Barrier gate-free two-qubit operation at the charge symmetry point

Spin qubits in quantum dots have emerged as a promising platform for quantum computing, with high-fidelity two-qubit gates typically achieved through control over the exchange interaction. Common methods rely on individual barrier gate control, adding complexity to device fabrication and operation. An alternative involves adjusting the detuning between quantum dots. However, this detuning-based approach moves the two charges away from the charge symmetry point, increasing sensitivity to charge noise and reducing operation fidelity. Here, we demonstrate a method for performing two-qubit operations without using pulses on individual barrier gates, instead relying on symmetric plunger gate pulses. By applying plunger gate pulses of over 300 mV in an isolated regime, we achieve tunability of the exchange interaction from 100 kHz to 60 MHz while remaining at the charge symmetry point, thus preserving qubit coherence. This method simplifies control and enables effective two-qubit operations in a 2x2 germanium quantum dot device [1]. We also propose a design using a single barrier grid instead of many individual barrier gates, which could reduce complexity and support growing the quantum dot arrays to much larger sizes.

[1] N.W. Hendrickx, W.I.L. Lawrie, et al., Nature 591, 580-585 (2021)