Apparatus for generating single photons and entangled pairs of photons

Abstract

Embodiments of the invention provide a device (300) for generating photons, comprising a quantum box (301) inserted into a micro-pillar optical cavity (302) having at least one optical mode, the quantum box (301) having at least one ground state and two states with one excitation, the optical cavity (302) having a bottom face and a top face, the bottom face bearing an electrical contact (305), the photon generating device (300) advantageously comprising: at least three electrical bonding pads (304a, 304b, 304c) electrically insulated from each other, said at least three electrical bonding pads (304a, 304b, 304c) being arranged around the top face of the cavity (302).

Description

Background Technology

[0001] The present invention relates generally to photon sources, and particularly to apparatus for generating single photons and entangled photon pairs, and methods for implementing the apparatus.

[0002] The deployment of quantum communication networks requires the establishment of single-photon sources capable of generating a series of light pulses, each consisting of one and only one photon. Such a source can provide a key for two remote contacts, allowing them to encrypt subsequent communications. The limitations of propagation channels, whether in fiber optics or free space, restrict the range of this application to within a few hundred kilometers. The range of quantum communication networks can be extended using quantum repeaters that rely on entangled photon pairs. The generation of pulses with single photons or entangled photon pairs can be achieved using nanoscale emitters, such that transitions between their electronic states correspond to the radiation of a single quantum dipole.

[0003] Furthermore, the creation of quantum computers relies on systems that can be manipulated as qubits. A qubit is a coherent superposition of two fundamental states (generally represented as |0> and |1>), allowing it to take on an infinite number of possible values, unlike binary bits which are manipulated by conventional computers with values ​​of 0 or 1. Qubits can be solid-state or possess photonic properties. While the first type offers flexibility in storage and processing, optical qubits allow for the transmission of quantum information over long distances. To enable the processing and transmission of quantum information, it is common practice to combine optical qubits, associated with the interface between the two elements, and solid-state qubits.

[0004] In recent years, the use of quantum boxes in applications including the deployment of quantum communication networks and the creation of quantum computers has seen significant growth. Interest in these nanostructures is explained by their similarity to atoms in terms of charge carrier confinement and the quantization of their energy levels. Such characteristics allow quantum boxes to generate single photons through a spontaneous emission process in response to appropriate light adaptation, thereby enabling electrons to migrate from the valence band to the conduction band. The same mechanism can be applied to placing two electrons at the same energy level in the conduction band and generating entangled photon pairs. Quantum boxes also allow for reliable interactions between light and the characteristics of confined charge carriers.

[0005] Standalone quantum boxes used as sources of single photons or entangled photon pairs are typically limited in terms of brightness and bit rate. Brightness quantifies the probability that each light pulse has a single photon or entangled photon pair, while bit rate measures the number of photons emitted per second and is equal to the product of the brightness as defined above and the emission clock rate of the light pulses that control the excitation of the quantum box. To improve the performance levels of quantum boxes in terms of brightness and bit rate, a known practice is to insert the quantum box into a resonant optical cavity. This configuration utilizes the Purcell effect (also known as a “micro-optical material coupling system”) to increase the spontaneous initial velocity of the quantum box in cavity mode and allows it to collect photons emitted by the quantum box more efficiently. Encapsulating the quantum box in an optical cavity also makes it possible to reduce the quantum box’s sensitivity to environmental perturbations (mechanical, electrical, etc.) and to produce indistinguishable single photons, i.e., single photons that are identical in terms of quantum state (same frequency, same polarization state, same spatial and temporal distribution).

[0006] Quantum boxes typically possess semiconductor properties obtained through molecular jet epitaxy, which involves growing semiconductor layers that differ in their gap energy and grid parameters. This difference produces nanoscale quantum boxes capable of confining charge carriers in three-dimensional space.

[0007] Electrons in the valence band of a quantum box can cross the conduction band to form electron-hole pairs—also known as excitons—along with holes remaining in the valence band. Exciton formation can occur by absorbing photons with energy greater than or equal to the stopband of the material forming the quantum box. The exciton state corresponding to exciton formation is an unstable state, and a neutral state (also called the fundamental state) is reconstructed by emitting photons according to a spontaneous emission process, recombinating electrons and holes. This state is characterized by a radiation lifetime on the order of nanoseconds and an emission wavelength (or frequency) corresponding to the stopband of the material forming the quantum box.

[0008] A quantum box can confine biexcitons, formed by two excitons coupled by the Coulomb interaction, to a shared fundamental state. The energy levels of the biexciton state are higher than those of the monoexciton state. Biexcitons are formed by the successive absorption of two photons. The relaxation of biexcitons also occurs through the spontaneous emission of two consecutively emitted photons. Because the Coulomb interaction varies depending on whether a single electron-hole pair or two electron-hole pairs are excited in the quantum box, the two photons are emitted at different wavelengths. Therefore, the wavelength of the photon emitted when the system transitions from a biexciton state to an exciton state is different from the wavelength of the photon emitted when the system transitions from an exciton state to a neutral state.

[0009] The polarization states of the absorbed photons used to form excitons and the photons emitted during electron-hole recombination obey optical selection rules governed by the Pauli exclusion principle and the conservation of moment. These selection rules depend on the spin states of the electron-hole pairs and stipulate that the bright exciton state emitting photons upon recombination corresponds to the bright exciton state with the opposite sign of the spin state. In the case of a quantum box with cylindrical symmetry, the system exhibits two energy-degenerate bright exciton states. Figure 1 The relaxation of a biexciton 103 formed in a semiconductor quantum box 100 with cylindrical symmetry (or "isotropy") is shown, wherein only bright exciton states are implemented. The relaxation of the biexciton 103 confined in the isotropic quantum box 100 is achieved by successively emitting two photons in a system with three energy levels. There are two possible approaches to this:

[0010] - Relax the biexciton 103 to the exciton 1020 by emitting a right-handed circularly polarized photon, and then relax the exciton 1020 to the fundamental state 101 by emitting a left-handed circularly polarized photon; or

[0011] - By emitting a left-handed circularly polarized photon, the biexciton 103 is relaxed to the exciton 1021, and then by emitting a right-handed circularly polarized photon, the exciton 1021 is relaxed to the fundamental state 101.

[0012] Given that these two pathways are indistinguishable, and since excitons 1020 and 1021 are degenerate, this results in the emission of a pair of polarization-entangled photons.

