Quantum simulation of conical intersections using trapped ions.

Conical intersections often control the reaction products of photochemical processes and occur when two electronic potential energy surfaces intersect. Theory predicts that the conical intersection will result in a geometric phase for a wavepacket on the ground potential energy surface, and although conical intersections have been observed experimentally, the geometric phase has not been directly observed in a molecular system. Here we use a trapped atomic ion system to perform a quantum simulation of a conical intersection. The ion's internal state serves as the electronic state, and the motion of the atomic nuclei is encoded into the motion of the ions. The simulated electronic potential is constructed by applying state-dependent optical forces to the ion. We experimentally observe a clear manifestation of the geometric phase using adiabatic state preparation followed by motional state measurement. Our experiment shows the advantage of combining spin and motion degrees for quantum simulation of chemical reactions.

Quantum Simulation of Polarized Light-Induced Electron Transfer with a Trapped-Ion Qutrit System.

Electron transfer within and between molecules is crucial in chemistry, biochemistry, and energy science. This study describes a quantum simulation method that explores the influence of light polarization on electron transfer between two molecules. By implementing precise and coherent control among the quantum states of trapped atomic ions, we can induce quantum dynamics that mimic the electron-transfer dynamics in molecules. We use three-level systems (qutrits), rather than traditional two-level systems (qubits), to enhance the simulation efficiency and realize high-fidelity simulations of electron-transfer dynamics. We treat the quantum interference between the electron coupling pathways from a donor with two degenerate excited states to an acceptor and analyze the transfer efficiency. We also examine the potential error sources that enter the quantum simulations. The trapped-ion systems have favorable scalings with system size compared to those of classical computers, promising access to richer electron-transfer simulations.

Crosstalk Suppression in Individually Addressed Two-Qubit Gates in a Trapped-Ion Quantum Computer.

Crosstalk between target and neighboring spectator qubits due to spillover of control signals represents a major error source limiting the fidelity of two-qubit entangling gates in quantum computers. We show that in our laser-driven trapped-ion system coherent crosstalk error can be modeled as residual Xσ[over ^]_{ϕ} interaction and can be actively canceled by single-qubit echoing pulses. We propose and demonstrate a crosstalk suppression scheme that eliminates all first-order crosstalk utilizing only local control of target qubits, as opposed to an existing scheme which requires control over all neighboring qubits. We report a two-qubit Bell state fidelity of 99.52(6)% with the echoing pulses applied after collective gates and 99.37(5)% with the echoing pulses applied to each gate in a five-ion chain. This scheme is widely applicable to other platforms with analogous interaction Hamiltonians.

Determination of Multimode Motional Quantum States in a Trapped Ion System.

Trapped atomic ions are a versatile platform for studying interactions between spins and bosons by coupling the internal states of the ions to their motion. Measurement of complex motional states with multiple modes is challenging, because all motional state populations can only be measured indirectly through the spin state of ions. Here we present a general method to determine the Fock state distributions and to reconstruct the density matrix of an arbitrary multimode motional state. We experimentally verify the method using different entangled states of multiple radial modes in a five-ion chain. This method can be extended to any system with Jaynes-Cummings-type interactions.

High-Fidelity Two-Qubit Gates Using a Microelectromechanical-System-Based Beam Steering System for Individual Qubit Addressing.

In a large scale trapped atomic ion quantum computer, high-fidelity two-qubit gates need to be extended over all qubits with individual control. We realize and characterize high-fidelity two-qubit gates in a system with up to four ions using radial modes. The ions are individually addressed by two tightly focused beams steered using microelectromechanical system mirrors. We deduce a gate fidelity of 99.49(7)% in a two-ion chain and 99.30(6)% in a four-ion chain by applying a sequence of up to 21 two-qubit gates and measuring the final state fidelity. We characterize the residual errors and discuss methods to further improve the gate fidelity towards values that are compatible with fault-tolerant quantum computation.

Prognostic Factors Affecting Clinical Outcomes of Arthroscopic Assisted Reduction and Volar Plating through Preservation of Pronator Quadratus for Intra-Articular Distal Radius Fracture.

