Improved noise cold atom sensor

Abstract

The invention relates to an ultracold atom sensor (10) comprising: an atom chip (ACh) including a first and a second waveguide (CPWX1, CPWX2) adapted for the propagation of microwave waves and direct currents, at least a first conducting wire (WIz) and a second conducting wire (WId, WId1) whose respective projections intersect at a point defining a first crossing point (C1), an atom generation device (ACG), a power supply device (PSD) including at least one microwave generator (GMW) and at least one direct current generator (DCG), said power supply device being configured to apply to said first and second waveguides, for the spatial separation of the two traps, said microwave signals to initiate said spatial separation, then said CMW electric currents in place of said microwave signals to maintain said spatial separation, Figure 7

Description

Title of the invention: Improved noise cold atom sensor FIELD OF INVENTION

[0001] The present invention relates to the field of inertial sensors and more specifically to cold atom inertial sensors integrated on an atomic chip. More particularly, the invention concerns cold atom sensors on an atomic chip using microwave fields for the spatial separation of the two states used when measuring inertial parameters (typically acceleration and rotational speed). STATE OF THE ART

[0002] A cold atom interferometer causes two electronic states, called the first internal state la> and the second internal state lb>, of an atom, such as rubidium-87, to interfere in a Ramsey-type sequence. A Ramsey-type interferometer sequence measures a phase q> accumulated during the execution of the sequence, from a measurement of at least one population of a chosen state la> or lb> (preferably a measurement of both populations for greater accuracy). The populations pa and pb of the two states la> and lb> respectively at the output of the interferometer are given by:

[0003] pa=l[l-cos( <p)] (D

[0004] pfe = l[l + cOS( <p)] (2)

[0005] The phase q> is related to the energy difference between E'b and E'a, equal respectively to the energies of the states a> and lb> modified by the implementation of the interferometric sequence.

[0006] and

[0007] 9=^Tr. (3)

[0008] with w the pulsation of the local oscillator producing the two pulses æ / 2 at the beginning and end of the interferometric sequence and TR the Ramsey time, i.e. the time elapsed between the two pulses tt / 2.

[0009] That is: [0°101 / < = 1[ l-cos(S^ TR-„>TR) ] w [00111 +

[0012] It is assumed that before the start of the Ramsey sequence all atoms are in the state la> as well as Eb > Ea with Ea and Eb the atomic energies of the states as a function of the atom and the transition considered.

[0013] To make this interferometer sensitive to accelerations and rotations, it is necessary to:

[0014] In the case of accelerations, separating the two states and then recombining them involves moving them along a straight line from their identical initial positions in opposite directions, then making them follow the same trajectory in the opposite direction until they return to the same position. This allows us to add a term related to the acceleration potential energy to the energy difference between the two states.

[0015] In the case of rotations, both states must follow a closed trajectory including a non-zero area, and this in opposite directions for the α and β. Thus, a term dependent on the Sagnac effect, and therefore on the rotational speed, is added to the energy difference between the two states.

[0016] A known method for achieving these trajectories is to use microwave splitters (waveguides into which microwave signals are applied). The resulting microwave fields then "dress" the states, which creates a force that allows them to be moved. This dressing modifies the energies of the states α and β, from Ea to E'a and from Eb to E'b.

[0017] The structure and operating principle of a gyroscope-type sensor are described in US patents 15 / 778605, 17 / 924340, 17 / 832615, and 17 / 832616, and are summarized below. For example, patent WO2017089489 describes an ultracold atom-on-chip gyroscope-type inertial sensor using trapped matter waves describing closed trajectories including an area.

[0018] Rotation measurements on this type of device are performed by exploiting the Sagnac effect. The phase shift induced by the Sagnac effect between two counter-rotating matter waves in a frame of reference rotating at angular velocity Q is given by:

[0019]

[0020] where A is the area inscribed in the atomic trajectories, m is the mass of the atoms and h is the Planck constant reduced.

[0021] Ultracold atoms are defined as atoms whose temperature is below 400 nanokelvins, preferably below 300 nanokelvins. The temperature of thermal ultracold atoms is, for example for Rubidium atoms, between 50 and 400 nanokelvins and preferably between 100 and 300 nanokelvins.

[0022] The principle is to create a trajectory traveled in a counter-propagative manner by two magnetically trapped atom clouds. The creation and movement of the magnetic trap along the trajectory are achieved by conducting wires and microwave guides according, for example, to the topology illustrated [Fig. 1].

[0023] Figure 1 schematically illustrates an ultracold atom chip 12 and the trajectory 16 of two atomic clouds CL1 and CL2. Part of the surface of the chip 1 forms a measurement plane 13. An axis normal to the measurement plane 13 defines the axis measurement Z, according to which a rotation measurement Qz is performed by the gyroscope.

[0024] The chip 1 includes means adapted to generate a first ultracold atom trap T1 and a second ultracold atom trap T2, a trap enabling the immobilization of an ultracold atom cloud 12 in an internal state different from that of the other trap, at a predetermined distance h from said measurement plane 13. For example, the trap T1 comprises atoms in the electronic level or state la> (cloud CL1) and the trap T2 comprises atoms in the state lb> (cloud CL2). The la> and lb> levels are separated by a frequency co0 / 2jr. For example, in the case of rubidium 87, these are the two hyperfine levels IF=1,mF=-1> and IF=2,mF=1>, separated by approximately 6.8 GHz.

[0025] These means also allow the clouds to be moved along the trajectory 16 located in a plane parallel to the measurement plane 13, at a height h above this plane, as illustrated [Fig. 1]. These means consist of waveguides and conducting wires as described below.

[0026] The means comprise a first waveguide CPW1 and a second waveguide CPW2 adapted for the propagation of microwaves at cob and coa frequencies. The waveguides are arranged symmetrically with respect to a Y-axis of the measurement plane, preferably parallel. The two waveguides CPW1 and CPW2 are connected to at least one voltage or current generator at microwave frequencies. For example, each of the waveguides is fabricated by depositing three parallel conducting wires to create a coplanar waveguide. In other embodiments, other types of waveguides can be used, in particular waveguides whose fabrication is compatible with microfabrication techniques by deposition or etching. For example, a microstrip line can be fabricated.

[0027] The means also include conductive wires integrated into the chip 1 and adapted to carry direct currents. The conductive wires are divided into one conductive wire WIz along an axis of symmetry Y perpendicular to X and contained in the measurement plane 13, and a plurality of n conductive wires Wldi, i being an index ranging from 1 to n, parallel to each other and parallel to the X axis, n being at least equal to 2. In the example of [Fig. 1], n=3, i.e., three conductive wires Wldl, WId2, and WId3. The wires are arranged so as to define n crossing points Ci (intersection between WIz and Wldi) located on the Y axis, here 3 crossing points C1, C2, C3.

[0028] Each conductor wire is connected to one or more current and / or voltage generators, which are themselves connected to a processing unit comprising at least one microprocessor. The voltage and / or current generators allow both direct and alternating currents to be driven in the wires. In particular, direct currents are driven in the conductor wires.

[0029] In the sensor, the atom chip 1 is placed in a vacuum chamber maintained, for example, using an ion pump and preferably comprising a shield magnetic. The sensor includes an ultracold atom generation device which comprises:

[0030] -an atom emitter (dispenser in English), for example made by a heating filament delivering a rubidium vapor;

[0031] -a primary atom trap (optical and / or magnetic), allowing pre-cooling and placement of an ultracold atom cloud in the vicinity of the chip, to charge the magnetic traps T1 and T2 described later with atoms.

