Atom laser coherence and its control via feedback

We present a quantum-mechanical treatment of the coherence properties of a single-mode atom laser. Specifically, we focus on the quantum phase noise of the atomic field as expressed by the first-order coherence function, for which we derive analytical expressions in various regimes. The decay of this function is characterized by the coherence time, or its reciprocal, the linewidth. A crucial contributor to the linewidth is the collisional interaction of the atoms. We find four distinct regimes for the linewidth with increasing interaction strength. These range from the standard laser linewidth, through quadratic and linear regimes, to another constant regime due to quantum revivals of the coherence function. The laser output is only coherent (Bose degenerate) up to the linear regime. However, we show that application of a quantum nondemolition measurement and feedback scheme will increase, by many orders of magnitude, the range of interaction strengths for which it remains coherent.Comment: 15 pages, 6 figures, revtex

Engineering Quantum States, Nonlinear Measurements, and Anomalous Diffusion by Imaging

We show that well-separated quantum superposition states, measurements of strongly nonlinear observables, and quantum dynamics driven by anomalous diffusion can all be achieved for single atoms or molecules by imaging spontaneous photons that they emit via resonance florescence. To generate anomalous diffusion we introduce continuous measurements driven by L\'evy processes, and prove a number of results regarding their properties. In particular we present strong evidence that the only stable L\'evy density that can realize a strictly continuous measurement is the Gaussian.Comment: revtex4-1, 17 pages, 7 eps figure

Universal spectral behavior of x2(ix)ϵx^2(ix)^\epsilon potentials

The PT-symmetric Hamiltonian $H=p^2+x^2(ix)^\epsilon$ ($\epsilon$ real) exhibits a phase transition at $\epsilon=0$. When $\epsilon\geq0$, the eigenvalues are all real, positive, discrete, and grow as $\epsilon$ increases. However, when $\epsilon<0$ there are only a finite number of real eigenvalues. As $\epsilon$ approaches -1 from above, the number of real eigenvalues decreases to one, and this eigenvalue becomes infinite at $\epsilon=-1$. In this paper it is shown that these qualitative spectral behaviors are generic and that they are exhibited by the eigenvalues of the general class of Hamiltonians $H^{(2n)}=p^{2n}+x^2(ix)^\epsilon$ ($\epsilon$ real, n=1, 2, 3, ...). The complex classical behaviors of these Hamiltonians are also examined.Comment: 8 pages, 7 figure

Feedback cooling of a single trapped ion

Based on a real-time measurement of the motion of a single ion in a Paul trap, we demonstrate its electro-mechanical cooling below the Doppler limit by homodyne feedback control (cold damping). The feedback cooling results are well described by a model based on a quantum mechanical Master Equation.Comment: 4 pages, 3 figure

From Paris to Projects: Clarifying the Implications of Canada’s Climate Change Mitigation Commitments for the Planning and Assessment of Projects and Strategic Undertakings (Full Report)

Canada has signed the Paris Agreement and made other international commitments to doing our fair share of what is needed to keep overall global warming to the Paris Agreement limit of well below 2ºC, and to aim for 1.5ºC, to avoid devastating climate change. However, we have not yet progressed far in translating these commitments into implications for decision making on proposed undertakings with significant implications for meeting those commitments.Clarifying those implications and determining how best to incorporate them in deliberations and decision making is overdue and now imperative. The federal government’s new Impact Assessment Act, which is now proceeding through Parliament’s legislative process, stands to require that all assessments decisions be based in part on evaluation of the extent to which the effects of the designated project hinder or contribute to the Government of Canada’s ability to meet its environmental obligations and its commitments in respect of climate change. (Impact Assessment Act, section 63(e)).In this report, we present the findings of an initial effort to delineate and address the gap between Paris and projects. We set out the needed steps and their main implications, especially for new assessment law, regulation and policy. The steps are not fully defined and many components include a range of possible options. Our intent and expectations have not been to deliver final answers but to establish a firm basis for informed conversation of a matter of pressing importance. The challenges identified in this report are numerous and demanding but reasonably clear.Our main findings and recommendations are summarized in part 5, the concluding section of the report

