The quantromon : A qubit-resonator system with orthogonal qubit and readout modes
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en
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6
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Applied Physics Letters, Volume 126, issue 25, pp. 1-6
Abstract
The measurement of a superconducting qubit is implemented by coupling it to a resonator. The common choice is transverse coupling, which, in the dispersive approximation, introduces an interaction term that enables the measurement. This cross-Kerr term provides a qubit-state dependent dispersive shift in the resonator frequency with the device parameters chosen carefully to get sufficient signal while minimizing Purcell decay of the qubit. We introduce a two-mode circuit, nicknamed quantromon, with two orthogonal modes implementing a qubit and a resonator. Unlike before, where the coupling term emerges as a perturbative expansion, the quantromon has intrinsic cross-Kerr coupling by design. Our experiments implemented in a hybrid 2D-3D circuit QED architecture demonstrate some unique features of the quantromon like weak dependence of the dispersive shift on the qubit-resonator detuning and intrinsic Purcell protection. In a tunable qubit-frequency device, we show that the dispersive shift ( 2 χ / 2 π ) changes by only 0.8 MHz, while the qubit-resonator detuning ( Δ / 2 π ) is varied between 0.398 and 3.288 GHz. We also demonstrate Purcell protection in a second device where we tune the orthogonality between the two modes. Finally, we demonstrate a single-shot readout fidelity of 98.3%, which is comparable to the state-of-the-art measurements without the use of a parametric amplifier and suggests a potential simplification of the measurement circuitry for scaling up quantum processors.Description
Publisher Copyright: © 2025 Author(s).
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Salunkhe, K V, Kundu, S, Das, S, Deshmukh, J, Patankar, M P & Vijay, R 2025, 'The quantromon : A qubit-resonator system with orthogonal qubit and readout modes', Applied Physics Letters, vol. 126, no. 25, 254001, pp. 1-6. https://doi.org/10.1063/5.0260171