Quantum information storage device comprising a plurality of optical waveguides, particularly for forming a multiplexed quantum memory, and methods of making and using such a device

Abstract

The present 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, each waveguide (4) having a narrower cross-sectional segment with a minimum lateral dimension less than λ, and an atomic trap configured to trap a single atomic cloud (20) around the narrower cross-sectional segment of the plurality of waveguides.

Description

[Technical Field]

[0001] The present invention relates to the field of quantum memories intended to store and, if necessary, read out quantum states transmitted by light.

[0002] More particularly, the present invention relates to a device for storing quantum information, comprising a plurality of waveguides and an atomic trap configured to trap a single atomic cloud around the plurality of waveguides, each waveguide making it possible to obtain an independent quantum memory.

[0003] The present invention also relates to methods of making and using such devices. [Background technology]

[0004] Quantum information storage is a key process in quantum information science, especially in quantum communication or quantum computing. Quantum memories store the quantum state of light without changing its properties, allowing the light to be released when needed. In other words, they store photonic qubits in a tangible medium and allow the qubits to be read out when needed.

[0005] Quantum memories have applications in the field of interconnection of quantum systems, in particular allowing quantum processors to be scaled up and accessed over long distances. For example, storing quantum information allows for the synchronization of qubits generated by various quantum processors, efficiently building quantum links between quantum processors and increasing their computational power. It also makes it possible to achieve long-distance quantum communication via quantum repeaters.

[0006] In this context, a major challenge is to multiplex quantum memories, i.e., store multiple qubits in parallel within a single system, in order to increase the success rate of various interconnection protocols within quantum information networks, whether short- or long-distance.

[0007] Several known techniques can be used to improve the multiplexing capability. These techniques are generally based on the storage of multiple optical degrees of freedom, i.e., multiple orthogonal spatial modes, multiple time modes, or multiple frequency modes. However, these techniques generally require compromises in terms of memory performance, especially storage efficiency, because, for example, they result in reduced absorption per mode. However, absorption per mode is an important parameter that governs efficiency. In addition, certain degrees of freedom are not necessarily compatible with certain storage protocols, for example, due to their limited lateral range or narrow spectral bandwidth.

[0008] It is known to use devices that store quantum information using optical fiber quantum memories. By combining atomic clouds with nanoscopic waveguides, it is possible to produce optical fiber quantum memories with particularly advantageous performance in terms of efficiency and storage time.

[0009] The first demonstration of an optical fiber quantum memory was performed with cooled atoms in a magneto-optic trap around a nanoscopic optical fiber. The corresponding device is described in the paper "Demonstration of a Memory for Tightly Guided Light in an Optical Nanofiber", Gouraud et al., Physical Review Letters, 114, 180503 (2015). The second demonstration was obtained using atoms trapped in a dipole trap established in the evanescent field around such a fiber. It is described in the paper "Storage of fiber guided light in a nanofiber-trapped ensemble of cold atoms", Sayrin et al., Optica 2, 353 (2015).

[0010] A third demonstration of an optical fiber quantum memory, in which atoms are also trapped in an evanescent dipole trap around the fiber, is described in the paper "Waveguide-coupled single collective excitation of atomic array," Corzo et al., Nature 566, 359 (2019).

[0011] 1 shows a device 1 for storing quantum information comprising an optical fiber quantum memory, as described in the last paper. The storage device 1 comprises a vacuum chamber 2 having an inlet 3 configured to allow atoms to be introduced into the chamber. The atoms are intended in particular to be supplied from one or more dispensers (e.g., using an electric current to heat a source of atoms, thus causing the release of atoms), to be trapped in a magneto-optical trap around an optical fiber 4, and then to be trapped in a dipole trap formed in an evanescent field around the optical fiber 4. The chamber also comprises two seal-tight conduits 5 and 6 that allow the optical fiber 4 to pass between the interior and exterior of the vacuum chamber.

