Fabrication and measurement of a niobium persistent current qubit

Recent successes with superconducting Josephson junction qubits make them prime candidates for the implementation of quantum computing. This doctoral thesis details the study of a niobium Josephson junction circuit for quantum computing applications. The thesis covers two main areas: 1) the fabrication of sub-micron niobium Josephson junction devices using a Nb/Al/A1Ox/Nb trilayer process and 2) measurements of unique quantum properties of a superconducting device proposed as a quantum bit--the Persistent Current (PC) qubit. The thesis discusses the fabrication of niobium Josephson junction devices which is integral to the design and measurement of the circuit. The devices were fabricated at MIT Lincoln Laboratory using optical projection lithography to define features. A technique to produce more uniform critical-current densities across a wafer is developed within the scope of the thesis. We also introduce experimental work on the PC qubit performed at dilution refrigerator temperatures (T [approximately] 12mK). Microwave spectroscopy was used to map the energy level separation between macroscopic quantum states of the qubit system. We measured the intrawell energy relaxation time [tau]d between quantum levels in this particular device. The intrawell relaxation measurements are important in determining whether a promising decoherence time can be achieved in Nb-based Josephson devices, which has a more mature fabrication process compared to other superconducting fabrication processes.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Nakada, Daniel Yuki, 1975-

Advisor dc:contributor.advisor

• Terry P. Orlando.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/18049

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/18049