Squeezing and over-squeezing of triphotons.

Quantum mechanics places a fundamental limit on the accuracy of measurements. In most circumstances, the measurement uncertainty is distributed equally between pairs of complementary properties; this leads to the 'standard quantum limit' for measurement resolution. Using a technique known as 'squeezing', it is possible to reduce the uncertainty of one desired property below the standard quantum limit at the expense of increasing that of the complementary one. Squeezing is already being used to enhance the sensitivity of gravity-wave detectors and may play a critical role in other high precision applications, such as atomic clocks and optical communications. Spin squeezing (the squeezing of angular momentum variables) is a powerful tool, particularly in the context of quantum light-matter interfaces. Although impressive gains in squeezing have been made, optical spin-squeezed systems are still many orders of magnitude away from the maximum possible squeezing, known as the Heisenberg uncertainty limit. Here we demonstrate how an optical system can be squeezed essentially all the way to this fundamental bound. We construct spin-squeezed states by overlapping three indistinguishable photons in an optical fibre and manipulating their polarization (spin), resulting in the formation of a squeezed composite particle known as a 'triphoton'. The symmetry properties of polarization imply that the measured triphoton states can be most naturally represented by quasi-probability distributions on the surface of a sphere. In this work we show that the spherical topology of polarization imposes a limit on how much squeezing can occur, leading to the quasi-probability distributions wrapping around the sphere-a phenomenon we term 'over-squeezing'. Our observations of spin-squeezing in the few-photon regime could lead to new quantum resources for enhanced measurement, lithography and information processing that can be precisely engineered photon-by-photon.

Ultrafast Stark-induced polaritonic switches.

A laser pulse, several meV red detuned from the excitonic line of a quantum well, has been shown to induce an almost instantaneous and rigid shift of the lower and upper polariton branches. Here we demonstrate that through this shift ultrafast all-optical control of the polariton population in a semiconductor microcavity should be achievable. In the proposed setup, a Stark field is used to bring the lower polariton branch in or out of resonance with a quasiresonant continuous-wave laser, thereby favoring or inhibiting the injection of polaritons into the cavity. Moreover, we show that this technique allows for the implementation of optical switches with extremely high repetition rates.

Adaptive quantum state tomography improves accuracy quadratically.

We introduce a simple protocol for adaptive quantum state tomography, which reduces the worst-case infidelity [1-F(ρ,ρ)] between the estimate and the true state from O(1/sqrt[N]) to O(1/N). It uses a single adaptation step and just one extra measurement setting. In a linear optical qubit experiment, we demonstrate a full order of magnitude reduction in infidelity (from 0.1% to 0.01%) for a modest number of samples (N ≈ 3 × 10(4)).

Improving quantum state estimation with mutually unbiased bases.

When used in quantum state estimation, projections onto mutually unbiased bases have the ability to maximize information extraction per measurement and to minimize redundancy. We present the first experimental demonstration of quantum state tomography of two-qubit polarization states to take advantage of mutually unbiased bases. We demonstrate improved state estimation as compared to standard measurement strategies and discuss how this can be understood from the structure of the measurements we use. We experimentally compared our method to the standard state estimation method for three different states and observe that the infidelity was up to 1.84 ± 0.06 times lower by using our technique than it was by using standard state estimation methods.

Super-resolving phase measurements with a multiphoton entangled state.

Interference phenomena are ubiquitous in physics, often forming the basis of demanding measurements. Examples include Ramsey interferometry in atomic spectroscopy, X-ray diffraction in crystallography and optical interferometry in gravitational-wave studies. It has been known for some time that the quantum property of entanglement can be exploited to perform super-sensitive measurements, for example in optical interferometry or atomic spectroscopy. The idea has been demonstrated for an entangled state of two photons, but for larger numbers of particles it is difficult to create the necessary multiparticle entangled states. Here we demonstrate experimentally a technique for producing a maximally entangled three-photon state from initially non-entangled photons. The method can in principle be applied to generate states of arbitrary photon number, giving arbitrarily large improvement in measurement resolution. The method of state construction requires non-unitary operations, which we perform using post-selected linear-optics techniques similar to those used for linear-optics quantum computing.

