EP1955422A2

EP1955422A2 - Single photon source and method for production and operation thereof

Info

Publication number: EP1955422A2
Application number: EP06818092A
Authority: EP
Inventors: Anatol Lochmann; Robert Seguin; Dieter Bimberg; Sven Rodt; Vladimir Gaysler
Original assignee: Technische Universitaet Berlin
Current assignee: Technische Universitaet Berlin
Priority date: 2005-11-30
Filing date: 2006-11-20
Publication date: 2008-08-13
Also published as: US20100074293A1; WO2007062625A2; US8404506B2; JP5221373B2; DE102005057800B4; WO2007062625A3; DE102005057800A1; JP2009517870A

Abstract

The invention relates, amongst other things, to a method for production of a single photon source (100) with a given operational performance. According to the invention, the given operational performance for the individual photon source (100) may be fixed by a directed setting of the fine structure gap (FSS) of the exciton energy level for at least one quantum dot (160', 520), wherein the at least one quantum dot is produced with a quantum dot size corresponding to the fine structure gap for setting.

Description

description

Single photon source and method for its production and operation

The invention relates to single photon sources and to methods for their production and operation. The term single photon source is understood to mean photon sources which can emit individual photons, in particular with a defined or predefined polarization, entangled photons and cascades of correlated photons.

Single-photon sources include the core element of quantum cryptography. This is far superior to conventional encryption technologies. When exchanging sensitive data, such as at online stores, it offers a total privacy based on the laws of quantum mechanics. First, the data is encrypted using a conventional method. The key with which these can be decoded again is then separated and transmitted, for example, in time before the actual data. When doing so with a single photon source using quantum cryptographic schemes, unauthorized eavesdropping is noticed. Only if the key has been proven not to be intercepted, the encrypted data packet is transmitted in a conventional manner. Thus, even larger amounts of data such as images or films, which are classified as worthy of protection, can be transmitted tap-proof in the usual speed, since the single-photon source is used only for the transmission of the key.

An ideal single photon gun ("photon gun") is a device that emits a single photon ("on demand") after a trigger signal, and only then. The central element of a single-photon source is optimally a quantized system with discrete energy levels. For this example, isolated atoms, molecules or quantum dots in question. Quantum dots offer decisive advantages. Counter ^¬ set to the isolated atom can be the discrete energy levels of a quantum dot non-resonant also stimulate. Embedded in a suitable semiconductor structure can thus realize an electrically operated structure. This is particularly important in terms of marketing potential as system integration is greatly simplified. For an optically excited structure, on the contrary, additional components would be required which would complicate the manufacture and later maintenance of the system and increase the cost.

For the realization of a single photon source, there are a number of approaches in the literature. In the following, three concepts are to be briefly explained from the multitude of published realization possibilities that come into question "at least in principle" for use in quantum cryptography.

One of the previously known concepts pursues the idea of a

Light-emitting diode whose electroluminescence is based on the emission of a single quantum dot (see the following references: Xu, DA Williams, JRA Cleaver, Appl Phys Lett, Vol. 85, No. 15 (11 October 2004); AJ Shields, RM Stevenson , RM Thompson, MB Ward, Z. Yuan, BE Kardynal, P. See, I., Farrer, C. Lobo, K. Cooper, DA Ritchie, Phys. Stat., SoI. (B) 238, No. 2, 353- 359 (2003); J. Seufert, M. Rambach, G. Bacher, A. Forchel, T. Passow, D. Hommel, Appl. Phys. Lett., Vol. 82, No. 22 (June 2, 2003); A. Fiore, JX Chen, M. Ilegems, Appl. Phys. Lett., Vol. 81, No. 10 (02. September 2002) and AJ Bennet, DC Unnitt, P. See, AJ Shields, P. Atkinson, K Cooper, DA Ritchie, Appl. Phys. Lett., Vol. 86, No. 4 (April 25, 2005) Despite the electrical excitation that is preferred for commercial application, this approach is not very satisfactory due to its modest efficiency This has two main causes: Firstly, the lack of preferential direction for the photo- low emission, too low efficiency; on the other, the spontaneous emission rate of Quan ^¬ is tenpunkten due to the relatively long radiative lifetime of the states (~ lns) very low. In addition, the emission is not polarized.

Another previously known concept is based on a resonant coupling of the energetic states of a quantum dot with the modes of a microcavity (see the following references: J. Vuckovic, D. Fattal, C. Santori, GS Solomon, Y. Yamamoto, Appl. Lett., Vol. 82, No. 21 (May 26, 2002); JM Gerad, D. Barrier, JY Marzin, R. Kuszelewicz, L. Manin, E. Costard, V. Thierry-Mig, T. Rivera, Appl Phys. Lett., Vol. 69, No. 4 (June 22, 1996); JM Gerad, D. Barrier, JY Marzin, R. Kuszelewicz, L. Manin, E. Costard, V. Thierry-Mig, T. Lett., Vol. 69, No. 4 (June 22, 1996) and E. Moreau, I. Robert, JM Gerad, I. Abram, L. Manin, V. Thierry-Mieg, Appl. Phys. Lett., Vol. 69, No. 4 (June 22, 1996) This prior art concept utilizes the Purcell effect, which describes the effect of such coupling on the spontaneous emission rate, and overall, because of high optical losses in the microcavity this second-named concept for a single person photon source still in need of much improvement.

A third previously known concept is based on heavily attenuated lasers. To make two-photon pulses unlikely, the laser pulses are attenuated to an intensity less than 0.1 photons per cycle. This limits the maximum data transfer rate, as> 90% of the clocks are "empty." In addition, the error rate is increased, as amplifiers can generate and measure photons, even if the clock was actually "empty". This limitation of gain limits the range of transmission. Furthermore, two-photon pulses can not be completely ruled out. However, such pulses mean a gap in safety, since now a listener by means of a Strahltei- lers can measure a photon and send the second photon on to the receiver (English, photon number splitting - PNS) and so a hearing protection is no longer given. The polarization of the emitted photons is also problematic: if the polarization state is completely uncontrolled, a polarization filter must be connected behind the single-photon source. This further reduces the number of photons and thus the data transmission rate.

Based on the listed prior art, the present invention seeks to provide a method for producing a single photon source, which can be carried out easily and reproducibly.

This object is achieved by a method with the features of claim 1. Advantageous embodiments of the method according to the invention are specified in subclaims.

