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 atomic 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 particular applications in an inertial quantum sensor. This inertial quantum sensor can be used in applications for measuring acceleration and / or rotation 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] Quantum sensors, particularly cold-atom interferometric sensors, exist that are based on the interactions between one or more laser sources and atoms in an ultra-high vacuum. Generally, an atomic interferometer comprises an atom source and a cold-atom trap configured to trap a cloud of atoms and then release it in free fall or direct it in a predetermined initial direction. The atomic interferometer also includes a laser source emitting a sequence of interrogating light pulses designed to interact with the fine structure of the atoms by photon transfer. Finally, the atomic interferometer includes 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 releasing them to measure their free-fall acceleration using a sequence of three laser pulses, thus creating an atomic interferometer. A quantum gravimeter from the company Exail, for example, makes it possible to measure local gravitational acceleration with an accuracy on the order of 1 in 1 billion. The measurement rate thus obtained is approximately 2 Hertz (Hz).

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

[0007] French 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 illustrated, for example, in [Fig. 1]. An orthonormal XYZ coordinate system 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 pyramidal in this case, receives the incident laser beam 20 and, by multiple reflections, generates three pairs of laser beams in the three spatial directions, for example, the counterpropagating beam pair 24 and 25 along the X and Y axes, respectively, and a counterpropagating beam pair along the Z axis.In the case of a pyramidal reflector 7 with four facets inclined at 45 degrees 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 counterpropagating beams oriented orthogonally to the incident laser beam. The incident beam is also reflected back 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 the beam(s) back-reflected by double reflection on two opposite faces of the pyramid.Advantageously, in a pyramidal reflector, a single incident laser beam is reflected off the different faces of a hollow pyramid to create three pairs of counter-propagating beams propagating in superimposed orthogonal directions within a region of space. Such a pyramidal reflector thus forms a trap by superimposing 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 low vapor of the atoms to be trapped is maintained. The 3D-M0T magneto-optical trap generally comprises three pairs of beams along the three spatial directions and a magnetic field with a specific configuration to trap the atoms in the three spatial directions. The magnetic field is generated, for example, by means of pairs of anti-Helmholtz coils 3.The trapping zone 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 are initially trapped and cooled in the overlap zone of three pairs of laser beams, inside the pyramidal reflector. This arrangement is suitable for forming an atomic interferometer sensitive to acceleration along the [missing information]. The longitudinal direction 5 of the incident laser beam 20 is targeted. Magneto-optical trapping is interrupted during a free-fall period, during which the atoms fall under the influence of local gravity. In practice, the magnetic field is first switched off to create an optical molasses, which allows the atoms to complete their cooling. The laser beam is then switched off, and the atoms are in free fall. During this time, a sequence of microwave and laser pulses is applied to prepare the atoms in a well-defined quantum state before they enter the interferometer. After a few tens of milliseconds of fall, the atoms have exited the trapping zone and the pyramidal reflector. The interferometric quantum sensor is generally hybridized with a measurement device 29 based on one or more conventional sensors, such as an accelerometer, barometer, inclinometer, and / or gyroscope.

[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 allow the matter waves associated with the atoms to be separated or recombined. The "ir" pulses allow the matter waves to be deflected. Other sequences of more than three pulses are also used, for example, a sequence of four light pulses, "ji / 2-ir-ir-ir / 2".In all cases, a first light pulse 21 interacts with the cloud of atoms 2 at the exit of the trap 3DM0T so as to spatially separate the wave associated with each atom into a first wave of atoms traveling along a first path and, respectively, a second wave of atoms traveling along a second path. At least one second light pulse 22 interacts with the two separated waves of atoms to redirect them. Finally, a last light pulse 23 spatially recombines the two waves of atoms. The sensitivity of the atomic 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 due to gravity.

[0010] The quantum interferometric sensor illustrated in [Fig. 1] allows all trapping, interferometry, and detection operations to be performed from a single laser beam 20 instead of a dozen laser beams in other quantum interferometric 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 quantum interferometric sensor as illustrated in [Fig. 1] is bulky. For inertial sensor applications mounted on a mobile platform (e.g., aircraft, surface vessel or submarine, autonomous land, air or marine vehicle), it is desirable to reduce the size of such a quantum interferometric sensor. Furthermore, in these applications, it is desirable to increase the measurement rate to at least approximately 10 Hz.

