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ObjectivesFibroblasts in synovium include fibroblast-like synoviocytes (FLS) in the lining andThy1+ connective-tissue fibroblasts in the sublining. We aimed to investigate their developmental origin and relationship with adult progenitors.MethodsTo discriminate betweenGdf5-lineage cells deriving from the embryonic joint interzone and otherPdgfrα-expressing fibroblasts and progenitors, adultGdf5-Cre;Tom;Pdgfrα-H2BGFPmice were used and cartilage injury was induced to activate progenitors. Cells were isolated from knees, fibroblasts and progenitors were sorted by fluorescence-activated cell-sorting based on developmental origin, and analysed by single-cell RNA-sequencing. Flow cytometry and immunohistochemistry were used for validation. Clonal-lineage mapping was performed usingGdf5-Cre;Confettimice.ResultsIn steady state,Thy1+ sublining fibroblasts were of mixed ontogeny. In contrast,Thy1-Prg4+ lining fibroblasts predominantly derived from the embryonic joint interzone and includedPrg4-expressing progenitors distinct from molecularly defined FLS. Clonal-lineage tracing revealed compartmentalisation ofGdf5-lineage fibroblasts between lining and sublining. Following injury, lining hyperplasia resulted from proliferation and differentiation ofPrg4-expressing progenitors, with additional recruitment of non-Gdf5-lineage cells, into FLS. Consistent with this, a second population of proliferating cells, enriched near blood vessels in the sublining, supplied activated multipotent cells predicted to give rise toThy1+ fibroblasts, and to feed into the FLS differentiation trajectory. Transcriptional programmes regulating fibroblast differentiation trajectories were uncovered, identifying Sox5 and Foxo1 as key FLS transcription factors in mice and humans.ConclusionsOur findings blueprint a cell atlas of mouse synovial fibroblasts and progenitors in healthy and injured knees, and provide novel insights into the cellular and molecular principles governing the organisation and maintenance of adult synovial joints.

The Quantum Scientific Computing Open User Testbed (QSCOUT) at Sandia National Laboratories is a trapped-ion qubit system designed to evaluate the potential of near-term quantum hardware in scientific computing applications for the U.S. Department of Energy and its Advanced Scientific Computing Research program. Similar to commercially available platforms, it offers quantum hardware that researchers can use to perform quantum algorithms, investigate noise properties unique to quantum systems, and test novel ideas that will be useful for larger and more powerful systems in the future. However, unlike most other quantum computing testbeds, the QSCOUT allows both quantum circuit and low-level pulse control access to study new modes of programming and optimization. The purpose of this article is to provide users and the general community with details of the QSCOUT hardware and its interface, enabling them to take maximum advantage of its capabilities.

Most near-term quantum information processing devices will not be capable of implementing quantum error correction and the associated logical quantum gate set. Instead, quantum circuits will be implemented directly using the physical native gate set of the device. These native gates often have a parameterization (e.g., rotation angles) which provide the ability to perform a continuous range of operations. Verification of the correct operation of these gates across the allowable range of parameters is important for gaining confidence in the reliability of these devices. In this work, we demonstrate a procedure for sample-efficient verification of continuously-parameterized quantum gates for small quantum processors of up to approximately 10 qubits. This procedure involves generating random sequences of randomly-parameterized layers of gates chosen from the native gate set of the device, and then stochastically compiling an approximate inverse to this sequence such that executing the full sequence on the device should leave the system near its initial state. We show that fidelity estimates made via this technique have a lower variance than fidelity estimates made via cross-entropy benchmarking. This provides an experimentally-relevant advantage in sample efficiency when estimating the fidelity loss to some desired precision. We describe the experimental realization of this technique using continuously-parameterized quantum gate sets on a trapped-ion quantum processor from Sandia QSCOUT and a superconducting quantum processor from IBM Q, and we demonstrate the sample efficiency advantage of this technique both numerically and experimentally., 29 pages, 12 figures. This manuscript supersedes arXiv:2101.04474