[0032] The sensor also includes a magnetic field source, external to the chip 1. It makes it possible to impose a homogeneous and stationary magnetic field Bc over a thickness at least on the order of a height h above the measurement plane 13. Advantageously, the direction of the homogeneous magnetic field is parallel to the measurement plane.

[0033] In [Fig. 1], the dashed trajectory 16 illustrates the trajectory of the ultracold atom clouds 12. This closed trajectory defines an area denoted A. A distance h separates the plane of the trajectory 16 and the measurement plane 13 of the chip. Preferably, h is between 500 nm and 1 mm, and preferably between 5 pm and 500 pm.

[0034] Fig. 2 illustrates the geometry of the guides and wires of the atomic chip as well as the traps T1 and T2.

[0035] The specific arrangement of the conducting wires and waveguides, combined with the homogeneous magnetic field source, makes it easy to obtain two traps T1 and T2 as illustrated in part a) of [Fig. 2]. Each trap T1 and T2 has a non-zero and identical minimum value V0, and an identical curvature, a necessary condition for the sensor to function. Indeed, as explained later, when a direct current is applied to at least two conducting wires at a crossing point, the potential minimum is located vertically above this crossing point. When microwave power is then applied to the waveguides, the central minimum transforms into two minima on either side of the initial minimum in the direction of the waveguides.If the initial minimum is not located at a strictly equidistant distance from the two waveguides, the two potential minima created will not have exactly the same minimum value V0 and the same curvature.

[0036] Part c) of [Fig. 2] illustrates the arrangement of the conducting wires defining the initial crossing point Cl and the waveguides (top view). Part b) of [Fig. 2] describes the corresponding arrangement of the conducting wires and waveguides printed on a chip in profile view, in cross-section along the conducting wire Wldl which crosses the conducting wire WIz along the axis of symmetry Y. The waveguides CPW1 and CPW2 are coplanar waveguides located on a first level NI. The insulating layer 18 advantageously flattens the measurement plane. The material of the The electrical insulating layer can be, for example, silicon dioxide, silicon nitride, or benzocyclobutene. A conductive material, such as gold, is used to manufacture the conductive wires and is deposited onto a substrate, forming a second layer, N2. The substrate can be, for example, silicon, aluminum nitride, or silicon carbide.

[0037] We see on part a) the symmetrical separation of ultracold atoms, specific to the internal state of said ultracold atoms, and more precisely the variations of potentials as a function of the X axis of chip 1.

[0038] Curve "a" exhibits a potential well corresponding to the combination of the homogeneous magnetic field and the field created by two intersecting conducting wires, wire WIz carrying current Iz and wire Wldl carrying current Idl. This results in a local potential well forming a three-dimensional atomic trap T. A cloud of ultracold atoms can be trapped and cooled within it.

[0039] Curve "b" schematically represents the potential created by the transmission of microwaves at frequency cob in the CPW1 waveguide. The field emitted by the passage of microwaves at frequency cob modifies the energy of the ultracold atoms and displaces the atoms from internal states lb>. Curve "e" illustrates the potential seen by the internal states lb> due to the contributions of the potentials illustrated by curves "a" and "b". Curve "e" exhibits a local potential minimum that allows for the local trapping of a cloud of ultracold atoms from internal states lb>.

[0040] Similarly, curve "d" schematically represents the potential created by the transmission of microwaves at the coa frequency in the CPW2 waveguide. The field emitted by the passage of microwaves at the coa frequency allows the energy of the ultracold atoms to be modified and the atoms to be displaced from internal states la>. Curve "c" illustrates the potential seen by the atoms in internal states la> due to the contributions of the potentials illustrated by curve "a" and by curve "d". Curve "c" exhibits a local energy minimum that allows a cloud of ultracold atoms in internal states la> to be trapped locally.

[0041] The combination of a DC magnetic trap (created by the direct currents in the wires and the homogeneous field Bc) and a microwave field creates what is called a "dressed" trap. A "dressed" trap is understood to be one created at least in part by an oscillating microwave, radio-frequency, or optical field. Changes in the microwave fields (power, frequency, and the waveguide in which they propagate) allow this dressed trap to be moved and thus the atoms to be moved. The DC magnetic trap is represented in [Fig. 2] by curve a. The microwave field at coa is represented in [Fig. 2] by curve d, and the microwave field at cob is represented in [Fig. 2] by curve b. The dressed trap Tl (combination of curves a and d for the state la>) is re presented by curve c and the dressed trap T2 (association of curves a and b) for the state lb> is represented by curve e.

[0042] Clouds of ultracold atoms in internal states α and β can be separated and trapped symmetrically with respect to the symmetry axis Y by simultaneously imposing the propagation of waves of frequency coa in CPW2 and cob in CPW1. To obtain two traps whose minima have the same value V0 and whose curvatures have the same value, it is important that the crossing point Cl be located equidistant from CPW1 and CPW2 on the symmetry axis Y.

[0043] Fig. 3 illustrates the principle of generating trajectory 16. Part a) of Fig. 3 schematically presents a sequence of the displacement of each of the ultracold atom clouds at characteristic times ti to t9. Part b) further illustrates a sequence of the different currents applied to the conducting wires, the powers applied to the waveguides and the frequencies imposed on the waveguides, for the times corresponding to those of part a).

[0044] In the sequence shown in [Fig. 3], the current Iz, not shown, flowing in WIz is stationary, at a constant value. In part b), the values ​​of the currents, powers, and frequencies are arbitrary. The frequency ordinate corresponds to a frequency variation, expressed in arbitrary units, around an average frequency value. The currents flowing through the conducting wires can be between 100 pA and 10 A, and the pulses injected into the waveguides can be between 6.6 GHz and 7 GHz in the case of using rubidium atoms.

[0045] In a step A0, there is a phase for preparing the atoms. A cloud of ultracold atoms 12 is generated, including phases of emission of said atoms, cooling of said atoms, initialization of said atoms in at least one internal state 1a, and trapping of a cloud of said ultracold atoms in a local potential minimum, at a distance h from the measurement plane (trap T, curve "a" of [Fig. 2] part a)). The height h is different from 0 because the homogeneous magnetic field Bc is non-zero. The trapping is carried out by passing direct currents through the wire WIz and through one of the wires Wldi, the crossing point of these two wires defining the starting point (here Cl with Wldl). A magnetic field at an angle Bc parallel to the plane of the atom chip is applied simultaneously, superimposed on the magnetic field created by the two preceding wires. The cloud of atoms is then trapped vertically from Cl, the intersection of the WIz and Wldl wires.

[0046] In a step B0, the internal states are initialized by coherently superimposing the ultracold atoms between the states la> and lb> by a first pulse TT / 2. This pulse can be produced by a laser, microwave emission, or more generally by a method emitting waves at a suitable transition frequency. The currents Iz and Li are imposed respectively on the wires conductors WIz and Wldl. The two internal states la> and lb> are coherently and spatially superimposed at the crossing point Cl.

[0047] The wave function is then:

[0048]

[0049] In a step C0, a cloud of atoms in internal state α₁> in a trap T1 is spatially separated from a cloud of atoms in internal state β₁> in another trap T2, and the traps are moved in opposite directions along a closed trajectory 16 contained in a plane perpendicular to the measurement axis Z. The cloud of atoms in internal state α₁> is symbolized by a disk with a light texture, and the cloud of atoms in internal state β₁> is symbolized by a disk with a darker texture. This step is carried out from t1 to t9.

