Chinese Physics B

Xue, Xi-Ling; Liu, Zhi-Hao; Chen, Han-Wu

doi: 10.1088/1674-1056/26/1/010301pmid: N/A

Janmark, Meyer, and Wong showed that continuous-time quantum walk search on known families of strongly regular graphs (SRGs) with parameters achieves full quantum speedup. The problem is reconsidered in terms of scattering quantum walk, a type of discrete-time quantum walks. Here, the search space is confined to a low-dimensional subspace corresponding to the collapsed graph of SRGs. To quantify the algorithm's performance, we leverage the fundamental pairing theorem, a general theory developed by Cottrell for quantum search of structural anomalies in star graphs. The search algorithm on the SRGs with k scales as N satisfies the theorem, and results can be immediately obtained, while search on the SRGs with k scales as does not satisfy the theorem, and matrix perturbation theory is used to provide an analysis. Both these cases can be solved in time steps with a success probability close to 1. The analytical conclusions are verified by simulation results on two SRGs. These examples show that the formalism on star graphs can be applied more generally.

Chen, Rui-Ke; Bao, Wan-Su; Wang, Yang; Bao, Hai-Ze; Zhou, Chun; Jiang, Mu-Sheng; Li, Hong-Wei

doi: 10.1088/1674-1056/26/1/010302pmid: N/A

Measurement-device-independent quantum cryptographic conferencing (MDI-QCC) protocol puts MDI quantum key distribution (MDI-QKD) forwards to multi-party applications, and suggests a significant framework for practical multi-party quantum communication. In order to mitigate the experimental complexity of MDI-QCC and remove the key assumption (the sources are trusted) in MDI-QCC, we extend the framework of MDI-QKD with an untrusted source to MDI-QCC and give the rigorous security analysis of MDI-QCC with an untrusted source. What is more, in the security analysis we clearly provide a rigorous analytical method for parameters’ estimation, which with simple modifications can be applied to not only MDI-QKD with an untrusted source but also arbitrary multi-party communication protocol with an untrusted source. The simulation results show that at reasonable distances the asymptotic key rates for the two cases (with trusted and untrusted sources) almost overlap, which indicates the feasibility of our protocol.

Guo, W J; Wei, L F

doi: 10.1088/1674-1056/26/1/010303pmid: N/A

Quantum teleportation with entanglement channels and a series of two-qubit SWAP gates between the nearest-neighbor qubits are usually utilized to achieve the transfers of unknown quantum state from the sender to the distant receiver. In this paper, by simplifying the usual SWAP gates we propose an approach to speed up the transmissions of unknown quantum information, specifically including the single-qubit unknown state and two-qubit unknown entangled ones, by a series of entangling and disentangling operations between the remote qubits with distant interactions. The generic proposal is demonstrated specifically with experimentally-existing Ising-type quantum channels without transverse interaction; liquid NMR-molecules driven by global radio frequency electromagnetic pulses and capacitively-coupled Josephson circuits driven by local microwave pulses. The proposal should be particularly useful to set up the connections between the distant qubits in a chip of quantum computing.

Ye, Guo-Dong; Huang, Xiao-Ling; Zhang, Leo Yu; Wang, Zheng-Xia

doi: 10.1088/1674-1056/26/1/010501pmid: N/A

In this paper, a novel image encryption algorithm is presented based on self-cited pixel summation. With the classical mechanism of permutation plus diffusion, a pixel summation of the plain image is employed to make a gravity influence on the pixel positions in the permutation stage. Then, for each pixel in every step of the diffusion stage, the pixel summation calculated from the permuted image is updated. The values from a chaotic sequence generated by an intertwining logistic map are selected by this summation. Consequently, the keystreams generated in both stages are dependent on both the plain image and the permuted image. Because of the sensitivity of the chaotic map to its initial conditions and the plain-image-dependent keystreams, any tiny change in the secret key or the plain image would lead to a significantly different cipher image. As a result, the proposed encryption algorithm is immune to the known plaintext attack (KPA) and the chosen plaintext attack (CPA). Moreover, experimental simulations and security analyses show that the proposed permutation-diffusion encryption scheme can achieve a satisfactory level of security.

Guo, Wei; Du, Lu-Chun; Liu, Zhen-Zhen; Yang, Hai; Mei, Dong-Cheng

doi: 10.1088/1674-1056/26/1/010502pmid: N/A

We investigate the transport of a deterministic Brownian particle theoretically, which moves in simple one-dimensional, symmetric periodic potentials under the influence of both a time periodic and a static biasing force. The physical system employed contains a friction coefficient that is speed-dependent. Within the tailored parameter regime, the absolute negative mobility, in which a particle can travel in the direction opposite to a constant applied force, is observed. This behavior is robust and can be maximized at two regimes upon variation of the characteristic factor of friction coefficient. Further analysis reveals that this uphill motion is subdiffusion in terms of localization (diffusion coefficient with the form at long times). We also have observed the non-trivially anomalous subdiffusion which is significantly deviated from the localization; whereas most of the downhill motion evolves chaotically, with the normal diffusion.

