Geometric nature, which appears in photon polarization, also appears in spin polarization under a zero magnetic field. These two polarized quanta, one travelling in vacuum and the other staying in matter, behave the same as geometric quantum bits or qubits, which are promising for noise resilience compared to the commonly used dynamic qubits. Here we show that geometric photon and spin qubits are entangled upon spontaneous emission with the help of the spin − orbit entanglement inherent in a nitrogen-vacancy center in diamond. The geometric spin qubit is defined in a degenerate subsystem of spin triplet electrons and manipulated with a polarized microwave. An experiment shows an entanglement state fidelity of 86.8%. The demonstrated entangled emission, combined with previously demonstrated entangled absorption, generates purely geometric entanglement between remote matters in a process that is insensitive of time, frequency, and space mode matching, which paves the way for building a noise-resilient quantum repeater network or a quantum internet.
Collision and gravitational accretion of particles is an important issue related to the origin of ring-satellite systems of giant planets in the solar system. The Hill radii of Pan, Daphnis, Atlas, and Prometheus are found to be within 15 % of the observed long axes of these satellites given by the best-fit model ellipsoids. Also, the densities of these satellites (0.4 -0.6 g cmˆ-3) are very low compared to the density of water ice and all approximately equal to the critical density at that distance, which is defined as the density of a body that entirely fills its Hill sphere. From these results, the small satellites within the orbit of Pandora are thought to be formed by accretion of small porous ring particles onto large dense cores, and further accretion seems to have been suppressed when the density of the satellite reaches the critical density at that distance. Local N-body simulations also demonstrated that a Hill sphere-filling body is produced by accretion of small porous particles onto a large dense core. However, it has not been studied how the degree of particle accretion onto moonlets in the inner parts of Saturn's rings depends on the distance from Saturn.
We demonstrated the optical trapping of silicon nanoparticles in superfluid helium. The silicon nanoparticles were produced via in-situ laser ablation in superfluid helium. The dispersed nanoparticles were optically trapped using near-infrared laser light. With the combination of semiconductor material and the wavelength of 1.5 μm, we can strongly suppress the heat generation in superfluid helium. The thermally stable situation provides us with an important platform for studying the fundamental properties of superfluid helium with the aid of the optical manipulation technique.
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