Quantum Dot Molecule Devices with Optical Control of Charge Status and Electronic Control of Coupling

Tunnel-coupled pairs of optically active quantum dots—quantum dot molecules (QDMs)—offer the possibility to combine excellent optical properties such as strong light-matter coupling with two-spin singlet–triplet ((Formula presented.)) qubits having extended coherence times. The (Formula presented.) basis formed using two spins is inherently protected against electric and magnetic field noise. However, since a single gate voltage is typically used to stabilize the charge occupancy of the dots and control the inter-dot orbital couplings, operation of the (Formula presented.) qubits under optimal conditions remains challenging. Here, an electric field tunable QDM that can be optically charged with one (1h) or two holes (2h) on demand is presented. A four-phase optical and electric field control sequence facilitates the sequential preparation of the 2h charge state and subsequently allows flexible control of the inter-dot coupling. Charges are loaded via optical pumping and electron tunnel ionization. One- and two-hole charging efficiencies of (93.5 ± 0.8)% and (80.5 ± 1.3)% are achieved, respectively. Combining efficient charge state preparation and precise setting of inter-dot coupling allows for the control of few-spin qubits, as would be required for the on-demand generation of 2D photonic cluster states or quantum transduction between microwaves and photons.