[0012] Various atomic interferometer architectures based on the use of independent laser beams on multiple axes have been proposed for embedded 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 by 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 a magneto-optical interferometer (MOT) using a single laser beam reflected from 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 containing a 1D grating configured to generate, by diffraction of the incident laser beam, three beams with orientations adapted 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 fabricate.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 provide a compact, robust and high-precision interferometric quantum sensor while enabling an increase in the rate of measurements.

[0015] Another object of the invention is to provide a system combining several interferometric quantum sensors or several magneto-optical traps in a single 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 prior art, the present invention proposes an interferometric quantum sensor comprising a vacuum chamber suitable for receiving a vapor of alkali or alkaline-earth atoms, a source laser configured to generate a laser beam propagating along a longitudinal direction and an optical reflector device.

[0017] According to the invention, the optical reflector device is arranged and configured to receive the laser beam in an internal 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 internal volume of the optical reflector device and in that the optical reflector device includes a first through-opening adapted to pass a first interferometric 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 that 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 features of the reflector according to the invention, taken individually or in all technically possible combinations, are as follows: - the optical reflector device includes a second through-port aperture (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 flat mirrors arranged on four faces of a pyramid with a square or rectangular base, each of the four flat mirrors forming an angle of 45 degrees with the longitudinal axis; - the optical reflector device comprises three flat mirrors arranged on three faces of a pyramid with an equilateral triangular base, each of the three flat mirrors forming an angle of approximately 35 degrees with the longitudinal axis; - the sensor includes an opto-mechanical support on which the flat mirrors are fixed; - the optical reflector device includes at least one concave conical surface whose axis coincides with the longitudinal axis and forms an angle at the apex of 45 degrees with the longitudinal axis; - the optical reflector device has an axial opening in the longitudinal axis, the axial opening being adapted for the passage of a portion of the laser beam; - the optical reflector device includes another mirror arranged facing the axial aperture, the other mirror being flat and arranged perpendicular to the longitudinal axis; - the interferometric quantum sensor includes means for generating a magnetic field gradient.

[0021] This disclosure enables the fabrication of a compact quantum accelerometer compatible with onboard acceleration or gravity measurements. This disclosure also enables multi-axis acceleration measurements with a single device.

[0022] Finally, the present disclosure makes it possible to combine several interferometric quantum sensors to perform 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 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, 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-hole of the optical reflector device of the first interferometric quantum sensor and the first through-hole 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 of the second interferometric quantum sensor being arranged to receive a portion of the laser beam propagating along the longitudinal direction through the axial aperture of the optical reflector of the first interferometric quantum sensor, and wherein the first through-aperture of the first interferometric quantum sensor and the first through-aperture of the second interferometric quantum sensor are aligned along parallel axes and separated by a non-zero distance D2.

[0025] Of course, the various features, variants, and embodiments of the invention can be combined with one another in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0026] In addition, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate one, non-limiting, 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 reflecting optical device according to a first method of implementation;

[0029] [Fig.3] is a front (left) and side (right) view of an optical device reflector 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 reflecting optical device in a sensor quantum interferometric according to another variant of the first embodiment;

[0031] [Fig. 5] is a front view of a reflecting 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 reflector 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 reflector 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 reflector in an interferometric quantum sensor according to yet another variant of the first embodiment;

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

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

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

[0038] The present disclosure proposes 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 zone 6 or Optical molasses cooling. The optical reflector device 10 is arranged in the interferometric quantum sensor to reflect 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 this disclosure, the optical reflector device 10 is provided with at least one first through-hole 8 adapted to allow at least one light beam 31 to pass 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] Figure 2 shows a reflecting optical device 10 according to a first embodiment. The reflecting optical device 10 comprises an opto-mechanical support 17, for example, generally polygonal or annular in shape, on which four mirrors 11, 12, 13, and 14 are fixed. The opto-mechanical support 17 is made of glass or metal. In the example illustrated in Figure 2, each mirror 11, 12, 13, 14 consists of a 45-degree prism, the 45-degree inclined face of which has 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 parallel flat faces. The four mirrors 11, 12, 13 and 14 are arranged to each form part of one of the four faces of a pyramid with a square or rectangular base.More precisely, each of the four mirrors 11, 12, 13, 14 forms a 45-degree angle 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 a 45-degree angle with the longitudinal axis 5. Mirrors 11 and 12 are arranged so that the normal to mirror 11 and the normal to mirror 12 lie in a first plane containing the longitudinal axis 5. Mirrors 13 and 14 are arranged so that the normal to mirror 13 and the normal to mirror 14 lie 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 three-dimensional magneto-optical trap or optical molasses from a single incident laser beam 20 propagating along the longitudinal axis 5.