[0050] Between t1 and t2, the microwave power injected into the waveguides CPW1 and CPW2 gradually increases from 0 to its maximum value. A cob frequency is sent into the waveguide CPW1 and a coa frequency is sent into the waveguide CPW2, which allows the two clouds of different internal states to be separated on either side of the axis of symmetry Y, by a distance d, up to the positions shown schematically in t2. The ultracold atom trap T described earlier at time ti is then transformed into two ultracold atom traps Tl and T2, each trap allowing the immobilization of a cloud of ultracold atoms with different internal states than the other trap (in this case internal states la> in one of the traps, for example Tl, and internal states lb> in the other trap T2, as described in part a) of [Fig.2].

[0051] A crossing point Ci corresponds to the crossing of wire WIz with wire Wldi.

[0052] Between t2 and t3, the current Idi is progressively switched off and Id2 is progressively increased at its maximum value (the time interval separating t2 and t3 is typically on the order of 10 ms and can be between 0.1 ms and 100 ms): the two traps T1 and T2 are moved to the right to the positions shown in t3.

[0053] Between t3 and t4 the current Id2 is progressively cut off and Id3 is progressively brought to its maximum value: the two traps are moved to the right to the positions shown schematically in t4.

[0054] Between t4 and t5, the microwave power is progressively cut off: the two traps are brought back to the same place on the chip, shown schematically in t5.

[0055] At t5, the pulsations of the two microwave guides are modified: the pulsation coa is imposed in CPW1 and the pulsation cob is imposed in CPW2.

[0056] Between t5 and t6, the power in the two waveguides gradually goes from 0 to its maximum value: the traps are separated in the vertical direction as shown schematically in figure t6.

[0057] Between t6 and t7, the current Id3 is progressively switched off and Id2 is progressively increased at its maximum value: the two traps T1 and T2 are moved to the left to the positions shown schematically in t7.

[0058] Between t7 and t8, the current Id2 is progressively cut off and Idi is progressively brought to its maximum value: the two traps are moved to the left to the positions shown schematically in t8. This operation can be repeated several times with other first conducting wires to increase the area included in the trajectory 16.

[0059] Between t8 and t9, the microwave power in the waveguides is progressively cut off. The two traps T1 and T2 move until they merge into a single trap located at the starting point shown schematically in tb.

[0060] Direct currents are thus applied to the two wires corresponding to the initial crossing point Cl, and over time these currents are successively applied to the different crossing points Ci located on the axis of symmetry, while simultaneously applying microwave power to the waveguides.

[0061] During step C0, the direct currents applied to the different wires Wldi vary continuously (increasing and decreasing) between 0 and a maximum value Idimax (normalized to 1 in [Fig. 3]), while the magnetic field Bc and the current Iz remain constant during the sequence. Throughout the sequence A0, B0, and C0, the two traps Tl and T2 remain at altitude h.

[0062] The two traps T1 and T2 move in the direction of the "ignition" of the crossing points: from crossing point Cl to crossing point Cn. The return is accomplished by reversing the microwave frequencies and successively igniting the direct currents in the wires corresponding to the different crossing points, traversing them from Cn to CL.

[0063] The traps are thus made to follow the closed trajectory 16.

[0064] The closed trajectory 16 of the atoms then contains an area A, the wave function atomic is therefore:

[0065] + exp(^>

[0066] With:

[0067] (p - +

[0068] In a step D0, the internal states la> and lb> are recombined by applying a second impulse tt / 2 to the ultracold atoms, which transfers the phase difference to the populations of the two atomic levels:

[0069] - 1 1 _ cos((p - (

[0070] = 2 [ 1 + cos(^ - Wt

[0071] where w is the angular frequency of the pulse 7T / 2.

[0072] The 7i / 2 pulses can be sent to the atoms via the microwave guides or via a separate microwave transmitter.

[0073] The sequence from the first to the second pulse æ / 2 inclusive is the Ramsey sequence (see above).

[0074] Then, in a step E0, the density of atoms in at least one internal state chosen from at least ai and bi is measured. This measurement can be performed, for example, by laser absorption by probing the resonance between the frequency specific to an internal state and that of the laser. Then, the Sagnac phase of the ultracold atoms is determined, and the rotational speed of the sensor about the Z-axis is calculated.

[0075] The measurement of at least one population of atoms in one of the states la> or lb> makes it possible to determine the Sagnac phase, for example for the internal state la> by considering equation (1), then the rotation speed Qz with equation (6).

[0076] The traps can travel this trajectory N times before measuring the Sagnac phase and thus measure a phase that will potentially be N times higher.

[0077] In order to implement the method described above, the ultracold atom sensor enabling a measurement of rotational speed Qz comprises:

[0078] -an atomic chip 1 as described above, with waveguides and conducting wires,

[0079] -an atom generation device for generating the ultracold atom cloud near the measurement plane 13 of the atom chip,

[0080] -a generator of the homogeneous magnetic field Bc

[0081] - at least one DC voltage or current generator suitable for controlling electric currents in the conducting wires and at least one microwave voltage or current generator connected to the waveguides,

[0082] -a detection system, typically of optical intensity, adapted to measure at least one population of ultracold atoms in an internal state, this measurement allowing the determination of the Sagnac phase and the rotation speed Qz.

[0083] The gyroscope-type sensor also includes at least one processor that controls the operation and implementation of the sensor, such as driving the signals applied to the wires and microwave guides according to a predetermined sequence (for example, the sequence in [Fig.3] b).

[0084] An accelerometer-type sensor has a "simplified" operation compared to the gyroscope, because the two clouds follow a straight path back and forth, as illustrated in [Fig. 4], which uses the same logic and formalism as [Fig. 3]. Here, only one wire Wld is needed, defining the crossing point C.

[0085] Part a) of [Fig. 4] schematically presents a sequence of the displacement of each of the ultracold atom clouds at characteristic times t1 to t3. Part b) illustrates the sequence of the different currents applied to the conducting wires, the powers applied to the waveguides, and the frequencies imposed on the waveguides. wave, for the times corresponding to those in part a). In the sequence shown in [Fig. 4], the current Iz, not shown, flowing through WIz is stationary, at a constant value. The current applied to Wld is also constant throughout the sequence.

[0086] Initially at ti no power is applied to the waveguides and the cloud is trapped above point C.

[0087] Between t1 and t'1, the microwave power injected into the waveguides CPW1 and CPW2 gradually increases from 0 to its maximum value, then the value remains maximum and constant between t'1 and t'2 via t2. A coa pulsation is sent into the waveguide CPW2 and a cob pulsation is sent into the waveguide CPW1, which allows the two clouds of different internal states to be separated on either side of the axis of symmetry Y up to the positions shown schematically in t2, these positions being maintained for the entire duration t'2-t'1, which can be short.

[0088] Between t'2 and t3, the microwave power in the waveguides is progressively cut off. The two traps T1 and T2 move until they merge into a single trap located at the starting point shown schematically in tb

[0089] For both types of sensor, and generally for any inertial sensor, considering formulas 3, 4 and 5, we see that the phase is sensitive to the energy difference between the two "dressed" levels E'b-E'a, which is expressed as a function of the energy difference between the two atomic levels Ea-Eb:

[0090] For the state la> the energy is modified from Ea to E'a with:

[0091]

[0092] For the state lb> the energy is modified from Eb to E'b with:

[0093] F< _ F (8) b ~

[0094] Where Q, (respectively) is the Rabi frequency associated with the dressing of the state la> (respectively lb>). To simplify the notation, all coupling factors are stored in the Rabi frequency, a function of the square root of the microwave power applied to the waveguides (amplitude of the microwave field).

