Quantum-information storage device comprising a plurality of optical waveguides, in particular for forming a multiplexed quantum memory, method of manufacture and use of such a device

Abstract

The invention relates to a quantum-information storage device (100) comprising: - a vacuum chamber (2), - a plurality of waveguides (4) configured to propagate light of wavelength λ and each having a segment of small cross section having a smallest transverse dimension less than λ, extending into the vacuum chamber, - an atomic trap configured to trap a single atomic cloud (20) around the segment of small section of the waveguides.

Description

[0001]Description Title: Quantum information storage device comprising a plurality of optical waveguides, in particular for forming a multiplexed quantum memory, manufacturing method and use of such a device Technical field The present invention relates to the field of quantum memories intended to store and read on demand quantum states transmitted by light. It relates more particularly to a quantum information storage device comprising a plurality of waveguides and an atomic trap configured to trap a single atomic cloud around the waveguides, each waveguide making it possible to obtain an independent quantum memory. The invention also relates to a manufacturing method and a use of such a device.Prior Art Quantum information storage is an important process in the implementation of quantum computing methods, particularly quantum communication or computation. Quantum memories store the quantum state of light without altering its properties and allow the light to be released on demand. In other words, they store a photonic quantum bit in a material medium and allow this quantum bit to be reread on demand. Applications of quantum memories cover the field of interconnection of quantum systems, and in particular the scaling up of quantum processors and their long-distance accessibility. Quantum information storage allows, for example, the synchronization of quantum bits emitted by different quantum processors to efficiently create quantum links between them and increase their computing capacities.It also enables long-distance quantum communications via quantum repeaters. In this context, a major challenge is to multiplex quantum memories, i.e., master the storage of several quantum bits in parallel in a single system in order to increase the success rates of various interconnection protocols within quantum information networks, whether short or long distance. Several known techniques can be used to improve multiplexing capabilities. These techniques are generally based on the use of several degrees of freedom of light: storage of several orthogonal spatial modes, several temporal modes or even several frequency modes. However, these techniques generally require compromises on memory performance, particularly storage efficiency, because they lead, for example, to lower absorption per mode.However, absorption per mode is a key parameter for efficiency. In addition, some degrees of freedom are not always compatible with certain storage protocols, for example due to a limited transverse extension or a narrow spectral band. It is known to produce a quantum information storage device implementing a fibered quantum memory. By coupling an atomic cloud and a nanoscopic waveguide, it is possible to produce a fibered quantum memory whose performances in terms of efficiency and storage time are particularly advantageous. A first demonstration of fibered quantum memory was carried out with atoms cooled in a magneto-optical trap around a nanoscopic optical fiber. The corresponding device is described in the article "Demonstration of a Memory for Tightly Guided Light in an Optical Nanofiber", Gouraud et al., Physical Review Letters, 114, 180503 (2015).A second demonstration was obtained with atoms trapped in a dipole trap established in the evanescent field around such a fiber. It is described in the article “Storage of fiber guided light in a nanofiber-trapped ensemble of cold atoms,” Sayrin et al., Optica 2, 353 (2015). A third demonstration of fibered quantum memory, in which the atoms are also trapped in an evanescent dipole trap around the fiber, is described in the article “Waveguide-coupled single collective excitation of atomic arrays,” Corzo et al., Nature 566, 359 (2019). Figure 1 represents a quantum information storage device 1 comprising a fibered quantum memory, as described in the latter article. The storage device 1 comprises a vacuum chamber 2 having an inlet 3 configured to allow the introduction of atoms into the chamber.The atoms may in particular come from one or more dispensers, for example controlled by electric current to heat a source of atoms and thus generate a release of atoms, and are intended to be captured in a magneto-optical trap around the optical fiber 4, then trapped in a dipole trap made in the evanescent field around the optical fiber 4. The chamber also comprises two sealed passages 5, 6 between the inside and the outside of the vacuum chamber allowing the entry and exit of the optical fiber 4. The optical fiber 4 is held in the chamber between a first support 7 and a second support 8, being fixed by gluing on these supports. The supports 7, 8 are themselves held