Interferometric quantum sensor and differential atomic interferometry system

Abstract

The present invention relates to an interferometric quantum sensor (100) comprising a laser source (4) configured to generate a laser beam (20) along a longitudinal direction (5) and a reflecting optical device (10). According to the invention, the reflecting optical device (10) is arranged and configured to receive the laser beam (20) in an internal volume delimited by the reflecting optical device (10) and to form a plurality of beams reflected in a plurality of directions, so as to trap atoms in a three-dimensional trapping and cooling zone (6), and in that the reflecting optical device (10) has a first through-hole aperture (8) adapted to pass a first interferometric light beam (31) through the reflecting optical device (10) and into the trapping and cooling zone (6) along a first axis (18) forming a non-zero angle with the longitudinal axis (5).Figure for the abbreviation: Figure 3.

Description

Title of the invention: Interferometric quantum sensor and differential atom interferometry system Technical field of the invention

[0001] The present invention relates to the technical field of quantum sensors of the atomic interferometer or cold atom interferometer type.

[0002] An atomic interferometer is sensitive to inertial effects such as accelerations and rotations and finds applications in particular in an inertial quantum sensor. This inertial quantum sensor can be used in applications for acceleration and / or rotation measurements along one or more measurement axes, for example along the vertical axis in a quantum gravimeter.

[0003] The invention also relates to an atomic interferometry system used for differential measurements, for example in a quantum gradiometer, also called a differential quantum gravimeter, to measure a local gravity acceleration gradient. State of the art

[0004] There are quantum sensors, in particular cold atom interferometric sensors, which are based on the interactions between one or more laser sources and atoms in an ultra-high vacuum space. Generally, an atomic interferometer comprises a source of atoms and a cold atom trap configured to trap a cloud of atoms and then let it fall freely or direct it in a determined initial direction. The atomic interferometer also comprises a laser source emitting a sequence of interrogation light pulses intended to interact with the fine structure of the atoms by photon transfer. Finally, the atomic interferometer comprises a device for measuring the state of the atoms at the end of the interferometry sequence.

[0005] In particular, a quantum gravimeter works by trapping atoms in a magneto-optical trap, then letting them fall to measure their free-fall acceleration using a sequence of three laser pulses creating an atomic interferometer. A quantum gravimeter from the company Exail, for example, can measure local gravitational acceleration with an accuracy of around 1 in 1 billion. The rate of the measurements thus obtained is approximately 2 Hertz (Hz).

[0006] The vast majority of interferometric quantum sensors use a three-dimensional magneto-optical trap, also called 3D-M0T or M0T3D (acronym for "Magneto-Optical Trap" in English). A 3D-M0T trap is configured to cool and gather atoms, in a cloud of cold atoms. By cold atoms, we mean here a cloud of atoms arranged at a point in the coordinate space (0, 0, 0) in an orthonormal frame (X, Y, Z). Cold atoms are for example atoms of rubidium (Rb), caesium (Cs), potassium (K) or strontium (Sr).

[0007] Patent FR 2928725 (P. Bouyer and A. Landragin) describes a quantum gravimeter based on the use of a single laser beam combined with a conical or pyramidal reflector to form the three-dimensional magneto-optical trap. Such a quantum sensor is for example illustrated in [Fig.l]. An orthonormal XYZ frame of reference is shown, where the Z axis is vertical. A laser source 4 generates a laser beam 20 along a longitudinal axis 5, which is for example arranged vertically, for local gravity measurements. The reflector, which is here pyramidal, receives the incident laser beam 20 and generates by multiple reflections three pairs of laser beams in the three directions of space, for example the pair of counter-propagating beams 24, respectively 25, along the X axis, respectively Y, and a pair of counter-propagating beams along the Z axis.In the case of a pyramidal reflector 7 with four facets inclined at 45 degrees relative to the axis 5 of the incident beam 20, the incident laser beam 20 is sufficiently extended spatially to form two pairs of reflected beams, each pair comprising two counter-propagating beams, oriented orthogonally relative to the incident laser beam. The incident beam is also reflected on itself by successive reflections on two opposite faces of the pyramid. Such a pyramidal reflector forms a trap by superposition of the incident laser beam, the four reflected beams perpendicular to the incident beam and beam(s) retro-reflected by double reflection on two opposite faces of the pyramid.Advantageously, in a pyramidal reflector, a single incident laser beam is reflected on the different faces of a hollow pyramid so as to create three pairs of counter-propagating beams propagating in orthogonal directions superimposed in a region of space. Such a pyramidal reflector thus forms a trap by superposition of three pairs of beams oriented along three orthogonal axes. The 3D-M0T trap is installed in an ultra-high vacuum chamber 1 in which a weak vapor of atoms that one wishes to trap is maintained. The 3D-M0T magneto-optical trap generally comprises three pairs of beams along the 3 directions of space and a magnetic field having a specific configuration to trap the atoms in the three directions of space. The magnetic field is generated for example by means of pairs of anti-Helmholtz coils 3.The trapping area of ​​the 3D-M0T trap is located at the intersection of the six laser beams and the point where the magnetic field is zero. In this configuration, the atoms 2 are initially trapped and cooled in the superposition area of ​​three pairs of laser beams, inside the pyramidal reflector 7. This arrangement is suitable to form an atom interferometer sensitive to acceleration along the longi direction. tudinal 5 of the incident laser beam 20. Magneto-optical trapping is interrupted for a free-fall time during which the atoms fall under the effect of local gravity. In practice, the magnetic field is first switched off to produce an optical molasses, which completes the cooling of the atoms. The laser beam is then switched off, and the atoms are then in free fall. During this time, a sequence of microwave and laser pulses is applied which prepares the atoms in a well-defined quantum state before their entry into the interferometer. After a few tens of milliseconds of fall, the atoms are released from the trapping zone and the pyramidal reflector. The interferometric quantum sensor is generally hybridized with a measuring device 29 based on one or more conventional sensors, such as an accelerometer, barometer, inclinometer and / or gyrometer.