[0013] It should be noted that the generation of a single photon can be achieved by recombination of excitons 1020 or 1021 into the fundamental state 101, and in this case, undergoing the biexciton state 103 is meaningless. The generation of biexciton 103 is necessary for the generation of entangled photon pairs.

[0014] However, in practice, semiconductor quantum boxes are anisotropic, which involves a lift of the exciton level degeneracy and thus a loss of entanglement in the emitted photons. This lift of degeneracy is primarily caused by anisotropic effects, piezoelectric effects, and mechanical confinement in the quantum box form. In anisotropic quantum boxes, bright exciton states are separated by energy levels (called "fine structure splitting"), and these bright exciton states are linear combinations of the fundamental states confined in symmetric quantum boxes. Exciton states in anisotropic quantum boxes exhibit light emission linearly polarized along two specific axes "x" and "y" corresponding to the crystallization direction (axis "z" is the growth axis). Figure 2The recombination of biexciton 203 in an anisotropic semiconductor quantum box 200 is illustrated. Relaxation of biexciton 203 to the fundamental state 201 can be accomplished solely based on a linear polarization state on one of the quantum box's specific axes ("x" or "y"), leaving exciton 2020 or 2021 (which in turn relaxes according to the same polarization state as biexciton 203). The enhancement of exciton level degeneracy leads to the complete or partial loss of entanglement between the resulting two photons.

[0015] Known practice is to generate single photons with improved performance levels by resonantly exciting the superposition of two bright exciton states and by using an anisotropic quantum box to utilize the time-varying phase ΔΦ between the two exciton states polarized according to "x" and "y", the speed of which is called the "transfer speed" because it controls the transition from the linearly polarized state of the emitted photon to an orthogonal state, as referenced Figure 10 (For a more detailed explanation) according to the following relationship: Proportional to the fine structure splitting value, This is the reduced Planck constant. Excitation can be accomplished using photons linearly polarized on an axis not collinear with a specific axis of the quantum box, ideally oriented at 45 degrees. To collect only photons produced by the quantum box, only photons linearly polarized in a direction perpendicular to the direction of the excitation photon are detected. Typically, the fine-structure splitting value determines the performance level of a single-photon source in terms of brightness and purity; purity quantifies the ability to produce a single photon during the same excitation period. Controlling the fine-structure splitting value is difficult during quantum box fabrication. A high fine-structure splitting value can increase the conversion speed, thereby increasing the brightness of the single-photon source. However, the probability that the quantum box emits more than one photon during the same photoexcitation period is non-negligible, which reduces the performance level of the single photon in terms of purity. Conversely, a low fine-structure splitting value reduces the conversion speed, which reduces the probability of emitting a second photon during the same excitation period. This low fine-structure splitting value increases the purity of the single-photon source but degrades the brightness because the quantum box emits faster in a polarization direction parallel to the excitation photon than in an orthogonal polarization direction, thus reducing brightness. Therefore, it is necessary to control the fine structure splitting value in order to generate single photons at a high rate while reducing the probability of emitting more than one photon during the same excitation cycle.

[0016] Because the degeneracy of the exciton states is enhanced, the use of the fabricated anisotropic quantum boxes is still unsuitable for the generation of entangled photon pairs. Therefore, it is necessary to statically reduce, or in particular eliminate, the fine structure splitting value in order to obtain entangled photon pairs by re-establishing the indistinguishability of the radiative emission paths from the biexcitons.

[0017] A known practice is to reduce and / or control the fine structure splitting value in a quantum box by applying a vertical electric field along with one or more strain fields (in the case of the mechanical type) in two or three directions in the environment in which the quantum box is inserted. Such a solution has been described in reference [1]. The application of such a strain field requires thinning the substrate on which the quantum box is manufactured so that the piezoelectric material can be placed as close as possible to the quantum box, thereby ensuring that the applied mechanical tension is well transmitted to the implemented quantum box. The thinning required to implement this method poses a technical challenge to the fabrication of the three-dimensional (3D) optical cavity incorporating the quantum box. Furthermore, the proximity of the quantum box to the surface makes it sensitive to environmental disturbances, which can cause indistinguishable loss of the generated single photons.

[0018] Another known practice is to apply electric fields in both dimensions of the space in which the quantum box is inserted in order to control the fine structure splitting value. In reference [2], this solution is implemented by inserting several (usually four) electrical bonding pads very close to the plane of the quantum box. It is known that the proximity of the quantum box to the surface defining such electrical bonding pads increases charge noise, which in turn reduces the performance level of the emitted photons in terms of indistinguishability.

[0019] Therefore, there is a need for a source of single photons or entangled photon pairs based on semiconductor quantum boxes, in which the splitting of fine structures can be controlled statically or dynamically without the drawbacks of existing technologies. Summary of the Invention

[0020] To this end, the present invention provides an apparatus for generating photons, the apparatus comprising a quantum box inserted into a micropillar-shaped optical cavity having at least one optical mode, the quantum box having at least one fundamental state and two states having a primary excitation, the optical cavity having a bottom surface and a top surface, the bottom surface having an electrical contact, characterized in that the apparatus comprises at least three electrically insulating pads, the at least three electrically insulating pads being arranged around the top surface of the cavity.

[0021] In one embodiment, the electrical bonding pads can be linked to the top surface of the cavity via semiconductor arms that are radially oriented relative to the cavity and have a width smaller than the width of the cavity in the tangential direction and at their ends closest to the cavity.

[0022] In another embodiment, electrical bonding pads may be linked to semiconductor arms that are radially oriented toward the cavity and whose ends may be separated from the top surface of the cavity by empty gaps or gaps filled with a dielectric of submicron width.

[0023] Advantageously, the micropillar optical cavity can be used to form a PIN diode, with the quantum cell located in the intrinsic region of the diode.

[0024] As a variant, the electrical bonding pad can be carried by a corresponding strut that is optically and electrically decoupled from the cavity.

[0025] In one embodiment, the device may further include at least three adjustable voltage sources for applying a corresponding and variable potential difference between each in the electrical bonding pad and the electrical contact carried by the bottom surface of the optical cavity.

[0026] In another embodiment, the micropillar optical cavity may have at least one first mode pair and at least one second mode pair, each mode pair being polarization degenerate, and wherein the quantum cell may also have a state with two elementary excitations.