[0040] Figure 3 shows the optical reflector device 10 arranged in the vacuum chamber 1 of the quantum interferometric sensor, such 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 beams. counterpropagative 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 back-reflected along the longitudinal axis 5 in the opposite direction to the incident laser beam 20. This gives three pairs of counter-propagating laser beams in three orthogonal directions of space. The optical reflector device 10 thus allows for the optical trapping of 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 allows for the trapping and cooling of a cloud of atoms from a single incident laser beam 20. Optionally, the interferometric quantum sensor includes means for generating a magnetic field, illustrated for example by a pair of anti-Helmholtz coils 3.

[0041] Optionally, the optical reflector device 10 includes an axial aperture 26 in the longitudinal axis 5 between the four mirrors 11, 12, 13, and 14. The axial aperture 26 is adapted to allow a portion 120 of the incident laser beam 20 to pass through. For example, the axial aperture 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] (right), the optical reflector device 10 further includes another mirror 15 arranged opposite this axial aperture 26. Advantageously, this other mirror 15 is fixed by a mount to the opto-mechanical support 17. The other mirror 15 is flat and arranged perpendicular to the longitudinal axis 5. Thus, this other mirror 15 allows a portion 120 of the incident laser beam to be reflected by simple reflection, along the longitudinal direction and at opposite direction to the incident laser beam 20.A quarter-wave plate 16 interposed between the optical device 10 and the mirror 15 allows the polarization of the beam reflected on the mirror 15 to be adjusted so that it contributes to the magneto-optical trapping or the optical molasses cooling of the atom cloud in the trapping and cooling zone 6.

[0042] Unlike a pyramidal reflecting optical device used in a prior art atomic interferometer, the faces of the mirrors 11, 12, 13, 14 do not extend over the entire surface of the pyramid faces. 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, are disjoint and separated from each other by approximately 10 mm. The reflecting optical device 10 has at least one first through-hole 8 that extends longitudinally along the first axis 18, forming a non-zero angle ALPHA with the longitudinal axis 5. The first through-hole 8 extends transversely on one side between the mirrors 11 and 14 and on the other side between the mirrors 12 and 13. The angle ALPHA is preferably equal to 90 degrees. By way of example, on the figures 2 and 3, the first axis 18 is perpendicular to the longitudinal axis 5, in other words, angle ALPHA is 90 degrees.

[0043] The first through-hole 8 is adapted for the passage of at least one first interferometric light beam 31 through the optical reflector device 10. Advantageously, the first interferometric light beam 31 propagates along the first axis 18 towards the atom cloud and comprises a sequence of at least three laser pulses. The first interferometric light beam 31 can be generated by the same laser source 4 as the incident laser beam 20 or by another laser source. The interferometric 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 interferometric light beam 31 along the first axis 18. The configuration of the quantum interferometric 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 stopped and the atom cloud falls freely. The optical reflector device 10 allows the pulse sequence of the interferometric light beam 31 to be directed at successive times, 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 allows the interferometry sequence to start very shortly after the cooling laser is switched off, while the atom cloud is still inside the optical reflector device 10.

[0045] For 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. We thus obtain an interferometric quantum sensor which has 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 interferometric 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-hole 9 extending longitudinally along a second axis 19 forming a non-zero angle BETA with the longitudinal axis 5. The second through-hole 9 extends transversely on one side between mirrors 11 and 13 and on the other side between mirrors 12 and 14. The angle BETA is preferably equal to 90 degrees. For example, in Figures 2, 6, and 7, the second axis 19 is perpendicular to the longitudinal axis 5; in other words, 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, in the optical reflector device 10 illustrated in [Fig. 4], the angle between the first axis 18 and the second axis 19 is not 90 degrees, for example, 120 degrees.

[0048] The second through-opening aperture 9 is adapted for the passage of at least one second interferometric light beam 32 through the optical reflector device 10. Advantageously, the second interferometric 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 apertures 8 and / or 9 are further adapted for the passage of other signals, for example, for fluorescence detection. Preferably, one or more pulses are applied to detect the state of the atoms on the two outputs of the quantum interferometric sensor. For this purpose, the detection system, which includes one or more detectors 27, 28, is positioned facing the second aperture 9, or, respectively, the first aperture 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 aperture 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 aperture 8.

