Density-matrix simulation of small surface codes under current and projected experimental noise

We present a full density-matrix simulation of the quantum memory and computing performance of the distance-3 logical qubit Surface-17, following a recently proposed quantum circuit and using experimental error parameters for transmon qubits in a planar circuit QED architecture. We use this simulation to optimize components of the QEC scheme (e.g., trading off stabilizer measurement infidelity for reduced cycle time) and to investigate the benefits of feedback harnessing the fundamental asymmetry of relaxation-dominated error in the constituent transmons. A lower-order approximate calculation extends these predictions to the distance-$5$ Surface-49. These results clearly indicate error rates below the fault-tolerance threshold of surface code, and the potential for Surface-17 to perform beyond the break-even point of quantum memory. At state-of-the-art qubit relaxation times and readout speeds, Surface-49 could surpass the break-even point of computation.Comment: 10 pages + 8 pages appendix, 12 figure

Measurement of the time-temperature dependent dynamic mechanical properties of boron/aluminum composites

A flexural vibration test and associated equipment were developed to accurately measure the low strain dynamic modulus and damping of composite materials from -200 C to over 500 C. The basic test method involves the forced vibration of composite bars at their resonant free-free flexural modes in a high vacuum cryostat furnace. The accuracy of these expressions and the flexural test was verified by dynamic moduli and damping capacity measurements on 50 fiber volume percent boron/aluminum (B/Al) composites vibrating near 2000 Hz. The phase results were summarized to permit predictions of the B/Al dynamic behavior as a function of frequency, temperature, and fiber volume fraction

High temperature dynamic modulus and damping of aluminum and titanium matrix composites

Dynamic modulus and damping capacity property data were measured from 20 to over 500 C for unidirectional B/Al (1100), B/Al (6061), B/SiC/Al (6061), Al2O3/Al, SiC/Ti-6Al-4V, and SiC/Ti composites. The measurements were made under vacuum by the forced vibration of composite bars at free-free flexural resonance near 2000 Hz and at amplitudes below 0.000001. Whereas little variation was observed in the dynamic moduli of specimens with approximately the same fiber content (50 percent), the damping of B/Al composites was found at all temperatures to be significantly greater than the damping of the Al2O3/Al and SiC/Ti composites. For those few situations where slight deviations from theory were observed, the dynamic data were examined for information concerning microstructural changes induced by composite fabrication and thermal treatment. The 270 C damping peak observed in B/Al (6061) composites after heat treatment above 460 C appears to be the result of a change in the 6061 aluminum alloy microstructure induced by interaction with the boron fibers. The growth characteristics of the damping peak suggest its possible value for monitoring fiber strength degration caused by excess thermal treatment during B/Al (6061) fabrication and use

Digital Quantum Rabi and Dicke Models in Superconducting Circuits

We propose the analog-digital quantum simulation of the quantum Rabi and Dicke models using circuit quantum electrodynamics (QED). We find that all physical regimes, in particular those which are impossible to realize in typical cavity QED setups, can be simulated via unitary decomposition into digital steps. Furthermore, we show the emergence of the Dirac equation dynamics from the quantum Rabi model when the mode frequency vanishes. Finally, we analyze the feasibility of this proposal under realistic superconducting circuit scenarios.Comment: 5 pages, 3 figures. Published in Scientific Report

Calculating energy derivatives for quantum chemistry on a quantum computer

Modeling chemical reactions and complicated molecular systems has been proposed as the `killer application' of a future quantum computer. Accurate calculations of derivatives of molecular eigenenergies are essential towards this end, allowing for geometry optimization, transition state searches, predictions of the response to an applied electric or magnetic field, and molecular dynamics simulations. In this work, we survey methods to calculate energy derivatives, and present two new methods: one based on quantum phase estimation, the other on a low-order response approximation. We calculate asymptotic error bounds and approximate computational scalings for the methods presented. Implementing these methods, we perform the world's first geometry optimization on an experimental quantum processor, estimating the equilibrium bond length of the dihydrogen molecule to within 0.014 Angstrom of the full configuration interaction value. Within the same experiment, we estimate the polarizability of the H2 molecule, finding agreement at the equilibrium bond length to within 0.06 a.u. (2% relative error).Comment: 19 pages, 1 page supplemental, 7 figures. v2 - tidied up and added example to appendice

