arXiv subjects

Shi-Yao Zhu

Publications and source records attributed to Shi-Yao Zhu.

At least 73 records · Page 4Linked to original sources

arXiv2013

Effect of atomic distribution on cooperative spontaneous emission

We study cooperative single-photon spontaneous emission from N multilevel atoms for different atomic distributions in optical vector theory. Instead of the average approximation for interatomic distance or the continuum approximation (sums over atoms replaced by integrals) for atomic distribution, the positions of every atom are taken into account by numerical calculation. It is shown that the regularity of atomic distribution has considerable influence on cooperative spontaneous emission. For a small atomic sample (compared with radiation wavelength), to obtain strong superradiance not only needs the uniform excitation (the Dicke state) but also requires the uniform atomic distribution. For a large sample, the uniform atomic distribution is beneficial to subradiance of the Dicke state, while the influence of atomic distribution on the timed Dicke state is weak and its time evolution obeys exponential decay approximately. In addition, we also investigate the corresponding emission spectrum and verify the directed emission for the timed Dicke state for a large atomic sample.

physics.optics↗

arXiv2013

Goos-Hänchen Shifts of Partially Coherent Light Fields

We investigate the Goos-Hänchen (GH) shifts of partially coherent fields (PCFs) by using the theory of coherence. We derive a formal expression for the GH shifts of PCFs in terms of Mercer's expansion, and then clearly demonstrate the dependence of the GH shift of each mode of PCFs on spatial coherence and beam width. We discuss the effect of spatial coherence on the resultant GH shifts, especially for the cases near the critical angles, such as totally reflection angle.

physics.optics↗

arXiv2013

Comment on "Spatial Coherence and Optical Beam Shifts"

This comment is to show that our simulation data, based on our theory and method in Ref. [J. Phys. B 41, 055401 (2008)], are also in agreement with the experimental data presented for $D_{p}-D_{s}$ in Ref. [Phys. Rev. Lett. \textbf{109}, 213901 (2012)]. We also demonstrate how to show the effect of spatial coherence on the GH shifts in this comment, therefore we disagree with the claims in Ref. [Phys. Rev. Lett. \textbf{109}, 213901 (2012)].

physics.optics↗

arXiv2013

Cooperative spontaneous emission of three identical atoms

We study the influence of the distribution of atoms on the cooperative spontaneous emission by a simple model of three identical atoms. The effects of counter rotating terms are included by a unitary transformation method. By discussing two special cases that the three atoms are arranged as an equilateral triangle and in a straight line, we find that the superradiance of the coherent system largely dependent on the homogeneity of the atoms' distribution. If the atoms distribute symmetrically, the superradiant emission will be enhanced. Next, we calculate the emission spectra of three identical atoms under the single-photon state. We find that the distribution of atoms also has a great impact on the lamb shift and the spectrum. If three atoms are placed into an equilateral triangle and the same dipole moment is perpendicular to the plane of the three atoms, the spectrum will degenerate into two peaks from the three peaks for general case.

quant-ph↗

arXiv2012

Higher order wave-particle duality

The complementarity of single-photon's particle-like and wave-like behaviors can be described by the inequality $D^2+V^2 \leq 1$, with $D$ being the path distinguishability and $V$ being the fringe visibility. In this paper, we generalize this duality relation to multi-photon case, where two new concepts, higher order distinguishability and higher order fringe visibility, are introduced to quantify the higher order particle-like and wave-like behaviors of multi-photons.

quant-ph↗

arXiv2012

Separability criterion for bipartite states and its generalization to multipartite systems

A group of symmetric operators are introduced to carry out the separability criterion for bipartite and multipartite quantum states. Every symmetric operator, represented by a symmetric matrix with only two nonzero elements, and their arbitrary linear combinations are found to be entanglement witnesses. By using these symmetric operators, Wootters' separability criterion for two-qubit states can be generalized to bipartite and multipartite systems in arbitrary dimensions.