Yang, Hong-ying; Zheng, Qiang; Zhi, Qi-jun

doi: 10.1088/1674-1056/26/1/010601pmid: N/A

Adopting the Milburn decoherence model, we investigate the performance of quantum Fisher information of the two-qutrit isotropic Heisenberg XY chain under decoherence. We find that the quantum Fisher information with respect to the decoherence rate and the magnetic field decreases exponentially in the long-time limit, which significantly reduces the precision of optimal quantum estimation. We also show that with the increase of the decoherence rate or the magnetic field, the QFIs go down considerably. Furthermore, we find that the precision of optimal quantum estimation can be enhanced by the entanglement in the input state.

Xu, Jie; Jiao, Ji-qing; Li, Qiang; Li, Shan-dong

doi: 10.1088/1674-1056/26/1/010701pmid: N/A

A special Fe3O4 nanoparticles–graphene (Fe3O4–GN) composite as a magnetic label was employed for biodetection using giant magnetoresistance (GMR) sensors with a Wheatstone bridge. The Fe3O4–GN composite exhibits a strong ferromagnetic behavior with the saturation magnetization of approximately 48 emu/g, coercivity of 200 Oe, and remanence of 8.3 emu/g, leading to a large magnetic fringing field. However, the Fe3O4 nanoparticles do not aggregate together, which can be attributed to the pinning and separating effects of graphene sheet to the magnetic particles. The Fe3O4–GN composite is especially suitable for biodetection as a promising magnetic label since it combines two advantages of large fringing field and no aggregation. As a result, the concentration x dependence of voltage difference between detecting and reference sensors undergoes the relationship of with an ultralow detection limit of 10 ng/mL (very close to the calculated limit of 7 ng/mL) and a wide detection range of 4 orders.

Jabbar, Saqib; Ahmad, Riaz; Chu, Paul K

doi: 10.1088/1674-1056/26/1/010702pmid: N/A

SrTiO3 (STO) and TiO2 are insulating materials with large dielectric constants and opposite signs of the quadratic coefficient of voltage (. Insertion of a TiO2 thin film between STO layers increases the linearity of the capacitance in response to an applied voltage, to meet the increasing demand of large-capacitance-density dynamic random access memory capacitors. Both STO and TiO2 suffer from the problem of high leakage current owing to their almost equivalent and low bandgap energies. To overcome this, the thickness of the thin TiO2 film sandwiched between the STO films was varied. A magnetron sputtering system equipped with radio frequency and direct current power supply was employed for depositing the thin films. TiN was deposited as the top and bottom metal electrodes to form a metal–insulator metal (MIM) structure, which exhibited a very large linear capacitance density of 21 fF/um2 that decreased by increasing the thickness of the TiO2 film. The leakage current decreased with an increase in the thickness of TiO2, and for a 27-nm-thick film, the measured leakage current was A. X-ray diffraction and Raman spectroscopy revealed that TiN, STO, and TiO2 films are crystalline and TiO2 has a dominant anatese phase structure.

Li, Xiang-Fu; Jiang, Gang; Wang, Hong-Bin; Sun, Qian

doi: 10.1088/1674-1056/26/1/013101pmid: N/A

The atomic structure and transition properties of H-like Al embedded in hot and dense plasmas are investigated using modified GRASP2K code. The plasma screening effect on the nucleus is described using the self-consistent field ion sphere model. The effective nuclear potential decreases much more quickly with increasing average free electron density, but increases slightly with increasing electron temperature. The variations of the transition energies, transition probabilities, and oscillator strengths with the free electron density and electron temperature are the same as that of the effective nuclear potential. The results reported in this work agree well with other available theoretical results and are useful for plasma diagnostics.

Jia, Z M; Zeng, Z N; Tang, W T; Li, R X

doi: 10.1088/1674-1056/26/1/013201pmid: N/A

A dc electric field is utilized to steer the electron motion after the molecular ion is excited by an ultrashort ultraviolet laser pulse. The numerical simulation shows that the electron localization distribution and the dissociation control ratio are dependent on the polarization direction and amplitude of the dc electric field. Most electrons of the dissociation state move opposite to the dc electric field and stabilize at the dressed-up potential well, for the dressed-down well is occupied by the electrons of the 1s state.