During the past decade, research into superconducting quantum bits (qubits) based on Josephson junctions has made rapid progress. Many foundational experiments have been performed, 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 attention since the first demonstration of macroscopic quantum coherence in Josephson junction circuits. 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 × 10(7) such colour centres. This provides a foundation for future quantum memories and hybrid devices coupling microwave and optical systems.

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The superconductor Sr4V2O6Fe2As2 with transition temperature at 37.2 K has been fabricated. It has a layered structure with the space group of p4/nmm, and with the lattice constants a = 3.9296Å and c = 15.6732Å. The observed large diamagnetization signal and zero-resistance demonstrated the bulk superconductivity. The broadening of resistive transition was measured under different magnetic fields leading to the discovery of a rather high upper critical field. The results also suggest a large vortex liquid region which reflects high anisotropy of the system. The Hall effect measurements revealed dominantly electron-like charge carriers in this material. The superconductivity in the present system may be induced by oxygen deficiency or the multiple valence states of vanadium.Since the discovery of superconductivity 1 at 26 K in oxy-arsenide LaF eAsO 1−x F x , tremendous attention has been paid to searching new superconductors in this family. Among the superconductors with several different structures, 2,3,4,5,6 the highest T c has been raised to 55-56 K 7,8,9,10,11 in doped oxy-iron-arsenides (F-doped LnFeAsO, the so-called 1111 phase, Ln=rare earth elements) or the fluoride derivative iron-arsenides (Lndoped AEFeAsF, AE=alkaline earth elements).12 The superconductivity can also be induced by applying a high pressure to the undoped parent samples.13,14 Although it remains unclear what governs the mechanism of superconductivity in the FeAs-based system, it turns out to be clear that the parent phase is accompanied by an antiferromagnetic (AF) order and the superconductivity can be induced by suppressing this magnetic order. A typical example was illustrated in the (Ba, Sr)F e 2 As 2 (so-called 122) system, the AF order is suppressed and superconductivity was induced by either doping K to the Ba or Sr sites, 2,15,16 or doping Co to the Fe sites. 17,18 On the other hand, superconductivity was also found in the parent phase of FeP-based system, such as LaFePO (T c = 2.75K)19 , or in LiFeAs. 3,4 Very recently superconductivity at about 17 K was found in another FeP based parent compound Sr 4 Sc 2 O 6 Fe 2 P 2 (so-called 42622).20 Due to the absence of the AF order in the superconductors mentioned above, one naturally questions whether the AF order is a prerequisite for the superconductivity in the iron-pnictide system. As far as we know, no superconductivity was detected in the parent phase of some FeAs-based compounds, including the 1111, 122 and the recently discovered 42622 and 32522 phases. 21,22,23,24,25 Although some trace of superconductivity was reported in the doped FeAs-based 42622 or 32522 compounds, the high-T c superconductivity was not supported by a clear large diamagnetization signal. 22,23 In this Letter, we report the discovery of superconductivity at about 37.2 K in the new compound Sr 4 V 2 O 6 Fe 2 As 2 . This work presents the unambiguous evidence for high temperature superconductivity in the FeAs-based 42622 system. The polycrystalline samples were synthesized by using a two-step solid state re...