BioComp: Collaborative Research: Is Resilient Quantum Computing in Solid State Systems Possible?

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This grant supports theoretical research on fundamental issues relatedto the implementation of quantum computation in solid-statedevices. Since the discovery that certain tasks could be performedwith great efficiency by algorithms based on quantum mechanics, anintense effort has been made to find suitable quantumhardware. Although several proposed implementations, such as thosebased on nuclear magnetic resonance and atomic trapping, have passedthe proof-of-principle, few-qubit phase, the path to achieving areliable multi-qubit quantum computer is still undefined.In this proposal we investigate the physical limitations to resilientcomputation with solid-state quantum bits (qubits), such assemiconductor quantum dots and superconductor junctions. Whilesolid-state qubits seem easily scalable from the fabricationviewpoint, they also present high decoherence rates as compared toother implementations. One major concern is that such strong decoherence may lead to errors occurring at a rate too large to be controlled.However, differently from other nuclear, atomic, and optical qubits, the interaction of solid-state quantum devices with the environment can introduce strong memory effects. As a result, temporal correlations may appear during the operation of multi-qubit systems. Current quantum error correction codes are not designed to cope with this situation, which may then invalidate any error threshold estimate for solid-state qubits based on the efficiency of those codes.We will explore these issues in a comprehensive way. Starting from athorough study of the mechanisms of decoherence in single- anddouble-qubit systems, we will study a model of multi-qubit systems inthe presence of correlated noise in a variety of realisticconditions. Our results will help set up new strategies for theoperation of multi-qubit systems. They will also let us understandwhat are the constraints that error correction codes will need tosatisfy in order to achieve fault-tolerant quantum computation inlarge-scale solid state implementations. To achieve our goals, we haveput together a team of researchers with expertise in nanoscale physics and computer science. The final outcome of our project will be a muchbetter understanding of how a real solid-state quantum computer wouldbehave.