Transcript Experiments at the ANU - University of Western Australia

Experiments towards beating
quantum limits
Stefan Goßler
for the experimental team of
The ANU
Centre of Gravitational Physics
Overview
I.
Squeezing in the GW detection band
II.
Off-resonant thermal noise
and the Standard Quantum Limit
Kirk McKenzie, Malcolm Gray, Ping Koy Lam, David McClelland
Conor Mow-Lowry, Stefan Goßler, Jeff Cumpston, Malcolm Gray,
David McClelland
Squeezing...
...in the gravitational wave detection band:
• Squeezed states
• Noise sources
• Results from the 2004 experiment
• The 2005 experiment
• Current results and limitations
• Summary
I. Squeezing
Squeezed states of light
The EM field has QM fluctuations:
ˆ  X
ˆ  1
X
The production of squeezed states
requires a non-linear process:
Optical Parametric Oscillators (OPO)
or
Optical Parametric Amplifier (OPA)
Use of squeezed states in Interferometric GW
detectors first proposed in 1980 by Caves.
Requires squeezing in the GW detection band!
I. Squeezing
OPO/OPA noise budget
Variance in the frequency domain
for the squeezed output:
Intra-cavity photon number@1064nm


VOUT
( )  CsVs ( )  ClVl  ( )  n C pVp ( )  CV ( )

Sqz.

 Seed

Loss

Pump


Detuning
For below threshold OPO
(without power in the seed beam):
n = 0 and Vs± = 1