According to the invention, a method for producing a single-photon source is provided, in which a predetermined operating behavior is determined by specific adjustment of the fine-structure splitting of the excitonic energy level of at least one quantum dot by producing the at least one quantum dot with a structure size (quantum dot size) corresponding to the fine-structure splitting to be set ,

The inventive method allows the reproducible production of quantum dots with desired electronic states and thus the reproducible production of single photon sources with predetermined properties. In fact, it has been found by the inventor that the fine-structure splitting of the excitonic energy level of quantum dots depends on material stresses. Based on this knowledge, the invention is based on the invention, by the choice of the structure size of the quantum or quantum points, ie by the choice of the quantum dot size, the degree of strain within the quantum dots and the degree of strain within the surrounding material structure (eg semiconductor structure). This also defines the fine structure splitting and possibly the energetic position of the excitonic energy level from which the photons are emitted. Simply by selecting the size or the volume of the quantum dots-that is, solely by the number of atoms that form the respective quantum dot-a single-photon source having the desired properties can thus be produced. With the method according to the invention, compact single photon sources can be produced which can emit defined linearly polarized single photons, entangled photon pairs or cascades of correlated photons.

It is regarded as advantageous if the material of the quantum dots and the material of the photon-carrying regions of the photon source are chosen so that the wavelength of the photons corresponds to the dispersion or absorption minimum of already laid telecom fibers (1.3 μm or 1.55) , This can be achieved, for example, with In (Ga) As based quantum dots in Ga (In, Al) As or In (Ga) P in Ga (In) P.

The described method is preferably carried out using established semiconductor technology methods.

To produce a single photon source which can generate entangled photon pairs, the at least one quantum dot is preferably formed with 800 to 5000 atoms of the quantum dot material. Such a small number of atoms or such a small quantum dot size leads to such a strain within the quantum dot and within the surrounding material structure that the fine structure splitting of the excitonic energy level becomes very small or - ideally this would be - zero; in the case of a very small or not existing fine structure splitting have the "bright" by the two; states of the exciton energy level emit photons ^¬ oriented identical frequencies and are entangled with each other.

For example, in the production of a single-photon pair generating entangled photons, a fine-structure splitting between-100 μeV and + 100 μeV is set by the choice of the quantum dot size. The ground state energy of the at least one quantum dot is preferably between 1.27 eV and 1.33 eV.

To produce a single photon source which can generate individual photons with defined polarization, the at least one quantum dot is preferably at 40,000 to

125000 atoms of quantum dot material formed. Such a large number of atoms or such a large structure size leads to such a large strain within the quantum dot and within the surrounding material structure that the fine structure splitting of the excitonic energy level (bright exciton in the ground state) becomes very large; In the case of a very large fine structure splitting, the photons emitted from the two states of the excitonic energy level have very different emission frequencies, so that the "unwanted" of the two photons can be filtered out or suppressed with a filter without much effort.

For example, in the production of a single photon source capable of producing individual photons of defined polarization, fine-structure splitting of at least

+300 μeV is set by the structure size of the at least one quantum dot accordingly - as mentioned - large. The greatest possible fine structure splitting simplifies, as already mentioned, for example, the "path filtering" of the unwanted additional photon. The ground state energy of the at least one quantum dot is preferably less than 1.1 eV for a single photon source that generates individual photons of defined polarization.

As an independent invention, a method for producing a single photon source is also considered, in which a cavity having one or more longitudinal resonance frequencies is produced, wherein several quantum dots are arranged within the cavity, which generate photons, each with its own emission frequency, during operation of the single photon source in which a charge carrier injection device is manufactured and arranged such that it can inject charge carriers into the region of the cavity during operation of the single photon source, and the quantum dots can excite the generation of the photons, and the density of the quantum dots is so low and the scattering is so large in size and material composition of the quantum dots, that during operation of the single photon source exclusively the emission frequency of a single quantum dot of one of the longitudinal resonance frequencies of Kavitä t and can be coupled out of the cavity.

With this method, single-photon sources can be produced in a very simple manner, which can be operated electrically and which additionally follow the concept of the resonant coupling of the excitonic states of the quantum dots with the modes of the cavity due to the presence of a cavity. The cavity provides a preferred direction for the emission of the photons, and in addition the spontaneous emission rate is increased by the utilization of the Purcell effect many times.

Preferably, the cavity is dimensioned such that the longitudinal natural frequency of the cavity used for coupling out the photons is the emission frequency of that quantum. corresponds to the lowest emission frequency of all excited quantum dots. This prevents that a generated photon reabsor ^¬ can again be biert undesirable.

In order to achieve that only a single quantum dot "actively" emits photons, the areal density of the quantum dots is preferably chosen to be less than 5 * 10 ⁹ per square centimeter A particularly preferred range is between 1 * 10 ⁸ and 5 * 10 ⁹ cm ^-2 .

The scattering in terms of size and material composition of the quantum dots is preferably selected to be so large that the emission frequencies of the quantum dots at the operating temperature of the photon source are mutually overlap-free.

Incidentally, it is considered advantageous if a current path limiting device is produced which bundles the current flow and thus the flow of the injected charge carriers in the region of the cavity in such a way that only a subgroup of the quantum dots produced is excited within the cavity. Such a current path limiting device, which could also be referred to as a "quantum dot selection device", makes it possible to actually actively operate only a single one even with a very large number of "excitable" quantum dots.

Furthermore, it is considered advantageous if a temperature adjusting device is produced with which the temperature of the single photon source for its operation can be lowered to a temperature value at which the emission spectra of the quantum dots located within the cavity are free of overlap. In the case of a temperature reduction, namely, the spectral width of the emission spectra of the quantum dots is reduced, so that very closely adjacent emission spectra that overlap at room temperature can be separated. In addition, can be through a temperature reduction will achieve a blue shift of the emission spectra, so that - if none of the single emission spectra of the quantum dots coincides with one of the longitudinal resonance frequencies of the cavity "on its own" - by a targeted temperature change of at least one of the single emission spectra in a resonance - And thus can be moved to a "decoupling".

As a self-contained invention, a method is also contemplated for making a single-photon source in which a cavity having one or more longitudinal resonant frequencies is fabricated, with at least one quantum dot layer disposed within the cavity, wherein a stimulator is fabricated and arranged to be exposed during the time period Operation of the single-photon source excites at least one quantum dot to generate the photons, and in which at the longitudinal to the emission direction of the photons extending side walls of the cavity, a highly reflective layer is applied.