[0095] Aa (respectively &b) is the mismatch between the frequency (respectively ÙY) of the microwave field dressing the la> state (respectively the lb> state) and the frequency of the wOa transition (respectively w«) considered for dressing the la> state (respectively lb> state). The frequencies ^0« and ww> are the frequencies of the atomic transitions used for the implementation of the interferometer.

[0096] We have:

[0097] ma-aîOa(9)

[0098] Aè= ^-o?o&(10)

[0099] The hyperfine frequency of the transition used is denoted by ^hfs.

[0100] An example of a transition used is the θ transition of Rubidium-87 between two hyperfine levels F=1 and F=2, as illustrated [Fig. 5], each level having Zeeman sublevels separated by the same magnitude aB, with a = 700 kHz / G for Rubidium-87, B being the direct magnetic field, or DC, to which the atoms are subjected. We have:

[0101] œOa = whfs-aB(U)

[0102] uOb = œhfs + aB (12)

[0103] The energy difference between the a and b to which the Ramsey interferometer is sensitive is then expressed as: 101041 E'„- É„ =Eb- E„ + ^ + l^= E„- E„- AE (13)

[0105] With 101061 +

[0107] The term AE intervenes in the oscillations of the populations given previously (formulas 5 and 6), therefore on the phase, and is the origin of the interferometer noise.

[0108] In practice, to ensure the operation of the interferometer (to guarantee symmetry) it is necessary to choose and A« = - (see for example the publication “Symmetric microwave potentials for interferometry with thermal atoms on a chip” (Ammar et al., Phys. Rev. A 91, 053623; 2015). This choice has the advantage of canceling the previous term and thus removing its effect. However, in practice, the cancellation of this AE term is not perfect, and this is where the difficulty lies. This is all the more problematic given that, experimentally:

[0109] the powers of the two microwave fields, which are proportional to C( q2 , have noise, and the equalization of the two Rabi frequencies is never perfect;

[0110] The two disagreement terms Aa and &h involve the value of the DC magnetic field trapping the atoms, which also contains noise (see formulas 9 to 12): [YES] = (¾ -whfs -«B (15)

[0112] A^ = - M / ifg-l- ü B (16)

[0113] It can be seen from the formulas above that the noise of the interferometer comes on the one hand from the DC magnetic field B, comprising the homogeneous magnetic field Bc applied to the atoms and the continuous magnetic field from the conducting wires (term A) and on the other hand from the microwave field (term Q).

[0114] Current solutions for reducing noise in the DC magnetic field involve using the most stable current sources possible. Current solutions for reducing noise in the microwave field amplitude involve implementing feedback loops on the microwave field amplitude to stabilize it as much as possible. possible.

[0115] These two solutions are not satisfactory because although they allow the noise level to be reduced, this noise still remains present in the error budget of the sensor.

[0116] One object of the present invention is to overcome the aforementioned drawbacks by providing an ultracold atom inertial sensor with a reduced noise level. DESCRIPTION OF THE INVENTION

[0117] The present invention relates to an ultracold atom sensor comprising: • an atomic chip placed in a vacuum chamber, comprising an XY plane, referred to as the measurement plane, normal to a Z-axis, and including: • a first and a second waveguide adapted to the propagation of microwave waves and direct currents, • at least one first conducting wire and a second conducting wire whose respective projections intersect at a point defining a first crossing point, • an atom generation device configured to generate a cloud of ultracold atoms near said XY plane of said atomic chip, • a generator of a homogeneous magnetic field, • a power supply unit comprising at least one microwave generator and at least one DC generator, the power supply unit being configured to: • apply microwave signals and direct currents (CMW currents) to the aforementioned first and second waveguides, • apply direct currents, known as CWI currents, to said conducting wires, said waveguides, said conducting wires and said power supply device being configured, during the implementation of the sensor, to spatially separate a first cloud of ultracold atoms in a first internal state from a second cloud of ultracold atoms in a second internal state, respectively forming a first and second traps of ultracold atoms by modifying an energy of said ultracold atoms, and to move said traps along a linear or closed trajectory contained in a plane perpendicular to Z,

[0118] said power supply device being configured to apply to said first and second waveguides, for the spatial separation of the two traps, said microwave signals to initiate said spatial separation, then said CMW electric currents in place of said microwave signals to maintain said spatial separation,

[0119] the sensor further comprising a detection system adapted to measure at least a population of so-called ultracold atonia in a so-called internal state.

[0120] According to one embodiment the sensor is of the accelerometer type, the trajectory followed by the two traps being linear.

[0121] According to another embodiment the sensor is of the gyroscope type comprising a plurality of second conducting wires defining a plurality of crossing points, said trajectory followed by the two traps being closed and traversed in the opposite direction by the first and second traps.

[0122] According to one embodiment, each waveguide comprises three wires, two outer ground wires and one inner signal wire, with the CMW current being injected into the signal wire.

[0123] According to one embodiment, the power supply device further comprises at least one polarization tee connected to at least one microwave generator and to at least one DC generator, and configured to apply said microwave signals and said CMW currents to said waveguides.

[0124] According to another aspect, the invention relates to a method for measuring an inertial parameter by an ultracold atom sensor comprising an atomic chip placed in a vacuum chamber, having an XY plane normal to a Z axis, said measurement plane, said atomic chip comprising: • a first and a second waveguide adapted to the propagation of microwave waves and direct currents, • at least one first conducting wire (Wl) and a second conducting wire whose respective projections intersect at a point defining a first crossing point, the process comprising the steps of:

[0125] A Generate a cloud of ultracold atoms near said XY plane of said atomic chip, including phases of emission of said atoms, cooling of said atoms, initialization of said atoms in at least one first internal state, and trapping of a cloud of said ultracold atoms in a local minimum potential, at a controlled height of said XY plane, said trapping being effected by passing direct currents through the first and second conducting wires,

[0126] B Initialize the first internal state and a second internal state of said ultracold atoms by coherently superimposing said ultracold atoms between said first and second internal states by a pulse ji / 2,

[0127] C Spatially separate a first cloud of ultracold atoms in the first internal state from a second cloud of ultracold atoms in the second internal state, by forming respectively a first and second traps of ultracold atoms by modifying the energies of said ultracold atoms, and moving said traps along a linear or closed trajectory contained in a plane perpendicular to Z and initialized at the first intersection,

[0128] said step of separation and displacement of the ultracold atoms being carried out by applying, according to a predetermined sequence, a homogeneous magnetic field to said ultracold atoms, direct currents, referred to as CWI currents, to said conducting wires, and microwave signals (IMW) and direct electric currents, referred to as CMW currents, to said waveguides,

[0129] the separation step comprising an initialization substep comprising the application of said microwave signals to said waveguides, and a maintenance substep comprising the application of said CMW currents in place of said microwave signals,

[0130] D Recombine said first and second internal states by applying to said ultracold atoms a second impulse ji / 2,

[0131] E Measure at least one population of said ultracold atoms in at least one said internal state.

[0132] According to one embodiment, the separation step includes a transient substep between the initialization substep and the maintenance substep, comprising an extinction of microwave signals and an ignition of CMW currents.