VOPO
( )  Cs ( )  Cl
Below threshold OPO is immune to laser
noise, pump noise and detuning noise!
(to first order)
I. Squeezing
2004 Experiment
•
Seed power was varied - transition
from OPA to OPO
•
OPO/OPA cavity locked to 1064 nm
•
Homodyne phase locked using noise
power locking [3][5].
– Noise power locking can be
used to lock a vacuum state.
•
Backscatter from PD reduced using
a Faraday Isolator
[3] Laurat et al PRA. 70 042315(2004), [5] McKenzie et al J.Opt B, accepted (2005)
I. Squeezing
Reducing the seed power
McKenzie, Grosse, Bowen,Whitcomb, Gray, McClelland, Lam PRL. 93 161105 (2004)
I. Squeezing
Zero Seed Power
•
Was the lowest frequency squeezing
result to date - at 300 Hz.
– (previous lowest was 50 kHz,
Laurat et al PRA. 70
042315(2004))
•
Covers SNL frequencies of first
generation detectors
•
Measurement limited at low
frequencies by the stability of the
unlocked OPO and homodyne ‘roll up’
I. Squeezing
New layout 2005
New photodetector design.
All (length) degrees of freedom locked!
Traveling wave cavity - Isolated from backscatter off PD
Resonant at pump frequency - effective pump power up to 12 W
I. Squeezing
In the Lab
I. Squeezing
In the Lab
I. Squeezing
Current Results
Squeezing down to
~100 Hz
Measured
squeezing strength:
~3 dB at 500 Hz
Inferred
squeezing strength:
~4.1dB at 500 Hz
I. Squeezing
Current limitations
•
Currently, only moderate pump power
(130 mW) can be used due to cavity
spatial mode instability
 We need to adjust our cavity
parameters (by a small amount) to
ensure higher order spatial modes
are not co-resonate with the TEM00
•
Noise locking used to lock homodyne
phase - Noise locking stability is poor
in comparison to standard (coherent)
locking techniques
 In the future we would like to phase
lock a second laser with a frequency
offset and use this to lock the
harmonic - fundamental phase as
well as the homodyne phase
•
Beam pointing limits low frequency
detection efficiency (coupling via
inhomogenity of photo detectors)
 Employ fast steering mirrors in front
of homodyne detection
I. Squeezing
Summary squeezing
•
•
•
•
Noise Coupling mechanism identified - the coherent fundamental field
Below threshold OPO is immune to laser, pump and detuning noise to first order!
All length degrees of freedom locked, OPO cavity locks indefinately.
If this squeezed state (~3 dB measured at 500 Hz) could be implemented
– Improve current LIGO SNL strain sensitivity increase by
2
– Equivalent of turning up the laser power by a factor of 2
•
Developing new generation of squeezer
– Operate at higher pump power - to generate larger amounts of squeezing
– Inject second laser to replace noise locking loop
I. Squeezing
Thermal noise and SQL
• Thermal noise in gravitational wave detectors
• Niobium flexure membrane as an inverted pendulum mirror suspension
• Experimental layout
• Frequency stabilisation
• Seismic isolation
• Current results and limitations
• Summary
II. Thermal noise and SQL
Thermal noise
1E-17
Overall noise
Seismic noise
Suspension thermal
Test-mass thermal
Shot
Strain sensitivity [1/sqrt Hz]
1E-18
1E-19
1E-20
1E-21
1E-22
1E-23
1E-24
1E-25
1E-26
10
100
1000
Frequency [Hz]
Thermal noise of mirrors and suspensions will eventually limit the sensitivity
of gravitational wave detectors in their most sensitive frequency band
Thermal noise will also be a major impediment to reaching SQL sensitivity
with a table-top experiment as is planned at the ANU
II. Thermal noise and SQL
Niobium Flexure Membrane
To investigate thermal noise
we use a niobium flexure membrane of 200 µm width
as an inverted pendulum to support a mirror of 0.25 g
Mirror
Limiters
Base
(Thanks to Ju Li from UWA for the help with niobium flexure!)
II. Thermal noise and SQL
Experimental layout
Uncoated
wedge
Isolator
Phase
Modulator
PD
l/4
P = 5e-7 mbar
l/4
F = 6000
Reference
Cavity
Flexure
PBS
P = 1e-6 mbar
500 mW
Nd:Yag
NPRO
PBS
PD
PD
II. Thermal noise and SQL
Frequency stabilisation
Zerodur reference cavity:
Stand-off plates
Finesse 6000
for eddy-current
damping
Suspended via two steel wire loops
from Marval18 cantilever springs
in high-vacuum envelope
Total loop gain
104
Gain
103
102
101
100
10-1
102
103
104
Frequency [Hz]
105
II. Thermal noise and SQL
Experimental layout
Uncoated
wedge
Isolator
Phase
Modulator
PD
P = 5e-7 mbar
l/4
F = 6000
Reference
Cavity
l/4
Flexure
PBS
P = 1e-6 mbar
500 mW
Nd:Yag
NPRO
PBS
PD
PD
II. Thermal noise and SQL
Upper mass
3 kg
Euler buckles
Rocking stage
50 kg
Euler buckels
Penultimate mass
9 kg
II. Thermal noise and SQL
~ 3.5 m
Suspended breadboard (35kg)
Test cavity
Preliminary results
-12
10
Test cavity spectrum
-13
10
Viscous damping Q=1550
-14
10
Laser frequency noise
-15
10
-16
10
Detection noise
-17
10
1
10
2
10
3
10
Frequency [Hz]
4
10
5
10
II. Thermal noise and SQL
Magnification 100 X
Preliminary results
-12
10
-13
10
Viscous damping Q=1550
-14
10
-15
10
-16
10
-17
10
1
10
2
10
3
10
Frequency [Hz]
4
10
5
10
II. Thermal noise and SQL
New Suspension Stage
Summary TN and SQL
• Measured thermal noise of a viscous damped system with Q=1550
• Move on to system with Q=45,000: structural damping?
Rel. Amplitude
Amplitude
6
4
2
0
-2
-4
-6
0
50
100
100
150
200
200
250
Time [s]
300
350
300
400
45
400
Time [s]
Towards the SQL:
• Design of torsion balance of about 1g to couple optical fluctuations to displacement
This opto-mechanical coupler will be based on a thin fused silica fiber
Design study based on 100 µm steel wire
• Study of coating-free mirrors based on total internal reflection
to avoid coating thermal noise
•This torsion balance will be incorporated into arm-cavity Michelson interferometer
SQL
II. Thermal noise and SQL