As stated above, the diameter of the cavity should be as small as possible to achieve maximum Purcell factors. In order to avoid that the reduction of the diameter of the cavity leads to the otherwise usually occurring optical losses - cf. The above statements on the prior art in connection with the second prior art concept - a highly reflective layer is proposed here, which rests on the side walls of the cavity. In this way, cavity qualities and Purcell factors can be achieved which are significantly higher than those in the concepts presented at the outset. The side wall roughness of this metal layer is of particular importance, since the associated light scattering significantly limits the realizable Purcell factors.

The highly reflective layer may be formed, for example, by a metal layer, e.g. B. gold layer can be realized. In addition, the field distribution is further optimized via A10 _x apertures within the cavity in order to reduce the optical losses in the sidewall region of the cavity.

As an independent invention also a single photon source for emitting single linearly polarized photons or entangled photon pairs, in particular for use in quantum cryptography, viewed with one or more

Quantum dots that generate photons each having an emission frequency during operation of the single photon source, with a cavity within which the quantum dots are arranged, wherein the cavity has one or more longitudinal resonance frequencies, and with a carrier injection device, which during operation of the single photon source in The charge carriers are injected into the region of the cavity and the quantum dots are excited to generate the photons. During operation of the single-photon source, only photons of a single quantum dot are extracted, namely the photons of the quantum dot whose emission frequency corresponds to one of the longitudinal resonance frequencies of the cavity.

It is advantageous in the case of the proposed single-photon source that, despite the presence of a plurality of "stimulable" quantum dots, only a single quantum dot can actually emit photons, because only at one quantum dot the emission frequency matches a resonant frequency of the cavity If the excited quantum dot precipitates out, by shifting the emission frequencies of the quantum dots (eg by changing the temperature) another quantum dot, namely, for example, the energy closest, can be selected by whose Emission frequency is brought into coincidence with one of the longitudinal resonance frequencies of the cavity.

Preferably, the cavity is dimensioned such that the longitudinal natural frequency of the cavity of the emission frequency used for coupling out the photons of the Quan ^¬ tenpunkts corresponds to having all of the excited quantum dots the lowest emission frequency.

The single-photon source preferably has a current path limiting device which concentrates the flow of the injected charge carriers in the region of the cavity and reduces the number of actually excited quantum dots.

Moreover, it is considered advantageous if the single-photon source has a plurality of quantum dots, which are arranged in a predetermined density and have a predetermined dispersion of their properties.

Particularly preferably, the excited subgroup of quantum dots is so small and the predetermined scattering of the properties of the quantum dots that at the operating temperature of the single photon source, the emission spectra of the quantum dots of the subgroup - at least some of them, but preferably all - are overlap-free.

For example, the density of quantum dots is less than 5 * 10 ⁹ per square centimeter. A particularly preferred range is between 1 × 10 ⁸ and 5 × 10 ⁹ cm ^-2 .

According to a particularly preferred embodiment of the single-photon source, it is provided that a temperature adjusting device is provided which lowers the temperature of the single-photon source for its operation to a predetermined operating temperature at which the emission spectra - at least some of them, but preferably all - are within the cavity Quantum dots are non-overlapping. As an independent invention also a single photon ^¬ is source to emit single linearly polarized photons or photon pairs - in particular for use in quantum cryptography - viewed, with at least one quantum dot, which generates during operation of the single-photon source photons having an emission frequency, with a cavity within of which the at least one quantum dot is arranged and which has a filter characteristic such that only a resonant coupling takes place between a single one of the quantum dots and the cavity, and with an excitation device which, during operation of the single photon source, generates the at least one quantum dot for generating the photons excites, wherein at the longitudinal to the emission direction of the photons extending side walls of the cavity, a highly reflective layer, in particular a metal layer is applied.

As already mentioned, the diameter of the cavity can be reduced and the Purcell factor can be increased by the highly reflective layer without significantly increasing the optical losses of the cavity.

As an independent invention, a method for driving a single photon source is considered, in which the

Temperature of the single photon source is adjusted such that the emission frequency of that quantum dot, which has the smallest emission frequency of all the excited quantum dots, coincides with a longitudinal natural frequency of a cavity of the single photon source.

As an independent invention, a method for driving a single-photon source is also considered, in which the emission spectrum of an exciting device used for the optical excitation is set so that the emission spectrum is energetically above the states of the "active" Furthermore, lies in a region in which the cavity of the single photon source is transparent.

The invention will be explained in more detail with reference to embodiments; thereby show exemplarily:

FIG. 1 schematically shows the generation of photons by a quantum dot on the basis of a schematic energy diagram for an exciton X and a bend XX;

FIG. 2 shows the measured fine structure splitting of the bright exciton in the ground state as a function of the exciton energy and the quantum dot size;

FIGS. 3A, 3B show the emission of defined polarized photons with high emission rate and the emission of polarization entangled photon pairs;

FIG. 4 shows a first exemplary embodiment of a single photon source according to the invention;

FIG. 5 shows the current flow within the single-photon source according to FIG. 4;

FIG. 6 shows the reflection spectrum of a lower Bragg mirror package and an upper Bragg mirror package of the single-photon source according to FIG. 4;

FIG. 7 shows the reflection spectrum of a cavity of the single-photon source according to FIG. 4 in detail; 8 shows luminescence properties of two quantum dots of the single-photon source in accordance with Fi gur ^¬ 4 at different temperatures;

FIG. 9 shows luminescence properties of an ensemble of quantum dots in the single-photon source according to FIG. 4 at different temperatures;

FIGS. 10a) -c) the decoupling of the photons of the quantum dot with the lowest emission frequency by means of a targeted temperature control;

FIG. 11 shows a further exemplary embodiment of a single photon source according to the invention; and

FIG. 12 shows the luminescence spectrum of a quantum dot and the electroluminescence of an excitation LED of the single-photon source according to FIG. 11 at low temperatures.

In the figures 1 to 12 identical reference numerals are used for identical or comparable elements for the sake of clarity.

FIG. 1 shows a schematic energy diagram for an exciton X and a bending XX in a quantum dot. The fine structure splitting FSS of the excitonic state results in FSS = E2 - El. The two mutually perpendicular polarization directions (π +, π-) of the emitted photons are shown.

