Quantum receiver system

Abstract

Quantum Reception System The present invention relates to a quantum reception system comprising a first optical receiver (102), the first optical receiver (102) comprising a first telescope (107) optically linked to the first telescope (107). The quantum reception system further comprises a second optical receiver (102) and the second optical receiver (102) comprising a second telescope (107). Each receiver (102) communicates the signals detected by the quantum analyzer (104) to a processing unit (103), and the processing unit (103) combines the detected signals. Figure for the abstract: 1

Description

Title of the invention: Quantum reception system

[0001] The present invention relates to satellite telecommunications systems and more particularly to quantum optical telecommunications. The transmission is made between two devices, for example an artificial satellite in orbit around a planet, typically the Earth, and a device on the ground.

[0002] Quantum communications are based on the exchange of photons between a transmitter and a receiver. Ideally, this exchange is on the order of a few photons emitted by a very low-power laser source. In practice, the emission of a single photon is complex, and a laser source emitting a few coherent photons or pairs of entangled photons is used in quantum transmissions.

[0003] The transmission of several photons, in the form of a packet of several photons or several packets of several photons or equivalently of an electromagnetic wave pulse for example, nevertheless jeopardizes the actual security of a communication intended to be secure between the transmitter and the receiver.

[0004] According to the laws of quantum mechanics, measuring the state of a particle or photon modifies the element being measured. Thus, when an emission comprises a packet of photons rather than a single photon, a third party can intercept photons without interrupting the communication or informing the transmitter and receiver of the interception, since some photons are not intercepted.

[0005] Thus, to secure quantum communications, various protocols have been developed, some of which rely on the use of several signals at varying intensities, only a portion of which, often a single photon, is useful for the exchange. The other signals are then considered decoys for a third party wishing to access the secure exchange.

[0006] Other protocols are based on quantum entanglement using pairs of entangled photons. Sending multiple pairs is problematic because it is necessary to ensure that the two measured photons are from the same pair. However, when several pairs of photons are sent, it is not certain that the measured photons are from the same pair. Entanglement-based protocols also have applications for quantum information networks.

[0007] Such protocols always rely on the exchange of a limited number of photons by a low-power emitting source. This constraint affects the transmitting and receiving equipment required to perform the transmissions. When the transmitter is contained within a satellite, the mass of the transmitting payload quantum mechanics is an important constraint, the emitter must also be resistant to launching.

[0008] Furthermore, specifically with regard to communications involving a transmitter onboard an artificial satellite, limited access to the orbiting transmitter is highly restrictive and prevents the system from being adapted in the event of a transmitter failure, or even from changing transmission parameters. Ground-based receiving systems are therefore adapted to overcome the limitations imposed by the transmitters.

[0009] Receiving systems generally comprise optical telescopes with large diameters, exceeding one and a half meters, optically connected to photon detectors. The telescope collects the photons, which are then guided by the telescope's optical elements and optical waveguides to a quantum analyzer, generally comprising at least two photon detectors.

[0010] The photon detector then emits a signal when a photon is detected, transforming from a photon reception signal into a deterministic signal linked to the detector. The detection signal, which may be an electrical signal, is transmitted to processing units by the quantum analyzer. The quantum analyzer thus enables the transmission of a detection signal, dependent on the detector, based on the photon detections, and therefore to discriminate between the detected photons. This discrimination can be linked to the optics upstream of the detectors, which can orient the photons according to their polarization, for example, onto one detector rather than another. Consequently, the quantum analyzer makes it possible, based on the photon collection by the system and its subsequent detection, to determine the quantum state of the transmitted photon for communication.

[0011] In practice, receiving systems are generally derived from astronomical observation systems. Since the received signal contains few photons, the collecting area of ​​the receivers must be as large as possible. Increasing the collecting area by increasing the diameter of the telescope is difficult, as large optical elements are complex to manufacture without defects, costly, and complex to implement and operate. Furthermore, the small number of transmitted photons requires long acquisition times, from a few minutes to several days for a low data rate. In the context of quantum key establishment in secure communication protocols, this low data rate limits the number of keys that can be established.

