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ChemPhysChem

True Single Photons at Room Temperature

Karl Otto Greulich

Published Sep 17, 2001• 0 citations
Publisher

Abstract

Textbooks on quantum mechanics suggest that single photons, badly needed to prove models of quantum electrodynamics and quantum cryptography, can be generated by attenuated multimolecule light sources. However, this is not possible, since such sources generate wavetrains. Only recently, true single-photon sources have been made available by groups in the US, Japan and France. The Stanford room temperature source, based on single terrylene molecules, is described in some detail.

DOI
10.1002/1439-7641(20010917)2:8/9<515::aid-cphc515>3.0.co;2-9

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Textbooks on quantum mechanics suggest that single photons, badly needed to prove models of quantum electrodynamics and quantum cryptography, can be generated by attenuated multimolecule light sources. However, this is not possible, since such sources generate wavetrains. Only recently, true single-photon sources have been made available by groups in the US, Japan and France. The Stanford room temperature source, based on single terrylene molecules, is described in some detail.
In the past, generation of single photons for subsequent use in physical or physicochemical experiments was difficult. In the last few years the situation has changed dramatically. Now, such sources based on a number of different techniques are available. Two of them produce antibunching photons by controlled recombination of electrons and holes in semiconductor heterojunctions. A second type of source is based on indium-arsenide quantum dots in high Q factor microcavities. Two further sources use single dibenz-anthanthrene or single terrylene molecules. While all but one sources have to be operated at temperatures close to zero Kelvin, the terrylene source works at room temperature and provides up to 10 billion photons before photodecay, i.e. it can be operated for hours. When the latter is operated at zero Kelvin, it is even more stable and can be used in a microscope to generate complete images. The present review compares and summarizes properties of these single optical photon sources and, in addition, tries to present an argument, why single photons cannot be particle like objects but must have a spatial extension of at least several tens of nanometers.
Crucial experiments of physics, such as the quantum mechanical version of the double slit experiment, have so far not been performed with true single (antibunching) photons. Instead, attenuated classical light sources such as bulbs or lasers have been suggested to provide the photons in these experiments. Since attenuators do not change photon statistics, i.e. do not convert classical into non - classical light, reliable single photon beams cannot be generated on this way. Antibunching sources, for example single molecules, are required. Due to the lack of such sources in the past, some extrapolations from the many - photon case to the one photon case have remained speculative, for example the long wavetrain model for a single photon. Alternative hypotheses, elaborated by considering details of the emission of single photons by single molecules are equally probable. Arguments are presented which disfavour the wavetrain model and favour the short pulse as a model for a photon.
Single molecules in suitable host crystals have been demonstrated to be useful single-photon emitters both at liquid-helium temperatures and at room temperature. The low-temperature source achieved controllable emission of single photons from a single terrylene molecule in p -terphenyl by an adiabatic rapid passage technique. In contrast with almost all other single-molecule systems, terrylene single molecules show extremely high photostability under continuous, high-intensity irradiation. A room-temperature source utilizing this material has been demonstrated, in which fast pumping into vibrational sidebands of the electronically excited state achieved efficient inversion of the emissive level. This source yielded a single-photon emission probability p (1) of 0.86 at a detected count rate near 300 000 photons s −1 , with very small probability of emission of more than one photon. Thus, single molecules in solids can be considered as contenders for applications of single-photon sources such as quantum key distribution.
The ability to generate single photons on demand is one of the most crucial tasks in quantum optics. Such a photon source could be used in quantum cryptography where each bit of information is encoded on a single photon, or to make quantum logic gates. Now two teams of researchers from Germany and France have shown that certain defects within synthetic diamond can emit single photons at room temperature. Moreover, these solid-state devices have a high quantum efficiency and could potentially be miniaturized – making them ideal candidates as single-photon sources for practical applications (C Kurtsiefer et al. 2000 Phys. Rev. Lett.85 290, R Broui et al.. xxx.lanl.gov/abs/quant-ph/0007032).
