In realizations of quantum computing, a two-level system (qubit) is often singled out from the many levels an anharmonic oscillator. these cases, simple qubit control fails on short time scales because coupling to leakage levels. We provide easy implement analytic formula that inhibits this any single-control analog or pixelated pulse. It based adding second proportional derivative first. For realistic parameters superconducting qubits, strategy reduces error by order magnitude relative...

The creation of a quantum network requires the distribution coherent information across macroscopic distances. We demonstrate entanglement two superconducting qubits, separated by more than meter coaxial cable, designing joint measurement that probabilistically projects onto an entangled state. By using continuous scheme, we are further able to observe single trajectories two-qubit state, confirming validity Bayesian formalism for cascaded system. Our results allow us resolve dynamics...

In qubits made from a weakly anharmonic oscillator the leading source of error at short gate times is leakage population out two dimensional Hilbert space that forms qubit. this article we develop general scheme based on an adiabatic expansion to find pulse shapes correct type error. We family solutions allows tailoring what practical implement for specific application. Our result contains and improves previously developed derivative removal by technique [F. Motzoi et al., Phys. Rev. Lett....

We employ pulse shaping to abate single-qubit gate errors arising from the weak anharmonicity of transmon superconducting qubits. By applying shaped pulses both quadratures rotation, a phase error induced by presence higher levels is corrected. Using derivative control on quadrature channel, we are able remove effect anharmonic for multiple qubits coupled microwave resonator. Randomized benchmarking used quantify average per gate, achieving minimum 0.007+/-0.005 using 4 ns-wide pulse.

We propose a two-qubit gate for neutral atoms in which one of the logical state components adiabatically follows two-atom dark formed by laser coupling to Rydberg and strong, resonant dipole-dipole exchange interaction between two excited atoms. Our exhibits optimal scaling intrinsic error probability $E \propto (B\tau)^{-1}$ with interatomic strength $B$ lifetime $\tau$. Moreover, is resilient variations strength, even finite double excitation, does not excite atomic motion experiences no...

With recent improvements in coherence times, superconducting transmon qubits have become a promising platform for quantum computing. They can be flexibly engineered over wide range of parameters, but also require us to identify an efficient operating regime. Using state-of-the-art optimal control techniques, we exhaustively explore the landscape creation and removal entanglement design parameters. We region outside usually considered strongly dispersive regime, where multiple sources...

In this theoretical investigation, we examine the effectiveness of a protocol incorporating periodic quantum resetting for preparing ground states frustration-free parent Hamiltonians. This uses steering Hamiltonian that enables local coupling between system and ancillary degrees freedom. At intervals, is reset to its initial state. For infinitesimally short times, dynamics can be approximated by Lindbladian whose steady state target finite however, spin chain ancilla become entangled...

In this article, we develop a numerical method to find optimal control pulses that accounts for the separation of timescales between variation input fields and applied Hamiltonian. traditional optimization methods, these are treated as being same. While approximation has had much success, in applications where controls filtered substantially or mixed with fast carrier, resulting optimized have little relation physical fields. Our technique remains numerically efficient dimension our search...

Many techniques in quantum control rely on frequency separation as a means for suppressing unwanted couplings. In its simplest form, the mechanism relies low bandwidth of pulses long duration. Here we perform higher-order quantum-mechanical treatment that allows higher precision and shorter times. particular, identify three kinds off-resonant effects: (i) simultaneous driven couplings (e.g., due to drive crosstalk), (ii) additional (initially undriven) transitions such those an infinite...

We show that the use of shaped pulses improves fidelity a Rydberg blockade two-qubit entangling gate by several orders magnitude compared to previous protocols based on square or optimal control pulses. Using analytical Derivative Removal Adiabatic Gate (DRAG) reduce excitation primary leakage states and an method finding we generate Bell with $F>0.9999$ in 300 K environment for time only $50\;{\rm ns}$, which is order faster than protocols. These results establish potential neutral atom...

The cross-resonant gate is an entangling for fixed frequency superconducting qubits introduced untunable qubits. While being simple and extensible, it suffers from long duration limited fidelity. Using two different optimal control algorithms, we probe the quantum speed limit a CNOT in this system. We show that ability to approach depends strongly on ansatz used describe pulse. A piecewise constant with single carrier leads experimentally feasible pulse shape, shorter than one currently...

The task of controlling a quantum system under time and bandwidth limitations is made difficult by unwanted excitations spectrally neighboring energy levels. In this article we review the Derivative Removal Adiabatic Gate (DRAG) framework. DRAG multi-transition variant counterdiabatic driving, where multiple low-lying gapped states in an adiabatic evolution can be avoided simultaneously, greatly reducing operation times compared to limit. its essence, method corresponds convergent version...