[0012] The use of large telescopes for signal reception is further complicated by their size and the installation of additional elements such as, for example, a dome. Moreover, in the case of orbiting satellites, it is necessary to be able to track the satellite's movement. These devices are difficult to because they are adaptable depending on the stream you want to receive, it is therefore not easy to modify the parameters of a transmission with a satellite on the receiver side.

[0013] The aim of the invention is therefore to provide a quantum satellite telecommunication system that increases the transmission rate and reduces the acquisition time. The collecting surface area ensuring the reception of photons is increased while reducing the size of the receiving system.

[0014] To this end, the invention relates to a quantum reception system comprising a first optical receiver, the first optical receiver comprising a first telescope. The quantum reception system further comprises a second optical receiver, the second optical receiver comprising a second telescope. Each optical receiver communicates detected signals to a processing unit, and the processing unit combines the detected signals.

[0015] The quantum receiving system, because it comprises two or more optical receivers, each including a telescope, offers a larger photon-collecting surface. Each telescope can be equipped with a separate quantum analyzer or can share its quantum analyzer with another telescope.

[0016] Each receiver is equipped with a telescope, and the receivers collect photons independently. The photons are collected by the telescopes, and the quantum analyzers detect the photons using photon detectors. The analyzers transmit a detection signal to a common processing unit. The processing unit thus ensures and centralizes the information processing for the quantum communication operation.

[0017] Thus, because the system includes several telescopes and several quantum analyzers, the throughput of quantum communication is improved at a lower cost.

[0018] The system thus defined offers a large photon collection area and resilience against hardware failure.

[0019] The invention also relates to a quantum reception method implementing a quantum reception system as described above, and advantageously, but necessarily, includes a pointing step for the optical receivers. The method comprises a pointing and tracking step during which the first receiver emits a pointing signal towards a satellite, and receivers of the system, being active in reception mode and receiving a pointing signal from the satellite, the telescopes of the active receivers that have received the pointing signal are oriented according to the pointing signal from the satellite.

[0020] According to other advantageous aspects of the invention, the quantum reception system comprises one or more of the following features, taken individually or in all technically possible combinations.

[0021] In one embodiment, the first optical receiver and the second optical receiver further comprise respectively a first mount and a second mount for orienting the first and second telescopes and each telescope of the receiving system is oriented along a proper direction of photon reception.

[0022] In one embodiment, the first optical receiver further includes a pointing device, the pointing device emits a signal to a satellite, the optical receiver receives a pointing signal from the satellite and the telescope mount of the receiver orients the telescope according to the pointing signal.

[0023] In one embodiment, the system further comprises a quantum analyzer, the quantum analyzer being optically linked to at least one of the telescopes of the system.

[0024] In one embodiment, the system further includes a cryostat for cooling a set of photon detectors shared by the two telescopes.

[0025] In one embodiment, the optical receiver telescopes are equipped with a system for compensating atmospheric disturbances for the reception of photons.

[0026] In one embodiment, the optical receivers further each include a dating system for determining an emission date and optionally the arrival date of the photon, the dating system transmitting the emission date and optionally the arrival date of the photon to the processing unit.

[0027] In one embodiment, each optical receiver of the system is composed of at least two telescopes, the at least two telescopes each being associated with a quantum analyzer and a common telescope mount to orient them in a common way.

[0028] In one embodiment, the quantum analyzer comprises an optical blade, the blade receiving photons from two separate sources.

[0029] In one embodiment, two optical receivers of the system form a pair, and the optical blade of a quantum analyzer of the pair is a polarized beam splitter, the quantum analyzer further includes a pair of photon detectors, the polarized beam splitter dividing a beam of photons in two to direct polarized lights onto the detectors of the quantum analyzer.

[0030] In one embodiment, the system comprises a set of optical receivers, the receivers of the set being spaced apart from each other, each separated by a predetermined distance and arranged in a pattern of concentric circles.

