The reconfigurable Josephson circulator/directional amplifier

Circulators and directional amplifiers are crucial non-reciprocal signal routing and processing components involved in microwave readout chains for a variety of applications. They are particularly important in the field of superconducting quantum information, where the devices also need to have minimal photon losses to preserve the quantum coherence of signals. Conventional commercial implementations of each device suffer from losses and are built from very different physical principles, which has led to separate strategies for the construction of their quantum-limited versions. However, as recently proposed theoretically, by establishing simultaneous pairwise conversion and/or gain processes between three modes of a Josephson-junction based superconducting microwave circuit, it is possible to endow the circuit with the functions of either a phase-preserving directional amplifier or a circulator. Here, we experimentally demonstrate these two modes of operation of the same circuit. Furthermore, in the directional amplifier mode, we show that the noise performance is comparable to standard non-directional superconducting amplifiers, while in the circulator mode, we show that the sense of circulation is fully reversible. Our device is far simpler in both modes of operation than previous proposals and implementations, requiring only three microwave pumps. It offers the advantage of flexibility, as it can dynamically switch between modes of operation as its pump conditions are changed. Moreover, by demonstrating that a single three-wave process yields non-reciprocal devices with reconfigurable functions, our work breaks the ground for the development of future, more-complex directional circuits, and has excellent prospects for on-chip integration

Comparing and combining measurement-based and driven-dissipative entanglement stabilization

We demonstrate and contrast two approaches to the stabilization of qubit entanglement by feedback. Our demonstration is built on a feedback platform consisting of two superconducting qubits coupled to a cavity which are measured by a nearly-quantum-limited measurement chain and controlled by high-speed classical logic circuits. This platform is used to stabilize entanglement by two nominally distinct schemes: a "passive" reservoir engineering method and an "active" correction based on conditional parity measurements. In view of the instrumental roles that these two feedback paradigms play in quantum error-correction and quantum control, we directly compare them on the same experimental setup. Further, we show that a second layer of feedback can be added to each of these schemes, which heralds the presence of a high-fidelity entangled state in realtime. This "nested" feedback brings about a marked entanglement fidelity improvement without sacrificing success probability.Comment: 40 pages, 12 figure

Small mammal diversity in Semi-deciduous Seasonal Forest of the southernmost Brazilian Pampa: the importance of owl pellets for rapid inventories in human-changing ecosystems

The Pampa biogeographic province covers a mere 2% of the Brazilian territory (176,496 km2). However, it stands out as a complex and diverse ecosystem, although its mammal communities are still scarcely understood. Human activities are transforming the territory into a mosaic of agroecosystems, native and exotic forest fragments, and grasslands. Here we conducted the first investigation to determine the richness of small mammal assemblages in the region based on extensive analyses of owl pellets (Tyto furcata). Craniodental remains were studied from samples collected from 12 Semi-deciduous Seasonal Forest sites in the municipality of São Lourenço do Sul, State of Rio Grande do Sul, Southern Brazil. A total of 2,617 individuals belonging to 19  taxa were recorded, including 2 marsupials (Didelphidae; 0.42%), 2 chiropterans (Molossidae, Phyllostomidae; 0.12%), and 15 rodents (Cricetidae, Muridae, Caviidae; 99.46%). The rodent genera Oligoryzomys, Mus, Calomys, and Akodon were the most common taxa. Large samples also included poorly known taxa, such as the cricetids Bibimys, Juliomys (recording here its southernmost occurrence), Lundomys, and Wilfredomys. From a biogeographical point of view, the recorded assemblage embraces a mixture of Platan, Pampean, and Atlantic Forest elements, highlighting the role of the southernmost Brazilian hills as a wedge favoring the penetration of forest micromammals to higher latitudes. Our findings testify to the great diversity of the Pampa, but also point to a growing homogeneity and dominance of rodent species that are widespread in agroecosystems. Rapid inventories based on owl pellets emerge as a suitable, economic, non-invasive tool to document these community changes.Fil: Stutz, Narla Shannay. Universidade Federal do Rio Grande do Sul; BrasilFil: Hadler, Patrícia. Universidade Federal de Santa Catarina; BrasilFil: Cherem, Jorge José. Cooperativa para a Conservação da Natureza (Caipora); BrasilFil: Pardiñas, Ulises Francisco J.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Diversidad y Evolución Austral; Argentina. Instituto Nacional de Biodiversidad; Ecuado

Robust concurrent remote entanglement between two superconducting qubits

Entangling two remote quantum systems which never interact directly is an essential primitive in quantum information science and forms the basis for the modular architecture of quantum computing. When protocols to generate these remote entangled pairs rely on using traveling single photon states as carriers of quantum information, they can be made robust to photon losses, unlike schemes that rely on continuous variable states. However, efficiently detecting single photons is challenging in the domain of superconducting quantum circuits because of the low energy of microwave quanta. Here, we report the realization of a robust form of concurrent remote entanglement based on a novel microwave photon detector implemented in the superconducting circuit quantum electrodynamics (cQED) platform of quantum information. Remote entangled pairs with a fidelity of $0.57\pm0.01$ are generated at $200$ Hz. Our experiment opens the way for the implementation of the modular architecture of quantum computation with superconducting qubits.Comment: Main paper: 7 pages, 4 figures; Appendices: 14 pages, 9 figure

Confining the state of light to a quantum manifold by engineered two-photon loss

Physical systems usually exhibit quantum behavior, such as superpositions and entanglement, only when they are sufficiently decoupled from a lossy environment. Paradoxically, a specially engineered interaction with the environment can become a resource for the generation and protection of quantum states. This notion can be generalized to the confinement of a system into a manifold of quantum states, consisting of all coherent superpositions of multiple stable steady states. We have experimentally confined the state of a harmonic oscillator to the quantum manifold spanned by two coherent states of opposite phases. In particular, we have observed a Schrodinger cat state spontaneously squeeze out of vacuum, before decaying into a classical mixture. This was accomplished by designing a superconducting microwave resonator whose coupling to a cold bath is dominated by photon pair exchange. This experiment opens new avenues in the fields of nonlinear quantum optics and quantum information, where systems with multi-dimensional steady state manifolds can be used as error corrected logical qubits