Programming anharmonic potentials in a superconducting harmonic oscillator

arXiv:2609.02405v1 Announce Type: new Abstract: Continuous-variable quantum systems offer a resource-efficient route to universal quantum information processing and analogue quantum simulation of real-world processes, such as molecular physics and chemical reactions. Realising these applications, however, requires non-Gaussian operations that implement anharmonic potentials, which are challenging to engineer on demand. Here, we demonstrate a systematic framework to implement programmable non-Gaussian phase gates $e^{-iV(\hat{X})}$, corresponding to the impulsive action of a potential $V(\hat{X})$, in a superconducting harmonic oscillator coupled to a transmon qubit. Using modular circuits derived from bosonic quantum signal processing, we realise a range of target anharmonic potentials on a single piece of hardware by varying a set of qubit rotations interleaved with a fixed calibrated control unitary. We first demonstrate a cubic phase gate, a key ingredient for universal quantum information processing. The resulting high-fidelity non-Gaussian states and the potential reconstructed using our pointwise force reconstruction method jointly confirm the cubic nature of the target gate. We then engineer a family of double-well potentials, relevant models of tunnelling and biased transfer processes, and experimentally validate the double-well topology and the tunable asymmetry. Finally, we engineer an approximate Morse gate, a step towards realistic potentials of molecular vibrational systems, and provide a concrete path towards high-quality engineering and reconstruction of the exponential form. Together, these results establish a practical and reconfigurable route towards continuous-variable quantum information processing and anharmonic quantum simulation.

Authors:Clara Yun Fontaine, Mansi Somani, Kehui Yu, May Chee Loke, Jonathan Schwinger, Pak-Tik Fong, Ni-Ni Huang, Adrian Copetudo, Mustafa Bakr, Hoi-Kwan Lau, Tanjung Krisnanda, Yvonne Y. Gao

Abstract:Continuous-variable quantum systems offer a resource-efficient route to universal quantum information processing and analogue quantum simulation of real-world processes, such as molecular physics and chemical reactions. Realising these applications, however, requires non-Gaussian operations that implement anharmonic potentials, which are challenging to engineer on demand. Here, we demonstrate a systematic framework to implement programmable non-Gaussian phase gates $e^{-iV(\hat{X})}$, corresponding to the impulsive action of a potential $V(\hat{X})$, in a superconducting harmonic oscillator coupled to a transmon qubit. Using modular circuits derived from bosonic quantum signal processing, we realise a range of target anharmonic potentials on a single piece of hardware by varying a set of qubit rotations interleaved with a fixed calibrated control unitary. We first demonstrate a cubic phase gate, a key ingredient for universal quantum information processing. The resulting high-fidelity non-Gaussian states and the potential reconstructed using our pointwise force reconstruction method jointly confirm the cubic nature of the target gate. We then engineer a family of double-well potentials, relevant models of tunnelling and biased transfer processes, and experimentally validate the double-well topology and the tunable asymmetry. Finally, we engineer an approximate Morse gate, a step towards realistic potentials of molecular vibrational systems, and provide a concrete path towards high-quality engineering and reconstruction of the exponential form. Together, these results establish a practical and reconfigurable route towards continuous-variable quantum information processing and anharmonic quantum simulation.

Main text: 6 pages with 4 figures. Supplemental Material: 20 pages with 4 figures and 15 tables

arXiv:2609.02405 [quant-ph]

(or arXiv:2609.02405v1 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2609.02405 arXiv-issued DOI via DataCite (pending registration)

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Programming anharmonic potentials in a superconducting harmonic oscillator

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