[0012] The optical fiber 4 is held within the chamber between a first holder 7 and a second holder 8, to which it is fixed by adhesive bonding. The holders 7 and 8 are themselves held by a plate 9 fixed within the chamber.

[0013] The optical fiber 4 comprises a smaller diameter segment between the two holders 7 and 8, the diameter of which is smaller than the wavelength of the light propagating through the optical fiber to control the quantum memory. In the described embodiment, lasers of wavelengths of about 686 nm and about 935 nm, corresponding to wavelengths that are particularly advantageous for cesium atoms, are used for the evanescent dipole trap, and the narrow segment has a diameter of about 400 nm.

[0014] During operation of device 1, atoms are cooled and trapped by a magneto-optical trap covering a narrow segment of optical fiber 4. When light propagating through optical fiber 4 reaches the narrow segment, most of the light energy escapes outside the optical fiber due to the small size of optical fiber 4. This causes an evanescent wave to form around the optical fiber, which can trap and interact with atoms in close proximity to the optical fiber.

[0015] The properties of the atomic medium around the narrow segment may be controlled by light propagating through the optical fiber 4. Quantum information is then exchanged between the atomic medium and the light flowing through the optical fiber 4, resulting in a quantum memory.

[0016] 2 is a detailed view of the conduit 5 between the exterior and interior of the vacuum chamber. A seal-tight junction between the interior and exterior is formed by a connector 17. The connector 17 has a PTFE portion for making airtight contact with the optical fiber 4.

[0017] 3 shows an apparatus 10 for drawing an optical fiber 4, which is used to create a narrow segment of optical fiber. The optical properties of the optical fiber during and after the drawing can be determined using a laser source 11 and a photodiode 12 configured to inject a signal into the optical fiber 4 and detect a signal emerging from the optical fiber, respectively.

[0018] Apparatus 10 includes two mechanical assemblies for applying traction, each including a high-precision translation stage 14 and a clamp 13. Clamp 13 holds optical fiber 4 relative to holders 27 and 28 disposed on stages 14. Dihydrogen and dioxygen gas generators 15 generate high-temperature flames 16 for heating and melting optical fiber 4 between the two stages 14. Heating optical fiber 4 while moving the two stages 14 apart draws optical fiber 4, which has the effect of reducing the diameter of the heated portion of the optical fiber.

[0019] Thus, to create the narrow segment, the optical fiber is heated and drawn, typically over a length of several centimeters, until a nanofiber is obtained with a diameter smaller than the wavelength of light propagating through the nanofiber.

[0020] The drawing process is computer controlled. The path of the stage 14 allows for the creation of various drawing profiles, in particular the length of the narrow segments to be controlled.

[0021] The drawing is preferably done so that the drawn fiber retains greater than 99% light transmission.

[0022] The optical fiber thus prepared is then fixed, preferably by adhesive bonding, to a first holder 7 and a second holder 8, and then transferred to the vacuum chamber 2. The holders 7 and 8 are fixed to a plate 9 installed in the vacuum chamber 2. Summary of the Invention [Problem to be solved by the invention]

[0023] The device described with reference to Figure 1 exhibits excellent performance, especially in terms of efficiency and storage time, but it comprises only one quantum memory and therefore does not allow for quantum memory multiplexing.

[0024] There is a need to improve existing devices for storing quantum information, particularly to allow for multiplexing of quantum memories.

[0025] It is an object of the present invention to at least partially meet this need. [Means for solving the problem]

[0026] To do this, the invention, according to one of its aspects, provides a device for storing quantum information, comprising: vacuum chamber, a plurality of waveguides configured to propagate light of wavelength λ, each waveguide including a narrower cross-sectional segment having a minimum lateral dimension less than λ, the plurality of waveguides extending into the vacuum chamber; an atom trap configured to trap a single atomic cloud around the narrower cross-sectional segments of the plurality of waveguides; The device according to claim 1, further comprising:

[0027] "Vacuum chamber" means 10 -8 It means a chamber configured so that a vacuum equivalent to a pressure of less than 1000 torr can be generated.