[0027] Advantageously, the device may further include: a second optical cavity coupled to the optical cavity into which the quantum box is inserted, the geometry of the first and second cavities and their coupling force being selected such that the assembly consisting of the two coupled cavities presents a first mode pair and a second mode pair, the first mode pair being polarization degenerate and resonating with the transition between the quantum box's two elementary excitation states and two states with one elementary excitation, the second mode pair being polarization degenerate and resonating with the transition between the quantum box's two states with one elementary excitation and the fundamental state, each pair having a radiation pattern with an overlap of 70% or more.

[0028] In particular, the second optical cavity can also be micropillar-shaped, with the two cavities arranged side by side.

[0029] A method for generating entangled photon pairs using a photon generation device is proposed, which may include the following steps:

[0030] - An electrical potential difference is applied between each of the electrical bonding pads and the electrical contact supported by the bottom surface of the optical cavity, the potential difference being selected as follows:

[0031] o minimizes the energy deviation between two states of the quantum box that have an excitation, and

[0032] o causes the transition between a state with two elementary excitations and a state with one elementary excitation to resonate with the first mode pair of the cavity, and causes the transition between a state with one elementary excitation and a fundamental state to resonate with the second mode pair of the cavity; and

[0033] - A state with two elementary excitations is filled into a quantum box by energy input.

[0034] A method for generating single photons using a photon generating device is also proposed, which may include the following steps:

[0035] - Apply a potential difference between each of the electrical bonding pads and the electrical contact supported by the bottom surface of the optical cavity, and

[0036] - Irradiate the quantum cell of the device with light pulses exhibiting a spectrum and polarization direction corresponding to the mode of the optical cavity, wherein the potential difference is chosen to modify the energies of the two eigenstates having a primary excitation, such that:

[0037] The state described resonates with the wavelength of the light pulse's spectrum; and

[0038] o maximizes the probability of emitting a single photon through the box, the single photon having a linear polarization orthogonal to the linear polarization of the illumination.

[0039] In one embodiment, the potential difference can also be selected to determine the orientation of a specific axis of the quantum box based on the midpoint between the two specific polarization axes of the optical cavity.

[0040] In another embodiment, the potential difference can be variable over time, and:

[0041] - During the first period in which the quantum box is illuminated for at least a portion of its duration, a first value is chosen to cause a non-minimum deviation in the energies of the two eigenstates having a primary excitation, the duration of which is chosen to induce a phase change between the two states between 45° and 135°, preferably between 80° and 100°; and

[0042] - During the second period immediately following the first period, a value is chosen that minimizes the energy difference between the two eigenstates with a primary excitation. Attached Figure Description

[0043] Other features and advantages of the invention will become apparent from the following description and accompanying drawings, wherein:

[0044] [ Figure 1 ]

[0045] and

[0046] [ Figure 2 The relaxation of biexcitons in isotropic and anisotropic quantum boxes are illustrated above.

[0047] [ Figure 3A ]

[0048] and

[0049] [ Figure 3B [This refers to an apparatus for generating single photons and entangled photon pairs according to an embodiment of the present invention.]

[0050] [ Figure 4 This illustrates the generation of an electric field with three components in space according to an embodiment of the present invention.

[0051] [ Figure 5 ]、

[0052] [ Figure 6 ]and

[0053] [ Figure 7 [This represents a portion of a top view of an apparatus for generating single-photon and entangled photon pairs according to different embodiments of the present invention.]

[0054] [ Figure 8 [This refers to a microcylindrical optical cavity incorporating a quantum box according to an embodiment of the present invention.]

[0055] [ Figure 9 [This image shows a partial top view of an apparatus for generating single photons and entangled photon pairs, which implements two optically coupled optical cavities according to another embodiment of the present invention.]

[0056] [ Figure 10 This represents the time-varying excited state of a quantum cell incorporated into a microcylindrical optical cavity. The quantum cell exhibits non-zero exchange anisotropy, while the optical cavity exhibits birefringence.

[0057] [ Figure 11 This indicates the application of a device for generating single photons according to an embodiment of the present invention.

[0058] [ Figure 12 This represents a method for calibrating anisotropic quantum boxes.

[0059] [ Figure 13A ]and

[0060] [ Figure 13B [This represents two methods for generating single photons according to two embodiments of the present invention.]

[0061] [ Figure 14 [This refers to a method for generating entangled photon pairs according to an embodiment of the present invention.]

[0062] [ Figure 15 [] indicates the experimental measurements of the fine structure splitting of the anisotropic quantum box under the action of the electric field generated according to an embodiment of the present invention. Detailed Implementation

[0063] Figure 3A and Figure 3B The figures show a top view and a cross-sectional view of an apparatus 300 for generating single photons and entangled photon pairs according to an embodiment of the present invention. The apparatus includes a quantum box 301 inserted into a microcylindrical optical cavity 302. The optical cavity 302 is cylindrical and connected to three pillars 303 via semiconductor arms 308a, 308b, and 308c.

[0064] The quantum box 301 can possess semiconductor properties obtained through molecular jet growth, which involves growing semiconductor layers with different gap energies and grid parameters. The layer forming the quantum box 301 can be an indium arsenide (InAs) layer, and the layer forming the substrate and encapsulation can be a gallium arsenide (GaAs) layer. The quantum box 301 can be in the form of a truncated cone, having a height of several nanometers along the growth axis and a base diameter of approximately 20 nanometers. These characteristics give the quantum box 301 near-atomic properties in terms of carrier confinement and energy level quantization.

[0065] The quantum box 301 can be in a neutral state (also called the fundamental state) or an excited state (also called an exciton or a state with one elementary excitation) corresponding to the formation of electron-hole pairs. The formation of an exciton in the presence of charge carriers already confined within the quantum box 301 corresponds to a triexciton, which can be quantized as positive or negative depending on the sign of the confined charge carriers. When two excitons are confined simultaneously, a biexciton is formed in the quantum box 301, also called a state with two elementary excitations.

[0066] Charge carriers, electrons, and holes are fermions characterized by half-integer spins: ±1 / 2 for electrons and ±3 / 2 for heavy holes. The exciton states of the symmetric quantum box 301 are bright when electron-hole recombination occurs according to a spontaneous emission process involving emitted photons. Bright exciton states (also called fundamental exciton states) correspond to a total angular moment equal to ±1 and are relaxed by emitting left- or right-handed circularly polarized photons according to the sign of the spin sum.

[0067] In practice, quantum box 301 is anisotropic, which implies a degeneracy enhancement of the exciton levels of quantum box 301. The bright exciton states (also known as eigenstates with a primary excitation) in the anisotropic quantum box 301 are linear combinations of the fundamental exciton states defined in the symmetric quantum box 301 and are separated by non-zero energies called fine-structure splits.

