A. V. Semenov

Low-temperature electron dephasing rates indicate magnetic disorder in superconducting TiN films

  1. A. I. Lomakin,
  2. E. M. Baeva,
  3. N. A. Titova,
  4. A. V. Semenov,
  5. A. V. Lubenchenko,
  6. M. A. Kirsanova,
  7. S. A. Evlashin,
  8. S. Saha,
  9. S. Bogdanov,
  10. A. I. Kolbatova,
  11. and G. N. Gol'tsman
We investigate electron transport and phase-breaking processes in thin titanium nitride (TiN) films of epitaxial quality. Previous studies show that a minute surface magnetic disorder
significantly reduces the critical temperature (Tc) and broadens the superconducting transition as the film thickness and device size decrease. We measure electron dephasing rates via magnetoresistance from Tc to ∼4Tc in various-thickness TiN films. Electron dephasing occurs on the picosecond timescale and is nearly independent of temperature, differing from the expected inelastic scattering due to the electron-phonon and electron-electron interactions near Tc, which occur over a nanosecond timescale. We propose spin-flip scattering as a possible additional phase-breaking mechanism. The significant increase in the dephasing rate for the thinnest film indicates that magnetic disorder resides near the surface of naturally oxidized films. Our research suggests that magnetic disorder may be a significant contributor to RF dissipation in superconducting devices based on TiN.
arxiv pdf

Experimental demonstration of a two-dimensional phonon cavity in the quantum regime

  1. A. N. Bolgar,
  2. J. I. Zotova,
  3. D. D. Kirichenko,
  4. I. S. Besedin,
  5. A. V. Semenov,
  6. R. S. Shaikhaidarov,
  7. and O. V. Astafiev
The quantum regime in acoustic systems is a focus of recent fundamental research in the new field of Quantum Acoustodynamics (QAD). Systems based on surface acoustic waves having an
advantage of easy integration in two-dimensions are particularly promising for the demonstration of novel effects in QAD and development of novel devices of quantum acousto-electronics. We demonstrate the vacuum mode of the surface acoustic wave resonator by coupling it to a superconducting artificial atom. The artificial atom is implemented into the resonator formed by two Brag mirrors. The results are consistent with expectations supported by the system model and our calculations. This work opens the way to map analogues of quantum optical effects into acoustic systems.
arxiv pdf

Coherent dynamics and decoherence in a superconducting weak link

  1. J.T. Peltonen,
  2. Z.H. Peng,
  3. Yu. P. Korneeva,
  4. B. M. Voronov,
  5. A. A. Korneev,
  6. A. V. Semenov,
  7. G. N. Gol'tsman,
  8. J. S. Tsai,
  9. and O. V. Astafiev
We demonstrate coherent dynamics of quantized magnetic fluxes in a superconducting loop with a weak link – a nanobridge patterned from the same thin NbN film as the loop. The
bridge is a short rounded shape constriction, close to 10 nm long and 20 – 30 nm wide, having minimal width at its center. Quantum state control and coherent oscillations in the driven time evolution of the tunnel-junctionless system are achieved. Decoherence and energy relaxation in the system are studied using a combination of microwave spectroscopy and direct time-domain techniques. The effective flux noise behavior suggests inductance fluctuations as a possible cause of the decoherence.
arxiv pdf