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The ability to filter quantum states is a key capability in quantum information science and technology, in which one-qubit fitters, or polarizers, have found wide application. Filtering on the basis of entanglement requires extension to multi-qubit fitters with qubit-qubit interactions. We demonstrated an optical entanglement filter that passes a pair of photons if they have the desired correlations of their polarization. Such devices have many important applications to quantum technologies.

The article discusses the study which shows that the exotic quantum processes are not required in order to reach the ultimate limits of measurement. An experiment reveals that the Heisenberg uncertainty limit can be achieved in the absence of entanglement and its findings indicate a new way for ultrahigh precision measurements. Moreover, the result of an optical phase measurement based on an interferometer is compared to other studies, particularly with Heisenberg's investigation and the study of Higgins and colleagues. Other relevant information on the said measurement is also presented.

Precision measurements are important across all fields of science. In particular, optical phase measurements can be used to measure distance, position, displacement, acceleration, and optical path length. Quantum entanglement enables higher precision than would otherwise be possible. We demonstrated an optical phase measurement with an entangled four-photon interference visibility greater than the threshold to beat the standard quantum limit-the limit attainable without entanglement. These results open the way for new high-precision measurement applications. [ABSTRACT FROM AUTHOR]

The article presents a study which develops new method for the quantum simulation of Hamiltonian spectra using eigenstate witness. Topics include the calculation of the eigenvalues for both ground and excited states, the scalability and performance of the eigenstate witness in simulating complex Hamiltonians, and the positive implication of the approach in quantum chemistry.

Linear optics underpins fundamental tests of quantum mechanics and quantum technologies. We demonstrate a single reprogrammable optical circuit that is sufficient to implement all possible linear optical protocols up to the size of that circuit. Our six-mode universal system consists of a cascade of 15 Mach-Zehnder interferometers with 30 thermo-optic phase shifters integrated into a single photonic chip that is electrically and optically interfaced for arbitrary setting of all phase shifters, input of up to six photons, and their measurement with a 12-single-photon detector system. We programmed this system to implement heralded quantum logic and entangling gates, boson sampling with verification tests, and six-dimensional complex Hadamards. We implemented 100 Haar random unitaries with an average fidelity of 0.999 ± 0.001. Our system can be rapidly reprogrammed to implement these and any other linear optical protocol, pointing the way to applications across fundamental science and quantum technologies. [ABSTRACT FROM AUTHOR]

The article discusses research that demonstrated a compiled version of Shor’s quantum factoring algorithm that operated on four qubits in which the processing takes place in a photonic circuit of numerous gates fashioned from integrated optical waveguides on a silica-on-silicon chip. This is pertinent, as proof-of-principle demonstrations of the algorithm had previously only been possible with liquid-state nuclear magnetic resonance.

The article discusses a delayed-choice experiment involving a quantum system. The authors note that the particle- or wave-like behavior that quantum systems exhibit depends on the experimental apparatus they are confronted by. They argue that the best way to capture wave-particle duality, which is the basis of quantum mechanics, is via the delayed-choice thought experiment in which a photon is forced to choose a behavior before the observer decides what to measure. An overview of experiment's results, in which both particle and wave behaviors are investigated simultaneously, and the authors' observation of strong nonlocal correlations, which show that the photon must simultaneously behave both as a particle and as a wave, is presented.

Emerging applications based on optical beams caring orbital angular momentum (OAM) will probably require photonic integrated devices and circuits for miniaturization, improved performance, and enhanced functionality. We demonstrate silicon-integrated optical vortex emitters, using angular gratings to extract Light confined in whispering gallery modes with high OAM into free-space beams with welL-controlled amounts of OAM. The smallest device has a radius of 3.9 micrometers. Experimental characterization confirms the theoretical prediction that the emitted beams carry exactly defined and adjustable OAM. Fabrication of integrated arrays and demonstration of simultaneous emission of multiple identical optical vortices provide the potential for Large-scale integration of optical vortex emitters on complementary metal-oxide-semiconductor compatible silicon chips for wide-ranging applications. [ABSTRACT FROM AUTHOR]

Linear optics underpins fundamental tests of quantum mechanics and quantum technologies. We demonstrate a single reprogrammable optical circuit that is sufficient to implement all possible linear optical protocols up to the size of that circuit. Our six-mode universal system consists of a cascade of 15 Mach-Zehnder interferometers with 30 thermo-optic phase shifters integrated into a single photonic chip that is electrically and optically interfaced for arbitrary setting of all phase shifters, input of up to six photons, and their measurement with a 12-single-photon detector system. We programmed this system to implement heralded quantum logic and entangling gates, boson sampling with verification tests, and six-dimensional complex Hadamards. We implemented 100 Haar random unitaries with an average fidelity of 0.999 ± 0.001. Our system can be rapidly reprogrammed to implement these and any other linear optical protocol, pointing the way to applications across fundamental science and quantum technologies., (Copyright © 2015, American Association for the Advancement of Science.)