Probing entanglement in a 2D hard-core Bose-Hubbard lattice.

Entanglement and its propagation are central to understanding many physical properties of quantum systems1-3. Notably, within closed quantum many-body systems, entanglement is believed to yield emergent thermodynamic behaviour4-7. However, a universal understanding remains challenging owing to the non-integrability and computational intractability of most large-scale quantum systems. Quantum hardware platforms provide a means to study the formation and scaling of entanglement in interacting many-body systems8-14. Here we use a controllable 4 × 4 array of superconducting qubits to emulate a 2D hard-core Bose-Hubbard (HCBH) lattice. We generate superposition states by simultaneously driving all lattice sites and extract correlation lengths and entanglement entropy across its many-body energy spectrum. We observe volume-law entanglement scaling for states at the centre of the spectrum and a crossover to the onset of area-law scaling near its edges.

Evolution of 1/f Flux Noise in Superconducting Qubits with Weak Magnetic Fields.

The microscopic description of 1/f magnetic flux noise in superconducting circuits has remained an open question for several decades despite extensive experimental and theoretical investigation. Recent progress in superconducting devices for quantum information has highlighted the need to mitigate sources of qubit decoherence, driving a renewed interest in understanding the underlying noise mechanism(s). Though a consensus has emerged attributing flux noise to surface spins, their identity and interaction mechanisms remain unclear, prompting further study. Here, we apply weak in-plane magnetic fields to a capacitively shunted flux qubit (where the Zeeman splitting of surface spins lies below the device temperature) and study the flux-noise-limited qubit dephasing, revealing previously unexplored trends that may shed light on the dynamics behind the emergent 1/f noise. Notably, we observe an enhancement (suppression) of the spin-echo (Ramsey) pure-dephasing time in fields up to B=100 G. With direct noise spectroscopy, we further observe a transition from a 1/f to approximately Lorentzian frequency dependence below 10 Hz and a reduction of the noise above 1 MHz with increasing magnetic field. We suggest that these trends are qualitatively consistent with an increase of spin cluster sizes with magnetic field. These results should help to inform a complete microscopic theory of 1/f flux noise in superconducting circuits.

Improving qubit coherence using closed-loop feedback.

Superconducting qubits are a promising platform for building a larger-scale quantum processor capable of solving otherwise intractable problems. In order for the processor to reach practical viability, the gate errors need to be further suppressed and remain stable for extended periods of time. With recent advances in qubit control, both single- and two-qubit gate fidelities are now in many cases limited by the coherence times of the qubits. Here we experimentally employ closed-loop feedback to stabilize the frequency fluctuations of a superconducting transmon qubit, thereby increasing its coherence time by 26% and reducing the single-qubit error rate from (8.5 ± 2.1) × 10-4 to (5.9 ± 0.7) × 10-4. Importantly, the resulting high-fidelity operation remains effective even away from the qubit flux-noise insensitive point, significantly increasing the frequency bandwidth over which the qubit can be operated with high fidelity. This approach is helpful in large qubit grids, where frequency crowding and parasitic interactions between the qubits limit their performance.

Multi-level quantum noise spectroscopy.

System noise identification is crucial to the engineering of robust quantum systems. Although existing quantum noise spectroscopy (QNS) protocols measure an aggregate amount of noise affecting a quantum system, they generally cannot distinguish between the underlying processes that contribute to it. Here, we propose and experimentally validate a spin-locking-based QNS protocol that exploits the multi-level energy structure of a superconducting qubit to achieve two notable advances. First, our protocol extends the spectral range of weakly anharmonic qubit spectrometers beyond the present limitations set by their lack of strong anharmonicity. Second, the additional information gained from probing the higher-excited levels enables us to identify and distinguish contributions from different underlying noise mechanisms.

Author Correction: Impact of ionizing radiation on superconducting qubit coherence.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Impact of ionizing radiation on superconducting qubit coherence.

