Banishing quasiparticles from Josephson-junction qubits: why and how to do it

• Published in: IEEE transactions on applied superconductivity Vol. 13; no. 2; pp. 989 - 993
• Main Authors: Lang, K.M., Nam, S., Aumentado, J., Urbina, C., Martinis, J.M.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.06.2003; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Analog circuits; Applied sciences; Circuit properties; Circuits; Classical and quantum physics: mechanics and fields; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Energy states; Exact sciences and technology; Fabrication; Josephson junctions; Metrology; Metrology, measurements and laboratory procedures; NIST; Physics; Proposals; Quantum computing; Quantum information; Reflection; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Superconducting devices; Units and standards; Quasiparticle; Andreev reflection; Shunt; Josephson junction; qubit; Coherence; Quantum information; quantum computation; Biased estimation; superconducting devices
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2003.814121

Current-biased Josephson junctions are prime candidates for the realization of quantum bits; however, a present limitation is their coherence time. In this paper it is shown qualitatively that quasiparticles create decoherence. We can decrease the number of quasiparticles present in the junctions by two methods - reducing the creation rate with current shunts and increasing the depletion rate with normal-metal traps. Experimental data demonstrate that both methods are required to significantly reduce the number of quasiparticles and increase the system's coherence. We conclude that these methods are effective and that the design of Josephson-junction qubits must consider the role of quasiparticles.