Generation of mesoscopic entangled states in a cavity coupled to an atomic ensemble

We propose a novel scheme for the efficient production of entangled states for N photons of the form |N>(a)|0>(b) + |0>(a)|N>(b) (NOON states) based on the resonant interaction of a pair of quantized cavity modes with an ensemble of atoms. We show that, in the strong-coupling regime, the adiabatic evolution of the system tends to a limiting state that describes mesoscopic entanglement between photons and atoms which can easily be converted to a purely photonic or atomic NOON state. We also demonstrate the remarkable property that the efficiency of this scheme increases exponentially with the cavity cooperativity factor, which gives efficient access to high number NOON states. The experimental feasibility of the scheme is discussed, and its efficiency is demonstrated numerically.     

Simple cases of spontaneous emission from an atom-photon cluster localized in a microcavity

The spontaneous emission from an atomic ensemble localized in a microcavity with the participation of microcavity photons and an external broadband quantized electromagnetic field at the Raman resonance of photons with an optically forbidden (two-photon) atomic transition has been studied. The average spontaneous decay intensity has been calculated for simple cases. It is shown that the dynamics of spontaneous emission from this atomic ensemble differs generally from the conventional superradiance (spontaneous emission of an atomic ensemble at a one-photon optically allowed transition from excited to the ground state. When the atomic ensemble is strongly excited, the delay times and the emission pulse shape differ significantly. The parameter ranges where the spontaneous emission from the atomic ensemble under consideration at a two-photon Raman transition can be described as conventional superradiance with renormalized parameters are found. In the case of single excitation the photon emission probability depends on the number of photons and atoms in the microcavity.     

Nonclassical interference and entanglement generation using a photonic crystal fiber pair photon source

We demonstrate two key components for optical quantum information processing: a bright source of heralded single photons; and a bright source of entangled photon pairs. A pair of pump photons produces a correlated pair of photons at widely spaced wavelengths (583 nm and 900 nm), via a chi((3)) four-wave mixing process. We demonstrate nonclassical interference between heralded photons from independent sources with a visibility of 95% (after correction for background), and an entangled photon pair source, with a fidelity of 89% with a Bell state.     

Photon production from the vacuum close to the superradiant transition: linking the dynamical Casimir effect to the Kibble-Zurek mechanism

The dynamical Casimir effect (DCE) predicts the generation of photons from the vacuum due to the parametric amplification of the quantum fluctuations of an electromagnetic field. The verification of such an effect is still elusive in optical systems due to the very demanding requirements of its experimental implementation. We show that an ensemble of two-level atoms collectively coupled to the electromagnetic field of a cavity, driven at low frequencies and close to a quantum phase transition, stimulates the production of photons from the vacuum. This paves the way to an effective simulation of the DCE through a mechanism that has recently found experimental demonstration. The spectral properties of the emitted radiation reflect the critical nature of the system and allow us to link the detection of the DCE to the Kibble-Zurek mechanism for the production of defects when crossing a continuous phase transition.     

应用激光质谱法选择探测一氧化碳

此文解决了激光质谱法中从含同质量数的N2分子的混合气体中选择CO分子这一问题,由于用紫外266nm激光不能从含N2分子的混合气体中选择CO分子,因此采用了可见激光来探测,发现用可见激光430～435nm的激光能成功地将CO分子选择探测出来。此外还着重分析了在可见波段和266nm激光下产生CO+离子的机理：在可见光波段443.55nm所对应的共振峰是CO分子吸收3光子的激光能量与A1Π态的振动量子数为2的振动态共振产生的;434.3nm所对应的共振峰是CO分子吸收3光子的激光能量与A1Π态的振动量子数为3的振动态共振产生的;CO分子吸收两光子的266nm激光能量与A1Π态第7振动态的某一高转动态相共振,处于该振动态的CO分子再继续吸收一个光子的266nm激光的能量至其电离态电离产生CO+离子。     

