Dispersion spreading of polarization-entangled states of light and two-photon interference

We study the interference structure of the second-order intensity correlation function for polarization-entangled two-photon light obtained from type II collinear frequency-degenerate spontaneous parametric down conversion (SPDC). The structure is visualized due to the spreading of the two-photon amplitude as two-photon light propagates through optical fiber with group-velocity dispersion (GVD). Because of the spreading, polarization-entangled Bell states can be obtained without any birefringence compensation at the output of the nonlinear crystal. Instead, proper time selection of the intensity correlation function is required. A birefringent material inserted at the output of the nonlinear crystal (either reducing the initial e-o delay between the oppositely polarized twin photons or increasing this delay) leads to a more complicated interference structure of the correlation function.     

Dispersion spreading of biphotons in optical fibers and two-photon interference

We present the first observation of two-photon polarization interference structure in the second-order Glauber correlation function of two-photon light generated via type-II spontaneous parametric down-conversion. In order to obtain this result, two-photon light is transmitted through an optical fiber and the coincidence distribution is analyzed by means of the start-stop method. Beyond the experimental demonstration of an interesting effect in quantum optics, these results also have considerable relevance for quantum communications.     

Reinterpretation of two-photon interference experiment using advanced field

The recent two-photon interference experiments by Wang, Zou, and Mandel, with and without a time-dependent light switch introduced into one of interferometer arms, indicate the collapse of photon waves along empty arms, not travelled by the detected photon, at a critical moment on the light cone backwards from the detected photon. It is proposed to interpret the Schrödinger's retarded wave equation as an operator acting on the advanced field satisfying the final condition of the experiment. In this time-symmetrical formulation the advanced field of the detected particle guides the retarded wave from the particle source not to enter empty arms, and the critical moment is interpreted as the time of the passage of the advanced field through the light switch. By changing the relative optical lengths of interferometer arms and observing the independence of the result of the experiment on the relative position of the detectors, we could conceive of the unarousal of the empty wave destined to collapse.     

Quantum interference of multimode two-photon pairs with a Michelson interferometer

We perform the second-order quantum interference experiment with the multimode photon pairs produced via an optical parametric oscillator far below threshold in a Michelson interferometer, measure the second-order correlation function in different cases. We find when the interferometer is highly unbalanced, the shape of the second-order correlation function is clearly dependent on the path length difference between two interfering beams. On the contrary, when the interferometer is nearly balanced, beside its height, the shape of the second-order correlation function is independent on the small path length difference. The second-order correlation function shows a multipeaked structure in both cases. All experimental results agree very well with the theoretical predictions.     

On nonclassical effects in two-photon optical bistability and two-photon laser

We analyse the fluctuations at steady state in the good quality cavity case in two-photon lasers with running wave and two-photon absorptive optical bistability in a ring cavity. In the case of two-photon laser we do not find any nonclassical effect, contrary to expectations. On the other hand, in two-photon optical bistability we find squeezing and antibunching in the low transmission branch. The maximum reduction of fluctuations that can be obtained is slightly larger than by a factor of two.     

Second-order interference of two independent and tunable single-mode continuous-wave lasers

The second-order temporal interference of two independent single-mode continuous-wave lasers is discussed by employing two-photon interference in Feynman's path integral theory. It is concluded that whether the second-order temporal interference pattern can or cannot be retrieved via two-photon coincidence counting rate is dependent on the resolution time of the detection system and the frequency difference between these two lasers. Two identical and tunable single-mode continuous-wave diode lasers are employed to verify the predictions. These studies are helpful to understand the physics of two-photon interference with photons of different spectra.     

Identifying two-photon high-dimensional entanglement in transverse patterns

We propose a scheme to explore two-photon high-dimensional entanglement associated with a transverse pattern by means of two-photon interference at a beamsplitter. We find that the topological symmetry of the angular spectrum of the two-photon state governs the nature of the two-photon interference. We prove that the anti-coalescence interference is the signature of two-photon entanglement. On the basis of this feature, we propose a special Mach–Zehnder interferometer incorporated with two spiral phase plates which can change the interference from a coalescence to an anti-coalescence type only for a two-photon entangled state. The scheme is simple and straightforward compared with the test for a Bell inequality.     

Observation on the incompatibility between the first-order and second-order interferences with laser beams

We observed experimentally that the first-order and second-order interference patterns of laser beams in a modified Michelson interferometer are complementary and the conditions for seeing one preclude the possibility to see the other. One- and two-photon interferences based on Feynman's path integral theory are employed to interpret the experimental results.     

