Special Condensed Matter Physics Seminar

Note Special Time!
4 p.m., Monday, February 5, 2007
Room 1201, Physics Building

Precision Material Engineering at Nanoscale: Elimination of Decoherence Sources in Superconducting Quantum Bits

Seongshik Oh

(NIST Boulder)

Abstract: Quantum computers based on the superconducting quantum bits (qubits) are considered promising due to their scalable architecture. However, decoherence is a major obstacle, and identifying and eliminating the decoherence sources is one of the most important tasks for superconducting quantum computation. Over the past few years, we have found that the amorphous insulators commonly used within and around the superconducting qubits contain a serious decoherence source, the nanoscopic fluctuators, which significantly deteriorates coherent qubit operation. In particular, the nanoscopic fluctuators residing in the amorphous AlO_x tunnel barrier, which is exclusively used in all the present-day superconducting qubits, are so strongly coupled to the qubit that they can even completely destroy the quantum information stored in the qubit. In order to address this problem, we have devised a precision material engineering technique for the nanometer-thick tunnel barrier and its interfaces, and fabricated the first superconducting qubit with a single-crystal Al₂O₃ tunnel barrier. In this new qubit, we have observed ~80% reduction in the density of the nanoscopic fluctuators as compared to the previous qubits with amorphous AlO_x tunnel barriers. This verifies that the amorphous structure of the tunnel barrier is the main origin of the detrimental fluctuators within the qubit. It also shows that the decoherence sources in the superconducting qubits can be identified and eliminated with the right practice of material engineering. In addition to the results on the superconducting qubits, I will present other examples of precision material engineering such as atomically-engineered complex oxides and show how artificial materials create new physics.

Host: Anlage
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