[0031] The invention thus makes it possible to obtain a modular system, depending on the number of optical receivers used, with a high photon reception capacity. In addition, the use of a cryostat for the detectors of several quantum analyzers and the use of two photon detectors per quantum analyzer reduce This greatly reduces the installation and maintenance costs of such a system. The system can therefore be deployed easily and at a lower cost.

[0032] Furthermore, quantum analyzers can be connected to two telescopes, or one telescope and a second source, using an optical plate to provide two optical inputs to the quantum analyzer. This second source can be a test or calibration device, thus facilitating the setup and maintenance of the system.

[0033] This optical blade can be a beam splitter such as a polarized beam splitter.

[0034] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0035] [Fig.1] [Fig.1] is a diagram of a quantum reception system according to the invention;

[0036] [Fig.2] [Fig.2] is a representation of a pointing and tracking step according to a method of implementing the invention;

[0037] [Fig.3] [Fig.3] is a representation of the architecture and placement of receivers of a quantum reception system according to the invention;

[0038] [Fig.4] [Fig.4] is a second representation of the architecture and placement of receivers according to the invention;

[0039] [Fig. 5] [Fig. 5] represents a diagram of receptor use according to a mode of realization of the invention;

[0040] [Fig.6] [Fig.6] is a quantum receiving system comprising two telescopes by mounting according to an embodiment of the invention;

[0041] [Fig.7] [Fig.7] is a schematic diagram of a quantum analyzer according to the state of the art used in an embodiment of the invention;

[0042] [Fig.8] [Fig.8] is a schematic of quantum analyzers according to an embodiment of the invention.

[0043] [Fig. 1] Fig. 1 is a schematic diagram of a quantum receiver system according to one embodiment of the invention. The system comprises at least two optical receivers 102; here, four receivers 102 are shown, each connected to a separate quantum analyzer 104, according to the embodiment presented here. The optical receivers 102 are separated by a predetermined distance, this distance being much smaller than the distance separating the system from a transmitter, for example, a satellite 106. The communication system is ground-based, as opposed to a satellite 106 transmitting at altitude. The set of optical receivers 102 includes a telescope 107 and a mount 110 for orienting the telescope 107 to receive the photons emitted by the satellite 106. Since the telescopes 107 are each equipped with a separate mount 110, they can be oriented in different directions to receive the photons. Mount 110 also allows tracking of satellite 106 during its movement and thus maximizing the number of photons received during a transmission.

[0044] Satellite 106 emits a beam 101 of photons. This beam diverges depending on the distance from satellite 106 and illuminates optical receivers 102 on the ground. The optical receivers 102 further include a quantum analyzer 104 which, upon receiving a photon from the telescope 107, generates a detection signal. Detection is performed according to the polarization of the photon emitted by satellite 106 and received by receiver 102.

[0045] Each quantum analyzer 104 comprises at least two single-photon detectors capable of detecting a single photon. The quantum analyzer 104, or each detector of the quantum analyzer, then transmits a detection signal to a processing unit 103 if the photon detector receives a photon. The processing unit 103 is connected to all the optical receivers 102. The processing unit 103 can then reconstruct a bit from the detection signal and establish the information carried by the photon. This determination of the transmitted bit is performed based on the detection signals received by the processing unit 103, the signals being generated by the quantum analyzers 104 according to, for example, the quantum state of the received photon.

[0046] The quantum analyzers 104 are optically linked to the telescopes 107. The photons received by the telescope 107 are directly transmitted to the associated quantum analyzer 104. The optical link can be achieved through direct optical coupling between the telescope 107 and the associated quantum analyzer 104. The link can also be achieved through a free-space optical chain or an optical waveguide such as optical fiber.

[0047] The optical receivers 102 may also include a photon detection timing system. These timing devices allow the corresponding photon emission time of the satellite 106 to be determined from the photon detection time. This information is transmitted to the processing unit 103 and allows the information transmitted by the satellite 106 to be reconstructed during the transmission.

