Upper Limit on Gravitational Wave Backgrounds at 0.2 Hz with Torsion-bar Antenna

We present the first upper limit on gravitational wave (GW) backgrounds at an unexplored frequency of 0.2 Hz using a torsion-bar antenna (TOBA). A TOBA was proposed to search for low-frequency GWs. We have developed a small-scaled TOBA and successfully found {\Omega}gw(f) < 4.3 \times 1017 at 0.2 Hz as demonstration of the TOBA's capabilities, where {\Omega}gw (f) is the GW energy density per logarithmic frequency interval in units of the closure density. Our result is the first nonintegrated limit to bridge the gap between the LIGO band (around 100 Hz) and the Cassini band (10-6 - 10-4 Hz).Comment: 4 pages, 5 figure

Laser power stabilization for second-generation gravitational wave detectors

We present results on the power stabilization of a Nd:YAG laser in the frequency band from 1 Hz to 100 kHz. High-power, low-noise photodetectors are used in a dc-coupled control loop to achieve relative power fluctuations down to 5×10−9 Hz−1/2 at 10 Hz and 3.5×10−9 Hz−1/2 up to several kHz, which is very close to the shot-noise limit for 80 mA of detected photocurrent on each detector. We investigated and eliminated several noise sources such as ground loops and beam pointing. The achieved stability level is close to the requirements for the Advanced LIGO gravitational wave detector

A new cosmic microwave background constraint to primordial gravitational waves

Primordial gravitational waves (GWs) with frequencies > 10^{-15} Hz contribute to the radiation density of the Universe at the time of decoupling of the cosmic microwave background (CMB). The effects of this GW background on the CMB and matter power spectra are identical to those due to massless neutrinos, unless the initial density-perturbation amplitude for the gravitational-wave gas is non-adiabatic, as may occur if such GWs are produced during inflation or some post-inflation phase transition. In either case, current observations provide a constraint to the GW amplitude that competes with that from big-bang nucleosynthesis (BBN), although it extends to much lower frequencies (~10^{-15} Hz rather than the ~10^{-10} Hz lower limit from BBN): at 95% confidence-level, Omega_gw h^2 < 6.9 x 10^{-6} for homogeneous (i.e., non-adiabatic) initial conditions. Future CMB experiments, like Planck and CMBPol, should allow sensitivities to Omega_gw h^2 < 1.4 x 10^{-6} and Omega_gw h^2 < 5 x 10^{-7}, respectively.Comment: 5 pages, 2 figures, submitted to Phys. Rev. Let

Some n-p (Hg,Cd)Te photodiodes for 8-14 micrometer heterodyne applications

The results describing the dc and CO2 laser heterodyne characteristics of a three element photodiode array and single element and four element photodiode arrays are presented. The measured data shows that the n(+)-p configuration is capable of achieving bandwidths of 475 to 725 MHz and noise equivalent powers of 3.2 x 10 to the minus 20th power W/Hz at 77 K and 1.0 x 10 to the minus 19th power W/Hz at 145 K. The n(+)-n(-)-p photodiodes exhibited wide bandwidths (approximately 2.0 GHz) and fairly good effective heterodyne quantum efficiencies (approximately 13-30 percent at 2.0 GHz). Noise equivalent powers ranging from 1.44 x 10 to the minus 19th power W/Hz to 6.23 x 10 to the minus 20th power W/Hz were measured at 2.0 GHz