[0028] The present invention advantageously allows multiple independent memories to be parallelized within the same device while maintaining the performance of prior art quantum memories, in particular a single atomic trap is used to create multiple independent memories.

[0029] It is based on placing a number of waveguides coupled to atoms in a vacuum chamber, where the atoms are preferably laser cooled and preferably have a temperature below 100 μK, more preferably below 20 μK.

[0030] By parallelizing fiber optic quantum memories, the individual memory performance is maintained, thus allowing a single device to have many individually accessible memories, and in addition, these memories are inherently fiber optic.

[0031] The cross section of the narrower cross section segment in particular has a smallest dimension of 300 nm to 500 nm, advantageously 350 nm to 450 nm.

[0032] The waveguides are configured to transmit at least one radiation of wavelength λ, which radiation is intended to form a dipole trap for capturing a portion of the atoms. Specifically, in an operational configuration, a portion of the atoms forming part of the atomic cloud obtained using an atomic trap, which may in particular be a magneto-optical trap (MOT), forms an atomic medium in the immediate vicinity of each narrow segment of the waveguides. At least one radiation of wavelength λ passing through the narrow segments and partially outside these segments allows a dipole trap for capturing atoms of the atomic cloud to be formed in the evanescent field around these segments. The value of λ therefore depends in particular on the composition of the atomic cloud. The wavelength λ is, for example, between 400 nm and 1000 nm.

[0033] The light propagating through the multiple waveguides may be centered around one or more wavelengths. Dipole traps are typically formed by two lasers of different wavelengths, one detuned in the red and one in the blue relative to the resonant frequency of the atoms.

[0034] Once the dipole trap is in place, other wavelengths can be propagated through the waveguides. In particular, other wavelengths can be used to store quantum information in memory. For example, one or more other wavelengths can also be used to generate control fields with a view to implementing an absorptive memory protocol (e.g., a protocol based on electromagnetically induced transparency (EIT)) or an emissive memory protocol (e.g., a protocol based on the Duan-Lukin-Cirac-Zoller protocol).

[0035] A device for storing quantum information according to the invention may also have the following optional features: the narrower cross-sectional segment of each waveguide is spaced less than 250 μm, preferably less than 100 μm, more preferably less than 5 μm, and more than 1 μm, preferably more than 3 μm, from the narrower cross-sectional segment of an adjacent waveguide; the waveguides are arranged, when viewed in cross section, at the nodes of a square or hexagonal lattice, or on concentric lines, preferably on homothetic lines, which are in particular circular or polygonal, in particular hexagonal; a plurality of said narrower cross-sectional segments being parallel to one another; the plurality of waveguides are optical fibers; The plurality of waveguides are fixed to a first holder (7) and to a second holder (8) on either side of the narrower cross-sectional segments of the plurality of waveguides, preferably by adhesive bonding, within the vacuum chamber; the device comprises a plurality of stacked first holders and a plurality of stacked second holders, the stacked holders enabling the plurality of waveguides to be positioned at various levels in the vacuum chamber; the first holder and the second holder are provided with a plurality of notches (21), in particular V-shaped notches, in which the plurality of waveguides can be at least partially accommodated; the narrower cross-sectional segments of the plurality of waveguides have a diameter of between 300 nm and 500 nm; The waveguides are lithographically patterned nanoscopic structures, in particular structures with photonic crystal type structures. Such waveguides can in particular be made of silicon nitride (SiN) or gallium indium phosphide (GaInP). Optical and e-beam lithography techniques can be used to obtain these waveguides; The atom trap comprises two coils, called longitudinal coils, disposed outside the chamber and extending on either side of the plurality of waveguides along a longitudinal axis thereof, wherein the longitudinal coils are configured to generate a magnetic field gradient that traps the atomic cloud; The atom trap comprises two coils, referred to as additional coils, disposed outside the chamber in a plane perpendicular to a plane containing the two longitudinal coils and extending on either side along a longitudinal axis of the plurality of waveguides, wherein the additional coils are configured to generate a magnetic field gradient that traps the atomic cloud; the longitudinal coil and / or the additional coil are rectangular coils; the atom trap comprising one or more lasers configured to cool the atomic cloud, preferably to a temperature below 100 μK; The vacuum chamber includes two seal-tight conduits configured to allow the plurality of waveguides to enter and exit, and the seal-tight conduits preferably include portions made of PTFE for making seal-tight contact with the plurality of waveguides.

