GEO600: The First Application of
Squeezed Light
Roman Schnabel, for the GEO600 group,
the Quantum Interferometry Group, and the LSC
Albert-Einstein-Institut (AEI)
Institut für Gravitationsphysik
Leibniz Universität Hannover
Outline
• Introduction to Squeezed Light
• The first squeezed-light laser for
GW detectors
• Sensitivity improvement of GEO600
with squeezed light
• Squeezed light as a key-technology
for GW astronomy
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R. Schnabel, LaThuile 2011, March 23
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Gravitational Waves
h:
Gravitational wave
astronomy requires
observatories that can
detect
h < 10-23
(over a band from e.g.
100Hz - 200Hz)
Merging neutron stars. Numerical relativity simulation of gravitational waves
emitted from two neutron stars which are about to merge in 4 ms [Rezzolla, AEI].
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Gravitational Wave Detection
Mirror 1
1) Test masses
2) Laser light
> km
Laser
3) Interference
4) Photo-electric effect
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Mirror 2
Photo diode
Photo-electric current
modulated at GW frequency
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Photo-Electric Current
Photons per time interval
(No signal, but photon shot noise)
N
Time intervals
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Photo-Electric Current
Photons per time interval
(GW signal?)
N
Time intervals
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Probability [rel. units]
Photon Counting Statistics
Coherent state   100
2
ˆ
 N  N    10000

Relative shot-noise ~

1
N
~
1
PLaser
N
N N

N N
Photon number N
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Increasing the Light Power
Mirror 1
Power-recycling mirror
Heating by light
absorption
High
power
laser
Mirror 2
Photo diode
Photo-electric current
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Is there a possibility to increase
the signal/quantum noise–ratio
without increasing the laser power?
Yes, by squeezed laser light!
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Shot-Noise in an Interferometer
Mirror
Beam
splitter
Laser
Due to zero point fluctuations
(vacuum noise)
Photo
diode
[Caves, Phys. Rev. D 23, 1693 (1981)]
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Squeezing the Shot-Noise
Mirror
C. M. Caves (1981):
Reduction of quantum
noise with squeezed light
Beam
splitter
Laser
Squeezed
light laser
Faraday
Rotator
Photo
diode
[Caves, Phys. Rev. D 23, 1693 (1981)]
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Probability [rel. units]
“Squeezed” Counting Statistics
Noise
squeezing
Squeezing factor: 10 dB
Squeezing factor: 3 dB
Photon number N
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Photo-Electric Current
Photons per time interval
(No signal)
N
Time intervals
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Photo-Electric Current - Squeezed
Photons per time interval
Squeezing the noise of a random
process without a measurement!?
N
Quantum mechanics:
Squeezing requires time/energy
(and amplitude/phase quadrature)
entangled photons
Time intervals
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Squeezing in the Wave Picture
X1
Quadrature squeezing at
sideband frequency W1
+
WcW1
Wc
X2
WcW1
W
+
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The GEO600 Squeezed Light Laser
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Generation of Squeezed Light (PDC)
Pump field input
(cw, 532nm)
c2-nonlinear crystal:
MgO:LiNbO3
Squeezed field output
(cw, 1064nm) by parametric
down-conversion (PDC)
Standing wave cavity
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History of Squeezed Light Generation
First squeezed light: [Slusher et al., PRL 55, 2409 (1985)]
Research labs with squeezed light (not complete):
- Kimble (CalTech): teleportation: [Furuzawa et al., SCIENCE 282, 706 (1998)]
- Grangier (Orsay); kitten: [Ourjoumtsev et al., SCIENCE, 312, 83 (2006)]
- Schiller and Mlynek (Konstanz): tomography: [Nature 387, 471 (1997).]
- Bachor and Lam (Canberra): 6dB at 1064nm [J. Opt. B 1, 469 (1999).]
- Leuchs (Erlangen); ~7 dB pulsed [Opt. Lett. 33, 116 (2008).]
- Polzik (Copenhagen), [Neergaard-Nielsen et al., PRL 97, 083604 (2006)]
- Furusawa (Tokyo); 9 dB: [Takeno et al., Opt. Express 15, 4321 (2007).]
- Fabre (Paris), Zhang, Peng (Shanxi);
- Andersen (Copenhagen); Mavalvala (MIT),...
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History of Squeezed Light Generation
Research & development towards the first application of squeezed light
- McClelland (ANU), power-recycling [McKenzie et al., PRL 88, 231102 (2002)]
- McClelland (ANU), audio-band [McKenzie et al., PRL 93, 161105 (2004)]
- RS (LUH), signal-recycling [Vahlbruch et al., PRL 95, 211102 (2005)]
- RS (LUH), control scheme [Vahlbruch et al., PRL 97, 011101 (2006)]
- RS (LUH), full band-width [Vahlbruch et al., New Journal of Phys. 9, 371 (2007)]
- Mavalvala (MIT), suspended mirrors [Goda et al., Nature Phys. 4, 472 (2008)]
- RS (LUH), 10dB [Vahlbruch et al., PRL 100, 033602 (2008)]
- RS (LUH), turn-key source [Vahlbruch et al., CQG 27, 084027 (2010)]
Recent review:
[R.S. et al., Nature Comm. 1:121 doi: 10.1038/ncomms1122 (2010)]
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Transport to the GEO600 GW Detector
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GEO600: Squeezed Light in Application
Observatory noise
without squeezed light
With squeezed light
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Squeezing the Shot-Noise (SN) and the
Radiation Pressure Noise (PRN)
[Jaekel and Reynaud,
Europhys. Lett. 13, 301 (1990)]
Laser
Filter cavities
Faraday
Rotator
Squeezed
light laser
[Kimble et al., Phys. Rev. D 65, 022002 (2001)]
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Squeezing SN and RPN
[Jaekel, Reynaud 1990]
Shot noise
QNDRegime
Squeezed Light Input
(8dB)
(SQL)
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Summary
• GEO600 now uses squeezed light and
achieves its best ever sensitivity (at
shot-noise limited frequencies)
• A real application of entangled
photons in squeezed light has been
realized
• Squeezing is mature and might
become a key-technology in all future
GW observatories, such as ET
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