A squeezed-light source generates of squeezing before any loss

PHYSICS · Multi-part · Fermi University Physics · Quantum Information & Technology · Physical realizations and quantum technologies · Physical realizations and quantum technologies

Quantum Information and Technology, Ch Quantum metrology and sensing

Problem

A squeezed-light source generates

12\,\mathrm{dB}

of squeezing before any loss, and the total detection efficiency from source to detector is

\eta=0.8

. ((a)) Find the source's squeeze parameter

r

and the squeezed quadrature's variance ratio

V_{\rm sq}/V_{\rm vac}

. ((b)) Using

V_{\rm out}/V_{\rm vac}=\eta\,V_{\rm sq}/V_{\rm vac}+(1-\eta)

, find the variance ratio actually observed after loss, and the squeezing this represents in decibels. ((c)) An interferometer's phase uncertainty scales as

\sqrt{V_{\rm out}/V_{\rm vac}}

relative to the unsqueezed (vacuum-limited) value. Find this factor, and state it as a plain reduction (for example "a twofold reduction"). ((d)) Find the detection efficiency

\eta

that would be needed to observe

8\,\mathrm{dB}

of squeezing from this same

12\,\mathrm{dB}

source. ((e)) Find the ceiling on the observed squeezing, in decibels, that no source however good could beat at

\eta=0.8

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