Gyroscopes based on nitrogen-vacancy centers in diamond

We propose solid-state gyroscopes based on ensembles of negatively charged nitrogen-vacancy (${\rm NV^-}$) centers in diamond. In one scheme, rotation of the nitrogen-vacancy symmetry axis will induce Berry phase shifts in the ${\rm NV^{-}}$ electronic ground-state coherences proportional to the solid angle subtended by the symmetry axis. We estimate sensitivity in the range of $5\times10^{-3} {\rm rad/s/\sqrt{Hz}}$ in a 1 ${\rm mm^3}$ sensor volume using a simple Ramsey sequence. Incorporating dynamical decoupling to suppress dipolar relaxation may yield sensitivity at the level of $10^{-5} {\rm rad/s/\sqrt{Hz}}$. With a modified Ramsey scheme, Berry phase shifts in the ${\rm ^{14}N}$ hyperfine sublevels would be employed. The projected sensitivity is in the range of $10^{-5} {\rm rad/s/\sqrt{Hz}}$, however the smaller gyromagnetic ratio reduces sensitivity to magnetic-field noise by several orders of magnitude. Reaching $10^{-5} {\rm rad/s/\sqrt{Hz}}$ would represent an order of magnitude improvement over other compact, solid-state gyroscope technologies.Comment: 3 figures, 5 page

Huddle test measurement of a near Johnson noise limited geophone

In this paper, the sensor noise of two geophone configurations (L-22D and L-4C geophones from Sercel with custom built amplifiers) was measured by performing two huddle tests. It is shown that the accuracy of the results can be significantly improved by performing the huddle test in a seismically quiet environment and by using a large number of reference sensors to remove the seismic foreground signal from the data. Using these two techniques, the measured sensor noise of the two geophone configurations matched the calculated predictions remarkably well in the bandwidth of interest (0.01 Hz–100 Hz). Low noise operational amplifiers OPA188 were utilized to amplify the L-4C geophone to give a sensor that was characterized to be near Johnson noise limited in the bandwidth of interest with a noise value of 10−11 m/Hz⎯⎯⎯⎯⎯√10−11 m/Hz at 1 Hz

Gravitational waves from cosmological compact binaries

We consider gravitational waves emitted by various populations of compact binaries at cosmological distances. We use population synthesis models to characterize the properties of double neutron stars, double black holes and double white dwarf binaries as well as white dwarf-neutron star, white dwarf-black hole and black hole-neutron star systems. We use the observationally determined cosmic star formation history to reconstruct the redshift distribution of these sources and their merging rate evolution. The gravitational signals emitted by each source during its early-inspiral phase add randomly to produce a stochastic background in the low frequency band with spectral strain amplitude between 10^{-18} Hz^{-1/2} and 5 10^{-17} Hz^{-1/2} at frequencies in the interval [5 10^{-6}-5 10^{-5}] Hz. The overall signal which, at frequencies above 10^{-4}Hz, is largely dominated by double white dwarf systems, might be detectable with LISA in the frequency range [1-10] mHz and acts like a confusion limited noise component which might limit the LISA sensitivity at frequencies above 1 mHz.Comment: 14 pages, 14 figures, uses mn.sty, submitted to MNRA

Ultra-low vibration pulse-tube cryocooler stabilized cryogenic sapphire oscillator with 10^-16 fractional frequency stability

A low maintenance long-term operational cryogenic sapphire oscillator has been implemented at 11.2 GHz using an ultra-low-vibration cryostat and pulse-tube cryocooler. It is currently the world's most stable microwave oscillator employing a cryocooler. Its performance is explained in terms of temperature and frequency stability. The phase noise and the Allan deviation of frequency fluctuations have been evaluated by comparing it to an ultra-stable liquid-helium cooled cryogenic sapphire oscillator in the same laboratory. Assuming both contribute equally, the Allan deviation evaluated for the cryocooled oscillator is sigma_y = 1 x 10^-15 tau^-1/2 for integration times 1 < tau < 10 s with a minimum sigma_y = 3.9 x 10^-16 at tau = 20 s. The long term frequency drift is less than 5 x 10^-14/day. From the measured power spectral density of phase fluctuations the single side band phase noise can be represented by L_phi(f) = 10^-14.0/f^4+10^-11.6/f^3+10^-10.0/f^2+10^-10.2/f+ 10^-11.0 for Fourier frequencies 10^-3<f<10^3 Hz in the single oscillator. As a result L_phi approx -97.5 dBc/Hz at 1 Hz offset from the carrier.Comment: 8 pages, 10 figures, presented at European Frequency and Time Forum, ESTEC, Noordwijk, Netherland, April 11-16th 2010 accepted in IEEE Trans. on Micro. Theory & Technique