Technologies that rely on quantum bits (qubits) require long coherence times and high-fidelity operations1. Superconducting qubits are one of the leading platforms for achieving these objectives2,3. However, the coherence of superconducting qubits is affected by the breaking of Cooper pairs of electrons4-6. The experimentally observed density of the broken Cooper pairs, referred to as quasiparticles, is orders of magnitude higher than the value predicted at equilibrium by the Bardeen-Cooper-Schrieffer theory of superconductivity7-9. Previous work10-12 has shown that infrared photons considerably increase the quasiparticle density, yet even in the best-isolated systems, it remains much higher10 than expected, suggesting that another generation mechanism exists13. Here we provide evidence that ionizing radiation from environmental radioactive materials and cosmic rays contributes to this observed difference. The effect of ionizing radiation leads to an elevated quasiparticle density, which we predict would ultimately limit the coherence times of superconducting qubits of the type measured here to milliseconds. We further demonstrate that radiation shielding reduces the flux of ionizing radiation and thereby increases the energy-relaxation time. Albeit a small effect for today's qubits, reducing or mitigating the impact of ionizing radiation will be critical for realizing fault-tolerant superconducting quantum computers.

Waveguide quantum electrodynamics with superconducting artificial giant atoms.

Models of light-matter interactions in quantum electrodynamics typically invoke the dipole approximation1,2, in which atoms are treated as point-like objects when compared to the wavelength of the electromagnetic modes with which they interact. However, when the ratio between the size of the atom and the mode wavelength is increased, the dipole approximation no longer holds and the atom is referred to as a 'giant atom'2,3. So far, experimental studies with solid-state devices in the giant-atom regime have been limited to superconducting qubits that couple to short-wavelength surface acoustic waves4-10, probing the properties of the atom at only a single frequency. Here we use an alternative architecture that realizes a giant atom by coupling small atoms to a waveguide at multiple, but well separated, discrete locations. This system enables tunable atom-waveguide couplings with large on-off ratios3 and a coupling spectrum that can be engineered by the design of the device. We also demonstrate decoherence-free interactions between multiple giant atoms that are mediated by the quasi-continuous spectrum of modes in the waveguide-an effect that is not achievable using small atoms11. These features allow qubits in this architecture to switch between protected and emissive configurations in situ while retaining qubit-qubit interactions, opening up possibilities for high-fidelity quantum simulations and non-classical itinerant photon generation12,13.

Implementation of the Standards for adult immunization practice: A survey of U.S. Health care providers.

The revised Standards for Adult Immunization Practice ("Standards"), published in 2014, recommend routine vaccination assessment, strong provider recommendation, vaccine administration or referral, and documentation of vaccines administered into immunization information systems (IIS). We assessed clinician and pharmacist implementation of the Standards in the United States from 2016 to 2018. Participating clinicians (family and internal medicine physicians, obstetricians-gynecologists, specialty physicians, physician assistants, and nurse practitioners) and pharmacists responded using an internet panel survey. Weighted proportion of clinicians and pharmacists reporting full implementation of each component of the Standards were calculated. Adjusted prevalence ratio (APR) estimates of practice characteristics associated with self-reported implementation of the Standards are also presented. Across all medical specialties, the percentages of clinicians and pharmacists implementing the vaccine assessment and recommendation components of the Standards were >80.0%. However, due to low IIS documentation, full implementation of the Standards was low overall, ranging from 30.4% for specialty medicine to 45.8% in family medicine clinicians. The presence of an immunization champion (APR, 1.40 [95% confidence interval {CI}, 1.26 to 1.54]), use of standing orders (APR, 1.41 [95% CI, 1.27 to 1.57]), and use of a patient reminder-recall system (APR, 1.39 [95% CI, 1.26 to 1.54]) were positively associated with adherence to the Standards by clinicians. Similar results were observed for pharmacists. Nonetheless, vaccination improvement strategies, i.e., having standing orders in place, empowering an immunization champion, and using patient recall-reminder systems were underutilized in clinical settings; full implementation of the Standards was inconsistent across all health care provider practices.

