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.

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...

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Here we report on the production and tomography of genuinely entangled Greenberger-Horne-Zeilinger states with up to ten qubits connecting to a bus resonator in a superconducting circuit, where the resonator-mediated qubit-qubit interactions are used to controllably entangle multiple qubits and to operate on different pairs of qubits in parallel. The resulting 10-qubit density matrix is probed by quantum state tomography, with a fidelity of 0.668±0.025. Our results demonstrate the largest entanglement created so far in solid-state architectures and pave the way to large-scale quantum computation.

The law of statistical physics dictates that generic closed quantum many-body systems initialized in nonequilibrium will thermalize under their own dynamics. However, the emergence of manybody localization (MBL) owing to the interplay between interaction and disorder, which is in stark contrast to Anderson localization that only addresses noninteracting particles in the presence of disorder, greatly challenges this concept because it prevents the systems from evolving to the ergodic thermalized state. One critical evidence of MBL is the long-time logarithmic growth of entanglement entropy, and a direct observation of it is still elusive due to the experimental challenges in multiqubit single-shot measurement and quantum state tomography. Here we present an experiment of fully emulating the MBL dynamics with a 10-qubit superconducting quantum processor, which represents a spin-1/2 XY model featuring programmable disorder and long-range spin-spin interactions. We provide essential signatures of MBL, such as the imbalance due to the initial nonequilibrium, the violation of eigenstate thermalization hypothesis, and, more importantly, the direct evidence of the long-time logarithmic growth of entanglement entropy. Our results lay solid foundations for precisely simulating the intriguing physics of quantum many-body systems on the platform of largescale multiqubit superconducting quantum processors.

Single crystals of A 1−x K x Fe 2 As 2 (A = Ba, Sr) with high quality have been grown successfully by an FeAs self-flux method. The samples have sizes up to 4 mm with flat and shiny surfaces. The x-ray diffraction patterns suggest that they have high crystalline quality and c-axis orientation. The non-superconducting crystals show a spin-density-wave (SDW) instability at about 173 and 135 K for the Sr-based and Ba-based compound, respectively. After doping K as the hole dopant into the BaFe 2 As 2 system, the SDW transition is smeared, and superconducting samples of the compound Ba 1−x K x Fe 2 As 2 (0 < x 0.4) are obtained. The superconductors, characterized by AC susceptibility and resistivity measurements, exhibit very sharp superconducting transitions at about 36, 32, 27 and 23 K for x = 0.40, 0.28, 0.25 and 0.23, respectively.

We report the preparation and verification of a genuine 12-qubit entanglement in a superconducting processor. The processor that we designed and fabricated has qubits lying on a 1D chain with relaxation times ranging from 29.6 to 54.6 µs. The fidelity of the 12-qubit entanglement was measured to be above 0.5544±0.0025, exceeding the genuine multipartite entanglement threshold by 21 statistical standard deviations. Our entangling circuit to generate linear cluster states is depth-invariant in the number of qubits and uses single-and double-qubit gates instead of collective interactions. Our results are a substantial step towards large-scale random circuit sampling and scalable measurement-based quantum computing.

In this paper we report the fabrication and superconducting properties of GdO 1−x F x FeAs. It is found that when x is equal to 0.17, GdO 0.83 F 0.17 FeAs is a superconductor with the onset transition temperature T on c ≈ 36.6K. Resistivity anomaly near 130K was observed for all samples up to x = 0.17, such a phenomenon is similar to that of LaO 1−x F x FeAs. Hall coefficient indicates that GdO 0.83 F 0.17 FeAs is conducted by electron-like charge carriers.