One-step quantum secure direct communication.

Quantum secure direct communication (QSDC) attracts much attention for it can transmit secret messages directly without sharing a key. In this article, we propose a one-step QSDC protocol, which only requires to distribute polarization-spatial-mode hyperentanglement for one round. In this QSDC protocol, the eavesdropper cannot obtain any message, so that this protocol is unconditionally secure in principle. This protocol is a two-way quantum communication and has high capacity for it can transmit two bits of secret messages with one pair of hyperentanglement. With entanglement fidelities of both polarization and spatial-mode degrees of freedom being 0.98, the maximal communication distance of this one-step QSDC can reach about 216 km. QSDC can also be used to generate the key. In this regard, the key generation rate is estimated about 2.5 times of that in the entanglement-based QKD with the communication distance of 150 km. With the help of future quantum repeaters, this QSDC protocol can provide unconditionally secure communication over arbitrarily long distance.

Experimental one-step deterministic polarization entanglement purification.

Entanglement purification is to distill high-quality entangled states from low-quality entangled states. It is a key step in quantum repeaters, determines the efficiency and communication rates of quantum communication protocols, and is hence of central importance in long-distance communications and quantum networks. In this work, we report the first experimental demonstration of deterministic entanglement purification using polarization and spatial mode hyperentanglement. After purification, the fidelity of polarization entanglement arises from 0.268±0.002 to 0.989±0.001. Assisted with robust spatial mode entanglement, the total purification efficiency can be estimated as 109 times that of the entanglement purification protocols using two copies of entangled states when one uses the spontaneous parametric down-conversion sources. Our work may have the potential to be implemented as a part of full repeater protocols.

Quantum hyperentanglement and its applications in quantum information processing.

Hyperentanglement is a promising resource in quantum information processing with its high capacity character, defined as the entanglement in multiple degrees of freedom (DOFs) of a quantum system, such as polarization, spatial-mode, orbit-angular-momentum, time-bin and frequency DOFs of photons. Recently, hyperentanglement attracts much attention as all the multiple DOFs can be used to carry information in quantum information processing fully. In this review, we present an overview of the progress achieved so far in the field of hyperentanglement in photon systems and some of its important applications in quantum information processing, including hyperentanglement generation, complete hyperentangled-Bell-state analysis, hyperentanglement concentration, and hyperentanglement purification for high-capacity long-distance quantum communication. Also, a scheme for hyper-controlled-not gate is introduced for hyperparallel photonic quantum computation, which can perform two controlled-not gate operations on both the polarization and spatial-mode DOFs and depress the resources consumed and the photonic dissipation.

Path-polarization hyperentangled and cluster states of photons on a chip.

Encoding many qubits in different degrees of freedom (DOFs) of single photons is one of the routes toward enlarging the Hilbert space spanned by a photonic quantum state. Hyperentangled photon states (that is, states showing entanglement in multiple DOFs) have demonstrated significant implications for both fundamental physics tests and quantum communication and computation. Increasing the number of qubits of photonic experiments requires miniaturization and integration of the basic elements, and functions to guarantee the setup stability, which motivates the development of technologies allowing the precise control of different photonic DOFs on a chip. We demonstrate the contextual use of path and polarization qubits propagating within an integrated quantum circuit. We tested the properties of four-qubit linear cluster states built on both DOFs, and we exploited them to perform the Grover's search algorithm according to the one-way quantum computation model. Our results pave the way toward the full integration on a chip of hybrid multi-qubit multiphoton states.

Viscoelastic properties of aqueous guar gum derivative solutions under large amplitude oscillatory shear (LAOS).

The industrial relevant nonlinear viscoelastic properties of aqueous carboxymethyl hydroxypropyl guar gum (CMHPG) and non-ionic hydroxypropyl guar gum (HPG) solutions between semi-dilute and concentrated solution state were investigated by large amplitude oscillatory shear flow (LAOS). Aqueous CMHPG and HPG solutions enter the nonlinear flow regime at deformations γ0>100%. The nonlinear stress waveforms were analyzed by FT-rheology and orthogonal stress decomposition along the MITlaos framework. A rheological fingerprint is generated (Pipkin space) showing that the guar gum derivative solutions undergo a shear-thinning at high strains, which is preceded by a thickening above a minimum strain rate at intermediate strains. The influence and breakup of superstructures/aggregates gives a "rheological fingerprint", a function of the applied deformation and time scale (Pipkin space). A characteristic process time was found that scales exponentially with the overlap parameter with an exponent of 4/2, and is proposed to represent the relaxation process of the superstructure in solution.

Structure-property relationships of carboxymethyl hydroxypropyl guar gum in water and a hyperentanglement parameter.

The viscoelastic properties of carboxymethyl hydroxypropyl guar gum (CMHPG) in aqueous solution were determined as function of concentration and of molecular weight, using SEC/MALLS/dRI and viscometry. The chain is more rigid as in native guar as was deduced from the molecular parameter in dilute solution. Superstructures are formed in moderately concentrated solutions as is shown from the comparison of steady state shear and small amplitude oscillatory shear (SAOS) experiments. The shear rate dependent viscosity of CMHPG can satisfactorily be described by the Carreau-Yasuda model with the rheological parameters (η0, λ0, n, b) obtained from the evaluation of viscosity data. A quantitative hyperentanglement parameter is introduced to account for the differences in responses in shear and SAOS experiments.