[0008] An interferometric sequence of three laser pulses is then applied outside the trapping zone of the 3D-M0T. The light pulses of an atomic interferometry sequence are generally spaced temporally by a duration T. A sequence of three light pulses called the "ji / 2-ir - ir / 2" sequence is generally used. The "ir / 2" pulses make it possible to separate or recombine the matter waves associated with the atoms. The "ir" pulses make it possible to deflect the matter waves. Other sequences of more than three pulses are also used, for example a sequence of four light pulses, "ir / 2-ir - ir - ir / 2".In all cases, a first light pulse 21 interacts with the atom cloud 2 at the exit of the 3DM0T trap so as to spatially separate the wave associated with each atom into a first atom wave traveling along a first path and, respectively, a second atom wave traveling along a second path. At least one second light pulse 22 interacts with the two separated atom waves to redirect them. Finally, a last light pulse 23 spatially recombines the two atom waves. The sensitivity of the atom interferometer is generally proportional to the square of the interrogation time T separating the pulses.

[0009] A detection system 27, 28 makes it possible to measure, generally by fluorescence or absorption, the state of the atoms in order to deduce the population of atoms in each of the output arms of the interferometer. From this, the phase shift between the two arms of the interferometer is deduced and, in the application to a quantum gravimeter, the value of the local acceleration of gravity.

[0010] The interferometric quantum sensor illustrated in [Fig. 1] makes it possible to carry out all the trapping, interferometry and detection operations, from a single laser beam 20 instead of around ten laser beams in other interferometric quantum sensors (Ménoret et al., “Gravity measurements below 109 g with a transportable absolute quantum gravimeter”, Scientific reports, 2018, DOI:10.1038 / s41598-018-30608-l).

[0011] However, the interferometric quantum sensor as illustrated in [Fig. 1] is in bulky. For inertial sensor applications on board a mobile carrier (e.g. aircraft, surface or submarine ship, autonomous land, air or sea vehicle) it is desirable to reduce the size of such an interferometric quantum sensor. In addition, in these applications it is desirable to increase the measurement rate to at least about 10 Hz.

[0012] Different atomic interferometer architectures based on the use of independent laser beams on several axes have been proposed for on-board inertial sensor applications. These configurations have the disadvantage of complexity and bulk, with a large number of beams to be precisely aligned with each other and with respect to the vacuum chamber.

[0013] The publication J. Lee et al. (“A compact cold-atom interferometer with a high data-rate grating magneto-optical trap and a photonic-integrated-circuit-compatible laser System”, Nature communications, 13-5131, 2022, DOI: 10.1038 / s41467-022-31410-4) discloses a configuration based on an MOT using a single laser beam that is reflected on a diffractive optical component, and a transverse beam for the interferometer. The planar diffractive optical component is based on a triangular geometry with three sectors each comprising a 1D grating configured to generate, by diffraction of the incident laser beam, three beams having adapted orientations to form a tetrahedral trap and trap atoms near the surface of the diffractive optical component. Such a configuration has the advantage of compactness. However, the diffractive optical component is complex to manufacture.Exposure of the diffractive optical component to rubidium atoms is likely to cause aging of this component and induce stray light.

[0014] One of the aims of the invention is to propose a compact, robust and high-precision interferometric quantum sensor while making it possible to increase the measurement rate.

[0015] Another aim of the invention is to propose a system combining several interferometric quantum sensors or several magneto-optical traps in the same interferometric quantum sensor, for local gradient measurements, the system being compact while allowing high-precision measurements at an increased rate. Presentation of the invention

[0016] In order to overcome the aforementioned drawbacks of the state of the art, the present invention proposes an interferometric quantum sensor comprising a vacuum chamber capable of receiving a vapor of alkali or alkaline-earth atoms, a laser source configured to generate a laser beam propagating in a longitudinal direction and a reflector optical device.

[0017] According to the invention, the optical reflector device is arranged and configured to receive the laser beam in an interior volume delimited by the optical reflector device and to form a plurality of beams reflected in a plurality of directions, so as to trap atoms of the atom vapor in a three-dimensional trapping and cooling zone located in the interior volume of the optical reflector device and in that the optical reflector device comprises a first through opening adapted to pass a first interferometry light beam through the optical reflector device and into the trapping and cooling zone along a first axis forming a non-zero angle with the longitudinal axis.

[0018] The interferometric quantum sensor advantageously has a compact architecture based on a pyramidal reflector allowing the measurement to be carried out on an axis which is not that of the pyramid and the beam used for three-dimensional trapping.

[0019] Such a reflector structure makes it possible to carry out acceleration measurements in a compact geometry, which has the advantage of not requiring waiting for the atoms to leave the trapping zone.

