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Scalable qubit architecture based on holes in quantum dot molecules

Spins confined in quantum dots are a leading candidate for solid-state quantum bits that can be coherently controlled by optical pulses. There are, however, many challenges to developing a scalable multibit information processing device based on spins in quantum dots, including the natural inhomogeneous distribution of quantum dot energy levels, the difficulty of creating all-optical spin manipulation protocols compatible with nondestructive readout, and the substantial electron-nuclear hyperfine interaction-induced decoherence. Here, we present a scalable qubit design and device architecture based on the spin states of single holes confined in a quantum dot molecule. The quantum dot molecule qubit enables a new strategy for optical coherent control with dramatically enhanced wavelength tunability. The use of hole spins allows the suppression of decoherence via hyperfine interactions and enables coherent spin rotations using Raman transitions mediated by a hole-spin-mixed optically excited state. Because the spin mixing is present only in the optically excited state, dephasing and decoherence are strongly suppressed in the ground states that define the qubits and nondestructive readout is possible. We present the qubit and device designs and analyze the wavelength tunability and fidelity of gate operations that can be implemented using this strategy. We then present experimental and theoretical progress toward implementing this design.