The advent of stable, highly squeezed states of light has generated great interest in the gravitational wave community as a means for improving the quantum-noise-limited performance of advanced ...interferometric detectors. To confidently measure these squeezed states, it is first necessary to measure the shot-noise across the frequency band of interest. Technical noise, such as non-stationary events, beam pointing, and parasitic interference, can corrupt shot-noise measurements at low Fourier frequencies, below tens of kilo-hertz. In this paper we present a qualitative investigation into all of the relevant noise sources and the methods by which they can be identified and mitigated in order to achieve quantum noise limited balanced homodyne detection. Using these techniques, flat shot-noise down to Fourier frequencies below 0.5 Hz is produced. This enables the direct observation of large magnitudes of squeezing across the entire audio-band, of particular interest for ground-based interferometric gravitational wave detectors. 11.6 dB of shot-noise suppression is directly observed, with more than 10 dB down to 10 Hz.
The Gravity Recovery and Climate Experiment (GRACE) has demonstrated that low–low satellite-to-satellite tracking enables monitoring the time variations of the Earth’s gravity field on a global ...scale, in particular those caused by mass-transport within the hydrosphere. Due to the importance of long-term continued monitoring of the variations of the Earth’s gravitational field and the limited lifetime of GRACE, a follow-on mission is currently planned to be launched in 2017. In order to minimise risk and the time to launch, the follow-on mission will be basically a rebuild of GRACE with microwave ranging as the primary instrument for measuring changes of the intersatellite distance. Laser interferometry has been proposed as a method to achieve improved ranging precision for future GRACE-like missions and is therefore foreseen to be included as demonstrator experiment in the follow-on mission now under development. This paper presents the top-level architecture of an interferometric laser ranging system designed to demonstrate the technology which can also operate in parallel with the microwave ranging system of the GRACE follow-on mission.
The field of squeezed states for gravitational-wave (GW) detector enhancement is rapidly maturing. In this review paper, we provide an analysis of the field circa 2013. We begin by outlining the ...concept and description of quantum squeezed states. This is followed by an overview of how quantum squeezed states can improve GW detection, and the requirements on squeezed states to achieve such enhancement. Next, an overview of current technology for producing squeezed states, using atoms, optomechanical methods and nonlinear crystals, is provided. We finally highlight the milestone squeezing implementation experiments at the GEO600 and LIGO GW detectors.
Precise optical control of microscopic particles has been mastered over the past three decades, with atoms, molecules and nano-particles now routinely trapped and cooled with extraordinary precision, ...enabling rapid progress in the study of quantum phenomena. Achieving the same level of control over macroscopic objects is expected to bring further advances in precision measurement, quantum information processing and fundamental tests of quantum mechanics. However, cavity optomechanical systems dominated by radiation pressure - so-called 'optical springs' - are inherently unstable due to the delayed dynamical response of the cavity. Here we demonstrate a fully stable, single-beam optical trap for a gram-scale mechanical oscillator. The interaction of radiation pressure with thermo-optic feedback generates damping that exceeds the mechanical loss by four orders of magnitude. The stability of the resultant spring is robust to changes in laser power and detuning, and allows purely passive self-locking of the cavity. Our results open up a new way of trapping and cooling macroscopic objects for optomechanical experiments.
Newtonian noise is likely to be a future challenge at low frequencies for Advanced LIGO and other second generation gravitational wave detectors. We present the TorPeDO system: a dual torsion ...pendulum sensor designed to measure local gravitational forces to high precision. Gravitational forces induce a differential rotation between the two torsion beams, which is measured with an optical read-out. Both torsion pendulums have a common suspension point, tunable centre of mass, and resonant frequency. This produces a high level of mechanical common mode noise cancellation. We report on a controls prototype of the TorPeDO system, presenting the frequency response and tuning range of both pendulums. A noise budget and mechanical cross-coupling model for this system are also presented. We demonstrate frequency tuning of the two torsion pendulums to a difference of 4.3 μHz.
Squeezed states of light have been recently used to improve the sensitivity of laser-interferometric gravitational-wave detectors beyond the quantum limit. To completely establish quantum engineering ...as a realistic option for the next generation of detectors, it is crucial to study and quantify the noise coupling mechanisms which injection of squeezed states could potentially introduce. We present a direct measurement of the impact of backscattered light from a squeezed-light source deployed on one of the 4 km long detectors of the laser interferometric gravitational wave observatory (LIGO). We also show how our measurements inform the design of squeezed-light sources compatible with the even more sensitive advanced detectors currently under construction, such as Advanced LIGO.
Second generation gravitational wave detectors are likely to be limited by Newtonian Noise at low frequencies. A dual torsion pendulum sensor aimed at exploring low- frequency gravitational-force ...noise is being studied at the ANU. This sensor is designed to measure local gravitational forces to high precision and will be limited by Newtonian noise. We report on a controls prototype which has been constructed and suspended, along with initial characterisation and testing of the two torsion pendulums. Large weights at the end of each bar reposition the centres of mass to the same point in space external to both bars. Since both bars have a common suspension point, resonant frequency (≈33.4 mHz), and centre of mass, mechanical disturbances and other noise will affect both bars in the same manner, providing a large mechanical common mode rejection.
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