Non-Gaussian noise spectroscopy with a superconducting qubit sensor.

Accurate characterization of the noise influencing a quantum system of interest has far-reaching implications across quantum science, ranging from microscopic modeling of decoherence dynamics to noise-optimized quantum control. While the assumption that noise obeys Gaussian statistics is commonly employed, noise is generically non-Gaussian in nature. In particular, the Gaussian approximation breaks down whenever a qubit is strongly coupled to discrete noise sources or has a non-linear response to the environmental degrees of freedom. Thus, in order to both scrutinize the applicability of the Gaussian assumption and capture distinctive non-Gaussian signatures, a tool for characterizing non-Gaussian noise is essential. Here, we experimentally validate a quantum control protocol which, in addition to the spectrum, reconstructs the leading higher-order spectrum of engineered non-Gaussian dephasing noise using a superconducting qubit as a sensor. This first experimental demonstration of non-Gaussian noise spectroscopy represents a major step toward demonstrating a complete spectral estimation toolbox for quantum devices.

Defect-Tolerant Plasmonic Elliptical Resonators for Long-Range Energy Transfer.

Energy transfer allows energy to be moved from one quantum emitter to another. If this process follows the Förster mechanism, efficient transfer requires the emitters to be extremely close (<10 nm). To increase the transfer range, nanophotonic structures have been explored for photon- or plasmon-mediated energy transfer. Here, we fabricate high-quality silver plasmonic resonators to examine long-distance plasmon-mediated energy transfer. Specifically, we design elliptical resonators that allow energy transfer between the foci, which are separated by up to 10 µm. The geometry of the ellipse guarantees that all plasmons emitted from one focus are collected and channeled through different paths to the other focus. Thus, energy can be transferred even if a micrometer-sized defect obstructs the direct path between the focal points. We characterize the spectral and spatial profiles of the resonator modes and show that these can be used to transfer energy between green- and red-emitting colloidal quantum dots printed with subwavelength accuracy using electrohydrodynamic nanodripping. Rate-equation modeling of the time-resolved fluorescence from the quantum dots further confirms the long-distance energy transfer.

Advisory Committee on Immunization Practices Recommended Immunization Schedule for Adults Aged 19 Years or Older - United States, 2019.

In October 2018, the Advisory Committee on Immunization Practices (ACIP)* voted to recommend approval of the Recommended Immunization Schedule for Adults, Aged 19 Years or Older, United States, 2019. The 2019 adult immunization schedule, available at https://www.cdc.gov/vaccines/schedules,† summarizes ACIP recommendations in two tables and accompanying notes. The 2019 adult immunization schedule has been approved by the CDC Director, the American College of Physicians, the American Academy of Family Physicians, the American College of Obstetricians and Gynecologists, and the American College of Nurse-Midwives.

Room-Temperature Strong Coupling of CdSe Nanoplatelets and Plasmonic Hole Arrays.

Exciton polaritons are hybrid light-matter quasiparticles that can serve as coherent light sources. Motivated by applications, room-temperature realization of polaritons requires narrow, excitonic transitions with large transition dipoles. Such transitions must then be strongly coupled to an electromagnetic mode confined in a small volume. While much work has explored polaritons in organic materials, semiconductor nanocrystals present an alternative excitonic system with enhanced photostability and spectral tunability. In particular, quasi-two-dimensional nanocrystals known as nanoplatelets (NPLs) exhibit intense, spectrally narrow excitonic transitions useful for polariton formation. Here, we place CdSe NPLs on silver hole arrays to demonstrate exciton-plasmon polaritons at room temperature. Angle-resolved reflection spectra reveal Rabi splittings up to 149 meV for the polariton states. We observe bright, polarized emission arising from the lowest polariton state. Furthermore, we assess the dependence of the Rabi splitting on the hole-array pitch and the number N of NPLs. While the pitch determines the in-plane momentum for which strong coupling is observed, it does not affect the size of the splitting. The Rabi splitting first increases with NPL film thickness before eventually saturating. Instead of the commonly used [Formula: see text] dependence, we develop an analytical expression that includes the transverse confinement of the plasmon modes to describe the measured Rabi splitting as a function of NPL film thickness.