[0133] According to a first embodiment, during the transient stage, the microwave signals are switched off and the CMW currents are switched on simultaneously. According to another embodiment, the transient stage has a duration of less than 100 ps.

[0134] According to a second embodiment, during the transient stage, said extinction of microwave signals takes place before or after said ignition of CMW currents.

[0135] According to one embodiment, during the displacement step, a spatial recombination of the two clouds takes place by progressively extinguishing the CMW currents.

[0136] According to one embodiment, during the displacement step, a spatial recombination of the two clouds takes place by switching off the CMW currents and simultaneously switching on the microwave signals, then gradually switching off the microwave signals.

[0137] The following description presents several embodiments of the device of the invention: these examples are not limiting to the scope of the invention. These embodiments present both the essential features of the invention and additional features related to the embodiments considered.

[0138] The invention will be better understood and other features, objectives and advantages thereof will become apparent from the following detailed description and with reference to the accompanying drawings given by way of non-limiting examples and in which:

[0139] Figure 1, already cited, illustrates an example of the topology of an atomic chip comprising conducting wires and microwave guides enabling movement magnetic traps along a closed trajectory.

[0140] The [Fig.2] already cited illustrates the geometry of the guides and wires of the atomic chip as well as the traps T1 and T2.

[0141] The [Fig.3] already cited illustrates in its lower part an example of application of the different signals to the wires and guides according to the state of the art, in the case of a gyroscope type sensor, to make the two traps T1 and T2 (and therefore the two clouds of trapped atoms) travel the closed trajectory, and in its upper part the position of the two clouds corresponding to chosen times.

[0142] The [Fig.4] already cited illustrates in its lower part an example of application of the different signals to the wires and guides according to the state of the art to make the two traps T1 and T2 (and therefore the two clouds of trapped atoms) travel the linear trajectory in the case of an accelerometer type sensor, and in its upper part the position of the two clouds corresponding to chosen times.

[0143] The [Fig.5] already cited illustrates the o transition of Rubidium 87 between two hyperfine levels F=1 and F=2 used for a cold atom inertial sensor, as well as the different frequencies of interest.

[0144] Fig. 6 illustrates the DC magnetic potential VDc Mw created by the application of direct currents to the waveguides.

[0145] Figure 7 illustrates an ultracold atom sensor 10 according to the invention.

[0146] Figure 8 illustrates the schematic diagram of an embodiment of the sensor according to the invention in which the superposition of a microwave current and a direct current in the signal wire of the waveguide is achieved with a polarization tee.

[0147] Figure 9 illustrates an embodiment in which an additional polarization tee TPoladd has been integrated at the output of the waveguide and before the termination TMW.

[0148] Fig. 10 illustrates on its left side the timing diagrams of the application of the different signals during the implementation of an accelerometer-type sensor according to the first variant of spatial recombination, and on its right side the movement of the two clouds at chosen times.

[0149] Fig. 11 illustrates on its left side the timing diagrams of the application of the different signals during the implementation of an accelerometer-type sensor according to the second variant of spatial recombination, and on its right side the movement of the two clouds at chosen times.

[0150] Fig. 12 illustrates the timing diagrams of the application of the different signals for the implementation of a gyroscope-type sensor, according to the first variant of spatial recombination.

[0151] Fig. 13 illustrates the movements of the two clouds at chosen times associated with the signals of Fig. 12.

[0152] Figure 14 illustrates the timing diagrams for applying the different signals for the implementation of a gyroscope-type sensor according to the second spatial recombination variant.

[0153] Fig. 15 illustrates the movements of the two clouds at chosen times associated with the signals of Fig. 14. DETAILED DESCRIPTION OF THE INVENTION

[0154] The Ramsey time TR is decomposed into two times, a time TR°ff during which no microwave signal is applied to the waveguides, and a time TR°n during which microwave signals are applied to the waveguides:

[0155] Tr = T°n + TRff

[0156] The noise N accumulated on the interferometer phase is given by:

[0157] N = aDCTR + aMWTRn ​​(17)

[0158] with oMW the phase noise of the interferometer integrating the noise produced by the microwave signals (only during T°n) and oDC the noise due to the continuous magnetic field alone (present throughout the sequence).

[0159] The unit of oMW and oDC is the Hz.

[0160] From formula 14, considering that there is an error or noise ÔB on the magnetic field DC and errors or noise ôQa and 8£lh on ila, we can rewrite the difference of the two displacements AE in the form:

[0161] AE= f + + + +

[0162] The effect of noise or errors on a'« and œb has been neglected because experimentally their effects are negligible.

[0163] The term, with:

[0164] ¢7^ = ^5^ + ^3^^55(^

[0165] then constitutes noise on the interferometer phase, to which must be added the noise on the other terms contained in the interferometer phase, i.e., in the energy difference Eb-Ea. For simplicity, we neglect the collisional shift, the detection noise, the Dicke effect, etc., and keep only the term corresponding to the energy difference in the presence of the DC magnetic field. The noise on this term (microwave fields off) involves only the noise on the DC magnetic field 8B and is of the form (see, for example, the publication "Magnetically trapped atoms for compact atomic docks" by P. Rosenbusch, Apppl. Phys. B (2009), 95, pp. 227-235):

[0166] 25(5-5^)55(19)

[0167] To give an idea of ​​the orders of magnitude of the different noises, we have, using Rubidium 87 as an example:

[0168] b = 431 Hz! G2,

[0169] the DC magnetic field is close to Bm — 3.23 G.

[0170] = -&h = 200 kHz

[0171] Q. = 50 kHz and = 50 kHz

[0172] 5B = ImG

[0173] B-Bm = 100 mG [°174] ÔQJQa = (%lb / tth= W3

[0175] Which gives:

[0176] , + abBl ~4 + -4) ~ 100 Hz.

[0177] And

[0178] 2b(B-Bm)ÔB~ 100 mHz.

[0179] It is observed that the presence of the two microwave fields greatly increases the noise level. This is the predominant factor that must be reduced.

[0180] The idea of ​​the invention is to reduce the noise level by replacing microwave fields (after separation of the two states) with DC currents in order to create two magnetic traps, each containing one state.

[0181] Thus, during the entire phase in which the two states ai> and lb> are kept separate, the two microwave fields used for the dressing are cut off. During this phase of the interferometer, the phase is no longer sensitive to noise on the DC magnetic field 5B, nor on the amplitude of the microwave fields and ôklh via the noise term, but the term remains sensitive to ÔB.

[0182] Microwave signals, typically IMW microwave currents, are first applied to perform the separation of the two clouds (initialization of spatial separation), as illustrated in Figures 3 and 4 from ti and up to t2. This step of progressively lighting up the waveguides is similar to what has been described in the prior art.

[0183] Then according to the invention the IMW currents are cut off and instead direct currents Idc-mw are applied to the microwave guides CPW1 and CPW2. Before and during the change of type of current applied to the waveguide, direct currents are applied to the conducting wires.

[0184] It is important to use microwave currents for the initial separation of the two states α and β of the interferometer because microwave currents allow the creation of selective traps of the internal state, which DC currents do not. It is important to create selective traps of the internal state at the beginning of the separation; otherwise, the two states would remain mixed after the separation.

