Digital-Analog Quantum Computing

Mikel Sanz

Paula García-Molina, Ana Martin, Mikel Garcia de Andoin +1 more

Abstract Noisy Intermediate-Scale Quantum (NISQ) devices lack error correction, limiting scalability for quantum algorithms. In this context, digital-analog quantum computing (DAQC) offers a more resilient alternative quantum computing paradigm that outperforms digital quantum computation by combining the flexibility of single-qubit gates with the robustness of analog simulations. This work explores the impact of noise on both digital and DAQC paradigms and demonstrates DAQC’s effectiveness in error mitigation. We compare the quantum Fourier transform and quantum phase estimation algorithms under a wide range of single and two-qubit noise sources in superconducting processors. DAQC consistently surpasses digital approaches in fidelity, particularly as processor size increases. Moreover, zero-noise extrapolation further enhances DAQC by mitigating decoherence and intrinsic errors, achieving fidelities above 0.95 for 8 qubits, and reducing computation errors to the order of 10 −3 . These results establish DAQC as a viable alternative for quantum computing in the NISQ era.

Michail A. Zak

Vicente Pina-Canelles, Manuel G. Algaba, Hermanni Heimonen +6 more

Digital-Analog Quantum Computation (DAQC) has recently been proposed as an alternative to the standard paradigm of digital quantum computation. DAQC creates entanglement through a continuous or analog evolution of the whole device, rather than by applying two-qubit gates. This manuscript describes an in-depth analysis of DAQC by extending its implementation to arbitrary connectivities and by performing the first systematic study of its scaling properties. We specify the analysis for three examples of quantum algorithms, showing that except for a few specific cases, DAQC is in fact disadvantageous with respect to the digital case.

Tshilidzi Marwala

Vicente Pina-Canelles, Manuel G. Algaba, Hermanni Heimonen +6 more

Abstract Digital–analog quantum computation (DAQC) has recently been proposed as an alternative to the standard paradigm of digital quantum computation (DQC). DAQC generates entanglement through a continuous or analog evolution of the whole device, rather than by applying two-qubit gates. This manuscript describes an in-depth analysis of errors in DAQC implementing Ising Hamiltonians used for arbitrary computations, which was missing from the previous literature, revealing that, overall, DAQC errors scale less favorably compared to those in DQC. As demonstrated, for an all-to-all connectivity, the leading error source for DAQC scales like Θ ( N 4 ) , while for the digital case, it scales like O ( N 2 ) for implementing an arbitrary Hamiltonian evolution. We further illustrate this result with our own simulations of the Quantum Fourier Transform, which in the previous literature were based on unrealistic parameter choices, biasing the result in favor of DAQC, and were limited to system sizes of up to only seven qubits. On the other hand, we develop a specific DAQC protocol for a star connectivity, which shows an advantage for the particular case of a GHZ state generation protocol.