[0020] Other non-limiting and advantageous characteristics of the reflector according to the invention, taken individually or in all technically possible combinations, are the following: - the optical reflector device comprises a second through opening (9) adapted to pass a second interferometric light beam through the optical reflector device and into the trapping and cooling zone along a second axis forming a non-zero angle with the longitudinal axis, the second axis forming a non-zero angle with the first axis; - the optical reflector device comprises four plane mirrors arranged on four faces of a pyramid with a square or rectangular base, each of the four plane mirrors forming an angle of 45 degrees with the longitudinal axis; - the optical reflector device comprises three plane mirrors arranged on three faces of a pyramid with an equilateral triangular base, each of the three plane mirrors forming an angle of approximately 35 degrees with the longitudinal axis; - the sensor has an opto-mechanical support on which the plane mirrors are fixed; - the optical reflector device comprises at least one concave conical surface with an axis coincident with the longitudinal axis and forming an angle at the apex of 45 degrees with the longitudinal axis; - the optical reflector device comprises an axial opening in the longitudinal axis, the axial opening being adapted for the passage of a portion of the laser beam; - the reflective optical device comprises another mirror arranged facing the axial opening, the other mirror being flat and arranged perpendicular to the longitudinal axis; - the interferometric quantum sensor comprises means for generating a magnetic field gradient.

[0021] The present disclosure allows the manufacture of a compact quantum accelerometer compatible with on-board acceleration or gravity measurements. The present disclosure also allows acceleration measurements to be carried out along several axes with a single device.

[0022] Finally, the present disclosure makes it possible to combine several interferometric quantum sensors to carry out gradient measurements along one or more axes.

[0023] The invention also relates to a differential atomic interferometry system comprising a first interferometric quantum sensor according to any one of the described embodiments and a second interferometric quantum sensor according to any one of the described embodiments, the first interferometric quantum sensor and the second interferometric quantum sensor sharing the vacuum chamber, the longitudinal axis of the first interferometric quantum sensor being parallel to the longitudinal axis of the second interferometric quantum sensor, and in which the first through aperture of the optical reflector device of the first interferometric quantum sensor and the first through aperture of the optical reflector device of the second interferometric quantum sensor are aligned along the same first axis.

[0024] The invention also relates to a differential atomic interferometry system comprising a first interferometric quantum sensor according to any one of the embodiments described and a second interferometric quantum sensor according to any one of the embodiments described, the first interferometric quantum sensor and the second interferometric quantum sensor sharing the vacuum chamber and the laser source, the longitudinal axis of the first interferometric quantum sensor being coincident with the longitudinal axis of the second interferometric quantum sensor,the optical reflector device of the second interferometric quantum sensor being arranged to receive a portion of the laser beam propagating in the longitudinal direction through the axial opening of the optical reflector device of the first interferometric quantum sensor and in which the first through opening of the first interferometric quantum sensor and the first through opening of the second interferometric quantum sensor are aligned along parallel axes and separated by a non-zero distance D2.

[0025] Of course, the various characteristics, variants and embodiments of the invention may be combined with each other in various combinations provided that they are not incompatible or mutually exclusive. Detailed description of the invention

[0026] Furthermore, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate a non-limiting form of embodiment of the invention and where:

[0027] [Fig-1] is a schematic view of an interferometric quantum sensor comprising a three-dimensional magneto-optical trap according to the prior art;

[0028] [Fig.2] is a perspective view of a reflective optical device according to a first embodiment;

[0029] [Fig.3] is a front (left) and side (right) view of an optical device re deflector according to a variant of the first embodiment and illustrates its use in an interferometric quantum sensor;

[0030] [Fig.4] is a front view of a reflective optical device in a sensor quantum interferometric according to another variant of the first embodiment;

[0031] [Fig.5] is a front view of a reflective optical device in a sensor quantum interferometric according to a second embodiment;

[0032] [Fig.6] is a front (left) and side (right) view of an optical device re deflector in an interferometric quantum sensor according to a variant of the first embodiment;

[0033] [Fig.7] is a front (left) and side (right) view of an optical device re deflector in an interferometric quantum sensor according to another variant of the first embodiment;

[0034] [Fig.8] is a front (left) and side (right) view of an optical device re deflector in an interferometric quantum sensor according to yet another variant of the first embodiment;

[0035] [Fig.9] is a side view of a differential atom interferometry system according to a first example of realization;

[0036] [Fig. 10] is a side view of a differential atomic interferometry system according to a second exemplary embodiment;

[0037] [Fig. 11] is a side view of a differential atomic interferometry system according to a third exemplary embodiment.

[0038] The present disclosure provides an interferometric quantum sensor comprising a three-dimensional cooling and trapping device based on the use of a single laser beam incident on a specific optical reflector device 10 to trap a cloud of atoms in a magneto-optical trapping or optical molasses cooling zone 6. The optical reflector device 10 is arranged in the interferometric quantum sensor for reflecting an incident laser beam 20 propagating along a longitudinal axis 5. For this purpose, the optical reflector device 10 has at least one reflective surface of hollow pyramidal or conical shape, the apex of which is located on the longitudinal axis 5 of the incident laser beam 20. According to the present disclosure, the optical reflector device 10 is provided with at least one first through opening 8 adapted to pass at least one light beam 31 through the optical reflector device 10 and into the trapping and cooling zone 6 along a first axis 18 forming a non-zero angle ALPHA with the longitudinal axis 5.