[0068] The micropillars forming the optical cavity 302 are cylindrical and consist of two stacked layers 3020 and 3022 surrounding a central region 3021. Such layers typically have semiconductor properties and can be P- or N-doped depending on the given configuration. For example, the top 3022 of the cavity can be P-type (or N-type) doped, while the bottom 3020 can be doped with the opposite type, such that, from an electrical perspective, the cavity forms a PN diode. Each of the two stacked layers 3020 and 3022 forms a Bragg mirror and is obtained by alternating layers composed of two materials with different refractive indices. The thickness and refractive index of each of the two layers (forming each of the two stacked layers 3020 and 3022) can be chosen such that their product equals λ / 4, where λ is the operating wavelength. The number of layer pairs forming the bottom stacked layer 3020 in contact with the substrate 305 can differ from the number of layer pairs forming the top stacked layer 3022. This difference can, for example, prioritize the upward emission of photons generated by the quantum box 301 to increase the brightness of the photon source 300. Each of the two Bragg mirrors 3020 and 3022 can refract incident light along the stacking axis over a wide wavelength range centered on the operating wavelength λ. The central region 3021 located between the two stacks 3020, 3022 can have a thickness equal to λ and is configured to contain the quantum box 301. The presence of the central region 3021 can alter the refractive index of the micropillar, making the two Bragg mirrors 3020, 3022 transmissive at the operating wavelength. The radius of the micropillar is on the order of a few micrometers and is selected to allow at least one optical mode (called the fundamental mode) to propagate through the micropillar with minimal energy. Advantageously, the radius of the micropillar can be selected to allow the propagation of several optical modes. The micropillar can have rotational symmetry, meaning that each propagation mode has two degenerate polarization states. Alternatively, the micropillar is a birefringent medium in which light propagates anisotropically. This birefringence property enhances the polarization degeneracy of the optical propagation mode, which is defined by the small and large axes of the micropillars, denoted as H and V, respectively.

[0069] Advantageously, the optical cavity 302 has at least one first optical mode pair and at least one second optical mode pair, each mode pair being polarization degenerate. For example, the optical cavity 302 with two polarization degenerate mode pairs is particularly used to generate entangled photons by matching the relaxation wavelength from biexciton (with two elementary excited states) to exciton (with one elementary excited state) with the energy of the first mode pair and by matching the relaxation wavelength from exciton to neutral state with the energy of the second mode pair.

[0070] The height of the pillars 303 can be equal to, greater than, or less than the height of the optical cavity 302. The optical cavity 302 can be placed at the center of the assembly formed by the three pillars 303 with a radial spacing sufficient to optically decouple the optical cavity 302 from the pillars 303. Furthermore, the pillars 303 must be electrically insulated from each other, except at their bottom surfaces, in relation to the electrical contacts 305, which will be described later. The pillars 303 can be formed by a stack of the same micropillars that form the optical cavity 302. This structure has the advantage of compatibility with many cleanroom manufacturing methods known to those skilled in the art. The manufacturing steps of this structure may include: thin-layer deposition to produce the stack; photolithography followed by dry etching, so that the optical cavity 302 and the three pillars 303 can be defined.

[0071] The top surface of each strut 303 (defined as the surface opposite to the surface in contact with the substrate 305) includes electrical bonding pads 304a, 304b, and 304c, sized such that the electrical bonding pads 304a, 304b, and 304c are entirely supported by the top surface of the corresponding strut 303. The three electrical bonding pads 304a, 304b, and 304c may have the same electrical properties and the same geometry, which may be triangular, rectangular, or other forms. The lateral dimensions of these electrical bonding pads 304a, 304b, and 304c, defined in a plane perpendicular to the stacking axis (growth axis), are preferably at least 10 times larger than the thickness of these pads 304a, 304b, and 304c defined according to the stacking axis. As an example, the electrical bonding pads 304a, 304b, and 304c are chosen to have a thickness of less than 50 nanometers and a lateral dimension of greater than 50 micrometers. This facilitates their connection to different voltage sources 306a, 306b, and 306c via a wiring method (also known as "wire bonding"). The electrical bonding pads 304a, 304b, and 304c are arranged symmetrically around the optical cavity 302, corresponding to the same radial spacing between each electrical bonding pad 304a, 304b, and 304c and the optical cavity 302, and corresponding to the same angular spacing between two adjacent electrical bonding pads.

[0072] The bottom surface of pillar 303 is connected to another electrical contact 305, thus the electrical contact 305 is carried by the bottom surface of optical cavity 302. The electrical contact 305 is fabricated on a surface with semi-conductive properties, the conductivity of which is increased by P or N doping. The electrical contact 305 can have a disk, rectangle, or another 2D geometry, which can completely cover the bottom surface of the assembly formed by optical cavity 302 and pillar 303. Such a configuration can apply a potential difference between each electrical bonding pad 304a, 304b, 304c arranged around the top surface of optical cavity 302 and the electrical contact 305 carried by the bottom surface of optical cavity 302 by providing corresponding voltages Ta, Tb, and Tc using three independent voltage sources 306a, 306b, 306c. The voltage provided by each voltage source 306a, 306b, 306c can be constant or time-varying.

[0073] Semiconductor arms 308a, 308b, and 308c are used to connect each of the electrical bonding pads 304a, 304b, and 304c to the top surface of the optical cavity 302. The material forming the semiconductor arms is doped to increase their conductivity, but this conductivity does not become metallic (degenerate doping). The semiconductor arms 308a, 308b, and 308c may have the same height as the optical cavity 302, and their length is long enough to connect the outside of the optical cavity 302 to the inside surface of the pillar 303. The electrical bonding pads 304a, 304b, and 304c are disposed above the pillar 303, and their width is small enough that two adjacent semiconductor arms 308a, 308b, and 308c are electrically insulated from their contacts on the outside of the optical cavity 302. Each semiconductor arm 308a, 308b, and 308c extends radially toward the corresponding pillar 303, such that a 120-degree angle is formed between every two adjacent semiconductor arms 308b and 308. The use of dielectric or semiconductor arms can amplify the horizontal component of the applied electric field by concentrating field lines.

[0074] Photons generated by quantum box 301 according to one of the optical modes and photons that excite quantum box 301 leave and penetrate optical cavity 302 according to the same or two different radiation patterns 307, each radiation pattern being characterized by having a given aperture angle.

