Dresden 2011 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 34: TR: Quantum Coherence and Quantum Information Systems 2 (jointly with MA and HL)

TT 34.7: Hauptvortrag

Mittwoch, 16. März 2011, 15:45–16:15, HSZ 03

Coupled evolution and coherence of two-electron spin qubits — •Hendrik Bluhm — Harvard University, Cambridge, USA and RWTH Aachen, Germany

One of the fundamental requirements for quantum computing is to coherently couple qubits in order to generate entanglement. For semiconductor qubits, such entangling gates have yet to be demonstrated in fully operational devices. I will give a brief overview of our recent experiments on enhancing the coherence of two-electron spin qubits in GaAs double quantum dots, and then focus on current progress towards the realization of two-qubit entangling gates.

By manipulating a qubit in a way that decouples its evolution from the fluctuations of its nuclear spin bath, we extended its coherence time to more than 200 µs, two orders of magnitude longer than previously measured. Operating the qubit as a feedback loop that controls the nuclear bath enables universal single qubit control with greatly improved gate fidelities.

Using the Coulomb interaction between two adjacent double dots, we demonstrate a dependence of the coherence of one qubit on the state of the other, which results in strong correlations in a joint single shot readout of the two qubits. In this operation, the control qubit completely dephases due to low frequency electrical noise. Using a spin echo pulse, the single-qubit dephasing time can be extended by an amount that is expected to enable a fully coherent cPHASE gate, which would entangle the two qubits.