基于波长330nm激光激发多色激光导星回波光子数的数值计算与探讨

采用无模激光器发射波长为330 nm的激光激发多色激光导星,需要考虑脉冲激光重频率、激光带宽、激光初始光斑直径以及大气透过率对回波光子数的影响.通过数值模拟,计算了高斯光束的脉冲激光和连续激光激发多色激光导星在实际大气中后向辐射330 nm和2207 nm波长的回波光子数.数值计算结果表明,在垂直发射和接收的情况下,当到达大气中间层的激光能量为1 W时,连续激光能够获得更多的回波光子数,并且回波光子数几乎无起伏.对于脉冲激光,提高脉冲激光重频率达到50 kHz以上时,多色激光导星330 nm的回波光子数随脉冲重频率的增加趋于有限值;当大气能见度小于5 km且大气相干长度为12.8 cm时,大约需要34 W以上的激光发射能量,才能获得满足使用自然星全倾斜探测的330 nm回波光子数.对于连续激光,相同情况下,大约需要20 W以上的激光发射能量.     

Precision measurements of the timelike electromagnetic form factors of pion, kaon, and proton

Using 20.7 pb(-1) of e(+)e(-) annihilation data taken at sq.rt(r) = 3.671 GeV with the CLEO-c detector, precision measurements of the electromagnetic form factors of the charged pion, charged kaon, and proton have been made for timelike momentum transfer of |Q(2)| = 13.48 GeV(2) by the reaction e(+)e(-) --> h(+)h(-). The measurements are the first ever with identified pions and kaons of |Q(2)| > 4 GeV(2), with the results F(13.48 GeV(2)) = 0.075 +/- 0.008(stat) +/- 0.005(syst) and F(K)(13.48 GeV(2)) = 0.063 +/- 0.004(stat) +/- 0.001(syst). The result for the proton, assuming G(p)(E) = G(p)(M), is G(p)(M)(13.48 GeV(2)) = 0.014 +/- 0.002(stat) +/- 0.001(syst), which is in agreement with earlier results.     

Influence of surface plasmon resonance wavelength on SERS activity of naturally grown silver nanoparticle ensemble

We present experimental results to quantify and optimize the surface‐enhanced Raman scattering (SERS) activity of naturally grown silver nanoparticles. Ag nanoparticle ensembles with mean equivalent radii ranging from 10.6 to 20.3 nm were prepared under ultrahigh vacuum conditions by Volmer–Weber growth on quartz plates. A tuning of the localized surface plasmon polariton resonance wavelength from 453 to 548 nm was performed by varying the morphology of the silver nanoparticles. The dependence of the SERS activity on the plasmon resonance wavelength was investigated with a Raman set‐up containing a microsystem light source with an emission line at 488 nm. Shifted excitation Raman difference spectroscopy was applied to remove the fluorescence‐based background from the SERS spectra of pyrene in water using two slightly different emission wavelengths (487.61 and 487.91 nm) of the microsystem light source. We demonstrate that the Raman activities for all SERS substrates are available in the nanomolar range in a water sample. However, the Raman activity crucially depends on the plasmon resonance wavelength of the nanoparticle ensembles. Although for an on‐resonance ensemble the limit of detection for pyrene in water is very low and was estimated to be 2 nmol/L, it increases rapidly to several tens of nanomol for slightly off‐resonance ensembles. Hence, the highest SERS activity was obtained with a nanoparticle ensemble exhibiting a plasmon resonance wavelength at 491 nm, which almost coincides with the excitation wavelengths. Copyright © 2012 John Wiley & Sons, Ltd.     