[0050] In one application example, 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 the magneto-optical trapping has stopped, allowing time for the atoms to cool in an optical molasses and for a quantum state preparation sequence to be applied. The configuration of the optical reflector device 10 makes it possible to reduce the total duration of the interferometry sequence and thus 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 atomic interferometer, in which the interferometry sequence starts only 40 ms after exiting the pyramidal trap but can last 100 to 200 ms.Furthermore, the quantum sensor described in this disclosure allows for the acquisition of multiple measurements over the same total duration, rather than a single measurement, which can then be averaged. However, the accuracy of the interferometric measurement decreases as the time between pulses increases. As the interferometry pulse sequence decreases, a shorter sequence allows for averaging measurements to improve accuracy.

[0051] In a gravimetry application, an interferometric quantum sensor comprising the optical reflector device of this disclosure is mounted on 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 with a total height of approximately 70 cm and measuring statically on land. However, this measurement accuracy of local gravity is already very high and sufficient for many applications of onboard inertial sensors, where measurement performance is intrinsically limited by the movements of the carrier, and where increasing the measurement rate is preferable to increasing 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 made from plates or prisms. Mirror 11 is arranged so that its normal lies in a first plane 41 containing the longitudinal axis 5. Mirror 12 is arranged so that its normal lies in a plane 42 containing the longitudinal axis 5. Mirror 13 is arranged so that its normal lies in a plane 43 containing the longitudinal axis 5. The planes 41, 42, and 43 are oriented at 120 degrees to each other. Advantageously, the three plane mirrors 11, 12, and 13 are fixed to an opto-mechanical support 17.The optical reflector device 10 is arranged in the vacuum chamber 1 of the quantum interferometric 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 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-hole 8 that extends longitudinally along the first axis 18.The first through-opening 8 extends transversely on one side between mirror 11 and on the other side between mirrors 12 and 13. As an example, in [Fig.4], the first axis 18 is perpendicular to the longitudinal axis 5. This interferometric quantum sensor allows the measurement of 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 whose axis coincides with the longitudinal axis 5 and which forms a vertex angle 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 portion of the cone 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 aperture 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 reflective 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 also arranged horizontally (parallel to the X-axis). The incident laser beam 20 is applied to trap atoms in the trapping and cooling zone 6. Then, the trapping is interrupted and the cloud of atoms falls freely. The optical reflector device 10 allows the interferometric light beam 32 to pass through to perform the pulse sequence 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 perform 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 has an axial aperture 26. The axial aperture 26 is adapted for the passage of a third interferometric light beam 33 through the optical reflector device 10. Advantageously, the third interferometric 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 interferometric light beam 33 has a diameter smaller than the diameter of the incident laser beam. Preferably, the third interferometric light beam 33 has a diameter smaller than the diameter of the axial aperture 26 so as to avoid any parasitic reflection on the mirrors 11, 12, 13, 14. In an example of application to a multiaxis 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 area. 6. Trapping and cooling. Then, the magneto-optical trapping is interrupted and the atom cloud falls freely. The optical reflector device 10 directs the pulse sequence of the third interferometric light beam 33 at successive times and measures the acceleration along the horizontal longitudinal axis 5. By alternating measurement sequences along the three axes, an interferometric quantum sensor is thus obtained, capable of measuring 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] Figure 8 illustrates an example of using a quantum sensor according to the first embodiment, in which the first interferometric beam is directed along axis 18, for example vertically. The fluorescence collection optical systems are advantageously arranged in apertures 37 and 38. In this way, the signal is collected as close as possible to the atoms, thus maximizing the number of photons collected. Alternatively, apertures 37 and 38 are used to pass a beam of atoms from a two-dimensional magneto-optical trap (2D-M0T), thereby accelerating the loading of the 3D magneto-optical trap and increasing 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 includes a reflective optical device according to any one of the embodiments described above. Advantageously, a mirror 15, respectively 115, is arranged opposite the central aperture 26, respectively 126 of the interferometric quantum sensor 100, respectively 110. The mirror 15, respectively 115, is flat 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. so as to receive another incident laser beam 201 along its longitudinal axis 51 and to cool and trap atoms in three dimensions in another trapping and cooling zone 61. The longitudinal axis 5 of the first interferometric quantum sensor 100 is parallel to 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. Furthermore, the two interferometric quantum sensors 10, 110 are arranged so that the first through-hole of the optical reflector of the first interferometric quantum sensor 100 and the first through-hole of the optical reflector 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 trap atoms simultaneously 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 from the interferometric light beam 31 is applied along the first axis 18. The acceleration along the axis 18 is detected and measured via the first interferometric quantum sensor 100 and, simultaneously, via the second interferometric quantum sensor 110. The difference between these two acceleration measurements yields a differential measurement or a spatial gradient of acceleration between two positions separated by a distance DL. The average of these two acceleration measurements yields 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] Figure 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 has a reflecting optical device as described above. More specifically, the first interferometric quantum sensor 100 has a central aperture 26 and the second interferometric quantum sensor 130 also has a central aperture 126. The two interferometric quantum sensors 100, 130 are arranged in the same vacuum chamber 1 (not shown in Figure 11) such 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 apertures 26 and 126 are aligned along the longitudinal axis 5. A mirror 15 is positioned opposite the two central apertures 26 and 126. In this way, the same mirror 15 is common to the first interferometric quantum sensor 100 and 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 that has passed through the first optical reflector 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 of the first interferometric quantum sensor 100 is larger than the optical reflector of the second interferometric quantum sensor 130. The two trapping and cooling zones 6 and 61 are separated by a distance D2.Furthermore, the two interferometric quantum sensors 100, 130 are arranged so that the first through-hole of the first interferometric quantum sensor 100 and the first through-hole 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 freely. An interferometric light beam is simultaneously applied 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. The acceleration along axis 18 is detected and measured via the first interferometric quantum sensor 100, and simultaneously the acceleration along 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 a distance D2.