FIG. 2 shows the measured fine-structure splitting of the bright exciton in the ground state using the example of InAs / GaAs as a function of the exciton energy and the quantum dot size. Schematically, the fine-structure splitting is more energetic Distance of the two exciton emission lines shown. It can be seen that the size of overgrown, epitaxial quantum dots is directly correlated with their strain and that in turn the strain determines the fine structure splitting; FIG. 2 shows by way of example a small InAs quantum dot consisting of 2400 atoms of the quantum dot material with the reference numeral 10 and a large InAs quantum dot consisting of 40,000 atoms of the quantum dot material with the reference numeral 15. Due to these relationships, it is possible to adjust the size of fine-structure splitting by producing quantum dots 10 and 15 of the corresponding size, respectively. The quantum dots shown only schematically in FIG. 2 preferably have the shape of a pyramid with a square base cut off at the top.

Single photon emitters based on quantum dots offer the significant advantage over existing solutions - such as. ^{For example} , the ^{low-power laser described earlier} in this example can produce on-demand ^{λλ photons} , which means that each pulse generates exactly one photon at 100% quantum efficiency, and a single-photon source to be used for quantum cryptography has to be used. On demand "either photons of a defined polarization state or pairs of polarization entangled photons can emit. For the generation of individual photons with a defined polarization, the fine structure splitting must be as large as possible in order to be able to select a single excitonic state with energetic filters (eg a matched cavity). For the generation of polarization-entangled photon pairs, the fine-structure splitting must at least approximately disappear. In this case, photons from the Biexziton → Excess → 0 decay cascade are used (see also FIG. 1). On the other hand, too great an energetic distance between the two existing excitonic states prevents the entanglement of the emitted photon pair. The decisive factor for producing corresponding single-photon sources based on quantum dots is thus the fine-structure splitting. It determines the energy splitting of the excitonic ground state in two competent ^¬ de polarized perpendicular to each other. Fine-structure splitting was first observed at epitaxial quantum dots in the 1990s. Without control over it, however, it was still considered as a disturbing parameter that prevents entangled photon pairs. Due to the method newly described here, a targeted size control of the fine structure splitting is now possible. The method presented here allows the control of the fine structure splitting directly by adjusting the quantum dot size during the production of the quantum dots. The fine structure splitting depends on the spatial symmetry of the electronic potential of a quantum dot. Tensions in the quantum dot structures lead to piezoelectric fields that influence the potential symmetry and thus the fine-structure splitting. The following applies: the greater the strain, the greater the fine structure splitting. Since the strain is dependent on the size of the quantum dots, the size of the fine structure splitting can be selected directly by choosing a specific quantum dot size.

FIGS. 3A and 3B show a schematic representation of two examples for this purpose. When a large fine-structure splitting (FIG. 3A) is selected, the emission from one exciton is increased by the one Purcell factor and suppressed by the other by one cavity. This results in defined polarized photons with a high emission rate. Electric pumping thus allows the controlled generation of photons of a defined polarization direction and high emission rate (eg for a BB84 application (quantum cryptographic transmission protocol)). Only when the fine-structure splitting disappears (compare FIG. 3B: quantum dots with FSS = 0) can polarization-interlinked photon pairs be generated. One of the entangled photons of the Biexiton → exciton → 0 decay cascade can be sent to a respective receiver 1 or 2 by a respective E-mitter (see FIG. 3B). For entangled photon pairs, measuring the polarization of one photon directly determines the measurement result of the polarization of the other photon. By exploiting this quantum mechanical effect, it is thus possible for information to be ^transmitted from one receiver to the other by one of the two receivers taking measurements on "his" photon and thus determining the measurement result of the second receiver.

FIG. 4 shows a first exemplary embodiment of a single-photon source 100 according to the invention in detail. One recognizes a substrate 105 of, for example, GaAs material, on which a lower Bragg mirror package 110 (preferably of oxide material) with mirror layer pairs 115 of different refractive index is applied. On the lower Bragg mirror package 110 is a lower, for example n-doped, electrical contact layer 120 of a charge carrier injection device formed by a pin diode structure 130. Between an eg p-doped upper electrical contact layer 140 of the pin diode structure 130 and the lower electrical contact layer 120 is an active layer 150 with a multiplicity of quantum dots 160 (eg of In (Ga) As) in a monolayer and an n-doped intermediate layer 165. The quantum dots 160 have a predetermined density and thus a predetermined mean distance to each other. Above the upper electrical contact layer 140 of the pin diode structure 130 is an upper Bragg mirror stack 170, through which photons 180 can emerge upwards out of the single-photon source 100. The upper mirror package 170 is preferably made of oxide material. Reference numerals 190 and 195 denote electrical connection ^¬ contacts of the single-photon source 100; Particularly preferably, contacts 190 and 195 are intracavity contacts. Intracavity contacts are those which are arranged between the two mirror packages 110 and 170.

In addition, above, below or within the active layer 150 there may be a strain matching layer for regulating the material stress in the region of the quantum dots with respect to the desired fine structure splitting as well as with regard to the adjustment of the emission wavelength.

In addition, in FIG. 4, a non-conductive layer 200 with an opening 210 can be seen; the nonconductive layer 200 forms a current aperture 220 through which the current I of the pin diode structure 130 flows.

The current flow I is shown in more detail in FIG. The upper part of the single-photon source 100 according to FIG. 4 can be seen in FIG. 5, bottom right. In the top left corner of FIG. 5, the flow of current is visualized in a three-dimensional view. It can be seen that the current aperture 220 forms a current path limiting device of the single photon source 100, which limits the current in such a way that only a subgroup 160 'of the quantum dots 160 is excited; the remaining quantum dots 160 "are not excited because no sufficient current flows in their region.

The current path I of the current I is also limited in the embodiment according to FIG. 5 by a suitable doping profile in the n-doped intermediate layer 165 and the p-doped contact layer 140. The doping increases in each case to the contacts in both layers and accordingly falls in the direction of the active layer 150 and in

Direction to the quantum dots 160; this is indicated in the figure 5 by the arrows Pl and P2. Generally: ever higher the doping level, the smaller the dilatation Strompfadauf ^¬ and the more inhomogeneous the aperture is traversed. The goal of the current path limitation is to excite as few quantum dots 160 'as possible from the quantum dot ensemble 160 and to leave as many quantum dots 160''as possible unaffected.