[0048] The entire set of detectors of a quantum analyzer 104 of the system may require cooling by a cryostat 105 in order to maintain optimal detection performance, and in particular to reduce thermal noise. The cryostat 105 may be a single unit, common to the entire system 100, or shared by several units depending on the cryostat's capacity.

[0049] The telescopes 107 can be Cassegrain or Ritchey-Chrétien type telescopes. The mounts 110 that support and orient the telescopes 107 can be operated mechanically or by electromechanical systems. The orientation direction of a telescope 107 is defined by its location on the ground and by the position of the satellite 106 during transmission; thus, each telescope 107 can have a different orientation. The telescopes 107 can also be equipped with a A system for compensating atmospheric disturbances, such as adaptive optics elements, aims to reduce the negative impact of disturbances during photon propagation in the turbulent atmosphere.

[0050] The reception of photons by the quantum receiving system is optimized by the presence of multiple optical receivers 102. Thus, each of the receivers 102 has its own mount, allowing it to track the satellite independently. Furthermore, this makes the system fault-resilient and increases the probability of photon reception by the system 100.

[0051] Furthermore, the multiple optical receivers 102 make it possible to increase the collecting area of ​​the system without using a larger telescope 107. This simplifies the implementation of such a system as well as its adaptability for transmissions according to different system parameters. It is indeed possible to activate or deactivate receivers 102 for certain transmissions, and therefore to modify the link data rate.

[0052] In an alternative embodiment, the quantum analyzers 104 are common to several telescopes 107.

[0053] [Fig. 2] Figure 2 is a representation of the pointing and tracking step according to the invention. The quantum receiving system comprises several ground-based optical receivers 102, as opposed to an altitude-based satellite transmitter. The system may, however, be located on a mobile or elevated platform. The optical receivers 102 are spaced far apart by a predetermined distance much smaller than the distance between the system and a transmitter. The receivers 102 are arranged such that a receiver 202 is located at the center of the set of receivers 102 to establish pointing and recover the maximum of the downlink signal during communication.

[0054] The arrangement of the set of receivers 102 shown here is circular, with a central receiver 202, which transmits the pointing signal 203 from the ground to the satellite. This arrangement is not, however, the only possible one. Preferably, the receiver 102 that transmits the pointing signal 203 should be closest to the center of the set of receivers 102, regardless of the configuration and arrangement of the receivers 102.

[0055] All or only some of the system's 102 receivers may be active during a transmission. The arrangement of all the 102 receivers is therefore modified by the activation or inactivation of some of the 102 receivers.

[0056] The signal 203 is emitted by a pointing device of the receiver 202; the signal 203 can be an optical or radio signal, destined for the satellite. It can be of low or high intensity.

[0057] The uplink signal 203 is received by the satellite 106, which also transmits a pointing signal 201, this time a downlink. The downlink pointing signal 201 spreads out according to the distance between the satellite and the receivers 102, thus widening the beam of the pointing signal 201. The signal 201 is received by the receiver that transmitted the uplink signal 203, and since the beam widens, it also illuminates all the receivers 102 active during transmission.

[0058] Each of the receivers 102 can then orient itself according to the received pointing signal 201. The mounts 110 of each telescope 107 allow them to be oriented independently. The orientation of the telescope 107 depends on the satellite's position in the sky as well as the position of the ground telescope relative to the satellite. Thus, as the satellite 106 moves in the sky, each telescope 107 can track the satellite and increase the probability of receiving a photon.

[0059] The pointing signals 203 and 201 are emitted continuously or discontinuously in order to allow rapid and efficient pointing when the satellite is visible to the receivers 102.

[0060] [Fig.3] [Fig.4] Fig.3 and Fig.4 are representations of a possible placement of receivers of a quantum reception system according to the invention.

[0061] Figure 3 shows the placement of ten optical receivers 102, arranged in a circle of six receivers 102. Each receiver 102 is separated from the others by a predetermined distance 300. The receivers 102 thus form a grid of receivers 102 on the ground. The distance 300 is small compared to the distance separating all the receivers 102 from a transmitter, for example, a satellite.

