Fermion superfluids of nonzero orbital angular momentum near resonance

We study the pairing of Fermi gases near the scattering resonance of the l not equal 0 partial wave. Using a model potential which reproduces the actual two-body low energy scattering amplitude, we have obtained an analytic solution of the gap equation. We show that the ground state of l=1 and l=3 superfluids are orbital ferromagnets with pairing wave functions Y11 and Y32, respectively. For l=2, there is a degeneracy between Y22 and a "cyclic state." Dipole energy will orient the angular momentum axis. The gap function can be determined by the angular dependence of the momentum distribution of the fermions.     

Microobject manipulations using laser beams with nonzero orbital angular momentum

Microobject manipulation with a laser is investigated. The functional capabilities of the laser manipulators can be significantly enhanced using beams with predetermined distributions of intensity and angular momentum. Beams with nonzero angular momentum are generated using phase and amplitude-phase masks. Such beams make it possible to rotate weakly absorbing particles and to move them along a given trajectory. Experimental results on the microobject motion along various trajectories (circle, triangle contour, self-intersecting curve, and Archimedes spiral) are presented.     

Efficient sorting of orbital angular momentum states of light

We present a method to efficiently sort orbital angular momentum (OAM) states of light using two static optical elements. The optical elements perform a Cartesian to log-polar coordinate transformation, converting the helically phased light beam corresponding to OAM states into a beam with a transverse phase gradient. A subsequent lens then focuses each input OAM state to a different lateral position. We demonstrate the concept experimentally by using two spatial light modulators to create the desired optical elements, applying it to the separation of eleven OAM states.     

Suppression of angular momentum transfer in cold collisions of transition metal atoms in ground States with nonzero orbital angular momentum

The Zeeman relaxation rate in cold collisions of Ti(3d(2)4s(2) 3F2) with He is measured. We find that collisional transfer of angular momentum is dramatically suppressed due to the presence of the filled 4s(2) shell. The degree of electronic interaction anisotropy, which is responsible for Zeeman relaxation, is estimated to be about 200 times smaller in the Ti-He complex than in He complexes with typical non-S-state atoms.     

Gravitational radiation by a particle with nonzero orbital angular momentum falling into a Kerr black hole

We have computed the energy of the gravitational waves induced by a particle with nonzero orbital angular momentum μL_z plunging into a Kerr black hole in an equatorial plane. It is found that for the same |L_z| a corotating particle emits more energy than a counter-rotating one, which is due to the change of the frequency of the quasi-normal mode with the increase of the angular momentum of the black hole.     

基于光子轨道角动量的密码通信方案研究

设计了一个基于两个正交的光子轨道角动量态的量子密码通信方案.在该方案中,Alice使用具有独特设计的激光器,随机发送有确定轨道角动量的光子;Bob采用由两个达夫棱镜组成的光束旋转器,对光子的轨道角动量态进行测量.对系统安全性的讨论表明,Eve采用截获重发、攻击单臂等攻击手段,其窃听行为都会被发现.理论证明,该方案不需要通信双方实时监测和调整参考系,同时避免了BB84,B92协议因发送基和测量基不一致而丢弃一半信息的问题,从而提高了密钥生成效率. 关键词： 量子保密通信 轨道角动量     

Free-space measurement-device-independent quantum-key-distribution protocol using decoy states with orbital angular momentum

In this paper, we propose a measurement-device-independent quantum-key-distribution(MDI-QKD) protocol using orbital angular momentum(OAM) in free space links, named the OAM-MDI-QKD protocol. In the proposed protocol,the OAM states of photons, instead of polarization states, are used as the information carriers to avoid the reference frame alignment, the decoy-state is adopted to overcome the security loophole caused by the weak coherent pulse source, and the high efficient OAM-sorter is adopted as the measurement tool for Charlie to obtain the output OAM state. Here, Charlie may be an untrusted third party. The results show that the authorized users, Alice and Bob, could distill a secret key with Charlie's successful measurements, and the key generation performance is slightly better than that of the polarization-based MDI-QKD protocol in the two-dimensional OAM cases. Simultaneously, Alice and Bob can reduce the number of flipping the bits in the secure key distillation. It is indicated that a higher key generation rate performance could be obtained by a high dimensional OAM-MDI-QKD protocol because of the unlimited degree of freedom on OAM states. Moreover,the results show that the key generation rate and the transmission distance will decrease as the growth of the strength of atmospheric turbulence(AT) and the link attenuation. In addition, the decoy states used in the proposed protocol can get a considerable good performance without the need for an ideal source.     

Manipulating atomic states via optical orbital angular-momentum

Optical orbital angular-momentum (OAM) has more complex mechanics than the spin degree of photons, and may have a broad range of application. Manipulating atomic states via OAM has become an interesting topic. In this paper, we first review the general theory of generating adiabatic gauge field in ultracold atomic systems by coupling atoms to external optical fields with OAM, and point out the applications of the generated adiabatic gauge field. Then, we review our work in this field, including the generation of macroscopic superposition of vortex-antivortex states and spin Hall effect (SHE) in cold atoms.      

Manipulating atomic states via optical orbital angular-momentum

Optical orbital angular-momentum (OAM) has more complex mechanics than the spin degree of photons, and may have a broad range of application. Manipulating atomic states via OAM has become an interesting topic. In this paper, we first review the general theory of generating adiabatic gauge field in ultracold atomic systems by coupling atoms to external optical fields with OAM, and point out the applications of the generated adiabatic gauge field. Then, we review our work in this field, including the generation of macroscopic superposition of vortex-antivortex states and spin Hall effect (SHE) in cold atoms.     

