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Hong Guo

Publications and source records attributed to Hong Guo.

At least 325 records · Page 18Linked to original sources
arXiv2010

Passive-scheme analysis for solving untrusted source problem in quantum key distribution

As a practical method, the passive scheme is useful to monitor the photon statistics of an untrusted source in a "Plug & Play" quantum key distribution (QKD) system. In a passive scheme, three kinds of monitor mode can be adopted: average photon number (APN) monitor, photon number analyzer (PNA) and photon number distribution (PND) monitor. In this paper, the security analysis is rigorously given for APN monitor, while for PNA, the analysis including statistical fluctuation and random noise, is addressed with a confidence level. The results show that the PNA can achieve better performance than the APN monitor and can asymptotically approach the theoretical limit of the PND monitor. Also, the passive scheme with the PNA works efficiently when the signal-to-noise ratio ($R^{SN}$) is not too low and so is highly applicable to solve the untrusted source problem in the QKD system.

quant-ph↗
arXiv2010

Truly Random Number Generation Based on Measurement of Phase Noise of Laser

We present a simple approach to realize truly random number generation based on measurement of the phase noise of a single mode vertical cavity surface emitting laser (VCSEL). The true randomness of the quantum phase noise originates from the spontaneous emission of photons and the random bit generation rate is ultimately limited only by the laser linewidth. With the final bit generation rate of 20 Mbit/s, the physically guaranteed truly random bit sequence passes the three standard random tests. Moreover, for the first time, a {\it continuously} generated random bit sequence up to 14 Gbit is verified by two additional criteria for its true randomness.

quant-ph↗
arXiv2010

The Linewidth of Ramsey Laser with Bad Cavity

We investigate a new laser scheme by using Ramsey separated-field technique with bad cavity. By studying the linewidth of the stimulated-emission spectrum of this kind of laser inside the cavity, we find its linewidth is more than two orders of magnitude narrower than atomic natural linewidth, and it is far superior to that of conventional optical Ramsey method and any other available subnatural linewidth spectroscopy at present. Since any cavity related noise is reduced to cavity-pulling effect in bad cavity laser, this Ramsey laser provides the possibility of precision subnatural linewidth spectroscopy, which is critical for the next generation of optical clock and atom interferometers.

quant-ph↗
arXiv2009

Non-Markovian Dynamics of Entanglement for Multipartite Systems

Entanglement dynamics for a couple of two-level atoms interacting with independent structured reservoirs is studied using a non-perturbative approach. It is shown that the revival of atom entanglement is not necessarily accompanied by the sudden death of reservoir entanglement, and vice versa. In fact, atom entanglement can revive before, simultaneously or even after the disentanglement of reservoirs. Using a novel method based on the population analysis for the excited atomic state, we present the quantitative criteria for the revival and death phenomena. For giving a more physically intuitive insight, the quasimode Hamiltonian method is applied. Our quantitative analysis is helpful for the practical engineering of entanglement.

quant-ph↗
arXiv2009

Quantum Zeno and anti-Zeno effect in atom-atom entanglement induced by non-Markovian environment

The dynamic behavior of the entanglement for two two-level atoms coupled to a common lossy cavity is studied. We find that the speed of disentanglement is a decreasing (increasing) function of the damping rate of the cavity for on/near (far-off) resonant couplings. The quantitative explanations for these phenomena are given, and further, it is shown that they are related to the quantum Zeno and anti-Zeno effect induced by the non-Markovian environment.

quant-ph↗
arXiv2009

Slow Light of an Amplitude Modulated Gaussian Pulse in Cesium Vapor

Slow light of an amplitude modulated Gaussian (AMG) pulse in cesium vapor is demonstrated and studied, as an appropriate amplitude modulation to a single pulse can expand its spectrum and thus increase the utilization efficiency of the bandwidth of a slow light system. In a single-$Λ$ type electromagnetically induced transparency (EIT) system, the slowed AMG pulse experiences severe distortion, mainly owing to the frequency dependent transmission of medium. Additionally, due to its spectral distribution, the frequency dependent dispersion of the medium causes simultaneous slow and fast light of different spectral components and thus a certain dispersive distortion of the AMG pulse. Further, a post-processing method is proposed to recover the slowed (distorted) pulse, which indicates that by introducing a linear optical system with a desired gain spectrum we can recover the pulse in an "all-optical" way. Finally, we discuss the limitations during this compensation procedure in detail. Although it is demonstrated in the cesium vapor using EIT, this method should be applicable to a wide range of slow light systems.

