Probing two-qubit capacitive interactions beyond bilinear regime using dual Hamiltonian parameter estimations

TL;DR

This paper demonstrates simultaneous control and measurement of two-electron spin qubits in a quantum dot array, revealing a capacitive interaction stronger than bilinear models and supporting high-fidelity entanglement.

Contribution

It introduces a method for real-time Hamiltonian estimation to control two-qubit interactions beyond bilinear regimes in quantum dot systems.

Findings

Strong two-qubit capacitive interaction (>190 MHz) observed.

Scaling of interaction exceeds bilinear predictions, aligning with recent theories.

High ratio (>16) between coherence and phase-flip time indicates potential for high-fidelity entanglement.

Abstract

We report the simultaneous operation and two-qubit coupling measurement of a pair of two-electron spin qubits that are actively decoupled from quasistatic nuclear noise in a GaAs quadruple quantum dot array. Coherent Rabi oscillations of both qubits (decay time $\approx$2 {\mu}s; frequency few MHz) are achieved by continuously tuning the drive frequency using rapidly converging real-time Hamiltonian estimators. By state conditional exchange oscillation measurements, we also observe strong two-qubit capacitive interaction (> 190 MHz). We show that the scaling of the capacitive interaction with respect to intra-qubit exchange energies is stronger than the bilinear form, consistent with recent theoretical predictions. We observe a high ratio (>16) between coherence and conditional phase-flip time, which supports the possibility of generating high-fidelity and fast quantum entanglement between encoded spin qubits using a simple capacitive interaction.