[0036] The present invention also provides a method for manufacturing a device for storing quantum information according to the present invention, comprising the steps of: (a) hot drawing a plurality of optical fibers between two holders and fixing them after drawing to obtain a plurality of optical fibers with narrower cross-sectional segments; (b) placing the plurality of optical fibers within the vacuum chamber; The present invention relates to the above method, which comprises the steps of:

[0037] Finally, the present invention relates to a method of using a device for storing quantum information 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 a plurality of atoms around the narrower cross-sectional segments of the plurality of waveguides with the atomic trap to form the atomic cloud. The present invention relates to the above method, which comprises the steps of:

[0038] Preferably, the method includes, after step (c1), a step (d1) of propagating light through each waveguide having a wavelength greater than the minimum lateral dimension of the narrower cross-sectional segments of the plurality of waveguides so as to form a dipole trap around each waveguide.

[0039] More preferably, the method of use includes, after step (d1), a step (e1) of transferring quantum information between laser light propagating through each of the plurality of waveguides and a portion of the atomic cloud trapped around the narrower cross-sectional segment of each of the plurality of waveguides in such a way as to achieve multiplexing of the quantum memory. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 shows a device for storing quantum information comprising an optical fiber quantum memory according to the prior art. [Figure 2] FIG. 2 is a detailed view of a conduit for routing an optical fiber between the exterior and interior of the ultra-high vacuum chamber of the device of FIG. [Figure 3] FIG. 3 shows a device for drawing optical fibers according to the prior art. [Figure 4] FIG. 4 shows a device for storing quantum information according to the invention. [Figure 5] FIG. 5 is a cross-sectional view of a stack of first holders with optical fibers fixed thereto. [Figure 6] FIG. 6 is a cross-sectional view of various arrangements of optical fibers that may be implemented in a storage device according to the present invention. [Figure 7] FIG. 7 is a cross-sectional view of various arrangements of optical fibers that may be implemented in a storage device according to the present invention. [Figure 8] FIG. 8 is a cross-sectional view of various arrangements of optical fibers that may be implemented in a storage device according to the present invention. [Figure 9] FIG. 9 shows the vacuum chamber of the device including cooling the laser beam. Modes for carrying out the invention

[0041] Throughout this application, the terms "vertical" and "horizontal" should be understood with reference to a device for storing quantum information according to the invention in an operational configuration in which the plurality of waveguides extend substantially horizontally between a first holder 7 and a second holder 8. Of course, the plurality of waveguides may be oriented differently.

[0042] 1-3 have already been described above and will not be described again below. The same reference numbers will be used below to designate the same or similar elements.

[0043] Figure 4 shows a device 100 for storing quantum information. The device 100 comprises a vacuum chamber 2, preferably made of metal, glass or a combination of these two materials.

[0044] The vacuum chamber 2 comprises an inlet 3 configured to allow atoms to flow into the chamber after a vacuum is created, the atoms intended to form an atomic cloud within the chamber.

[0045] The chamber 2 further comprises sealed conduits 5 and 6 which allow access to a number of waveguides, which in the illustrated embodiment are optical fibers 4.

