Manipulation of nonreciprocal unconventional photon blockade in a cavity-driven system composed of an asymmetrical cavity and two atoms with weak dipole–dipole interaction

We present a work of manipulating collective unconventional photon blockade(UCPB)and nonreciprocal UCPB(NUCPB)in a cavity-driven system composed of an asymmetrical single-mode cavity and two interacting identical twolevel atoms(TLAs).When the atoms do not interact directly,the frequency and intensity restrictions of collective UCPB can be specified,and a giant NUCPB exists due to the splitting of optimal atom–cavity coupling strength in proper parameter regime.However,if a weak atom–atom interaction which provides a new and feeble quantum interference pathway to UCPB is taken into account,two restrictions of UCPB are combined complexly,which are rigorous to be matched simultaneously.Due to the push-and-pull effect induced by weak dipole–dipole interaction,the UCPB regime is compressed more or less.NUCPB is improved as a higher contrast is present when the two complex UCPB restrictions are matched,while it is suppressed when the restrictions are mismatched.In general,whether NUCPB is suppressed or promoted depends on its working parameters.Our findings show a prospective access to produce giant quantum nonreciprocity by a couple of weakly interacting atoms.

Photon bunching and anti-bunching with two dipole-coupled atoms in an optical cavity

We investigate the effect of the dipole–dipole interaction(DDI) on the photon statistics with two atoms trapped in an optical cavity driven by a laser field and subjected to cooperative emission. By means of the quantum trajectory analysis and the second-order correlation functions, we show that the photon statistics of the cavity transmission can be flexibly modulated by the DDI while the incoming coherent laser selectively excites the atom–cavity system’s nonlinear Jaynes–Cummings ladder of excited states. Finally, we find that the effect of the cooperatively atomic emission can also be revealed by the numerical simulations and can be explained with a simplified picture. The DDI induced nonlinearity gives rise to highly nonclassical photon emission from the cavity that is significant for quantum information processing and quantum communication.

Levitation and lateral forces between a point magnetic dipole and a superconducting sphere

The dipole–dipole interaction model is employed to investigate the angular dependence of the levitation and lateral forces acting on a small magnet in an anti-symmetric magnet/superconducting sphere system. Breaking the symmetry of the system enables us to study the lateral force which is important in the stability of the magnet above a superconducting sphere in the Meissner state. Under the assumption that the lateral displacement of the magnet is small compared to the physical dimensions of our proposed system, analytical expressions are obtained for the levitation and lateral forces as a function of the geometrical parameters of the superconductor as well as the height, the lateral displacement, and the orientation of the magnetic moment of the magnet. The dependence of the levitation force on the height of the levitating magnet is similar to that in the symmetric magnet/superconducting sphere system within the range of proposed lateral displacements. It is found that the levitation force is linearly dependent on the lateral displacement whereas the lateral force is independent of this displacement. A sinusoidal variation of both forces as a function of the polar and azimuthal angles specifying the orientation of the magnetic moment is observed. The relationship between the stability and the orientation of the magnetic moment is discussed for different orientations.

Entanglement transfer between atoms in two distant cavities via an optical fibre

This paper presents a treatment of the entanglement transfer between atoms in two distant cavities coupled by an optical fibre. If the atoms resonantly and collectively interact with the local single-mode cavity fields and the dipole-dipole interaction between the atoms is neglected, then it shows that a complete transfer of entanglement from one pair of atoms to another can be deterministically realized. Furthermore, it also investigates the effects of dipole-dipole interaction on entanglement transfer on the condition that the interaction between the atoms and the cavity is much weaker than the coupling between the cavity and the fibre.

Exact solution of entanglement of the double Jaynes-Cummings model without rotating wave approximation

This paper investigates the influences of atom field coupling and dipole-dipole coupling for atoms on the entanglement between two atoms by means of concurrence, The results show that the sudden death occurs when the atom field coupling is strong enough, and the collapse and the revival appear when the dipole-dipole interaction is strong enough.

Dynamical stability of dipolar condensate in a parametrically modulated one-dimensional optical lattice

We study the stabilization properties of dipolar Bose–Einstein condensate in a deep one-dimensional optical lattice with an additional external parametrically modulated harmonic trap potential. Through both analytical and numerical methods, we solve a dimensionless nonlocal nonlinear discrete Gross–Pitaevskii equation with both the short-range contact interaction and the long-range dipole–dipole interaction. It is shown that, the stability of dipolar condensate in modulated deep optical lattice can be controled by coupled effects of the contact interaction, the dipolar interaction and the external modulation. The system can be stabilized when the dipolar interaction, the contact interaction, the average strength of potential and the ratio of amplitude to frequency of the modulation satisfy a critical condition. In addition, the breather state, the diffused state and the attractive-interaction-induced-trapped state are predicted. The dipolar interaction and the external modulation of the lattice play important roles in stabilizing the condensate.

The dynamics of three coupled dipolar Bose Einstein condensates

The dynamics of the three coupled dipolar Bose–Einstein condensates containing N bosons is investigated within a mean-field semiclassical picture based on the coherent-state method. Varieties of periodic solutions （configured as vortex, single depleted well, and dimerlike states） are obtained analytically when the fixed points are identified on the N=constant. The system dynamics are studied via numeric integration of trimer motion equations, thus revealing macroscopic effects of population inversion and self-trapping with different initial states. In particular, the trajectory of the oscillations of the populations in each well shows how the dynamics of the condensates are effected by the presence of dipole–dipole interaction and gauge field.

Quantum information processing with nuclear spins mediated by a weak-mechanically controlled electron spin

We propose a scheme to achieve nuclear–nuclear indirect interactions mediated by a mechanically driven nitrogen-vacancy(NV)center in a diamond.Here we demonstrate twoqubit entangling gates and quantum-state transfer between two carbon nuclei.When the dipole–dipole interaction strength is much larger than the driving field strength,the scheme is robust against decoherence caused by coupling between the NV center(nuclear spins)and the environment.Conveniently,precise control of dipole coupling is not required so this scheme is insensitive to fluctuating positions of the nuclear spins and the NV center.Our scheme provides a general blueprint for multi-nuclear-spin gates and for multi-party communication.