Dielectric loss from two-level states is shown to be a dominant decoherence source in superconducting quantum bits. Depending on the qubit design, dielectric loss from insulating materials or the tunnel junction can lead to short coherence times. We show that a variety of microwave and qubit measurements are well modeled by loss from resonant absorption of two-level defects. Our results demonstrate that this loss can be significantly reduced by using better dielectrics and fabricating junctions of small area . With a redesigned phase qubit employing low-loss dielectrics, the energy relaxation rate has been improved by a factor of 20, opening up the possibility of multiqubit gates and algorithms.

Intracellular transport via the microtubule motors kinesin and dynein plays an important role in maintaining cell structure and function. Often, multiple kinesin or dynein motors move the same cargo. Their collective function depends critically on the single motors' detachment kinetics under load, which we experimentally measure here. This experimental constraint-combined with other experimentally determined parameters-is then incorporated into theoretical stochastic and mean-field models. Comparison of modeling results and in vitro data shows good agreement for the stochastic, but not mean-field, model. Many cargos in vivo move bidirectionally, frequently reversing course. Because both kinesin and dynein are present on the cargos, one popular hypothesis explaining the frequent reversals is that the opposite-polarity motors engage in unregulated stochastic tugs-of-war. Then, the cargos' motion can be explained entirely by the outcome of these opposite-motor competitions. Here, we use fully calibrated stochastic and mean-field models to test the tug-of-war hypothesis. Neither model agrees well with our in vivo data, suggesting that, in addition to inevitable tugs-of-war between opposite motors, there is an additional level of regulation not included in the models. Bidirectional motion of subcellular cargos such as mRNA particles, virus particles, endosomes, and lipid droplets is quite common (1), driven by plus-end kinesin and minus-end dynein. Bidirectional motion emerges when frequent switches occur between travel directions, and travel direction reflects which motor (s) dominates. Cells can regulate the switching frequency to control "net" transport, but the physical mechanism(s) underlying this control remains open. Two mechanisms have been proposed. The first suggests that plus-end and minus-end motors always engage in stochastic unregulated tugs-of-war, and overall cargo motion is explained by the outcomes of these mechanical tugsof-war. This model was proposed theoretically to explain lipiddroplet motion (2) but has been adopted to explain endosome motion (3,4). An alternative model suggests that in addition to competition between opposite-polarity motors, there is a "switch" mechanism or mechanisms that achieve further coordination between the motors. Such regulation may be dynamic (5), static (6), or a combination of the two. The crucial question is this: Can tug-of-war models, which exclusively consider cargos with fixed distributions of motors moving along microtubules unaffected by regulatory pathways, explain the characteristics of motility in vivo? Alternatively, are there significant motility characteristics not captured by tug-of-war models, pointing to a richer transport subsystem with important regulatory contributions?There are two theoretical approaches to modeling collective motor transport. The mean-field approach (Fig. 1A) assumes all engaged motors share load equally (7). The stochastic model (Fig. 1B) simulates individual motors going through their mechanochemical cycle (8), where each mo...

Actin dynamics are required for proper cilia spacing, global coordination of cilia polarity, and coordination of metachronic cilia beating, whereas cytoplasmic microtubule dynamics are required for local coordination of polarity between neighboring cilia.

Planar cell polarity (PCP) is a property of epithelial tissues where cellular structures coordinately orient along a two-dimensional plane lying orthogonal to the axis of apical-basal polarity. PCP is particularly striking in tissues where multiciliate cells generate a directed fluid flow, as seen, for example, in the ciliated epithelia lining the respiratory airways or the ventricles of the brain. To produce directed flow, ciliated cells orient along a common planar axis in a direction set by tissue patterning, but how this is achieved in any ciliated epithelium is unknown. Here, we show that the planar orientation of Xenopus multiciliate cells is disrupted when components in the PCP-signaling pathway are altered non-cell-autonomously. We also show that wild-type ciliated cells located at a mutant clone border reorient toward cells with low Vangl2 or high Frizzled activity and away from those with high Vangl2 activity. These results indicate that the PCP pathway provides directional non-cell-autonomous cues to orient ciliated cells as they differentiate, thus playing a critical role in establishing directed ciliary flow.

