Gravitational wave detection using dual input Michelson interferometer

We propose a new scheme for interferometric gravitational wave detection using a dual input Michelson interferometer. The scheme allows us to put a phase modulator outside the interferometer without requiring arm-length unbalance. Moreover, the scheme can realize sub-shot-noise sensitivity using an amplitude squeezed state of light as one of the dual inputs.     

运行双协议相位调制的量子密钥分发系统

基于差分编码方式提出一种改进方案.在Alice端用光纤马赫-曾德干涉仪产生双脉冲差分信号；在Bob端，用双法拉第反射式麦克尔逊干涉仪代替光纤马赫-曾德干涉仪，这种干涉仪能自动补偿环境引起的偏振抖动和光纤双折射引起的相位漂移，从而提高系统稳定性.双协议(即双脉冲差分协议联合BB84协议)的使用，增强了系统的安全性.该系统具有高效、安全、简洁、稳定等优点，在实验上实现了长期稳定的密钥分发和量子保密通信，误码率<5%，传输距离达80km.     

Super-sensitive phase estimation with coherent boosted light using parity measurements

We consider a passive and active hybrid interferometer for phase estimation, which can reach the sub-shot-noise limit in phase sensitivity with only the cheapest coherent sources. This scheme is formed by adding an optical parametric amplifier before a Mach-Zehnder interferometer. It is shown that our hybrid protocol can obtain a better quantum Cramer-Rao bound than the pure active(e.g., SU(1,1)) interferometer, and this precision can be reached by implementing the parity measurements. Furthermore, we also draw a detailed comparison between our scheme and the scheme suggested by Caves[Phys. Rev. D 23 1693(1981)], and it is found that the optimal phase sensitivity gain obtained in our scheme is always larger than that in Caves' scheme.     

Heterodyne interferometer scheme using a double pass in an acousto-optic modulator

We introduce a heterodyne interferometer scheme utilizing the double-pass arrangement of the deflected beams of an acousto-optic modulator. To prove our new idea, the interferometer has been applied for measuring small amplitude vibrations. The output intermediate frequency signal from the interferometer is processed by using an I/Q demodulator. In theory, it can provide the quantum noise limited sensitivity, whereas, in our present Letter, the sensitivity of the phase measurement is limited by the resolution of the 16?bit A/D converter used for processing the I/Q signals. Details of our interferometer scheme are discussed.     

Double-polarization fiber ring interferometer based on a single-mode isotropic fiber for gyroscopy

We propose and implement the scheme of a whole-fiber double-polarization ring interferometer based on an isotropic fiber for gyroscopy purposes. The results of an experimental study of the output signal of the interferometer based on the proposed scheme are presented. The shift of the zero point of the interferometer signal (at a level of 3°/h) and the drift of the zero point (at a level of 1°/h) are determined. The rotation sensitivity of the interferometer is measured. It amounts to 0.1°/h, which agrees well with the calculation allowing for the shot noise of the photoelectric current at the output of the scheme. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 4, pp. 328–332, April 2008.     

Enhanced phase sensitivity with a nonconventional interferometer and nonlinear phase shifter

We propose a theoretical scheme of an enhanced phase sensitivity by introducing a nonlinear phase shifter to the nonconventional interferometer consisting of a balanced beam splitter (BBS) and an optical parameter amplifier (OPA), a modified nonlinear interferometer (MNI). Then we use coherent state and even coherent state as inputs and homodyne detection at one output port of the MNI for phase sensitivity, both without and with photon losses. We find that the nonlinear phase shifter can not only improve phase sensitivity, but also significantly resist the decoherence from photon losses. In comparison to both the BBS+OPA scheme with linear phase shifter and the traditional Mach–Zehnder interferometer with nonlinear one, the phase sensitivity of the MNI scheme shows the best performance. It is interesting that the nonlinear phase shifter can stimulate potential of the OPA, although there is no improvement in signal-to-noise ratio beyond standard quantum limit for the BBS+OPA scheme with a linear phase shifter.     