Influence of atmospheric turbulence on states of light carrying orbital angular momentum

We have experimentally studied the degradation of mode purity for light beams carrying orbital angular momentum (OAM) propagating through simulated atmospheric turbulence. The turbulence is modeled as a randomly varying phase aberration, which obeys statistics postulated by Kolmogorov turbulence theory. We introduce this simulated turbulence through the use of a phase-only spatial light modulator. Once the turbulence is introduced, the degradation in mode quality results in crosstalk between OAM modes. We study this crosstalk in OAM for 11 modes, showing that turbulence uniformly degrades the purity of all the modes within this range, irrespective of mode number.     

Effects of low-order atmosphere-turbulence aberrations on the entangled orbital angular momentum states

Based on Zernike-model expansion of turbulence phase aberrations and non-Kolmogorov spectrum model of index-of-refraction fluctuation, we analyze the effects of low-order Zernike turbulence aberrations on orbital angular momentum (OAM) entanglement states in a weak fluctuation region. The signal photon detection probability of OAM entanglement states propagating in a slant turbulence channel with non-Kolmogorov turbulence Z-tilt, defocus, astigmatism, and coma aberrations are modeled, respectively. The results demonstrate that turbulence Z-tilt aberration is the dominant aberration, coma is the second, and astigmatism is the third, but that the defocus aberration has no impact on the detection probability. As the power-law exponent of the non-Kolmogorov spectrum increases from 3 to 4, the detection probability decreases.     

螺旋相位光束轨道角动量态测量的实验研究

对螺旋光束的轨道角动量态的测量技术进行了实验研究.建立了一套利用Mach-Zehnder干涉仪测量光束轨道角动量态的系统,对利用空间光调制器生成的携带不同轨道角动量的光束进行了测量,通过Mach-Zehnder干涉仪分离出了具有不同角量子数的螺旋光束. 关键词： 轨道角动量 空间光调制器 Mach-Zehnder干涉仪     

Optical storage of orbital angular momentum via Rydberg electromagnetically induced transparency

In this Letter, we report on the successful optical storage of orbital angular momentum(OAM) using Rydberg electromagnetically induced transparency(EIT) in cold rubidium atoms. With a storage time of 1.4 μs, the retrieved structure is highly similar, showing the ability of storing light's OAM at a principal quantum number of 20. The results at higher principal quantum numbers(n ? 25; 30) are also measured. These results show the promise of image processing based on a Rydberg atomic system.     

Generalized model for orbital angular momentum states generated by parallel aligned phase wedges

A generalized model of a double-wedge phase element containing two side-by-side parallel phase ramps with arbitrary slope angles is proposed. We study the diffracted optical field of a double-wedge element in terms of orbital angular momentum states. Analytical calculations reveal how the radius and position of the illuminating laser beam affect the composition of orbital angular momentum generated by the phase wedges.     

利用衍射光栅探测涡旋光束轨道角动量态的研究进展

涡旋光束是一种携带有轨道角动量的光束,在光学扳手、光通信、旋转探测等领域具有重要的应用价值.由于轨道角动量态是涡旋光束的特征值,因此如何探测光束的轨道角动量态分布至关重要.国内外学者已经提出了多种探测涡旋光束的技术,如干涉法、衍射光栅法、多普勒分析法、超材料表面法等.这些技术中,衍射光栅测量法较为简单易行,应用较广.本综述主要介绍了几种当前利用衍射光栅测量涡旋光束轨道角动量态的主流方法,同时也介绍了如何利用衍射光栅来测量光束的轨道角动量谱.     

Approximate analytical solutions of scattering states for Klein-Gordon equation with Hulthén potentials for nonzero angular momentum

In this paper, using the exponential function transformation approach along with an approximation for the centrifugal potential, the radial Klein-Gordon equation with the vector and scalar Hulthén potential is transformed to a hypergeometric differential equation. The approximate analytical solutions of t-waves scattering states are presented. The normalized wave functions expressed in terms of hypergeometric functions of scattering states on the “k/2π scale” and the calculation formula of phase shifts are given. The physical meaning of the approximate analytical solution is discussed.      

A simple scheme for quantum networks based on orbital angular momentum states of photons

We propose a new quantum network scheme using orbital angular momentum states of photons to route the network and spin angular momentum states to encode the information. A four-user experimental scheme based on this efficient quantum network is analyzed in detail, which is particularly appealing for the free space quantum key distribution. Users can freely exchange quantum keys with each other.     

Acousto-optic generation of orbital angular momentum states of light in a tapered optical fiber

We demonstrate an acousto-optic mode converter based on a tapered optical fiber to efficiently generate orbital angular momentum states of light. In our scheme an acoustic wave is deployed to the waist of tapered optical fiber where two degenerate HE₂₁ modes leading to +1 and −1 orbital angular momentum eigen-modes are resonantly excited. The excitation of TM₀₁ and TE₀₁ modes is suppressed by enlarging the intermodal index difference between near-degenerate spatial modes. Numerical calculation for optimization of the taper diameter is provided. The experimental characterization of generated states is performed by analyzing the output far-field pattern and the spatial interference fringes with a uniform reference beam.