Y. Kubo

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

Storage and retrieval of microwave fields at the single-photon level in a spin ensemble

  1. C. Grezes,
  2. B. Julsgaard,
  3. Y. Kubo,
  4. W. L. Ma,
  5. M. Stern,
  6. A. Bienfait,
  7. K. Nakamura,
  8. J. Isoya,
  9. S. Onoda,
  10. T. Ohshima,
  11. V. Jacques,
  12. D. Vion,
  13. D. Esteve,
  14. R. B. Liu,
  15. K. Mølmer,
  16. and P. Bertet
We report the storage of microwave pulses at the single-photon level in a spin-ensemble memory consisting of 1010 NV centers in a diamond crystal coupled to a superconducting LC resonator.
The energy of the signal, retrieved 100μs later by spin-echo techniques, reaches 0.3% of the energy absorbed by the spins, and this storage efficiency is quantitatively accounted for by simulations. This figure of merit is sufficient to envision first implementations of a quantum memory for superconducting qubits.
arxiv pdf

Quantum technologies with hybrid systems

  1. G. Kurizki,
  2. P. Bertet,
  3. Y. Kubo,
  4. K. Mølmer,
  5. D. Petrosyan,
  6. P. Rabl,
  7. and J. Schmiedmayer
An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing
effort, devices for information processing, secure communication and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multi-tasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and the challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field.
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