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Event Number 2800

  Monday, October 29th, 2012

Condensed Matter Theory Group Seminar
Progress in Superconducting Quantum Circuits
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Robert McDermott
Abstract: Superconducting integrated circuits incorporating Josephson junctions are an attractive candidate for scalable quantum computing in the solid state. Currently, fidelity of multiqubit operations is limited by decoherence and by added noise of the qubit measurement. In this talk I describe work to improve qubit coherence and measurement fidelity. First, I describe the incorporation of crystalline silicon into phase qubit circuits; the improved qubits display energy relaxation times that are a factor 2-3 greater than those achieved with the best available amorphous materials. Next, I will describe efforts to understand and eliminate pure dephasing. We have shown that the dephasing is due to flux noise induced by surface magnetic states at the superconductor-insulator interface; in recent work we have demonstrated a fabrication process that has led to a noise suppression by more than an order of magnitude. Finally (and if time permits), I will discuss development of a novel microwave amplifier based on a variant of the dc Superconducting QUantum Interference Device (dc SQUID). With these devices we have achieved noise performance within a factor of 2 of the standard quantum limit at 8 GHz. Preliminary measurements show a significant improvement in single-shot quantum nondemolition measurement fidelity.
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