Superconducting quantum circuits

Sorin Paraoanu,KVANTTI group,Low Temperature Laboratory, Helsinki University of Technology

Scientific Advisory Board Meeting,Center of Excellence in Low Temperature Quantum Phenomena and Devices Helsinki University of Technology Thursday, November 12, 2009

Summary:• general overview of recent scientific research (2008-2009) in the Kvantti group: - quantum coherence versus fragmentation - materials research - entanglement and dissipation in superconducting quantum circuits • highlighted result: Autler-Townes effect in a superconducting qubit• management

General overview (2008-2009)

• Quantum coherence versus fragmentation

• Nanoelectronics and materials research

• Entanglement and dissipation in superconducting circuits

G. S. Paraoanu, Phase coherence and fragmentation in weakly interacting bosonic gases, Phys. Rev. A 77, 041605R (2008); G. S. Paraoanu, Localization of the relative phase via measurements, J. Low Temp. Phys. 153, 285 (2008); G. S. Paraoanu, Evolution of fragmented states, J. Phys.: Conf. Ser. 150, 032079 (2009).

J. Kallioinen, M. R. Hassan, G. S. Paraoanu, and J. Korppi-Tommola, Dye-sensitized nanostructured TiO2 film based photoconductor, J. Photochem. Photobiol. A 195, 352 (2008). K. Chalapat, K. Sarvala, J. Li, and G. S. Paraoanu, Wideband Reference-Plane Invariant Method for Measuring Electromagnetic Parameters of Materials, IEEE Trans. Microw. Theory Tech. 57, 2257 (2009);J. J. Toppari, T. Kühn, A. M. Halvari, and G. S. Paraoanu, Method for finding the critical temperature of the island in a SET structure, J. Phys.: Conf. Ser. 150, 022088 (2009); M. Rinkiö , A. Johansson, G. S. Paraoanu, and P. Törmä, High-speed memory from carbon nanotube field-effect transitors with high-k gate dielectric, Nano Lett. 9, 643 (2009);

K. Chalapat, G.S. Paraoanu, and K. Sarvala, Broadband reference-plane invariant method and algorithm for measuring electromagnetic properties of materials, National Board of Patents and Registration Finland (pending).

J. Li, K. Chalapat, and G. S. Paraoanu, Entanglement of superconducting qubits via microwave fields: classical and quantum regimes, Phys. Rev. B 78, 064503 (2008);J. Li, K. Chalapat, and G. S. Paraoanu, Enhancement of sudden death of entanglement for driven qubits, J. Low Temp. Phys. 153, 294 (2008); J. Li, K. Chalapat, and G. S. Paraoanu, Measurement-induced entanglement of two superconducting qubits, J. Phys.: Conf. Ser. 150, 022051 (2009);J. Li and G. S. Paraoanu, Decay of entanglement in coupled, driven systems with bipartite decoherence, Eur. J. Phys. D. (2009), DOI: 10.1140/epjd/e2009-00247-9;J. Li and G.S. Paraoanu, Generation and propagation of entanglement in driven coupled-qubit systems, New J. Phys. 11, 113020 (2009);M. A. Sillanpää, J. Li, K. Cicak, F. Altomare, J. I. Park, R. W. Simmonds, G. S. Paraoanu, and P. J. Hakonen, Autler-Townes effect in a superconducting three-level system, Phys. Rev. Lett. 103, 193601 (2009).

highlighted result

Autler-Townes effect in a superconducting qubit

Collaboration between the NANO group, the Kvantti group, and NIST:

M. A. Sillanpää, J. Li, K. Cicak, F. Altomare, J. I. Park, R. W. Simmonds, G. S. Paraoanu, and P. J. Hakonen, Autler-Townes effect in a superconducting three-level system, Phys. Rev. Lett. 103, 193601 (2009).

Samples made at NIST:

Measurements/data analysis done at LTL:

Circuit parameter determination

Rabi oscillation betwen higher excited levels (levels 2 and 1)

Comparison between theory and experiment:

(b) is a theoretical simulation of a model which includes cross-couplings and up to the fifth level (solid lines). The dotted line is an analytical result corresponding to a simplified 3-level model with no cross-couplings.

Management

Group structure and changes: PI dr. Sorin Paraoanu2 Ph.D. students 2008-2009: Khattiya Chalapat and Jian Li1 Ph.D. student (Khartikeyan S. Kumar) joined the group in sept. 2009Summer students: Sampo Saarinen (2009) - with Nano group, Mikko Ervasti (2008).

PI has spend two months at IQOQI Vienna (Prof. A . Zeilinger) as a Templeton Fellow

Infrastructure: • cryogenics: design/installation of the tail of the shielded room, the space for fridge,

the pumping and gas handling system. S.H.E. still alive but more tests are needed. New can should be tested soon. New high-frequency wiring in progress.

• electronics: a few major pieces of high-frequency equipment (vector network analyzer, microwave signal generator, waveform generator), others need to be aquired soon (pulse generator, ultrafast data card).

• electromagnet for materials research: installation done.

Changes in the research plan: No significant changes, but shifting of certain priorities occurred.