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Reports on Progress in Physics

Single-photon sources

Brahim Lounis, Michel Orrit

Published Apr 21, 2005• 908 citations
Publisher

Abstract

The concept of the photon , central to Einstein's explanation of the photoelectric effect, is exactly 100 years old. Yet, while photons have been detected individually for more than 50 years, devices producing individual photons on demand have only appeared in the last few years. New concepts for single-photon sources, or 'photon guns', have originated from recent progress in the optical detection, characterization and manipulation of single quantum objects. Single emitters usually deliver photons one at a time. This so-called antibunching of emitted photons can arise from various mechanisms, but ensures that the probability of obtaining two or more photons at the same time remains negligible. We briefly recall basic concepts in quantum optics and discuss potential applications of single-photon states to optical processing of quantum information: cryptography, computing and communication. A photon gun's properties are significantly improved by coupling it to a resonant cavity mode, either in the Purcell or strong-coupling regimes. We briefly recall early production of single photons with atomic beams, and the operation principles of macroscopic parametric sources, which are used in an overwhelming majority of quantum-optical experiments. We then review the photophysical and spectroscopic properties and compare the advantages and weaknesses of various single nanometre-scale objects used as single-photon sources: atoms or ions in the gas phase and, in condensed matter, organic molecules, defect centres, semiconductor nanocrystals and heterostructures. As new generations of sources are developed, coupling to cavities and nano-fabrication techniques lead to improved characteristics, delivery rates and spectral ranges. Judging from the brisk pace of recent progress, we expect single photons to soon proceed from demonstrations to applications and to bring with them the first practical uses of quantum information.

DOI
10.1088/0034-4885/68/5/r04

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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.

