RSS icon
Twitter icon
Facebook icon
Vimeo icon
YouTube icon

Anomalous avoided level crossings in a Cooper-pair box spectrum

TitleAnomalous avoided level crossings in a Cooper-pair box spectrum
Publication TypeJournal Article
Year of Publication2008
AuthorsZ. Kim, V. Zaretskey, Y. Yoon, J. F. Schneiderman, M. D. Shaw, P. M. Echternach, F. C. Wellstood, and B. S. Palmer
JournalPhys. Rev. B
Volume78
Date Publishedoct
ISSN1098-0121
Keywords2008, FLICKER 1/F NOISE, JOSEPHSON-JUNCTIONS, QUBIT, Single Fellow, SINGLE-ELECTRON TRANSISTORS, SMALL TUNNEL-JUNCTIONS
Abstract

We have observed a few distinct anomalous avoided level crossings and voltage-dependent transitions in the excited-state spectrum of an Al/AlO(x)/Al Cooper-pair box (CPB). The device was measured at 40 mK in the 15-50 GHz frequency range. We find that a given level crosses the CPB spectrum at two different gate voltages; the frequency and splitting size of the two crossings differ and the splitting size depends on the Josephson energy of the CPB. We show that this behavior is not only consistent with the CPB being coupled to discrete charged "two-level" quantum systems, which move atomic distances in the CPB junctions, but that the spectra provide information about the fluctuators, which is not available from phase qubit spectra of anomalous avoided levels. In particular by fitting a model Hamiltonian to our data, we extract microscopic parameters for each fluctuator, including well asymmetry, tunneling amplitude, and the minimum hopping distance for each fluctuator. The tunneling rates range from less than 3.5-13 GHz, which represent values between 5 and 150% of the well asymmetry, and the dipole moments give a minimum hopping distance of 0.3-0.8 A. We have also found that these discrete two-level systems have a pronounced effect on the relaxation time (T(1)) of the quantum states of the CPB and hence can be a source of dissipation for superconducting quantum bits.

URLhttp://prb.aps.org/abstract/PRB/v78/i14/e144506 http://apps.webofknowledge.com/full\_record.do?product=WOS&search\_mode=GeneralSearch&qid=2&SID=3BoaAEpOPA@Jjha4jbH&page=1&doc=1

Subscribe to A Quantum Bit 

Quantum physics began with revolutionary discoveries in the early twentieth century and continues to be central in today’s physics research. Learn about quantum physics, bit by bit. From definitions to the latest research, this is your portal. Subscribe to receive regular emails from the quantum world. Previous Issues...

Sign Up Now

Sign up to receive A Quantum Bit in your email!

 Have an idea for A Quantum Bit? Submit your suggestions to jqi-comm@umd.edu