[0039] [Fig. 2] represents a reflective optical device 10 according to a first embodiment. The reflective optical device 10 comprises an optomechanical support 17, for example of a generally polygonal or annular shape, on which four mirrors 11, 12, 13 and 14 are fixed. The optomechanical support 17 is made of glass or metal. In the example illustrated in [Fig. 2], each mirror 11, 12, 13, 14 consists of a 45-degree prism, the face of which inclined at 45 degrees comprises a reflective coating, for example metallic or dielectric. Advantageously, the four prisms are of identical dimensions and arranged in a square (i.e. at the same distance) around the longitudinal optical axis. Alternatively, the four mirrors 11, 12, 13, 14 are plane mirrors formed from a plate with plane and parallel faces. The four mirrors 11, 12, 13 and 14 are arranged to each form a part of one of the four faces of a pyramid with a square or rectangular base.More specifically, each of the four mirrors 11, 12, 13, 14 forms an angle of 45 degrees with the longitudinal axis 5 of the atomic interferometer. In other words, the normal to each of the four mirrors 11, 12, 13, 14 forms an angle of 45 degrees with the longitudinal axis 5. The mirrors 11 and 12 are arranged so that the normal to the mirror 11 and the normal to the mirror 12 are in a first plane containing the longitudinal axis 5. The mirrors 13 and 14 are arranged so that the normal to the mirror 13 and the normal to the mirror 14 are in a second plane containing the longitudinal axis 5 and perpendicular to the first plane. The optical reflector device 10 makes it possible to form a magneto-optical trap or a three-dimensional optical molasses from a single incident laser beam 20 propagating along the longitudinal axis 5.

[0040] [Fig. 3] shows the optical reflector device 10 arranged in the vacuum chamber 1 of the interferometric quantum sensor, so that the axis of symmetry of the virtual pyramid formed by the four mirrors 11, 12, 13, 14 coincides with the longitudinal axis 5 of the incident laser beam 20. The optical reflector device 10 receives the incident laser beam 20. Each mirror 11, 12, 13, 14 reflects a portion of the incident laser beam 20 so as to form two pairs of counter-propagating beams in two directions perpendicular to the longitudinal axis 5. By double reflection on the pair of mirrors 11 and 12, a portion of the laser beam is retro-reflected along the longitudinal axis 5 in the opposite direction to the incident laser beam 20. Three pairs of counter-propagating laser beams are thus obtained in three orthogonal directions in space. The optical reflector device 10 thus makes it possible to optically trap a cloud of atoms in the trapping and cooling zone 6 located between the four mirrors 11, 12, 13, 14 and on the longitudinal axis 5. Advantageously, the four mirrors are identical and the trapping and cooling zone 6 is located approximately halfway up the four mirrors 11, 12, 13, 14. The optical reflector device 10 makes it possible to trap and cool a cloud of atoms from a single incident laser beam 20. Optionally, the interferometric quantum sensor comprises means for generating a magnetic field, illustrated for example by a pair of anti-Helmholtz coils 3.

[0041] Optionally, the optical reflector device 10 comprises an axial opening 26 in the longitudinal axis 5 between the four mirrors 11, 12, 13 and 14. The axial opening 26 is adapted to pass a portion 120 of the incident laser beam 20. For example, the axial opening 26 is circular and has a diameter between one third and one half of the diameter of the incident laser beam 20. In this case, as illustrated for example in [Fig. 3] (on the right), the optical reflector device 10 further comprises another mirror 15 arranged facing this axial opening 26. Advantageously, this other mirror 15 is fixed by a mount to the opto-mechanical support 17. The other mirror 15 is planar and arranged perpendicular to the longitudinal axis 5. Thus, this other mirror 15 makes it possible to reflect a portion 120 of the incident laser beam by simple reflection, along the direction longitudinal and in the opposite direction to the incident laser beam 20.A quarter-wave plate 16 interposed between the optical device 10 and the mirror 15 makes it possible to adjust the polarization of the beam reflected on the mirror 15 so that it contributes to the magneto-optical trapping or to the optical molasses cooling of the cloud of atoms in the trapping and cooling zone 6.

[0042] Unlike a pyramidal optical reflector device used in an atomic interferometer of the prior art, the faces of the mirrors 11, 12, 13, 14 do not extend over the entire surface of the faces of the pyramid. For example, as illustrated in [Fig.2], the lateral faces of the mirrors 11, 12, 13, 14 are not all contiguous but on the contrary disjointed and separated from each other by approximately 10 mm. The optical reflector device 10 has at least one first through opening 8 which extends longitudinally along the first axis 18 forming a non-zero angle ALPHA with the longitudinal axis 5. The first through opening 8 extends transversely on the one hand between the mirrors 11 and 14 and on the other hand between the mirrors 12 and 13. The angle ALPHA is preferably equal to 90 degrees. For example, in Figures 2 and 3, the first axis 18 is perpendicular to the longitudinal axis 5, in other words, the angle ALPHA is 90 degrees.

[0043] The first through opening 8 is adapted for the passage of at least a first interferometry light beam 31 through the optical reflector device 10. Advantageously, the first interferometry light beam 31 propagates along the first axis 18 towards the cloud of atoms and comprises a sequence of at least three laser pulses. The first interferometry light beam 31 can be generated by the same laser source 4 as the incident laser beam 20 or by another laser source. The interferometry sequence can be of the Raman or Bragg type. This configuration requires the alignment of only two beams: the incident laser beam along the longitudinal axis 5 and the first interferometry light beam 31 along the first axis 18. The configuration of the interferometric quantum sensor is relatively compact and simple to manufacture, assemble and use.