We propose and analyze a protocol for stabilizing maximally entangled state of two noninteracting qubits using active state-dependent feedback from continuous two-qubit half-parity measurement in coordination with concurrent, noncommuting dynamical decoupling drive. demonstrate that such drive can be simultaneous the feedback, while also playing key part itself. show robust stabilization near-unit fidelity achieved even presence realistic nonidealities, as time delay loop, imperfect...

The difficulty of an optimization task in quantum information science depends on the proper mathematical expression physical target. Here we demonstrate power functionals targeting arbitrary perfect two-qubit entangler, which allow generation a maximally entangled state from some initial product state. We show for two platforms current interest, i.e., nitrogen vacancy centers diamond and superconducting Josephson junctions, that entangler can be reached faster with higher fidelity than both...

While a large number of algorithms for optimizing quantum dynamics different objectives have been developed, common limitation is the reliance on good initial guesses, being either random or based heuristics and intuitions. Here we implement tabula rasa deep exploration version Deepmind AlphaZero algorithm systematically averting this limitation. employs neural network in conjunction with lookahead guided tree search, which allows predictive hidden variable approximation parameter landscape....

State-of-the-art quantum algorithms routinely tune dynamically parametrized cost functionals for combinatorics, machine learning, equation solving, and energy minimization. However, large search complexity often demands many (noisy) measurements, leading to the increasing use of classical probability models estimate which areas in functional landscape are highest interest. Introducing deep learning based modeling landscape, we demonstrate order-of-magnitude increases accuracy speed over...

Shortening quantum circuits is crucial to reducing the destructive effect of environmental decoherence and enabling useful algorithms. Here, we demonstrate an improvement in such compilation tasks via a combination using hybrid discrete-continuous optimization across continuous gate set, architecture-tailored implementation. The parameters are discovered with gradient-based algorithm, while tandem optimal orderings learned deep reinforcement learning based on projective simulation. To test...

Abstract While quantum circuits are reaching impressive widths in the hundreds of qubits, their depths have not been able to keep pace. In particular, cloud computing gates on multi-qubit, fixed-frequency superconducting chips continue hover around 1% error range, contrasting with progress seen carefully designed two-qubit chips, where rates pushed towards 0.1%. Despite strong impetus and a plethora research, experimental demonstration suppression these multi-qubit devices remains...

Abstract We investigate for optimal photon absorption a quantum electrodynamical model of an inhomogeneously-broadened spin ensemble coupled to single-mode cavity. Solutions this problem under experimental assumptions are developed in the Schr"odinger picture without using perturbation theory concerning cavity-spin interactions. Furthermore, we exploit possibility modulating frequency and coupling rate resonator. consider one-photon input pulse show some scenarios, where exact formulas...

The Mølmer-Sørensen gate is a widely used entangling for ion platforms with inherent robustness to trap heating. performance limited by coherent errors, arising from the Lamb-Dicke (LD) approximation and sideband errors. Here, we provide explicit analytical formulas errors up fourth order in LD parameter, using Magnus expansion match numerical precision, overcome significant orders-of-magnitude underestimation of previous theory methods. We show that fourth-order terms are unavoidable, being...

Achieving precise control over quantum systems presents a significant challenge, especially in many-body setups, where residual couplings and unintended transitions undermine the accuracy of operations. In superconducting qubits, parasitic interactions -- both between distant qubits with spurious two-level can severely limit performance gates. this work, we introduce pulse-shaping technique that uses spectrally balanced microwave pulses to suppress undesired transitions. Experimental results...

We derive a stochastic Schr\"{o}dinger equation that describes the homodyne measurement record of strongly interacting atomic system. this for general system, where we use rotating wave approximation in linear atom-light interaction part, and resulting is expressed terms operators only. Weak measurements are theoretically described positive operator-valued measures. Among different weak schemes, several earlier references studied Gaussian quantum continuous detail. Here consider setup. then...

We present a few-parameter ansatz for pulses to implement broad set of simultaneous single-qubit rotations in frequency-crowded multilevel systems. Specifically, we consider system two qutrits whose working and leakage transitions suffer from spectral crowding (detuned by $\delta$). In order achieve precise controllability, make use driving fields (each having quadratures) at different tones arbitrary rotations. Expanding the waveforms terms Hanning windows, show how analytic containing...

While the on-chip processing power in circuit QED devices is growing rapidly, an open challenge to establish high-fidelity quantum links between qubits on different chips. Here, we show entanglement transmon cQED chips with $49%$ concurrence and $73%$ Bell-state fidelity. We engineer a half-parity measurement by successively reflecting coherent microwave field off two nearly identical transmon-resonator systems. By ensuring measured output does not distinguish $|01\ensuremath{\rangle}$ from...