Bright filter-free source of indistinguishable photon pairs.

We demonstrate a high-brightness source of pairs of indistinguishable photons based on a type-II phase-matched doubly-resonant optical parametric oscillator operated far below threshold. The cavityenhanced down-conversion output of a PPKTP crystal is coupled into two single-mode fibers with a mode coupling efficiency of 58%. The high degree of indistinguishability between the photons of a pair is demonstrated by a Hong-Ou-Mandel interference visibility of higher than 90% without any filtering at an instantaneous coincidence rate of 450,000 pairs/s per mW of pump power per nm of down-conversion bandwidth. For the degenerate spectral mode with a linewidth of 7 MHz at 795 nm a rate of 70 pairs/(s mW MHz) is estimated, increasing the spectral brightness for indistinguishable photons by two orders of magnitude compared to similar previous sources.

Simulating and Optimising Quantum Thermometry Using Single Photons.

A classical thermometer typically works by exchanging energy with the system being measured until it comes to equilibrium, at which point the readout is related to the final energy state of the thermometer. A recent paper noted that with a quantum thermometer consisting of a single spin/qubit, temperature discrimination is better achieved at finite times rather than once equilibration is essentially complete. Furthermore, preparing a qubit thermometer in a state with quantum coherence instead of an incoherent one improves its sensitivity to temperature differences. Implementing a recent proposal for efficiently emulating an arbitrary quantum channel, we use the quantum polarisation state of individual photons as models of "single-qubit thermometers" which evolve for a certain time in contact with a thermal bath. We investigate the optimal thermometer states for temperature discrimination, and the optimal interaction times, confirming that there is a broad regime where quantum coherence provides a significant improvement. We also discuss the more practical question of thermometers composed of a finite number of spins/qubits (greater than one), and characterize the performance of an adaptive protocol for making optimal use of all the qubits.

A developmental psychopathology model of childhood traumatic stress and intersection with anxiety disorders.

Empirical findings regarding childhood traumatic stress are placed within a developmental life-trajectory model that incorporates a tripartite etiology of posttrauma distress. This approach recognizes an intricate matrix of child-intrinsic factors, developmental maturation and experience, life events, and evolving family and social ecologies. Of central developmental importance in the field of traumatic stress is the ontogenesis of appraisal, emotional response, emotional and physiological regulation, and consideration of protective action with regard to danger. The complexity of traumatic situations and their aftermath suggests the relevance of multiple stress diatheses in understanding individual variability in proximal and distal effects. Neurobiological systems that subserve danger mature over childhood and adolescence. Neurophysiological and neurohormonal studies among traumatized children and adolescents suggest potential neurodevelopmental stage-related vulnerabilities within these systems. Advances in child development and traumatic stress provide tools for investigating proximal and distal interplay of psychopathology, disturbances in the acquisition and maintenance of developmental competencies, and life-trajectory outcomes. A developmental psychopathology model suggests different avenues by which dangerous circumstances, childhood traumatic experiences, and posttraumatic stress disorder (PTSD) can intersect with other anxiety disorders over the life span.

A behavioral animal model of posttraumatic stress disorder featuring repeated exposure to situational reminders.

The purpose of this study was to evaluate an animal model of posttraumatic stress disorder (PTSD) in mice. The model featured repeated exposures to situational reminders of a traumatic stress, which consisted of a brief electric shock, and included assessment of two behavioral parameters and the startle reflex. The findings indicated an initial, but unsustained, increase in locomotor activity in a neutral environment due to traumatic stress. Exposure to situational reminders was associated with a persistent bidirectional abnormal behavioral pattern in a fear-provoking environment and a progressive increase over time in the magnitude of the startle reflex. Exposure to situational reminders also produced an increase in aggressive behavior. This animal model appears to produce behavioral changes analogous to those seen in patients with PTSD.

Posttraumatic stress disorder in elderly and younger adults after the 1988 earthquake in Armenia.