It is safe to say that, when the concept of the photon was first introduced, the generation of single photons was not being considered. Until the emergence of the ideas and methods of quantum optics, the `single-photon regime' was attained by strongly attenuating a laser beam to ensure that the probability of having more than one photon became negligible. However, such attenuated beams differ from `true' single photons in at least two respects: first, the vacuum probability is much higher than the probability of detecting a photon, so one gets predominantly a `no-photon' regime with occasional detection of a photon; second, the probability of getting two photons is never zero, but essentially follows a Poisson law. Although the weak beam has been useful in quantum optics, the advent of quantum information science has placed stringent demands on optical sources, namely that sources produce single photons either on demand or heralded. In particular secure quantum cryptography and linear optical quantum computing depend on the availability of such single-photon sources. The combination of strict requirements for single photons, plus new technologies, is driving an exciting research effort into single-photon generation. This Focus Issue recognizes that single-photon sources are rapidly developing and presents research articles covering the spectrum of activity in the field. Significant advances are reported for single-photon and photon-pair sources constructed from quantum dots in pillar microcavities, parametric down converters, falling neutral atoms and trapped ions in cavities, defects in diamond nanocrystals and a single molecule in a solid. In addition to producing single-photon pulses, one article reports on the latest developments regarding the production of photon number states in a microwave cavity. Another article discusses the application of a nitrogen-vacancy-based single-photon source to an experimental demonstration of quantum key distribution in open air. Photodetection performs a critical role in assessing single-photon sources as well as heralding the arrival of a single photon based on detecting a correlated partner, and this issue presents the latest results on single-photon counting with a superconducting niobium nitride hot-electron bolometer. Another article provides a detailed study of how to characterize single-photon sources via intensity noise analyses. Photodetection is also important for post-selection-based processing for non-deterministic quantum information tasks, and this issue presents an analysis of photodetection and post-selection used in another way: enhancing the efficiency of single-photon sources by interferometry, photodetection and post-selection. New Journal of Physics appreciates the rapid pace of development in the area of single photons on demand. This Focus Issue presents the latest developments and also points to a bright future with better photon sources. Focus on Single Photons on Demand Contents Photon statistics characterization of a single-photon source R Alleaume, F Treussart, J-M Courty and J-F Roch Photon statistics of a non-stationary periodically driven single-photon source M Hennrich, T Legero, A Kuhn and G Rempe On the measurement of two-photon single-mode coupling efficiency in parametric down-conversion photon sources S Castelletto, I P Degiovanni, A Migdall and M Ware Single-photon sources based on single molecules in solids W E Moerner Single-photon generation with InAs quantum dots Charles Santori, David Fattal, Jelena Vuckovic, Glenn S Solomon and Yoshihisa Yamamoto Visible single-photon generation from semiconductor quantum dots Thomas Aichele, Valery Zwiller and Oliver Benson Enhanced correlated photon pair emission from a pillar microcavity M Benyoucef, S M Ulrich, P Michler, J Wiersig, F Jahnke and A Forchel Experimental open-air quantum key distribution with a single-photon source R Alleaume, F Treussart, G Messin, Y Dumeige, J-F Roch, A Beveratos, R Brouri-Tualle, J-P Poizat and P Grangier Post-processing with linear optics for improving the quality of single-photon sources Dominic W Berry, Stefan Scheel, Casey R Myers, Barry C Sanders, Peter L Knight and Raymond Laflamme A single-photon source based on a single Ca+ ion Christian Maurer, Christoph Becher, Carlos Russo, Jurgen Eschner and Rainer Blatt A calcium ion in a cavity as a controlled single-photon source M Keller, B Lange, K Hayasaka, W Lange and H Walther Quantum optics with single quantum dot devices Valery Zwiller, Thomas Aichele and Oliver Benson The creation and detection of arbitrary photon number states using cavity QED Benjamin T H Varcoe, Simon Brattke and Herbert Walther Stable single-photon source in the near infrared T Gaebel, I Popa, A Gruber, M Domhan, F Jelezko and J Wrachtrup Colloidal CdSe/ZnS quantum dots as single-photon sources X Brokmann, G Messin, P Desbiolles, E Giacobino, M Dahan and J P Hermier Towards a periodic deterministic source of arbitrary single-photon states Evan Jeffrey, Nicholas A Peters and Paul G Kwiat Fabrication of a superconducting niobium nitride hot electron bolometer for single-photon counting R Romestain, B Delaet, P Renaud-Goud, I Wang, C Jorel, J-C Villegier and J-Ph Poizat High-quality asynchronous heralded single-photon source at telecom wavelength Sylvain Fasel, Olivier Alibart, Sebastien Tanzilli, Pascal Baldi, Alexios Beveratos, Nicolas Gisin and Hugo Zbinden Philippe Grangier, Institut d'Optique Theorique et Appliquee, Orsay, France Barry Sanders, University of Calgary, Canada Jelena Vuckovic, Stanford University, CA, USA
Quantum Key Distribution (QKD) allows the distribution of cryptographic keys between multiple users in an information-theoretic secure way, exploiting quantum physics. While current QKD systems are mainly based on attenuated laser pulses, deterministic single-photon sources could give concrete advantages in terms of secret key rate (SKR) and security owing to the negligible probability of multi-photon events. Here, we introduce and demonstrate a proof-of-concept QKD system exploiting a molecule-based single-photon source operating at room temperature and emitting at 785nm. With an estimated SKR of 0.5 Mbps, our solution paves the way for room-temperature single-photon sources for quantum communication protocols.