M. H. Devoret

Stabilizing a Bell state of two superconducting qubits by dissipation engineering

  1. Z. Leghtas,
  2. U. Vool,
  3. S. Shankar,
  4. M. Hatridge,
  5. S.M. Girvin,
  6. M.H. Devoret,
  7. and M. Mirrahimi
We propose a dissipation engineering scheme that prepares and protects a maximally entangled state of a pair of superconducting qubits. This is done by off-resonantly coupling the two
qubits to a low-Q cavity mode playing the role of a dissipative reservoir. We engineer this coupling by applying six continuous-wave microwave drives with appropriate frequencies. The two qubits need not be identical. We show that our approach does not require any fine-tuning of the parameters and requires only that certain ratios between them be large. With currently achievable coherence times, simulations indicate that a Bell state can be maintained over arbitrary long times with fidelities above 94%. Such performance leads to a significant violation of Bell’s inequality (CHSH correlation larger than 2.6) for arbitrary long times.
arxiv pdf

Demonstrating a Driven Reset Protocol of a Superconducting Qubit

  1. K. Geerlings,
  2. Z. Leghtas,
  3. I. M. Pop,
  4. S. Shankar,
  5. L. Frunzio,
  6. R. J. Schoelkopf,
  7. M. Mirrahimi,
  8. and M. H. Devoret
Qubit reset is crucial at the start of and during quantum information algorithms. We present the experimental demonstration of a practical method to force qubits into their ground state,
based on driving certain qubit and cavity transitions. Our protocol, nicknamed DDROP (Double Drive Reset of Population) is tested on a superconducting transmon qubit in a 3D cavity. Using a new method for measuring population, we show that we can prepare the ground state with a fidelity of at least 99.5 % in less than 3 microseconds; faster times and higher fidelity are predicted upon parameter optimization.
arxiv pdf

Improving the Quality Factor of Microwave Compact Resonators by Optimizing their Geometrical Parameters

  1. K. Geerlings,
  2. S. Shankar,
  3. E. Edwards,
  4. L. Frunzio,
  5. R. J. Schoelkopf,
  6. and M. H. Devoret
Applications in quantum information processing and photon detectors are stimulating a race to produce the highest possible quality factor on-chip superconducting microwave resonators.
We have tested the surface-dominated loss hypothesis by systematically studying the role of geometrical parameters on the internal quality factors of compact resonators patterned in Nb on sapphire. Their single-photon internal quality factors were found to increase with the distance between capacitor fingers, the width of the capacitor fingers, and the impedance of the resonator. Quality factors were improved from 210,000 to 500,000 at T = 200 mK. All of these results are consistent with our starting hypothesis.
arxiv pdf