I. Diniz

Towards a spin-ensemble quantum memory for superconducting qubits

  1. C. Grezes,
  2. Y. Kubo,
  3. B. Julsgaard,
  4. T. Umeda,
  5. J. Isoya,
  6. H. Sumiya,
  7. H. Abe,
  8. S. Onoda,
  9. T. Ohshima,
  10. K. Nakamura,
  11. I. Diniz,
  12. A. Auffeves,
  13. V. Jacques,
  14. J.-F. Roch,
  15. D. Vion,
  16. D. Esteve,
  17. K. Moelmer,
  18. and P. Bertet
This article reviews efforts to build a new type of quantum device, which combines an ensemble of electronic spins with long coherence times, and a small-scale superconducting quantum
processor. The goal is to store over long times arbitrary qubit states in orthogonal collective modes of the spin-ensemble, and to retrieve them on-demand. We first present the protocol devised for such a multi-mode quantum memory. We then describe a series of experimental results using NV center spins in diamond, which demonstrate its main building blocks: the transfer of arbitrary quantum states from a qubit into the spin ensemble, and the multi-mode retrieval of classical microwave pulses down to the single-photon level with a Hahn-echo like sequence. A reset of the spin memory is implemented in-between two successive sequences using optical repumping of the spins.
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

Electron spin resonance detected by a superconducting qubit

  1. Y. Kubo,
  2. I. Diniz,
  3. C. Grezes,
  4. T. Umeda,
  5. J. Isoya,
  6. H. Sumiya,
  7. T. Yamamoto,
  8. H. Abe,
  9. S. Onoda,
  10. T. Ohshima,
  11. V. Jacques,
  12. A. Dréau,
  13. J.-F. Roch,
  14. A. Auffeves,
  15. D. Vion,
  16. D. Esteve,
  17. and P. Bertet
A new method for detecting the magnetic resonance of electronic spins at low temperature is demonstrated. It consists in measuring the signal emitted by the spins with a superconducting
qubit that acts as a single-microwave-photon detector, resulting in an enhanced sensitivity. We implement this new type of electron-spin resonance spectroscopy using a hybrid quantum circuit in which a transmon qubit is coupled to a spin ensemble consisting of NV centers in diamond. With this setup we measure the NV center absorption spectrum at 30mK at an excitation level of thicksim15,mu_{B} out of an ensemble of 10^{11} spins.
arxiv pdf