[0062] One receptor is at the center of a first circle, and three receptors are arranged outside the circle, along a second circle with a diameter larger than the first circle. Thus, they form a set of two concentric circles. A receptor 302 is located at the center of the circles of the receptors 102.

[0063] The central receiver 302 transmits the pointing signal 203 towards the satellite with which the receivers 102 are communicating. Since it is located in the center of the other receivers 102, when the satellite transmits its downward pointing signal 201, the beam aimed at this receiver 302 illuminates a majority, or even all, of the surrounding receivers 102. This illumination is due to the broadening of the photon beam emitted by the satellite and also allows the receivers 102 to subsequently receive the signal emitted by the satellite during communication.

[0064] Figure 4 shows a second arrangement of optical receivers 102 comprising twenty-six optical receivers 102 arranged in concentric circles. One receiver 402 is located at the center of the concentric circles. The optical receivers 102 are separated from each other by a distance 400. This distance 400 is small compared to the distance separating the entire array of receivers 102 from a transmitter. The receivers 102 Since they are separated by a distance of 400, this distance acts as a grid to define the arrangement. By varying the distance of 400, the arrangement of the 102 receivers is modified, creating more or less compact receiving systems.

[0065] In the same way as in [Fig.3], the central receiver 402 emits the pointing signal 203, so that when a satellite transmits in its direction, the spread beam illuminates the other receivers 102 around.

[0066] The arrangements shown in [Fig. 3] and 4 are not the only arrangements envisaged. Furthermore, a system may consist of telescopes of different sizes, which can create particular configurations depending on the size of the telescopes.

[0067] The receivers 102 can be arranged in triangular patterns or polygonal geometric shapes. One of the receivers 102 is located at the center or as close as possible to the center of an arrangement, regardless of the shape, for the emission of the pointing signal 203.

[0068] Furthermore, all 102 receptors may be active during communication, or only some of them. In this case, the arrangement of the active 102 receptors is different.

[0069] [Fig. 5] [Fig. 5] represents a diagram of receptor use according to a mode of implementation of the invention. The quantum receiver system shown is in a configuration similar to that of [Fig. 4]. It comprises twenty-six optical receivers 102 arranged in three concentric circles. The assembly also includes a central optical receiver 502.

[0070] The optical receivers 102 are separated by a distance 400, creating a mesh of optical receivers 102. This distance 400 is considered to be the minimum distance between two optical receivers 102.

[0071] A subset of ten receivers 503 out of the twenty-six are active during a transmission. The central receiver 502 is among the active receivers 503 and emits the pointing signal 203 for a transmission with a satellite. The satellite also emits a pointing signal 201 to the active receivers 503 of the transmission.

[0072] Whether or not receivers 102 are activated for a transmission depends on several criteria, such as the data rate required for the transmission. It is therefore easy to change the data rate depending on the number of active receivers 503. Furthermore, this allows, depending on the arrangement of the receivers 503, adaptation to transmissions from several different satellites. Since each transmission has its own characteristics, it becomes possible, with a single system, to have different transmissions depending on the different activations of the optical receivers 102.

[0073] The activation of the receptors 503 forms in certain cases a pattern different from that of the physical arrangement of the optical receptors 102. A receptor 102 The central receiver is always located at, or near the center of, the pattern formed by the active receivers 503. The central receiver is the one that emits the pointing signal 203; thus, several optical receivers 102 can include a pointing device depending on the activation patterns considered. In this way, for each transmission with a different activation pattern, there is a pointing signal emitted by a ground-based optical receiver 102, near the center of the pattern. Therefore, when a satellite emits a beam of photons pointed towards the central receiver, the active receivers around the receiver that emitted the pointing signal 203 are also illuminated by the beam.

[0074] The activation of certain optical receivers 102 also makes it possible to modify the distance between two optical receivers 102. This new distance is greater than the minimum distance 400 and makes it possible to vary the mesh of receivers 102 without modifying the physical arrangement of the receivers 102, by the simple activation during a communication.

