다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

We point out a general framework that encompasses most cases in which quantum effects enable an increase in precision when estimating a parameter (quantum metrology) The typical quantum precision-enhancement is of the order of the square root of the number of times the system is sampled We prove that this is optimal and we point out the different strategies (classical and quantum) that permit to attain this bound

Quantum metrology

A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Researchers demonstrate a microwave generator based on a high-Q optical resonator and a frequency comb functioning as an optical-to-microwave divider. They generate 10 GHz electrical signals with a fractional frequency instability of ≤8 × 10−16 at 1 s.

/pdf/generation-of-ultrastable-microwaves-via-optical-frequency-4zkqlu6ady.pdf

Generation of ultrastable microwaves via optical frequency division

https://www.repository.cam.ac.uk/bitstream/1810/264501/1/Fu_et_al-2017-Progress_in_Material_Science-VoR.pdf

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

In this Letter we report on an all-optical-fiber approach to the generation of ultra-low-noise microwave signals. We make use of two erbium fiber mode-locked lasers phase locked to a common ultrastable laser source to generate an 11.55 GHz signal with an unprecedented relative phase noise of -111 dBc/Hz at 1 Hz from the carrier. The residual frequency instability of the microwave signals derived from the two optical frequency combs is below 2.3x10(-16) at 1 s and about 4x10(-19) at 6.5x10(4) s (in 5 Hz bandwidth, three days of continuous operation).

Ultra-low-noise microwave extraction from fiber-based optical frequency comb

This paper reports on the Si-glass anodic bonding process to fill micro Cs vapor cells with a buffer gas (Ar or Ne) at a controlled pressure (up to 20 kPa), which is one of the technological key steps to fabricate Cs vapor cells for miniature atomic clocks. In the atmosphere of these gases, the applicable bonding voltage was not high enough to achieve strong bonding because of the electrical breakdown caused by ionization of the gas. To improve the bonding quality, an original two-step anodic bonding method was proposed. The first step of the anodic bonding, which intends to pre-seal the gas in microcells, is carried out in the presence of a buffer gas by applying a voltage lower than the breakdown voltage. Subsequently, the second bonding is performed in air at sufficiently high voltages to improve the sealing quality. By employing optical spectroscopy, it was demonstrated that the cells maintain the buffer gas at an appropriate pressure for atomic clock operation. The accelerated aging tests show that Cs vapor as well as the buffer gas remained in the cells without any significant change in the pressure, which allow us to estimate the lifetime of the cells to be at least 3 years. Further CPT experiments revealed that the buffer-gas pressure change is less than 6.13 × 10−4 kPa throughout the aging test at 125 °C for more than 3 weeks. These results show that these microcells are appropriate for applications to atomic frequency references.

Microfabrication of cesium vapor cells with buffer gas for MEMS atomic clocks

The authors use a single laser beam with synchronously modulated polarization and phase to trap atoms in a superposition state, decoupled from the light. Thanks to the linear architecture of this setup, it can serve as a compact, high-performance vapor-cell atomic clock. Such systems based on coherent population trapping are desired as successors to the well-known rubidium clock, particularly for applications in navigation and telecommunication. This setup offers frequencies an order of magnitude more stable than from a typical industrial clock.

/pdf/high-performance-coherent-population-trapping-clock-with-45b8uwlcie.pdf

High-Performance Coherent Population Trapping Clock with Polarization Modulation

Understanding amplifier phase noise is a critical issue in many fields of engineering and physics, such as oscillators, frequency synthesis, telecommunication, radar, and spectroscopy; in the emerging domain of microwave photonics; and in exotic fields, such as radio astronomy, particle accelerators, etc. Focusing on the two main types of base noise in amplifiers, white and flicker, the power spectral density of the random phase φ(t) is Sφ(f) = b0 + b-1/f. White phase noise results from adding white noise to the RF spectrum in the carrier region. For a given RF noise level, b0 is proportional to the reciprocal of the carrier power P0. By contrast, flicker results from a near-dc 1/f noise-present in all electronic devices-which modulates the carrier through some parametric effect in the semiconductor. Thus, b-1 is a parameter of the amplifier, constant in a wide range of P0. The consequences are the following: Connecting m equal amplifiers in parallel, b-1 is 1/m times that of one device. Cascading m equal amplifiers, b-1 is m times that of one amplifier. Recirculating the signal in an amplifier so that the gain increases by a power of m (a factor of m in decibels) as a result of positive feedback (regeneration), we find that b-1 is m2 times that of the amplifier alone. The feedforward amplifier exhibits extremely low b-1 because the carrier is ideally nulled at the input of its internal error amplifier. Starting with an extensive review of the literature, this article introduces a system-oriented model which describes the phase flickering. Several amplifier architectures (cascaded, parallel, etc.) are analyzed systematically, deriving the phase noise from the general model. There follow numerous measurements of amplifiers using different technologies, including some old samples, and in a wide frequency range (HF to microwaves), which validate the theory. In turn, theory and results provide design guidelines and give suggestions for CAD and simulation. To conclude, this article is intended as a tutorial, a review, and a systematic treatise on the subject, supported by extensive experiments.

Phase noise in RF and microwave amplifiers

We use two fiber-based femtosecond frequency combs and a low-noise carrier suppression phase detection system to characterize the optical to microwave synchronization achievable with such frequency divider systems. By applying specific noise reduction strategies, a residual phase noise as low as -120 dBc/Hz at 1 Hz offset frequency from a 11.55 GHz carrier is measured. The fractional frequency instability from a single optical-to-frequency divider is 1.1E-16 at 1 s averaging down to below 2E-19 after only 1000 s. The corresponding rms time deviation is lower than 100 attoseconds up to 1000 s averaging duration.

Rodolphe Boudot

Papers

Ultra-low-noise microwave extraction from fiber-based optical frequency comb

Microfabrication of cesium vapor cells with buffer gas for MEMS atomic clocks

High-Performance Coherent Population Trapping Clock with Polarization Modulation

Phase noise in RF and microwave amplifiers

Sub-100 attoseconds optics-to-microwave synchronization