Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Nature Communications

Observation of dark states in a superconductor diamond quantum hybrid system

Xiaobo Zhu, Yuichiro Matsuzaki, Robert Amsüss, Kosuke Kakuyanagi, Takaaki Shimo-Oka, Norikazu Mizuochi, Kae Nemoto, Kouichi Semba, William J. Munro, Shiro Saito

Published Apr 8, 2014• 64 citations
Publisher

Abstract

The hybridization of distinct quantum systems has opened new avenues to exploit the best properties of these individual systems. Superconducting circuits and electron spin ensembles are one such example. Strong coupling and the coherent transfer and storage of quantum information has been achieved with nitrogen vacancy centres in diamond. Recently, we have observed a remarkably sharp resonance (~1 MHz) at 2.878 GHz in the spectrum of flux qubit negatively charged nitrogen vacancy diamond hybrid quantum system under zero external magnetic field. This width is much narrower than that of both the flux qubit and spin ensemble. Here we show that this resonance is evidence of a collective dark state in the ensemble, which is coherently driven by the superposition of clockwise and counter-clockwise macroscopic persistent supercurrents flowing in the flux qubit. The collective dark state is a unique physical system and could provide a long-lived quantum memory. Recently, a sharp resonance was observed in the spectrum of a flux-qubit nitrogen-vacancy-centre hybrid quantum system that is much narrower than that of either the flux qubit or the spin ensemble. Zhu et al.investigate this resonance and find evidence of a coherently driven collective dark state.

DOI
10.1038/ncomms4524

Related papers

Observation of dark states in a superconductor diamond quantum hybrid system

Xiaobo Zhu, Yuichiro Matsuzaki, Robert Amsüss +7 more

Abstract The hybridization of distinct quantum systems has opened new avenues to exploit the best properties of these individual systems. Superconducting circuits and electron spin ensembles are one such example. Strong coupling and the coherent transfer and storage of quantum information has been achieved with nitrogen vacancy centres in diamond. Recently, we have observed a remarkably sharp resonance (~1 MHz) at 2.878 GHz in the spectrum of flux qubit negatively charged nitrogen vacancy diamond hybrid quantum system under zero external magnetic field. This width is much narrower than that of both the flux qubit and spin ensemble. Here we show that this resonance is evidence of a collective dark state in the ensemble, which is coherently driven by the superposition of clockwise and counter-clockwise macroscopic persistent supercurrents flowing in the flux qubit. The collective dark state is a unique physical system and could provide a long-lived quantum memory.

Bulletin of the American Physical Society•Mar 3, 2014•0 citations

Long-lived dark states in a superconductor diamond hybrid quantum system

William J. Munro, Xiaobo Zhu, Yuichiro Matsuzaki +7 more

The research into quantum science and technology has reached an interesting stage where we can now in principle engineer composite systems to exploit the best properties of these individual systems. Such hybridization techniques have been demonstrated for instance with superconducting circuits and electron spin ensembles where strong coupling and the coherent transfer & storage of quantum information has been achieved. However in these cases, generally the hybrid system properties have not exceeded those of the individual systems. Recently we have observed a remarkably sharp resonance in the spectrum of flux qubit NV- diamond hybrid quantum system with no external magnetic field applied to the diamond. What is surprising is that its measured line-width is much narrower than that of both the flux-qubit and spin ensemble. We show this resonance is evidence of a collective & long-lived dark state.

•Jan 1, 2014•0 citations

Coherent coupling of a superconducting flux qubit to an electron spin ensemble in diamond

Xiaobo Zhu, Shiro Saito, Alexander Kemp +10 more

We report evidence of coherent strong coupling, observation of vacuum Rabi oscillations, between a superconducting artificial atom (a flux qubit) and a macroscopic number of electron spins in the form of nitrogen–vacancy color centres in diamond.

Research in Optical Sciences•Jan 1, 2012•3 citations

Hybridization of superconducting flux qubits and diamond ensembles

William J. Munro, Shiro Saito, Xiaobo Zhu +7 more

The development of moderate scale quantum devices requires stable quantum bits in which we can process, store and transport quantum information. Superconducting flux qubits are well known for their processing ability while electron-spin nitrogen-vacancy centers in diamond are a natural memory candidate. Here we report on strong coupling and coherent exchange of a single quantum of energy between these hybrid systems as well as the realization of a quantum memory operation.

