molecular oxygen (1O2) by azide anion in solvent mixtures.

The azide ion is a strong physical quencher of singlet molecular oxygen (1O2) and is frequently employed to show involvement of 1O2 in oxidation processes. Rate constants (k(q)) for the quenching of 1O2 by azide are routinely used as standards to calculate k(q) values for quenching by other substrates. We have measured k(q) for azide in solvent mixtures containing deuterium oxide (D2O), acetonitrile (MeCN), 1,4-dioxane, ethanol (EtOH), propylene carbonate (PC), or ethylene carbonate (EC), mixtures commonly used for many experimental studies. The rate constants were calculated directly from 1O2 phosphorescence lifetimes observed after laser pulse excitation of rose bengal (RB), used to generate 1O2. In aqueous mixtures with MeCN and carbonates, the rate constant increased nonlinearly with increasing volume of organic solvent in the mixtures. k(q) was 4.78 x 10(8) M(-1) s(-1) in D2O and increased to 26.7 x 10(8) and 27.7 x 10(8) M(-1) s(-1) in 96% MeCN and 97.7% EC/PC, respectively. However, in EtOH/D2O mixtures, k(q) decreased with increasing alcohol concentration. This shows that a higher solvent polarity increases the quenching efficiency, which is unexpectedly decreased by the proticity of aqueous and alcohol solvent mixtures. The rate constant values increased with increasing temperature, yielding a quenching activation energy of 11.3 kJ mol(-1) in D2O. Our results show that rate constants in most solvent mixtures cannot be derived reliably from k(q) values measured in pure solvents by using a simple additivity rule. We have measured the rate constants with high accuracy, and they may serve as a reliable reference to calculate unknown k(q) values.

Quantum state reduction and conditional time evolution of wave-particle correlations in cavity QED.

We report measurements in cavity QED of a wave-particle correlation function which records the conditional time evolution of the field of a fraction of a photon. Detection of a photon prepares a state of well-defined phase that evolves back to equilibrium via a damped vacuum Rabi oscillation. We record the regression of the field amplitude. The recorded correlation function is nonclassical and provides an efficiency independent path to the spectrum of squeezing. Nonclassicality is observed even when the intensity fluctuations are classical.

Body size and composition in Polynesians.

OBJECTIVES: To compare the relationship between body size and body composition in New Zealanders of Polynesian and European descent and to develop specific regression equations for fat mass for Polynesians. SUBJECTS: 189 Maori (93 males, 96 females), 185 Samoans (88 males, 97 females) and 241 Europeans (89 males, 152 females) aged 20-70 y. MEASUREMENTS: Height, weight, four skinfold thicknesses, bioelectrical impedance analysis (BIA) and dual energy X-ray absorptiometry (DXA). RESULTS: At higher body mass index levels, Polynesians (Maori and Samoans combined) had a significantly higher ratio of lean mass:fat mass compared with Europeans. Four multiple regression equations incorporating resistance and reactance, height and weight, sum of four skinfolds or sum of two skinfolds were developed in two-thirds of the Polynesian participants using DXA fat mass as the dependent variable. In the remaining one-third of participants, the mean difference between fat mass predicted by these equations (r2 range 0.89-0.93) and DXA fat mass ranged from -0. 06 to +0.25 kg (s.d. -3.67 to +3.71 kg). CONCLUSION: At higher BMI levels, Polynesians were significantly leaner than Europeans, implying the need for separate BMI definitions of overweight and obesity for Polynesians. The regression equations using BIA, height and weight or skinfold thicknesses were good predictors of body composition in Polynesians.