[0068] According to a variant of the system in [Fig. 11], the two interferometric quantum sensors 100, 130 each have a second through-hole, arranged perpendicular to the first through-holes. Advantageously, the second through-hole of the first interferometric quantum sensor 100 and the second through-hole of the second sensor quantum interferometric 130 are aligned along parallel axes, for example to the Y axis, and also separated by the distance D2. This configuration allows to perform another differential measurement or another spatial gradient of acceleration between two positions separated by the distance D2 along another axis, perpendicular to the axes 18, 118.

[0069] Alternatively or complementaryly, after the simultaneous trapping and cooling of the atoms in the two trapping and cooling zones 6 and 61, the trapping is simultaneously stopped and the two atom clouds fall freely. Then, an interferometric light beam is applied along the longitudinal axis 5 common to the first interferometric quantum sensor 100 and 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 a distance D2.

[0070] This gives us 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 achieve 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 measurement axes can be modified according to the applications.

[0074] Differential measurements find applications, for example, in inertial measurement unit (IMU) calibration. Indeed, the components of the acceleration gradient provide additional information compared to a simple measurement along a single axis. Thanks to common-mode rejection effects, the sensitivity of the interferometric system is greatly improved, resulting in excellent performance for differential measurements.

Claims

Demands

1. Interferometric quantum sensor (100) comprising a vacuum chamber (1) suitable for receiving a vapor of alkali or alkaline-earth atoms, a laser source (4) configured to generate a laser beam (20) propagating along 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 internal volume delimited by the reflecting optical device (10) and to form a plurality of beams reflected in a plurality of directions,in order to trap atoms of the atomic vapor (1) in a three-dimensional trapping and cooling zone (6) located in the internal volume of the optical reflector device (10), and in that the optical reflector device (10) has a first through-port opening (8) adapted to pass a first interferometric light beam (31) through the optical reflector device (10) and into the trapping and cooling zone (6) along a first axis (18) forming an angle perpendicular to the longitudinal axis (5).

2. Interferometric quantum sensor according to claim 1 in which the optical reflector device (10) has a second through-port aperture (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 an angle perpendicular to the longitudinal axis (5), the second axis (19) forming a non-zero angle with the first axis (18).

3. Interferometric quantum sensor according to claim 1 or 2 in which the optical reflector 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. Interferometric quantum sensor according to claim 1 or 2 wherein the optical reflector device (10) 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 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 are fixed.

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) whose axis coincides with the longitudinal axis (5) and forms a vertex angle of 45 degrees with the longitudinal axis (5).

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

8. Interferometric quantum sensor according to claim 7 in which the optical reflector device (10) comprises another mirror (15) arranged facing the axial aperture (26), the other mirror (15) being planar and arranged perpendicular to the longitudinal axis (5).

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

10. Differential atomic interferometry system comprising a first interferometric quantum sensor (100) according to any one of claims 1 to 9 and a second interferometric quantum sensor (110) according to any 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-hole of the optical reflector device of the first interferometric quantum sensor (100) and the first through-hole of the optical reflector device of the second interferometric quantum sensor (110) are aligned along the same first axis (18).

11. 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 quantum sensor interferometric (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 along the longitudinal direction (5) through the axial aperture (26) of the optical reflector device (10) of the first interferometric quantum sensor (100) and in which the first through aperture of the first interferometric quantum sensor (100) and the first through aperture 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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