path to sub-quantum-noise-limited gravitational-wave interferometry
DESCRIPTION
Path to Sub-Quantum-Noise-Limited Gravitational-wave Interferometry. MIT Corbitt, Goda, Innerhofer, Mikhailov, Ottaway, Wipf. TeV Particle Astrophysics August 2006. Caltech Australian National University Universitat Hannover/AEI LIGO Scientific Collaboration. Outline. - PowerPoint PPT PresentationTRANSCRIPT
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TeV Particle AstrophysicsAugust 2006
CaltechAustralian National University
Universitat Hannover/AEILIGO Scientific Collaboration
MITCorbitt, Goda, Innerhofer, Mikhailov, Ottaway, Wipf
Path to Sub-Quantum-Noise-Limited
Gravitational-wave Interferometry
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Outline
The quantum noise limit in GW ifos Sub-quantum noise limited ifos
Injecting squeezed vacuum Setting requirements – the wishlist
Generating squeezed states Nonlinear optical media – “crystal” Radiation pressure coupling – “ponderomotive”
Recent progress and present status
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Optical Noise Shot Noise
Uncertainty in number of photons detected
Higher circulating power Pbs low optical losses
Frequency dependence light (GW signal) storage time in the interferometer
Radiation Pressure Noise Photons impart momentum to cavity mirrors
Fluctuations in number of photons Lower power, Pbs
Frequency dependence response of mass to forces
1( )
bs
h fP
2 4( ) bsPh fM f
Optimal input power depends on frequency
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Initial LIGO
Input laser power ~ 6 W
Circulating power ~ 20 kW
Mirror mass10 kg
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A Quantum Limited Interferometer
LIGO I
Ad LIGO
Seism
ic
Suspension
thermal
Test mass thermal
QuantumInput laser power > 100 W
Circulating power > 0.5 MW
Mirror mass40 kg
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Some quantum states of light
Heisenberg Uncertainty Principle for EM field
Phasor diagram analogy Stick dc term Ball fluctuations Common states
Coherent state Vacuum state Amplitude squeezed state Phase squeezed state
McKenzie
ˆ ˆ 1X X
Associated with amplitude and phase
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Squeezed input vacuum state in Michelson Interferometer
X+
X
X+
XX+
X
X+
X
Consider GW signal in the phase quadrature Not true for all
interferometer configurations
Detuned signal recycled interferometer GW signal in both quadratures
Orient squeezed state to reduce noise in phase quadrature
Laser
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Sub-quantum-limited interferometer
Quantum correlations X+
X
Input squeezing
Narrowband
Broadband
BroadbandSqueezed
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Squeezed vacuum states for GW detectors
Requirements Squeezing at low frequencies (within GW band) Frequency-dependent squeeze angle Increased levels of squeezing Long-term stable operation
Generation methods Non-linear optical media ((2) and (3) non-linearites)
crystal-based squeezing Radiation pressure effects in interferometers
ponderomotive squeezing
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How to make a squeezed state?
Correlate the ‘amplitude’ and ‘phase’ quadratures Correlations noise reduction
How to correlate quadratures? Make noise in each quadrature not independent of the
other (Nonlinear) coupling process needed
For example, an intensity-dependent refractive index couples amplitude and phase
Squeezed states of light and vacuum
0
2( ) n I z
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Squeezing using nonlinear optical media
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Optical Parametric Oscillator
† † †bH i a a a ba
SHG
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Squeezed Vacuum
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Low frequency squeezing at ANU
ANU group quant-ph/0405137McKenzie et al., PRL 93, 161105 (2004)
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Injection in a power recycled Michelson interferometer
K.McKenzie et al. Phys. Rev. Lett., 88 231102 (2002)
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Injection in a signal recycled interferometer
Vahlbruch et al. Phys. Rev. Lett., 95 211102 (2005)
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Squeezing using radiation pressure coupling
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The principle
Use radiation pressure as the squeezing mechanism Consider an optical cavity with high stored power and
a phase sensitive readout Intensity fluctuations (radiation pressure) drive the
motion of the cavity mirrors Mirror motion is then imprinted onto the phase of the
light
Analogy with nonlinear optical media Intensity-dependent refractive index changes couple
amplitude and phase
0
2( ) n I z
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The “ponderomotive” interferometer
Key ingredients Low mass, low noise
mechanical oscillator mirror – 1 gm with 1 Hz resonant frequency
High circulating power – 10 kW
High finesse cavities15000
Differential measurement – common-mode rejection to cancel classical noise
Optical spring – noise suppression and frequency independent squeezing
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Noise budget
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Noise suppression
Dis
pla
cem
en
t /
Forc
e
5 kHz K = 2 x 106 N/m Cavity optical mode diamond rod
Frequency (Hz)
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Conclusions
Advanced LIGO is expected to reach the quantum noise limit in most of the band
QND techniques needed to do better Squeezed states of the EM field appears to be
the most promising approach Crystal squeezing mature
3 to 4 dB available in f>100 Hz band Ponderomotive squeezing getting closer
Factors of 2 to 5 improvements foreseeable in the next decade Not fundamental but technical
Need to push on this to be ready for future instruments
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The End