1. Interferometric speed meter as a low-frequency gravitational-wave detector
Helge Müller-Ebhardt
Max-Planck-Institut für Gravitationsphysik (AEI) and Leibniz Universität Hannover
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2. Speed meter idea
measure position difference after time delay → measure speed
[Braginsky & Khalili, 1990]
conserved momentum usually proportional to speed → real QND (?)
no: because the coupling to speed changes conserved momentum
[Khalili, 2002]

3. Position meter vs. speed meter
RP noise constant below half-linewidth
[Purdue & Chen, 2002]
broadband RP noise cancellation w/ balanced homodyne detection w/o filters
shot noise limited below linewidth
can use light masses and squeezing
increase only due to signal transfer

4. Interferometric speed meter realizations
either Michelson interferometer with additional sloshing cavity or with polarizing optics
or Sagnac ifo with
non-zero area
zero area → insensitive to rotations
no arm cavities
ring cavities in arms → optimize sensitivity to frequencies of interest
size of vacuum system?

5. Demonstration of squeezed zero-area Sagnac
Limited mainly by losses in the ifo (5.5%) due to non-optimized coatings for angles of incidence
12.7 dB squeezing inserted
8.2 dB
shot noise supression
[Eberle et al., 2010]

6. Squeezed LF interferometric GW detector
zero-area Sagnac ifo with 10 km long arm cavities, 40 kg test-mass mirrors, linewidth of 80 Hz and a laser power of 90 W at the central beam splitter → 10 kW circulating power
low mass
low laser power but rather high linewidth
allows use of cyrogenics
start with pure squeezed state of 12.4 dB
optical losses for input-squeezing and detection similar to experiment
[Eberle et al., 2010]

7. Squeezed LF interferometric GW detector
zero-area Sagnac ifo with 10 km long arm cavities, 40 kg test-mass mirrors, linewidth of 80 Hz and a laser power of 90 W at the central beam splitter → 10 kW circulating power
low laser power but rather high linewidth
loss in arm cavity:
40 ppm per reflective surface
allows use of cyrogenics
start with pure squeezed state of 12.4 dB
optical losses for input-squeezing and detection similar to experiment
[Eberle et al., 2010]

8. Optimization LF GW detector with cyrogenic optics
GW detector with 10 km long arm cavities, 10 kW circulating power
Saganc ifo
w/ 40 kg test-mass, 10 dB squeezing, w/o detuned SR and filter cavities
Michelson ifo
w/ 200 kg test-mass and detuned SR,
w/o squeezing
60 cm long suspension and 16 K at test-mass
BH-BH inspiral range:
Michelson ifo: 5800 Mpc
Sagnac ifo: Mpc

9. Optimization LF GW detector with cyrogenic optics
GW detector with 10 km long arm cavities, 10 kW circulating power
Saganc ifo
w/ 40 kg test-mass, 10 dB squeezing, w/o detuned SR, filter cavities
Michelson ifo
w/ 200 kg test-mass, detuned SR
w/o squeezing
60 cm long suspension and 16 K at test-mass
simple integration:
Michelson ifo: 1.2 x 10^48
Sagnac ifo: x 10^48

10. Optimization LF GW detector with cyrogenic optics
GW detector with 10 km long arm cavities, 50 kW circulating power
Saganc ifo
w/ 40 kg test-mass, 10 dB squeezing, w/o detuned SR, filter cavities
Michelson ifo
w/ 200 kg test-mass, detuned SR
w/o squeezing
60 cm long suspension and 16 K at test-mass
simple integration:
Michelson ifo: 2 x 10^48
Sagnac ifo: x 10^48

11. Conclusion speed meter advantages as LF detector
- moderate test-mass weight
- compatible with input-squeezing w/o filter cavities
- broadband noise spectrum
for LF detector important desicion between position and speed meter
how much circulating power can be tolerated by cooling system
what about thermoelastic noise
what about gravity gradiant and seimic noise
what about optical loss
full parameter optimization:
- for what kind of GW sources or for what kind of noise-curve shape
- which paramters