双光子失谐对慢光和光存储影响的实验研究

利用电磁感应透明(EIT)效应在87Rb热原子气室中进行了慢光和光存储的实验研究,在单光子红失谐650 MHz处测量了双光子失谐对光脉冲延迟和光存储的影响.结果表明:在双光子失谐0—0.5 MHz范围内存在显著的光脉冲延迟和光存储恢复信号,其慢光波形与理论计算结果基本相符;而恢复光脉冲信号随着双光子失谐的变化出现形变,这是由于多个EIT子系统之间的干涉引起的.这一研究结果为连续变量光场在热原子系综中的存储提供了实验参考.     

Single-ion two-photon source

A single trapped ion is converted into a pseudo-two-photon source by splitting its resonance fluorescence, delaying part of it and by recombining both parts on a beam splitter. A destructive two-photon interference is observed with a contrast reaching 83(5)%. The spectral brightness of our two-photon source is quantified and shown to be comparable to parametric down-conversion devices.     

Nonreciprocal two-photon transmission and statistics in a chiral waveguide QED system

We study the nonreciprocal properties of transmitted photons in a chiral waveguide quantum electrodynamics (QED) system, including single- and two-photon transmissions and second-order correlations. For the single-photon transmission, the nonreciprocity is induced by the effects of chiral coupling and atomic dissipation in the weak coupling region. It vanishes in the strong coupling regime when the effect of atomic dissipation becomes ignorable. In the case of two-photon transmission, there exist two ways of going through the emitter: independently as plane waves and formation of bound state. Besides the nonreciprocal behavior of plane waves, the bound state that differs in two directions also alters transmission probabilities. In addition, the second-order correlation of transmitted photons depends on the interference between plane wave and bound state. The destructive interference leads to the strong antibunching in the weak coupling region, while the effective formation of bound state leads to the strong bunching in the intermediate coupling region. However, the negligible interactions for left-propagating photons hardly change the statistics of the input coherent state.     

Second-order temporal interference of two independent light beams at an asymmetrical beam splitter

The second-order temporal interference of classical and nonclassical light at an asymmetrical beam splitter is discussed based on two-photon interference in Feynman's path integral theory. The visibility of the second-order interference pattern is determined by the properties of the superposed light beams, the ratio between the intensities of these two light beams, and the reflectivity of the asymmetrical beam splitter. Some requirements about the asymmetrical beam splitter have to be satisfied in order to ensure that the visibility of the second-order interference pattern of nonclassical light beams exceeds the classical limit. The visibility of the second-order interference pattern of photons emitted by two independent single-photon sources is independent of the ratio between the intensities. These conclusions are important for the researches and applications in quantum optics and quantum information when an asymmetrical beam splitter is employed.     

One-photon and two-photon double-slit interference in spontaneous and stimulated parametric down-conversions

We theoretically discuss two-photon double-slit interference for spontaneous and stimulated parametric down-conversions and compare it with one-photon case. We show that two-photon sub-wavelength interference can exist in a general interaction of spontaneous parametric down-conversion (SPDC) for both type I and type II crystals. In low gain SPDC, interference effect can be attributed to the previous study based on two-photon entangled state. But the important fact is that the sub-wavelength interference will not be washed out even if in very high gain SPDC, revealing the macroscopic nature. We propose an alternative scheme to observe sub-wavelength interference with a joint-intensity measurement, which occurs for a type I crystal in the high gain case. The theoretical analysis shows that the effect originates from classical thermal correlation. However, we also formulate the one-photon and two-photon double-slit interference in the stimulated process, and show amplified interference patterns.     

双光子吸收的Franz-Keldysh效应

从实验上证实Hg_0.695Cd_0.305Te 光电二极管空间电荷区中存在双光子吸收的Franz-Keldysh效应.利用一个皮秒Nd:YAG激光器抽运的光学参量产生器和差频产生器作为激发光源,测量了入射波长为λ₀=7.92μm的脉冲激光所激发的光响应随入射光强的变化关系.脉冲光响应峰值强度随入射光强的增大呈现二次幂函数增强趋势.采用等效RC电路模型将脉冲光伏信号峰值与入射光强相关联,得到空间电荷区中强电场下单光束 关键词： Franz-Keldysh效应 碲镉汞 双光子吸收 脉冲光伏信号     