quant-ph↗

arXiv2012

An optical diode made from a `flying' photonic crystal

Optical diodes controlling the flow of light are of principal significance for optical information processing 1. They transmit light from an input to an output, but not in reverse direction. This breaking of time reversal symmetry is typically achieved via non-linear 2,3 or magnetic effects 4, which imposes limits to all-optical control 5-7, on-chip integration 7-11, or single-photon operation 12. Here, we propose an optical diode which requires neither magnetic fields nor strong input fields. It is based on a flying photonic crystal. Due to the Doppler effect, the crystal has a band gap with frequency depending on the light propagation direction relative to the crystal motion. Counter-intuitively, our setup does not involve the movement of any material parts. Rather, the flying photonic crystal is realized by optically inducing a spatially periodic but moving modulation of the optical properties of a near-resonant medium. The flying crystal not only opens perspectives for optical diodes operating at low light levels or integrated in small solid state devices, but also enables novel photonic devices such as optically tunable mirrors and cavities.

physics.optics↗

arXiv2012

Quantum Information transmission

We present a scheme of quantum information transmission, which transmits the quantum information contained in a single qubit via the quantum correlation shared by two parties (a two-qubit channel), whose quantum discord is non-zero. We demonstrate that the quantum correlation, which may have no entanglement, is sufficient to transmit the information of a quantum state. When the correlation matrix of the two-qubit channel is of full rank (rank three), the information of the qubit in either a mixed state or a pure state can be transmitted. The quantum discord of a channel with rank larger than or equal to three is always non-zero. Therefore, non-zero quantum discord is also necessary for our quantum information transmission protocol.

quant-ph↗

arXiv2011

A new criteria for zero quantum discord

We propose a new criterion to judge zero quantum discord for arbitrary bipartite states. A bipartite quantum state has zero quantum discord if and only if all blocks of its density matrix are normal matrices and commute with each other. Given a bipartite state with zero quantum discord, how to find out the set of local projectors, which do not disturb the whole state after being imposed on one subsystem, is also presented. A class of two-qubit X-state is used to test the criterion, and an experimental scheme is proposed to realize it. Consequently, we prove that the positive operator-valued measurement can not extinguish the quantum correlation of a bipartite state with nonzero quantum discord.

quant-ph↗

arXiv2011

Jaynes-Cummings model:Counter rotating effect on the vacuum Rabi splitting and atom-cavity dynamics

he effect of the counter-rotating terms in the Jaynes-Cummings model is investigated with an extended coherent-state approach. The counter-rotating terms greatly modify the vacuum Rabi splitting. Two peaks with different heights in the weak coupling regime and more than two peaks in the intermediate coupling regime are predicted. The collapses and revivals in the evolution of the atomic population inversion disappear in the intermediate coupling regime, but reappear in the strong coupling regime. This reappearance is similar to that under the rotating-wave approximation, attributed to the summation of periodic cosine functions of the evolution.

quant-ph↗

arXiv2011

Tunneling states in graphene heterostructures consisting of two different graphene superlattices

We have theoretically investigated the properties of electronic transport in graphene heterostructures, which are consisted of two different graphene superlattices with one-dimensional periodic potentials. It is found that such heterostructures possess an unusual tunneling state occurring inside the original forbidden gaps, and the electronic conductance is greatly enhanced and Fano factor is strongly suppressed near the energy of the tunneling state. Finally we present the matching condition of the impedance of the pseudospin wave for occuring the tunneling state by using the Bloch-wave expansion method.

cond-mat.mes-hall↗

arXiv2011

Quantum state transfer in frequency down-conversion via nondegenerate optical parametric amplifier

By utilizing the nondegenerate optical parametric amplifier, the quantum state transfer from a pump state with high frequency to a signal state of lower frequency is studied theoretically. The noiseless state transfer is characterized by frequency conversion efficiency and noise figure. It is shown that the quantum state can be well preserved during the frequency conversion as long as the optical parametric amplifier is operated far below the threshold, and meanwhile injected with an input idler field with a power density about ten times greater than that of the pump. The dependence of the noise figure and conversion efficiency on the idler amplitude, the analyzing frequency and the cavity extra loss is also discussed.

