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Center for Nonlinear Studies |
The interaction between two quantum bits enables entanglement, the two-particle correlations that are at the heart of quantum information science. In semiconductor quantum dots much work has been focused on demonstrating single spin qubit control using optical techniques. However, optical control of two spin qubits remains a major challenge for scaling to a full-fledged quantum information platform. Here we combine advances in vertically-stacked quantum dots with ultrafast laser techniques to achieve optical control of the entangled state of two spins. We demonstrate ultrafast optical control of two interacting electron [1] or hole [2] spins in two separate QDs using optical initialization, single-qubit gates with short pulses, and two-qubit gates with longer pulses or through precession in the exchange field. Local entanglement between the two spins is inferred from the coherent evolution of superposition states as measured in Ramsey fringes. The two-qubit gate speeds achieved here are over an order of magnitude faster than in other systems. These results demonstrate the viability and advantages of optically controlled quantum dot spins for multi-qubit systems.
Host: Dibyendu Roy, T-4 and CNLS, 667-0404