OBJECTIVE: This study was undertaken 1 1/2 years after the 1988 earthquake in Armenia to assess the frequency and severity of posttraumatic stress reactions among elderly and younger adult victims and to assess the relation of exposure, age, sex, and death of a family member to these reactions. METHOD: One hundred seventy-nine subjects of both sexes were evaluated with the Posttraumatic Stress Disorder (PTSD) Reaction Index. A subgroup of 60 individuals were also assessed for PTSD with the DSM-III-R criteria. RESULTS: There was a strong association between the presence of severe symptoms on the index and a DSM-III-R diagnosis of PTSD. Elderly and younger adult victims in cities closer to the epicenter (higher exposure) had significantly higher index scores than elderly and adult victims in more distant locations. In comparison with previous studies of natural disasters, much greater rates of chronic severe posttraumatic stress reactions were found among the highly exposed individuals. Although there was no difference in total mean score on the Posttraumatic Stress Disorder Reaction Index, a significant difference in symptom profile was found between the elderly and younger adults; the elderly scored higher on arousal symptoms and lower on intrusive symptoms. There was a positive correlation between loss of family members and severity of posttraumatic stress reaction. CONCLUSIONS: These findings indicate that after a major natural disaster with subsequent multiple adversities, a substantial proportion of the adult population may experience severe and chronic posttraumatic stress reactions. The risk factors identified in this study may prove useful in screening exposed individuals for appropriate treatment.

Prospective study of posttraumatic stress, anxiety, and depressive reactions after earthquake and political violence.

OBJECTIVE: The authors sought to assess the severity and longitudinal course of posttraumatic stress, anxiety, and depressive reactions among two groups of adults differentially exposed to severe and mild earthquake trauma and a third group exposed to severe violence. They also examined interrelationships among these reactions and predictors of outcome and compared posttraumatic stress disorder (PTSD) symptom category profile and course between those exposed to earthquake and those exposed to violence. METHOD: Seventy-eight non-treatment-seeking subjects were assessed with self-report instruments approximately 1.5 and 4.5 years after the 1988 Spitak earthquake in Armenia and the 1988 pogroms against Armenians in Azerbaijan. RESULTS: The two groups that had been exposed to severe trauma (earthquake or violence) had high initial and follow-up PTSD scores that did not remit over the 3-year interval. Overall, depressive symptoms subsided. Posttraumatic stress, anxiety, and depressive reactions were highly intercorrelated within and across both time intervals. No significant differences in PTSD severity, profile, or course were seen between subjects exposed to severe earthquake trauma versus those exposed to severe violence. CONCLUSIONS: After exposure to severe trauma, either an earthquake or violence, adults are at high risk of developing severe and chronic posttraumatic stress reactions that are associated with chronic anxiety and depressive reactions. Clinical evaluation and therapeutic intervention should include specific attention to these reactions. Early mental health intervention is recommended to prevent their chronicity.

Basal cortisol, dexamethasone suppression of cortisol, and MHPG in adolescents after the 1988 earthquake in Armenia.

OBJECTIVE: This study evaluated basal salivary cortisol, 3-methoxy-4-hydroxyphenylglycol (MHPG), and cortisol suppression following dexamethasone administration in adolescents exposed to two levels of earthquake-related trauma. METHOD: Five years after the 1988 earthquake, saliva samples were obtained from 37 adolescents from two cities in Armenia at different distances from the epicenter. Baseline saliva samples were obtained at 8:00 a.m., 4:00 p.m., and 11:00 p.m., following which 0.5 mg of dexamethasone was administered. Nine and 17 hours later, saliva samples were again obtained. Subjects were evaluated for posttraumatic stress and depressive reactions through use of self-report instruments. RESULTS: Significantly lower mean baseline 8:00 a.m. cortisol levels and greater day 24:00 p.m. cortisol suppression following dexamethasone were observed in the more symptomatic adolescents living in the city closer to the epicenter. Of the three symptom categories of posttraumatic stress disorder (PTSD), only intrusion (category B) symptoms were significantly correlated with basal morning cortisol levels and percent suppression by dexamethasone. The more highly exposed adolescents also exhibited a more rapid decline in MHPG levels over the course of day 1. CONCLUSIONS: The findings indicate that chronic posttraumatic stress reactions among adolescents exposed to catastrophic disaster are associated with hypothalamic-pituitary-adrenal (HPA) axis alterations. The findings are congruent with those previously described in adults with chronic PTSD. Persistent intrusion (category B) symptoms may constitute continued episodes of distress and evoke repeated physiological stress responses, which, over time, alter HPA axis function. The MHPG findings suggest that there may be diurnal changes associated with severity of posttraumatic stress symptoms.

