Robustness of error-suppressing entangling gates in cavity-coupled transmon qubits

Ultracold trapped atomic ions excited into highly energetic Rydberg states constitute a promising platform for scalable quantum information processing. Elementary building blocks for such tasks are high-fidelity and sufficiently fast entangling two-qubit gates, which can be achieved via strong dipole–dipole interactions between microwave-dressed Rydberg ions, as recently demonstrated experimentally (Zhang et al 2020 Nature 580 345). We theoretically investigate the performance of three protocols leading to controlled-phase gate operations. Starting from a microscopic description of Rydberg ions in a linear Paul trap, we derive an effective Hamiltonian that faithfully captures the essential dynamics underlying the gate protocols. We then use an optimization scheme to fine-tune experimentally controllable parameters like laser detuning and Rabi frequency to yield maximal gate fidelity under each studied protocol. We show how non-adiabatic transitions resulting from fast laser driving relative to the characteristic time scales of the system detrimentally affect the fidelity. Despite this, we demonstrate that in the realistic scenario of Rydberg ions with finite radiative lifetimes, optimizing the best found gate protocol enables achievement of fidelities as high as 99.25 % for a gate time of 0.2 μ s . This considerably undercuts entangling gate durations between ground state ions, for which gate times are typically limited by the comparably slower time scales of vibrational modes. Overall, this places trapped Rydberg ions into the regime where fast high-accuracy quantum computing and eventually quantum error correction become possible.

This paper presents a comparative study of proxy-modeling methodology (also known as surrogate modeling or metamodeling) as a computationally cheap alternative to full numerical simulation in assisted history matching, production optimization and forecasting. The study demonstrates the solution space complexity for different simulation models and the applicability of the proxy-models to mimic it. Focus is given to the practical aspects of model construction and to the limitations of which engineers should be aware. Results of stochastic optimization driven by full numerical simulation are compared to the proxy-model solutions in order to demonstrate strengths and weaknesses of each approach and determine desirable areas of application. Several simulation models of different complexity were used to demonstrate the impact of model structure, number of uncertainty parameters and type of problem on simulation model response and on efficiency of proxy-model application. The results are presented for different datasets, proxy-models and simulation model outputs to demonstrate the dependence of the approximation quality on these parameters. The dependence of the proxy-model prediction quality on sampling method, and on uncertainty domain complexity has been revealed. The efficiency of proxy-model application in history matching and production optimization was compared to stochastic optimization with full reservoir simulation. The results of this study have demonstrated that with increasing complexity of the solution space and number of uncertainties, the application of the proxy-modeling methodology is not recommended for history matching. In the history matching case, the use of full reservoir simulations, combined with stochastic search methods, is preferable and, above a certain level of complexity, the only acceptable solution. Nevertheless, proxy-modeling might be a good approach for certain production optimization projects and appropriate tool for forecasting of Hydrocarbons Initially In Place (HCIIP) and oil recovery (OR). This study suggests areas of application for proxy-models and full numerical simulation. It addresses pros and cons of both approaches in reservoir simulation and provides advice for their efficient application.

Rare earth ions in crystals exhibit narrow spectral features and hyperfine-split ground states with exceptionally long coherence times. These features make them ideal platforms for quantum information processing in the solid state. Recently, we reported on the first high-resolution spectroscopy of single ions in yttrium orthosilicate nanocrystals via the transition at a wavelength of 488 nm. Here we show that individual praseodymium ions can also be detected on the more commonly studied transition at 606 nm. In addition, we present the first measurements of the second-order autocorrelation function, fluorescence lifetime, and emission spectra of single ions in this system as well as their polarization dependencies on both transitions. Furthermore, we demonstrate that by a proper choice of the crystallite, one can obtain narrower spectral lines and, thus, resolve the hyperfine levels of the excited state. We expect our results to make single-ion spectroscopy accessible to a larger scientific community.

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Phosphorus donor impurities in silicon are a promising candidate for solid-state quantum computing due to their exceptionally long coherence times and high fidelities. However, individual addressability of exchange coupled donors with separations ~15 nm is challenging. We show that by using atomic precision lithography, we can place a single P donor next to a 2P molecule 16 ± 1 nm apart and use their distinctive hyperfine coupling strengths to address qubits at vastly different resonance frequencies. In particular, the single donor yields two hyperfine peaks separated by 97 ± 2.5 MHz, in contrast to the donor molecule that exhibits three peaks separated by 262 ± 10 MHz. Atomistic tight-binding simulations confirm the large hyperfine interaction strength in the 2P molecule with an interdonor separation of ~0.7 nm, consistent with lithographic scanning tunneling microscopy images of the 2P site during device fabrication. We discuss the viability of using donor molecules for built-in addressability of electron spin qubits in silicon.