Single Molecules•Mar 1, 2001•13 citations
The concept of the photon , central to Einstein's explanation of the photoelectric effect, is exactly 100 years old. Yet, while photons have been detected individually for more than 50 years, devices producing individual photons on demand have only appeared in the last few years. New concepts for single-photon sources, or 'photon guns', have originated from recent progress in the optical detection, characterization and manipulation of single quantum objects. Single emitters usually deliver photons one at a time. This so-called antibunching of emitted photons can arise from various mechanisms, but ensures that the probability of obtaining two or more photons at the same time remains negligible. We briefly recall basic concepts in quantum optics and discuss potential applications of single-photon states to optical processing of quantum information: cryptography, computing and communication. A photon gun's properties are significantly improved by coupling it to a resonant cavity mode, either in the Purcell or strong-coupling regimes. We briefly recall early production of single photons with atomic beams, and the operation principles of macroscopic parametric sources, which are used in an overwhelming majority of quantum-optical experiments. We then review the photophysical and spectroscopic properties and compare the advantages and weaknesses of various single nanometre-scale objects used as single-photon sources: atoms or ions in the gas phase and, in condensed matter, organic molecules, defect centres, semiconductor nanocrystals and heterostructures. As new generations of sources are developed, coupling to cavities and nano-fabrication techniques lead to improved characteristics, delivery rates and spectral ranges. Judging from the brisk pace of recent progress, we expect single photons to soon proceed from demonstrations to applications and to bring with them the first practical uses of quantum information.
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
We introduce the basic concepts and characteristic properties of single-photon emitters based on resonator effects in optical cavities, and provide a review of the most prominent implementations. First we discuss the elementary principles of cavity quantum electrodynamics, which determine how single quantum systems couple to the quantised field modes of optical resonators, and then show how to exploit these principles in order to generate single photons on demand. Furthermore, we elucidate how to study the properties of the photons, namely their singleness and their spectral characteristics. In particular, it is explained how to use a Hanbury-Brown and Twiss interferometer to determine whether the photons arrive one-by-one, and how to probe their mutual indistinguishability with two-photon interference experiments of the Hong–Ou–Mandel type. Finally, we present a classification scheme applicable to most cavity-based photon emitters realised to date. This scheme allows us to assess the pros and cons of the most significant approaches – in particular with regard to photonic quantum computing and quantum communication, which are among the most promising applications to date.
Over the past ten years, on-demand single photon generation has been realized in numerous physical systems including neutral atoms, ions, molecules, semiconductor quantum dots, impurities and defects in solids, and superconductor circuits. The motivations for generation and detection of single photons are two-fold: basic and applied science. On the one hand, a single photon plays a central role in the experimental foundation of quantum mechanics and measurement theory. On the other hand, an efficient and high-quality single-photon source is needed to implement quantum key distribution, quantum repeaters and photonic quantum information processing. Written by top authors from academia and industry, this is the only textbook focused on single-photon devices and thus fills the gap for a readily accessible update on the rapid progress in the field.
Due to their quantum nature, single-photon emitters generate individual photons in bursts or streams. They are paramount in emerging quantum technologies such as quantum key distribution, quantum repeaters, and measurement-based quantum computing. Many such systems have been reported in the last three decades, from Rubidium atoms coupled to cavities to semiconductor quantum dots and color centers implanted in waveguides. This review article highlights different material systems with deterministic and controlled single photon generation. We discuss and compare the performance metrics, such as purity and indistinguishability, for these sources and evaluate their potential for different applications. Finally, a new potential single-photon source, based on the Rydberg exciton in solid state metal oxide thin films, is introduced, briefly discussing its promising qualities and advantages in fabricating quantum chips for quantum photonic applications.
The generation of non-classical states of light [1] is an important scientific challenge with many potential applications. For example, squeezed states of light [2] have generated much interest in the past decade, because measurements can be performed with noise levels that are lower than those available with classical light. A particularly novel non-classical source of light is a triggered single-photon source: a source that has the property to emit with a high degree of certainty one (and only one) photon at a user-specified time. Such a deterministic source of single photons can be important for quantum information processing [3], quantum cryptography [4] and certain quantum computation problems [5]. A single quantum emitter such as a molecule or an atom is a good potential source because it can emit only one photon at a time. The emitted light is antibunched [6, 7] and consists of single photons separated by random time intervals, which depend on the excited state lifetime and on the pumping rate. Thus triggered emission of single photons can be obtained with controlled excitation of a single emitter. The first demonstration of a single photons source [8] using a single molecule in a solid is based on a rapid adiabatic passage method [9] to excite the molecule. In the effective spin picture, the Bloch vector follows the driving magnetic field adiabatically if the laser-molecule frequency detuning is swept slowly through the resonance. Since the passage inverts the field, the system goes from the ground to the excited state. From this fluorescent state the molecule can emit only a single photon. The molecular resonance is swept by Stark effect at fixed laser frequency. This is done easily by applying a radio frequency electric field to the molecule. The results showed photon states with statistics that differ radically from those of coherent states. But this method requires cryogenic temperatures (2K) since narrow zero phonon lines are needed for the adiabatic following. At room temperature a source of triggered single photons based on the concept of pulsed optical excitation of a single highly fluorescent molecule has been demonstrated [10]. A short pulse of green laser light pumps the molecule from the ground state to a vibronically excited level of the first electronic excited state. After fast (ps) relaxation to the lowest electronic excited state, the molecule subsequently emits a single photon. A frequency-doubled mode-locked Nd-YAG laser is used to pump highly stable single terrylene molecules contained in a p-terphenyl molecular crystal where they are protected from exposure to diffusing quenchers (such as oxygen). The result shows that the photons are emitted after the laser pulses at times separated by the laser repetition time within the lifetime of terrylene in p-terphenyl. Since the pump pulse width is very short compared to the fluorescence lifetime, the probability of two (or more) photon emission per pulse is always zero. At the maximum laser power, 90% of the laser pulses lead to a single photon emission. The parameters of this source (repetition rate and single photon generation probability) were limited only by the laser system used; nevertheless, this performance already surpasses that of previous work. The high performance combined with the vanishing two photon emission probability and the simplicity of this source suggests that it can be considered for a variety of quantum optical experiments and for secure quantum cryptography [11]. Semiconductor quantum dots (QD) are other potential systems for single photon generation [12]. QDs are often referred to as “artificial atoms” because many of their optical properties, such as ultranarrow transitions, arise from discrete, atomic-like energy levels [13, 14]. To reinforce this analogy a study of the photon antibunching in this system was needed. QDs differ from atoms and molecules since the creation of multiple excitons is possible in QDs. Consequently, if two electron-hole pairs can radiatively recombine, the simultaneous emission of two photons from a QD is then possible. Thus different regimes of photon statistics were expected because the probability of multiple exciton creation depends on excitation intensity. The fluorescence intensity correlation function of a single CdSe quantum dot has been investigated [15] using a coincidence setup (start-stop experiment). A strong photon antibunching has been observed over a large range of intensities (0.1-100 kW/cm2). The lack of coincidence at zero time delay indicates a highly efficient Auger ionization process [16], which suppresses multi-photon emission in these colloidal quantum dots. This result shows that room temperature single photon sources can be achieved with colloidal nanoparticles.
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.