[0046] The optical fiber 4 is a drawn fiber, i.e., a fiber including a narrow segment with a smaller diameter, located within the vacuum chamber 2. The diameter of the non-narrow segment of the optical fiber is typically 100 μm to 150 μm. The narrow segment is configured to have a diameter smaller than the wavelength of the light propagating through the optical fiber, with the aim of loading a portion of the atoms of the atomic cloud into the dipole trap and controlling the quantum memory. Thus, a portion of the energy carried by the light is localized around the narrow segment, creating an evanescent field suitable for forming the dipole trap. Preferably, the diameter of the narrow segment is 25% to 75% of the wavelength. This diameter is, for example, 300 nm to 500 nm, and the wavelength of the light source used is, for example, 600 nm to 1000 nm.

[0047] The narrow segment advantageously has a length of at least 0.1 cm, at least 0.5 cm or at least 1 cm, and at most 5 cm, at most 3 cm or at most 1 cm.

[0048] In one embodiment, a laser having a wavelength of 686 nm to 935 nm is used. These wavelengths are particularly suitable for manipulating atomic media consisting of cesium atoms, in particular for forming dipole traps. However, other wavelengths may also be used.

[0049] In an operational configuration, device 100 comprises a single atomic cloud 20 surrounding optical fiber 4, or at least a narrow segment thereof. Particularly advantageously, device 100 uses a single atomic trap to form the atomic cloud, and allows multiple dipole traps to be loaded.

[0050] The atomic cloud 20 comprises alkali metal atoms, advantageously cesium atoms or rubidium atoms. Preferably, the atomic cloud 20 comprises only cesium atoms or only rubidium atoms. The atomic cloud 20 preferably has a low temperature, i.e. a temperature below 100 μK.

[0051] The atomic cloud 20 extends along the length of the waveguides and preferably has a length of 0.5 cm to 5 cm and a lateral extent of 1 mm to 5 mm. The atomic cloud may have an ovoid shape, with the lateral extent of the ovoid being greatest at the midpoint of its length and smallest at its axial ends. To cover a large volume and therefore maximize the number of narrower segments of waveguides placed within the cloud, it is advantageous to maximize the elongation of the atomic cloud and its lateral size.

[0052] The device 100 comprises an atom trap configured to trap atoms introduced into the vacuum chamber to form an atomic cloud 20 around a narrow segment of the plurality of waveguides 4. In the example shown in Fig. 4, the atom trap is a magneto-optical trap and comprises two longitudinal coils 24, preferably rectangular, elongated in the direction in which the plurality of waveguides 4 extend and arranged on either side of the vacuum chamber. Optionally, the atom trap also comprises two additional rectangular coils elongated in the direction in which the plurality of waveguides 4 extend and arranged in a plane perpendicular to the plane in which the two longitudinal coils 24 are arranged on either side of the vacuum chamber.

[0053] The additional rectangular coil advantageously allows for a greater elongation of the atomic cloud.

[0054] The rectangular nature of all coils also facilitates elongation of the atomic cloud.

[0055] The atom trap advantageously comprises one or more cooling lasers configured to cool the atomic cloud.

[0056] The initial atom trap can also be another type of trap, in particular a magnetic trap, or a dipole trap formed using at least one additional laser beam, the additional laser beam having a wavelength detuned to the atomic resonance, and directed through free space towards the narrower segments of the multiple waveguides.

[0057] When atomic clouds 20 are formed around the waveguides, propagation of light of a wavelength well selected depending on the composition of the atomic cloud allows for the formation of dipole traps around narrow segments of the waveguides and the manipulation of the properties of the atomic medium within these dipole traps.

[0058] The multiple waveguides are independent of each other. Thus, a multiplexed quantum memory is obtained, with as many individual quantum memories as there are waveguides. Advantageously, a single atomic cloud is used to load all dipole traps. This results in a significant saving in terms of resources required to achieve the multiplexed quantum memory.

[0059] Optical fiber drawing

[0060] The optical fibers 4 can be individually drawn on the drawing device 10 according to the drawing process described with reference to FIG.

[0061] Micro-positioning of the holder and fixing of the fiber

[0062] Once drawn on the drawing apparatus, optical fiber 4 is positioned and secured in a first holder 7 and in a second holder 8, with the narrower cross-sectional segment of the fiber located between holders 7 and 8.

