Spatiotemporal Single-Photon Airy Bullets.

Uninhibited control of the complex spatiotemporal quantum wave function of a single photon has so far remained elusive even though it can dramatically increase the encoding flexibility and thus the information capacity of a photonic quantum link. By fusing temporal waveform generation in an atomic ensemble and spatial single-photon shaping, we hereby demonstrate for the first time complete spatiotemporal control of a propagation invariant (2+1)D Airy single-photon optical bullet. These correlated photons are not only self-accelerating and impervious to spreading as their classical counterparts, but can be concealed and revealed in the presence of strong classical stray light.

Universal dimension reduced phase compensation algorithm for an optical phased array.

Optical phased arrays (OPAs) can achieve non-mechanical beam deflection. Many types of OPA face the problem of low deflection efficiency due to the phase distortion induced by mutual coupling between nearby channels. In this Letter, a universal optimization algorithm is proposed to compensate for this structural phase distortion, in which the adjacent sampling principal component analysis (AS-PCA) method is introduced to reduce the dimension of the solution space. Simulations and experimental results on different classes of OPA verified that this method can considerably optimize the deflection beam with a rapid convergence speed, irrespective of the scale of OPA, and maintain the universal feature, laying the foundation for large-scale, high-density OPA in-line optimization. We envision it to become a general method on different platforms.

Quantum Interference between Photons and Single Quanta of Stored Atomic Coherence.

Essential for building quantum networks over remote independent nodes, the indistinguishability of photons has been extensively studied by observing the coincidence dip in the Hong-Ou-Mandel interferometer. However, indistinguishability is not limited to the same type of bosons. For the first time, we hereby observe quantum interference between flying photons and a single quantum of stored atomic coherence (magnon) in an atom-light beam splitter interface. We demonstrate that the Hermiticity of this interface determines the type of quantum interference between photons and magnons. Consequently, not only the bunching behavior that characterizes bosons is observed, but counterintuitively, fermionlike antibunching as well. The hybrid nature of the demonstrated magnon-photon quantum interface can be applied to versatile quantum memory platforms, and can lead to fundamentally different photon distributions from those occurring in boson sampling.

Spin-orbit coupling and quantum spin Hall effect for neutral atoms without spin flips.

We propose a scheme which realizes spin-orbit coupling and the quantum spin Hall effect for neutral atoms in optical lattices without relying on near resonant laser light to couple different spin states. The spin-orbit coupling is created by modifying the motion of atoms in a spin-dependent way by laser recoil. The spin selectivity is provided by Zeeman shifts created with a magnetic field gradient. Alternatively, a quantum spin Hall Hamiltonian can be created by all-optical means using a period-tripling, spin-dependent superlattice.

Realizing the Harper Hamiltonian with laser-assisted tunneling in optical lattices.

We experimentally implement the Harper Hamiltonian for neutral particles in optical lattices using laser-assisted tunneling and a potential energy gradient provided by gravity or magnetic field gradients. This Hamiltonian describes the motion of charged particles in strong magnetic fields. Laser-assisted tunneling processes are characterized by studying the expansion of the atoms in the lattice. The band structure of this Hamiltonian should display Hofstadter's butterfly. For fermions, this scheme should realize the quantum Hall effect and chiral edge states.

Bragg scattering as a probe of atomic wave functions and quantum phase transitions in optical lattices.

We have observed Bragg scattering of photons from quantum degenerate ^{87}Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose position and momentum width is Heisenberg limited. The spatial coherence of the wave function leads to revivals in the Bragg scattered light due to the atomic Talbot effect. The decay of revivals across the superfluid to Mott insulator transition indicates the loss of superfluid coherence.

Diffusion-trapped Airy beams in photorefractive media.

We report the first experimental observation of self-trapped Airy beams in a nonlinear medium. As opposed to screening or photovoltaic spatial solitons, this new class of self-localized beams owes its existence to carrier diffusion effects. The asymmetric action of two-wave mixing supports the asymmetric intensity profile of the Airy states, with a balance that is independent of the beam intensity (unlike solitons). Further, the self-trapped wave packets self-bend during propagation at an acceleration rate that is independent of the thermal energy associated with the diffusive nonlinearity.

Curved plasma channel generation using ultraintense Airy beams.

Plasma channel generation (or filamentation) using ultraintense laser pulses in dielectric media has a wide spectrum of applications, ranging from remote sensing to terahertz generation to lightning control. So far, laser filamentation has been triggered with the use of ultrafast pulses with axially symmetric spatial beam profiles, thereby generating straight filaments. We report the experimental observation of curved plasma channels generated in air using femtosecond Airy beams. In this unusual propagation regime, the tightly confined main intensity feature of the axially nonsymmetric laser beam propagates along a bent trajectory, leaving a curved plasma channel behind. Secondary channels bifurcate from the primary bent channel at several locations along the beam path. The broadband radiation emanating from different longitudinal sections of the curved filament propagates along angularly resolved trajectories.

Self-healing properties of optical Airy beams.

We investigate both theoretically and experimentally the self-healing properties of accelerating Airy beams. We show that this class of waves tends to reform during propagation in spite of the severity of the imposed perturbations. In all occasions the reconstruction of these beams is interpreted through their internal transverse power flow. The robustness of these optical beams in scattering and turbulent environments is also studied experimentally. Our observations are in excellent agreement with numerical simulations.

Accelerating finite energy Airy beams.

We investigate the acceleration dynamics of quasi-diffraction-free Airy beams in both one- and two-dimensional configurations. We show that this class of finite energy waves can retain their intensity features over several diffraction lengths. The possibility of other physical realizations involving spatiotemporal Airy wave packets is also considered.

Observation of discrete quadratic surface solitons.

We report the first observation of discrete quadratic surface solitons in self-focusing and defocusing periodically poled lithium niobate waveguide arrays. By operating on either side of the phase-matching condition and using the cascading nonlinearity, both in-phase and staggered discrete surface solitons were observed. This represents the first experimental demonstration of staggered/gap surface solitons at the interface of a semi-infinite nonlinear lattice. The experimental results were found to be in good agreement with theory.

Enhanced third-order nonlinear effects in optical AlGaAs nanowires.

We report the first observation of enhanced third-order nonlinear effects in AlGaAs nanowires. AlGaAs nanowaveguides with widths varying from 100 to 600nm were fabricated and characterized. Nonlinear phase shifts of approximately pi were experimentally observed at 1.55mum with peak powers of 30-40W in 600mum long, 550nm wide guides.