[0075] In addition, the activation or not of certain receivers makes it possible to limit the flow rate or to increase it over time depending on the physical availability of the elements subject to hazards such as failures.

[0076] [Fig. 6] Fig. 6 is a quantum receiving system comprising two telescopes per mount according to an embodiment of the invention. The system 600 is in communication with a satellite 106 emitting photon fluxes towards the optical receivers 602 of the system 600.

[0077] The optical receivers 602 each comprise two telescopes 604-605 forming a two-telescope optical receiver 607 sharing a single mount. These telescopes can incorporate an adaptive optics module to increase the receiving capacity of the telescope 604-605. The telescopes 604-605 are supported and moved by a separate mount for each pair of telescopes 604-605.

[0078] The 604 telescope is further optically linked to a quantum analyzer, not shown in [Fig. 6]. The quantum analyzer comprises at least two photon detectors capable of detecting a single photon. The optical link between the 604 telescope and the quantum analyzer can be a direct optical coupling or an optical chain, including optical fibers.

[0079] In one embodiment, each of the 604-605 telescopes can be optically linked to a single quantum analyzer, distinct for the two telescopes in a pair. Furthermore, in other embodiments, the quantum analyzer is capable of receiving photons from two telescopes, and the quantum analyzer can be common to both 604-605 telescopes.

[0080] The detectors of the quantum analyzers of a single 602 receiver may require cooling by one or more cryostats. Several 602 receivers can share a common cryostat to reduce system installation and maintenance costs while maintaining good photon detection capabilities.

[0081] The telescopes 604 and 605 of a receiver 602 receive photons from the satellite 106, and the photon detectors of the receiver 602 detect the received photons. When a photon is detected, the optical receiver 602 transmits a signal to the processing unit. All optical receivers 602, each equipped with two telescopes 607, transmit the detection signals to the same processing unit, which is not shown in this figure.

[0082] Each pair of telescopes 604-605 is therefore capable of performing detection independently. In this way, an optical receiver 602 has a photon-collecting surface that is doubled.

[0083] In this way, for the same surface area, it is possible to concentrate a larger number of telescopes and thus obtain a larger photon-collecting surface. Since the transmission rate is defined in particular by the number of receivers 602 available for communication, increasing the number of telescopes 604-605 increases the system's throughput 600.

[0084] The 600 system is not limited to two telescopes per mount and can include N telescopes per mount. The N telescopes are then orientable in a common manner.

[0085] The 600 system can also be deployed on smaller areas while preserving the transmission quality and throughput.

[0086] [Fig. 7] Figure 7 is a schematic diagram of a prior art quantum analyzer used in an embodiment of the invention. The quantum analyzer 704 shown is used in a receiving system according to the invention and comprises a non-polarizing beam splitter 701, two polarizing beam splitters 702-703, and four single-photon detectors 704-707. The quantum analyzer 704 is optically linked to a telescope 707 by waveguides, for example, an optical fiber.

[0087] In quantum communication using photon polarization to transmit information, as described by quantum communication protocols such as BB84 (Bennett-Brassard 1984), it is necessary to have as many photon detectors as there are different polarizations. The quantum analyzer 104 therefore includes four photon detectors 704-707 in order to correctly detect photons according to their polarization.

[0088] The quantum analyzer 704 is contained within an optical receiver. More specifically, it ensures the detection of a photon by the receiver. Each detector A 704 quantum analyzer may require cooling by a cryostat not shown in [Fig. 7]. The cryostat can be shared by one or more 704 quantum analyzers and ensures optimal detection conditions.

[0089] The non-polarizing beam splitter is, for example, a beam splitter 701 which reflects a portion of the received beam into a first beam towards a first polarized beam splitter 702. The second portion of the beam which is not reflected by the beam splitter is transmitted directly towards a second polarized beam splitter 703. The photons are thus either reflected or transmitted according to a probability, for example 50%, making transmission or reflection equiprobable.