by a plate 9 fixed in the chamber. The optical fiber 4 comprises, between the two supports 7, 8, a portion of reduced diameter, less than the wavelength of the light propagating in the optical fiber to control the quantum memory.In the described embodiment, lasers with wavelengths of the order of 686 nm and of the order of 935 nm, corresponding to wavelengths particularly advantageous for cesium atoms, are implemented for the evanescent dipole trap and the narrowed portion has a diameter of the order of 400 nm. During operation of the device 1, atoms are cooled and trapped by means of a magneto-optical trap which covers the narrowed portion of the optical fiber 4. When the light propagating in the fiber 4 reaches the narrowed portion, a large part of the energy of the light flows outside the fiber due to its reduced size. This forms an evanescent wave around the fiber which can trap atoms in the vicinity of the fiber and interact with them. The properties of the atomic medium around the narrowed portion can be controlled by light propagating in the optical fiber 4.Quantum information can then be exchanged between the atomic medium and the light circulating in the optical fiber 4: a quantum memory is obtained. Figure 2 is a detailed view of the passage 5 between the outside and the inside of the vacuum chamber. The sealed junction between the inside and the outside is made by a connector 17. The latter comprises a part made of PTFE to make the sealed contact with the optical fiber 4. Figure 3 represents a drawing bench 10 of an optical fiber 4 used to create the narrowed portion of the optical fiber. The optical properties of the fiber during and after drawing can be controlled by a laser source 11 and a photodiode 12 configured respectively to inject a signal into the optical fiber 4 and to detect the signal at the output of the fiber. The bench 10 comprises two mechanical pulling assemblies each comprising a high-precision plate 14 movable in translation and a press 13.The presses 13 hold the optical fiber 4 on supports 27, 28 positioned on the plates 14. A dihydrogen and dioxygen generator 15 makes it possible to generate a high-temperature flame 16 intended to heat the optical fiber 4 between the two plates 14 to melt it. The heating of the optical fiber combined with the separation of the two plates 14 results in the stretching of the optical fiber 4 which has the effect of reducing the diameter of the optical fiber in its heated part. Thus, to produce the narrowed portion, the optical fiber is heated and stretched over a typical length of a few centimeters, until a nanofiber is obtained whose diameter is smaller than the wavelength of the light propagating in the nanofiber. The drawing process is computer-controlled. The trajectory of the plates 14 makes it possible to produce various drawing profiles, in particular to control the length of the narrowed portion.The drawing is preferably carried out so that the drawn fiber retains an optical transmission greater than 99%. The optical fiber thus prepared is then transferred into the vacuum chamber 2 after having been fixed to the first support 7 and to the second support 8, preferably by gluing. The supports 7, 8 are fixed to the plate 9 which is installed in the vacuum chamber 2. A device as described with reference to FIG. 1 offers excellent performance, particularly in terms of efficiency and storage time. However, it only comprises a single quantum memory and therefore does not allow the multiplexing of quantum memories. There is a need to improve existing quantum information storage devices, particularly to allow the multiplexing of quantum memories. The aim of the invention is to meet this need at least in part.Disclosure of the invention To this end, the invention relates, according to one of its aspects, to a quantum information storage device comprising: - a vacuum chamber, - a plurality of waveguides configured to propagate light of wavelength O and each having a portion of reduced cross-section having a smallest transverse dimension less than O, extending in the vacuum chamber, - an atomic trap configured to trap a single atomic cloud around the portion of reduced cross-section of the waveguides. By "vacuum chamber", is meant a chamber configured to allow a vacuum to be established corresponding to pressures less than or equal to 10. -8Torr. The invention advantageously makes it possible to preserve the performance of prior art quantum memories while parallelizing several independent memories in the same device. In particular, a single atomic trap is used to prepare a large number of independent memories. It is based on the placement in a vacuum chamber of a plurality of waveguides coupled to atoms, preferably laser-cooled, preferably having a temperature below 100 µK, more preferably below 20 µK. By parallelizing fibered quantum memories, the individual performance of the memories can be maintained. A single device thus makes it possible to obtain a large number of individually accessible memories. In addition, these memories are intrinsically fibered. The portions of reduced cross-section may in particular have a smaller dimension in their cross-section of between 300 nm and 500 nm,advantageously between 350 nm and 450 nm. The plurality of waveguides