Crosstalk is a leading source of failure in multiqubit quantum information processors. It can arise from a wide range of disparate physical phenomena, and can introduce subtle correlations in the errors experienced by a device. Several hardware characterization protocols are able to detect the presence of crosstalk, but few provide sufficient information to distinguish various crosstalk errors from one another. In this article we describe how gate set tomography, a protocol for detailed characterization of quantum operations, can be used to identify and characterize crosstalk errors in quantum information processors. We demonstrate our methods on a two-qubit trapped-ion processor and a two-qubit subsystem of a superconducting transmon processor., 20 pages, 8 figures, 6 tables

Microfabricated surface ion traps are a principal component of many ion-based quantum information science platforms. The operational parameters of these devices are pushed to the edge of their physical capabilities as the experiments strive for increasing performance. When the applied radio-frequency (RF) voltage is increased excessively, the devices can experience damaging electric discharge events known as RF breakdown. We introduce two novel techniques for in situ detection of RF breakdown, which we implemented while characterizing the breakdown threshold of surface ion traps produced at Sandia National Laboratories. In these traps, breakdown did not always occur immediately after increasing the RF voltage, but often minutes or even hours later. This result is surprising in the context of the suggested mechanisms for RF breakdown in vacuum. Additionally, the extent of visible damage caused by breakdown events increased with the applied voltage. To minimize the probability for damage when RF power is first applied to a device, our results strongly suggest that the voltage should be ramped up over the course of several hours and monitored for breakdown.

There are several accepted surgical treatment options available for carpal tunnel syndrome, thumb carpometacarpal joint (CMC), osteoarthritis (OA), and wrist degenerative joint disease. We sought to obtain the views and preferences from a cohort of certified hand therapists (CHT) and hypothesized that this source may identify differences in procedures that are otherwise widely believed to have clinical equipoise. Five hundred twelve CHTs were surveyed regarding their experience, volume, and referral base along with their subjective assessments and preferences regarding open versus endoscopic carpal tunnel release (CTR), various surgical procedures for CMC OA, and proximal row carpectomy (PRC) versus 4-corner fusion (4-CF). The average CHT surveyed had 15.2 years experience and had a referral base of 7.7 different hand surgeons. Twenty-seven percent of respondents perceived superior pain control and incisional tenderness following open CTR compared to that of endoscopic CTR. However, 68% of CHTs would elect to undergo an open CTR themselves. There was no clear consensus for the optimal reconstructive technique for thumb CMC OA. As compared to that of 4-CF, PRC was thought to result in superior pain control (34 versus 22%), motion (43 versus 18%), and earlier discharge from therapy (32 versus 19%); however, 53% of respondents would prefer a 4-CF for themselves. Hand therapists are intimately involved in the care of surgical patients and provide an educated and unique source for evaluating postoperative outcomes.

The ability to control spins in semiconductors is important in a variety of fields including spintronics and quantum information processing. Due to the potentially fast dephasing times of spins in the solid state [1-3], spin control operating on the picosecond or faster timescale may be necessary. Such speeds, which are not possible to attain with standard electron spin resonance (ESR) techniques based on microwave sources, can be attained with broadband optical pulses. One promising ultrafast technique utilizes single broadband pulses detuned from resonance in a three-level Lambda system [4]. This attractive technique is robust against optical pulse imperfections and does not require a fixed optical reference phase. Here we demonstrate the principle of coherent manipulation of spins theoretically and experimentally. Using this technique, donor-bound electron spin rotations with single-pulse areas exceeding pi/4 and two-pulses areas exceeding pi/2 are demonstrated. We believe the maximum pulse areas attained do not reflect a fundamental limit of the technique and larger pulse areas could be achieved in other material systems. This technique has applications from basic solid-state ESR spectroscopy to arbitrary single-qubit rotations [4, 5] and bang-bang control[6] for quantum computation., 15 pages, 4 figures, submitted 12/2008. Since the submission of this work we have become aware of related work: J. Berezovsky, M. H. Mikkelsen, N. G. Stoltz, L. A. Coldren, and D. D. Awschalom, Science 320: 349-352 (2008)

Using an ensemble of ions to register one qubit each, the so-called trapped ion quantum computer could serve as a universal computing machine, with the advantages in speed and power that a quantum device could bring. However, actually making a suitably large trap is far from trivial. The authors microfabricate a ring-shaped ion trap and demonstrate its storage of 400 evenly spaced calcium ions. Its circularly symmetric trapping potential furthermore enables fundamental experiments on e.g. simulated Hawking radiation or the Aharonov-Bohm effect.