quant-ph↗
arXiv2009

Determine the galaxy bias factors on large scales using bispectrum method

We study whether the bias factors of galaxies can be unbiasedly recovered from their power spectra and bispectra. We use a set of numerical N-body simulations and construct large mock galaxy catalogs based upon the semi-analytical model of Croton et al. (2006). We measure the reduced bispectra for galaxies of different luminosity, and determine the linear and first nonlinear bias factors from their bispectra. We find that on large scales down to that of the wavenumber k=0.1h/Mpc, the bias factors b1 and b2 are nearly constant, and b1 obtained with the bispectrum method agrees very well with the expected value. The nonlinear bias factor b2 is negative, except for the most luminous galaxies with M<-23 which have a positive b2. The behavior of b2 of galaxies is consistent with the b2 mass dependence of their host halos. We show that it is essential to have an accurate estimation of the dark matter bispectrum in order to have an unbiased measurement of b1 and b2. We also test the analytical approach of incorporating halo occupation distribution to model the galaxy power spectrum and bispectrum. The halo model predictions do not fit the simulation results well on the precision requirement of current cosmological studies.

astro-ph.CO↗
arXiv2009

Security bound of continuous-variable quantum key distribution with noisy coherent states and channel

Security of a continuous-variable quantum key distribution protocol based on noisy coherent states and channel is analyzed. Assuming the noise of coherent states is induced by Fred, a neutral party relative to others, we prove that the prepare and measurement scheme and entanglement-based scheme are equivalent. Then, we show that this protocol is secure against Gaussian collective attacks even if the channel is lossy and noisy, and further, a lower bound to the secure key rate is derived.

quant-ph↗
arXiv2009

A bias free true random number generator

We propose a new approach to nondeterministic random number generation. In theory, the randomness originated from the uncorrelated nature of consecutive laser pulses with Poissonian photon number distribution and that of the consecutive single photon detections is used to generate random bit. In experiment, von Neumann correction method is applied to extract the final random bit. This method is proved to be bias free in randomness generation, provided that the single photon detections are mutually independent, and further, it has the advantage in generation efficiency of random bits since no postprocessing is needed. A true random number generator based on this new method is realized and its randomness is guaranteed using three batteries of statistical tests.

quant-ph↗
arXiv2009

Dark-Sates in Electromagnetically Induced Transparency Controlled by a Microwave Field

The rigorous dark-sate conditions, i.e., two-photon resonance, for a Lambda-type electromagnetically induced transparency (EIT) are extended with the system controlled by a microwave field. The extended dark-states are found to be extremely sensitive to the phase of the microwave field in a narrow interval. However, the dark-state is no longer the requirement for EIT in this scheme and EIT without dark states is present.

quant-ph↗
arXiv2009

A determination of dark matter bispectrum with a large set of N-body simulations

We use a set of numerical N-body simulations to study the large-scale behavior of the reduced bispectrum of dark matter and compare the results with the second-order perturbation theory and the halo models for different halo mass functions. We find that the second-order perturbation theory (PT2) agrees with the simulations fairly well on large scales of k<0.05 h/Mpc, but it shows a signature of deviation as the scale goes down. Even on the largest scale where the bispectrum can be measured reasonably well in our simulations, the inconsistency between PT2 and the simulations appears for the colinear triangle shapes. For the halo model, we find that it can only serve as a qualitative method to help study the behavior of Q on large scales and also on relatively small scales. The failure of second-order perturbation theory will also affect the precise determination of the halo models, since they are connected through the 3-halo term in the halo model. The 2-halo term has too much contribution on the large scales, which is the main reason for the halo model to overpredict the bispectrum on the large scales. Since neither of the models can provide a satisfying description for the bispectrum on scales of about 0.1h/Mpc for the requirement of precision cosmology, we release the reduced bispectrum of dark matter on a large range of scales for future analytical modeling of the bispectrum.