[0075] Each electrical bonding pad 304a, 304b, 304c generates a fundamental electric field through the potential difference between it and the electrical contact 305 supported by the bottom surface of the optical cavity 302, controlling its characteristics in terms of intensity and orientation. The composite electric field, dominant in the central region 3021 and experienced by the quantum box 301, is the vector sum of three fundamental electric fields generated from the potential difference between each of the three electrical bonding pads 304a, 304b, 304c arranged around the top surface of the optical cavity 302 and the electrical contact 305 supported by the bottom surface of the optical cavity 302. This composite electric field has three components: a vertical component defined in the same direction as the growth axis (stack axis) of the optical cavity 302, and two horizontal components defined in the stacked plane forming the two Bragg mirrors 3020, 3022. The characteristics of this composite electric field in terms of orientation and intensity can be deterministically tuned by acting on one or more of the fundamental electric fields by means of the associated potential difference.

[0076] Figure 4 The diagram illustrates an electric field with three components defined within an orthogonal trihedron, generated by placing four electrical contacts according to the above configuration. Two voltage sources, 306a and 306b, are shown, and the fundamental and composite electric fields are represented by dashed and solid lines, respectively. The different components of the composite electric field can be:

[0077] - Adjust the fine structure splitting value of quantum box 301;

[0078] - The emission wavelength associated with the relaxation of its bright exciton state; and

[0079] - The orientation of a specific axis of the quantum box 301 is defined, and the quantum box 301 can emit photons or be excited by photons in that orientation.

[0080] To adjust these three parameters, at least three degrees of freedom are required, therefore at least three independent voltage sources are linked to three non-collinear electrical bonding pads.

[0081] From an experimental perspective, due to defects in the manufacturing process, the intrinsic parameters of the quantum box 301, such as the fine structure splitting, are not known precisely in advance. Relevant parameters of the quantum box 301, such as the fine structure splitting, emission wavelength, and orientation of a specific axis, are typically measured after the production of the device 300 used to generate single photons and entangled photon pairs.

[0082] Figure 5This is a top view showing a portion of an apparatus 300 for generating single photons and entangled photon pairs according to another embodiment of the present invention. In such an embodiment, the semiconductor arms 308a, 308b, 308c as described above do not directly contact the optical cavity 302. The separation between each semiconductor arm 308a, 308b, 308c and the optical cavity 302 is ensured by a dielectric material layer 309. The dielectric material layer 309 is configured to ensure electrical insulation between the optical cavity 302 and the semiconductor arms 308a, 308b, 308c, and its thickness is on the order of tens of nanometers to several micrometers. The dielectric material forming the dielectric layer 309 can be void. The electrical insulation of the optical cavity 302 from its adjacent environment prevents any strong current from passing through the optical cavity 302 and interfering with the operation of the quantum box 301.

[0083] Figure 6 Another embodiment of the invention is shown, in which the optical cavity 302 is not connected to the different pillars 303 using semiconductor arms. In such an embodiment, the pillars 303 are arranged symmetrically around the optical cavity 302, and the radial spacing between the optical cavity 302 and each pillar 303 is chosen to be, for example, less than 10 micrometers. Such radial spacing allows the quantum cell 301 to be subjected to an electric field strong enough to act on the characteristic parameters of the quantum cell 301 (including its fine structure splitting value). The separation between the optical cavity 302 and the pillars 303 can be ensured by a dielectric material or voids.

[0084] Figure 7 Another embodiment of the invention is illustrated, in which electrical bonding pads 304a, 304b, and 304c are supported by a cylindrical hollow structure 3030 surrounding an optical cavity 302. The hollow structure 3030 may be formed of a dielectric material capable of electrically insulating the electrical bonding pads 304a, 304b, and 304c. The hollow structure 3030 may have the same height as the optical cavity 302, and the top surface of the hollow structure is selected to be wide enough to accommodate the electrical bonding pads 304a, 304b, and 304c. Furthermore, as... Figure 5 As described in the embodiments, semiconductor arms 308a, 308b, 308c associated with the dielectric material layer 309 are used to connect electrical bonding pads 304a, 304b, 304c to the optical cavity 302. Alternatively, as... Figure 6 As depicted, by bringing the electrical bonding pads 304a, 304b, and 304c sufficiently close to the optical cavity 302, or as... Figure 3A and Figure 3B As depicted, the connection between the electrical bonding pads 304, 304b, and 304c and the optical cavity 302 can be ensured by using semiconductor arms 308a, 308b, and 308c.

[0085] Figure 8The diagram illustrates the structure of a micropillar-type optical cavity 302 according to an embodiment of the invention. In such an embodiment, the two top and bottom Bragg mirrors 3022 and 3020 forming the micropillar are P-doped and N-doped, respectively. The central region 3021 containing the quantum box 301 remains intrinsic, such that, from an electrical perspective, the micropillar forms a PIN diode. The concentration of the impurity used to generate the doping (P or N) can be uniform along the entire length of each of the two Bragg mirrors 3020 and 3022. Alternatively, the impurity concentration can be varied in a decreasing manner, minimizing it in the region in contact with the central region 3021. The variation in impurity concentration can be linear, logarithmic, or other. Advantageously, different voltages applied to the optical cavity 302 doped according to one of the above configurations correspond to the reverse polarization of the PIN junction formed by the optical cavity 302. Such reverse polarization ensures that no significant current flows through the quantum box 301, interfering with its photon emission. Alternatively, the optical cavity 302 is forward biased, which generates a significant current that passes through the quantum box 301 and may thus interfere with its operation.

[0086] According to an embodiment of the invention, each of the electrical bonding pads 304a, 304b, and 304c surrounding the top surface of the optical cavity 302 is connected to one of the terminals of the adjustable voltage sources 306a, 306b, and 306c. Each of the adjustable voltage sources 306a, 306b, and 306c is configured to apply a potential difference between the electrical bonding pad 304a, 304b, and 304c to which it is connected and an electrical contact 305 carried by the bottom surface of the optical cavity 302, which is shared by all implemented adjustable voltage sources 306a, 306, and 306c. The voltage generated by each adjustable voltage source 306a, 306b, and 306c, measured between the corresponding electrical bonding pad 304a, 304b, and 304c and the electrical contact 305, can be positive, zero, or negative.