is configured to transmit at least one light of wavelength O intended to produce a dipole trap trapping a portion of the plurality of atoms. Indeed, in the operating configuration, a portion of the plurality of atoms forming part of the atomic cloud obtained using the atomic trap, which may in particular be a magneto-optical trap (MOT), forms an atomic medium in the immediate vicinity of each narrowed portion of the waveguides. The at least one light of wavelength O circulating in the narrowed portions and partly outside these portions makes it possible to create dipole traps trapping atoms of the atomic cloud in the evanescent field around these portions. Thus, the value of O depends in particular on the composition of the atomic cloud. The wavelength O is for example between 400 and 1000 nm. Light propagating in waveguides canbe centered around one or more wavelengths. A dipole trap is typically made using two lasers of different wavelengths, one being detuned in the red with respect to a resonance frequency of the atoms and the other in the blue. Once the dipole trap is in place, other wavelengths can circulate in the waveguides. In particular, another wavelength is used to store the quantum information in the memory. One or more other wavelengths can also be used to create control fields, for example to create an absorptive memory protocol such as based for example on electromagnetically induced transparency (EIT) or an emissive memory protocol such as based on the Duan-Lukin-Cirac-Zoller protocol. A quantum information storage device according to the invention can also have one orseveral of the following optional features: - the reduced section portion of each waveguide is arranged less than 250 µm from a reduced section portion of an adjacent waveguide, preferably less than 100 µm, more preferably less than 5 µm, and more than 1 µm, preferably more than 3 µm; - the waveguides are arranged, in a cross-section, according to the nodes of a grid or a hexagonal mesh, or according to concentric lines, preferably homothetic, in particular circular or polygonal, in particular hexagonal; - the reduced section portions are parallel to each other; - the waveguides are optical fibers; - the waveguides are fixed in the vacuum chamber to a first support and to a second support, preferably by gluing, on either side of the reduced section portion of the waveguides; - the device comprises a plurality of stacked first supports and second supportsstacked, the stacking of the supports making it possible to position the guides at different levels in the vacuum chamber; - the first support and the second support comprise a plurality of notches, in particular V-shaped, in which the guides can be at least partially received; such notches can position the guides laterally precisely; - the reduced section portion of the waveguides is of circular section and has a diameter of between 300 nm and 500 nm; - the waveguides are lithographed nanoscopic structures, in particular structures comprising a photonic crystal type structuring. Such waveguides can in particular be made of silicon nitride SiN or gallium-indium phosphide GaInP. Optical and electronic lithography techniques can be used to obtain these waveguides; - the atomic trap comprises two coils, called longitudinal, arranged outside the chamber and extending according tothe longitudinal axis of the waveguides on either side thereof, the longitudinal coils being configured to produce a magnetic field gradient trapping the atomic cloud; - the atomic trap comprises two coils, called additional coils, arranged outside the chamber in a plane perpendicular to a plane containing the two longitudinal coils and extending along the longitudinal axis of the waveguides on either side thereof, the additional coils being configured to produce a magnetic field gradient trapping the atomic cloud; - the longitudinal coils and / or the additional coils are rectangular coils; - the atomic trap comprises one or more lasers configured to cool the atomic cloud, preferably to a temperature less than or equal to 100 µK; - the vacuum chamber comprises two sealed passages configured to allow the entry and exit of the waveguides, the sealed passages preferably comprisinga part made of PTFE to make the sealed contact with the waveguides. The invention also relates to a method for manufacturing a quantum information storage device according to the invention, comprising the steps of: (a) hot-drawing and fixing after stretching between two supports a plurality of optical fibers, so as to obtain the plurality of optical fibers having a portion of reduced section; (b) arranging the plurality of optical fibers in the vacuum chamber. The invention finally relates to the use of a quantum information storage device according to the invention, comprising the steps of: (a1) creating a vacuum in the vacuum chamber; (b1) introducing a plurality of atoms, preferably cesium or rubidium, into the vacuum chamber; (c1) trapping the plurality of atoms around the portions of reduced section of the waveguides by means of the atomic trap to form the atomic cloud. Preferably the use comprisesafter step (c1) a step (d1) consisting of propagating in each waveguide a light of wavelength greater than the smallest transverse dimension