Berlin 2014 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 43: Quantum information: Concepts and methods II

Q 43.4: Talk

Thursday, March 20, 2014, 15:00–15:15, Kinosaal

Efficient Optimal Control for a Unitary Operation under Dissipative Evolution — •Michael H. Goerz, Daniel M. Reich, and Christiane P. Koch — Universität Kassel, Institut für Theoretische Physik

We show that optimizing a quantum gate for an open quantum system requires propagation of only three states irrespective of the dimension of Hilbert space. This represents a significant reduction in computational resources compared to the complete basis of Liouville space that is commonly believed necessary for this task. The reduction is based on two observations: The target is not a general dynamical map but a unitary operation; and the gate fidelity of a unitary operation can be estimated from a reduced set of properly chosen states. We illustrate our claim by optimization of two-qubit gates for trapped atoms and for superconducting qubits. The choice of states and their relative weight can be guided by physical understanding; for example, in the case of the Rydberg gate, the Hamiltonian only allows for diagonal gates, allowing to further reduce the number of required states to two. For both examples, we find that the optimization with a reduced set of states reaches gate fidelities that are only limited by the decoherence.