[0044] For example, in a vertical gravimeter or accelerometer application, illustrated in [Fig. 3], the longitudinal axis 5 is arranged horizontally and the first axis 18 vertically (Z axis). The incident laser beam 20 is applied to trap the atoms in the trapping and cooling zone 6. Then, the trapping is interrupted and the atom cloud falls in free fall. The optical reflector device 10 makes it possible to direct the sequence of pulses of the interferometry light beam 31 at successive instants, corresponding to successive positions of the atom cloud along the Z axis at a very short distance from the trapping and cooling zone 6. Consequently, this configuration makes it possible to start the interferometry sequence very soon after stopping the cooling laser when the atom cloud is still inside the optical reflector device 10.

[0045] By way of example, the length of the mirrors 11, 12, 13, 14 is 10 mm and the total length of the optical reflector device 10 is 20 mm in the direction of the longitudinal axis 5. This configuration makes it possible to reduce the length of the interferometric quantum sensor along the longitudinal axis 5. This results in an interferometric quantum sensor having the advantage of being very compact.

[0046] The incident laser beam 20 has a diameter at 1 / e2 generally between 10 mm and 50 mm. In one example, the incident laser beam 20 has a diameter at 1 / e2 of 30 mm and the interferometry light beam 31 has a diameter at 1 / e2 of 10 mm.

[0047] According to another particularly advantageous aspect of the present disclosure, illustrated for example in Figures 2, 6 and 7, the optical reflector device 10 has at least one second through opening 9 which extends longitudinally along a second axis 19 forming a non-zero angle BETA with the longitudinal axis 5. The second through opening 9 extends transversely on the one hand between the mirrors 11 and 13 and on the other hand between the mirrors 12 and 14. The angle BETA is preferably equal to 90 deg. By way of example, in Figures 2, 6 and 7, the second axis 19 is perpen dicular to the longitudinal axis 5, in other words, the angle BETA is 90 degrees. The second axis 19 also forms a non-zero angle with the first axis 18. In the example of [Fig.2], 6 or 7, the second axis 19 is perpendicular to the first axis 18. However, for example for the optical reflector device 10 illustrated in [Fig.4], the angle between the first axis 18 and the second axis 19 is other than 90 degrees, for example 120 deg.

[0048] The second through opening 9 is adapted for the passage of at least one second interferometry light beam 32 through the optical reflector device 10. Advantageously, the second interferometry light beam 32 propagates along the second axis 19 towards the trapping and cooling zone 6 and comprises a sequence of at least three laser pulses.

[0049] Advantageously, the openings 8 and / or 9 are further adapted for the passage of other signals, for example to carry out fluorescence detection. Preferably, one or more pulses are applied to detect the state of the atoms on the two outputs of the interferometric quantum sensor. For this purpose, the detection system, which comprises one or more detectors 27, 28, is arranged facing the second opening 9, or, respectively, the first opening 8, as close as possible to the atoms. In this way, the atoms are illuminated with the beam 5 or with the interferometric light beam 31, and the fluorescence is collected with the detector(s) facing the second opening 9. Similarly, the atoms are illuminated with the beam 5 or with the interferometric light beam 32, and the fluorescence is collected with the detector(s) facing the first opening 8.

[0050] In an exemplary application, the trapping duration is 50 ms, and the total duration of the interferometry sequence is 20 ms. The interferometry pulse sequence is applied at respective times, e.g., 10 ms, 20 ms, and 30 ms after stopping the magneto-optical trapping, the time to cool the atoms in an optical molasses, and to apply a quantum state preparation sequence. The configuration of the reflector optical device 10 makes it possible to reduce the total duration of the interferometry sequence and thus to increase the acquisition frequency of the atomic interferometry measurements. This configuration has the disadvantage of reducing the accuracy of the measurements compared to a prior art atom interferometer, in which the interferometry sequence only starts 40 ms after exiting the pyramid trap but can last 100 to 200 ms.In addition, the quantum sensor of the present disclosure allows for acquiring, instead of a single measurement, multiple measurements over the same total duration, which can then be averaged. Although the accuracy of the interferometric measurement decreases as the duration between pulses in the interferometry pulse sequence decreases, a shorter sequence allows for averaging the measurements to improve accuracy.

[0051] In a gravimetry application, an interferometric quantum sensor comprising the optical reflector device of the present disclosure is carried on board a boat. This interferometric quantum sensor makes it possible to measure local gravity with an accuracy of 107. This measurement accuracy is two orders of magnitude lower than that of an interferometric quantum sensor having a total height of approximately 70 cm and measuring statically on land. However, this local gravity measurement accuracy is already very high and sufficient for many onboard inertial sensor applications, where the measurement performance is intrinsically limited by the movements of the wearer, and where increasing the measurement rate is preferable to increasing the intrinsic accuracy.

