Alexander N. Korotkov

Controlled catch and release of microwave photon states

  1. Yi Yin,
  2. Yu Chen,
  3. Daniel Sank,
  4. P. J. J. O'Malley,
  5. T. C. White,
  6. R. Barends,
  7. J. Kelly,
  8. Erik Lucero,
  9. Matteo Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. A. Vainsencher,
  13. J. Wenner,
  14. Alexander N. Korotkov,
  15. A. N. Cleland,
  16. and John M. Martinis
, in which the resonant cavity confines photons and promotes"]strong light-matter interactions. The cavity end-mirrors determine the performance of the coupled system, with higher mirror reflectivity yielding better quantum coherence, but higher mirror transparency giving improved measurement and control, forcing a compromise. An alternative is to control the mirror transparency, enabling switching between long photon lifetime during quantum interactions and large signal strength when performing measurements. Here we demonstrate the superconducting analogue, using a quantum system comprising a resonator and a qubit, with variable coupling to a measurement transmission line. The coupling can be adjusted through zero to a photon emission rate 1,000 times the intrinsic photon decay rate. We use this system to control photons in coherent states as well as in non-classical Fock states, and dynamically shape the waveform of released photons. This has direct applications to circuit quantum electrodynamics [3], and may enable high-fidelity quantum state transfer between distant qubits, for which precisely-controlled waveform shaping is a critical and non-trivial requirement [4, 5].
arxiv pdf

Simple quantum error detection and correction for superconducting qubits

  1. Kyle Keane,
  2. and Alexander N. Korotkov
We analyze simple quantum error detection and quantum error correction protocols relevant to current experiments with superconducting qubits. We show that for qubits with energy relaxation
the repetitive N-qubit codes cannot be used for quantum error correction, but can be used for quantum error detection. In the latter case it is sufficient to use only two qubits for the encoding. In the analysis we demonstrate a useful technique of unraveling the qubit energy relaxation into „relaxation“ and „no relaxation“ scenarios. Also, we propose and numerically analyze several two-qubit algorithms for quantum error detection/correction, which can be readily realized at the present-day level of the phase qubit technology.
arxiv pdf