FIG. 6 shows the reflection spectrum of the lower Bragg mirror package 110 and the upper Bragg mirror package 170. Each mirror package is basically designed for a lenlänge Wel ^¬ λ. It consists of pairs of layers of a material with a high refractive index and a material with a low refractive index, the optical thickness of which is λ / 4. The higher the refractive index contrast (compare curve 250 for a high refractive index contrast and curve 255 for a small refractive index contrast), the wider the stopband Δλ, the smaller the penetration depth of the wave into the mirrors and the fewer mirror pairs needed for high reflectivity ,

A microcavity 260 is formed by the lower Bragg mirror package 110 and the upper Bragg mirror package 170 (see Fig. 4). The term microcavity is to be understood as meaning cavities having a size in the micrometer range. FIG. 7 shows the reflection spectrum of the cavity 260 in detail. The higher the quality of the cavity, the smaller the spectral width Δλc of so-called cavity dips 265 of the cavity 260. Cavity dips are the longitudinal modes of the cavity. The quality of the cavity is defined by the spectral width Δλc of the cavity dips 265. The higher the quality, the narrower the cavity dip. The free spectral range Δλf between the cavity dips is dependent on the length L of the cavity. The larger this is, the closer the cavity dips 265 are together. The modes of the cavity form a stationary spatial field distribution. The cavity length L is preferably as small as possible, ideally a length L = λ / 2, where λ denotes the wavelength of the emitted photons. As already mentioned, quantum dots have discrete energy states and therefore a discrete luminescence spectrum. The states and thus the luminescence shafts of a quantum dot depend sensitively on three parameters: material composition, size and shape of the quantum dots as well as the temperature. Since the temperature is the only variable parameter after completion of the device, it is of particular importance. Therefore, it should be discussed at this point even closer to him. If the temperature is increased, there is a line broadening and red shift of the luminescence. This is shown in FIG. 8.

FIG. 8 shows the luminescence of two individual quantum dots: Curves 270 and 270 'indicate the luminescence

Room temperature, curves 275 and 275 'at low temperatures

(~ 4K). With an increase in temperature, it comes to a

Line broadening and a redshift; in case of a

Reduction of the temperature leads to a line width reduction and to a blue shift of the luminescence.

The distance between the maxima remains constant.

In the epitaxial growth of quantum dots, a fluctuation in size and composition occurs around a mean value. This has a direct effect on the luminescence properties. There is a distribution around a mean photon energy. The low-temperature discrete luminescence spectrum of an ensemble of quantum dots of similar size and material composition fuses at room temperature into a broad, red-shifted emission spectrum. This is shown by FIG. 9 by way of example.

FIG. 9 shows a luminescence spectrum of an ensemble in terms of size and material composition of similar quantum dots, once at room temperature (curve 280) and at low temperatures (curve 285). The intensity distribution of the emission spectrum reflects the distribution function of the quantum points again. It is easy to see that the number of excited quantum dots decreases the more the size and composition of quantum dots move away from their mean. A resonant excitation of individual quantum dots can only be achieved if the emission peaks of the quantum dots do not overlap. This can be achieved by a sufficient energetic distance between the quantum dots, or by lowering the operating temperature, thereby separating the emission lines.

The single-photon source 100 shown in FIG. 4 can theoretically be divided into two basic elements: The first basic element is formed by the p-i-n diode structure 130, within which the monolayer quantum dots 160 is located. The second primitive is formed by a single quantum dot resonantly coupled to the microcavity 260. In order to achieve that only one single actual photon can emit to the outside of the excited quantum dots 160 'according to FIG. 1, the selection effect of the cavity dip 265 is used. For this purpose, the single photon source 100 is operated in a temperature range in which the luminescence spectrum consists of individual, non-overlapping emission lines.

The number of excited quantum dots 160 '- based on the total number of quantum dots 160 - has already been considerably limited by the current path limiting device. The remaining electrically excited quantum dots 160 'are - as already indicated above - subject to a certain distribution with respect to their energetic states. By changing the temperature, it can now be achieved, given a sufficiently small cavity-dip width Δλc, that only a single quantum dot is resonantly coupled to the cavity 260. The situation illustrated in FIG. 10 a) corresponds in principle to the conditions in a VCSEL structure (Vertical Cavity Surface Emitting Laser). The cavity dip 265 'lies at the maximum of the thermally broadened luminescence distribution 300 of the quantum dots. There, most states of the individual quantum dots overlap, which means that many quantum dots are resonantly coupled to the cavity at the same time. This is very welcome in a laser structure because most quantum dots contribute to the induced emission. By lowering the temperature, the situation changes fundamentally.

In Figure 10b), no quantum dot state is in resonance with the microcavity. The cavity dip 265 'is located at the edge of the luminescence distribution of the quantum dot ensemble. More specifically, on the longer wavelength side (i.e., in the low-frequency side view).

The enlargement of the detail in FIG. 10 c) reveals that one of the luminescence lines 305 can be brought into resonance with the cavity by further cooling. If this happens, only a single quantum dot is in resonance with the cavity. Reabsorption of the photons of this quantum dot in resonance with the cavity is not possible since the excitation energies for the other quantum dots of the surrounding pin diode structure 130 are higher.

The structure of FIG. 4 is thus capable of resonantly coupling a single, electrically excited quantum dot 160 'to the microcavity 260.

In order to clarify the mode of operation of the single-photon source 100, the differences between previously known ones should be clarified

VCSEL laser structures and the single-photon source 100 shown in FIG. Despite the great similarities between a VCSEL and the structure proposed here, there are a number of significant differences that originate in the totally opposite application of the two components. On the one hand, these are design differences, on the other hand, the properties of the individual components are used with different goals. In single photon source 100, the active layer consists of only one monolayer of quantum dots. The aim of the growth of this monolayer is to achieve the lowest possible density and a high fluctuation in terms of size and material composition of the quantum dots 160. This is ensured by proper guidance of crystal growth. Both aim to maximize the energetic distance between the individual luminescent lines of the quantum dots, so that a selection of a single line and thus the resonant coupling of a single quantum dot can be realized. With the VCSEL laser, on the other hand, this is precisely what should be avoided. Therefore, multiple quantum dot layers with maximum density are placed in the cavity. The fluctuation of the quantum dots in the

Growth should be minimal, so that the broadening of the luminescence lines at room temperature and the consequent overlap can bring as many quantum dots into resonance with the cavity. Therefore, the VCSEL structure is also designed so that the "cavity dip" at operating temperature is at the maximum of the luminescence distribution.

