Entanglement Demonstrated in Superconducting Qubits UCSB|IBM In Science 313, 5792 and concurrent PhysicsWeb, Scientific American reviews, Martinis et al. report experimental verification of entanglement between two superconducting qubits. "By using simultaneous measurement and state tomography, we demonstrated entanglement between two solid-state qubits. Single qubit operations and capacitive coupling between two super-conducting phase qubits were used to generate a Bell-type state. Full two-qubit tomography yielded a density matrix showing an entangled state with fidelity up to 87%. Our results demonstrate a high degree of unitary control of the system, indicating that larger implementations are within reach."

Symposium on Quantum Technologies Cambridge|MIT "Substantial advances in nanoscale science and engineering have made it possible to engineer a wide range of physical systems whose behaviour is governed by the laws of quantum mechanics. Quantum technologies seek to exploit these quantum effects to develop novel practical applications – from secure communications systems to novel computing devices more powerful than existing computers, new measurement devices more accurate than their classical counterparts, or to facilitate chemical reactions using photonic reagents, which might lead to the discovery new materials – to mention only a few potential applications. This Symposium aims to bring together a range of theoretical and experimental scientists and engineers from academia and industry to discuss the current state of the art of various emerging quantum technologies, and the promises and challenges that lie ahead."

Macroscopic Entanglement in Quantum Computation Tokyo | 東京大学 "We investigate macroscopic entanglement of quantum states in quantum computers, where we say a quantum state is entangled macroscopically if the state has superposition of macroscopically distinct states. When the solutions are such that the problem becomes hard in the sense that classical algorithms take more than polynomial steps to find a solution, macroscopically entangled states are always used in Grover's algorithm and almost always used in Shor's algorithm. Since they are representative algorithms for unstructured and structured problems, respectively, our results support strongly the conjecture that quantum computers utilize macroscopically entangled states when they solve hard problems much faster than any classical algorithms."

Time Reversal and Super-resolving Phase Measurements Queensland "We demonstrate phase super-resolution in absence of entangled states. The key insight is to use the inherent time-reversal symmetry of quantum mechanics: our theory shows that it is possible to measure, as opposed to prepare, entangled states. Our approach is robust, requiring only photons that exhibit classical interference: we experimentally demonstrate high-visibility phase super-resolution with three, four, and six photons using a standard laser and photon counters. Our six-photon experiment demonstrates the best phase super-resolution yet reported with high visibility and resolution."

Selective Qubit Coupling via Stripline Cavity Chalmers "We theoretically investigate selective coupling of superconducting charge qubits mediated by a superconducting stripline cavity with a tunable resonance frequency. The frequency control is provided by a flux biased dc-SQUID attached to the cavity. Selective entanglement of the qubit states is achieved by sweeping the cavity frequency through the qubit-cavity resonances. The circuit is scalable, and allows to keep the qubits at their optimal points with respect to decoherence during the whole operation. We derive an effective quantum Hamiltonian for the basic, two-qubit-cavity system, and analyze appropriate circuit parameters. We present a protocol for performing Bell inequality measurements, and discuss a composite pulse sequence generating a universal control-phase gate."