O. Buisson

Fast high fidelity quantum non-demolition qubit readout via a non-perturbative cross-Kerr coupling

  1. R. Dassonneville,
  2. T. Ramos,
  3. V. Milchakov,
  4. L. Planat,
  5. É. Dumur,
  6. F. Foroughi,
  7. J. Puertas,
  8. S. Leger,
  9. K. Bharadwaj,
  10. J. Delaforce,
  11. K. Rafsanjani,
  12. C. Naud,
  13. W. Hasch-Guichard,
  14. J.J. García-Ripoll,
  15. N. Roch,
  16. and O. Buisson
Qubit readout is an indispensable element of any quantum information processor. In this work we propose an original coupling scheme between qubit and cavity mode based on a non-perturbative
cross-Kerr interaction. It leads to an alternative readout mechanism for superconducting qubits. This scheme, using the same experimental techniques as the perturbative cross-Kerr coupling (dispersive interaction), leads to an alternative readout mechanism for superconducting qubits. This new process, being non-perturbative, maximizes speed of qubit readout, single-shot fidelity and its quantum non-demolition (QND) behavior at the same time, while minimizing the effect of unwanted decay channels such as, for example, the Purcell effect. We observed 97.4 % single-shot readout fidelity for short 50 ns pulses. Using long measurement, we quantified the QND-ness to 99 %.
arxiv pdf

A V-shape superconducting artificial atom based on two inductively coupled transmons

  1. É. Dumur,
  2. B. Küng,
  3. A. K. Feofanov,
  4. T. Weissl,
  5. N. Roch,
  6. C. Naud,
  7. W. Guichard,
  8. and O. Buisson
Circuit quantum electrodynamics systems are typically built from resonators and two-level artificial atoms, but the use of multi-level artificial atoms instead can enable promising
applications in quantum technology. Here we present an implementation of a Josephson junction circuit dedicated to operate as a V-shape artificial atom. Based on a concept of two internal degrees of freedom, the device consists of two transmon qubits coupled by an inductance. The Josephson nonlinearity introduces a strong diagonal coupling between the two degrees of freedom that finds applications in quantum non-demolition readout schemes, and in the realization of microwave cross-Kerr media based on superconducting circuits.
arxiv pdf

Ultrafast QND measurements based on diamond-shape artificial atom

  1. I. Diniz,
  2. E. Dumur,
  3. O. Buisson,
  4. and A. Auffèves
We propose a Quantum Non Demolition (QND) read-out scheme for a superconducting artificial atom coupled to a resonator in a circuit QED architecture, for which we estimate a very high
measurement fidelity without Purcell effect limitations. The device consists of two transmons coupled by a large inductance, giving rise to a diamond-shape artificial atom with a logical qubit and an ancilla qubit interacting through a cross-Kerr like term. The ancilla is strongly coupled to a transmission line resonator. Depending on the qubit state, the ancilla is resonantly or dispersively coupled to the resonator, leading to a large contrast in the transmitted microwave signal amplitude. This original method can be implemented with state of the art Josephson parametric amplifier, leading to QND measurements in a few tens of nanoseconds with fidelity as large as 99.9 %.
arxiv pdf