[0063] Before the fiber is positioned, the holders 7 and 8 are mounted on a high precision translation stage to allow fine positioning of the holders.

[0064] Preferably, the optical fiber holders 7 and 8 are provided with a V-shaped notch 21 in which the optical fiber is placed, as can be seen in Figure 5. The V-shaped notch improves the precision with which the fiber is positioned because the fiber is clamped against the sidewalls of the notch regardless of its manufacturing tolerances.

[0065] After the optical fiber 4 is placed on the holders 7 and 8, it is fixed to one another, preferably by adhesive bonding. The optical fiber segments fixed to the holders 7 and 8 are not drawn segments and typically have a non-narrow diameter of 100 μm to 150 μm.

[0066] Advantageously, the position of the optical fibers on the holders 7 and 8 is controlled by a camera using a microscope lens.

[0067] Once the optical fiber is secured to the holders 7 and 8, another optical fiber is placed on the drawing apparatus to be drawn, and then placed on and secured to the holders 7 and 8.

[0068] Advantageously, the holders 7 and 8 may be provided with a number of V-shaped notches, which allow a number of optical fibers to be placed thereon.

[0069] Advantageously, multiple holders may also be stacked vertically to form multiple stages, thus allowing more optical fiber to be placed in the vacuum chamber. To this end, an optical fiber is drawn and fixed in a first holder 7 and then in a second holder 8. Next, a first additional holder 7 and a second additional holder 8 are fixed to the first holder 7 and the second holder 8, preferably by adhesive bonding, and then the drawn optical fiber is fixed to these additional holders in succession. This procedure may be repeated to stack more additional holders, for example to obtain stacks of 5 or more holders, 10 or more holders, or 50 or more holders.

[0070] 5 shows a stack of two first holders 7, each having a plurality of V-shaped notches 21 in which the optical fibers 4 are placed. The holders 7 are fixed to each other by adhesive 22. A second holder 8 may also be stacked in the same manner.

[0071] The holders 7 and 8 are then fixed to a plate 9, preferably a metal plate, in the case of a set of stacked holders 7 and 8. The plate 9 is then placed in the vacuum chamber 2.

[0072] Thus, very accurate positioning of the optical fibers 4 within the vacuum chamber 2 is obtained.

[0073] Multiple waveguide arrangement

[0074] 6 to 8 show various possible configurations for the placement of the optical fiber 4. These configurations are not limited to optical fibers, but can also be applied to other types of waveguides.

[0075] The evanescent field of light around the narrow segment of each waveguide decreases exponentially and becomes weak at a typical distance of 1 μm from the outer surface of the waveguide for diameters as small as 300-500 nm. Therefore, the minimum spacing between each waveguide is preferably greater than 1 μm, more preferably greater than 10 μm. However, the spacing between each waveguide may be 250 μm or less, 200 μm or less, 100 μm or less, 20 μm or less, 10 μm or less, 5 μm or less, or 2 μm or less.

[0076] As an example, if the atomic cloud has a lateral extent of at least 2 mm around a narrow segment of the waveguides, it is possible to place 10 x 10 optical fibers within the atomic cloud while ensuring that each optical fiber still has a large optical thickness, i.e., that the atoms around the fiber still exhibit a high level of optical absorption, without interfering with the formation of a magneto-optical trap intended to capture the atomic cloud in close proximity to the optical fibers.

[0077] Higher densities of waveguides, on the order of 100x100 waveguides in the atomic cloud, can be obtained using other types of waveguides or by using atomic clouds with greater lateral extent.

[0078] To maximize the number of optical fibers that can be enveloped by the atomic cloud, it is advantageous to arrange the optical fibers in a compact manner.

[0079] As shown in FIG. 6, the optical fibers 4 may be assembled so that, in cross section, they are arranged at the nodes of a square lattice of L rows of N fibers contained in the atomic cloud 20 .

[0080] Alternatively, the optical fibers 4 may be arranged on homothetic concentric lines when viewed in cross section, as shown in FIG.