•Jan 1, 2013•0 citations

Towards Realizing a Quantum Memory for a Superconducting Qubit: Storage and Retrieval of Quantum States

Shiro Saito, Xiaobo Zhu, Robert Amsüss +7 more

We have built a hybrid system composed of a superconducting flux qubit (the processor) and an ensemble of nitrogen-vacancy centers in diamond (the memory) that can be directly coupled to one another, and demonstrated how information can be transferred from the flux qubit to the memory, stored, and subsequently retrieved. We have established the coherence properties of the memory and succeeded in creating an entangled state between the processor and memory, demonstrating how the entangled state's coherence is preserved. Our results are a significant step towards using an electron spin ensemble as a quantum memory for superconducting qubits.

arXiv:1308.5130•Physical Review Letters•Sep 5, 2013•112 citations

Coupling spin ensembles via superconducting flux qubits

Yueyin Qiu, Wei Xiong, Lin Tian +1 more

We study a hybrid quantum system consisting of spin ensembles and superconducting flux qubits, where each spin ensemble is realized using the nitrogen-vacancy centers in a diamond crystal and the nearest-neighbor spin ensembles are effectively coupled via a flux qubit. We show that the coupling strengths between flux qubits and spin ensembles can reach the strong and even ultrastrong coupling regimes by either engineering the hybrid structure in advance or tuning the excitation frequencies of spin ensembles via external magnetic fields. When extending the hybrid structure to an array with equal coupling strengths, we find that in the strong-coupling regime, the hybrid array is reduced to a tight-binding model of a one-dimensional bosonic lattice. In the ultrastrong-coupling regime, it exhibits quasiparticle excitations separated from the ground state by an energy gap. Moreover, these quasiparticle excitations and the ground state are stable under a certain condition that is tunable via the external magnetic field. This may provide an experimentally accessible method to probe the instability of the system.

arXiv:1401.3095•Physical Review A•Apr 22, 2014•35 citations
The hybridization of distinct quantum systems has opened new avenues to exploit the best properties of these individual systems. Superconducting circuits and electron spin ensembles are one such example. Strong coupling and the coherent transfer and storage of quantum information has been achieved with nitrogen vacancy centres in diamond. Recently, we have observed a remarkably sharp resonance (~1 MHz) at 2.878 GHz in the spectrum of flux qubit negatively charged nitrogen vacancy diamond hybrid quantum system under zero external magnetic field. This width is much narrower than that of both the flux qubit and spin ensemble. Here we show that this resonance is evidence of a collective dark state in the ensemble, which is coherently driven by the superposition of clockwise and counter-clockwise macroscopic persistent supercurrents flowing in the flux qubit. The collective dark state is a unique physical system and could provide a long-lived quantum memory. Recently, a sharp resonance was observed in the spectrum of a flux-qubit nitrogen-vacancy-centre hybrid quantum system that is much narrower than that of either the flux qubit or the spin ensemble. Zhu et al.investigate this resonance and find evidence of a coherently driven collective dark state.
Abstract The hybridization of distinct quantum systems has opened new avenues to exploit the best properties of these individual systems. Superconducting circuits and electron spin ensembles are one such example. Strong coupling and the coherent transfer and storage of quantum information has been achieved with nitrogen vacancy centres in diamond. Recently, we have observed a remarkably sharp resonance (~1 MHz) at 2.878 GHz in the spectrum of flux qubit negatively charged nitrogen vacancy diamond hybrid quantum system under zero external magnetic field. This width is much narrower than that of both the flux qubit and spin ensemble. Here we show that this resonance is evidence of a collective dark state in the ensemble, which is coherently driven by the superposition of clockwise and counter-clockwise macroscopic persistent supercurrents flowing in the flux qubit. The collective dark state is a unique physical system and could provide a long-lived quantum memory.
The research into quantum science and technology has reached an interesting stage where we can now in principle engineer composite systems to exploit the best properties of these individual systems. Such hybridization techniques have been demonstrated for instance with superconducting circuits and electron spin ensembles where strong coupling and the coherent transfer & storage of quantum information has been achieved. However in these cases, generally the hybrid system properties have not exceeded those of the individual systems. Recently we have observed a remarkably sharp resonance in the spectrum of flux qubit NV- diamond hybrid quantum system with no external magnetic field applied to the diamond. What is surprising is that its measured line-width is much narrower than that of both the flux-qubit and spin ensemble. We show this resonance is evidence of a collective & long-lived dark state.
We have built a hybrid system composed of a superconducting flux qubit (the processor) and an ensemble of nitrogen-vacancy centers in diamond (the memory) that can be directly coupled to one another, and demonstrated how information can be transferred from the flux qubit to the memory, stored, and subsequently retrieved. We have established the coherence properties of the memory and succeeded in creating an entangled state between the processor and memory, demonstrating how the entangled state's coherence is preserved. Our results are a significant step towards using an electron spin ensemble as a quantum memory for superconducting qubits.
We study a hybrid quantum system consisting of spin ensembles and superconducting flux qubits, where each spin ensemble is realized using the nitrogen-vacancy centers in a diamond crystal and the nearest-neighbor spin ensembles are effectively coupled via a flux qubit. We show that the coupling strengths between flux qubits and spin ensembles can reach the strong and even ultrastrong coupling regimes by either engineering the hybrid structure in advance or tuning the excitation frequencies of spin ensembles via external magnetic fields. When extending the hybrid structure to an array with equal coupling strengths, we find that in the strong-coupling regime, the hybrid array is reduced to a tight-binding model of a one-dimensional bosonic lattice. In the ultrastrong-coupling regime, it exhibits quasiparticle excitations separated from the ground state by an energy gap. Moreover, these quasiparticle excitations and the ground state are stable under a certain condition that is tunable via the external magnetic field. This may provide an experimentally accessible method to probe the instability of the system.