This chapter reviews the characteristic figure of merits of the deterministic single-photon source (SPS) based on a quantum emitter in a semiconductor solid-state system. SPS is a solid-state device capable of emitting single photons on demand. The most fundamental characteristic of the SPS is that it should emit only one photon at a time. This ability is tested in the so-called Hanbury, Brown, and Twiss experiment. A second characteristic for the SPS is that the emitted photons should be quantum mechanically indistinguishable, meaning that the emitted photons should have the same wavelength, phase variation across the pulse, polarization, optical mode profile, etc. The third important characteristic of the SPS is its efficiency or brightness. The ideal SPS should be deterministic and provide single photons on demand. It should act as a "single-photon gun" such that every trigger releases exactly one photon into the collection optics. A major workhorse for generating single photons has been the spontaneous parametric down-conversion process.
This chapter reviews the characteristic figure of merits of the deterministic single-photon source (SPS) based on a quantum emitter in a semiconductor solid-state system. SPS is a solid-state device capable of emitting single photons on demand. The most fundamental characteristic of the SPS is that it should emit only one photon at a time. This ability is tested in the so-called Hanbury, Brown, and Twiss experiment. A second characteristic for the SPS is that the emitted photons should be quantum mechanically indistinguishable, meaning that the emitted photons should have the same wavelength, phase variation across the pulse, polarization, optical mode profile, etc. The third important characteristic of the SPS is its efficiency or brightness. The ideal SPS should be deterministic and provide single photons on demand. It should act as a "single-photon gun" such that every trigger releases exactly one photon into the collection optics. A major workhorse for generating single photons has been the spontaneous parametric down-conversion process.
The article surveys the state of the art in the design, development and application of devices for deterministically generating single photons on demand. Both the defined function and requisite form of such ‘single-photon’ sources are explained in detail. Their attributes and characteristics, in particular the photon-counting statistics of the light that they generate, are presented in conjunction with the experimental apparatus (most notably the Hanbury-Brown and Twiss interferometer) for measuring them. Promising applications of single-photon sources within quantum key distribution, quantum information processing, as well as metrology and fundamental tests of quantum mechanics, are described. The utility and relative advantages of single-photon sources vis-á-vis more conventional sources of light are explained in terms of application-specific requirements and the respective abilities of different sources to fulfil them. The article collects, classifies and sorts the most significant work towards realizing practical single-photon sources to date. Though emanating from a diverse set of technological disciplines, with different research and application objectives in mind, the relative advantages and drawbacks of each approach are assessed, to give the reader a broad yet coherent and critical review of a rapidly developing research front.
Single-photon sources (SPS) play a key-role in many applications, spanning from quantum metrology, to quantum information and to the foundations of quantum mechanics. Even if an ideal SPS (i. e. emitting indistinguishable, ”on-demand” single photons, at an arbitrarily fast repetition rate) is far to be realized due to real-world deviations from the ideality, much effort is currently devoted to improving the performance of real sources. With regards to the emission probability, it appears natural to employ sources that are in principle deterministic in the single- photon emission (single quantum emitters such as single atoms, ions, molecules, quantum dots, or color centers in diamond) as opposed to probabilistic ones (usually heralded SPS based on parametric down-conversion). We present an overview of our latest results concerning a work-in-progress NIR pulsed single photon source based on single quantum emitters (color centers in diamond) exploiting recently reported centers. They are particularly interesting because of the narrow emission line (tipically less than 5 nm), the shorter excited state lifetime with respect to NV centres (1 - 2 ns compared to 12 ns, allowing a ten-fold photon emission rate upon saturation) and the polarized emission.
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.
Solid-state sources capable of emitting single photons on demand are of great interest in quantum information applications. Ideally, such a source should emit exactly one photon into the collection optics per trigger, the emitted photons should be indistinguishable, and the source should be electrically driven. Several design strategies addressing these requirements have been proposed. In the cavity-based source, light emission is controlled using resonant cavity quantum electrodynamics effects, whereas in the waveguide-based source, broadband electric field screening effects are employed to direct the light emission into the optical mode of interest. For all the strategies, accurate modeling and careful optical engineering is required to achieve high performance. In this study, we discuss the models and numerical techniques used to analyze such structures. The physical effects governing the light emission profile and the possibilities of tailoring it as well as the mechanisms governing the coherence are elucidated. The major design strategies pursued to optimize the single-photon source performance and the remaining challenges are reviewed.
Solid-state sources capable of emitting single photons on demand are of great interest in quantum information applications. Ideally, such a source should emit exactly one photon into the collection optics per trigger, the emitted photons should be indistinguishable and the source should be electrically driven. Several design strategies addressing these requirements have been proposed. In the cavity-based source, light emission is controlled using resonant cavity quantum electrodynamics effects, whereas in the waveguide-based source, broadband electric field screening effects are employed to direct the light emission into the optical mode of interest. For all the strategies, accurate modeling and careful optical engineering is required to achieve high performance.
The desiderata for an ideal photon source are high brightness, high single-photon purity, and high indistinguishability. Defining brightness at the first collection lens, these properties have been simultaneously demonstrated with solid-state sources, however absolute source efficiencies remain close to the 1% level, and indistinguishability only demonstrated for photons emitted consecutively on the few nanosecond scale. Here we employ deterministic quantum dot-micropillar devices to demonstrate solid-state single-photon sources with scalable performance. In one device, an absolute brightness at the output of a single-mode fibre of 14% and purities of 97.1-99.0% are demonstrated. When non-resontantly excited, it emits a long stream of photons that exhibit indistinguishability up to 70%---above the classical limit of 50%---even after 33 consecutively emitted photons, a 400 ns separation between them. Resonant excitation in other devices results in near-optimal indistinguishability values: 96% at short timescales, remaining at 88% in timescales as large as 463 ns, after 39 emitted photons. The performance attained by our devices brings solid-state sources into a regime suitable for scalable implementations.