Outcome of psychotherapy among early adolescents after trauma.

OBJECTIVE: The authors evaluated the effectiveness of brief trauma/grief-focused psychotherapy among early adolescents exposed to the 1988 earthquake in Armenia. METHOD: Posttraumatic stress and depressive reactions among treated and not treated subjects were evaluated pre- and postintervention, at 1 1/2 and 3 years after the earthquake, respectively. RESULTS: Severity of posttraumatic stress symptoms significantly decreased among the subjects given psychotherapy, while severity of these symptoms increased significantly among the subjects not treated with psychotherapy. The improvement in posttraumatic stress symptoms was attributable to improvement in all three symptom categories (intrusion, avoidance, and arousal) of posttraumatic stress disorder (PTSD). There was no change in severity of depressive symptoms among subjects given psychotherapy. However, depressive symptoms among subjects not treated with psychotherapy significantly worsened over time. The changes in severity of posttraumatic stress and depressive symptoms were positively correlated within both groups. CONCLUSIONS: The findings demonstrate the efficacy of trauma/grief-focused brief psychotherapy in alleviating PTSD symptoms and preventing the worsening of comorbid depression among early adolescents after a catastrophic disaster. The results support the broad use of such school-based interventions after major disasters and demonstrate the cross-cultural applicability of Western psychotherapeutic approaches.

Posttraumatic stress and depressive reactions among Nicaraguan adolescents after hurricane Mitch.

OBJECTIVE: This study determined the severity of posttraumatic stress and depressive reactions among Nicaraguan adolescents after Hurricane Mitch and the relationship of these reactions to objective and subjective features of hurricane exposure, death of a family member, forced relocation, and thoughts of revenge. METHOD: Six months after the hurricane, 158 adolescents from three differentially exposed cities were evaluated by using a hurricane exposure questionnaire, the Child Posttraumatic Stress Disorder Reaction Index, and the Depression Self-Rating SCALE: RESULTS: Severe levels of posttraumatic stress and depressive reactions were found among adolescents in the two most heavily affected cities. Severity of posttraumatic stress and depressive reactions and features of objective hurricane-related experiences followed a "dose-of-exposure" pattern that was congruent with the rates of death and destruction across cities. Level of impact (city), objective and subjective features, and thoughts of revenge accounted for 68% of the variance in severity of posttraumatic stress reaction. Severity of posttraumatic stress reaction, death of a family member, and sex accounted for 59% of the variance in severity of depression. CONCLUSIONS: After a category 5 hurricane, adolescents in heavily affected areas with extreme objective and subjective hurricane-related traumatic features of exposure experience severe and chronic posttraumatic stress and comorbid depressive reactions. The recovery of the severely affected Nicaraguan adolescents is vital to the social and economic recovery of a country ravaged by years of political violence and poverty. These findings strongly indicate the need to incorporate public mental health approaches, including systematic screening and trauma/grief-focused interventions, within a comprehensive disaster recovery program.

Psychiatric comorbidity in children after the 1988 earthquake in Armenia.

OBJECTIVE: To determine current rates of posttraumatic stress disorder (PTSD), depressive disorder, and separation anxiety disorder (SAD) among children 1 1/2 years after the 1988 earthquake in Armenia; to determine current rates of comorbid PTSD and depressive disorder; and to assess the contribution of exposure, gender, loss of family members, and loss of residence. METHOD: Two hundred eighteen school-age children from three cities at increasing distances from the epicenter were evaluated using the Child Posttraumatic Stress Disorder Reaction Index, the Depression Self-Rating Scale, and the section on SAD from the Diagnostic Interview for Children and Adolescents. RESULTS: On the basis of these evaluations, high rates of current PTSD, depressive disorder, and their co-occurrence were found among victims residing in the two heavily impacted cities. SAD was comparatively less frequent, although symptoms of SAD had been pervasive throughout the region. Severity of posttraumatic stress and depressive reactions were highly correlated. Extent of loss of family members was independently correlated with each. CONCLUSION: After a catastrophic natural disaster, children are at risk for comorbid PTSD and secondary depression. Based on the findings, an interactive model is proposed of postdisaster psychopathology. Early clinical intervention is recommended to prevent chronic posttraumatic stress reactions and secondary depression.

