Multilevel spectroscopy of two-level systems coupled to a dc SQUID phase qubit
Artikel i vetenskaplig tidskrift, 2010

We report spectroscopic measurements of discrete two-level systems (TLSs) coupled to a dc superconducting quantum interference device phase qubit with a 16μ m 2 area Al/ AlO x /Al junction. Applying microwaves in the 10-11 GHz range, we found eight avoided level crossings with splitting sizes from 10 to 200 MHz and spectroscopic lifetimes from 4 to 160 ns. Assuming the transitions are from the ground state of the composite system to an excited state of the qubit or an excited state of one of the TLS states, we fit the location and spectral width to get the energy levels, splitting sizes, and spectroscopic coherence times of the phase qubit and TLSs. The distribution of splittings is consistent with noninteracting individual charged ions tunneling between random locations in the tunnel barrier and the distribution of lifetimes is consistent with the AlOx in the junction barrier having a frequency-independent loss tangent. To check that the charge of each TLS couples independently to the voltage across the junction, we also measured the spectrum in the 20-22 GHz range and found tilted avoided level crossings due to the second excited state of the junction and states in which both the junction and a TLS were excited.


Tauno Palomaki

Chalmers, Mikroteknologi och nanovetenskap (MC2), Kvantkomponentfysik

S. K. Dutta

University of Maryland

Georgetown University

R. M. Lewis

University of Maryland

Northrop Grumman corporation

A. J. Przybysz

University of Maryland

H. Paik

Yale University

University of Maryland

B. K. Cooper

University of Maryland

H. Kwon

University of Maryland

J. R. Anderson

University of Maryland

C. J. Lobb

University of Maryland

F.C. Wellstood

University of Maryland

E. Tiesinga

National Institute of Standards and Technology

Physical Review B - Condensed Matter and Materials Physics

1098-0121 (ISSN)

Vol. 81 Art. no. 144503- 144503