Photon assisted tunneling in bilayer graphene double quantum dots

Spin qubits in semiconductor quantum dots (QDs) are attractive candidates for solid state quantum computation. Singlet-triplet qubits, where the logical qubits are encoded in a two-electron spin system in double quantum dots (DQDs), turned out to be of special interest. In such systems, control over the interdot tunnel coupling and, hence, the exchange interaction is essential. Bilayer graphene (BLG) is an attractive host material for spin qubits due to its small spin-orbit and hyperfine interaction, as well as its gate voltage controllable band gap. Only recently, it has become possible to confine single electrons in BLG QDs and to understand their spin and valley texture [1]. However, microwave manipulation has not been demonstrated, so far.

Here, we perform photon-assisted tunneling (PAT) spectroscopy, which relies on resonant microwave excitation of electrons across the interdot transition [2]. In power-dependent measurements, we explore multi-photon processes up to 10^th order. We use PAT as a probe for the interdot tunnel coupling in BLG DQDs. We can control and measure the interdot tunnel coupling in a range of several GHz which is suitable for qubit operations.

[1] L. Banszerus et al., Nat. Commun. 12,5250 (2021).

[2] T. H. Oosterkamp et al., Nature 395, 873 (1998).