Coupling superconducting qubits via a cavity bus

Superconducting circuits are promising candidates for constructing quantum bits (qubits) in a quantum computer; single-qubit operations are now routine, and several examples of two-qubit interactions and gates have been demonstrated. These experiments show that two nearby qubits can be readily coupled with local interactions. Performing gate operations between an arbitrary pair of distant qubits is highly desirable for any quantum computer architecture, but has not yet been demonstrated. An efficient way to achieve this goal is to couple the qubits to a 'quantum bus', which distributes quantum information among the qubits. Here we show the implementation of such a quantum bus, using microwave photons confined in a transmission line cavity, to couple two superconducting qubits on opposite sides of a chip. The interaction is mediated by the exchange of virtual rather than real photons, avoiding cavity-induced loss. Using fast control of the qubits to switch the coupling effectively on and off, we demonstrate coherent transfer of quantum states between the qubits. The cavity is also used to perform multiplexed control and measurement of the qubit states. This approach can be expanded to more than two qubits, and is an attractive architecture for quantum information processing on a chip.     

Cavity cooling of a single atom

All conventional methods to laser-cool atoms rely on repeated cycles of optical pumping and spontaneous emission of a photon by the atom. Spontaneous emission in a random direction provides the dissipative mechanism required to remove entropy from the atom. However, alternative cooling methods have been proposed for a single atom strongly coupled to a high-finesse cavity; the role of spontaneous emission is replaced by the escape of a photon from the cavity. Application of such cooling schemes would improve the performance of atom-cavity systems for quantum information processing. Furthermore, as cavity cooling does not rely on spontaneous emission, it can be applied to systems that cannot be laser-cooled by conventional methods; these include molecules (which do not have a closed transition) and collective excitations of Bose condensates, which are destroyed by randomly directed recoil kicks. Here we demonstrate cavity cooling of single rubidium atoms stored in an intracavity dipole trap. The cooling mechanism results in extended storage times and improved localization of atoms. We estimate that the observed cooling rate is at least five times larger than that produced by free-space cooling methods, for comparable excitation of the atom.     

The Pristionchus pacificus genome provides a unique perspective on nematode lifestyle and parasitism

Here we present a draft genome sequence of the nematode Pristionchus pacificus, a species that is associated with beetles and is used as a model system in evolutionary biology. With 169 Mb and 23,500 predicted protein-coding genes, the P. pacificus genome is larger than those of Caenorhabditis elegans and the human parasite Brugia malayi. Compared to C. elegans, the P. pacificus genome has more genes encoding cytochrome P450 enzymes, glucosyltransferases, sulfotransferases and ABC transporters, many of which were experimentally validated. The P. pacificus genome contains genes encoding cellulase and diapausin, and cellulase activity is found in P. pacificus secretions, indicating that cellulases can be found in nematodes beyond plant parasites. The relatively higher number of detoxification and degradation enzymes in P. pacificus is consistent with its necromenic lifestyle and might represent a preadaptation for parasitism. Thus, comparative genomics analysis of three ecologically distinct nematodes offers a unique opportunity to investigate the association between genome structure and lifestyle.     

Genomic analysis of Bartonella identifies type IV secretion systems as host adaptability factors

The bacterial genus Bartonella comprises 21 pathogens causing characteristic intraerythrocytic infections. Bartonella bacilliformis is a severe pathogen representing an ancestral lineage, whereas the other species are benign pathogens that evolved by radial speciation. Here, we have used comparative and functional genomics to infer pathogenicity genes specific to the radiating lineage, and we suggest that these genes may have facilitated adaptation to the host environment. We determined the complete genome sequence of Bartonella tribocorum by shotgun sequencing and functionally identified 97 pathogenicity genes by signature-tagged mutagenesis. Eighty-one pathogenicity genes belong to the core genome (1,097 genes) of the radiating lineage inferred from genome comparison of B. tribocorum, Bartonella henselae and Bartonella quintana. Sixty-six pathogenicity genes are present in B. bacilliformis, and one has been lost by deletion. The 14 pathogenicity genes specific for the radiating lineage encode two laterally acquired type IV secretion systems, suggesting that these systems have a role in host adaptability.     

Strong coupling of a single photon to a superconducting qubit using circuit quantum electrodynamics

The interaction of matter and light is one of the fundamental processes occurring in nature, and its most elementary form is realized when a single atom interacts with a single photon. Reaching this regime has been a major focus of research in atomic physics and quantum optics for several decades and has generated the field of cavity quantum electrodynamics. Here we perform an experiment in which a superconducting two-level system, playing the role of an artificial atom, is coupled to an on-chip cavity consisting of a superconducting transmission line resonator. We show that the strong coupling regime can be attained in a solid-state system, and we experimentally observe the coherent interaction of a superconducting two-level system with a single microwave photon. The concept of circuit quantum electrodynamics opens many new possibilities for studying the strong interaction of light and matter. This system can also be exploited for quantum information processing and quantum communication and may lead to new approaches for single photon generation and detection.