For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data. r

We present the analysis of between 50 and 100 h of coincident interferometric strain data used to search for and establish an upper limit on a stochastic background of gravitational radiation. These data come from the first LIGO science run, during which all three LIGO interferometers were operated over a 2-week period spanning August and September of 2002. The method of cross correlating the outputs of two interferometers is used for analysis. We describe in detail practical signal processing issues that arise when working with real data, and we establish an observational upper limit on a f Ϫ3 power spectrum of gravitational waves. Our 90% confidence limit is ⍀ 0 h 100 2 р23Ϯ4.6 in the frequency band 40-314 Hz, where h 100 is the Hubble constant in units of 100 km/sec/Mpc and ⍀ 0 is the gravitational wave energy density per logarithmic frequency interval in units of the closure density. This limit is approximately 10 4 times better than the previous, broadband direct limit using interferometric detectors, and nearly 3 times better than the best narrow-band bar detector limit. As LIGO and other worldwide detectors improve in sensitivity and attain their design goals, the analysis procedures described here should lead to stochastic background sensitivity levels of astrophysical interest.

We perform a search for gravitational wave bursts using data from the second science run of the LIGO detectors, using a method based on a wavelet time-frequency decomposition. This search is sensitive to bursts of duration much less than a second and with frequency content in the 100 -1100 Hz range. It features significant improvements in the instrument sensitivity and in the analysis pipeline with respect to the burst search previously reported by LIGO. Improvements in the search method allow exploring weaker signals, relative to the detector noise floor, while maintaining a low false alarm rate, O0:1 Hz. The sensitivity in terms of the root-sum-square (rss) strain amplitude lies in the range of h rss 10 ÿ20 ÿ 10 ÿ19 Hz ÿ1=2 . No gravitational wave signals were detected in 9.98 days of analyzed data. We interpret the search result in terms of a frequentist upper limit on the rate of detectable gravitational wave bursts at the level of 0.26 events per day at 90% confidence level. We combine this limit with measurements of the B. ABBOTT et al.PHYSICAL REVIEW D 72, 062001 (2005) 062001-2 detection efficiency for selected waveform morphologies in order to yield rate versus strength exclusion curves as well as to establish order-of-magnitude distance sensitivity to certain modeled astrophysical sources. Both the rate upper limit and its applicability to signal strengths improve our previously reported limits and reflect the most sensitive broad-band search for untriggered and unmodeled gravitational wave bursts to date.

The measurement of quantum signals that traveled through long distances is of fundamental and technological interest. We present quantum-limited coherent measurements of optical signals, sent from a satellite in geostationary Earth orbit to an optical ground station. We bound the excess noise that the quantum states could have acquired after having propagated 38 600 km through Earth's gravitational potential as well as its turbulent atmosphere. Our results indicate that quantum communication is feasible in principle in such a scenario, highlighting the possibility of a global quantum key distribution network for secure communication.Quantum mechanics has successfully undergone a number of fundamental experimental tests since its development [1][2][3]. Still some aspects pose both a theoretical and an experimental challenge, such as the relation of quantum mechanics and gravity [4][5][6]. Quantum-limited measurements of quantum states traveling through long distances in outer space provide both an offer to test quantum mechanics under such extreme conditions and a prerequisite for its use in quantum technology [7]. To this end satellite quantum communication [8][9][10][11][12][13][14][15] promises to provide the currently missing links for global quantum key distribution (QKD). Important experiments in satellite quantum communication have been reported or are currently being devised and set up [16][17][18][19][20][21][22].This work presents and discusses quantum-limited measurements on optical signals sent from a GEOstationary satellite. We report on the first bound of the possible influence of physical effects on the quantum states traveling through Earth's gravitational potential and evaluating its impact on quantum communication.Optical [27]). In parallel, free space quantum communication has made its steps out of laboratories into real-world scenarios [28][29][30][31]. It has turned out that detecting field quadratures (continuous variables) is well suited to combat disturbances from atmospheric turbulence and stray light [32][33][34]. Using these methods, the first implementation of an intra-urban free space quantum link using quantum coherent detection has been reported [35,36]. The advantage of stray light immunity applies as well to classical coherent satellite communication [37]. The similarity between these classical and quantum technologies allows us to make use of the platform of a technologically mature Laser Communication Terminal (LCT) [38][39][40] for future quantum communication (see Fig 1).An important step on this way is to precisely characterize system and channel with respect to their quantum noise behavior. Coherent quantum communication employs encoding of quantum states in phase space and works at the limit of the Heisenberg uncertainty relation [41], but is susceptible to additional technical noise. Our task here is to characterize whether quantum coherence properties are preserved after propagation of quantum states over 38 600 km, through a large part of graviarXiv:1608.03511v2 [quant-...

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