U.S. clinicians' and pharmacists' reported barriers to implementation of the Standards for Adult Immunization Practice.

BACKGROUND: The Standards for Adult Immunization Practice (Standards), revised in 2014, emphasize that adult-care providers assess vaccination status of adult patients at every visit, recommend vaccination, administer needed vaccines or refer to a vaccinating provider, and document vaccinations administered in state/local immunization information systems (IIS). Providers report numerous systems- and provider-level barriers to vaccinating adults, such as billing, payment issues, lower prioritization of vaccines due to competing demands, and lack of information about the use and utility of IIS. Barriers to vaccination result in missed opportunities to vaccinate adults and contribute to low vaccination coverage. Clinicians' (physicians, physician assistants, nurse practitioners) and pharmacists' reported barriers to assessment, recommendation, administration, referral, and documentation, provider vaccination practices, and perceptions regarding their adult patients' attitudes toward vaccines were evaluated. METHODS: Data from non-probability-based Internet panel surveys of U.S. clinicians (n = 1714) and pharmacists (n = 261) conducted in February-March 2017 were analyzed using SUDAAN. Weighted proportion of reported barriers to assessment, recommendation, administration, referral, and documentation in IIS were calculated. RESULTS: High percentages (70.0%-97.4%) of clinicians and pharmacists reported they routinely assessed, recommended, administered, and/or referred adults for vaccination. Among those who administered vaccines, 31.6% clinicians' and 38.4% pharmacists' submitted records to IIS. Reported barriers included: (a) assessment barriers: vaccination of adults is not within their scope of practice, inadequate reimbursement for vaccinations; (b) administration barriers: lack of staff to manage/administer vaccines, absence of necessary vaccine storage and handling equipment and provisions; and (c) documentation barriers: unaware if state/city has IIS that includes adults or not sure how their electronic system would link to IIS. CONCLUSION: Although many clinicians and pharmacists reported implementing most of the individual components of the Standards, with the exception of IIS use, there are discrepancies in providers' reported actual practices and their beliefs/perceptions, and barriers to vaccinating adults remain.

Clinicians' and Pharmacists' Reported Implementation of Vaccination Practices for Adults.

INTRODUCTION: Despite the proven effectiveness of immunization in preventing morbidity and mortality, adult vaccines remain underutilized. The objective of this study was to describe clinicians' and pharmacists' self-reported implementation of the Standards for Adult Immunization Practice ("the Standards"; i.e., routine assessment, recommendation, and administration/referral for needed vaccines, and documentation of administered vaccines, including in immunization information systems). METHODS: Two Internet panel surveys (one among clinicians and one among pharmacists) were conducted during February-March 2017 and asked respondents about their practice's implementation of the Standards. T-tests assessed associations between clinician medical specialty, vaccine type, and each component of the Standards (March-August 2017). RESULTS: Implementation of the Standards varied substantially by vaccine and provider type. For example, >80.0% of providers, including obstetrician/gynecologists and subspecialists, assessed for and recommended influenza vaccine. However, 24.3% of obstetrician/gynecologists and 48.9% of subspecialists did not stock influenza vaccine for administration. Although zoster vaccine was recommended by >89.0% of primary care providers, <58.0% stocked the vaccine; by contrast, 91.6% of pharmacists stocked zoster vaccine. Vaccine needs assessments, recommendations, and stocking/referrals also varied by provider type for pneumococcal; tetanus, diphtheria, acellular pertussis; tetanus diphtheria; human papillomavirus; and hepatitis B vaccines. CONCLUSIONS: This report highlights gaps in access to vaccines recommended for adults across the spectrum of provider specialties. Greater implementation of the Standards by all providers could improve adult vaccination rates in the U.S. by reducing missed opportunities to recommend vaccinations and either vaccinate or refer patients to vaccine providers.