[0052] In a variant of the first embodiment, illustrated in [Fig.4], the optical reflector device comprises three plane mirrors 11, 12, 13 arranged on three faces of a pyramid with an equilateral triangular base, each of the three plane mirrors 11, 12, 13 forming an angle of approximately 35 degrees, ±1 or 2 degrees, with the longitudinal axis 5. The plane mirrors 11, 12, 13 can be manufactured from plates or prisms. The mirror 11 is arranged so that the normal to the mirror 11 is in a first plane 41 containing the longitudinal axis 5. The mirror 12 is arranged so that its normal is in a plane 42 containing the longitudinal axis 5. The mirror 13 is arranged so that its normal is in a plane 43 containing the longitudinal axis 5. The planes 41, 42, 43 are oriented at 120 degrees from each other. Advantageously, the three plane mirrors 11, 12, 13 are fixed to an opto-mechanical support 17.The optical reflector device 10 is arranged in the vacuum chamber 1 of the interferometric quantum sensor, so that the axis of symmetry of the virtual pyramid formed by the three mirrors 11, 12, 13 coincides with the longitudinal axis 5 of the incident laser beam 20. The optical reflector device 10 receives the incident laser beam 20. Each mirror 11, 12, 13 reflects a portion of the incident laser beam 20 so as to form a tetrahedral trap. This optical reflector device 10 thus makes it possible to form a magneto-optical trap or a 3D optical molasses from a single incident laser beam 20 propagating along the longitudinal axis 5 and three plane mirrors 11, 12, 13. The optical reflector device 10 illustrated in [Fig.4] also has a first through opening 8 which extends longitudinally along the first axis 18.The first through opening 8 extends transversely on the one hand between the mirror 11 and on the other hand between the mirrors 12 and 13. For example, in [Fig.4], the first axis 18 is perpendicular to the longitudinal axis 5. This interferometric quantum sensor makes it possible to measure an acceleration along an axis transverse to the longitudinal axis 5.

[0053] According to a second embodiment, the optical reflector device 10 comprises at least one concave conical surface with an axis coincident with the longitudinal axis 5 and forming an angle at the apex of 45 degrees with the longitudinal axis 5. In the example illustrated in [Fig.5], the optical reflector device 10 comprises two portions 111, 112 of a cone. The internal conical surface 111, 112 of each cone portion is for example metallized to form a reflecting mirror. The two internal conical surfaces 111, 112 are spaced so as to provide a first through opening 8 which extends longitudinally along a first axis 18 forming a non-zero angle ALPHA with the longitudinal axis 5.

[0054] More generally, the optical reflector device 10 may comprise one, two, three, four or more reflecting surfaces.

[0055] In an example of application to a horizontal accelerometer, illustrated in [Fig.6], the longitudinal axis 5 is arranged horizontally (parallel to the Y axis) and the second axis 19 is arranged horizontally (parallel to the X axis). The incident laser beam 20 is applied to trap the atoms in the trapping and cooling zone 6. Then, the trapping is interrupted and the cloud of atoms falls in free fall. The optical reflector device 10 allows the interferometry light beam 32 to pass to carry out the sequence of pulses at successive times and to measure the acceleration along the second axis 19 which is horizontal.

[0056] The use of interferometric beams 31, respectively 32, along two distinct axes 18 and 19 makes it possible to carry out acceleration measurements along two independent measurement axes using a single interferometric quantum sensor. This results in an interferometric quantum sensor sensitive to accelerations or rotations along several measurement axes.

[0057] In the example illustrated in [Fig. 7], the optical reflector device 10 comprises an axial opening 26. The axial opening 26 is adapted for the passage of a third interferometry light beam 33 through the optical reflector device 10. Advantageously, the third interferometry light beam 33 propagates along the longitudinal axis 5 towards the trapping and cooling zone 6 and comprises a sequence of at least three laser pulses. The third interferometry light beam 33 has a diameter smaller than the diameter of the incident laser beam. Preferably, the third interferometry light beam 33 has a diameter smaller than the diameter of the axial opening 26 so as to avoid any parasitic reflection on the mirrors 11, 12, 13, 14. In an example of application to a multi-axis accelerometer, illustrated in [Fig.7], the longitudinal axis 5 is arranged horizontally (parallel to the Y axis), the first axis 18 is arranged vertically (parallel to the Z axis) and the second axis 19 is arranged horizontally (parallel to the X axis). The incident laser beam 20 is applied to trap the atoms in the trapping and cooling zone 6. Then, the magneto-optical trapping is interrupted and the atom cloud falls in free fall. The optical reflector device 10 makes it possible to . directing the pulse sequence of the third interferometric light beam 33 at successive times and measuring the acceleration along the longitudinal axis 5 which is horizontal. By alternating measurement sequences along the three axes, we thus obtain a quantum interferometric sensor capable of measuring the accelerations along the three axes X, Y and Z.

[0058] In the different embodiments, the first opening 8, the second opening 9 and / or the axial opening 26 can also be used to inject the atoms towards the trapping and cooling zone 6 via a two-dimensional trap for example.

[0059] [Fig.8] represents an example of use of a quantum sensor according to the first embodiment, in which the first interferometric beam is directed along the axis 18, for example vertical. The optical fluorescence collection systems are advantageously arranged in the openings 37, 38. In this way, the signal is collected as close as possible to the atoms, which makes it possible to maximize the number of photons collected. Alternatively, the openings 37, 38 are used to pass a jet of atoms from a two-dimensional magneto-optical trap (2D-M0T), so as to accelerate the loading of the 3D magneto-optical trap and increase the measurement rate.

[0060] The present disclosure also proposes an atomic interferometry system comprising several optical reflector devices arranged in series or in parallel, preferably in the same vacuum chamber to simultaneously form several magneto-optical traps and several atomic interferometers.

