title: Coherence and decay of higher energy levels of a superconducting transmon qubit.
abstract: We present measurements of coherence and successive decay dynamics of higher energy levels of a superconducting transmon qubit. By applying consecutive π pulses for each sequential transition frequency, we excite the qubit from the ground state up to its fourth excited level and characterize the decay and coherence of each state. We find the decay to proceed mainly sequentially, with relaxation times in excess of 20  μs for all transitions. We also provide a direct measurement of the charge dispersion of these levels by analyzing beating patterns in Ramsey fringes. The results demonstrate the feasibility of using higher levels in transmon qubits for encoding quantum information.
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA and Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU Oxford, United Kingdom.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Peterer
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Bader
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Xiaoyue
authors.initials: X
authors.lastname: Jin
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Fei
authors.initials: F
authors.lastname: Yan
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Archana
authors.initials: A
authors.lastname: Kamal
authors.affiliation: MIT Lincoln Laboratory, 244 Wood Street, Lexington, Massachusetts 02420, USA.
authors.forename: Theodore J
authors.initials: TJ
authors.lastname: Gudmundsen
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU Oxford, United Kingdom.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Leek
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Terry P
authors.initials: TP
authors.lastname: Orlando
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA and MIT Lincoln Laboratory, 244 Wood Street, Lexington, Massachusetts 02420, USA.
authors.forename: William D
authors.initials: WD
authors.lastname: Oliver
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Simon
authors.initials: S
authors.lastname: Gustavsson