Magnetic flux noise is a dominant source of dephasing and energy relaxation in superconducting qubits. The noise power spectral density varies with frequency as 1/f α with α ∼ < 1 and spans 13 orders of magnitude. Recent work indicates that the noise is from unpaired magnetic defects on the surfaces of the superconducting devices. Here, we demonstrate that adsorbed molecular O2 is the dominant contributor to magnetism in superconducting thin films. We show that this magnetism can be suppressed by appropriate surface treatment or improvement in the sample vacuum environment. We observe a suppression of static spin susceptibility by more than an order of magnitude and a suppression of 1/f magnetic flux noise power spectral density by more than a factor of 5. These advances open the door to realization of superconducting qubits with improved quantum coherence.A quantum computer will allow efficient solutions for certain problems that are intractable on conventional, classical computers, including factoring and quantum simulation. Superconducting quantum bits ("qubits") based on Josephson junctions are a leading candidate for scalable quantum information processing in the solid state [1, 2]. Gate and measurement operations have attained a level of fidelity that should enable quantum error correction [3, 4], and there is interest in scaling to larger systems [5, 6]. However, qubit performance is limited by dephasing [7,8]. The dominant source of dephasing is low-frequency 1/f magnetic flux noise [9][10][11]. Uncontrolled variation of the flux bias of the qubit leads to the accumulation of spurious phase during periods of free evolution, resulting in a rapid decay of qubit coherence. Magnetic flux noise was first identified in the 1980s [12,13]. Efforts to avoid flux noise include operation at a "sweet spot" where the device is insensitive to first order to magnetic flux fluctuations [14], or elimination of superconducting loops that allow the frequency of the qubit to be tuned in situ [15]. However, restriction to fixedfrequency qubits results in longer gate times, and static disorder in the junction critical currents makes it difficult to target specific frequencies, leading to frequency clashes in larger multiqubit circuits. In the context of a quantum annealer [16,17], flux noise degrades performance by limiting the number of qubits that can tunnel coherently. For these reasons, there is strong motivation to understand and eliminate the flux noise.Recent experiments indicate that there is a high density of unpaired surface spins in superconducting integrated circuits [18] and it is believed that fluctuations of * Present address: Northrop Grumman Corporation, Linthicum, Maryland 21203, USA † Electronic address: rfmcdermott@wisc.edu these spins give rise to the 1/f flux noise [19][20][21]. There is experimental evidence that interactions between the surface spins are significant [22]. To date, however, there has been no experimental data pointing toward the microscopic nature of the surface magnetic defects, althou...

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The advent of immune-checkpoint inhibitors (ICI) in modern oncology has significantly improved survival in several cancer settings. A subgroup of women with breast cancer (BC) has immunogenic infiltration of lymphocytes with expression of programmed death-ligand 1 (PD-L1). These patients may potentially benefit from ICI targeting the programmed death 1 (PD-1)/PD-L1 signaling axis. The use of tumor-infiltrating lymphocytes (TILs) as predictive and prognostic biomarkers has been under intense examination. Emerging data suggest that TILs are associated with response to both cytotoxic treatments and immunotherapy, particularly for patients with triple-negative BC. In this review from The International Immuno-Oncology Biomarker Working Group, we discuss (a) the biological understanding of TILs, (b) their analytical and clinical validity and efforts toward the clinical utility in BC, and (c) the current status of PD-L1 and TIL testing across different continents, including experiences from low-to-middle-income countries, incorporating also the view of a patient advocate. This information will help set the stage for future approaches to optimize the understanding and clinical utilization of TIL analysis in patients with BC.

We have studied the one-dimensional Kondo chain at half filling using a density matrix formulation of the numerical renormalization group. The charge gap is larger than the spin gap for all antiferromagnetic values of the exchange coupling J. A new type of excitation, a neutral spin singlet, consists of a particle and a hole which are repulsive for J^5t and attractive for J^5t. As /-* 0, RKKY interactions become more important and the staggered susceptibility #(