[0061] Figures 9-10 illustrate a first example of an atomic interferometry system comprising a first interferometric quantum sensor 100 and a second interferometric quantum sensor 110 arranged in parallel. Each interferometric quantum sensor 100, 110 comprises a reflective optical device according to any one of the embodiments described above. Advantageously, a mirror 15, respectively 115, is arranged facing the central opening 26, respectively 126 of the interferometric quantum sensor 100, respectively 110. The mirror 15, respectively 115, is planar and arranged perpendicular to the longitudinal axis 5, respectively 51. The two interferometric quantum sensors 100, 110 are preferably arranged in the same vacuum chamber 1 (not shown in Figures 9-10).The first interferometric quantum sensor 100 is arranged to receive an incident laser beam 20 along its longitudinal axis 5 and to cool and trap atoms in three dimensions in a trapping and cooling zone 6. The second interferometric quantum sensor 110 is arranged to receive another incident laser beam 201 along its longitudinal axis 51 and to cool and trap atoms in three dimensions in another zone 61 of . trapping and cooling. The longitudinal axis 5 of the first interferometric quantum sensor 100 is parallel and located at a non-zero distance DI from the longitudinal axis 51 of the second interferometric quantum sensor 110. Consequently, the two trapping and cooling zones 6 and 61 are separated by the distance Dl. In addition, the two interferometric quantum sensors 10, 110 are arranged so that the first through-opening of the optical reflector device of the first interferometric quantum sensor 100 and the first through-opening of the optical reflector device of the second interferometric quantum sensor 110 are aligned along the same first axis 18.

[0062] The incident laser beams 20 and 201 are applied simultaneously so as to simultaneously trap atoms in the two trapping and cooling zones 6 and 61. Then, the trapping is simultaneously interrupted and the two clouds of atoms fall simultaneously in free fall. The same sequence of pulses of the interferometric light beam 31 is applied along the first axis 18. The acceleration is detected and measured along the axis 18 via the first interferometric quantum sensor 100 and, simultaneously via the second interferometric quantum sensor 110. The difference between these two acceleration measurements makes it possible to obtain a differential measurement or a spatial gradient of acceleration between two positions separated by the distance DL. The average of these two acceleration measurements makes it possible to obtain the average acceleration of the sensor.

[0063] In the example illustrated in [Fig.9], the interferometric system is arranged so that the measurement axis 18 is vertical. The acceleration and the acceleration gradient are thus measured along the vertical axis.

[0064] In the example illustrated in [Fig. 10], the interferometric system is arranged so that the measurement axis 18 is horizontal. The acceleration and the acceleration gradient are thus measured along the horizontal axis.

[0065] [Fig. 11] shows another atomic interferometry system architecture comprising a first interferometric quantum sensor 100 and a second interferometric quantum sensor 130 arranged in parallel. Each interferometric quantum sensor 100, 130 comprises a reflective optical device as described above. More specifically, the first interferometric quantum sensor 100 has a central opening 26 and the second interferometric quantum sensor 130 also has a central opening 126. The two interferometric quantum sensors 100, 130 are arranged in the same vacuum chamber 1 (not shown in [Fig. 11]) so that the longitudinal axis 5 of the first interferometric quantum sensor 100 coincides with the longitudinal axis 51 of the second interferometric quantum sensor 130. The central openings 26 and 126 are aligned along the longitudinal axis 5. A mirror 15 is arranged facing the two or central openings 26 and 126. In this way, the same mirror 15 is common to the first interferometric quantum sensor 100 and to the second interferometric quantum sensor 130.

[0066] The first interferometric quantum sensor 100 is arranged to receive the incident laser beam 20 along its longitudinal axis 5 and to cool and trap three-dimensional atoms in a first trapping and cooling zone 6. The second interferometric quantum sensor 130 is arranged to receive a portion 220 of the incident laser beam having passed through the first optical reflector device along the longitudinal axis 5 and to cool and trap the three-dimensional atoms in a second trapping and cooling zone 61. Advantageously, the optical reflector device of the first interferometric quantum sensor 100 is larger than the optical reflector device of the second interferometric quantum sensor 130. The two trapping and cooling zones 6 and 61 are separated by a distance D2.In addition, the two interferometric quantum sensors 100, 130 are arranged so that the first through opening of the first interferometric quantum sensor 100 and the first through opening of the second interferometric quantum sensor 130 are aligned along parallel axes 18, respectively 118, separated by the distance D2.

[0067] The incident laser beam 20 is applied so as to simultaneously trap and cool atoms in the two trapping and cooling zones 6 and 61. Then, the trapping is simultaneously interrupted and the two clouds of atoms fall in free fall. An interferometric light beam along the first axis 18 of the first interferometric quantum sensor 100 and an interferometric light beam along the first axis 118 of the second interferometric quantum sensor 130 are simultaneously applied. The acceleration along the axis 18 is detected and measured via the first interferometric quantum sensor 100 and, simultaneously, the acceleration along the axis 118 via the second interferometric quantum sensor 110. The difference between these two acceleration measurements makes it possible to obtain a differential measurement or a spatial gradient of acceleration between two positions separated by the distance D2.

[0068] According to a variant of the system of [Fig. 11], the two interferometric quantum sensors 100, 130 each comprise a second through-opening, arranged perpendicular to the first through-openings. Advantageously, the second through-opening of the first interferometric quantum sensor 100 and the second through-opening of the second interferometric quantum sensor 130 are aligned along parallel axes, for example to the Y axis, and also separated by the distance D2. This configuration makes it possible to carry out another differential measurement or another spatial acceleration gradient between two separate positions of the distance D2 along another axis, perpendicular to axes 18, 118.