[0081] According to another advantageous variant, the optical fibers 4 are arranged, in cross section, at the nodes of a hexagonal lattice, as shown in FIG.

[0082] Fixing a carrier to the vacuum chamber

[0083] At the end of the optical fiber drawing and fixing process, a preferably compact configuration is obtained, for example in the form of an array of N×L nanofibers fixed in holders 7 and 8 or in a stack of holders 7 and 8.

[0084] The holders 7 and 8 are fixed to a plate 9, for example a metal plate, which can be transported between the drawing device 10 and the vacuum chamber 2. The plate 9 is then placed in the vacuum chamber 2.

[0085] Preparation of the atomic cloud

[0086] In the context of the present invention, a single atomic cloud 20 is advantageously prepared using an atom trap configured to trap atoms introduced into the vacuum chamber through inlet 3 in proximity to multiple waveguides. The configuration of the atom trap defines the size of the atomic cloud.

[0087] Preferably, the atom 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 plurality of waveguides 4. The longitudinal rectangular coils 24 generate a magnetic field gradient configured to trap atoms of the atomic cloud 20.

[0088] 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 transverse coil 24. The additional rectangular coils extend in a direction parallel to coil 24.

[0089] There may also be a compression phase achieved through increasing the magnetic field gradient. Increasing the steepness of the magnetic field gradient may compress the atomic cloud, favoring the formation of dipole traps around each waveguide, thereby increasing the number of atoms in proximity to the multiple waveguides.

[0090] One or more cooling laser beams are advantageously employed in combination with the coil.

[0091] According to a first alternative, three laser beams are directed towards the narrower segments of the waveguides. Mirrors are placed perpendicular to the beams on the opposite side of the chamber to reflect the laser beams, thus resulting in three retroreflected laser beams.

[0092] Preferably, the two 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 laser beams through the intersection of the latter laser beams.

[0093] According to a second alternative, six non-retroreflected laser beams are directed onto narrower segments of the waveguides, the first three beams being directed in the same direction as the three laser beams of the first alternative, and the other three being directed in opposite directions to each of the first three beams.

[0094] FIG. 9 shows three reflected laser beams 29 directed towards narrower segments of the multiple waveguides within the vacuum chamber 2.

[0095] Advantageously, the atomic cloud 20 has a maximum lateral extent of between 1 mm and 5 mm and a length of between 0.5 cm and 5 cm, preferably about 2 cm.

[0096] The dimensions of the atomic cloud 20 are selected so that the atomic cloud covers the entire narrow segments of the multiple waveguides, and thus a single atomic cloud is sufficient to achieve a multiplexed quantum memory.

[0097] After the atomic cloud 20 is prepared, a dipole trap formed in the evanescent field of each waveguide is loaded, preferably by directing a laser beam into the waveguides, employing two optical frequencies (blue and red detuned relative to the atomic transitions of the constituent atoms of the atomic cloud).

[0098] The dipole trap allows atoms to be optically trapped in the evanescent field of each waveguide by a laser beam propagating through the multiple waveguides.

[0099] Each waveguide then represents an independent quantum memory, thus achieving quantum memory multiplexing.

[0100] However, other variations and modifications can be provided without departing from the scope of the invention.

[0101] For example, the atoms of the atomic cloud may be atoms of atomic elements other than cesium, and in particular rubidium.

Claims

1. A device (100) for storing quantum information, comprising: a vacuum chamber (2); a plurality of waveguides (4) configured to propagate light of wavelength λ, each waveguide (4) including a narrower cross-sectional segment having a minimum lateral dimension less than λ, the plurality of waveguides extending into the vacuum chamber; an atom trap configured to trap a single atomic cloud (20) around the narrower cross-sectional segments of the plurality of waveguides; The device (100) comprises:

2. 2. The device of claim 1, wherein the narrower cross-sectional segment of each waveguide is spaced less than 250 μm, preferably less than 100 μm, more preferably less than 5 μm, and more than 1 μm, preferably more than 3 μm, from the narrower cross-sectional segment of an adjacent waveguide.