Selective darkening of degenerate transitions for implementing quantum controlled-NOT gates

We present a theoretical analysis of the selective darkening method for implementing quantum controlled-NOT (CNOT) gates. This method, which we recently proposed and demonstrated, consists of driving two transversely-coupled quantum bits (qubits) with a driving field that is resonant with one of the two qubits. For specific relative amplitudes and phases of the driving field felt by the two qubits, one of the two transitions in the degenerate pair is darkened, or in other words, becomes forbidden by effective selection rules. At these driving conditions, the evolution of the two-qubit state realizes a CNOT gate. The gate speed is found to be limited only by the coupling energy J, which is the fundamental speed limit for any entangling gate. Numerical simulations show that at gate speeds corresponding to 0.48J and 0.07J, the gate fidelity is 99% and 99.99%, respectively, and increases further for lower gate speeds. In addition, the effect of higher-lying energy levels and weak anharmonicity is studied, as well as the scalability of the method to systems of multiple qubits. We conclude that in all these respects this method is competitive with existing schemes for creating entanglement, with the added advantages of being applicable for qubits operating at fixed frequencies (either by design or for exploitation of coherence sweet-spots) and having the simplicity of microwave-only operation.Comment: 25 pages, 5 figure

Fresh market tomatoes

"In Missouri, there are opportun' ties for producing and marketing fresh market tomatoes, if growers can achieve high yields of uniformly high quality tomatoes. Resources essential for profitable production are productive land, sufficient water for irrigation, and adequate family labor. Timely and thorough implementation of cultural practices is required through all stages of production."--First page.Arthur E. Gaus, Henry F. DiCarlo, John B. Lower (Department of Horticulture College of Agriculture)New 10/83/10

Metastable oxygen atom detection using rare gas matrices

The use of solid rare gas matrices as detectors of metastable oxygen atoms is investigated. A 100 eV electron beam colliding with N2O target gas is used as the source of O(1S). The parameters considered are surface temperature, time delay of excimer emission and spectral response to O(1S). In all cases, detector sensitivity maximized at temperatures ≤20 K. Krypton was found to provide the most sensitive surface and neon the least

Electron impact dissociation of N2O and CO2 with single particle detection of O(1D2)

Production of metastable O(1D2) atoms following controlled electron impact on N2O and CO2 targets has been studied using a neon rare gas matrix detector operating at a temperature of \u3c20 K. A 100 eV pulsed electron beam was used in conjunction with time-of-flight (TOF) techniques to establish O-atom fragment kinetic energies. Probable dissociation channels are discussed

Clinician Perspectives on Factors Affecting Shared Decision Making about Lung Cancer Screening

Background/Objective. In 2015, the Centers for Medicare and Medicaid Services (CMS) announced coverage for annual lung cancer screening (LCS) with low dose computed tomography (LDCT) for individuals who are 55 to 77 years of age, have \u3e 30 pack years of smoking history, and undergo shared decision making (SDM) prior to screening. Most referrals for LCS are initiated in primary care. Currently, little is known about how primary care physicians view SDM and barriers in practice to SDM about LCS. This study aimed to gather information to help fill these knowledge gaps. Methods. I worked with senior leadership in the Department of Medicine to identify a set of internal medicine physicians at Thomas Jefferson University (TJU) and contacted them via email requesting their participation in an interview about SDM in LCS. I developed an interview guide that included questions about the following: understanding of SDM, perceptions about SDM in LCS, and receptivity to use of an online decision support intervention (DSI). I completed in-person, audio recorded interviews, which were transcribed for analysis. I then analyzed the interview transcripts using NVivo qualitative analysis software. Results. Nine physicians were interviewed from a pool of twenty-three physicians over a period of three weeks. With regards to understanding of SDM, physicians were in agreement that SDM is a joint decision based on a discussion about the risks and benefits of an intervention that considers patient values and medical status. Physician perceptions of SDM in LCS was influenced by patient comorbidities, LCS controversies and complexity, and limited office time. Receptivity to using an online DSI was generally positive and particularly favored its patient education component and easing of physician workload. Conclusions. Observations from this study highlight a common general understanding of SDM, yet mixed approaches to SDM in LCS. Strong support also exists for a DSI that educates patients about LCS and saves physicians time. Future steps include interviewing a set of family medicine physicians to investigate potential differences in viewpoints compared to internal medicine physicians