Experimentelle Untersuchung von Kohärenz und Verschränkung in Josephson-Phasenqubits

• Antragsteller: Professor Dr. Alexey V. Ustinov, Ph.D.
• Fachliche Zuordnung: Experimentelle Physik der kondensierten Materie
• Förderung: Förderung von 2003 bis 2011
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 5414868

• Erstellungsjahr: 2010

Zusammenfassung der Projektergebnisse

The major results obtained within this project are in implementation of a microwave scheme for reading out a Josephson phase qubit and investigation of qubit interaction with microscopic two-level defects. Our new low-dissipative readout method allows to determine the qubit state in about 25 µs, which is a factor of about 20 faster than the conventional readout performed by switching detector. This readout scheme allows for reading out multiple qubits using a single microwave line by employing frequency-division multiplexing. The study of the qubit interaction with microscopic two-level defects allows us to better understand the origins of qubit decoherence. We pursued experiments in which the phase qubit is coupled strongly to individual defects. In such a hybrid system, consisting of the macroscopic phase qubit and nanometer-sized TLS, we were able to perform a variety of interesting experiments, ranging from the implementation of coherent two-qubit gates, the study of qubit-induced TLS decoherence, and the demonstration of direct TLS manipulation by resonant driving.

Projektbezogene Publikationen (Auswahl)

• Temperature dependence of coherent oscillations in Josephson phase qubits. Phys. Rev. Lett. 99, 170504 (2007)
  J. Lisenfeld, A. Lukashenko, and A. V. Ustinov
  
• High-contrast readout of superconducting qubits beyond the single-shot resolution limit. Appl. Phys. Lett. 91, 232502 (2007)
  J. Lisenfeld, A. Lukashenko, and A.V. Ustinov
  
• A tunable rf SQUID manipulated as flux and phase qubit. Phys. Scr. T 137, 014011 (2009)
  S. Poletto, F. Chiarello, M. G. Castellano, J. Lisenfeld, A. Lukashenko, P. Carelli, and A. V. Ustinov
  
• Coherent oscillations in a superconducting tunable flux qubit manipulated without microwaves. New J. Phys. 11, 013009 (2009)
  S. Poletto, F. Chiarello, M. G. Castellano, J. Lisenfeld, A. Lukashenko, C. Cosmelli, G. Torrioli, P. Carelli and A. V. Ustinov
  
• Dispersive readout scheme for a Josephson phase qubit. Appl. Phys. Lett. (2010)
  T. Wirth, J. Lisenfeld, A. Lukashenko, A. V. Ustinov
  
• Measuring the temperature dependence of individual two-level systems by direct coherent control. Phys. Rev. Lett. 105, 230504 (2010)
  J. Lisenfeld, C. Müller, J. H. Cole, P. Bushev, A. Lukashenko, A. Shnirman, and A. V. Ustinov
  
• Quantum hybrid system surveyed using multi-photon spectroscopy. Phys. Rev. B 82, 134530 (2010)
  P. Bushev, C. Müller, J. Lisenfeld, J. H. Cole, A. Lukashenko, A. Shnirman, J. Martinis, and A.V. Ustinov
  
• Rabi spectroscopy of a strongly driven qubit-fluctuator system. Phys. Rev. B (Rapid Commun.) 81, 100511 (2010)
  J. Lisenfeld, C. Müller, J. H. Cole, P. Bushev, A. Lukashenko, A. Shnirman, and A.V. Ustinov