A direct approach to realising quantum filters for high-precision measurements. (arXiv:2002.07644v5 [quant-ph] UPDATED)
<a href="http://arxiv.org/find/quant-ph/1/au:+Bentley_J/0/1/0/all/0/1">Joe Bentley</a>, <a href="http://arxiv.org/find/quant-ph/1/au:+Nurdin_H/0/1/0/all/0/1">Hendra Nurdin</a>, <a href="http://arxiv.org/find/quant-ph/1/au:+Chen_Y/0/1/0/all/0/1">Yanbei Chen</a>, <a href="http://arxiv.org/find/quant-ph/1/au:+Miao_H/0/1/0/all/0/1">Haixing Miao</a>

Quantum noise sets a fundamental limit to the sensitivity of high-precision
measurements. Suppressing it can be achieved by using non-classical states and
quantum filters, which modify both the noise and signal response. We find a
novel approach to realising quantum filters directly from their
frequency-domain transfer functions, utilising techniques developed by the
quantum control community. It not only allows us to construct quantum filters
that defy intuition, but also opens a path towards the systematic design of
optimal quantum measurement devices. As an illustration, we show a new optical
realisation of an active unstable filter with anomalous dispersion, proposed
for improving the quantum-limited sensitivity of gravitational-wave detectors.

Quantum noise sets a fundamental limit to the sensitivity of high-precision
measurements. Suppressing it can be achieved by using non-classical states and
quantum filters, which modify both the noise and signal response. We find a
novel approach to realising quantum filters directly from their
frequency-domain transfer functions, utilising techniques developed by the
quantum control community. It not only allows us to construct quantum filters
that defy intuition, but also opens a path towards the systematic design of
optimal quantum measurement devices. As an illustration, we show a new optical
realisation of an active unstable filter with anomalous dispersion, proposed
for improving the quantum-limited sensitivity of gravitational-wave detectors.

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