Measurements of Capacitive Coupling Within a Quadruple-Quantum-Dot Array

Abstract

We present measurements of the capacitive coupling energy and the inter-dot capacitances in a linear quadruple quantum dot array in undoped Si/SiGe. With the device tuned to a regime of strong (>1 GHz) intra-double dot tunnel coupling, as is typical for double dot qubits, we measure a capacitive coupling energy of 20.9 ± 0.3 GHz. In this regime, we demonstrate a fitting procedure to extract all the parameters in the 4D Hamiltonian for two capacitively coupled charge qubits from a 2D slice through the quadruple dot charge stability diagram. We also investigate the tunability of the capacitive coupling energy, using inter-dot barrier gate voltages to tune the inter-and intradouble dot capacitances, and change the capacitive coupling energy of the double dots over a range of 15-32 GHz. We provide a model for the capacitive coupling energy based on the electrostatics of a network of charge nodes joined by capacitors, which shows how the coupling energy should depend on inter-double dot and intra-double dot capacitances in the network, and find that the expected trends agree well with the measurements of coupling energy.

Programable two-qubit gates in capacitively coupled flopping-mode spin qubits

“…We have investigated the realization of single-step twoqubit gates in capacitively coupled flopping-mode spin qubits. In particular, by calculating the Makhlin invariants from the physical Hamiltonian for the qubit-qubit interaction, we have demonstrated that multiple two-qubit quantum gates can be realized with the same setup by using realistic experimental parameters [31,47,48]. Interestingly, a variety of two-qubit gates can be realized with fidelity higher than 95%, even accounting for dephasing.…”

“…[11,44]; in experiments, they are directly accessible but depend on the geometry and gates and are necessarily renormalized due to unavoidable screening effects [31]. Hence, below we consider values of the inter-DQD coupling |g| ∼ 15 − 30 μeV as reported in recent experiments [31]. Notice that we assume that any exchange coupling is strongly suppressed due to the absence of tunneling between the two DQDs.…”

“…Motivated by recent experimental work on capacitive coupling between QD qubits [13,16,17,31,32] and in QD arrays with different spatial configurations [33][34][35][36][37], we consider here the capacitive coupling between flopping-mode spin qubits [38][39][40][41] and investigate the realization of two-qubit gates. As shown in Fig.…”

Progress toward a capacitively mediated CNOT between two charge qubits in Si/SiGe

“…To perform capacitively-coupled two-qubit measurements, we fabricate a linear chain of four quantum dots using an overlapping-aluminum gate architecture (Fig. 1a) 14,15,20,21 . The fabrication details for this device have been reported elsewhere 15 .…”

“…1a) 14,15,20,21 . The fabrication details for this device have been reported elsewhere 15 . Measurements are performed in an Oxford Triton 400 dilution refrigerator with a~15 mK mixing chamber temperature.…”