of the reduced cross-sectional portion of the waveguides so as to create a dipole trap around each waveguide. More preferably, the use comprises after step (d1) a step (e1) consisting of transferring quantum information between laser lights propagating in each of the waveguides and a part of the atomic cloud trapped around the reduced cross-sectional portion of each of the waveguides, carrying out a multiplexing of quantum memories. Brief description of the drawings [Fig 1] Figure 1 represents a quantum information storage device comprising a fibered quantum memory according to the state of the art. [Fig 2] Figure 2 is a detail view of a passage for optical fiber between the exterior and the interior of the ultra-high vacuum chamber of the device of Figure 1. [Fig 3] The[Fig 3] represents a state-of-the-art optical fiber pulling bench. [Fig 4] Figure 4 represents a quantum information storage device according to the invention. [Fig 5] Figure 5 is a cross-sectional view of a stack of first supports on which optical fibers are fixed. [Fig 6] [Fig 7] [Fig 8] Figures 5 to 8 are cross-sectional views of different arrangements of a plurality of optical fibers that can be implemented in a storage device according to the invention. [Fig 9] Figure 9 represents a vacuum chamber of a device comprising cooling laser beams. Detailed description Throughout the present application, the terms "vertical" and "horizontal" are to be understood with reference to a quantum information storage device according to the invention in the operating configuration, in which the waveguides extend substantially horizontally between the first support 7 and thesecond support 8. Of course, the waveguides can be oriented differently. Figures 1 to 3 have already been described in the preamble and will not be commented on below. The same numerical references have been retained in the following to designate identical or similar elements. Figure 4 illustrates a quantum information storage device 100. This device 100 comprises a vacuum chamber 2, which is preferably made of metal, glass or a combination of these two materials. The vacuum chamber 2 comprises an inlet 3 configured to allow the entry of a plurality of atoms into the chamber when the vacuum is created. The plurality of atoms is intended to form an atomic cloud within the chamber. The chamber 2 further comprises sealed passages 5, 6 allowing the entry and exit of a plurality of waveguides. In the illustrated embodiment, the waveguides are optical fibers 4. The optical fibers 4 are optical fibersstretched, that is to say comprising a narrowed portion, of reduced diameter, extending within the vacuum chamber 2. The diameter of the optical fibers in the non-narrowed portions is typically between 100 µm and 150 µm. The narrowed portions are configured to have a diameter smaller than the wavelengths of light propagating in the optical fibers to charge dipole traps trapping a portion of the atomic cloud and to control quantum memories. Thus, a portion of the energy carried by the light is localized around the narrowed portions and form an evanescent field suitable for producing the dipole traps. Preferably, the diameter of the narrowed portions is between 25% and 75% of these wavelengths. This diameter is for example between 300 nm and 500 nm, the light sources used having for example wavelengths between 600 nm and 1000 nm. The narrowed portions advantageously have a lengthgreater than or equal to 0.1 cm, 0.5 cm or 1 cm and less than or equal to 5 cm, 3 cm or 1 cm. In one embodiment, lasers having wavelengths of 686 nm and 935 nm are used. These wavelengths are particularly suitable for the manipulation of an atomic medium consisting of cesium atoms, in particular for the creation of dipole traps. Other wavelengths may however be used. In the operating configuration, the device 100 comprises a single atomic cloud 20 enveloping the optical fibers 4 at least in their narrowed portion. In a particularly advantageous manner, the device 100 makes it possible to use a single atomic trap to form the atomic cloud and load a large number of dipole traps. The atomic cloud 20 comprises alkali metal atoms, advantageously cesium or rubidium. Preferably, it comprises only cesium atoms or only rubidium atoms. Atomic cloud 20 ispreferably cold, i.e. having a temperature below 100 µK. The atomic cloud 20 extends along the longitudinal axis of the waveguides and preferably has a length of between 0.5 cm and 5 cm and an extension in a transverse direction of between 1 mm and 5 mm. The atomic cloud may have an ovoid shape, the extension in the transverse direction being maximum at mid-length and minimum at its axial ends. In order to cover a large volume and therefore maximize the number of reduced sections of waveguides located in the cloud, it is advantageous to maximize the elongation of the atomic cloud as well as its transverse size. The device 100 comprises an atomic trap configured to trap the atoms introduced into the vacuum chamber to form the atomic cloud 20 around the narrowed portion of the waveguides 4. In the example illustrated in FIG. 4, the atomic trap is a magneto-optical trap and comprises two longitudinal coils 24, ofpreferably rectangular, elongated in the direction in which the waveguides 4 