Reabsorption by non excited quantum dots, however, has a negative effect on ^'the two devices. In the case of the VCSEL, the approach to avoid this is to stimulate as electrically as possible all the quantum dots in the cavity. For this purpose, the current flow through the aperture is made as homogeneous as possible, so that quantum dots that are not in the middle of the aperture are also pumped. As already mentioned above, the latter is undesirable in the case of the single-photon source 100 according to FIG. 4, since as few as possible, ide- ally only a single quantum dot should be electrically excited. Now to prevent Reabsorptionsverluste to non-excited quantum dots Einzelpho ^¬ is ion source 100 is preferably designed to be the ca- vity dip 265 is at operating temperature on the low energy side of the luminescence. If the cavity resonates with a quantum dot whose recombination energy is smaller than that of all other quantum dots, the photons emitted by it can no longer be reabsorbed within the structure, because their energy is too small for absorption by the remaining quantum dots.

There are also differences with regard to the choice of the cavity length L between a VCSEL laser and the single-photon source 100 according to FIG. 4. The VCSEL focuses on the optimum placement of as many layers as possible in the maxima of the spatial field distribution within the cavity. As a rule, the VCSEL cavity length is one to five times the emission wavelength of the laser. One of the primary goals in the design of the single-photon source 100, however, is the optimal utilization of the Purcell effect and the associated increase in the spontaneous emission rate. Since the mode volume plays an essential role in this case, the cavity length is chosen as small as possible, ideally the cavity length is λ / 2, which is possible by choosing a small mean refractive index (smaller than the refractive index of the adjacent upper and lower mirror layer).

The described single-photon source 100 fulfills all of the requirements listed above for a component that can be used for quantum cryptography. In the first place, the possibility of directly processing electrical signals should be mentioned. System integration is thereby considerably simplified. The resonant coupling of the quantum dot states with the modes of a microcavity ensures by using the Purcelleffektes a sufficient spontaneous emission rate. Together with the cavity also provided by the cavity nen emission preferred direction, the efficiency is thus to Be ^¬ dürfnissen a realistic component adjusted. The optical losses that occur when coupling into glass fibers, are minimal. The reason for this lies in the identical to the VCSEL radiation characteristic, which is characterized by small opening angle and round beam profiles. Through the use of quantum dots, the device is to use microns in principle able to inte for telecommunications ^¬ ressanten wavelengths of 1.3 microns and 1.55. Through the structural similarity to the VCSEL provides Asked before ^¬ single photon source 100 beyond the pre ^¬ in part, is that their production methods with established Me ^¬ and can be realized process.

If the single photon source 100 according to FIG. 4 is intended to generate entangled photon pairs, the quantum dots 160 in the case of In (Ga) As are preferably formed with 800 to 5000 atoms of the quantum dot material. With such a size of the quantum dots, the fine structure splitting is generally sufficiently small to be able to generate entangled photon pairs; Preferably, the fine-structure splitting is within an interval between -100 μeV and + 100 μeV, more preferably between -50 μeV and + 50 μeV. The ground state energy of the quantum dots is, for example, between 1.27 eV and 1.33 eV.

In contrast, if the single-photon source 100 according to FIG. 4 is intended to generate individual photons with a defined polarization, the quantum dots 160 are preferably formed with 40,000 to 125,000 atoms of the quantum dot material. With such a size of the quantum dots 160, the fine-structure splitting is generally sufficiently large to be able to "filter away" the unwanted photons generated, preferably a fine-structure splitting of at least +400 μeV, more preferably of at least +500 μeV or more is set For example, the ground state energy of the quantum dots is less than 1.1 eV. FIG. 11 shows a further exemplary embodiment of a single-photon source 100. One recognizes a substrate 500 with a lower Bragg mirror package or DBR mirror package (DBR: Distributed Bragg Reflector) 505, an LED structure 510 located above it and a microcavity 515 located above the LED structure 510. In contrast to the single-photon source 100 According to FIG. 4, very few quantum dots are contained in the cavity 515 according to FIG. 11. In the following, it is assumed by way of example that only a single quantum dot 520 is contained in the cavity, which is illuminated by the LEDs controllable via contacts 525 and 530 Structure 510 is optically excited. By means of the Bragg mirror package 505 located below the LED structure 510, the coupling-out efficiency of the LED structure 510 operating as a "pump LED" is increased.

The cavity 515 utilizes the Purcell effect, which describes the influence of the resonant coupling of the energetic states of the quantum dot 520 with the modes of the cavity 515 on the spontaneous emission rate. The parameter that quantifies this effect is the Purcell factor F. This depends on the quality and the fashion volume of the

Cavity and describes the ratio of the lifetimes of a quantum mechanical state outside and within a cavity according to:

Fp = / τ cav.

The connection between Purcell factor and the cavity parameters is given by

F _p = 3Q (λ _Q / n) / 4π V

with λ: wavelength, n: refractive index, V: mode volume. Here are the for the design of the cavity 515 major Para ^¬ meters the mode volume V and the quality factor Q of the cavity 515. The challenge in designing the cavity 515 is especially in the realization of a sufficiently small NEN mode volume V. To a significant influence to achieve the spontaneous emission rate through the Purcell effect, are small Kavitätsdurchmesser d of 0.5μm to max. 3μm worthwhile. As you can see immediately, the Purcell factor is easily increased by decreasing the cavity diameter since F-I / V holds.

The quality factor Q is dependent on the inner and outer optical losses of the cavity 515. Internal losses occur due to light absorption, external losses due to partial decoupling by the resonator mirrors due to their finite reflectivity and various scattering mechanisms. As the column diameter d of the cavity 515 decreases, the outer optical losses of the cavity increase. This is due to a decrease in mirror reflectivities due to increasingly curved wavefronts, a decreasing horizontal waveguide, and the increasing light scattering caused by roughnesses on the column jacket 540 of the cavity. Since the quality of the cavity is directly incorporated in the Purcell factor, it can easily be seen that an increase in the Purcell factor is limited only by the reduction in the cavity diameter d. The requirement for small column diameters d, however, entails the problem that the optical losses increase greatly with decreasing diameter, so that there is a dramatic deterioration of the quality factor Q of the cavity.

In order to counteract the optical losses of the cavity which increase as the diameter of the column d is reduced, the column jacket 540 of the single-photon source 100 shown in FIG. 11 is provided with a highly reflective coating 550. The highly reflective coating 550 may be formed by a gold layer, for example. With the- In this configuration, Purcell factors can be achieved which are significantly higher than with single-photon sources 100 with uncoated or differently coated cavities.