quant-ph↗

arXiv2011

High reflection emission assisted by phase compensation via anomalous dispersion

The reflection spectrum of a probe light in a -type three-level atomic system coupled by an off-resonant standing-wave is investigated experimentally and theoretically. We show that the maximum value of reflection coefficient occurs when both of the coupling and probe lights are tuned off resonances from the atomic transitions. The nature of enhanced reflection is attributed to the phase compensation caused by the anomalous dispersion, which leads to a significant reduction of nonlinear phase mismatch in atomic four-wave mixing. At certain detuning of coupling and probe frequencies near two-photon resonance, there exits a best compensation, so the reflection efficiency reaches its maximum. The dependences of efficiency on the intensity of coupling fields and the density of atoms are also studied.

quant-ph↗

arXiv2010

Complementarity and uncertainty in a two-way interferometer

In terms of operator, the two complementary quantities, the predictability and visibility, are reinvestigated in a two-way interferometer. One Hermitian operator and one non-Hermitian operator (composed of two Hermitian operators) are introduced for the predictability and visibility, respectively. The predictability and visibility can not be measured exactly simultaneously, due to the non-commutation between the two operators. The sum of the variances of the predictability and visibility (the total variance), is used to measure the uncertainty, which is linked to the complementarity relation through the equation, $(δ_P)^2+(δ_Vf)^2+P^2+V^2=2$ . This new description for the predictability and visibility connects the complementarity and the uncertainty relations, although neither of them can be derived directly from the other.

physics.optics↗

arXiv2010

Electronic Band gaps and transport properties inside graphene superlattices with one-dimensional periodic squared potentials

The electronic transport properties and band structures for the graphene-based one-dimensional (1D) superlattices with periodic squared potentials are investigated. It is found that a new Dirac point is formed, which is exactly located at the energy which corresponds to the zero (volume) averaged wavenumber inside the 1D periodic potentials. The location of such a new Dirac point is robust against variations in the lattice constants, and it is only dependent on the ratio of potential widths. The zero-averaged wavenumber gap associated with the new Dirac point is insensitive to both the lattice constant and the structural disorder, and the defect mode in the zero-averaged wavenumber gap is weakly dependent on the insident angles of carriers.

cond-mat.mes-hall↗

arXiv2009

The reversibility of the Goos-Hänchen shift near the band-crossing structure of one-dimemsional photonic crystals containing left-handed metamaterials

We perform a theoretical investigation on the Goos-Hächen (GH) shift in one-dimensional photonic crystals (1DPCs) containing left-handed metamaterials (LHMs). We find an unusal effect of the GH shift near the photonic band-crossing structure, which is located at the condition, $% -k_{z}^{(A)}d_{A}=k_{z}^{(B)}d_{B}=mπ$ $(m=1,2,3...)$, under the inclined incident angle, here A denotes the LHM layer and B denotes the dielectric layer. Above the frequency of the band-crossing point (BCP), the GH shift changes from negative to positive as the incident angle increases, while the GH shift changes reversely below the BCP frequency. This effect is explained in terms of the phase property of the band-crossing structure.

physics.optics↗

arXiv2008

Realization of Dirac Point with Double Cones in Optics

The Dirac point with a double-cone structure for optical fields, an optical analogy Dirac fermions in graphene, can be realized in optically homogenous metamaterials. The condition for the realization of Dirac point in optical systems is the varying of refractive index from negative to zero and then to positive. Our analytical and numerical analysis have verified that, similar to electrons in graphene, the light field near the Dirac point possesses of the pseudodiffusive property, obeying the 1/L scaling law, where L is the propagating distance of light inside the media.

physics.optics↗

arXiv2008

Hanbury Brown-Twiss effect and thermal light ghost imaging

We show that the essential physics of the Hanbury Brown-Twiss (HBT) and the thermal light ghost imaging experiments is the same, i.e., due to the intensity fluctuations of the thermal light. However, in the ghost imaging experiments, a large number of bits information needs to be treated together, whereas in the HBT there is only one bit information required to be obtained. In the HBT experiment far field is used for the purpose of easy detection, while in the ghost image experiment near (or not-far) field is used for good quality image.

physics.optics↗