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arXiv:2209.14817 · Communications Physics

Robust oscillator-mediated phase gates driven by low-intensity pulses

Íñigo Arrazola, Jorge Casanova

Published May 29, 2023• 0 citations
arXivHTMLPDF

Abstract

Abstract Robust qubit-qubit interactions mediated by bosonic modes are central to many quantum technologies. Existing proposals combining fast oscillator-mediated gates with dynamical decoupling require strong pulses or fast control over the qubit-boson coupling. Here, we present a method based on dynamical decoupling techniques that leads to faster-than-dispersive entanglement gates with low-intensity pulses. Our method is general, i.e., it is applicable to any quantum platform that has qubits interacting with bosonic mediators via longitudinal coupling. Moreover, the protocol provides robustness to fluctuations in qubit frequencies and control fields, while also being resistant to common errors such as frequency shifts and heating in the mediator as well as crosstalk effects. We illustrate our method with an implementation for trapped ions coupled via magnetic field gradients. With detailed numerical simulations, we show that entanglement gates with infidelities of 10−3 or 10−4 are possible with current or near-future experimental setups, respectively.

DOI
10.1038/s42005-023-01243-8

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We present a scheme designed to suppress the dominant source of infidelity in entangling gates between quantum systems coupled through intermediate bosonic oscillator modes. Such systems are particularly susceptible to residual qubit-oscillator entanglement at the conclusion of a gate period that reduces the fidelity of the target entangling operation. We demonstrate how the exclusive use of discrete shifts in the phase of the field moderating the qubit-oscillator interaction is sufficient to both ensure multiple oscillator modes are decoupled and to suppress the effects of fluctuations in the driving field. This approach is amenable to a wide variety of technical implementations including geometric phase gates in superconducting qubits and the Molmer-Sorensen gate for trapped ions. We present detailed example protocols tailored to trapped-ion experiments and demonstrate that our approach has the potential to enable multiqubit gate implementation with a significant reduction in technical complexity relative to previously demonstrated protocols.
In quantum computing systems where entangling logic gates are mediated via bosonic oscillator modes (e.g.e.g.e.g. trapped ions), residual coupling between qubits and oscillator is a dominant source of gate infidelity. This work shows how discrete phase modulation of the field mediating the entangling operation ensures that the system of qubits is decoupled from multiple oscillator modes, even in the presence of common time-varying sources of noise and hardware instability. The results demonstrate the capabilities of quantum control to drive major performance advances in quantum computing.
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Abstract We present a robust quantum optimal control framework for implementing fast entangling gates on ion-trap quantum processors. The framework leverages tailored laser pulses to drive the multiple vibrational sidebands of the ions to create phonon-mediated entangling gates and, unlike the state of the art, requires neither weak-coupling Lamb–Dicke approximation nor perturbation treatment. With the application of gradient-based optimal control, it enables finding amplitude- and phase-modulated laser control protocols that work without the Lamb–Dicke approximation, promising gate speeds on the order of microseconds comparable to the characteristic trap frequencies. Also, robustness requirements on the temperature of the ions and initial optical phase can be conveniently included to pursue high-quality fast gates against experimental imperfections. Our approach represents a step in speeding up quantum gates to achieve larger quantum circuits for quantum computation and simulation, and thus can find applications in near-future experiments.