Generation of narrow-band photon pairs for quantum memory

We demonstrate a narrow-band photon pair source on a rubidium (Rb) D₂ line (780 nm) using a periodical poled KTiOPO₄ crystal via a degenerate optical parametric oscillator far below threshold. The single longitudinal mode is selected by a spectral filtering cavity. The measured cross correlation between two photons shows that the generated photon has a linewidth of 21 MHz, which is comparable to the typical linewidth of an atomic-based quantum memory. The detected photon pair rate is about 2.7/s/MHz/mW. This system could be utilized for many applications in quantum information field, such as the storage and retrieval of a photon in Rb atomic ensemble and so on.     

Ultrafast double-quantum-coherence spectroscopy of excitons with entangled photons

We calculate the four-wave-mixing signal of excitons generated at k(4) = k(1) + k(2) - k(3) by two pulsed entangled photon pairs (k(1), k(2))and(k(3), k(4)), where all four modes are chronologically ordered. Entangled photons offer an unusual combination of bandwidths and temporal resolution not possible by classical beams. Contributions from different resonances can be selected by varying the parameters of the photon wave function. The signal scales linearly rather than quadratically with the laser field intensity, which allows performance of the measurements at low powers.     

Quantum gravity corrections to neutrino propagation

Massive spin-1/2 fields are studied in the framework of loop quantum gravity by considering a state approximating, at a length scale L much greater than Planck length l(P), a spin-1/2 field in flat spacetime. The discrete structure of spacetime at l(P) yields corrections to the field propagation at scale L. Neutrino bursts ( &pmacr; approximately 10(5) GeV) accompanying gamma ray bursts that have traveled cosmological distances L are considered. The dominant correction is helicity independent and leads to a time delay of order (&pmacr;l(P))L/c approximately 10(4) s. To next order in &pmacr;l(P), the correction has the form of the Gambini and Pullin effect for photons. A dependence L(-1)(os) approximately &pmacr;(2)l(P) is found for a two-flavor neutrino oscillation length.     

Electron impact ionization in the presence of a laser field: a kinematically complete (ngammae,2e) experiment

Single ionization of He by 1 keV electron impact in the presence of an intense (I=4 x 10(12) W/cm(2)) laser field (lambda=1064 nm) has been explored in a kinematically complete experiment using a reaction microscope. Distinct differences in the singly to fully differential cross sections compared to the field-free situation are observed which cannot be explained by a first-order quantum calculation. Major features, such as the number of photons exchanged and the modification of the energy spectrum of emitted electrons, can be understood qualitatively within a simple classical model.     

用于CSRe上16O5+离子精密激光谱学实验的极紫外光子探测系统的研制

高电荷态离子的精密谱学研究不仅为强场QED效应、相对论效应、电子关联效应等基础前沿理论模型的精确检验提供了良好的条件,而且对同位素移动、高电荷态离子光钟等诸多前沿物理研究具有重要意义。为了在兰州重离子加速器冷却储存环的CSRe上开展相对论能量类锂16O5+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2光学跃迁精密测量的激光谱学实验研究,研制了一套适用于前向发射荧光收集测量的新型非拦截式极紫外光子探测系统。该探测系统主要由抛物面型SiC反射镜、镀有CsI的微通道板(MCP)探测器以及高速步进电机等部分组成。在CSRe的高温烘烤环境和超高真空实验环境下,该探测系统能够在不影响储存环内离子束正常运转的同时实现对极紫外波段(50~200 nm)前向发射光子的高效探测,其探测效率较CSRe上现有光子通道倍增管荧光探测器提升约50倍。该探测系统不仅能够为CSRe上高电荷态离子的精密激光谱学实验提供高效实时的探测工具,亦为将来在大科学装置HIAF上开展更高能量、更高电荷态重离子的精密激光谱学实验研究奠定了坚实的基础。     

A Family of Balance Relations for the Two-Dimensional Navier--Stokes Equations with Random Forcing

For the 2D Navier--Stokes equation perturbed by a random force of a suitable kind we show that, if g(F) is an arbitrary real continuous function with (at most) polynomial growth, then the stationary in time vorticity field (t,x) satisfies where M_1 is a number, independent of g, which measures the strength of the random forcing. Another way of stating this result is that, in the unique stationary measure of this system, the random variables g((t,x) and |(t,x)|² are uncorrelated for each t and each x.This revised version was published online in March 2005 with corrections to the page numbers.     