[0185] The DC magnetic potential Mw created by the application of these direct currents I The DC magnetic potential (VDC_Mw) in the waveguides is illustrated [Fig. 6]. This DC magnetic potential (VDC_Mw) replaces the DC magnetic potential created by the microwave fields resulting from the application of the IMW microwave currents, illustrated by curves c) and e) in Figure 2a). The DC magnetic potential (VDC_Mw) allows the cold atoms to continue to be trapped and the spatial separation of the two clouds to be maintained for as long as necessary during the remainder of the Ramsey sequence. Curve a), taken from [Fig. 2a], illustrates the DC magnetic potential created by the application of direct currents in the two conducting wires (beginning of the sequence, before the clouds separate and therefore before the microwave currents are switched on).

[0186] Figure 7 illustrates an ultracold atom sensor 10 according to the invention. The sensor 10 comprises an atom chip ACh placed in a vacuum chamber, having an XY plane, referred to as the measurement plane, normal to a Z-axis. The ACh chip has a first waveguide CPW1 and a second waveguide CPWX2 adapted for the propagation of microwave waves and direct currents, and at least a first conducting wire WIz and a second conducting wire Wld whose respective projections intersect at a point defining a first crossing point CL. The two waveguides are arranged symmetrically about a Y-axis; typically, but not exclusively, they are parallel to each other. The sensor also includes an atom generation device ACG configured to generate a cloud CL of ultracold atoms near said XY plane of said atom chip and a generator GB of a homogeneous magnetic field Bc.

[0187] The sensor 10 according to the invention also includes a PSD power supply device comprising at least one GMW microwave generator and at least one GDC direct current generator. There may be one microwave generator per waveguide or one generator common to both waveguides. Similarly, there may be a single GDC generator common to all wires and waveguides, or several generators.

[0188] The PSD power supply device is configured to apply microwave signals, typically IMW currents, and continuous electrical currents IDc mw, known as CMW currents, to the waveguides CPW1 and CPW2, and to apply continuous currents IDc wi, known as CWI currents, to the conducting wires.

[0189] The waveguides, the conducting wires and the power supply device are configured, during the implementation of the sensor, i) to spatially separate a first cloud of ultracold atoms CL1 in a first internal state la> from a second cloud of ultracold atoms CL2 in a second internal state lb>, forming respectively a first trap of ultracold atoms Tl and a second trap T2 by modifying the energy of the atoms, and ii) to move the traps (Tl, T2) along a linear or closed trajectory contained in a plane perpendicular to Z.

[0190] According to the invention, the PSD feeding device is configured to apply to the first and second waveguides, for the spatial separation of the two traps, the IMW microwave signals to initiate spatial separation, then CMW IDc mw electric currents instead of IMW microwave signals (currents) to maintain spatial separation.

[0191] Finally, the sensor 10 according to the invention includes an SDET detection system adapted to measure at least a population of said ultracold atoms in said internal state.

[0192] The cold atom sensor has a structure identical to that described in the prior art, with the difference that the waveguides are suitable for the propagation of direct currents and that the power supply device allows direct currents to be applied to the waveguides as claimed.

[0193] By applying direct currents to the waveguides instead of microwave signals for a significant portion of the Ramsey sequence, the noise component due to these crMWTRn ​​signals (formula 17) is considerably reduced because of the decrease in T^1. This reduces the amount of noise accumulated on the interferometer phase. It has been shown above that this noise component is what limits the measurement, and any gain on this noise component directly translates into a gain in measurement sensitivity.

[0194] A first type of sensor according to the invention is an accelerometer, the trajectory followed by the two traps is linear as illustrated [Fig.4] a). Two intersecting wires in Cl IWz and Iwd are necessary to define the starting / ending point of the trajectory, and the displacement is here coincided with the spatial separation.

[0195] A second type of sensor is a gyroscope. The atomic chip then comprises a plurality of second conducting wires Wldi (Wldl, Wld2, Wld3) defining a plurality of crossing points Ci (Cl, C2, C3) as illustrated [Fig.1], and the path followed by the two traps is closed and traversed in the opposite direction by the two traps, as described [Fig.3] a).

[0196] The gyroscope according to the invention is compatible with any atomic chip geometry comprising two microwave guides and conducting wires, as described in the aforementioned US documents 15 / 778605, US 17 / 924340, US 17 / 832615 and US 17 / 832616.

[0197] During the implementation of the sensor according to the invention, the separation of the two clouds is achieved using microwave signals, and once the clouds are separated, the separation is maintained by the CMW direct currents applied to the waveguides. The switching off of the microwave fields and their replacement by two DC currents can be accomplished in three different ways.

[0198] In a first embodiment, the PSD power supply device is configured so that the microwave signals are switched off simultaneously with the DC electrical currents. This mode allows for rapid switching off of the microwave currents. croondes, therefore to reduce (see equation (17)) and therefore to reduce the accumulation of noise due to the term ^mw.

[0199] According to a first embodiment, the time tttans during which the switching off and on simultaneously occurs is rapid, meaning that the rising or falling edge is rapid compared to the frequencies of the magnetic trap. Typically, tttans must be less than or equal to 100 ps.

[0200] According to a second embodiment, the simultaneous switching off and on is achieved with two slow ramps (a slow RF ramp descends and at the same time a DC ramp ascends), which means that the ramps must be slow compared to the frequencies of the magnetic trap. Typically, the time lag must be at least 10 ms.

[0201] Between these two values ​​of ttrans according to a third embodiment the ramps have complex shapes to make adiabatic shortcuts.

[0202] In a second embodiment, the PSD power supply device is configured so that the microwave signals are switched off before the CMW electric currents are switched on. This mode allows for even faster switching off of the microwave currents than the first mode, but complicates the transfer between traps using IMW microwave currents and traps using DC Idcmw currents. The time during which nothing is applied is denoted tint. This time should be less than the inverse of the trap frequency cop. The trap frequency illustrates its "stiffness". The shape of the magnetic potential creating the trap is approximated in the vicinity of the minimum by a parabola. Let r be the distance to the potential minimum Vo; the potential can be written as:

[0203] y~ Vo + 1 nw2r2

[0204] Thus it is appropriate that:

[0205] t. t ±

[0206] In a third embodiment, the PSD power supply device is configured so that the microwave signals are switched off after the CMW electrical currents have been switched on. This mode simplifies the transfer between traps using IMW microwave currents and traps using IDC mw- DC currents.

[0207] According to one embodiment, each waveguide comprises three wires: two outer ground wires and one inner signal wire, and the CMW direct current is injected into the signal wire (coplanar waveguides). However, the sensor 10 according to the invention can incorporate any type of microwave guide compatible with the application of direct currents, such as microstrips.

[0208] According to one embodiment, the superposition of a microwave current and a direct current in the signal wire of the waveguide is achieved with a polarization tee. Thus, the PSD power supply device further comprises at least one polarization tee. The TPol configuration is connected to the microwave generator and the DC generator, and configured as the input of each waveguide to apply the microwave signal (microwave current IMW) and the CMW current (DC current IDcmw) to the waveguides, as illustrated in the schematic diagram in [Fig. 8]. A bias tee is a component with two inputs, one for a DC current and the other for an oscillating current, and an output that allows for the superposition of the DC and oscillating currents. The output can also be used as an input for the superposition of the DC and oscillating currents; in this case, the two inputs become two outputs, one providing the DC current and the other the oscillating current. To prevent unwanted reflections of the microwave signal that has passed through the microwave guideguides, a microwave termination TMW is integrated at the output of the atomic chip, as also illustrated in [Fig. 8].

