The performance of optical measurement systems is ultimately limited by the
quantum nature of light. In this thesis, two techniques for circumventing the
standard quantum measurement limits are modelled and tested experimentally.
These techniques are electro-optic control and the use of squeezed light.
An optical parametric amplifier is used to generate squeezing at
1064nm. The parametric amplifier is pumped by the output of a second
harmonic generation cavity, which in turn is pumped by a Nd:YAG laser.
By using various frequency locking techniques, the quadrature phase of
the squeezing is stabilised, therefore making our squeezed source
suitable for long term measurements. The best recorded squeezing is
5.5dB (or 70\%) below the standard quantum limit. The stability of
our experiment makes it possible to perform a time domain measurement
of photocurrent correlations due to squeezing. This technique allows
direct visualisation of the quantum correlations caused by squeezed
light.
On the road to developing our squeezed source, methods of frequency
locking optical cavities are investigated. In particular, the tilt
locking method is tested on the second harmonic generation cavity
used in the squeezing experiment. The standard method for locking
this cavity involves the use of modulation sidebands, therefore leading to a
noisy second harmonic wave. The modulation free tilt-locking method,
which is based on spatial mode interference, is shown to be a
reliable alternative.
In some cases, electro-optic control may be used to suppress quantum
measurement noise. Electro-optic feedback is investigated as a method
for suppressing radiation pressure noise in an optical cavity.
Modelling shows that the `squashed' light inside a feedback loop can
reduce radiation pressure noise by a factor of two below the standard
quantum limit. This result in then applied to a thermal noise
detection system. The reduction in radiation pressure noise is shown
to give improved thermal noise sensitivity, therefore proving that
the modified noise properties of light inside a feedback loop can be
used to reduce quantum measurement noise.
Another method of electro-optic control is electro-optic feedforward.
This is also investigated as a technique for manipulating quantum
measurements. It is used to achieve noiseless amplification of a
phase quadrature signal. The results clearly show that a feedforward
loop is a phase sensitive amplifier that breaks the quantum limit for
phase insensitive amplification. This experiment is the first
demonstration of noiseless phase quadrature amplification.
Finally, feedforward is explored as a tool for improving the
performance of quantum nondemolition measurements. Modelling shows
that feedforward is an effective method of increasing signal transfer
efficiency. Feedforward is also shown to work well in conjunction with
meter squeezing. Together, meter squeezing and feedforward provide a
comprehensive quantum nondemolition enhancement package. Using the
squeezed light from our optical parametric amplifier, an experimental
demonstration of the enhancement scheme is shown to achieve record
signal transfer efficiency of $T_{s}+T_{m}=1.81$.
| Identifer | oai:union.ndltd.org:ADTP/216724 |
| Date | January 2002 |
| Creators | Buchler, Benjamin Caird, ben.buchler@anu.edu.au |
| Publisher | The Australian National University. Faculty of Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.anu.edu.au/legal/copyright/copyrit.html), Copyright Benjamin Caird Buchler |
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