Abstract
Quantum phenomena such as entanglement can improve fundamental limits on the sensitivity of a measurement probe. In optical interferometry, a probe consisting of N entangled photons provides up to a sqrt{N} enhancement in phase sensitivity compared to a classical probe of the same energy. Here, we employ high-gain parametric down-conversion sources and photon-number-resolving detectors to perform interferometry with heralded quantum probes of sizes up to N = 8 (i.e. measuring up to 16-photon coincidences). Our probes are created by injecting heralded photon-number states into an interferometer, and in principle provide quantum-enhanced phase sensitivity even in the presence of significant optical loss. Our work paves the way toward quantum-enhanced interferometry using large entangled photonic states.
Highlights
IntroductionOptical interferometry provides a means to sense very small changes in the path of a light beam
Optical interferometry provides a means to sense very small changes in the path of a light beam. These changes may be induced by a wide range of phenomena, from pressure and temperature variations that impact refractive index, to modifications of the space-time metric that characterize gravitational waves
We address a number of key challenges in order to scale-up quantum-enhanced interferometry using definite photon-number states of light
Summary
Optical interferometry provides a means to sense very small changes in the path of a light beam. These changes may be induced by a wide range of phenomena, from pressure and temperature variations that impact refractive index, to modifications of the space-time metric that characterize gravitational waves. The uncertainty Δφ in a measurement of this phase difference is limited fundamentally by the quantum noise of the illuminating light beams. This noise can be reduced by employing light exhibiting nonclassical properties such as entanglement and squeezing in order to improve the sensitivity of an interferometer beyond classical limits[1]. Quantum states of light are most effective when it is desirable to maximize the phase sensitivity per photon inside an interferometer, such as in gravitational wave detectors[2,3] or when characterizing delicate photosensitive samples[4–8]
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