extend and arranged on either side of the vacuum chamber. Optionally, it also comprises two additional rectangular coils elongated in the direction in which the waveguides 4 extend, arranged on either side of the vacuum chamber in a plane perpendicular to the plane containing the two longitudinal coils 24. The additional rectangular coils advantageously make it possible to increase the elongation of the atomic cloud. The rectangular nature of all the coils also promotes the elongation of the atomic cloud. The atomic trap advantageously comprises one or more cooling lasers configured to cool the atomic cloud. The initial atomic trap could also be another type of trap, in particular a magnetic trap or a dipole trap produced using at least one additional laser beam. This laser beamadditional has a wavelength detuned from the atomic resonance and propagates in free space towards the reduced sections of the waveguides. When the atomic cloud 20 is formed around the waveguides, the circulation of light of a wavelength well chosen according to the composition of the atomic cloud makes it possible to create dipole traps around the narrowed portions of the waveguides and to manipulate the properties of the atomic medium in these dipole traps. The waveguides are independent of each other. This gives a multiplexed quantum memory comprising as many individual quantum memories as there are waveguides. Advantageously, a single atomic cloud is used to load all the dipole traps: this represents a significant gain in terms of resources required to produce the multiplexed quantum memory. Drawing of optical fibers The optical fibers 4 can be drawn individually on adrawing bench 10 according to the drawing method described with reference to Figure 3. Micro-positioning of the supports and fixing of the fibers Once drawn on the drawing bench, the optical fiber 4 is positioned and fixed on a first support 7 and on a second support 8, the reduced section portion of the fiber being arranged between the supports 7, 8. Before positioning a fiber, the supports 7, 8 can be arranged on high-precision translation plates to carry out micro-positioning of the supports. Preferably, the supports 7, 8 of the optical fiber comprise V-shaped notches 21 in which the optical fiber is positioned, as visible in Figure 5. A V-shaped notch improves the precision of the positioning of the fiber, since the fiber is wedged against the sides of the notch, independently of its manufacturing tolerances. After positioning the optical fiber 4 on the supports 7 and 8, the latter is fixed to each of these,preferably by gluing. The portions of the optical fiber that are fixed to the supports 7, 8 are not stretched portions and have an unreduced diameter typically between 100 µm and 150 µm. Advantageously, the positioning of the optical fibers on the supports 7, 8 is controlled by a camera using a microscope objective. When the optical fiber is fixed to the supports 7, 8, another optical fiber can be placed on the drawing bench to be stretched, then positioned and fixed on the supports 7, 8. Advantageously, a support 7, 8 can have a plurality of V-shaped notches 21 allowing a plurality of optical fibers to be positioned thereon. Also advantageously, a plurality of supports can be stacked vertically to form several tiers and thus allow the positioning of a larger number of optical fibers in the vacuum chamber. To do this, optical fibers are successively stretched and fixed on the firstsupport 7 and on the second support 8. A first additional support 7 and a second additional support 8 are then fixed on the first and second supports 7, 8, preferably by gluing, and then stretched optical fibers are successively fixed on the additional supports. The procedure can be repeated to stack a larger number of additional supports, for example to obtain a stack of 5 or more supports, 10 or more supports or 50 or more supports. Figure 5 shows a stack of two first supports 7 having a plurality of V-shaped notches 21 in which the optical fibers 4 are arranged. The supports 7 are fixed together by an adhesive 22. The second supports 8 can be stacked in the same way. The supports 7, 8 or in the case of stacking, the sets of stacked supports 7, 8, are then fixed on a plate 9, preferably metallic. The plate 9 is then installed in the vacuum chamber 2. We obtainthus a very precise positioning of the plurality of optical fibers 4 within the vacuum chamber 2. Arrangement of the waveguides Figures 6 to 8 illustrate different possible configurations for the arrangement of the optical fibers 4. These configurations are not limited to optical fibers and are applicable to other types of waveguides. The evanescent field of light around the narrowed portion of each waveguide decreases exponentially and, for reduced diameters between 300 and 500 nm, becomes small at typical distances of 1 µm from the outer surface of the waveguide. Thus, the minimum spacing between each waveguide is preferably greater than 1 µm, more preferably greater than 10 µm. The spacing between each waveguide may however be less than or equal to 250 µm, 200 µm, 100 µm, 20 µm, 10 µm, 5 µm or 2 µm. For example, in the case where the atomic cloud has a transverse extension of at least 2 mm aroundnarrowed portions of the waveguides, it