A Straightforward Introduction to Continuous Quantum Measurement

We present a pedagogical treatment of the formalism of continuous quantum measurement. Our aim is to show the reader how the equations describing such measurements are derived and manipulated in a direct manner. We also give elementary background material for those new to measurement theory, and describe further various aspects of continuous measurements that should be helpful to those wanting to use such measurements in applications. Specifically, we use the simple and direct approach of generalized measurements to derive the stochastic master equation describing the continuous measurements of observables, give a tutorial on stochastic calculus, treat multiple observers and inefficient detection, examine a general form of the measurement master equation, and show how the master equation leads to information gain and disturbance. To conclude, we give a detailed treatment of imaging the resonance fluorescence from a single atom as a concrete example of how a continuous position measurement arises in a physical system.Comment: 24 pages, 3 eps figues. To appear in Contemporary Physic

From Paris to Projects Clarifying the Implications of Canada’s Climate Change Mitigation Commitments for the Planning and Assessment of Projects and Strategic Undertakings (Summary Report)

By signing the Paris Agreement, Canada made a commitment to do our fair share to limit global average temperature rise to “well below 2°C” relative to pre-industrial levels, and to pursue “efforts to limit the increase to 1.5°C.” The federal Impact Assessment Act that is now before Parliament requires consideration of whether assessed undertakings would “hinder or contribute to” meeting Canada’s climate change commitments.So far, however, Canada has done little to define what the Paris Agreement entails for planning, assessment and decision making on projects and other undertakings with significant implications for meeting the Paris commitments. That leaves a serious gap in law, policy and practice between Canada’s commitments and the assessment of major undertakings.Assessments are an important venue for proactive climate change mitigation. They guide decision making on major extractive and infrastructure projects and other undertakings that will entrench existing practices or drive key transitions for many decades. If these assessments are to contribute to meeting our climate change mitigation commitments, we need to understand what meeting those commitments entails – how far we have to go and what we have to do to close the gap between our current efforts and our promised accomplishments.To inform serious efforts to fill that gap, this paper examines• what the Paris Agreement’s temperature goals imply for global and Canadian GHG reduction targets in light of “fair share” principles and feasible pathways;• what is needed to raise Canadian climate change mitigation ambitions to the Paris Agreement level, and ensure sufficiently strengthened and clarified targets, frameworks and applied tools to inform evaluations of particular undertakings; and• how to translate these needs and tools into well-specified and authoritative requirements for effective application under federal assessment law.Our intent has not been to deliver final answers but to establish a reasonably firm working base for comparing what we are doing with what is needed to meet our Paris commitments

Blast cells surviving acute myeloid leukemia induction therapy are in cycle with a signature of FOXM1 activity