astro-ph.CO↗
arXiv2009

Slow light of an amplitude modulated Gaussian pulse in electromagnetically induced transparency medium

The slow light effects of an amplitude modulated Gaussian (AMG) pulse in a cesium atomic vapor are presented. In a single-$Λ$ type electromagnetically induced transparency (EIT) medium, more severe distortion is observed for an AMG pulse than a Gaussian one. Using Fourier spectrum analysis, we find that the distortion, as well as the loss, is dominantly caused by linear absorption than dispersion. Accordingly, a compensation method is proposed to reshape the slow light pulse based on the transmission spectrum. In addition, we find a novel way to obtain simultaneous slow and fast light.

quant-ph↗
arXiv2008

The effect of dipole-dipole interaction for two atoms with different couplings in non-Markovian environment

Using the nonperturbative method, we study the exact entanglement dynamics of two two-level dipole-dipole interacting atoms coupled to a common non-Markovian reservoir with different coupling strengths. Besides analyzing the conditions for the existence of steady state, we find, though the dipole-dipole interaction could destroy the stationary entanglement, that relatively strong dipole-dipole interaction does suppress the disentanglement in the initial period of time. These results are helpful for the practical engineering of the entanglement in the future.

quant-ph↗
arXiv2008

Experimental quantum key distribution with an untrusted source

The photon statistics of a quantum key distribution (QKD) source is crucial for security analysis. In this paper, we propose a practical method, with only a beam splitter and photodetector involved, to monitor the photon statistics of a QKD source. By implementing in a Plug&Play QKD system, we show that the method is highly practical. The final secure key rate is 52 bit/s, comparing to 78 bit/s when the source is treated as a trusted source.

quant-ph↗
arXiv2008

Conductance spectra of metallic nanotube bundles

We report a first principles analysis of electronic transport characteristics for (n,n) carbon nanotube bundles. When n is not a multiple of 3, inter-tube coupling causes universal conductance suppression near Fermi level regardless of the rotational arrangement of individual tubes. However, when n is a multiple of 3, the bundles exhibit a diversified conductance dependence on the orientation details of the constituent tubes. The total energy of the bundle is also sensitive to the orientation arrangement only when n is a multiple of 3. All the transport properties and band structures can be well understood from the symmetry consideration of whether the rotational symmetry of the individual tubes is commensurate with that of the bundle.

cond-mat.mes-hall↗
arXiv2007

Non-equilibrium vertex correction: disorder scattering in magnetic tunnel junctions

We report a first principles formalism and its numerical implementation for treating quantum transport properties of nanoelectronic devices with atomistic disorder. We developed a nonequilibrium vertex correction (NVC) theory to handle the configurational average of random disorder at the density matrix level so that disorder effects to nonlinear and nonequilibrium quantum transport can be calculated from atomic first principles in a self-consistent and efficient manner. We implemented the NVC into a Keldysh non-equilibrium Green's function (NEGF) based density functional theory (DFT) and applied the NEGF-DFT-NVC formalism to magnetic tunnel junctions with interface roughness disorder. Our results show that disorder has dramatic effects to nonlinear spin injection and tunnel magneto-resistance ratio.

cond-mat.mes-hall↗
arXiv2007

Atom--photon momentum entanglement with quantum interference

With quantum interference of two-path spontaneous emissions, we propose a novel scheme to coherently control the atom--photon momentum entanglement through atomic internal coherence. A novel phenomenon called ``momentum phase entanglement'' is reported, and we found, under certain conditions, that more controllable entangled state can be produced with super--high degree of entanglement.

quant-ph↗