Macroscopic Quantum Coherence Research Team

Macroscopic quantum scattering has been in Josephson qubit-based research observed. A nearly perfect reflection, inelastic scattering (resonance fluorescence), Mollow triplet, electromagnetically induced transparency, Autler-Townes doublet, optical pumped population inversion, amplification by stimulated emission and other very rich physics were revealed. One of the resulting series of papers has already been accepted by Science magazine. For the integration of the qubits, the previous qubit-based coupler was carefully analyzed by varying its bias point, resulting in a guideline for the coupler's optimization. For the long decoherence time, we correlated flux noise in a coupled flux qubit, and learned the dominant contribution local fluctuation in decoherence. Quantum non-demolition readout was successfully demonstrated. For the future quantum current standard, a new current turnstile was developed and its parallel operation was demonstrated. Surface/interface states of superconductors were studied and their influence upon tunnel barrier and leakage current was discovered. An aluminum-based nano-mechanical resonator was developed.

Research Fields

Physics / Engineering

Research Subjects

• Quantum coherence in superconducting circuit
• Quantum bit
• Quantum information processing

Publications

1. Astafiev, O., Ioffe, L., Kafanov, S., Pashkin, Y., Arutyunov, K., Shahar, D., Cohen, O., Tsai, J.,
   "Coherent quantum phase slip"
   Nature 484, 355-358 (2012).
2. Abdumalikov, A., Astafiev, O., Pashkin, Y., Nakamura, Y., Tsai, J.,
   "Dynamics of Coherent and Incoherent Emission from an Artificial Atom in a 1D Space"
   Phys. Rev. Lett. 107, 043604-1-043604-4 (2011).
3. Bylander, J., Gustavsson, S., Yan, F., Yoshihara, F., Harrabi, K., Fitch, G., Cory, D., Nakamura, Y., Tsai, J., Oliver, W.,
   "Noise spectroscopy through dynamical decoupling with a superconducting flux qubit"
   Nature Physics 7, 565-570 (2011).
4. Astafiev, O., Abdumalikov, A., Zagoskin, A., Pashkin, Y., Nakamura, Y., Tsai, J.,
   "Ultimate on-chip quantum amplifier"
   Phys. Rev. Lett. 104, 183603-1-183603-4 (2010).
5. Abdumalikov, A., Astafiev, O., Zagoskin, A., Pashkin, Y., Nakamura, Y., Tsai, J.,
   "Electromagnetically induced transparency on a single artificial atom"
   Phys. Rev. Lett. 104, 193601-1-193601-4 (2010).
6. Astafiev, O., Zagoskin, A., Abdumalikov, A., Pashkin, Y., Yamamoto, T., Inomata, K., Nakamura, Y., Tsai, J.,
   "Resonance Fluorescence of a Single Artificial Atom"
   Science 327, 840-843 (2010).
7. Astafiev, O., Inomata, K., Niskanen, A., Yamamoto, T., Pashkin, Y., Nakamura, Y., Tsai, J.,
   "Single artificial-atom lasing"
   Nature 449, 588-590 (2007).
8. Niskanen, A., Harrabi, K., Yoshihara, F., Nakamura, Y., Lloyd, S., Tsai, J.,
   "Quantum Coherent Tunable Coupling of Superconducting Qubits"
   Science 316, 723-726 (2007).
9. Yamamoto, T., Pashkin, Y., Astafiev, O., Nakamura, Y., Tsai, J.,
   "Demonstration of conditional gate operation using superconducting charge qubits"
   Nature 425, 941-944 (2003).
10. Pashkin, Y., Yamamoto, T., Astafiev, O., Nakamura, Y., Averin, D., Tsai, J.,
    "Quantum oscillations in two coupled charge qubits"
    Nature 421, 823-826 (2003).