S. Puri

A stabilized logical quantum bit encoded in grid states of a superconducting cavity

  1. P. Campagne-Ibarcq,
  2. A. Eickbusch,
  3. S. Touzard,
  4. E. Zalys-Geller,
  5. N. E. Frattini,
  6. V. V. Sivak,
  7. P. Reinhold,
  8. S. Puri,
  9. S. Shankar,
  10. R. J. Schoelkopf,
  11. L. Frunzio,
  12. M. Mirrahimi,
  13. and M.H. Devoret
The majority of quantum information tasks require error-corrected logical qubits whose coherence times are vastly longer than that of currently available physical qubits. Among the
many quantum error correction codes, bosonic codes are particularly attractive as they make use of a single quantum harmonic oscillator to encode a correctable qubit in a hardware-efficient manner. One such encoding, based on grid states of an oscillator, has the potential to protect a logical qubit against all major physical noise processes. By stroboscopically modulating the interaction of a superconducting microwave cavity with an ancillary transmon, we have successfully prepared and permanently stabilized these grid states. The lifetimes of the three Bloch vector components of the encoded qubit are enhanced by the application of this protocol, and agree with a theoretical estimate based on the measured imperfections of the experiment.
arxiv pdf

Gated conditional displacement readout of superconducting qubits

  1. S. Touzard,
  2. A. Kou,
  3. N. E. Frattini,
  4. V. V. Sivak,
  5. S. Puri,
  6. A. Grimm,
  7. L. Frunzio,
  8. S. Shankar,
  9. and M.H. Devoret
We have realized a new interaction between superconducting qubits and a readout cavity that results in the displacement of a coherent state in the cavity, conditioned on the state of
the qubit. This conditional state, when it reaches the cavity-following, phase-sensitive amplifier, matches its measured observable, namely the in-phase quadrature. In a setup where several qubits are coupled to the same readout resonator, we show it is possible to measure the state of a target qubit with minimal dephasing of the other qubits. Our results suggest novel directions for faster readout of superconducting qubits and implementations of bosonic quantum error-correcting codes.
arxiv pdf

Resonance fluorescence from an artificial atom in squeezed vacuum

  1. D.M. Toyli,
  2. A.W. Eddins,
  3. S. Boutin,
  4. S. Puri,
  5. D. Hover,
  6. V. Bolkhovsky,
  7. W. D. Oliver,
  8. A. Blais,
  9. and I. Siddiqi
We present an experimental realization of resonance fluorescence in squeezed vacuum. We strongly couple microwave-frequency squeezed light to a superconducting artificial atom and detect
the resulting fluorescence with high resolution enabled by a broadband traveling-wave parametric amplifier. We investigate the fluorescence spectra in the weak and strong driving regimes, observing up to 3.1 dB of reduction of the fluorescence linewidth below the ordinary vacuum level and a dramatic dependence of the Mollow triplet spectrum on the relative phase of the driving and squeezed vacuum fields. Our results are in excellent agreement with predictions for spectra produced by a two-level atom in squeezed vacuum [Phys. Rev. Lett. \textbf{58}, 2539-2542 (1987)], demonstrating that resonance fluorescence offers a resource-efficient means to characterize squeezing in cryogenic environments.
arxiv pdf