In this paper we present full scale numerical simulation of cross-well observations for shale gas exploration. The main technology used in production is based on hydro fracturing, however it is reported as a rule only about 20% of fluid used for fracturing gets back. Thus some fluid remains in the fractures blocking them from gas penetration. On the base of the full scale numerical simulation the principal ability to use time-lapse 3C cross-well observations in order to recover extremely fine variations of the background, including movement of watering zone was shown. Moreover strong diffraction was observed from the gas-water contact which allows to exploit intensively developed approaches of diffracted/scattered waves elimination and imaging to recognize the movement of the contact.

Modeling of active control of microparticles is important in a number of different microfluidic applications, including bioflows and self-assembled structures. We present here a fast method for simulating the dynamics of many particles in complex microgeometries. The method is based on a spatial distribution of finite force multipoles and requires much less resolution than full direct numerical simulations. The numerical formulation is summarized, and examples are given for Stokes flow and low Reynolds number flow in smooth and rough microchannels. Comparisons made with full direct numerical simulations and experiments validate the accuracy and efficiency of the proposed approach.

Herein, micromechanical simulations for three different states of spheroidized steel (C45EC) are conducted under quasi‐static tensile loading based on the actual texture and crystallographic orientation from electron backscatter diffraction (EBSD) data. Data denoising is conducted with MTex (open‐source Toolbox with MATLAB) for cleaning up the EBSD data. Crystal plasticity‐based full phase numerical simulations are performed on these constructed representative volume elements (RVEs) to analyze the local stress and strain evolution in C45EC steels. The local results of the simulations exhibit important insights into deformation evolution influenced by the size and clustering of cementite particles as well as crystallographic orientations of ferrite grains. It is observed that the full phase simulation model helps predict the local microstructural details for overall mechanically improved properties of the steels. Spheroidized steel samples (97%) show the most favorable mechanical response as adequate strain hardening with extended elongation is desired for cold‐working of parts. The current work is another step forward to fine‐tune the microstructural attributes of medium carbon steels for an improved mechanical response.

Electrodes modified with different signal-responsive materials were designed as switchable electrochemical interfaces controlled by various physical or chemical signals. Electrodes with the electrochemical activity switched ON and OFF by light signals were developed using monolayers or thin films of photoisomerizable compounds. Functionalized magnetic particles associated with the electrode surfaces allowed switching processes controlled by an external magnetic field. Electrochemical transformations proceeding at modified electrode surfaces upon application of different potentials were able to switch the interfacial resistance between low and high values, thus affecting electrochemical properties of the surfaces. Electrode surfaces functionalized with materials responding to chemical signals allowed the switching processes controlled by chemical or biochemical inputs. Most of the designed switchable electrode interfaces have very limited possibilities for scaling up the complexity of the information-processing systems associated with the electrode surfaces. Recent advances in unconventional chemical computing and specifically in the design of molecular-based logic systems allow their coupling with switchable electrodes resulting in very sophisticated interfaces for processing chemical information and its transduction into electronic signals. Future applications of the signal-responsive electrodes integrated with the chemical information-processing systems in “smart” chemically controlled biosensors, actuators, and memory units could be envisaged.

We investigate a method for entangling two singlet-triplet qubits in adjacent double quantum dots via capacitive interactions. In contrast to prior work, here we focus on a regime with strong interactions between the qubits. The interplay of the interaction energy and simultaneous large detunings for both double dots gives rise to the double charge resonant regime, in which the unpolarized (1111) and fully polarized (0202) four-electron states in the absence of interqubit tunneling are near degeneracy, while being energetically well-separated from the partially polarized (0211 and 1102) states. A rapid controlled-phase gate may be realized by combining time evolution in this regime in the presence of intraqubit tunneling and the interqubit Coulomb interaction with refocusing ${\pi}$ pulses that swap the singly occupied singlet and triplet states of the two qubits via, e.g., magnetic gradients. We calculate the fidelity of this entangling gate, incorporating models for two types of noise -- charge fluctuations in the single-qubit detunings and charge relaxation within the low-energy subspace via electron-phonon interaction -- and identify parameter regimes that optimize the fidelity. The rates of phonon-induced decay for pairs of GaAs or Si double quantum dots vary with the sizes of the dipolar and quadrupolar contributions and are several orders of magnitude smaller for Si, leading to high theoretical gate fidelities for coupled singlet-triplet qubits in Si dots. We also consider the dependence of the capacitive coupling on the relative orientation of the double dots and find that a linear geometry provides the fastest potential gate.