is possible to position 10 x 10 optical fibers in the atomic cloud while preserving a high optical thickness for each optical fiber, i.e. a high degree of absorption of light by the atoms around the fiber, and without disturbing the formation of a magneto-optical trap intended to trap the atomic cloud near the optical fibers. A greater density of waveguides, of the order of 100 x 100 waveguides in the atomic cloud, can be obtained with other types of waveguides or with an atomic cloud of increased transverse extension. It is advantageous to arrange the optical fibers in a compact configuration to maximize the number of fibers that can be enveloped by the atomic cloud. As shown in Figure 6, the optical fibers 4 can be assembled so as to be arranged, in a transverse section, according to the nodes of a grid of L lines comprising N fibersincluded in the atomic cloud 20. Alternatively, the fibers 4 can be arranged in a cross-section along homothetic concentric lines, as illustrated in Figure 7. According to another advantageous variant, the fibers 4 are arranged in a cross-section along the nodes of a hexagonal mesh, as illustrated in Figure 8. Fixing the support in the vacuum chamber At the end of the process of pulling and fixing the optical fibers, a preferably compact configuration is obtained, for example in the form of a matrix of N x L nanofibers fixed on the supports 7, 8 or on the stack of supports 7, 8. The supports 7, 8 are fixed on a plate 9, for example metallic, allowing their transport between the pulling bench 10 and the vacuum chamber 2. The plate 9 is then installed inside the vacuum chamber 2. Preparation of the atomic cloud In the context of the invention, the single atomic cloud 20 is advantageously prepared using a trapatomic trap configured to trap atoms introduced into the vacuum chamber through the inlet 3 near the waveguides. The configuration of the atomic trap determines the dimensions of the atomic cloud. Preferably, the atomic trap is a magneto-optical trap and comprises at least two longitudinal rectangular coils 24 arranged on either side of the vacuum chamber 2 and extending in the longitudinal direction of the waveguides 4. The longitudinal rectangular coils 24 produce a magnetic field gradient configured to trap the atoms of the atomic cloud 20. Optionally, the length of the magneto-optical trap can be increased by using a configuration further comprising at least two additional rectangular coils arranged on either side of the vacuum chamber in a plane perpendicular to the plane formed by the transverse coils 24. The additional rectangular coils extend in a direction parallel to thecoils 24. A compression phase by increasing the magnetic field gradient may also be present. By increasing the intensity of the magnetic field gradient, the atomic cloud can be compressed to facilitate the creation of dipole traps around each waveguide by increasing the number of atoms near the waveguides. One or more cooling laser beams are advantageously implemented in combination with the coils. According to a first alternative, three laser beams are oriented towards the reduced portion of the waveguides. Mirrors are arranged perpendicular to the beams on the opposite side of the chamber in order to reflect the laser beams: three retroreflected laser beams are then obtained. Preferably, two of the laser beams propagate in the same plane, forming an angle of, for example, 90° at their intersection, and the third laser beam propagates perpendicular to the plane of the first two beamslaser through the intersection of the latter. According to a second alternative, six non-retroreflected laser beams are oriented towards the reduced portion of the waveguides. Three first beams are oriented like the three laser beams of the first alternative, the other three being each oriented in a direction opposite to those of the first three beams. Figure 9 represents three retroreflected laser beams 29 directed towards the reduced portion of the waveguides in the vacuum chamber 2. Advantageously, the atomic cloud 20 has a maximum extension in the transverse direction of between 1 mm and 5 mm, and a length of between 0.5 cm and 5 cm, preferably being of the order of 2 cm. The dimensions of the atomic cloud 20 are chosen so that the atomic cloud covers the entirety of the narrowed portions of the waveguides, so that a single atomic cloud is sufficient to produce the multiplexed quantum memory. After the cloudatomic cloud 20 is prepared, dipole traps made in the evanescent field of each waveguide are loaded. Preferably, these are dipole traps with two optical frequencies, detuned in the blue and red of the atomic transition of the atoms constituting the atomic cloud, made by injecting laser beams directly into the waveguides. The dipole traps make it possible to optically trap the atoms in the evanescent field of each waveguide by means of laser beams propagating in the waveguides. Each waveguide then represents an independent quantum memory. A multiplexing of quantum memories has therefore been achieved. Other variants and improvements can be provided without departing from the scope of the invention. For example, the atoms of the atomic cloud can be atoms of an atomic element other than cesium, in particular rubidium.

