We study the quantum phase transition from a superfluid to a Mott insulator of ultracold atoms in a threedimensional optical lattice with adjustable filling factors.Based on the density-adjustable Bose-Einstein conden...We study the quantum phase transition from a superfluid to a Mott insulator of ultracold atoms in a threedimensional optical lattice with adjustable filling factors.Based on the density-adjustable Bose-Einstein condensate we prepared,the excitation spectrum in the superfluid and the Mott insulator regime is measured with different ensemble-averaged filling factors.We show that for the superfluid phase,the center of the excitation spectrum is positively correlated with the ensemble-averaged filling factor,indicating a higher sound speed of the system.For the Mott insulator phase,the discrete feature of the excitation spectrum becomes less pronounced as the ensemble-averaged filling factor increases,implying that it is harder for the system to enter the Mott insulator regime with higher filling factors.The ability to manipulate the filling factor affords further potential in performing quantum simulation with cold atoms trapped in optical lattices.展开更多
We investigate the influence of a gravitational wave background on particles in circular motion. We are especially interested in waves leading to stationary orbits. This consideration is limited to circular orbits per...We investigate the influence of a gravitational wave background on particles in circular motion. We are especially interested in waves leading to stationary orbits. This consideration is limited to circular orbits perpendicular to the incidence direction. As a main result of our calculation, we obtain in addition to the well-known alteration of the radial distance a time dependent correction term for the phase modifying the circular motion of the particle. A background of gravitational waves creates some kind of uncertainty.展开更多
基金Supported by the National Natural Science Foundation of China(Grant Nos.61703025,91736208,1150432&and 11920101004)the National Program on Key Basic Research Project of China(Grant Nos.2016YFA0301501 and 2017YFA0304204).
文摘We study the quantum phase transition from a superfluid to a Mott insulator of ultracold atoms in a threedimensional optical lattice with adjustable filling factors.Based on the density-adjustable Bose-Einstein condensate we prepared,the excitation spectrum in the superfluid and the Mott insulator regime is measured with different ensemble-averaged filling factors.We show that for the superfluid phase,the center of the excitation spectrum is positively correlated with the ensemble-averaged filling factor,indicating a higher sound speed of the system.For the Mott insulator phase,the discrete feature of the excitation spectrum becomes less pronounced as the ensemble-averaged filling factor increases,implying that it is harder for the system to enter the Mott insulator regime with higher filling factors.The ability to manipulate the filling factor affords further potential in performing quantum simulation with cold atoms trapped in optical lattices.
文摘We investigate the influence of a gravitational wave background on particles in circular motion. We are especially interested in waves leading to stationary orbits. This consideration is limited to circular orbits perpendicular to the incidence direction. As a main result of our calculation, we obtain in addition to the well-known alteration of the radial distance a time dependent correction term for the phase modifying the circular motion of the particle. A background of gravitational waves creates some kind of uncertainty.