We report on an all-optical switch that operates at low light levels. It consists of laser beams counterpropagating through a warm rubidium vapor that induce an off-axis optical pattern. A switching laser beam causes this pattern to rotate even when the power in the switching beam is much lower than the power in the pattern. The observed switching energy density is very low, suggesting that the switch might operate at the single-photon level with system optimization. This approach opens the possibility of realizing a single-photon switch for quantum information networks and for improving transparent optical telecommunication networks., Comment: 20 pages, 6 figures; published in Science; http://www.sciencemag.org/cgi/content/short/308/5722/672

Here we give details of an experiment using trapped ions and photons that demonstrates a Bell inequality violation with a Bell signal of S = 2.22±0.07. This type of experimental setup has the potential to close both the detection and locality loopholes and could serve as a fundamental verification of quantum mechanics. I give a survey of the modifications needed, including down-conversion of emitted photons to wavelengths that travel with low-loss in fibers, and increasing the photon-collection efficiency by using high numerical aperture optics or an optical cavity.

Trapped ions entangled via photonic interactions are promising avenues for quan-tum information processing. Here, we report advances towards combining photonic gates be-tween distant ions with Coulombic gates between nearby ions to demonstrate scalable quantum networks.

Spin-based quantum computing and magnetic resonance techniques rely on the ability to measure the coherence time, T 2 , of a spin system. We report on the experimental implementation of all-optical spin echo to determine the T 2 time of a semiconductor electron-spin system. We use three ultrafast optical pulses to rotate spins an arbitrary angle and measure an echo signal as the time between pulses is lengthened. Unlike previous spin-echo techniques using microwaves, ultrafast optical pulses allow clean T 2 measurements of systems with dephasing times (T * 2 ) fast in comparison to the timescale for microwave control. We measure a 7 μs coherence time, which is similar to previous measurements in quantum dots and indicates that nuclear spin diffusion is the primary mechanism for decoherence. This demonstration is a critical step towards optical, dynamic decoupling, which can eliminate fast decoherence and can be integrated into quantum computer architectures based on opticallycontrolled spin qubits.

We report on the optical investigation of single electron spins bound to fluorine donor impurities in ZnSe. Measurements of photon antibunching establish the presence of single, isolated optical emitters, and magneto-optical studies are consistent with the presence of an exciton bound to the spin-impurity complex. The isolation of this single donor-bound exciton complex and its potential homogeneity offer promising prospects for a scalable semiconductor qubit with an optical interface., Comment: 3.1 pages, 3 figures

Spin-based quantum computing and magnetic resonance techniques rely on the ability to measure the coherence time, T2, of a spin system. We report on the experimental implementation of all-optical spin echo to determine the T2 time of a semiconductor electron-spin system. We use three ultrafast optical pulses to rotate spins an arbitrary angle and measure an echo signal as the time between pulses is lengthened. Unlike previous spin-echo techniques using microwaves, ultrafast optical pulses allow clean T2 measurements of systems with dephasing times T2* fast in comparison to the timescale for microwave control. This demonstration provides a step toward ultrafast optical dynamic decoupling of spin-based qubits., 4 pages, 3 figures

This paper utilizes data from the 1981 Canadian Time Use Pilot Study and from a small Halifax time-budget study to look at subjective and contextual dimensions of leisure for women and men. The Canadian study (n=2685) had information on the time spent in daily activities as well as on the settings and social contexts of those activities. The Halifax study included similar time-budget information on 60 married couples, but also incorporated subjective ratings of all diary events in terms of perceived work or leisure. Using subjective weightings from the Halifax study, estimates of subjective leisure were made for different categories of daily activity and for different Canadian population subgroups. Hypercodes were used to look at the effect of social roles on leisure time, and the AID procedure was used to analyze the contextual dimensions of leisure for men and women. The results show that objective activity and well as subjective leisure vary by population subgroup. Constraints to leisure include being female, being employed, having children, and, to some degree, being married. Of the contextual dimensions, subjective leisure was shown to be influenced primarily by type of objective activity. Location, time of day and day of the week also influenced leisure designations, but to a lesser extent. This study suggests the potential usefulness of subjective weightings of activities in order to gain a greater understanding of leisure patterns and participation.