Claims

Claims 1. A quantum information storage device (100) comprising: - a vacuum chamber (2), - a plurality of waveguides (4) configured to propagate light of wavelength O and each having a portion of reduced cross-section having a smallest transverse dimension less than O, extending in the vacuum chamber, - an atomic trap configured to trap a single atomic cloud (20) around the portion of reduced cross-section of the waveguides.

2. A device according to claim 1, the portion of reduced cross-section of each waveguide being arranged less than 250 µm from a portion of reduced cross-section of an adjacent waveguide, preferably less than 100 µm, more preferably less than 5 µm, and more than 1 µm, preferably more than 3 µm. 3.Device according to one of the preceding claims, the waveguides being arranged, in a transverse section, according to the nodes of a grid or a hexagonal mesh, or according to concentric lines, preferably homothetic, in particular circular or polygonal, in particular hexagonal.

4. Device according to any one of the preceding claims, the portions of reduced section being parallel to each other.

5. Device according to one of the preceding claims, the waveguides being optical fibers.

6. Device according to claim 5, the vacuum chamber comprising two sealed passages (5, 6) configured to allow the entry and exit of the waveguides, the sealed passages preferably comprising a part made of PTFE to achieve sealed contact with the waveguides. 7.Device according to one of the preceding claims, the waveguides being fixed in the vacuum chamber to a first support (7) and to a second support (8), preferably by gluing, on either side of the reduced section portion of the waveguides.

8. Device according to the preceding claim, comprising a plurality of stacked first supports (7) and stacked second supports (8), the stacking of the supports making it possible to position the guides at different levels in the vacuum chamber.

9. Device according to one of claims 7 or 8, the first support and the second support comprising a plurality of notches (21), in particular V-shaped, in which the guides can be at least partially received.

10. Device according to one of claims 1 to 4, the waveguides being lithographed nanoscopic structures, in particular structures comprising a photonic crystal type structuring.

11. Device according to one of the preceding claims, the reduced section portion of the waveguides being of circular section and having a diameter of between 300 nm and 500 nm.

12. Device according to one of the preceding claims, the atomic trap comprising two coils, called longitudinal coils (24), arranged outside the chamber and extending along the longitudinal axis of the waveguides on either side thereof, the longitudinal coils being configured to produce a magnetic field gradient trapping the atomic cloud. 13.Device according to the preceding claim, the atomic trap comprising two coils, called additional coils, arranged outside the chamber in a plane perpendicular to a plane containing the two longitudinal coils (24) and extending along the longitudinal axis of the waveguides on either side thereof, the additional coils being configured to produce a magnetic field gradient trapping the atomic cloud.

14. Device according to one of claims 12 or 13, the longitudinal coils and / or the additional coils being rectangular coils.

15. Device according to one of the preceding claims, the atomic trap comprising one or more lasers configured to cool the atomic cloud, preferably to a temperature below 100 µK. 16.Method for manufacturing a quantum information storage device according to claim 5, comprising the steps of: (a) hot-stretching and fixing after stretching between two supports a plurality of optical fibers, so as to obtain the plurality of optical fibers (4) having a portion of reduced section; (b) arranging the plurality of optical fibers in the vacuum chamber (2).

17. Use of a quantum information storage device according to one of claims 1 to 15, comprising the steps of:. (a1) creating a vacuum in the vacuum chamber; (b1) introducing a plurality of atoms, preferably caesium or rubidium, into the vacuum chamber; (c1) trapping the plurality of atoms around the reduced cross-section portions of the waveguides by means of the atomic trap to form the atomic cloud.

18. Use according to the preceding claim, comprising after step (c1) a step (d1) consisting of propagating in each waveguide a light of wavelength greater than the smallest transverse dimension of the reduced cross-section portion of the waveguides so as to create a dipolar trap around each waveguide. 19.Use according to the preceding claim, comprising after step (d1) a step (e1) consisting of transferring quantum information between a laser light propagating in each of the waveguides and a part of the atomic cloud trapped around the portion of reduced section of each of the waveguides, carrying out a multiplexing of quantum memories.

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