Differential-phase-shift quantum key distribution experiment with a planar light-wave circuit Mach-Zehnder interferometer

A differential-phase-shift quantum key distribution experiment was carried out with a planar light-wave circuit (PLC) Mach-Zehnder interferometer. This scheme has two advantages: it requires no polarization control and has a high repetition frequency, provided that a stable interferometer is available. Stable polarization-insensitive operation was achieved with an interferometer fabricated by PLC technology. Raw key creation at a rate of 3076 bits/s with a 5.0% quantum bit-error rate was achieved over 20 km of fiber. The stability of the PLC interferometer was examined.     

Digital measuring scheme for half-wave voltage of Y-tap multiple integrated optical circuit

A high-precision digital measuring scheme for half-wave voltage of Y-tap multiple integrated optical circuits is proposed. This scheme is based on Sagnac interferometer modulated with digital step waveform whose frequency is half of eigen frequency of the interferometer. The technology and measuring precision are discussed. An experimental setup is made and the temperature-dependences of half-wave voltage of two samples are studied. Analysis and experimental study prove that this scheme is convenient and accurate.     

Wide measurement range scanning heterodyne interferometer utilizing astigmatic position sensing scheme

A scanning heterodyne I/Q-interferometer scheme is proposed to overcome phase ambiguity caused by the periodic nature of its phase-dependent signal. A position sensing scheme using an astigmatic method in the confocal arrangement has been interfaced to the interferometer to retrieve the real phase value during a scanning process. The experimental results show that the vertical measurement range can be expanded up to 16 μm. The potential of this interferometer on the scanning microscopy of a rough surface is discussed.     

切比雪夫光混沌发生器的优化

研究了利用马赫-曾德尔干涉仪来构造扩频序列的设计方法,并对以往提出的切比雪夫光混沌序列发生器的构造原理和方案进行了分析,针对其受到器件尺寸限制的不足,提出了利用余弦函数的性质对其改进的新方案,从而消除了原方案在设计上的局限性.同时通过外加电压对马赫-曾德尔干涉仪两臂折射率的调节增加了波长适应性功能,使得光混沌序列发生器可以在不同的入射波长下得到不同的切比雪夫光混沌序列. 关键词： 切比雪夫映射 混沌序列 Lyapunov指数 光混沌序列发生器     

Mach–Zehnder interferometer with squeezed and EPR entangled optical fields

We study a scheme for Mach-Zehnder(MZ) interferometer as a quantum linear device by injecting two-mode squeezed input states into two ports of interferometer.Two-mode squeezed states can be changed into two types of inputs for MZ interferometer:two squeezed states and Einstein-Podolsky-Rosen(EPR) entangled states.The interference patterns of the MZ interferometer vary periodically as the relative phase of the two arms of the interferometer is scanned,and are measured by the balanced homodyne detection system.Our experiments show that there are different interference patterns and periodicity of the output quantum states for two cases which depend on the relative phase of input optical fields.Since MZ interferometer can be used to realize some quantum operations,this work will have the important applications in quantum information and metrology.     

A reflection interferometer with a noninverted response function based on a phase grating

It is shown that the inclusion of a simple phase grating in the optical scheme of a resonator provides the possibility of performing spectral investigations in reflected light with characteristics of a Fabry-Perot interferometer. The response function of the interferometer is examined, and experimental results are presented.     

A simple thermal phase stabilizer for real-time optical fibre holographic interferometry

An optical fibre interferometer can be made to phase-stabilize by simply attaching a short length of one arm of the interferometer to a straight copper track and heating the track with an electric current. This feedback thermal stabilization scheme works well even for relatively short fibre lengths and there is no need to treat or unjacket the fibre. A fibre-optic Michelson interferometer stabilized by this method successfully provided object and reference beams for real-time holographic interferometric measurements of the distortion of heated test objects.     