[0069] Alternatively or additionally, after the simultaneous trapping and cooling of the atoms in the two trapping and cooling zones 6 and 61, the trapping is simultaneously interrupted and the two clouds of atoms fall in free fall. Then, an interferometric light beam is applied along the longitudinal axis 5 common to the first interferometric quantum sensor 100 and to the second interferometric quantum sensor 130. The acceleration along the longitudinal axis 5 is detected and measured via the first interferometric quantum sensor 100 and, simultaneously, the acceleration along the longitudinal axis 5 via the second interferometric quantum sensor 110. The difference between these two acceleration measurements makes it possible to obtain a differential measurement or a spatial gradient of acceleration along the longitudinal axis 5 between the two positions separated by the distance D2.

[0070] We thus obtain a differential measurement or a spatial gradient of acceleration along one, two or three transverse directions.

[0071] The interferometric system combining two or more interferometric sensors according to the present disclosure has the advantage of being very compact. Increasing the number of interferometric quantum sensors makes it possible to access higher orders of acceleration measurement without multiplying the number of laser beams to be aligned.

[0072] From such an architecture, gradient measurements can be carried out on several axes.

[0073] In addition, the orientation of the measuring axes can be modified according to the applications.

[0074] Differential measurements find applications, for example, in the recalibration of inertial units. Indeed, the components of the acceleration gradient provide additional information compared to a simple measurement on one axis. Thanks to common mode rejection effects, the sensitivity of the interferometric system is greatly improved, which makes it possible to obtain excellent performance on differential measurements.

Claims

Claims

1. Interferometric quantum sensor (100) comprising a vacuum chamber (1) capable of receiving a vapor of alkali or alkaline-earth atoms, a laser source (4) configured to generate a laser beam (20) propagating in a longitudinal direction (5) and a reflecting optical device (10), characterized in that the reflecting optical device (10) is arranged and configured to receive the laser beam (20) in an interior volume delimited by the reflecting optical device (10) and to form a plurality of beams reflected in a plurality of directions,so as to trap atoms of the atom vapor (1) in a three-dimensional trapping and cooling zone (6) located in the interior volume of the optical reflector device (10) and in that the optical reflector device (10) comprises a first through opening (8) adapted to pass a first interferometry light beam (31) through the optical reflector device (10) and into the trapping and cooling zone (6) along a first axis (18) forming a non-zero angle with the longitudinal axis (5).,

2. Interferometric quantum sensor according to claim 1 in which the optical reflector device (10) comprises a second through opening (9) adapted to pass a second interferometric light beam (32) through the optical reflector device (10) and into the trapping and cooling zone (6) along a second axis (19) forming a non-zero angle with the longitudinal axis (5), the second axis (19) forming a non-zero angle with the first axis (18).

3. An interferometric quantum sensor according to claim 1 or 2 wherein the reflective optical device (10) comprises four plane mirrors (11, 12, 13, 14) arranged on four faces of a pyramid with a square or rectangular base, each of the four plane mirrors (11, 12, 13, 14) forming an angle of 45 degrees with the longitudinal axis (5).

4. An interferometric quantum sensor according to claim 1 or 2 wherein the reflective optical device (10) comprises three plane mirrors (11, 12, 13) arranged on three faces of an equilateral triangular base pyramid, each of the three plane mirrors (11, 12, 13) forming an angle of approximately 35 degrees with the longitudinal axis (5).

5. Interferometric quantum sensor according to claim 3 or 4 comprising an opto-mechanical support (17) on which the plane mirrors.

6. Interferometric quantum sensor according to claim 1 or 2 wherein the optical reflector device (10) comprises at least one concave conical surface (111, 112) with an axis coincident with the longitudinal axis (5) and forming an angle at the apex of 45 degrees with the longitudinal axis (5).

7. Interferometric quantum sensor according to one of claims 1 to 6 in which the optical reflector device (10) comprises an axial opening (26) in the longitudinal axis (5), the axial opening (26) being adapted for the passage of a portion of the laser beam (120).

8. An interferometric quantum sensor according to claim 7 wherein the reflective optical device (10) comprises another mirror (15) arranged facing the axial opening (26), the other mirror (15) being planar and arranged perpendicular to the longitudinal axis (5).

9. Interferometric quantum sensor according to one of claims 1 to 8 comprising means for generating (3) a magnetic field gradient.

10. A differential atomic interferometry system comprising a first interferometric quantum sensor (100) according to one of claims 1 to 9 and a second interferometric quantum sensor (110) according to one of claims 1 to 9, the first interferometric quantum sensor (100) and the second interferometric quantum sensor (110) sharing the vacuum chamber (1), the longitudinal axis (5) of the first interferometric quantum sensor (100) being parallel to the longitudinal axis (51) of the second interferometric quantum sensor (110), and wherein the first through aperture of the optical reflector device of the first interferometric quantum sensor (100) and the first through aperture of the optical reflector device of the second interferometric quantum sensor (110) are aligned along the same first axis (18).

11. A differential atomic interferometry system comprising a first interferometric quantum sensor (100) according to claim 7 and a second interferometric quantum sensor (130) according to claim 8, the first interferometric quantum sensor (100) and the second interferometric quantum sensor (130) sharing the vacuum chamber (1) and the laser source (4), the longitudinal axis (5) of the first interferometric quantum sensor (100) being coincident with the longitudinal axis (51) of the second interferometric quantum sensor (130), the optical reflector device (310) of the second interferometric quantum sensor (130) being arranged to receive a portion of the laser beam (120) propagating in the longitudinal direction (5) through the axial opening (26) of the optical reflector device (10) of the first interferometric quantum sensor (100) and in which the first through opening of the first interferometric quantum sensor (100) and the first through opening of the second interferometric quantum sensor (130) are aligned along parallel axes (18, 118) and separated by a non-zero distance D2.

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