About AlO _x -Aperturen which are marked in Figure 11 with the reference numeral 560, the field distribution can be moreover, within the cavity 515 even further in the Hin ^¬ view of minimal losses and minimal mode volume optimized by the optical field distribution as far as possible from the column edge 540 of the cavity is kept away. In addition, the effective refractive index within the cavity is reduced by the AlO _x layers and is smaller than the refractive index of the top and bottom adjacent mirror layers, consisting for example of GaAs. This first enables a minimum cavity length of λ / 2.

The emission spectrum of the LED 510 used for the optical excitation is preferably chosen such that the excitation is energetically above the states of the quantum dot 520; the cavity 515 is preferably transparent in this wavelength range.

The curve 600 of FIG. 12 shows the luminescence spectrum of the quantum dot 520 at low temperatures; Curve 610 shows the electroluminescence of the excitation LED. Reference numerals 265, 265 'and 265' 'indicate the longitudinal modes of the cavity 515.

The single-photon source 100 shown in FIG. 11 likewise fulfills all of the requirements set out at the outset for a component which can be used for quantum cryptography. First of all, the single photon source 100 is capable of directly processing electrical signals. By exploiting the purcell effect, the spontaneous emission rate is sufficiently high and can be further increased because of the effective suppression of optical losses due to the mirroring of the cavity shell 540. The cavity 515 also has a positive effect the radiation characteristic. This results in a round beam profile, so that any optical losses are reduced when coupled into fibers. Even if there are several quantum dots in the cavity 515, which are excited optically for the emission of photons, the filter characteristic of the cavity ensures that only photons within a very narrow frequency band, ie photons of a single quantum dot, are coupled out of the cavity , Here, quantum dots with emission wavelengths of 1.3 μm or 1.55 μm can be realized. Thus, with this single photon source 100 already laid fiber optic networks can be used. The production of the single photon sources 100 can be realized by already established methods. Also, systems integration can rely on mature technologies.

If the single photon source 100 according to FIG. 11 is intended to generate entangled photon pairs, the quantum dot 520 is preferably formed with 800 to 5000 atoms of the quantum dot material. By choosing the size of the quantum dot 520, a fine-structure splitting between -100 μeV and + 100 μeV or better between only -50 μeV and + 50 μeV - ideally would be exactly zero - is preferably set. The ground state energy of the quantum dot 520 is, for example, between 1.27 eV and 1.33 eV. The height h of the quantum dot in this case is preferably between 0.3 nm and 0.9 nm.

On the other hand, if the single photon source 100 according to FIG. 11 is to generate individual photons with a defined polarization, the quantum dot 520 is preferably formed with 40,000 to 125,000 atoms of the quantum dot material. With such a size of the quantum dot 520, the fine-structure splitting usually becomes sufficiently large to be able to "filter away" the unwanted co-produced photons, preferably a fine-structure splitting of at least +400 μeV, more preferably of at least +500 μeV or more is set Ground state energy of the quantum dot 520 is, for example less than 1.1 eV. The height h of the quantum dot is greater than 2 nm, preferably in the case ^¬ sem.

reference numeral

10 small quantum dot

15 large quantum dot 100 single photon source

105 substrate

110 lower Bragg mirror package

115 mirror layer pairs

120 lower electrical contact layer 130 pin diode structure

140 upper electrical contact layer

150 active layer

160 quantum dots

160 'excited quantum dots 160 "unexcited quantum dots

165 interlayer

170 upper Bragg mirror package

180 photons

190,195 electrical connection contacts 200 non-conductive layer

210 opening

220 current aperture

250 curve for high refractive index contrast

255 Curve for small refractive index contrast 260 microcavity

265,265 ', 265' 'cavity dips

270, 270 'curves

280, 285 curves

500 substrate 505 lower Bragg mirror package

510 LED structure

515 microcavity

520 single quantum dot

525, 530 contacts 540 pillar edge

550 highly reflective coating

600, 610 curves x exciton

XX Biexciton

FSS fine structure splitting π +, π- perpendicular polarization directions

Pl, P2 doping profiles

Δλc spectral width of a cavity dips

Δλf free spectral range between cavity dips L length of the cavity

Claims

claims

A method of manufacturing a single photon source (100) having a predetermined performance, wherein in the method

- the predetermined operating behavior of the single-photon source (100) through a specific adjustment of the Feinstrukturauf ^¬ cleavage (FSS) of the exciton energy level is at least set of a quantum dot (160 ', 520), - by the einzu the at least one quantum dot at a ^¬ alternate forming fine structure splitting corresponding quanta ^¬ point size is produced.

2. The method according to claim 1, characterized in that generating for producing an entangled photon pairs

Single photon source (100) which is formed at least one quantum dot (160 ', 520) having 800 to 5000 atoms of the quantum dot material.

3. The method according to claim 1 or 2, characterized in that for the production of an entangled photon pair-generating single photon source by the choice of the quantum dot size a fine structure splitting (FSS) between -100 μeV and +100 μeV is set.

4. The method according to any one of the preceding claims, characterized in that for producing an entangled photon pair-generating single photon source (100) the ground state energy of the at least one quantum dot is set between 1.27 eV and 1.33 eV.

5. The method according to any one of the preceding claims, characterized in that for producing a single photon with a defined polarization generating single photon source (100) of the at least one quantum dot (160 ', 520) is formed with 40,000 to 125,000 atoms of the quantum dot material.

6. The method according to any one of the preceding claims, characterized in that for the production of a single photon with defined polarization generating single photon source

(100) a fine-structure splitting (FSS) of at least +300 μeV is set by the choice of the quantum dot size.

7. The method according to any one of the preceding claims, characterized in that for producing a single photon with a defined polarization generating single photon source (100), the ground state energy of the at least one quantum dot (160 ', 520) is set smaller than 1.1 eV.

8. A process for producing a single-photon source (100), in particular according to one of the preceding claims, characterized in that

in that a cavity (260) having one or more longitudinal resonance frequencies (265, 265 ', 265' ') is produced, wherein a plurality of quantum dots (160) are arranged inside the cavity, which photons (160) are irradiated during the operation of the single photon source. 180), each with its own

Generate emission frequency,

in that a charge carrier injection device (130) is manufactured and arranged in such a way that it injects charge carriers into the region of the cavity during the operation of the single photon source and excites the quantum dots (160 ') for generating the photons, and

that the area density of the quantum dots (160 ') is so small and the variance in size and material composition of the quantum dots (160') chosen so large that during the operation of the single photon source only the emission frequency of a single quantum dot corresponds to one of the longitudinal resonance frequencies of the cavity and can be decoupled from the cavity.