Moral development and psychopathological interference in conscience functioning among adolescents after trauma.

OBJECTIVES: To compare moral development and psychopathological interference with conscience functioning (PI) among adolescents exposed to different degrees of earthquake-related trauma and to investigate the relationship of moral development and PI to exposure to trauma, severity of posttraumatic stress disorder (PTSD) symptoms, postearthquake adversities, and extent of loss of nuclear family members. METHOD: Adolescents (N = 193) from 2 cities at different distances from the epicenter were evaluated. The Stilwell Structured Conscience Interview was used to assess moral development and PI. Structured self-report instruments were used to obtain ratings of severity of earthquake-related trauma, posttraumatic stress symptoms, and postearthquake adversities. RESULTS: Adolescents in the city near the epicenter manifested advanced moral development as compared with their counterparts in the less affected city. Concomitantly, they endorsed responses indicating PI. Levels of PI were significantly correlated with severity of PTSD symptoms. CONCLUSION: In the aftermath of a catastrophic natural disaster, children assume greater responsibilities and confront a multitude of morally challenging interpersonal situations which may result in an advancement of their moral development. Yet, at the same time, PTSD symptoms and negative schematizations of self and others may give rise to disturbances in conscience functioning. The findings suggest that therapeutic consideration should be given to assisting children in integrating the horror of their traumatic experiences and the harshness of posttrauma adversities into an adaptive schema of good and evil in themselves and the world.

A public mental health approach to the postdisaster treatment of children and adolescents.

This article describes the implementation of mental health intervention programs for children, adolescents,and their families exposed to natural disaster and violence. Recommendations are made regarding needed levels of organization, methods of screening and triage, training and supervision of mental health staff, design and implementation of treatment approaches, and longitudinal monitoring of course of recovery and intervention outcome.

Are researchers bound by child abuse reporting laws?

OBJECTIVE: To discuss issues concerning mandatory reporting of child abuse in research settings. METHOD: An overview of existing Federal and State statutes regarding mandatory reporting of child abuse is presented. A critical review of the literature addresses the following issues: (1) whether researchers have a moral duty to place the health and safety of children above concerns about confidentiality and the benefits of obtaining new knowledge; (2) whether the Certificate of Confidentiality preempts reporting requirements; (3) whether researchers who are not health professionals (such as child developmentalists, psychobiologists, neuroscientists) should be required to report; and (4) whether researchers should be required to expand their protocols to include more in-depth investigation of potential abuse. RESULTS: Existing child abuse reporting laws do not specifically designate researchers as among the category of individuals mandated to report suspected child abuse. Currently, Human Subject Protection Committees and Federal funding agencies are tending to interpret reporting laws as applying to researchers, including requiring that research subjects are informed of this responsibility in consenting procedures. It is unclear whether the Certificate of Confidentiality preempts child abuse reporting laws. CONCLUSION: The authors recommend that legislatures specifically designate researchers as mandated reporters to ensure more uniform reporting practices in research settings. For both investigators and Human Subject Protection Committees, inclusion of researchers among the categories of those mandated to report would also help address issues of immunity from civil and criminal liability for "good faith" reports that turn out to be false and injurious.

Experimental joint weak measurement on a photon pair as a probe of Hardy's paradox.

It has been proposed that the ability to perform joint weak measurements on postselected systems would allow us to study quantum paradoxes. These measurements can investigate the history of those particles that contribute to the paradoxical outcome. Here we experimentally perform weak measurements of joint (i.e., nonlocal) observables. In an implementation of Hardy's paradox, we weakly measure the locations of two photons, the subject of the conflicting statements behind the paradox. Remarkably, the resulting weak probabilities verify all of these statements but, at the same time, resolve the paradox.