Beating the standard quantum limit: Phase super-sensitivity of N-photon interferometers

Abstract

Quantum metrology promises greater sensitivity for optical phase measurements than could ever be achieved classically. Here we present a theory of the phase sensitivity for the general case where the detection probability is given by an $N$ photon interference fringe. We find that the phase sensitivity has a complex dependence on both the intrinsic efficiency of detection $\eta$ and the interference fringe visibility $V$. Most importantly, the phase that gives maximum phase sensitivity is in general not the same as the phase at which the slope of the interference fringe is a maximum, as has previously been assumed. We determine the parameter range where quantum enhanced sensitivity can be achieved. In order to illustrate these theoretical results, we perform a four photon experiment with $\eta =3/4$ and $V=82\pm 6$% (an extension of our previous work [Science \textbf{316}, 726 (2007)]) and find a phase sensitivity 1.3 times greater than the standard quantum limit at a phase different to that which gives maximum slope of the interference fringe.

submitted for publication Oct 2007, 5pages, 3figures

References in corpus (4)

• Beating the Standard Quantum Limit with Four Entangled Photons
• Entanglement-free Heisenberg-limited phase estimation
• Phase detection at the quantum limit with multi-photon Mach-Zehnder interferometry
• Multiphoton path entanglement by non-local bunching

Cited by in corpus (2)

• Manipulating multi-photon entanglement in waveguide quantum circuits
• All path-symmetric pure states achieve their maximal phase sensitivity in conventional two-path interferometry