9. Method according to claim 8, characterized in that the cavity (260) is dimensioned such that the longitudinal egg used for coupling out the photons (180) natural frequency (265) of the cavity of the emission frequency corresponds desjeni ^¬ gen quantum dot, the excited by all Quan ^¬ tenpunkten the lowest emission frequency has.

10. The method according to any one of the preceding claims 8 or 9, characterized in that the surface density of the quantum dots (160) is chosen to be less than 5xlO ⁹ per square centimeter.

11. The method according to any one of the preceding claims 8 - 10, characterized in that the variation in size and material composition of the quantum dots (160) is chosen so large that the emission lines of the quantum dots are overlapping-free at the operating temperature of the single photon source.

12. The method according to any one of the preceding claims 8 - 11, characterized in that a current path limiting device (220) is produced, which bundles the flow of the injected charge carriers in the region of the cavity (260) such that only a subgroup (160 ') of the existing quantum dots within the cavity is excited.

13. The method according to any one of the preceding claims 8 - 12, characterized in that a temperature adjusting device is produced, with which the temperature of the single photon source for their operation can be lowered to a temperature value at which all emission spectra (275, 275 ') _/ or at least one of them, the quantum dots located within the cavity are non-overlapping.

14. A method for producing a single-photon source (100), in particular according to one of the preceding claims 1 to 7, characterized in that a cavity (515) having one or more longitudinal resonance frequencies (265) is produced, wherein is sorted least one quantum dot layer within the cavity at ^¬,

- That an excitation means (510) is prepared and arranged to ^¬ such that during the operation of the single photon source at least one quantum dot (520) for Gene ^¬ tion of photons (180) excites, and

- That at the longitudinal to the emission direction of the photons extending side walls (540) of the cavity, a highly reflective layer (550) is applied.

15. The method according to claim 14, characterized in that as a highly reflective layer (550), a metal layer, in particular a gold layer is applied.

16. A single photon source (100) for emitting single linearly polarized photons (180) or entangled pairs of photons (180), in particular for use in quantum cryptography, with one or more quantum dots (160) which, during operation of the single photon source, photons each generate an emission frequency,

a cavity (260) within which the quantum dots are arranged, the cavity having one or more longitudinal resonant frequencies (265, 265 ', 265' ') and carrier injection means (130) during operation of the single photon source injected charge carriers into the region of the cavity and excited the quantum dots to generate the photons,

- During the operation of the single photon source only photons of a single quantum dot (160 ') are coupled out, namely the photons of that quantum dot whose emission frequency corresponds to one of the longitudinal resonance frequencies (265) of the cavity.

17. Single photon source according to claim 16, characterized in that the cavity (260) is dimensioned such that the longi used for coupling the photons (180) tudinale natural frequency (265) frequency corresponds to the cavity of the Emissionsfre ^¬ of the quantum dot, the geregten all at ^¬ quantum dots, the lowest emission frequency on ^¬.

18, single-photon source according to any one of the preceding claims 16 - 17, characterized in that the Einzelpho ^¬ ion source comprises a current path limiting means (220) ^¬ which converges the flow of the injected carriers in the region of the cavity.

19, single-photon source according to any one of the preceding An ^¬ claims 16 - 18, characterized in that the single-photon source comprises a plurality of quantum dots (160) which are arranged in a predetermined area density and a predetermined scattering have its properties, by the current path limiting means (220 ) only a subset of the quantum dots (160 ') is excited.

20. Single photon source according to one of the preceding claims 16 - 19, characterized in that the excited subgroup (160 ') of the quantum dots is so small and the predetermined scattering of the properties of the quantum dots is so large that at the operating temperature of the single photon source at least one emission spectrum or all Emission spectra of the quantum dots of the subgroup are overlap-free.

21. Single photon source according to one of the preceding claims 16 - 20, characterized in that the area density of the quantum dots (160) is less than 5xlO ⁹ per square centimeter.

22. A single photon source according to any one of the preceding claims 16-21, characterized in that the single-photon source comprises a temperature adjuster which adjusts the temperature of the single-photon source for the operation of the Lowers single photon source to a predetermined operating temperature value, in which at least one emission spectrum, preferably all emission spectra of the quantum dots located within the cavity are overlap-free.

23, single-photon source for emitting single linearly po ^¬ larisierter photons or photon pairs, in particular for use in quantum cryptography, generated with -at least one quantum dot (520) of the drive during operation of the single-photon source photons (180) having an emission frequency,

A cavity (260), within which the at least one quantum dot is arranged, with a filter characteristic such that only a resonant coupling takes place between a single one of the quantum dots and the cavity,

An excitation device (510) which, during operation of the single photon source, excites the at least one quantum dot (520) to generate the photons,

- Wherein on the longitudinal direction to the emission direction of the photons running side walls (540) of the cavity, a highly reflective layer (550) is applied.

24. Single photon source according to claim 23, characterized in that the highly reflective layer (550) is a metal layer, in particular a gold layer.

25. A method for driving a single photon source (100), in particular a single photon source according to one of the preceding claims 16 - 22, characterized in that the temperature of the single photon source (100) is set such that the emission frequency of that quantum dot of all the excited quantum dots ( 160 ') has the smallest emission frequency, coincides with a longitudinal natural frequency (265) of the cavity of the single photon source (100).

26. A method for driving the single-photon source (100), in particular a single-photon source according to one of the preceding claims 23 - 24, characterized in that the emission spectrum of the excitation means (510) used for the optical excitation is adjusted so that the emission spectrum is energetically above the states of the quantum dot (520) and also lies in an area where the cavity (515) is transparent.

27. The method according to any one of the preceding claims 1 to 15, characterized in that the height (h) of the at least one quantum dot is set to a value between 0.3 nm and 0.9 nm for producing an entangled photon pair-generating single photon source (100) ,

28. The method according to any one of the preceding claims 1 to 15, characterized in that the height (h) of the at least one quantum dot is set to a value greater than 2 nm to produce a single photon with defined polarization generating single photon source (100).

29. A method for producing a single photon source (100) with a predetermined operating behavior, wherein in the method, the predetermined performance of the single photon source (100) by setting the set voltage of at least one quantum dot (160 ', 520) is determined by the at least one Quantum dot is produced with one of the set tension corresponding quantum dot size.