Observation of anticrossings in the exciton state of single quantum dots via electrical tuning of the fine-structure splitting

Single quantum dots have many potential applications across the field of quantum computation, ranging from the generation of single photons or entangled photon pairs to the storage and manipulation of qubits. Single InAs quantum dots are optically active and thus can be used as an interface between photonic flying qubits and spin-based stationary qubits. Incorporating single InAs quantum dots into semiconductor devices allows the stationary qubits to be manipulated, making this system a promising candidate for quantum computation. It is well known that the exciton state of quantum dots is split into two polarisation dependent states; the energy difference between the states is the fine-structure splitting, (s). A vertical electric field has been used to tune |s| over a large range of ∼ 100μeV, such that a dot which has |s| over 50μeV at zero field has been tuned to emit polarisation entangled photon pairs[1]. We observe coherent coupling between the two polarisation eigenstates. This coupling results in an anticrossing as the two states are tuned close to each other, and a rotation of the eigenstates through 90° as |s| is swept through its minimum value.