[0087] Figure 9This is a top view of an apparatus 300 for generating single-photon and entangled photon pairs according to another embodiment of the present invention, the apparatus comprising two optical cavities 302, 310. One of the two optical cavities 302 includes a quantum box 301 and can be configured according to one of the embodiments described above. The other optical cavity 310 does not include any quantum box and may have optical geometric parameters (size, form) different from those of the first optical cavity 302. The two implemented optical cavities 302, 310 are configured to be optically coupled according to a given coupling force. The assembly formed by the two optical cavities 302, 310 has two polarization degenerate optical mode pairs. The first polarization degenerate optical mode pair is configured to resonate with the transition between a state having two elementary excitations (biexcitons) and two states having one elementary excitation (exciton). The second polarization degenerate optical mode pair is configured to resonate with the transition between the two states of the quantum box 301 having one elementary excitation (exciton) and the fundamental state (also called the neutral state). The modes in each optical mode pair have radiation patterns 307 with an overlap of 70% or more. The coupling between the two optical cavities 302 and 310 can also be configured according to the embodiment described in patent application [3].

[0088] According to embodiments of the invention, the number of electrical bonding pads arranged around the top surface of the optical cavity 302 is greater than three. The number of such electrical bonding pads can be odd or even, and can be less than twenty. The electrical bonding pads can be arranged asymmetrically around the optical cavity 302, such that at least three electrical bonding pads and their associated semiconductor arms are not oriented in parallel directions. This means that the angular spacing between adjacent electrical bonding pads and the radial spacing measured from the optical cavity 302 can be non-constant for all implemented electrical bonding pads. Furthermore, the electrical bonding pads can be placed at different distances from the electrical contact 305, i.e., the electrical bonding pads can be placed in different planes perpendicular to the lamination axis.

[0089] According to embodiments of the invention, the apparatus 300 for generating single photons and entangled photon pairs may include a cooling unit, such as one employing the Peltier effect or a cryogenic system using nitrogen or helium, configured to control and maintain a constant operating temperature for the quantum box 301. Such an operating temperature can be between 4 Kelvin and 100 Kelvin. This low operating temperature limits the interaction between the quantum box 301 and its adjacent environment and maintains the consistency between the excited state and the fundamental state over time intervals long enough to manipulate the state of the quantum box 301.

[0090] Figure 10The diagram illustrates the time-varying state 400 of a bright exciton state in a quantum box 301 inserted into a micropillar-shaped optical cavity 302, where both quantum box 301 and optical cavity 302 are characterized by non-zero anisotropy. The anisotropy of optical cavity 302 means that the degeneracy of its modes is enhanced by utilizing low-energy and high-energy modes H and V that match the specific polarization axes of the micropillar. The anisotropy of quantum box 301 means that the degeneracy between two excited states separated by non-zero energies, known as fine-structure splitting, is enhanced. Each of the two excited states (also called eigenstates) of quantum box 301 is associated with a given linear polarization state X or Y, from which a photon can be emitted or excited by a photon. Typically, the modes H and V of optical cavity 302 do not coincide with the polarization directions x and y of quantum box 301, and this non-coincidence can be quantified by an angle denoted as θ. The resonant excitation of the exciton levels of quantum cell 301 by linearly polarized photons according to one of the modes H or V of optical cavity 302 results in the excitation of two eigenstates weighted according to the value of the angle θ. This result in excited states 4021 or 4020 is unstable, and its phase changes with time at a rate proportional to the fine-structure splitting value. This behavior can be used to collect only single photons generated by quantum cell 301, for example, by exciting quantum cell 301 with photons linearly polarized according to H of optical cavity 302, and by collecting only photons generated according to linearly polarized states perpendicular to the axis used in the excitation (in this case, the axis V of optical cavity 302). In such a configuration, increasing the fine-structure splitting value can cause photons to be emitted in the detected polarization direction before they are spontaneously emitted in the polarization direction of the excitation. In the second stage, the fine-structure splitting value should be reduced to limit the probability of emitting two photons instead of one photon in the same excitation region.

[0091] Figure 11 This illustrates a device 300 for generating single photons according to an embodiment of the present invention. Such an embodiment implements an anisotropic quantum box 301 incorporated within a micropillar-shaped birefringent optical cavity 302. An electric field of adjustable intensity and direction is applied to the quantum box 301 via electrically bonded pads 304a, 304b, 304c, and 305 arranged according to one of the above embodiments, with pad 304c and an associated voltage source 306c... Figure 11The device 300 for generating single photons is hidden. It includes an excitation laser source 501 configured to generate light pulses designed to optically pump the quantum box 301 to transition its state from a neutral state to an excited state. The polarization state of the light pulses is linear according to one of the specific axes of the optical cavity 302, and the associated wavelength is chosen such that the energy of the photons is sufficient to excite the quantum box 301. The duration of the light pulses and their repetition frequency determine the rate at which the device 300 generates photons per second. The device 300 also includes a polarization splitter cube 502 and a converging lens 503, which are respectively configured to: isolate the photons generated in the optical cavity 302 according to the linear polarization state in a direction perpendicular to the direction of the excited photons, and to improve the optical coupling of the polarization splitter cube 502 to the optical cavity 302. The specific axes H and V of the optical cavity 302 are configured to be non-collinear with the specific axes x and y of the quantum box 301 by an angle θ (ideally equal to 45 degrees).

[0092] Figure 12 This describes a method for calibrating a 600-degree anisotropic quantum box 301, which is subjected to conditions such as Figure 4 The electric field is shown. The three components of the synthetic electric field in space are independently adjustable via at least three adjustable voltage sources. The method is iterative and includes, at each iteration: modifying the intensity of at least one of the three components of the synthetic electric field (step 601); and in a second stage, measuring one or more interest characteristic parameters of the quantum box 301 associated with the applied synthetic electric field (step 602). The method can stop when the desired interest characteristic parameter values ​​are obtained and can return to the voltage values ​​applied to different electrical bonding pads. The first iteration of the method can correspond to a synthetic electric field of zero intensity.

[0093] This calibration method can be used to identify the operating point of the device 300 used to generate entangled photon pairs. The characteristic parameters of interest for such a device include: fine structure splitting, which must be significantly reduced, ideally set to zero; and the emission wavelength, corresponding to biexciton relaxation and exciton relaxation.

[0094] This calibration method can also be used to find the optimal operating point of the device 300 for generating single photons in a static mode, wherein the fine-structure splitting of the anisotropic quantum box 301 characterized by the static mode is statically tuned before any excitons are generated. The fine-structure splitting must allow a transition rate sufficient to enable the excited state to relax into a linearly polarized state perpendicular to the polarization state of the excited photon at the end of the transition time, which is less than the duration of the excitation light pulse. The fine-structure splitting can be further optimized such that:

[0095] - It is greater than the lower limit of the relaxation of the excited state according to a linear polarization state perpendicular to the polarization state of the excited photon at the end of the transition time, which is shorter than the lifetime of spontaneous emission of the excited state to at least one-third of it (preferably).

