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arXiv:quant-ph/0408194

A Single Photon Source With Linear Optics and Squeezed States

Casey R. Myers, Marie Ericsson, Raymond Laflamme

Published Aug 31, 2004• 2 citations
arXivHTMLPDF

Abstract

Quantum information processing using photons has recently been stimulated by the suggestion to use linear optics, single photon sources and detectors. The recent work by Knill has also shown that errors in photon detectors leads to a high error rate threshold (around 29%). An important missing element are good single photon sources. In this paper we show how to make a single photon source using squeezed states, linear optics and conditional measurement. We use degenerate squeezed vacuum states, in contrast to the normal non-degenerate squeezed vacuum states used for single photon production. We show that we can get a photon with certainty when detectors click appropriately, the last event happening up to around 25% of the time. We also show the robustness of this method with respect to a variety of potential imperfections.

DOI
10.48550/arxiv.quant-ph/0408194

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Quantum information processing using photons has recently been stimulated by the suggestion to use linear optics, single photon sources and detectors. The recent work by Knill has also shown that errors in photon detectors leads to a high error rate threshold (around 29%). An important missing element are good single photon sources. In this paper we show how to make a single photon source using squeezed states, linear optics and conditional measurement. We use degenerate squeezed vacuum states, in contrast to the normal non-degenerate squeezed vacuum states used for single photon production. We show that we can get a photon with certainty when detectors click appropriately, the last event happening up to around 25% of the time. We also show the robustness of this method with respect to a variety of potential imperfections.
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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.
Non-classical squeezed states of light are becoming increasingly important to a range of metrology and other quantum optics applications in cryptography, quantum computation and biophysics. Applications such as improving the sensitivity of advanced gravitational wave detectors and the development of space-based metrology and quantum networks will require robust deployable vacuum-compatible sources. To date non-linear photonics devices operated under high vacuum have been simple single pass systems, testing harmonic generation and the production of classically correlated photon pairs for space-based applications. Here we demonstrate the production under high-vacuum conditions of non-classical squeezed light with an observed 8.6 dB of quantum noise reduction down to 10 Hz. Demonstration of a resonant non-linear optical device, for the generation of squeezed light under vacuum, paves the way to fully exploit the advantages of in-vacuum operations, adapting this technology for deployment into new extreme environments.
Single photons are the smallest excitation states of the elctromagnetic field. They can be experimentally created but there is no apparatus that performs this task with 100% efficiency. Many techniques and theorems of optical quantum information theory use single photons. In order to utilize them for information processing, it is reasonable to know if they had been successfully produced. In other words: One needs heralded single photons. How to achieve this, is the main result of this diploma thesis. The task has been to improve the efficiency of already existing single photon sources. An apparatus had to be found which postprocesses the output of such sources in order to either herald the photons or at least to improve the efficiency. This apparatus is explicitly allowed to use other optical sources, for example coherent states (laser). The situation has been formally represented by the assumption that single photon sources produce a mixture of vacuum and the single photon state. 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This mixture propagates through a Mach-Zehnder interferometer. The interferometer is adjusted such that it is transparent for incoming light. In addition to the interferometer alone a two-photon absorbing medium is placed in one of its arms. For this reason there is a chance that the two-photon contribution entering the interferometer is absorbed within this medium. We cannot exclude this unfortunate case. A detector is placed in one of the two output modes. The interferometer is adjusted such that the single photon state does not leave in the mode in which the detector is placed, but always in the other mode. The detector can only click if the two-photon state propagates through the interferometer and if it is not destroyed in the absorbing medium. If the detector then receives one photon it is obvious that another one must leave in the other mode. The whole phenomenon is very similar to the concept of null measurement. 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