Experimental demonstration of switching entangled photons based on the Rydberg blockade effect

The long-range interaction between Rydberg-excited atoms endows a medium with large optical nonlinearity. Here, we demonstrate an optical switch to operate on a single photon from an entangled photon pair under a Rydberg electromagnetically induced transparency configuration. With the presence of the Rydberg blockade effect, we switch on a gate field to make the atomic medium nontransparent thereby absorbing the single photon emitted from another atomic ensemble via the spontaneous fourwave mixing process. In contrast to the case without a gate field, more than 50% of the photons sent to the switch are blocked,and finally achieve an effective single-photon switch. There are on average 1-2 gate photons per effective blockade sphere in one gate pulse. This switching effect on a single entangled photon depends on the principal quantum number and the photon number of the gate field. Our experimental progress is significant in the quantum information process especially in controlling the interaction between Rydberg atoms and entangled photon pairs.     

Detection and spectral measurement of single photons in communication bands using up-conversion technology

Quantum information systems are commonly operated in conventional communication bands (1310 and 1550 nm) over an optical fiber to take advantage of low transmission loss. However, the detection and spectral measurement of single photons in these communication bands are limited due to high noise and low sensitivity of single photon detectors in the wavelength ranges. To demonstrate high efficiency detection and high sensitivity spectral measurement, we have implemented a single photon detector and a spectrometer based on frequency up-conversion technology. This detector and spectrometer uses a 5-cm periodically poled lithium niobate (PPLN) waveguide and a tunable pump laser around 1550 nm, to convert signal photons around 1310 to 710 nm. The converted photons are then detected by a silicon-based avalanche photodiode (APD). The overall detection efficiency of the single photon detector is as high as 32%, which is three times higher than commercial InGaAs APDs. The sensitivity of the spectrometer is measured to be −126 dBm, which is at least three orders-of-magnitude better than any commercial optical spectrum analyzer in this wavelength range.     

Path integrals for the quantum microcanonical ensemble

Path integral representations for the quantum microcanonical ensemble are presented. In the quantum microcanonical ensemble, two operators are of primary interest. First, rhoinsertion mark=delta(E-Hinsertion mark) corresponds to the microcanonical density matrix and can be used to calculate expectation values. Second, Ninsertion mark=Theta(E-Hinsertion mark) can give the number of states with energy E(n) and Theta(x,x('),E)=. A path integral formalism leads to exact integral representations for Omega(x,x('),E) and Theta(x,x('),E). We present both phase space and configuration space forms. For simple systems, such as the free particle and harmonic oscillator, exact solutions are possible. For more complicated systems, expansion schemes or numerical evaluations are required. A perturbative calculation and numerical integration results are presented for the quantum anharmonic oscillator.     

The contribution of bends and constrictions of a superconducting film to the photon detection by a single-photon superconducting detector

The contribution of bends and constrictions by a superconducting film to the detection by a singlephoton superconducting detector is investigated. It has been shown that, for currents smaller than the minimal detection current of a straight film, the detection efficiency of a film with a constriction attains saturation upon an increase in the current, which coincides qualitatively with the behavior of this dependence observed in the experiment. It has also been found that the effect of bends in the film and the external magnetic field on the detection efficiency for low-energy photons is essential, while for high-energy photons no such influence is observed.     

Energy storage effect and retrieval in manganese doped zinc silicate

It is shown that a significant amount of energy can be stored at room temperature for long periods in the manganese activated zinc silicates upon excitation by short wavelength UV photons (>3.65eV), and X-ray radiation. The stored energy can be stimulated by long wavelength photons (infrared and red) resulting in visible green emission. This effect has potential application in high energy radiation detection and imaging.