The promise of nanoscience stems from the fundamentally new behavior that emerges at the nanoscale. Here, we propose to explore, control and exploit one of the most dramatic aspects of this unusual behavior: quantum entanglement of spins. Our nanoscale system of choice is an array of semiconductor quantum dots that each contain one single electron. Thanks to a string of recent breakthroughs, it is now possible to initialize, coherently manipulate and read out the spin state of one such electron, and to couple it coherently to a spin in a neighboring dot. Today, we are at the brink of a new era in this field, in which entanglement will play the central part. The primary goal of this proposal, therefore, is to experimentally demonstrate that electron spins in quantum dots can really be entangled, and to control this entanglement in time. We will then use this capability to implement various quantum information protocols such as quantum algorithms and teleportation, which intrinsically rely on entanglement to realize tasks that are classically impossible. In order to push the level of coherent control to its limits, we will suppress fluctuations in the normally uncontrolled spin environment, and pursue novel quantum dot technologies which offer an intrinsically ‘quiet’ environment. Our long-term dream is to demonstrate that the accuracy threshold for fault-tolerant quantum computation can be reached in this system, which would permit quantum coherence and entanglement to be preserved indefinitely. This research is presently very much at the stage of exploratory research and is bound to produce surprising and unexpected outcomes. Furthermore, we are convinced that pushing the frontier of quantum control in nanoscale devices has a real potential to lead to future quantum technologies.
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