[0209] Preferably to ensure good separation between direct currents and microwave signals at the output of the microwave guide, an additional polarization tee TPoladd is integrated at the output of the waveguide and before the termination TMW, as illustrated in the schematic diagram of [Fig.9].

[0210] According to another aspect, the invention relates to a method for measuring an inertial parameter using an ultracold atom sensor according to the invention as described above. The method comprises a first step A consisting of generating a CL cloud of ultracold atoms near the XY plane of the atom chip, including phases of atom emission, atom cooling, atom initialization in at least one first internal state, and trapping of an ultracold atom cloud in a local potential minimum, at a controlled height above the measurement XY plane, the trapping being effected by passing direct currents through the first and second conducting wires. This step is similar to step AO described in the prior art.

[0211] In a step B, the first internal state la> and the second internal state lb> of the ultracold atoms are initialized by coherently superimposing the ultracold atoms between the first and second internal states by a pulse ji / 2. This step is similar to step B0 described in the prior art.

[0212] In a step C, the first cloud of ultracold atoms in the first internal state is spatially separated from the second cloud of ultracold atoms in the second internal state, forming respectively a first ultracold atom trap T1 and a second ultracold atom trap T2. This separation is achieved by modifying the energies of the ultracold atoms. The traps (T1, T2) are then moved along a linear (accelerometer) or closed (gyroscope) trajectory contained in a plane perpendicular to Z and initialized at the first crossing point.

[0213] Step C of separation and displacement of the ultracold atoms is carried out by ap- applying, according to a predetermined sequence: • a homogeneous magnetic field Bc with ultracold atoms, • Direct currents, known as CWI currents, to the conducting wires, • microwave signals, typically IMW microwave currents, and continuous electrical currents, known as CMW currents, to the waveguides.

[0214] In the method according to the invention, the separation step comprises an initialization substep Cinit, which includes the application of microwave signals to said waveguides, and a maintenance substep Cmaint, which includes the application of CMW electric currents instead of said microwave signals. The originality of the method according to the invention lies in the separation and displacement step C, and particularly in the Cmaint step.

[0215] In a step D, the first and second internal states are recombined (the two clouds are then spatially coincident again once the trajectory has been traversed) by applying a second pulse ji / 2 to the ultracold atoms, which closes the Ramsey sequence initialized with the first pulse ji / 2. This step is similar to the DO step described in the prior art.

[0216] Finally, in a step E, at least one population of ultracold atoms is measured in at least one said internal state, from which a value of an inertial parameter (acceleration, velocity and / or angle of rotation with respect to a given axis) is deduced. This step is similar to step E0 described in the prior art.

[0217] In the process according to the invention, the usual sequence used to separate and recombine the two states la> and lb> is modified.

[0218] The usual sequence consists of: • Gradually turn on the two microwave fields each in a waveguide (CPW1 and CPW2) of the chip, this allows the two states la> and lb> to be separated; • Maintain the two microwave fields in the CPW 1 and CPW2 guides to keep the two states an and lbn separate (this separation with the microwave fields is shown in [Fig.2] a)); • Gradually turn off the two microwave fields to spatially recombine the two states la> and lb>. This spatial recombination is different from the recombination of step D. The spatial recombination takes place once just before step D for the accelerometer (time t3 of [Fig.4] a)), and takes place twice during the closed trajectory for the gyroscope (times t5 and tç of [Fig.3] a)).

[0219] The sequence according to the invention is, for the example of a three-wire coplanar waveguide, described below. • Gradually turn on both microwave fields, each in its own guide of the chip wave, this allows to separate the two states la> and lb>; • Once the states are separated, preferably quickly, switch off the two microwave fields and preferably simultaneously and quickly switch on a DC current in the two signal lines of the two microwave guides. This creates two separate DC magnetic traps, each containing one of the two internal states ai and bi (these two traps are shown in [Fig. 6]); • Spatially recombine the two states during the movement step, according to two variants:

[0220] According to a first variant, by progressively switching off the two DC currents flowing through the two signal lines of the two microwave guides;

[0221] According to a second variant, by switching off, preferably rapidly, the two DC currents flowing through the two signal lines of the two microwave guides and, preferably at the same time, by rapidly switching on the two microwave fields, then by gradually switching off the two microwave fields to recombine the two states a1> and lb>.

[0222] Preferably the separation step of the process according to the invention includes a transient substep Ctrans between the initialization substep Cinit and the maintenance substep Cmaint, comprising the extinction of microwave signals and the ignition of CMW currents.

[0223] The interruption of microwave fields and their replacement by two DC currents can be carried out according to the three variants described above:

[0224] First variant: during the transient stage, the microwave signals are switched off and the CMW currents are switched on simultaneously. Preferably, the transient stage has a duration of less than 100 ps.

[0225] Second variant: during the transient stage, the extinction of microwave signals takes place prior to the ignition of CMW currents.

[0226] Third variant: during the transient stage, the extinction of MW signals after the ignition of CMW currents

[0227] We will now illustrate the process according to the invention with examples of chronograms.

[0228] We call: • P1MW and P2mw are the microwave signal power applied respectively to waveguides CPW1 and CPW2. • coa is the pulse sent into the CPW2 waveguide and cob is the pulse sent into the CPW1 waveguide, • Iz the intensity of the direct current applied to the first conducting wire WIz • Id, Idb, Id2, Id3 are the intensities of the direct currents, also called CWI currents applied to the second conductor(s), • IlDC-MwCt I2DC-mw the intensities of the direct currents called CMW applied respectively to the waveguides CPW1 and CPW2.

[0229] Figures 10(a), 1a), illustrate the timing diagrams for the application of the different signals during the implementation of an accelerometer-type sensor according to the first and second spatial recombination variants, respectively, during step C of separation / displacement. Figures 10(b) and 11(b) illustrate the displacement of the two clouds at selected times. These figures further illustrate the first variant of the extinction / ignition sequencing, namely, the extinction of the MW powers simultaneously with the ignition of the CMW currents.

[0230] Throughout the sequence a coa pulse is applied to CPW2 and cob to CPW1 (same as [Fig.4] a)).

[0231] In [Fig. 10], between t1 and t2, microwave powers are applied to the waveguides. At t2, the two wave clouds CL1 and CL2 are separated. Then, between t2 and t3, the MW signal is gradually switched off, and the DC currents I1Dc-Mwet and I2DC-mw are simultaneously switched on. Between t3 and t4, these currents are maintained for measurement. Then, between t4 and t5, the currents I1Dc-Mwet and I2DC-Mw are gradually decreased, spatially recombining the two wave clouds (first variant of spatial recombination). At t5, the two wave clouds are spatially recombined.

[0232] According to a first embodiment, the currents Id and Iz remain constant. According to a second embodiment illustrated [Fig. 10], a) the current Iz decreases slightly when the currents IlDc-Mwet and I2dc.mw are applied, in order to increase the potential barrier between the two states ([Fig. 6]). When these currents are no longer applied, Iz increases slightly again. According to this second embodiment, Id preferably varies like Iz.

[0233] In [Fig. 11], the beginning of the sequence is identical up to time t4. Between t4 and t5', simultaneously with the switching off of the DC currents, the microwave signals are switched back on; the clouds are still separated. Between t5' and t6', spatial recombination takes place by progressively switching off the MW signals (second variant of spatial recombination). At t6', the two clouds are spatially recombined.