Arrays of identical and individually addressable qubits lay the foundation for the creation of scalable quantum hardware such as quantum processors and repeaters. Silicon-vacancy (SiV) centers in diamond offer excellent physical properties such as low inhomogeneous broadening, fast photon emission, and a large Debye–Waller factor. The possibility for all-optical ultrafast manipulation and techniques to extend the spin coherence times makes them promising candidates for qubits. Here, we have developed arrays of nanopillars containing single (SiV) centers with high yield, and we demonstrate ultrafast all-optical complete coherent control of the excited state population of a single SiV center at the optical transition frequency. The high quality of the chemical vapor deposition (CVD) grown SiV centers provides excellent spectral stability, which allows us to coherently manipulate and quasi-resonantly read out the excited state population of individual SiV centers on picosecond timescales using ultrafast optical pulses. Furthermore, this work opens new opportunities to create a scalable on-chip diamond platform for quantum information processing and scalable nanophotonics applications.

Individual neutral atoms excited to Rydberg states are a promising platform for quantum simulation and quantum information processing. However, experimental progress to date has been limited by short coherence times and relatively low gate fidelities associated with such Rydberg excitations. We report progress towards high-fidelity quantum control of Rydberg-atom qubits. Enabled by a reduction in laser phase noise, our approach yields a significant improvement in coherence properties of individual qubits. We further show that this high-fidelity control extends to the multi-particle case by preparing a two-atom entangled state with a fidelity exceeding 0.97(3), and extending its lifetime with a two-atom dynamical decoupling protocol. These advances open up new prospects for scalable quantum simulation and quantum computation with neutral atoms.

Kitaev’s 0–π qubit encodes quantum information in two protected, near-degenerate states of a superconducting quantum circuit. In a recent work, we have shown that the coherence times of a realistic 0–π device can surpass that of today’s best superconducting qubits (Groszkowski et al 2018 New J. Phys. 20 043053). Here we address controllability of the 0–π qubit. Specifically, we investigate the potential for dispersive control and readout, and introduce a new, fast and high-fidelity single-qubit gate that can interpolate smoothly between logical X and Z. We characterize the action of this gate using a multi-level treatment of the device, and analyze the impact of circuit-element disorder and deviations in control and circuit parameters from their optimal values. Furthermore, we propose a cooling scheme to decrease the photon shot-noise dephasing rate, which we previously found to limit the coherence times of 0–π devices within reach of current experiments. Using this approach, we predict coherence time enhancements between one and three orders of magnitude, depending on parameter regime.

Neutral atom qubit is a promising candidate platform for realizing quantum information processing in recent years due to its natural scalability, long coherence time, and reconfigurable array structure. However, the fidelity of basic logic operations such as the ‘NOT’ gate is still not high enough at present, which is constrained by noise. In this paper, we propose a new pulse optimization scheme for neutral atom qubits. We studied the composite pulses by introducing multi-phase superposition to enhance their noise robustness, achieving a fidelity up to 99.99 % in a noisy environment. The composite pulses improve the fidelity of the ‘NOT’ gate of neutral atom qubit and promote the neutral atom platform towards high-fidelity and scalable quantum information processing.

The echo information processing platform is an important part of the phased array radar system. With the increasing demands of the airborne phased array radar mission on bus transmission bandwidth, computational processing speed, system response time, and data processing capability, the traditional echo information processing platform has been difficult to meet the requirements of technological development. Based on the advantages of high transmission bandwidth, rich I/O resources and strong scalability of VPX bus, this paper proposes a design scheme of echo information processing platform based on VPX bus, focusing on the composition of information processing platform and the design principle of each functional module. Based on the idea of dataflow driving, a new peer-to-peer backplane architecture is adopted. The test results show that the information processing platform only needs 20.2s to complete 32K*32K complex image processing. The performance is superior, stable and reliable.