Background: This study aimed to evaluate the clinical and radiological outcomes following an arthroscopic-assisted reduction and volar plating (AR-VP) surgery through pronator quadratus (PQ) preservation for treating intra-articular distal radius fractures (IA-DRFs) and to assess prognostic factors that affect functional outcomes. Methods: Between March 2014 and February 2017, 54 patients who had intra-articular DRF and underwent AR-VP through the PQ preservation technique and completed 1-year follow-up were enrolled. Patients were divided into the satisfactory group (excellent and good results) and an unsatisfactory group (fair and poor results) based on the modified Mayo Wrist Scoring System (MMWS) scored at 1-year follow-up to determinate prognostic factors that affected clinical outcomes. Patients' demographics, clinical outcome measures (VAS, DASH, PRWE, etc.), and pre-and post-operative radiographic parameters were analyzed. Results: The outcomes according to MMWS were 10 excellent, 22 good, 14 fair, and 8 poor. A univariate analysis showed a significant difference between the groups (p < .05) for all radiographic parameters, sex, and the presence of an intra-articular comminution. In the multivariate analysis, female gender, presence of an intra-articular comminution, and difference of palmar articular tilt compared to uninjured wrist (> 20.1°) at trauma were considered as significant poor prognostic factors of functional outcome. Conclusions: AR-VP surgery through PQ preservation for intra-articular DRFs has reliable clinical and radiological outcomes. However, female gender, presence of an intra-articular comminution, and difference of palmar articular tilt compared to the uninjured wrist (> 20.1°) at initial injury were considered poor prognostic factors for AR-VP through PQ preservation for intra-articular DRF.

Efficient isotope-selective pulsed laser ablation loading of 174Yb+ ions in a surface electrode trap.

We report a highly efficient loading of 174Yb+ ions in a surface electrode ion trap by using single pulses from a Q-switched Nd:YAG laser to ablate neutral atoms, combined with a two-photon photo-ionization process. The method is three orders of magnitude faster to load a single ion as compared to traditional resistively heated sources and can load large collections of ions in seconds. The negligible thermal load of this method enables the use of this ablation-based loading scheme in ion traps operating under cryogenic conditions.

Bounding the outcome of a two-photon interference measurement using weak coherent states.

The interference of two photons at a beam splitter is at the core of many quantum photonic technologies, such as quantum key distribution or linear-optics quantum computing. Observing high-visibility interference is challenging because of the difficulty of realizing indistinguishable single-photon sources. Here, we perform a two-photon interference experiment using phase-randomized weak coherent states with different mean photon numbers. We place a tight upper bound on the expected coincidences for the case when the incident wavepackets contain single photons, allowing us to observe the Hong-Ou-Mandel effect. We find that the interference visibility is at least as large as 0.995-0.013+0.005.

Scalable cryogenic readout circuit for a superconducting nanowire single-photon detector system.

The superconducting nanowire single-photon detector (SNSPD) is a leading technology for quantum information science applications using photons, and is finding increasing uses in photon-starved classical imaging applications. Critical detector characteristics, such as timing resolution (jitter), reset time, and maximum count rate, are heavily influenced by the readout electronics that sense and amplify the photon detection signal. We describe a readout circuit for SNSPDs using commercial off-the-shelf amplifiers operating at cryogenic temperatures. Our design demonstrates a 35 ps timing resolution and a maximum count rate of over 2 × 107 counts per second, while maintaining <3 mW power consumption per channel, making it suitable for a multichannel readout.

Provably secure and high-rate quantum key distribution with time-bin qudits.

The security of conventional cryptography systems is threatened in the forthcoming era of quantum computers. Quantum key distribution (QKD) features fundamentally proven security and offers a promising option for quantum-proof cryptography solution. Although prototype QKD systems over optical fiber have been demonstrated over the years, the key generation rates remain several orders of magnitude lower than current classical communication systems. In an effort toward a commercially viable QKD system with improved key generation rates, we developed a discrete-variable QKD system based on time-bin quantum photonic states that can generate provably secure cryptographic keys at megabit-per-second rates over metropolitan distances. We use high-dimensional quantum states that transmit more than one secret bit per received photon, alleviating detector saturation effects in the superconducting nanowire single-photon detectors used in our system that feature very high detection efficiency (of more than 70%) and low timing jitter (of less than 40 ps). Our system is constructed using commercial off-the-shelf components, and the adopted protocol can be readily extended to free-space quantum channels. The security analysis adopted to distill the keys ensures that the demonstrated protocol is robust against coherent attacks, finite-size effects, and a broad class of experimental imperfections identified in our system.

