Dephasing of a superconducting flux qubit.

In order to gain a better understanding of the origin of decoherence in superconducting flux qubits, we have measured the magnetic field dependence of the characteristic energy relaxation time (T(1)) and echo phase relaxation time (T(2)(echo)) near the optimal operating point of a flux qubit. We have measured T(2)(echo) by means of the phase cycling method. At the optimal point, we found the relation T(2)(echo) approximately 2T(1). This means that the echo decay time is limited by the energy relaxation (T(1) process). Moving away from the optimal point, we observe a linear increase of the phase relaxation rate (1/T(2)(echo)) with the applied external magnetic flux. This behavior can be well explained by the influence of magnetic flux noise with a 1/f spectrum on the qubit.

[1]  M Ueda,et al.  Multiphoton transitions in a macroscopic quantum two-state system. , 2004, Physical review letters.

[2]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[3]  Garg,et al.  Quantum mechanics versus macroscopic realism: Is the flux there when nobody looks? , 1985, Physical review letters.

[4]  Orlando,et al.  Josephson Persistent-Current Qubit , 2022 .

[5]  J. Clarke,et al.  Low‐frequency noise in dc superconducting quantum interference devices below 1 K , 1987 .

[6]  Y. Pashkin,et al.  Coherent control of macroscopic quantum states in a single-Cooper-pair box , 1999, Nature.

[7]  Yuriy Makhlin,et al.  Dephasing of solid-state qubits at optimal points. , 2003, Physical review letters.

[8]  J. Martinis,et al.  Rabi oscillations in a large Josephson-junction qubit. , 2002, Physical review letters.

[9]  J. Clarke,et al.  Flicker (1∕f) noise in the critical current of Josephson junctions at 0.09–4.2K , 2004 .

[10]  D. DiVincenzo,et al.  Dephasing of a superconducting qubit induced by photon noise. , 2005, Physical review letters.

[11]  J. E. Mooij,et al.  Coherent Quantum Dynamics of a Superconducting Flux Qubit , 2003, Science.

[12]  P. Joyez,et al.  Manipulating the Quantum State of an Electrical Circuit , 2002, Science.

[13]  M Ueda,et al.  Parametric control of a superconducting flux qubit. , 2006, Physical review letters.

[14]  R. J. Schoelkopf,et al.  Dispersive measurements of superconducting qubit coherence with a fast latching readout , 2006 .

[15]  C. Tesche,et al.  Can a noninvasive measurement of magnetic flux be performed with superconducting circuits? , 1990, Physical review letters.

[16]  J. Johansson,et al.  Vacuum Rabi oscillations in a macroscopic superconducting qubit oscillator system. , 2005, Physical review letters.

[17]  Hideaki Takayanagi,et al.  Coherent control of a flux qubit by phase-shifted resonant microwave pulses , 2005 .

[18]  A. Niskanen,et al.  Decoherence of flux qubits due to 1/f flux noise. , 2006, Physical review letters.

[19]  Y. Makhlin,et al.  Quantum-state engineering with Josephson-junction devices , 2000, cond-mat/0011269.

[20]  Alfred G. Redfield,et al.  On the Theory of Relaxation Processes , 1957, IBM J. Res. Dev..

[21]  Yuriy Makhlin,et al.  Decoherence from ensembles of two-level fluctuators , 2006 .

[22]  Temperature square dependence of the low frequency charge noise in the Josephson junction qubits. , 2006, Physical review letters.

[23]  D Vion,et al.  NMR-like control of a quantum bit superconducting circuit. , 2004, Physical review letters.

[24]  Barenco,et al.  Conditional Quantum Dynamics and Logic Gates. , 1995, Physical review letters.

[25]  R. K. Wangsness,et al.  The Dynamical Theory of Nuclear Induction , 1953 .