All-Optical Quantum Computing with Femtosecond Coherent Control of Excitons in Semiconductor Quantum Dots

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*****NON-TECHNICAL ABSTRACT*****The power of quantum mechanics will allow quantum computers, once realized, to perform tasks that are well beyond the power of classical computers. An example of such a task is the breaking of strong encryption, an important topic for national security. Quantum information, however, is much more volatile and difficult to handle than classical information, and approaches for quantum computation demonstrated so far can handle a few quantum bits at best. This individual investigator award supports an experimental research program to demonstrate quantum gating in semiconductor quantum dots of nanometer size. Quantum dots are made from layers of semiconductors and behave like artificial atoms whose quantum states can be controlled by sequences of very fast laser pulses. The project will investigate the basic elements for quantum circuits. The experiments will concentrate on optimum control and measurement of the quantum states in quantum dots, the rate of errors from loss of the volatile quantum information (decoherence), the maximum speed with which the dots can process quantum information, and coupling mechanisms between dots necessary for two-bit gates. The research will involve graduate and undergraduate students and therefore have a strong educational component in important fields such as ultrafast optics, nanoscience and quantum engineering.***** TECHNICAL ABSTRACT*****This individual investigator award supports an experimental research program that explores femtosecond coherent quantum control of excitonic states in semiconductor quantum dots as a potential platform for scalable quantum computing. The quantum dots are controlled with multi-color optical pulse sequences derived by Fourier domain pulse shaping of femtosecond laser pulses. The experimental program will investigate strongly confined high-quality single and coupled InGaAs and AlGaAs quantum dots that have nanosecond coherence times, allowing potentially thousands of quantum operations before decoherence occurs. The first part of the project will concentrate on single quantum dots and explore new methods of controlling and measuring their quantum states. The experiments will explore the sources of decoherence during quantum operations, such as excitation-induced polaronic lattice distortion with phonon emission. The second part of the project will concentrate on scalability and aims to demonstrate quantum gating of bits located in separate quantum dots. This project integrates research and education of graduate and undergraduate students, and provides hands-on experience in important fields such as ultrafast optics, nanoscience, and quantum engineering.