Xiu-Bo Chen

Optical properties of Nb doped SrTiO3 from first principles study

Abstract The electronic and optical properties of Nb doped SrTiO 3 are studied by ab initio linear muffin-tin orbital method in the atomic sphere approximation. The equilibrium lattice constants of SrTi 1− x Nb x O 3 with x =0.0, 0.25 and 0.5 are found by minimization of the total energy curves. The computated lattice constants are in good agreement with experimental data. Our electronic band calculation shows that the Fermi level of SrTi 1− x Nb x O 3 with x ≥0.125 moves into the conduction bands and the system shows metallic behavior. The numerical results indicate that the Nb impurity atoms would lead to the distortion of the band edges. The complex dielectric function of SrTiO 3 and Nb doped SrTiO 3 are calculated using the random-phase approximation. The doping effect on the optical properties of SrTi 1− x Nb x O 3 is discussed.

AN EFFICIENT PROTOCOL FOR THE QUANTUM PRIVATE COMPARISON OF EQUALITY WITH A FOUR-QUBIT CLUSTER STATE

In this paper, we further research the quantum private comparison protocol with the semi-honest participant, in which two parties can test the equality of their information without revealing the content to anyone. Considering both the success of protocol and the security of information, we first give a reasonable and significant description about the semi-honest model in quantum secure communications. Moreover, based on the feature of four-qubit cluster state which has the great robust against decoherence, we propose a new protocol for the quantum private comparison. Our protocol ingeniously utilizes the special symmetry of the four-qubit cluster state to enhance the efficiency of comparison. This new protocol is secure. The participants only know the result of comparison; cannot know each others private information. TP cannot learn anything about the private information, even about the comparison result and the length of secret inputs.

CRYPTANALYSIS OF THE QUANTUM STATE SHARING PROTOCOL USING FOUR SETS OF W-CLASS STATES

Recently, a protocol is proposed for the quantum state sharing (QSTS) of an arbitrary three-photon state using four sets of W-class states. Unfortunately, its security analysis is inadequate. In this paper, we find the security loophole of this QSTS protocol. It is mainly caused by the fake quantum channel, whose security is not guaranteed by the legal participants. We present a simple but feasible strategy, by which an eavesdropper can successfully steal the exact secret. Furthermore, a secure QSTS protocol is put forward. The security of our improved protocol is analyzed in details.

OPTICAL PROPERTIES OF GAAS/ALGAAS NEAR A SURFACE QUANTUM WELL

Abstract We have investigated the photo-modulated reflection spectra of GaAs quantum wells where the top barrier is confined by thin Al 0.3 Ga 0.7 As layers. The optical transitions spectra of the first heavy hole hh1 and the first light hole lh1 states to the first electron sublevel e1 are observed. Due to the increase of the confinement potential in the near-surface quantum well by varying the Al 0.3 Ga 0.7 As top barrier thickness, we observe a significant blue-shift of the transition lines (hh1 to e1 and lh1 to e1) compared to the transition lines of the quantum well with a thick semiconductor barrier. The experimental observation on the energy shift and the variation of the strength ratio between the transitions e1–hh1 and e1–lh1 can be modeled by a rectangular well combined with a vacuum potential and built-in field.

A NOVEL QUANTUM STEGANOGRAPHY PROTOCOL BASED ON PROBABILITY MEASUREMENTS

Quantum steganography is the art of hiding the fact that communications, which transmit the secret message in an insecure quantum channel, are occurring. This paper presents a novel quantum steganography protocol based on probability measurements for transmitting n qubits secret message in an insecure quantum channel. In the protocol, senders embed the secret message into the cover data by POVM measurements. Then, receivers can correctly extract the secret message and recover the cover data with a certain probability by selecting two sets of appropriate protective measurement operators to act projective measurements, respectively. More importantly, the existence of the secret message has no influence on the cover data. In addition, the security of our protocol does not rely on other protocols. The paper analyzes the secrecy and the security in detail.

CLASSICAL COMMUNICATION COSTS IN QUANTUM INFORMATION PROCESSING

Classical communication plays an important role in quantum information processing such as remote state preparation and quantum teleportation. First, in this paper, we present some simple faithful remote state preparation of an arbitrary n-qubit state by constructing entanglement resources and special measurement basis for the sender. Then to weigh the classical resource required, we present an information-theoretical model to evaluate the classical communication cost. By optimizing the classical communication in quantum protocols, we obtain the optimal classical communication cost. This model can also be applied to the quantum teleportation. Moreover, based on the present computation model, we reinvestigate some remote state preparation and teleportation protocols in which the classical communication cost was imperfectly computed. Finally, some problems will be presented.

Arsenic implantation-induced intermixing effects on AlGaAs/GaAs single QW structures

Abstract The effects of intermixing Al 0.54 Ga 0.46 As/GaAs/Al 0.54 Ga 0.46 As quantum well (QW) enhanced by arsenic ion implantation and subsequent annealing have been investigated by photoluminescence and photo-modulated reflectance measurements. Comparing with as-grown QW, obvious blueshifts of all the transitions were observed. The H 22 transition was found to be much less sensitive to the implantation doses than that of H 11 . The experimental results are different from the theoretical results calculated by using the model of error function profile of Al composition. The results are fruitful for understanding the potential profile after intermixing enhanced by arsenic ion implantation, and also for the application of implantation enhanced intermixing effects on devices, such as QW lasers and photodetectors, opto-nonlinear devices, etc..

A Spatial Domain Quantum Watermarking Scheme

This paper presents a spatial domain quantum watermarking scheme. For a quantum watermarking scheme, a feasible quantum circuit is a key to achieve it. This paper gives a feasible quantum circuit for the presented scheme. In order to give the quantum circuit, a new quantum multi-control rotation gate, which can be achieved with quantum basic gates, is designed. With this quantum circuit, our scheme can arbitrarily control the embedding position of watermark images on carrier images with the aid of auxiliary qubits. Besides reversely acting the given quantum circuit, the paper gives another watermark extracting algorithm based on quantum measurements. Moreover, this paper also gives a new quantum image scrambling method and its quantum circuit. Differ from other quantum watermarking schemes, all given quantum circuits can be implemented with basic quantum gates. Moreover, the scheme is a spatial domain watermarking scheme, and is not based on any transform algorithm on quantum images. Meanwhile, it can make sure the watermark be secure even though the watermark has been found. With the given quantum circuit, this paper implements simulation experiments for the presented scheme. The experimental result shows that the scheme does well in the visual quality and the embedding capacity.

Random quantum evolution

The quantum no-cloning theorem and no-deleting theorem may be the most important quantum features for quantum communications or quantum computations. In this paper, we concentrate typical properties of random quantum evolution. We obtain that universal random evolutions change the generic unknown pure states into their orthogonal states approximately. Moreover, typical random evolutions distort the von Neumann entropy with constants. These results are extended to mixed states with a stronger orthogonal preparation ability. These typical characters are very important for quantum information retrieving or various quantum tasks.

Carrier capture cross-section of nonradiative recombination centres introduced by proton implantation in GaAs

Using room-temperature photoluminescence spectroscopy, we have studied the nonradiative recombination centres introduced by 35 keV proton implantation in semi-insulating GaAs. The effective capture cross-section value σ is deduced to be 1.1 × 10−12 cm2 with a Monte Carlo simulation. Through the analysis of the density of states of several possible defect configurations with Vienna ab initio simulation package, the nonradiative recombination centres are considered to be mainly composed of As vacancies and As-related defect complexes.