Precision tomography of a three-qubit donor quantum processor in silicon.

Nuclear spins were among the first physical platforms to be considered for quantum information processing1,2, because of their exceptional quantum coherence3 and atomic-scale footprint. However, their full potential for quantum computing has not yet been realized, owing to the lack of methods with which to link nuclear qubits within a scalable device combined with multi-qubit operations with sufficient fidelity to sustain fault-tolerant quantum computation. Here we demonstrate universal quantum logic operations using a pair of ion-implanted 31P donor nuclei in a silicon nanoelectronic device. A nuclear two-qubit controlled-Z gate is obtained by imparting a geometric phase to a shared electron spin4, and used to prepare entangled Bell states with fidelities up to 94.2(2.7)%. The quantum operations are precisely characterized using gate set tomography (GST)5, yielding one-qubit average gate fidelities up to 99.95(2)%, two-qubit average gate fidelity of 99.37(11)% and two-qubit preparation/measurement fidelities of 98.95(4)%. These three metrics indicate that nuclear spins in silicon are approaching the performance demanded in fault-tolerant quantum processors6. We then demonstrate entanglement between the two nuclei and the shared electron by producing a Greenberger-Horne-Zeilinger three-qubit state with 92.5(1.0)% fidelity. Because electron spin qubits in semiconductors can be further coupled to other electrons7-9 or physically shuttled across different locations10,11, these results establish a viable route for scalable quantum information processing using donor nuclear and electron spins.

Attitude change after a curriculum on the science and philosophy of well-being and happiness for high school students: A classroom-randomized trial.

BACKGROUND: Multiple interventions have been tested to promote well-being in high school students, often focusing on depression prevention. AIMS: To test the impact of a one-semester active learning curriculum covering the modern science and philosophy of well-being and happiness on attitudinal measures related to the curriculum and standard measures of depression and well-being. SAMPLE: Subjects were first-year students in an urban high school in Beijing, China (equivalent to US tenth grade). METHODS: Nine classrooms were randomly assigned to the intervention curriculum (n = 252), and nine classrooms were randomly assigned to a traditional psychology curriculum (n = 263). Students completed questionnaires pre- and post-semester including a Positive Attitude Scale (PAS, concerning Relatedness, Competence, Autonomy, Gratitude, Calmness, Mindfulness, and Hope), Positive and Negative Affect Scale (PANAS), Centers for Epidemiological Studies Depression Scale (CES-D), Life Satisfaction Scale (LS), Subjective Happiness Scale (SHS), Meaning in Life Questionnaire (MLQ), and a test of knowledge about well-being (Knowledge Test, KT). RESULTS: In a hierarchical linear model, there were statistically significant intervention effects on six of the seven subscales of the PAS, on PANAS balance, and on the KT. CES-D, LS, SHS, and MLQ were improved but not significantly so. Notable overall secular trends in measures of well-being were observed, with a peak in September and nadir in April. CONCLUSIONS: A one-semester course for high school students regarding well-being and happiness demonstrated significant changes in positive attitudes, affective balance, and knowledge about happiness. Circannual trends in well-being measures over the academic year have implications for those designing school intervention studies.

Personality strengths in romantic relationships: Measuring perceptions of benefits and costs and their impact on personal and relational well-being.

Three studies using samples of people in romantic relationships were conducted to create a new individual difference measure of partner strengths in couples. The 2 perceptions of partner strengths included (1) appreciation of their use and effectiveness and (2) recognition of costs associated with their use. Factor analyses supported 2-factors and we found that greater appreciation of partner strengths predicted greater relationship satisfaction, commitment, investment, intimacy, self-expansion, and support for goal pursuit; recognizing significant costs with partner strengths was inversely related to several outcomes. Using a 1-week daily diary, we found that appreciation of partner strength use and recognition of costs associated with these strengths predicted daily relationship satisfaction and whether basic psychological needs were met within the relationship. The explanatory power of partner strength perceptions could not be explained by the actual character strengths or Big Five personality traits of partners, support for positive self-disclosures (capitalization), or gratitude for relationship partners. Finally, we found that the relational consequences of partner strength perceptions were not just "in the head" of the perceiver-influencing partner relational outcomes. This research program provides evidence for the use of a new measure of how strengths are perceived to better understand romantic couples and aspirational targets in clinical interventions. (PsycINFO Database Record

Stability amidst turmoil: Grit buffers the effects of negative life events on suicidal ideation.

The goal of the current study is to examine the role of grit as a resilience factor that reduces the risk for suicidal ideation conferred by negative life events. Participants (N=209) completed measures of negative life events and grit at baseline and a measure of suicidal ideation at follow-up four weeks later. Poisson regression analyses found that higher levels of grit buffered the relationship between negative life events and suicidal ideation such that negative life events only predicted suicidal ideation if grit was low. These results suggest that high grit can abate the increased suicidal ideation associated with negative life events. Aside from absolute levels of suicidal ideation, being able to predict or buffer dramatic shifts in suicidal ideation can be a useful diagnostic tool during interventions.

