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Biomedical subjects

A M Steinberg

Publications and source records attributed to A M Steinberg.

At least 19 recordsLinked to original sources
PubMed2005

Quantum nonlocality obtained from local states by entanglement purification.

We have applied an entanglement purification protocol to produce a single entangled pair of photons capable of violating a Clauser-Horne-Shimony-Holt Bell inequality from two pairs that individually could not. The initial poorly entangled photons were created by a controllable decoherence that introduced complex errors. All of the states were reconstructed using quantum state tomography which allowed for a quantitative description of the improvement of the state after purification.

Journal Article↗
PubMed2004

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.

Journal Article↗
PubMed2004

Extracting joint weak values with local, single-particle measurements.

Weak measurement is a new technique which allows one to describe the evolution of postselected quantum systems. It appears to be useful for resolving a variety of thorny quantum paradoxes, particularly when used to study properties of pairs of particles. Unfortunately, such nonlocal or joint observables often prove difficult to measure directly in practice (for instance, in optics-a common testing ground for this technique-strong photon-photon interactions would be needed to implement an appropriate von Neumann interaction). Here we derive a general, experimentally feasible, method for extracting these joint weak values from correlations between single-particle observables.

Journal Article↗
PubMed2003

Experimental application of decoherence-free subspaces in an optical quantum-computing algorithm.

For a practical quantum computer to operate, it is essential to properly manage decoherence. One important technique for doing this is the use of "decoherence-free subspaces" (DFSs), which have recently been demonstrated. Here we present the first use of DFSs to improve the performance of a quantum algorithm. An optical implementation of the Deutsch-Jozsa algorithm can be made insensitive to a particular class of phase noise by encoding information in the appropriate subspaces; we observe a reduction of the error rate from 35% to 7%, essentially its value in the absence of noise.

Journal Article↗
PubMed2003

Diagnosis, prescription, and prognosis of a bell-state filter by quantum process tomography.

We apply the techniques of quantum process tomography to characterize errors and decoherence in a prototypical two-photon operation, a singlet-state filter. The quantum process tomography results indicate a large asymmetry in the process and also the required operation to correct for this asymmetry. We quantify residual errors and decoherence of the filtering operation after this modification.

Journal Article↗
PubMed2002

Quantum state preparation and conditional coherence.

It is well known that spontaneous parametric down-conversion can be used to probabilistically prepare single-photon states. We have performed an experiment in which arbitrary superpositions of zero- and one-photon states can be prepared by appropriate postselection. The optical phase, which is meaningful only for superpositions of photon number, is related to the relative phase between the zero- and one-photon states. Whereas the light from spontaneous parametric down-conversion has an undefined phase, we show that this technique collapses one beam to a state of well-defined optical phase when a measurement succeeds on the other beam.

Journal Article↗
PubMed2001

Nonlinear optics with less than one photon.

We demonstrate suppression and enhancement of spontaneous parametric down-conversion via quantum interference with two weak fields from a local oscillator (LO). Effectively, pairs of LO photons up-convert with high efficiency for appropriate phase settings, exhibiting an effective nonlinearity enhanced by at least 10 orders of magnitude. This constitutes a two-photon switch and promises to be applicable to a wide variety of quantum nonlinear optical phenomena.

Journal Article↗
PubMed2001

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.

Adjustment Disorders↗
PubMed2000

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.

Adult↗
PubMed1999

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.

Adult↗
PubMed1999

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.

Child↗
PubMed1999

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.

Adolescent↗
PubMed1998

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.

Adolescent↗
PubMed1997

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.

Adolescent↗
PubMed1996

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.

Adaptation, Psychological↗
PubMed1996

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.

Adolescent↗