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arXiv:quant-ph/0510113 · Physical Review A

Heralded single-photon generation using imperfect single-photon sources and a two-photon-absorbing medium

Thomas Konrad, Artur Scherer, Michael Nock, Jürgen Audretsch

Published Mar 21, 2006• 7 citations
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Abstract

We propose a setup for a heralded, i.e., announced generation of a pure single-photon state given two imperfect sources whose outputs are represented by mixtures of the single-photon Fock state $\ensuremath{\mid}1⟩$ with the vacuum $\ensuremath{\mid}0⟩$. Our purification scheme uses beam splitters, photodetection, and a two-photon-absorbing medium. The admixture of the vacuum is fully eliminated. We discuss two potential realizations of the scheme.

DOI
10.1103/physreva.73.032327

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We propose a setup for a heralded, i.e., announced generation of a pure single-photon state given two imperfect sources whose outputs are represented by mixtures of the single-photon Fock state \ensuremath∣1⟩\ensuremath{\mid}1⟩\ensuremath∣1⟩ with the vacuum \ensuremath∣0⟩\ensuremath{\mid}0⟩\ensuremath∣0⟩. Our purification scheme uses beam splitters, photodetection, and a two-photon-absorbing medium. The admixture of the vacuum is fully eliminated. We discuss two potential realizations of the scheme.
Realistic single-photon sources do not generate single photons with certainty. Instead they produce statistical mixtures of photons in Fock states $\ensuremath{\mid}1⟩$ and vacuum (noise). We describe how to eliminate the noise in the output of the sources by means of another noisy source or a coherent state and cross-phase-modulation (XPM). We present a scheme that announces the production of pure single photons and thus eliminates the vacuum contribution. This is done by verifying a XPM-related phase shift with a Mach-Zehnder interferometer.
Triggered single-photon sources produce the vacuum state with nonzero probability, but produce a much smaller multiphoton component. It is therefore reasonable to approximate the output of these photon sources as a mixture of the vacuum and single-photon states with probabilities $1\ensuremath{-}p$ and ppp, respectively. Here we are concerned with increasing the efficiency ppp by directing multiple copies of the single-photon-vacuum mixture into a linear optical device and applying photodetection on some outputs. We prove that it is impossible, under certain conditions, to increase ppp via linear optics and conditional preparation based on photodetection. We also establish a class of photodetection events for which ppp can be improved, although with an added multiphoton component. In addition we prove that it is not possible to obtain perfect single-photon states via this method from imperfect (p<1)(p<1)(p<1) inputs.
We propose a heralded single-photon source based on injecting a superposition of oppositely squeezed states onto a beam splitter. Our superposition of squeezed states is composed of only even photon number states (the number of photons is equal to 2,6,10,...2,6,10,...2,6,10,...) meaning the probability for an emitted single photon given as a heralded single-photon event is higher than what one can achieve from the usual two-mode squeezed state. This enables one to realize an enhanced heralded single-photon source. We discuss how to create this superposition of squeezed states utilizing a single-mode squeezed state and the cross-Kerr nonlinearity. Our proposed method significantly improves the probability of emitting the heralded single photon compared to spontaneous parametric down-conversion.
Sources of single photons in pure quantum states are essential to many quantum optics applications. We explore a technique, known as group-velocity matching, that enables the heralded generation of pure single photons through nonlinear optical processes. It reduces or eliminates the requirement of spectral filtering that conventional sources rely on to achieve high purity, therefore increasing both heralding efficiency and photon flux. Implementation in both spontaneous parametric downconversion and spontaneous four-wave mixing is studied as we discuss several recent experimental realizations demonstrating purity of more than 0.84 for the heralded photons.
The interaction between single or a fixed number of photons with a single absorber is of fundamental interest in quantum technology. The harnessing of light matter interactions at the single particle limit has several potential applications ranging from quantum communication and quantum metrology to quantum imaging. In this letter, a setup for heralded two-photon absorption at the single absorber level is proposed. The setup is based on a heralded two-photon source utilizing spontaneous parametric down-conversion, entanglement swapping and sum frequency generation for joint detection. The feasibility of the scheme is discussed by reviewing recent achievements in utilizing entangled and correlated photons for two-photon absorption as well as single photon absorption experiments at the limit of single absorbers in the context of applications in imaging (here mainly microscopy) and spectroscopy.
We propose a scheme based on the multiplexing of heralded multiphoton sources for the generation of multiphoton Fock states. We theoretically analyze the performance of multiplexed multiphoton sources based on output-extended incomplete binary-tree multiplexers. We show that this system can be used to generate multiphoton states with considerably higher multiphoton probabilities than those that can be achieved with a single heralded multiphoton source. For multiplexed two-photon sources, we present detailed results on the optimization of the mean number of photon pairs generated in the heralded sources and the number of multiplexed units, which are relevant for the experimental realization.