3. 3. The device according to claim 1 or 2, wherein the plurality of waveguides are arranged, in cross section, at the nodes of a square or hexagonal lattice, or on concentric lines, preferably on similar lines, which are in particular circular or polygonal, in particular hexagonal.

4. The device of any one of claims 1 to 3, wherein the narrower cross-sectional segments are parallel to one another.

5. The device of any one of claims 1 to 4, wherein the plurality of waveguides are optical fibers.

6. 6. The device of claim 5, wherein the vacuum chamber comprises two sealed conduits (5, 6) configured to allow the plurality of waveguides to enter and exit, the sealed conduits preferably including portions made of PTFE for airtight contact with the plurality of waveguides.

7. 7. The device according to any one of claims 1 to 6, wherein the plurality of waveguides are fixed in the vacuum chamber to a first holder (7) and to a second holder (8) on either side of the narrower cross-sectional segments of the plurality of waveguides, preferably by adhesive bonding.

8. 8. The device of claim 7, wherein the device comprises a plurality of stacked first holders (7) and a plurality of stacked second holders (8), which allow the plurality of stacked holders to be arranged at different levels in the vacuum chamber.

9. 9. The device according to claim 7 or 8, wherein the first holder and the second holder are provided with a plurality of cutouts (21), in particular V-shaped cutouts, in which the plurality of waveguides can be at least partially accommodated.

10. 5. The device according to claim 1, wherein the plurality of waveguides are lithographically patterned nanoscopic structures, in particular structures comprising photonic crystal type structures.

11. The device of any one of claims 1 to 10, wherein the narrower cross-sectional segments of the plurality of waveguides are circular in cross-section and have a diameter of between 300 nm and 500 nm.

12. 12. The device of claim 1, wherein the atom trap comprises two coils, called longitudinal coils (24), located outside the chamber and extending on either side of the plurality of waveguides along a longitudinal axis thereof, the longitudinal coils being configured to generate a magnetic field gradient that traps the atomic cloud.

13. 13. The device of claim 12, wherein the atom trap comprises two coils, referred to as additional coils, arranged outside the chamber in a plane perpendicular to the plane containing the two longitudinal coils (24) and extending on either side along a longitudinal axis of the plurality of waveguides, wherein the additional coils are configured to generate a magnetic field gradient that traps the atomic cloud.

14. 14. The device according to claim 12 or 13, wherein the longitudinal coil and / or the additional coil is a rectangular coil.

15. 15. The device according to any one of claims 1 to 14, wherein the atom trap comprises one or more lasers configured to cool the atomic cloud, preferably to a temperature below 100 μK.

16. 6. A method for manufacturing a device for storing quantum information according to claim 5, comprising the steps of: (a) hot drawing a plurality of optical fibers between two holders and fixing them after drawing to obtain a plurality of optical fibers (4) with narrower cross-sectional segments; (b) placing the plurality of optical fibers in the vacuum chamber (2); The method, comprising the steps of:

17. (a1) creating a vacuum in the vacuum chamber; (b1) introducing a plurality of atoms, preferably cesium or rubidium, into the vacuum chamber; (c1) trapping a plurality of atoms around the narrower cross-sectional segments of the plurality of waveguides with the atomic trap to form the atomic cloud. A method of using a device for storing quantum information according to any one of claims 1 to 15, comprising:

18. 18. The method of claim 17, further comprising, after step (c1), the step (d1) of propagating light through each waveguide having a wavelength greater than the minimum lateral dimension of the narrower cross-sectional segments of the plurality of waveguides so as to form a dipole trap around each waveguide.

19. 20. The method of claim 18, further comprising, after step (d1), a step (e1) of transferring quantum information between laser light propagating through each of the plurality of waveguides and a portion of the atomic cloud trapped around the narrower cross-sectional segment of each of the plurality of waveguides in such a way as to achieve quantum memory multiplexing.

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