[0234] Figures 12 and 14 illustrate the timing diagrams for the application of the different signals for the implementation of a gyroscope-type sensor, respectively, according to the first and second variants of spatial recombination, during step C of separation / displacement. Figures 13 and 15 illustrate the displacements of the two clouds at selected times. These figures also illustrate the first variant of the extinction / ignition sequencing, namely, the extinction of the MW powers simultaneously with the ignition of the CMW currents.

[0235] In Figures 12 and 13, the two clouds are separated by applying MW power to the two waveguides (between t1 and t2). This is achieved by applying DC currents Id1 and Idz in WIz and Wid1, respectively. Then, between t2 and t3, the MW signals are replaced by the DC currents I1Dc-Mwet and I2DC-Mw. Between t3 and t4, the two clouds are moved along the Y-axis from the first crossing point C1 to the second crossing point C2 by switching off the current Id1 and switching on the current Id2 in WId2. Between t4 and t5, the two clouds are moved along the Y-axis from the second crossing point C2 to the third crossing point C2 by switching off the current Id2 and switching on the current Id3 in WId3. Then between t5 and t6 we proceed to the first spatial recombination of the two clouds in C3 (finalizing the half path of the closed trajectory) by extinguishing the continuous currents IlDc-Mwet I2DC Mw (first variant of spatial recombination).At t6 the frequencies applied to the waveguides are reversed and we start again for the second half-turn, again proceeding to the separation of the two clouds by applying MW fields to the guides between t6 and t7.

[0236] Here too, according to an embodiment illustrated in [Fig. 12], the current Iz is slightly decreased when the currents I1Dc-Mwet and I2DC are applied, and increases again when they are switched off, and the currents Idl and Id3 follow the variations of Iz. According to another embodiment, the currents Iz and Idl, Id2 and Id3 do not exhibit two plateaus (see, for example, the variation of Idl in [Fig. 3]).

[0237] In Figures 14 and 15, the sequence is identical up to t5. Between t5 and t6', the DC currents are switched off simultaneously and the microwave signals are switched on again; the clouds are still separated. Between t6' and t7', spatial recombination occurs by progressively switching off the MW signals (second variant of spatial recombination). The same will occur between t1' and t12', where the DC currents are switched off simultaneously and the microwave signals are switched on; then between t12' and t13', spatial recombination occurs by progressively switching off the MW signals.

Claims

1. Claims Ultra-cold atony sensor (10) comprising: • an atomic chip (ACh) placed in a vacuum chamber, comprising an XY plane called the measurement plane normal to a Z axis, and comprising: • a first and a second waveguide (CPWX1, CPWX2) adapted to the propagation of microwave waves and direct currents, • at least a first conductive wire (WIz) and a second conductive wire (Wld, Wldl) whose respective projections intersect at a point defining a first crossing point (Cl), • an atom generation device (ACG) configured to generate a cloud of ultracold atoms near said XY plane of said atomic chip, • a generator (GB) of a homogeneous magnetic field (Bc), • a power supply device (PSD) comprising at least one microwave generator (GMW) and at least one direct current generator (GDC), the power supply device being configured to: • applying microwave signals (IMW) and direct electric currents (IDc mw) called CMW currents to said first and second waveguides, • apply direct currents known as CWI currents to said conductive wires, • said waveguides, said conductive wires and said power supply device being configured, during the implementation of the sensor, to spatially separate a first cloud (CL1) of ultracold atoms in a first internal state from a second cloud (CL2) of ultracold atoms in a second internal state, by respectively forming a first (Tl) and second (T2) ultracold atom traps by modifying an energy of said ultracold atoms, and to move said traps (Tl, T2) along a linear or closed trajectory included in a plane perpendicular to Z, • said power supply device being configured to apply to said first and second waveguides, for the spatial separation of the two traps, said microwave signals to initiate said spatial separation, then said CMW electric currents in place of said microwave signals to maintain said spatial separation, • the sensor further comprising a detection system (SDET) adapted to measure at least one population of said ultracold atoms in a said internal state.

2. Sensor according to one of the preceding claims of accelerometer type, said trajectory followed by the two traps being linear.

3. Sensor according to one of the preceding claims of gyroscope type comprising a plurality of second conductive wires (Wldi) defining a plurality of crossing points (Ci), said trajectory followed by the two traps being closed and traveled in opposite directions by the first and the second trap.

4. Sensor according to one of the preceding claims in which each waveguide comprises three wires, two external ground wires and an internal signal wire, the CMW current being injected into the signal wire.

5. Sensor according to one of the preceding claims wherein the power supply device further comprises at least one polarization tee connected to said at least one microwave generator and to said at least one direct current generator, and configured to apply said microwave signals and said CMW currents to said waveguides.

6. Method for measuring an inertial parameter by an ultracold atom sensor comprising an atomic chip (ACh) placed in a vacuum chamber, comprising an XY plane normal to a Z axis called the measurement plane, said atomic chip comprising: • a first and a second waveguide (CPWX1, CPWX2) adapted to the propagation of microwave waves and direct currents, • at least a first conductive wire (Wl) and a second conductive wire (W2) whose respective projections are intersecting at a point defining a first crossing point (0),

7. the method comprising the steps of: A Generating a cloud of ultracold atoms near said XY plane of said atomic chip, including phases of emitting said atoms, cooling said atoms, initializing said atoms in at least a first internal state, and trapping a cloud of said ultracold atoms in a local minimum of potential, at a controlled height of said XY plane, said trapping being carried out by passing direct currents in the first and second conductive wires, B Initialize the first internal state and a second internal state of said ultracold atoms by coherently superimposing said ultracold atoms between said first and second internal states by a pulse ji / 2, C Spatially separating a first cloud of ultracold atoms in the first internal state from a second cloud of ultracold atoms in the second internal state, respectively forming a first (Tl) and second (T2) ultracold atom trap by modifying the energies of said ultracold atoms, and moving said traps (Tl, T2) along a linear or closed trajectory included in a plane perpendicular to Z and initialized at the first crossing point, said step of separating and moving the ultracold atoms being carried out by applying, according to a predetermined sequence, a homogeneous magnetic field (Bc) to said ultracold atoms, direct currents, called CWI currents, to said conductive wires, and microwave signals (IMw) and direct electric currents, called CMW currents, to said waveguides, the separation step comprising an initialization sub-step comprising the application of said microwave signals to said waveguides,and a holding sub-step comprising applying said CMW electric currents in place of said microwave signals, D Recombining said first and second internal states by applying to said ultracold atoms a second pulse ji / 2, E Measure at least one population of said ultracold atoms in at least one said internal state. Method according to the preceding claim in which the separation step comprises a transitional sub-step between the initialization sub-step and the maintenance sub-step, comprising an extinction microwave signals and ignition of CMW currents.

8. Method according to the preceding claim in which, during the transient step, the extinction of the microwave signals and the ignition of the CMW currents are carried out simultaneously.

9. Method according to the preceding claim in which the transient step has a duration of less than 100 ps.

10. A method according to claim 6 wherein, during the transient step, said extinction of the microwave signals occurs before or after said ignition of the CMW currents.

11. Method according to one of claims 6 to 10 in which during the displacement step a spatial recombination of the two clouds takes place by progressively extinguishing the CMW currents.

12. Method according to one of claims 6 to 10 in which during the displacement step, a spatial recombination of the two clouds takes place by switching off the CMW currents and simultaneously switching on the microwave signals again, then by gradually switching off the microwave signals.

Images