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Coherent oscillations in superconducting flux qubit without microwave pulse

Coherent oscillations in superconducting flux qubit without microwave pulse. S. Poletto 1 , J. Lisenfeld 1 , A. Lukashenko 1 M.G. Castellano 2 , F. Chiarello 2 , C. Cosmelli 3 , P. Carelli 4 , A.V. Ustinov 1. 1 Physikalisches Institut III, Universität Erlangen-Nürnberg - Germany

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Coherent oscillations in superconducting flux qubit without microwave pulse

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  1. Coherent oscillations insuperconducting flux qubit without microwave pulse S. Poletto1, J. Lisenfeld1, A. Lukashenko1 M.G. Castellano2, F. Chiarello2, C. Cosmelli3, P. Carelli4, A.V. Ustinov1 1 Physikalisches Institut III, Universität Erlangen-Nürnberg - Germany 2 Istituto di Fotonica e Nanotecnologie del CNR – Italy 3 INFN and Università di Roma “la Sapienza” - Italy 4 Università degli Studi dell’Aquila - Italy

  2. Outline Outline • Circuit description • Observation of coherent oscillations without microwaves • Theoretical interpretation • Summary and conclusions S.Poletto

  3. Circuit description

  4. Circuit description For Φx = Φ0/2 the potential is a symmetric double well Qubit parameters Fully controllable system S.Poletto

  5. Circuit description The system is fully gradiometric, realized in Nb, designed by IFN-CNR, fabricated by Hypres (100 A/cm2) Flux bias Fc 1/100 coupling Readout SQUID flux bias Fx junctions 100mm S.Poletto

  6. Coherent oscillations without microwaves

  7. ? ? Coherent oscillations without microwaves Main idea (energy potential view) E2 E1 E0 system preparation evolution readout Population of the ground and exited states is determined by the potential symmetry and barrier modulation rate S.Poletto

  8. ? ? Coherent oscillations without microwaves Main idea (fluxes view) x c Readout S.Poletto

  9. Coherent oscillations without microwaves Experimental results • Oscillations for preparation of the left |L and right |R states • Frequency changes depending on pulse amplitude c S.Poletto

  10. Theoretical interpretation

  11. Theoretical interpretation Symmetric double-well potential (Φx = Φ0/2 )  description in the base {|L, |R} |L |R It is possible to describe the system in the energy base {|0, |1} as well |1 |0 S.Poletto

  12. |1 |0 Theoretical interpretation ? expected oscillation frequency of up to 35 GHz S.Poletto

  13. Theoretical interpretation Frequency dependence on pulse amplitude (Φc) Green dots: experimental data Blue line: theoretical curve S.Poletto

  14. Theoretical interpretation Note: In the case of asymmetric potential one should take into account a non-adiabatic population of the states {|0, |1} S.Poletto

  15. Conclusions

  16. Summary and conclusions Advantages of the demonstrated approach • Oscillations are obtained without using microwave pulses • Due to large energy level spacing the system can evolve athigh temperature (up to h/kB  1.1K) • High frequency of coherent oscillations (up to 35 GHz) allow for high speed quantum gates • A qubit coherence time of ~ 500 ns should be sufficient to implement an error correction algorithm • (required ~104 operations during the coherence time. • See e.g.: arXiv:quant-ph/0110143) S.Poletto

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