From Springer Nature via Jisc Publications RouterHistory: received 2020-12-01, accepted 2021-10-05, registration 2021-10-06, pub-electronic 2021-10-28, online 2021-10-28, collection 2021-12Publication status: PublishedFunder: Cancer Research UK; doi: http://dx.doi.org/10.13039/501100000289; Grant(s): C5759/A20971Funder: Kay Kendall Leukaemia Fund; doi: http://dx.doi.org/10.13039/501100000402; Grant(s): KKL954Funder: Christie Charity; doi: http://dx.doi.org/10.13039/100013684; Grant(s): NAFunder: Imago Biosciences; Grant(s): NAFunder: cancer research uk; Grant(s): A27412Funder: blood cancer ukFunder: the oglesby charitable trustAbstract: Background: Disease relapse remains common following treatment of acute myeloid leukemia (AML) and is due to chemoresistance of leukemia cells with disease repopulating potential. To date, attempts to define the characteristics of in vivo resistant blasts have focused on comparisons between leukemic cells at presentation and relapse. However, further treatment responses are often seen following relapse, suggesting that most blasts remain chemosensitive. We sought to characterise in vivo chemoresistant blasts by studying the transcriptional and genetic features of blasts from before and shortly after induction chemotherapy using paired samples from six patients with primary refractory AML. Methods: Leukemic blasts were isolated by fluorescence-activated cell sorting. Fluorescence in situ hybridization (FISH), targeted genetic sequencing and detailed immunophenotypic analysis were used to confirm that sorted cells were leukemic. Sorted blasts were subjected to RNA sequencing. Lentiviral vectors expressing short hairpin RNAs were used to assess the effect of FOXM1 knockdown on colony forming capacity, proliferative capacity and apoptosis in cell lines, primary AML cells and CD34+ cells from healthy donors. Results: Molecular genetic analysis revealed early clonal selection occurring after induction chemotherapy. Immunophenotypic characterisation found leukemia-associated immunophenotypes in all cases that persisted following treatment. Despite the genetic heterogeneity of the leukemias studied, transcriptional analysis found concerted changes in gene expression in resistant blasts. Remarkably, the gene expression signature suggested that post-chemotherapy blasts were more proliferative than those at presentation. Resistant blasts also appeared less differentiated and expressed leukemia stem cell (LSC) maintenance genes. However, the proportion of immunophenotypically defined LSCs appeared to decrease following treatment, with implications for the targeting of these cells on the basis of cell surface antigen expression. The refractory gene signature was highly enriched with targets of the transcription factor FOXM1. shRNA knockdown experiments demonstrated that the viability of primary AML cells, but not normal CD34+ cells, depended on FOXM1 expression. Conclusions: We found that chemorefractory blasts from leukemias with varied genetic backgrounds expressed a common transcriptional program. In contrast to the notion that LSC quiescence confers resistance to chemotherapy we find that refractory blasts are both actively proliferating and enriched with LSC maintenance genes. Using primary patient material from a relevant clinical context we also provide further support for the role of FOXM1 in chemotherapy resistance, proliferation and stem cell function in AML

An Open-System Quantum Simulator with Trapped Ions

The control of quantum systems is of fundamental scientific interest and promises powerful applications and technologies. Impressive progress has been achieved in isolating the systems from the environment and coherently controlling their dynamics, as demonstrated by the creation and manipulation of entanglement in various physical systems. However, for open quantum systems, engineering the dynamics of many particles by a controlled coupling to an environment remains largely unexplored. Here we report the first realization of a toolbox for simulating an open quantum system with up to five qubits. Using a quantum computing architecture with trapped ions, we combine multi-qubit gates with optical pumping to implement coherent operations and dissipative processes. We illustrate this engineering by the dissipative preparation of entangled states, the simulation of coherent many-body spin interactions and the quantum non-demolition measurement of multi-qubit observables. By adding controlled dissipation to coherent operations, this work offers novel prospects for open-system quantum simulation and computation.Comment: Pre-review submission to Nature. For an updated and final version see publication. Manuscript + Supplementary Informatio

Key stages in mammary gland development: The mammary end bud as a motile organ

In the rodent, epithelial end buds define the tips of elongating mammary ducts. These highly motile structures undergo repeated dichotomous branching as they aggressively advance through fatty stroma and, turning to avoid other ducts, they finally cease growth leaving behind the open, tree-like framework on which secretory alveoli develop during pregnancy. This review identifies the motility of end buds as a unique developmental marker that represents the successful integration of systemic and local mammotrophic influences, and covers relevant advances in ductal growth regulation, extracellular matrix (ECM) remodeling, and cell adhesion in the inner end bud. An unexpected growth-promoting synergy between insulin-like growth factor-1 and progesterone, in which ducts elongate without forming new end buds, is described as well as evidence strongly supporting self-inhibition of ductal elongation by end-bud-secreted transforming growth factor-β acting on stromal targets. The influence of the matrix metalloproteinase ECM-remodeling enzymes, notably matrix metalloproteinase-2, on end bud growth is discussed in the broader context of enzymes that regulate the polysaccharide-rich glycosaminoglycan elements of the ECM. Finally, a critical, motility-enabling role for the cellular architecture of the end bud is identified and the contribution of cadherins, the netrin/neogenin system, and ErbB2 to the structure and motility of end buds is discussed