[0090] The polarized beam splitters 702-703, like the beam splitter 701, divide the received beam into two, either by reflecting it or by allowing it to pass through the splitter. This division is performed according to the polarization of the photons that make up the beam. Part of the photons 710 is thus reflected onto the detector 706 and the other part transmitted directly to the detector 707. Similarly, a photon 911 is transmitted to the detector 704 or reflected to the detector 705 depending on its polarization.

[0091] The quantum analyzer 704 further includes a photon timing system not shown in [Fig. 7]. When the photon is received by the telescope 707 and then detected by the quantum analyzer 704, the photon timer estimates the arrival time of the detected photon. From this arrival time, it is then possible to determine the emission time by a transmitter such as a satellite, taking into account propagation effects.

[0092] The quantum analyzer 704 further includes a second input 708 which can be optically linked to a second telescope.

[0093] In one embodiment, two telescopes share the same quantum analyzer, for example dynamically or systematically. This makes it possible to halve the number of quantum analyzers.

[0094] The second input 708 of the quantum analyzer 704 can also, for example, be optically linked to another device, such as a calibration or testing device for the quantum analyzer 704.

[0095] The receiver transmits a signal to the system's processing unit. The signal includes a detection signal and the arrival time estimated by the photon timer. The processing unit is then connected to each of the quantum analyzers. The accumulation of bits by the processing unit ensures the reconstruction of the information resulting from the measurement of the polarization state of the received photon. The processing unit thus allows the received information to be processed for, for example, the exchange of encryption keys or already encrypted quantum communications.

[0096] The operation of the quantum analyzer 704 described above applies to a beam of several photons, as well as to a single photon transmitted for quantum communication. The photon is then collected by all the receivers and detected by a single photon detector 704-707, which performs the measurement. Thus, the photon is split by the first beam splitter 701 into two parts, each part of the photon being directed towards the polarized beam splitters 702-703, where a further splitting guides each part of the photon onto the photon detectors 704-707.

[0097] [Fig. 8] Figure 8 is a schematic of quantum analyzers according to one embodiment of the invention. Two telescopes 807-808 are shown, telescopes 807 and 808 being connected to quantum analyzers 804 and 814, respectively. Quantum analyzers 804 and 814 may need to be connected to a common cryostat or separate cryostats, depending on the system configuration.

[0098] Each of the quantum analyzers 804, 814 comprises a polarized beam splitter 802-803 and two photon detectors 815-816 for the quantum analyzer 804 and 817-818 for the second quantum analyzer 814.

[0099] The two telescopes 807-808 originate from two different optical receivers or are two telescopes on the same mount of an optical receiver. Since the two quantum analyzers 804, 814 lack a beam splitter, it is the physical separation of the telescopes 807-808, and therefore of the quantum analyzers 804, 814, that acts as a non-polarizing beam splitter.

[0100] The wave function of photons transmitted by a satellite is spatially spread. The distance between telescope 807 and telescope 808 is a physical beam splitter which, with a certain probability, allows the photon to be received by either telescope 807 or telescope 808. This is similar to how a beam splitter divides a beam with a certain probability of transmission or reflection. The absence of a beam splitter therefore does not hinder the detection of photons by detectors 815-818, and the system according to the embodiment presented functions similarly to the system in [Fig. 7].

[0101] In the embodiment of [Fig. 8], in order to obtain the four polarizations necessary for optical transmission of polarized photons as described by BB84, for example, the receivers are grouped in pairs. Thus, two optical receivers, each comprising a quantum analyzer 804, 814, together comprise four photon detectors 815-818, making the measurements equiprobable.

[0102] Optical receivers are then simpler to make and less expensive, each comprising only two photon detectors 815-818 and a polarized beam splitter 802-803.

[0103] The quantum analyzers 804-814 each include a second input 809-810 which can be optically linked to a second telescope.

[0104] In one embodiment, two telescopes share the same 804-814 quantum analyzer, for example dynamically or systematically.