Advisory Committee on Immunization Practices Recommended Immunization Schedule for Adults Aged 19 Years or Older - United States, 2018.

In October 2017, the Advisory Committee on Immunization Practices (ACIP) voted to approve the Recommended Immunization Schedule for Adults Aged 19 Years or Older, United States, 2018. The 2018 adult immunization schedule summarizes ACIP recommendations in two figures and a table of contraindications and precautions for vaccines recommended for adults, and is intended is to assist health care providers in implementing the current ACIP recommendations for vaccinating adults. The schedule can be found at https://www.cdc.gov/vaccines/schedules.* The full ACIP recommendations for each vaccine are available at https://www.cdc.gov/vaccines/hcp/acip-recs/index.html. The 2018 adult immunization schedule has also been approved by the American College of Physicians (https://www.acponline.org), the American Academy of Family Physicians (https://www.aafp.org), the American College of Obstetricians and Gynecologists (https://www.acog.org), and the American College of Nurse-Midwives (http://www.midwife.org). The ACIP-recommended use of each vaccine is developed after an in-depth review of vaccine-related data, including data on disease epidemiology, vaccine efficacy and effectiveness, vaccine safety, feasibility of program implementation, and economic aspects of immunization policy (1).

Photocatalytic Water-Splitting Enhancement by Sub-Bandgap Photon Harvesting.

Upconversion is a photon-management process especially suited to water-splitting cells that exploit wide-bandgap photocatalysts. Currently, such catalysts cannot utilize 95% of the available solar photons. We demonstrate here that the energy-conversion yield for a standard photocatalytic water-splitting device can be enhanced under solar irradiance by using a low-power upconversion system that recovers part of the unutilized incident sub-bandgap photons. The upconverter is based on a sensitized triplet-triplet annihilation mechanism (sTTA-UC) obtained in a dye-doped elastomer and boosted by a fluorescent nanocrystal/polymer composite that allows for broadband light harvesting. The complementary and tailored optical properties of these materials enable efficient upconversion at subsolar irradiance, allowing the realization of the first prototype water-splitting cell assisted by solid-state upconversion. In our proof-of concept device the increase of the performance is 3.5%, which grows to 6.3% if concentrated sunlight (10 sun) is used. Our experiments show how the sTTA-UC materials can be successfully implemented in technologically relevant devices while matching the strict requirements of clean-energy production.

A customizable class of colloidal-quantum-dot spasers and plasmonic amplifiers.

Colloidal quantum dots are robust, efficient, and tunable emitters now used in lighting, displays, and lasers. Consequently, when the spaser-a laser-like source of high-intensity, narrow-band surface plasmons-was first proposed, quantum dots were specified as the ideal plasmonic gain medium for overcoming the significant intrinsic losses of plasmons. Many subsequent spasers, however, have required a single material to simultaneously provide gain and define the plasmonic cavity, a design unable to accommodate quantum dots and other colloidal nanomaterials. In addition, these and other designs have been ill suited for integration with other elements in a larger plasmonic circuit, limiting their use. We develop a more open architecture that decouples the gain medium from the cavity, leading to a versatile class of quantum dot-based spasers that allow controlled generation, extraction, and manipulation of plasmons. We first create aberration-corrected plasmonic cavities with high quality factors at desired locations on an ultrasmooth silver substrate. We then incorporate quantum dots into these cavities via electrohydrodynamic printing or drop-casting. Photoexcitation under ambient conditions generates monochromatic plasmons (0.65-nm linewidth at 630 nm, Q ~ 1000) above threshold. This signal is extracted, directed through an integrated amplifier, and focused at a nearby nanoscale tip, generating intense electromagnetic fields. More generally, our device platform can be straightforwardly deployed at different wavelengths, size scales, and geometries on large-area plasmonic chips for fundamental studies and applications.