Examining the latent structure of anxiety sensitivity in adolescents using factor mixture modeling.

Anxiety sensitivity has been implicated as an important risk factor, generalizable to most anxiety disorders. In adults, factor mixture modeling has been used to demonstrate that anxiety sensitivity is best conceptualized as categorical between individuals. That is, whereas most adults appear to possess normative levels of anxiety sensitivity, a small subset of the population appears to possess abnormally high levels of anxiety sensitivity. Further, those in the high anxiety sensitivity group are at increased risk of having high levels of anxiety and of having an anxiety disorder. This study was designed to determine whether these findings extend to adolescents. Factor mixture modeling was used to examine the best fitting model of anxiety sensitivity in a sample of 277 adolescents (M age = 11.0 years, SD = 0.81). Consistent with research in adults, the best fitting model consisted of 2 classes, 1 containing adolescents with high levels of anxiety sensitivity (n = 25) and another containing adolescents with normative levels of anxiety sensitivity (n = 252). Examination of anxiety sensitivity subscales revealed that the social concerns subscale was not important for classification of individuals. Convergent and discriminant validity of anxiety sensitivity classes were found in that membership in the high anxiety sensitivity class was associated with higher mean levels of anxiety symptoms, controlling for depression and externalizing problems, and was not associated with higher mean levels of depression or externalizing symptoms controlling for anxiety problems.

Simulation of stochastic quantum systems using polynomial chaos expansions.

We present an approach to the simulation of quantum systems driven by classical stochastic processes that is based on the polynomial chaos expansion, a well-known technique in the field of uncertainty quantification. The polynomial chaos technique represents the density matrix as an expansion in orthogonal polynomials over the principle components of the stochastic process and yields a sparsely coupled hierarchy of linear differential equations. We provide practical heuristics for truncating this expansion based on results from time-dependent perturbation theory and demonstrate, via an experimentally relevant one-qubit numerical example, that our technique can be significantly more computationally efficient than Monte Carlo simulation.

When is rumination an adaptive mood repair strategy? Day-to-day rhythms of life in combat veterans with and without posttraumatic stress disorder.

Prior research suggests that rumination and chronic negative emotions serve to maintain emotional disorders. However, some evidence suggests that pondering the nature and meaning of negative experiences can be adaptive. To better understand the function of this dimension of rumination, we studied the use of this strategy in response to negative emotions as they unfold from day to day in veterans with (n=27) and without (n=27) post traumatic stress disorder (PTSD). For two weeks, veterans completed daily questions about when they experienced a bad mood and how often they used rumination to feel differently. It was hypothesized that rumination would attenuate negative emotional reactions in veterans without PTSD, but that rigid, intense negative emotions would persist in veterans with PTSD. Using multilevel modeling, we found that on the same day, rumination was positively associated with negative affect. Because covariation fails to address directionality, we also examined lagged effects from one occasion to the next. For veterans without PTSD, more frequent use of rumination predicted less intense negative affect the next day; there was no support for a model with negative affect predicting rumination the next day. For veterans with PTSD, the prior day's intensity of negative affect was the only predictor of intensity of negative affect the next day. Results support the value of distinguishing within-day and across day effects, and the presence of PTSD, to clarify contexts when rumination is adaptive.

Exposure to Hazardous Neighborhood Environments in Late Childhood and Anxiety.

This investigation examined the relationship between living in disordered neighborhoods during childhood and anxiety 1 year later. Objective measures of neighborhood environment and individual data from a study of mental health in suburban children were utilized. Linear regression models were used to assess relationships between neighborhood hazard and anxiety. Childhood neighborhood disorder was inversely associated with generalized anxiety (ß = 0.037, p<0.01) and social phobia (ß = -0.33, p=0.03), but not other forms of anxiety including separation anxiety or panic disorder. We suspect that children with early exposure to disordered neighborhoods are either desensitized to toxic environments or that anxiety is not well specified for this population.

Stroboscopic generation of topological protection.

Trapped neutral atoms offer a powerful route to robust simulation of complex quantum systems. We present here a stroboscopic scheme for realization of a Hamiltonian with n-body interactions on a set of neutral atoms trapped in an addressable optical lattice, using only 1- and 2-body physical operations together with a dissipative mechanism that allows thermalization to finite temperature or cooling to the ground state. We demonstrate this scheme with application to the toric code Hamiltonian, ground states of which can be used to robustly store quantum information when coupled to a low temperature reservoir.