Experimental scheme of quantum cryptography on the nonorthogonal states with time shift and a minimum number of optical components

A new scheme of experimental quantum cryptography on the nonorthogonal states is described. Nonorthogonality is achieved by the time shift of states in different messages. For this scheme to be efficient, it is sufficient to balance the arms of an interferometer at the receiver and transmitter ends to an accuracy of 1–2 cm. This is a fundamental advantage of this scheme over, e.g., the most developed cryptosystem based on phase coding, where the maximum transmission distance has been achieved. In the latter system, the arms of the interferometer need to be balanced with an accuracy of fractions of a micron for a distance of several tens of kilometers.     

Balanced heterodyne signal extraction in a postmodulated Sagnac interferometer at low frequency

We describe a balanced-heterodyne postmodulated Sagnac interferometer signal extraction method that is suitable for gravitational wave detection. The method is simple to implement by placement of a polarization-selective modulator after the beam splitter in the dark port of the interferometer. The postmodulated Sagnac interferometer retains its common path advantage and exhibits insensitivity to laser frequency noise below, at, and above the heterodyne frequency. Balanced detection reduces sensitivity to laser amplitude noise. In this scheme mirror displacement signals were rf demodulated and observed from 0.2 to 10kHz.     

Persistent and enhanced spin-nematic squeezing in a spinor Bose-Einstein condensate

We propose a simple scheme to realize the persistent spin-nematic squeezing in a spinor Bose–Einstein condensate by rapidly turning-off the external magnetic field at a time that maximal spin-nematic squeezing occurs. We observe that the optimal spin-nematic squeezing can be maintained in a nearly fixed direction. For a proper initial magnetic field, the optimal squeezing can be obviously enhanced. We further construct a spin-mixing interferometer, where the quantum correlation of the squeezed state (generated by our scheme) is fully utilized in the phase measurement, and show the phase sensitivity of the interferometer has a significant enhancement.     

Ring resonator in a Sagnac interferometer as a birefringence magnifier

A novel birefringence magnification technique that uses a ring resonator in a Sagnac interferometer is proposed and demonstrated. An enhancement factor of 38 was obtained experimentally. The scheme can be used to increase measurement sensitivity to small birefringence and polarization mode dispersion and to decrease the threshold for nonlinear switching and laser mode locking by a Sagnac interferometer.     

VISAR准零程差调试方法研究

介绍了任意反射面速度干涉仪(VISAR)中马赫-曾德干涉仪必须满足的准零程差条件.根据白光光程差调试精度高但不易相干的特点,提出了先利用激光粗调,再利用白光调试来实现零程差精密调节的方案.详细分析了激光粗调马赫-曾德干涉仪的调试原理、调试精度以及光程差不确定性.针对光程差不确定性,提出了改进的激光粗调方案,将光程差调节精度由毫米量级提高到微米量级,大大减小了白光调试的盲区,使白光精调变得简易可行.干涉仪最终光程差调试精度为1.6 μm.     

Simple delay scheme for quantum cryptography based on a Mach-Zehnder optic fiber interferometer

A simple experimental scheme is proposed for a relativistic quantum cryptosystem based on a Mach-Zehnder optic fiber interferometer. In this scheme, quantum mechanical laws, along with the restrictions imposed by the Special Relativity, ensure the detection of any eavesdropping attempt.     

Low noise amplification of an optically carried microwave signal: application to atom interferometry

In this paper, we report a new scheme to amplify a microwave signal carried on a laser light at λ=852 nm. The amplification is done via a semiconductor tapered amplifier and this scheme is used to drive stimulated Raman transitions in an atom interferometer. Sideband generation in the amplifier, due to self-phase and amplitude modulation, is investigated and characterized. We also demonstrate that the amplifier does not induce any significant phase-noise on the beating signal. Finally, the degradation of the performances of the interferometer due to the amplification process is shown to be negligible.