Design and characterization of an integrated surface ion trap and micromirror optical cavity.

We have fabricated and characterized laser-ablated micromirrors on fused silica substrates for constructing stable Fabry-Perot optical cavities. We highlight several design features which allow these cavities to have lengths in the 250-300 µm range and be integrated directly with surface ion traps. We present a method to calculate the optical mode shape and losses of these micromirror cavities as functions of cavity length and mirror shape, and confirm that our simulation model is in good agreement with experimental measurements of the intracavity optical mode at a test wavelength of 780 nm. We have designed and tested a mechanical setup for dampening vibrations and stabilizing the cavity length, and explore applications for these cavities as efficient single-photon sources when combined with trapped Yb171+ ions.

Optimal architectures for long distance quantum communication.

Despite the tremendous progress of quantum cryptography, efficient quantum communication over long distances (≥ 1000 km) remains an outstanding challenge due to fiber attenuation and operation errors accumulated over the entire communication distance. Quantum repeaters (QRs), as a promising approach, can overcome both photon loss and operation errors, and hence significantly speedup the communication rate. Depending on the methods used to correct loss and operation errors, all the proposed QR schemes can be classified into three categories (generations). Here we present the first systematic comparison of three generations of quantum repeaters by evaluating the cost of both temporal and physical resources, and identify the optimized quantum repeater architecture for a given set of experimental parameters for use in quantum key distribution. Our work provides a roadmap for the experimental realizations of highly efficient quantum networks over transcontinental distances.

Correlation of clinical symptoms and function with fatty degeneration of infraspinatus in rotator cuff tear.

PURPOSE: The aim of this study was to analyse the correlation of clinical symptoms and function with the fatty degeneration of the infraspinatus in rotator cuff tears. METHODS: A total of 152 patients who had rotator cuff tears was enroled retrospectively. The infraspinatus muscle was divided into two compartments according to the bundle of fibres, and the patients were divided into four groups that reflected fatty degeneration. The muscle strength of the shoulder and clinical symptoms was investigated. RESULTS: The severity of the rotator cuff tear and retraction increased with fatty degeneration of both the superior and inferior parts in the infraspinatus muscles. Because of the increasing fatty degeneration of the superior part of the infraspinatus, the shoulder strength index (SSI) of abduction had poor results. Additionally, as the fatty degeneration of the inferior part of the infraspinatus increased, the SSI of abduction and external rotation had worse results. CONCLUSIONS: Fatty degeneration of the superior part of the infraspinatus has no correlation with the power of external rotation but has a negative correlation with the power of abduction. Moreover, fatty degeneration of the inferior part of the infraspinatus has a negative correlation with both the power of abduction and external rotation. LEVEL OF EVIDENCE: Retrospective study, Level IV.

Ultrafast and fault-tolerant quantum communication across long distances.

Quantum repeaters (QRs) provide a way of enabling long distance quantum communication by establishing entangled qubits between remote locations. In this Letter, we investigate a new approach to QRs in which quantum information can be faithfully transmitted via a noisy channel without the use of long distance teleportation, thus eliminating the need to establish remote entangled links. Our approach makes use of small encoding blocks to fault-tolerantly correct both operational and photon loss errors. We describe a way to optimize the resource requirement for these QRs with the aim of the generation of a secure key. Numerical calculations indicate that the number of quantum memory bits at each repeater station required for the generation of one secure key has favorable polylogarithmic scaling with the distance across which the communication is desired.

Novel synthetic methodology for controlling the orientation of zinc oxide nanowires grown on silicon oxide substrates.

