Abstract
We describe an experiment in which photon pairs from a pulsed parametric down-conversion (PDC) source were coupled into single-mode fibers with heralding efficiencies as high as 70%. Heralding efficiency or mode preparation efficiency is defined as the probability of finding a photon in a fiber in a definite state, given the detection of its twin. Heralding efficiencies were obtained for a range of down-conversion beam-size configurations. Analysis of spatial and spectral mode selection, and their mutual correlation, provides a practical guide for engineering PDC-produced single photons in a definite mode and spectral emission band. The spectrum of the heralded photons were measured for each beam configuration, to determine the interplay between transverse momentum and spectral entanglement on the preparation efficiency.
Highlights
Parametric down-conversion (PDC) is known to produce a quantum state of light with a two-photon field description [1, 2]
We note that if a photon-number resolving detector were used as the herald detector, the analysis presented here would apply to a heralded source of multi-photons as well
We used a spectral filter F1 centered at 789.3 nm with full width half maximum (FWHM) of 5 nm in the heralding channel to obtain the best heralding efficiency
Summary
Parametric down-conversion (PDC) is known to produce a quantum state of light with a two-photon field description [1, 2]. The prepared state will be pure only if we project the first PDC photon (called the heralding photon) into a single mode. Recent studies target applications based on PDC, such as quantum metrology [5] and quantum information [6, 7] that work by preparing one photon by measuring its twin. To optimize this process, it is crucial to properly define and measure the efficiency of that preparation
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