[0096] (at least one-fifth of the land);

[0097] - It is less than the upper limit of the quantum box 301 that can emit more than one photon during the duration of the excitation light pulse.

[0098] Figure 13A This is a flowchart of a method 700a for generating single photons using a device 300 for generating photons, according to an embodiment of the present invention. In such an embodiment, the fine structure splitting characterizing the anisotropic quantum box 301 is statically adjusted. The first step 701a of the method includes applying a potential difference between each of the electrical bonding pads 304a, 304b, 304c and an electrical contact 305 carried by the bottom surface of the optical cavity 302 to generate a synthetic electric field experienced by the quantum box 301. As described above, the components of such synthetic electric field are adjusted to optimize the fine structure splitting value. In addition to matching the wavelengths of the single photons generated by the quantum box 301, applying the synthetic electric field in three spatial directions can define the orientation of a particular axis of the quantum box 301 so as not to be collinear with a particular axis of the optical cavity 302 into which the quantum box 301 is inserted. Advantageously, the particular axis of the quantum box 301 is oriented at a 45-degree angle relative to the particular axis of the optical cavity 302.

[0099] The second step 702a of the method includes illuminating the quantum box 301 with a series of light pulses, the wavelength spectrum and polarization state of which correspond to one of the modes of the optical cavity 302 inserted into the quantum box 301. The duration of the light pulses is selected to be sufficient to excite the quantum box 301 and enable it to emit at least one photon according to a spontaneous emission process.

[0100] Figure 13B This is a flowchart of a method 700b for generating single photons using a device 300 for generating photons, according to another embodiment of the present invention. In such an embodiment, the fine structure splitting of the anisotropic quantum box 301 is dynamically controlled. This dynamic control is achieved by modulating the synthetic electric field experienced by the quantum box 301 so that the fine structure splitting value can be modified within a time interval less than the spontaneous emission time of the quantum box 301.

[0101] The first step 701b of the method includes illuminating the quantum box with a series of light pulses, the wavelength spectrum and polarization state of which correspond to the mode of the optical cavity 302 incorporating the quantum box 301. The duration of the light pulses is chosen to be sufficient to excite the quantum box and enable it to emit at least one photon according to a spontaneous emission process.

[0102] The second step 702b of the method includes applying a potential difference between each of the electrical bonding pads 304a, 304b, 304c and the electrical contact 305 carried by the bottom surface of the optical cavity 302 to generate a synthetic electric field experienced by the quantum box 301. The fine structure splitting value increases as a function of the strength of the synthetic electric field, which must be kept below a threshold corresponding to damage to the quantum box 301, i.e., a threshold at which the electrical and optical features determined during the calibration of the quantum box 301 can no longer be reconstructed. The strength of the synthetic electric field is chosen such that the phase of the resulting excited state changes considerably over time, between 45 and 135 degrees, and preferably between 80 and 100 degrees. This phase change over time must also occur within a time shorter than the lifetime of spontaneous emission of the exciton state (shorter than the lifetime of spontaneous emission of the exciton state to at least one-third, preferably at least one-fifth (at least by a factor of 3 and preferably by at least a factor of 5)).

[0103] The third step 703b of the method can be triggered immediately after the phase of the required initial exciton state has changed over time. Such a step of the method involves modifying the strength of the synthesized electric field to minimize the energy deviation between the two eigenstates with a primary excitation.

[0104] Figure 14 This describes a method 800 for generating entangled photon pairs using a device 300 for generating photons, according to an embodiment of the present invention. The device 300 implements an anisotropic quantum box 301 incorporated in an optical cavity 302 having at least one first optical mode pair and one second optical mode pair, each of which is polarization degenerate. Entanglement of the generated photons is achieved through static control of the fine-structure splitting characterizing the implemented anisotropic quantum box 301. A first step 801 of the method includes applying a potential difference at each of the electrical bonding pads 304a, 304b, 304c and an electrical contact 305 carried by the bottom surface of the optical cavity 302. Such a potential difference is optimized to reduce the energy deviation between two states having a primary excitation defined by the fine-structure splitting of the quantum box 301. In particular, step 801 may include canceling the fine-structure splitting, which makes the quantum box 301 a system with three energy levels relative to biexciton relaxation. The potential difference is also set such that:

[0105] - The transition between a state with two elementary excitations and a state with one elementary excitation and the first optical cavity 302

[0106] Modes resonate; and

[0107] - A transition between a primary excited state and a fundamental state resonates with the second mode pair of the optical cavity 302.

[0108] The second step 802 of the method includes filling the quantum box 301 with a state having two elementary excitations by means of an energy input. The generation of this biexciton state XX can be achieved by exciting the quantum box 301 with two consecutive photons of suitable energies: a first energy photon ω... X Sufficient to trigger the transition of the first exciton, the second energy photon ω XX Unlike ω X This generates a second exciton, thereby obtaining a biexciton state XX, or alternatively, obtaining two energy photons (ω). XX +ω X ) / 2.

[0109] Figure 15 Experimental measurements characterizing the fine-structure splitting of an anisotropic quantum cell 301 incorporated in a micropillar-shaped optical cavity 302, according to an embodiment of the invention, are shown, with the top surface of the optical cavity 302 surrounded by two electrically bonded pads 304a and 304b. The experimental measurements were taken for two voltage ranges applied to the electrically bonded pads 304a and 304b, illustrating the technical advantages of the embodiments of the invention in deterministic control of the fine-structure splitting values. These measurements were obtained for a configuration where the quantum cell 301 is excited by a laser with energy greater than that corresponding to an optical transition of an exciton. This non-resonant excitation can fill the two exciton states 2020 and 2021 of photons subsequently emitted at two different wavelengths. The wavelength difference between the two photons allows the extraction of the fine-structure splitting value. Figure 15 The results of such measurements are shown, where the color scale reflects the absolute value of the fine-structure split as a function of the two voltages applied to contacts 304a and 304b. The figure shows how the absolute value of the fine-structure split varies with the applied voltages and changes sign by canceling each other out over the entire range of voltage 1 and voltage 2 paired together.