This study presents a simple method to reproducibly obtain well-aligned vertical ZnO nanowire arrays on silicon oxide (SiOx) substrates using seed crystals made from a mixture of ammonium hydroxide (NH4OH) and zinc acetate (Zn(O2CCH3)2) solution. In comparison, high levels of OH(-) concentration obtained using NaOH or KOH solutions lead to incorporation of Na or K atoms into the seed crystals, destroying the c-axis alignment of the seeds and resulting in the growth of misaligned nanowires. The use of NH4OH eliminates the metallic impurities and ensures aligned nanowire growth in a wide range of OH(-) concentrations in the seed solution. The difference of crystalline orientations between NH4OH- and NaOH-based seeds is directly observed by lattice-resolved images and electron diffraction patterns using a transmission electron microscope (TEM). This study obviously suggests that metallic impurities incorporated into the ZnO nanocrystal seeds are one of the factors that generates the misaligned ZnO nanowires. This method also enables the use of silicon oxide substrates for the growth of vertically aligned nanowires, making ZnO nanostructures compatible with widely used silicon fabrication technology.

Optical performance test and validation of microcameras in multiscale, gigapixel imagers.

Wide field-of-view gigapixel imaging systems capable of diffraction-limited resolution and video-rate acquisition have a broad range of applications, including sports event broadcasting, security surveillance, astronomical observation, and bioimaging. The complexity of the system integration of such devices demands precision optical components that are fully characterized and qualified before being integrated into the final system. In this work, we present component and assembly level characterizations of microcameras in our first gigapixel camera, the AWARE-2. Based on the results of these measurements, we revised the optical design and assembly procedures to construct the second generation system, the AWARE-2 Retrofit, which shows significant improvement in image quality.

High speed, high fidelity detection of an atomic hyperfine qubit.

Fast and efficient detection of the qubit state in trapped ion systems is critical for implementing quantum error correction and performing fundamental tests such as a loophole-free Bell test. In this work we present a simple qubit state detection protocol for a (171)Yb+ hyperfine atomic qubit trapped in a microfabricated surface trap, enabled by high collection efficiency of the scattered photons and low background photon count rate. We demonstrate average detection times of 10.5, 28.1, and 99.8 µs, corresponding to state detection fidelities of 99%, 99.856(8)%, and 99.915(7)%, respectively.

Design of a spherical focal surface using close-packed relay optics: erratum.

A coding error was found in calculating the optimal packing distribution of our geodesic array. The error was corrected and the new optimization results in slightly improved packing density. The overall approach and algorithm remain unchanged.

Oversampled triangulation of AWARE-10 monocentric ball lens using an auto-stigmatic microscope.

In our development of multiscale, gigapixel camera architectures, there is a need for an accurate three-dimensional position alignment of large monocentric lenses relative to hemispherical dome structures. In this work we describe a method for estimating the position of the objective lens in our AWARE-10 four-gigapixel camera using the retro-reflected signal of a custom-designed auto-stigmatic microscope. We show that although the physical constraints of the system limit the numerical aperture of the microscope probe beam to around 0.016, which results in poor sensitivity in the axial direction, the lateral sensitivity is more than sufficient to verify that the position of the objective is within optical tolerances.

A testbed for wide-field, high-resolution, gigapixel-class cameras.

The high resolution and wide field of view (FOV) of the AWARE (Advanced Wide FOV Architectures for Image Reconstruction and Exploitation) gigapixel class cameras present new challenges in calibration, mechanical testing, and optical performance evaluation. The AWARE system integrates an array of micro-cameras in a multiscale design to achieve gigapixel sampling at video rates. Alignment and optical testing of the micro-cameras is vital in compositing engines, which require pixel-level accurate mappings over the entire array of cameras. A testbed has been developed to automatically calibrate and measure the optical performance of the entire camera array. This testbed utilizes translation and rotation stages to project a ray into any micro-camera of the AWARE system. A spatial light modulator is projected through a telescope to form an arbitrary object space pattern at infinity. This collimated source is then reflected by an elevation stage mirror for pointing through the aperture of the objective into the micro-optics and eventually the detector of the micro-camera. Different targets can be projected with the spatial light modulator for measuring the modulation transfer function (MTF) of the system, fiducials in the overlap regions for registration and compositing, distortion mapping, illumination profiles, thermal stability, and focus calibration. The mathematics of the testbed mechanics are derived for finding the positions of the stages to achieve a particular incident angle into the camera, along with calibration steps for alignment of the camera and testbed coordinate axes. Measurement results for the AWARE-2 gigapixel camera are presented for MTF, focus calibration, illumination profile, fiducial mapping across the micro-camera for registration and distortion correction, thermal stability, and alignment of the camera on the testbed.