We describe a fast quantum computer based on optically controlled electron spins in charged quantum dots that are coupled to microcavities. This scheme uses broad-band optical pulses to rotate electron spins and provide the clock signal to the system. Non-local two-qubit gates are performed by phase shifts induced by electron spins on laser pulses propagating along a shared waveguide. Numerical simulations of this scheme demonstrate high-fidelity single-qubit and two-qubit gates with operation times comparable to the inverse Zeeman frequency., 4 pages, 4 figures, introduction is clarified, the section on two-qubit gates was expanded and much more detail about gate fidelities is given, figures were modified, one figure replaced with a figure showing gate fidelities for relevant parameters

We observe millisecond spin-flip relaxation times of donor-bound electrons in high-purity n-GaAs . This is three orders of magnitude larger than previously reported lifetimes in n-GaAs . Spin-flip times are measured as a function of magnetic field and exhibit a strong power-law dependence for fields greater than 4 T . This result is in qualitative agreement with previously reported theory and measurements of electrons in quantum dots., 4 pages, 4 figures

Photonic circuits require elements that can control optical signals with other optical signals. Ultra-low-light-level operation of all-optical switches opens the possibility of photonic devices that operate in the single-quantum regime, a prerequisite for quantum-photonic devices. We describe a new type of all-optical switch that exploits the extreme sensitivity to small perturbations displayed by instability-generated dissipative optical patterns. Such patterns, when controlled by applied perturbations, enable control of microwatt-power-level output beams by an input beam that is over 600 times weaker. In comparison, essentially all experimental realizations of light-by-light switching have been limited to controlling weak beams with beams of either comparable or higher power, thus limiting their implementation in cascaded switching networks or computation machines. Furthermore, current research suggests that the energy density required to actuate an all-optical switch is of the order of one photon per optical cross section. Our measured switching energy density of ~4.4 × 10 -2 photons per cross section suggests that our device can operate at the single-photon level with modest system improvement.

Implementations of quantum information processing systems based on optically controlled electron spins in semiconductor quantum dots are particulary appealing due to several features. These features include inherent ultrafast gate operation times, reasonably long decoherence times, small optical control power and a natural ability to link to optical fiber communication networks. We will discuss the current state of the art in the experimental implementations of the main elements of semiconductor spin qubits: qubit initialization, single-qubit gates, two-qubit gates, entanglement distribution, projective measurement, quantum memory and indistinguishable single-photon generation.

Les AA. etudient les facteurs qui influencent le niveau de participation orale des etudiants dans le cadre des cours dispenses dans l'enseignement superieur. Ils interessent plus particulierement au sexe et a l'âge des etudiants. Ils presentent un certain nombre de donnees collectees en 1993, au sein d'une universite americaine, concernant differents types de cours, differentes disciplines. Ils etudient les motifs de non-participation des etudiants

Albino rats with neocortical-septal lesions exhibited the sustained emotionality following a three week recovery period that has been observed in hooded Ss. The maintenance of this behavior could not be accounted for in terms of locus or laterality of the neocortical lesion.

The Office of Medical Applications of Research of the National Institutes of Health conducted a survey to evaluate the effectiveness of mass mailing of consensus statements as compared with traditional dissemination methods. The consensus statement on osteoporosis, published earlier in JAMA , was selected for study. Physicians (N=695) within each of five relevant specialties in two comparable metropolitan areas were surveyed. Findings suggest that while a small but significant increase of awareness resulted from direct mailing, this increase should be weighed against costs and effectiveness of other methods. ( JAMA 1986;255:1328-1330)