[0110] According to one embodiment of the present invention, the formation of initially neutral excitons in the quantum box 301 is carried out by non-resonant optical pumping, which includes exciting the quantum box 301 with photons having energies greater than the stopband of the material forming the quantum box 301.

[0111] According to another embodiment of the invention, the geometry of the micropillar forming the optical cavity 302 defined in a plane perpendicular to the growth axis can be elliptical, polygonal, or other.

[0112] This invention is not limited to the embodiments described above as non-limiting examples. It includes all variations that can be conceived by those skilled in the art.

[0113] References

[0114] [1] Trotta, Rinaldo et al., "Highly Entangled Photons from Hybrid Piezoelectric-Semiconductor Quantum Dot Devices", Nano Letters 14.6 (2014): 3439-3444.

[0115] [2] K. Kowalik, O. Krebs, A. Lemaitre, S. Laurent, P. Senellart, P. Voisin, JA. Gaj. “Influence of an in-plane electric field on exciton fine structure in InAs-GaAs self-assembled quantum dots.” Applied Physics Letters 86(4), 041907

[0116] [3]WO / 20111 / 089336 "Source of polarized entangled photon pairs and method for manufacturing a game".

Claims

1. A device (300) for generating photons, comprising a quantum cell (301) inserted into a microcylindrical optical cavity (302) having at least one optical mode, the quantum cell (301) having at least one fundamental state and two states having a primary excitation, the microcylindrical optical cavity (302) having a bottom surface and a top surface, the bottom surface carrying an electrical contact (305), the device comprising: The device comprises at least three electrically insulated pads (304a, 304b, 304c) arranged around the top surface of the micropillar optical cavity (302), characterized in that the device further comprises at least three adjustable voltage sources (306a, 306b, 306c) for applying a corresponding and variable potential difference between each of the electrical pads (304a, 304b, 304c) and the electrical contact (305) carried by the bottom surface of the micropillar optical cavity (302).

2. The apparatus (300) according to claim 1, wherein, The electrical bonding pads (304a, 304b, 304c) are linked to the top surface of the micropillar optical cavity (302) via semiconductor arms (308a, 308b, 308c), the semiconductor arms (308a, 308b, 308c) being radially oriented relative to the micropillar optical cavity (302) and having a width smaller than the width of the micropillar optical cavity (302) in the tangential direction and at their ends closest to the micropillar optical cavity (302).

3. The apparatus (300) according to claim 1, wherein, The electrical bonding pads (304a, 304b, 304c) are linked to semiconductor arms oriented radially toward the micropillar optical cavity (302), and the ends of the semiconductor arms are separated from the top surface of the micropillar optical cavity (302) by empty gaps (309) or gaps filled with a submicron-width dielectric.

4. The apparatus (300) according to any one of the preceding claims, wherein, The micropillar-shaped optical cavity (302) forms a PIN diode, and the quantum box (301) is located in the intrinsic region (3021) of the diode.

5. The apparatus (300) according to any one of claims 1-3, wherein, The electrical bonding pads (304a, 304b, 304c) are supported by corresponding pillars (303) that are optically and electrically decoupled from the micropillar optical cavity (302).

6. The apparatus (300) according to any one of claims 1-3, wherein, The micropillar-shaped optical cavity (302) has at least one first mode pair and at least one second mode pair, each mode pair being polarization degenerate, and wherein the quantum box (301) also has a state with two elementary excitations.

7. The apparatus (300) according to claim 6 further comprises: A second optical cavity (310) coupled to the microcylindrical optical cavity (302), the quantum box (301) being inserted into the microcylindrical optical cavity (302), the geometry of the microcylindrical optical cavity (302) and the second optical cavity (310) and their coupling force being selected such that the assembly consisting of the two coupled cavities has a first mode pair and a second mode pair, the first mode pair being polarization degenerate and resonating with the transition between the quantum box (301) having two elementary excitations and two states having one elementary excitation, the second mode pair being polarization degenerate and resonating with the transition between the quantum box (301) having two states having one elementary excitation and a fundamental state, each of the modes having a radiation pattern with 70% or more overlap.

8. The apparatus (300) according to claim 7, wherein, The second optical cavity (310) is also micropillar type, and the micropillar type optical cavity (302) and the second optical cavity (310) are arranged side by side.

9. A method (700a) for generating a single photon using the apparatus (300) according to any one of claims 1 to 6, comprising the following steps: An electrical potential difference is applied between each of the electrical bonding pads (304a, 304b, 304c) and the electrical contact (305) supported by the bottom surface of the micropillar optical cavity (302); and The quantum box (301) of the device is irradiated with light pulses that present a spectrum and polarization direction corresponding to the mode of the micropillar optical cavity (302). The potential difference is chosen to modify the energies of two eigenstates with a single elementary excitation in the following manner: This causes the state to resonate with the wavelength of the light pulse's spectrum; and The probability of the quantum box (301) emitting a single photon is maximized, and the single photon exhibits a linear polarization orthogonal to the linear polarization of the illumination.

10. The method according to claim 9, wherein, The potential difference is further selected such that the orientation of the axis of the quantum box (301) is determined based on the midpoint between the directions of the two polarization axes of the micropillar optical cavity (302).

11. The method (700a) according to any one of claims 9 and 10, wherein, The potential difference is variable over time, and: During the first period in which the quantum box (301) is irradiated for at least a portion of its duration, a first value is chosen to cause a non-minimum deviation in the energies of two eigenstates having a primary excitation, and the duration of the first period is chosen to cause a phase change between the two states between 45° and 135°. During the second period immediately following the first period, a value is chosen that minimizes the deviation between the energies of two eigenstates with a primary excitation.

12. The method according to claim 11, wherein, The duration of the first cycle is selected to cause a phase change between 80° and 100° between the two states.

13. A method (800) for generating entangled photon pairs using the apparatus (300) according to any one of claims 6 to 8, the method comprising the steps of: An electrical potential difference is applied between each of the electrical bonding pads (304a, 304b, 304c) and the electrical contact (305) supported by the bottom surface of the micropillar optical cavity (302), the potential difference being selected as follows: Minimize the energy difference between two states of the quantum box (301) that have a primary excitation; and The transition between a state with two elementary excitations and a state with one elementary excitation resonates with the first mode pair of the microcylindrical optical cavity (302), and the transition between a state with one elementary excitation and the fundamental state resonates with the second mode pair of the microcylindrical optical cavity (302). The quantum box (301) is filled with a state having two elementary excitations by energy input.

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