arXiv subjects

Shengmei Zhao

Publications and source records attributed to Shengmei Zhao.

25 records · Page 2Linked to original sources

arXiv2018

Thermal effects of the quantum states generated from the isomorphs of PPKTP crystal

We theoretically and numerically investigate the temperature-dependent properties of the biphotons generated from four isomorphs of periodically poled $\mathrm{KTiOPO_4}$ (PPKTP): i.e., PPRTP, PPKTA, PPRTA and PPCTA. It is discovered that the first type of group-velocity-matched (GVM) wavelength is decreased by 6.4, 1.2, 8.9, 25.6 and 6.3 nm, while the phase-matched wavelength is decreased by 4.4, -0.4, -1.2, 29.1 and 59.5 nm for PPKTP, PPRTP, PPKTA, PPRTA and PPCTA, respectively, when the temperature is increased from 20$\,^{\circ}\mathrm{C}$ to 120$\,^{\circ}\mathrm{C}$. Although the maximal spectral purity of the heralded single photons is not changed at different temperature, the Hong-Ou-Mandel (HOM) interference shows different patterns due to a shift of the joint spectral amplitude. These thermal effects are very important for precise control of the quantum state for the future applications in quantum information processing, for example, in quantum interference or spectroscopy.

quant-ph↗

arXiv2018

Influence of oceanic turbulence on propagation of Airy vortex beam carrying orbital angular momentum

With Rytov approximation theory, we derive the analytic expression of detection probability of Airy vortex beam carrying orbital angular momentum (OAM) through an anisotropic weak oceanic turbulence. We investigate the influences of turbulence parameters and beam parameters on the propagation properties of Airy-OAM beam. The numerical simulation results show that the anisotropic oceanic turbulence with a lower dissipation rate of temperature variance, smaller ratio of temperature and salinity contributions to the refractive index spectrum, higher dissipation rate of kinetic energy per unit mass of fluid, bigger inner scale factor, larger anisotropic coefficient causes the larger detection probability of Airy-OAM beam. Moreover, the Airy-OAM beam with a smaller topological charge, larger main ring radius and longer wavelength, has strong resistance to oceanic turbulent interference. Additionally, the detection probability decreases with the increase of receiving aperture size. In comparison with Laguerre-Gaussian-OAM beam, Airy-OAM beam has more anti-interference to turbulence when its topological charge is larger than 5 due to its non-diffraction and self-healing characteristics. The results are useful for underwater optical communication link using Airy-OAM beam.

physics.class-ph↗

arXiv2018

High-dimensional measurement-device-independent quantum key distribution based on spatial basis

Improving the secret key rate is one of the vital issues in practical applications of quantum key distribution (QKD). In this paper, we propose an experimental scheme of high-dimensional measurement-device-independent quantum key distribution (MDI-QKD) based on spatial basis aiming to increase the key rate. Two groups of discrete position basis and momentum basis are applied as conjugate spaces to generate quantum secret key. The position states are transmitted by single-mode fibers and represented by the index of the fiber, while the momentum state is a coherent superposition of the position states characterized by the phase gradient. The measurement of each momentum basis is realized by multi-slit diffraction. This experimental proposal can be implemented with standard optical elements. In addition to an enhanced key rate in a higher dimension, this high-dimensional MDI-QKD exhibits a comparable security level/performance compared to conventional polarization-based MDI-QKD.

physics.optics↗

arXiv2018

Manipulating orbital angular momentum entanglement by using the Heisenberg Uncertainty principle

Orbital angular momentum entanglement is one of the most intriguing topics in quantum physics. A broad range of research have been dedicated either to unravel its underlying physics or to expand the entanglement dimensions and degrees. In this paper, we present a theoretical study on the orbital angular momentum entanglement by employing the Heisenberg uncertainty principle to quantum position correlation within the azimuthal region. In this study, we decompose the pump light into a set of pump cone states characterized by their radii. The OAM entanglement can be manipulated by controlling the radius of the pump cone state, the length of the nonlinear crystal and the OAM carried by the pump field,which is followed by a detailed discussion. We expect that our research will bring us a deeper understanding of the OAM entanglement, and will do help to the high-dimensional quantum information tasks based on OAM entanglement.

physics.optics↗

arXiv2014

Turbulence Mitigation Scheme for Optical Communications using Orbital Angular Momentum Multiplexing Based on Channel Coding and Wavefront Correction

The free-space optical (FSO) communication links with orbital angular momentum (OAM) multiplexing have been demonstrated that they can largely enhance the systems' capacity without a corresponding increase in spectral bandwidth, but the performance of the system is unavoidably disturbed by atmospheric turbulence (AT). Different from the existed AT disturbance, the OAM-multiplexed systems will cause both the burst and random errors for a single OAM state carrier and the `crosstalk' interference between the different OAM states carriers. In this paper, we propose a turbulence mitigation method to improve AT tolerance of OAM-multiplexed FSO communication links. In the proposed scheme, we use channel codes to correct the burst and random errors caused by AT for a single OAM state carrier; And we use wavefront correction method to correct the `crosstalk' interference between the different OAM states carriers. The improvements of AT tolerance are discussed by comparing the performance of OAM-multiplexed FSO communication links with or without channel coding or Shark-Hartmann wavefront correction method. The numerical simulation results show that the OAM-multiplexed FSO communication links have enhanced their AT tolerance. The usage of channel codes and wavefront correction methods together has improved greatly the performance of OAM-multiplexed FSO communication links over atmospheric turbulence.

physics.optics↗

arXiv2012

Experimental realization of large-alphabet quantum key distribution protocol using orbital angular momentum entanglement

We experimentally demonstrate a quantum key distribution (QKD) protocol using photon pairs entangled in orbit angular momentum (OAM). In our protocol, Alice and Bob modulate their OAM states on each entangled pair with spatial light modulators (SLMs), respectively. Alice uses a fixed phase hologram in her SLM, while Bob designs $N$ different suitable phase holograms and uses them to represent his $N$-based information in his SLM. With coincidences, Alice can fully retrieve the key stream sent by Bob without information reconciliation or privacy amplification. We report the experiment results with N=3 and the sector states with OAM eigenmodes l=1 and l=-1. Our experiment shows that the coincidence rates are in relatively distinct value regions for the three different key elements. Alice could recover fully Bob's keys by the protocol. Finally, we discuss the security of the protocol both form the light way and against the general attacks.

quant-ph↗

arXiv2012

Performance of Polar Codes on wireless communications Channel

We discuss the performance of polar codes, the capacity-achieving channel codes, on wireless communication channel in this paper. By generalizing the definition of Bhattacharyya Parameter in discrete memoryless channel, we present the special expression of the parameter for Gaussian and Rayleigh fading the two continuous channels, including the recursive formulas and the initial values. We analyze the applications of polar codes with the defined parameter over Rayleigh fading channel by transmitting image and speech. By comparing with low density parity-check codes(LDPC) at the same cases, our simulation results show that polar codes have better performance than that of LDPC codes. Polar codes will be good candidate for wireless communication channel.

cs.IT↗