Abstract
Quantum computers will allow calculations beyond existing classical computers. However, current technology is still too noisy and imperfect to construct a universal digital quantum computer with quantum error correction. Inspired by the evolution of classical computation, an alternative paradigm merging the flexibility of digital quantum computation with the robustness of analog quantum simulation has emerged. This universal paradigm is known as digital-analog quantum computing. Here, we introduce an efficient digital-analog quantum algorithm to compute the quantum Fourier transform, a subroutine widely employed in several relevant quantum algorithms. We show that, under reasonable assumptions about noise models, the fidelity of the quantum Fourier transformation improves considerably using this approach when the number of qubits involved grows. This suggests that, in the Noisy Intermediate-Scale Quantum (NISQ) era, hybrid protocols combining digital and analog quantum computing could be a sensible approach to reach useful quantum supremacy.
Highlights
Almost four decades ago, a new paradigm, based on laws of quantum mechanics, had been put forward by Manin [1] and Feynman [2]
This shows that the banged DAQC (bDAQC) protocol is the best option if one wants to implement the quantum Fourier transform (QFT) on a system built up from several qubits. (c) Fidelity evolution with growing errors
Even though we have considered a sensible choice for the noise model of the digital-analog quantum computation (DAQC) implementation, this model will not be accurate until comparing it against experimental data
Summary
A new paradigm, based on laws of quantum mechanics, had been put forward by Manin [1] and Feynman [2]. The first series of commercial digital quantum processors based on superconducting circuits have been introduced by companies, such as IBM, Rigetti, Google, and Alibaba These devices belong to the so-called noisy intermediatescale quantum (NISQ) era in which their performance still faces multiple technical constraints. If our analog resource is the natural interaction Hamiltonian in the platform, applying fast single-qubit rotations in certain order, one can generate an arbitrary Hamiltonian They claim that this codification is susceptible to smaller errors than digital quantum computing when performing quantum simulations. The fidelity between the ideal transformation and the one achieved by the DAQC behaves qualitatively better with the number of qubits than the fidelity offered by the digital implementation This new paradigm has its own noise sources, it eliminates the errors derived from the entangling two-qubit gates. Getting rid of these sources of errors allows us to successfully implement relevant quantum algorithms in the NISQ era
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