Enhanced narrow spectral line and double electromagnetically induced two-photon transparency induced by double dark resonances

We theoretically investigate the features of two-photon absorption in a five-level atomic system with interacting dark resonances. It is found that two-photon absorption can be completely suppressed at two different frequencies due to the application of two coherent coupling fields and the atomic system exhibits double electromagnetically induced transparency windows against two-photon absorption. The position and width of the double two-photon transparency windows can be controlled via properly adjusting the frequency detuning and the intensities of the two coupling fields. In addition, one enhanced narrow central line can be observed in the two-photon absorption spectra, which may find applications in high-precision spectroscopy. Form a physical point of view, we explicitly explain these results in terms of quantum interference induced by three different two-photon excitation channels in the dressed-state picture.     

Mode-locked two-photon states

The concept of mode locking in laser is applied to a two-photon state with frequency entanglement. Cavity enhanced parametric down conversion is found to produce exactly such a state. The mode-locked two-photon state exhibits a comblike correlation function. An unbalanced Hong-Ou-Mandel type interferometer is used to measure the correlation function. A revival of the typical interference dip is observed. We will discuss a scheme for engineering of quantum states in time domain.     

Properties of pulsed entangled two-photon fields

The dependence of one- and two-photon characteristics of pulsed entangled two-photon fields generated in spontaneous parametric down-conversion on the pump-pulse properties (shape of the pump-pulse spectrum and its internal structure) is examined. It is shown that entangled two-photon fields with defined properties can be generated. A general relation between the spectra of the down-converted fields is established. As a special case the interference of two partially overlapping pulsed two-photon fields is studied. The fourth-order interference pattern of entangled two-photon fields is investigated in the polarization analog of the Hong-Ou-Mandel interferometer. Received: 23 December 1998 / Received in final form: 14 April 1999     

Internal Reflection Spectroscopy

Abstract

This review‐type article deals with small, stable, compact, inexpensive, and low‐resolution interferometers mainly based on continuous or back and forth rotational motion to create the optical path difference. These interferometers are suitable for low‐resolution Fourier Transform Infrared (FTIR) spectroscopy. The paper introduces the most typical interferometers illustrated with figures. For example, interferometers with retroreflectors such as corner cubes are presented. This work aims at developing a tilt compensated optical design where the optical path difference of the interferometer will be achieved with rotational scanning. The most important property of this optical design is large mechanical tolerances to make manufacturing easy and inexpensive. New interferometers based on rotational motion are described. The mechanical angle tolerances of these interferometers can be up to three orders of magnitude larger than the angle tolerances in commonly used corner cubes.     

Functional polymers by two-photon 3D lithography

In the presented work, two-photon 3D lithography and selective single-photon photopolymerization in a prefabricated polydimethylsiloxane matrix is presented as an approach with potential applicability of waveguide writing in 3D by two-photon polymerization.Photopolymers based on acrylate chemistry were used in order to evaluate the optical capabilities of the available two-photon system. Several photoinitiators, tailored for two-photon absorption, were tested in a mixture of trimethylolpropane triacrylate and ethoxylated trimethylolpropane triacrylate. Best results were obtained with a recently synthesized diynone-based photoinitiator. Feature resolutions in the range of 300 nm were achieved. Due to the cross-conjugated nature of that donor-π-acceptor-π-donor system a high two-photon absorption activity was achieved. Therefore, a resin mixture containing only 0.025 wt% of photoinitiator was practical for structuring by two-photon polymerization. The required initiator content was therefore a factor of 100 lower than in traditional one-photon lithography.The aim of the second part of this work was to fabricate optical waveguides by selectively irradiating a polymer network, which was swollen by a monomer. The monomer was polymerized by conventional single-photon polymerization and the uncured monomer was removed by evaporation at elevated temperatures. This treatment leads to a local change in refractive index. Refractive index changes in the range of Δn = 0.01 (Δn/n = 0.7%) were achieved, which is sufficient for structuring waveguides for optoelectronic applications.     

对白光干涉法测量透明介质折射率实验的探讨

在时域中求解得到,光路中存在色散介质的情况下,白光双光束干涉光强度.由此证明了:用白光干涉法测量得到的是白光在色散介质中的群折射率,而并非相关报道中认为的折射率;讨论了介质厚度及色散对于涉条纹的可见度和干涉条纹显现时动镜移动范围的影响.上述结论得到了实验验证.