Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 33: Superconductivity, Measuring Devices, Matter at Low Temperature: Poster Session

TT 33.48: Poster

Wednesday, March 28, 2012, 15:00–19:00, Poster B

Comparing coherence time of Josephson junction phase qubits made of different materials — •Kirill Lakhmanskiy^1,2, Jürgen Lisenfeld², and Alexey V. Ustinov² — ¹Kotel’nikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 125009 Moscow, Russia — ²Physikalisches Institut, Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany

Superconducting phase qubits suffer from energy relaxation which occurs predominantly in the dielectrics used to insulate the qubit junction or to make a shunt capacitor. This is verified from our measurements on phase qubits made using either SiO_x or SiN_x dielectrics. The latter circuits achieve an energy relaxation time T₁ of about 40 ns which is 8 times longer than for the identically made SiO_x circuits. We also plan to explore an alternative idea to replace the lossy tunnel junction by a nanowire, leaving the shunt capacitor unchanged. Such a qubit circuit can be fabricated without junction dielectric and should thus achieve longer coherence times.