OREANDA-NEWS. NTT, in conjunctions with its partners from the National Institute of Informatics and Osaka University, observes a hidden long-lived quantum state in a hybrid system composed of a superconducting flux qubit and an electron spin ensemble in diamond.

Since this technology provides a new approach to realize long-lived quantum memories, our results have a potential to reduce the resources and development costs to construct a scalable quantum computation, and therefore our results could make a breakthrough to realize ultra-fast quantum information processing in the future. Our results will be published in Nature Communications on April 8.

This research is granted by the Japan Society for the Promotion of Science (JSPS) through the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program), initiated by the Council for Science and Technology Policy (CSTP). This research was also executed under the Commissioned Research of National Institute of Information and Communications Technology (NICT), Japan.

NTT, NII, and Osaka University firstly determined the mechanism for how the state was long-lived. As such, it is an attractive candidate of a quantum memory in a superconductor diamond quantum hybrid system. We have found that this narrow resonance line is direct evidence of a dark state in the hybrid system.

A dark state is usually undetectable in an experiment due to quantum interference that significantly suppresses the amount of a signal from the system to the detector. Although this state is known to be long-lived, it is difficult to use this state for a practical application such as quantum memory if one cannot experimentally detect any signals from the state. We theoretically showed that, in a superconductor diamond quantum hybrid system, the quantum interference of the dark state does not work sufficiently due to magnetic field noise and strain in the diamond. Hence one could observe a signal from the dark state. We experimentally detected such a signal, and showed that the lifetime of the dark state was around 150 ns, an order of magnitude longer than the previous diamond quantum-memory lifetime of 20 ns.

If we could use this dark state for quantum memory, it is expected that the lifetime of a quantum memory would be significantly improved. By combining this long-lived quantum memory with a quantum processor such as superconducting flux qubit, we can reduce the resources and development costs to realize a quantum computer. This quantum technology would provide us with prospects to implement ultra-fast calculation much faster than the current computers can perform.