During the past decade, research into superconducting quantum bits (qubits) based on Josephson junctions has made rapid progress1. Many foundational experiments have been performed2,3,4,5,6,7,8, and superconducting qubits are now considered one of the most promising systems for quantum information processing. However, the experimentally reported coherence times are likely to be insufficient for future large-scale quantum computation. A natural solution to this problem is a dedicated engineered quantum memory based on atomic and molecular systems. The question of whether coherent quantum coupling is possible between such natural systems and a single macroscopic artificial atom has attracted considerable attention9,10,11,12 since the first demonstration of macroscopic quantum coherence in Josephson junction circuits2. Here we report evidence of coherent strong coupling between a single macroscopic superconducting artificial atom (a flux qubit) and an ensemble of electron spins in the form of nitrogen–vacancy colour centres in diamond. Furthermore, we have observed coherent exchange of a single quantum of energy between a flux qubit and a macroscopic ensemble consisting of about 3 × 107 such colour centres. This provides a foundation for future quantum memories and hybrid devices coupling microwave and optical systems.
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Clarke, J. & Wilhelm, F. K. Superconducting quantum bits. Nature 453, 1031–1042 (2008)
Nakamura, Y., Pashkin & Tsai, J. S. Coherent control of macroscopic quantum states in a single-Cooper-pair box. Nature 398, 786–788 (1999)
Vion, D. et al. Manipulating the quantum state of an electrical circuit. Science 296, 886–889 (2002)
Chiorescu, I., Nakamura, Y., Harmans, C. J. P. M. & Mooij, J. E. Coherent quantum dynamics of a superconducting flux qubit. Science 299, 1869–1871 (2003)
Sillanpää, M. A., Park, J. I. & Simmonds, R. W. Coherent quantum state storage and transfer between two phase qubits via a resonant cavity. Nature 449, 438–442 (2007)
Majer, J. et al. Coupling superconducting qubits via a cavity bus. Nature 449, 443–447 (2007)
DiCarlo, L. et al. Demonstration of two-qubit algorithms with a superconducting quantum processor. Nature 460, 240–244 (2009)
Ansmann, M. et al. Violation of Bell’s inequality in Josephson phase qubits. Nature 461, 504–506 (2009)
Sørensen, A. S. van der Wal, C. H., Childress, L. I. & Lukin, M. D. Capacitive coupling of atomic systems to mesoscopic conductors. Phys. Rev. Lett. 92, 063601 (2004)
Tian, L., Rabl, P., Blatt, R. & Zoller, P. Interfacing quantum-optical and solid-state qubits. Phys. Rev. Lett. 92, 247902 (2004)
Rabl, P. et al. Hybrid quantum processors: molecular ensembles as quantum memory for solid state circuits. Phys. Rev. Lett. 97, 033003 (2006)
Marcos, D. et al. Coupling nitrogen-vacancy centers in diamond to superconducting flux qubits. Phys. Rev. Lett. 105, 210501 (2010)
Brune, M. et al. Quantum Rabi oscillation: a direct test of field quantization in a cavity. Phys. Rev. Lett. 76, 1800–1803 (1996)
Chiorescu, I., Groll, N., Bertaina, S., Mori, T. & Miyashita, S. Magnetic strong coupling in a spin-photon system and transition to classical regime. Phys. Rev. B 82, 024413 (2010)
Wu, H. et al. Storage of multiple coherent microwave excitations in an electron spin ensemble. Phys. Rev. Lett. 105, 140503 (2010)
Schuster, D. I. et al. High-cooperativity coupling of electron-spin ensembles to superconducting cavities. Phys. Rev. Lett. 105, 140501 (2010)
Kubo, Y. et al. Strong coupling of a spin ensemble to a superconducting resonator. Phys. Rev. Lett. 105, 140502 (2010)
Amsüss, R. et al. Cavity QED with magnetically coupled collective spin states. Phys. Rev. Lett. 107, 060502 (2011)
Raizen, M. G., Thompson, R. J., Brecha, R. J., Kimble, H. J. & Carmichael, H. J. Normal-mode splitting and linewidth averaging for two-state atom in an optical cavity. Phys. Rev. Lett. 63, 240–243 (1989)
Naydenov, B. et al. Enhanced generation of single optically active spins in diamond by ion implantation. Appl. Phys. Lett. 96, 163108 (2010)
Neumann, P. et al. Excited-state spectroscopy of single NV defects in diamond using optically detected magnetic resonance. N. J. Phys. 11, 013017 (2009)
Zhu, X., Kemp, A., Saito, S. & Semba, K. Coherent operation of a gap-tunable flux qubit. Appl. Phys. Lett. 97, 102503 (2010)
Fedorov, A. et al. Strong coupling of a quantum oscillator to a flux qubit at its symmetry point. Phys. Rev. Lett. 105, 060503 (2010)
Mooij, J. E. et al. Josephson persistent-current qubit. Science 285, 1036–1039 (1999)
Johansson, J. et al. Vacuum Rabi oscillations in a macroscopic superconducting qubit LC oscillator system. Phys. Rev. Lett. 96, 127006 (2006)
Hanson, R., Dobrovitski, V. V., Feiguin, A. E., Gywat, O. & Awschalom, D. D. Coherent dynamics of a single spin interacting with an adjustable spin bath. Science 320, 352–355 (2008)
Mizuochi, N. et al. Coherence of single spins coupled to a nuclear spin bath of varying density. Phys. Rev. B 80, 041201(R) (2009)
Jelezko, F., Gaebel, T., Popa, I., Gruber, A. & Wrachtrup, J. Observation of coherent oscillations in a single electron spin. Phys. Rev. Lett. 92, 076401 (2004)
Gruber, A. et al. Scanning confocal optical microscopy magnetic resonance on single defect centers. Science 276, 2012–2014 (1997)
Kurtsiefer, Zarda, P., Mayer, S. & Weinfurter, H. A stable solid-state source of single photons. Phys. Rev. Lett. 85, 290–293 (2000)
We thank T. Tawara, H. Gotoh and T. Sogawa for optical measurements at an early stage of this work. We also thank H. Tanji, Y. Matsuzaki, S. J. Devitt, J. Schmiedmayer and J. E. Mooij for discussions. This work was supported in part by the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST), Scientific Research of Specially Promoted Research (grant no. 18001002) by MEXT, a Grant-in-Aid for Scientific Research on Innovative Areas (grant no.22102502), and Scientific Research (A) grant no. 22241025 from the Japanese Society for the Promotion of Science (JSPS). M.S.E. was supported by a JSPS fellowship.
The authors declare no competing financial interests.
About this article
Cite this article
Zhu, X., Saito, S., Kemp, A. et al. Coherent coupling of a superconducting flux qubit to an electron spin ensemble in diamond. Nature 478, 221–224 (2011). https://doi.org/10.1038/nature10462
Improvement on the manipulation of a single nitrogen-vacancy spin and microwave photon at single-quantum level
Communications in Theoretical Physics (2021)
One-step implementation of a coherent conversion between microwave and optical cavities via an ensemble of nitrogen-vacancy centers
Physical Review A (2021)
One-step Realization of a Cross-Kerr Nonlinearity Between Two Ensembles of NV Centers via a Superconducting Flux Qubit
International Journal of Theoretical Physics (2021)
Physical Review B (2021)
Physical Review Applied (2021)