Abstract
Digital-analog quantum computation aims to reduce the currently infeasible resource requirements needed for near-term quantum information processing by replacing sequences of one- and two-qubit gates with a unitary transformation generated by the systems' underlying Hamiltonian. Inspired by this paradigm, we consider superconducting architectures and extend the cross-resonance effect, up to first order in perturbation theory, from a two-qubit interaction to an analog Hamiltonian acting on 1D chains and 2D square lattices which, in an appropriate reference frame, results in a purely two-local Hamiltonian. By augmenting the analog Hamiltonian dynamics with single-qubit gates we show how one may generate a larger variety of distinct analog Hamiltonians. We then synthesize unitary sequences, in which we toggle between the various analog Hamiltonians as needed, simulating the dynamics of Ising, $XY$, and Heisenberg spin models. Our dynamics simulations are Trotter error-free for the Ising and $XY$ models in 1D. We also show that the Trotter errors for 2D $XY$ and 1D Heisenberg chains are reduced, with respect to a digital decomposition, by a constant factor. In order to realize these important near-term speedups, we discuss the practical considerations needed to accurately characterize and calibrate our analog Hamiltonians for use in quantum simulations. We conclude with a discussion of how the Hamiltonian toggling techniques could be extended to derive new analog Hamiltonians which may be of use in more complex digital-analog quantum simulations for various models of interacting spins.
Highlights
Classical computers are ill suited for simulating quantum systems due to their exponentially growing Hilbert spaces
A quantum annealer uses quantum fluctuations to efficiently solve optimization problems, but it can be used as an adiabatic quantum simulator [5,6]
We compute the Trotter error when it is present and find that it is reduced by a constant factor with respect to a digital decomposition of the same model
Summary
Classical computers are ill suited for simulating quantum systems due to their exponentially growing Hilbert spaces. A quantum annealer uses quantum fluctuations to efficiently solve optimization problems, but it can be used as an adiabatic quantum simulator [5,6] Going beyond this distinction, a novel paradigm for digital-analog (DA) quantum computation [7,8,9,10] and simulation [11,12,13,14,15,16] has been proposed. The DA quantum-computation paradigm provides an attractive near-term solution to alleviate the current difficulties associated with implementing useful quantum algorithms with near-term devices Despite this promise, the success of the DA approach relies on having a quantum platform with well-defined qubits, controllable pulses, and an accurate characterization of the underlying interaction Hamiltonian. We compute the Trotter error when it is present and find that it is reduced by a constant factor with respect to a digital decomposition of the same model
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