[0105] The second input 809-810 allows an optical signal, composed of one or more photons, to be sent directly to the polarized beam splitter 803 for the quantum analyzer 814, respectively 802 for the quantum analyzer 804.

[0106] The second input 809-810 of the quantum analyzer 804-814 can also, for example, be optically linked to another device, such as a calibration or testing device for the quantum analyzer 804-814.

[0107] The operation of the quantum analyzers 804-814 described above applies to a beam of several photons, as well as to a single photon transmitted for quantum communication. The photon is then collected by all the receivers and detected by a single photon detector 804-807 which performs the measurement. Thus, the photon is split by the polarized beam splitters 802-803 and each part of the photon is guided onto the photon detectors 804-807.

Claims

Demands

1. Quantum receiving system comprising a first optical receiver (102), the first optical receiver (102) comprising a first telescope (107), said quantum receiving system being characterized in that the quantum receiving system further comprises a second optical receiver (102), the second optical receiver (102) comprising a second telescope and each optical receiver (102) communicating detected signals to a processing unit (103) and the processing unit (103) combining the detected signals.

2. Quantum receiving system according to claim 1, the first optical receiver (102) and the second optical receiver (102) further comprise respectively a first mount and a second mount (110) for orienting the first and second telescope (107) and each telescope (107) of the receiving system is oriented along a proper direction of photon reception.

3. Quantum receiving system according to claim 1 or claim 2, the first optical receiver (202) further comprising a pointing device, the pointing device emits a signal (203) to a satellite (106), the optical receiver (202) receives a pointing signal (201) from the satellite (106) and the telescope mount of the receiver orients the telescope (202) according to the pointing signal (201).

4. Quantum receiving system according to any one of claims 1 to 3, the system further comprising a quantum analyzer (104), the quantum analyzer (104) being optically linked to at least one of the telescopes (107) of the system.

5. Quantum receiving system according to any one of claims 1 to 4, the system further comprising a cryostat (105) for cooling a set of photon detectors (704-707, 815-818) shared by the two telescopes (102).

6. Quantum reception system according to any one of claims 1 to 5, the telescopes (107) of the optical receivers (102) are equipped with an atmospheric perturbation compensation system for the reception of photons.

7. Quantum receiver system according to any one of claims 1 to 6, the optical receivers (102) further each comprising a dating system for determining an emission date and possibly the arrival date of the photon, the dating system transmitting the emission date and possibly the arrival date of the photon to the processing unit (103).

8. Quantum receiver system according to any one of claims 1 to 7, each optical receiver (602) of the system is composed of at least two telescopes (604, 605), the at least two telescopes (604, 605) each being associated with a quantum analyzer (601) and a common telescope mount for orienting them in a common manner.

9. Quantum receiving system according to any one of claims 1 to 8, the quantum analyzer (704, 804, 814) comprises an optical blade (701, 802, 803), the optical blade (701, 802, 803) receiving photons from two separate sources (707, 708, 807, 809).

10. Quantum receiver system according to any one of claims 1 to 9, two optical receivers of the system form a pair, and the optical blade (802, 803) of a quantum analyzer (804, 814) of the pair is a polarized beam splitter, the quantum analyzer (804, 814) further comprises a pair of photon detectors (815-818), the polarized beam splitter dividing a photon beam in two to direct polarized lights onto the detectors (815-818) of the quantum analyzer (804, 814).

11. Quantum receiver system according to any one of claims 1 to 10, the system comprises an array of optical receivers (102), the receivers (102) of the array being spaced apart from each other, each separated by a predetermined distance (300) and arranged in a pattern of concentric circles.

12. Quantum receiving method implementing a quantum receiving system according to any one of claims 1 to 11, the method includes a pointing and tracking step during which the first receiver (202) emits a pointing signal (203) towards a satellite and receivers (102) of the system being active in receiving and receive a pointing signal (201) from the satellite, the telescopes of the active receivers (102) having received the pointing signal (203) are oriented according to the pointing signal from the satellite (203).

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