L. Frunzio

Ten Milliseconds for Aluminum Cavities in the Quantum Regime

  1. M. Reagor,
  2. Hanhee Paik,
  3. G. Catelani,
  4. L. Sun,
  5. C. Axline,
  6. E. Holland,
  7. I.M. Pop,
  8. N.A. Masluk,
  9. T. Brecht,
  10. L. Frunzio,
  11. M.H. Devoret,
  12. L.I. Glazman,
  13. and R. J. Schoelkopf
A promising quantum computing architecture couples superconducting qubits to microwave resonators (circuit QED), a system in which three-dimensional microwave cavities have become a
valuable resource. Such cavities have surface-to-volume ratios, or participation ratios a thousandfold smaller than in planar devices, deemphasizing potentially lossy surface elements by an equal amount. Motivated by this principle, we have tested aluminum superconducting cavity resonators with internal quality factors greater than 0.5 billion and intrinsic lifetimes reaching 0.01 seconds at single photon power and millikelvin temperatures. These results are the first to explore the use of superconducting aluminum, a ubiquitous material in circuit QED, as the basis of highly coherent (Q~10^7-10^9) cavity resonators. Measurements confirm the cavities‘ predicted insensitivity to quasiparticles (kinetic inductance fraction-5ppm) and an absence of two level dielectric fluctuations.
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

Photon Shot Noise Dephasing in the Strong-Dispersive Limit of Circuit QED

  1. A. P. Sears,
  2. A. Petrenko,
  3. G. Catelani,
  4. L. Sun,
  5. Hanhee Paik,
  6. G. Kirchmair,
  7. L. Frunzio,
  8. L. I. Glazman,
  9. S. M. Girvin,
  10. and R. J. Schoelkopf
We study the photon shot noise dephasing of a superconducting transmon qubit in the strong-dispersive limit, due to the coupling of the qubit to its readout cavity. As each random arrival
or departure of a photon is expected to completely dephase the qubit, we can control the rate at which the qubit experiences dephasing events by varying textit{in situ} the cavity mode population and decay rate. This allows us to verify a pure dephasing mechanism that matches theoretical predictions, and in fact explains the increased dephasing seen in recent transmon experiments as a function of cryostat temperature. We investigate photon dynamics in this limit and observe large increases in coherence times as the cavity is decoupled from the environment. Our experiments suggest that the intrinsic coherence of small Josephson junctions, when corrected with a single Hahn echo, is greater than several hundred microseconds.
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