Cold atom sensor with improved noise

Abstract

The invention relates to a cold atomic sensor (10) with improved noise, comprising: an atomic chip (ACh) comprising: a first waveguide (CPWX1) and a second waveguide (CPWX2) adapted to propagate microwaves and a DC current, at least a first conductive line (WIz) and a second conductive line (WId, WId1), the respective projections of which are tangent at a point defining a first intersection (C1); an atom generating device (ACG); a power supply device (PSD) comprising at least one microwave generator (GMW) and at least one DC current generator (GDC), the power supply device being configured to apply a microwave signal to the first and second waveguides and spatially separate the two traps, thereby initiating the spatial separation, and then apply a CMW current instead of the microwave signal, thereby maintaining the spatial separation.

Description

Technical Field

[0001] The present invention is in the field of inertial sensors and more specifically in the field of cold atom inertial sensors integrated on an atom chip. More specifically, the present invention relates to spatially separated cold atom sensors on an atom chip for measuring two states used in measuring inertial parameters (typically acceleration and rotational velocity) using microwave fields. Prior art

[0002] Cold atom interferometry interferes with two electronic states of an atom (e.g., rubidium 87) called a first internal state |a> and a second internal state |b> in a Ramsey sequence. The Ramsey interferometer sequence measures the phase that is accumulated when the sequence is performed by measuring at least one population of the selected state |a> or |b> (preferably both populations for higher accuracy). The corresponding population number p of the two states |a> and |b>a at the output of the interferometer is a and p b Given by:

[0003]

[0004]

[0005] Phase With E' b and E' a The energy difference between b and E' a are respectively equal to the energies of states a> and |b> that are changed by implementing the interferometric measurement sequence.

[0006] as well as

[0007]

[0008] where ω is the angular frequency of the local oscillator that generates two π / 2 pulses at the beginning and end of the interferometry sequence, and T R is the Ramsey time, i.e. the time that has elapsed between two π / 2 pulses.

[0009] set up:

[0010]

[0011]

[0012] Assume that before the Ramsey sequence begins, all atoms are in state |a> and E b >E a , where Ea and E b is the atomic energy that depends on the state of the atom and the transition under consideration.

[0013] In order to make this interferometer sensitive to acceleration and rotation, it is necessary to:

[0014] In the case of acceleration, two states are separated and then recombined, that is, the two states are moved in two opposite directions along a straight line from the same initial position and then made to travel along the same path in opposite directions until they return to the same position. This makes it possible to add a term related to the potential energy of the acceleration to the energy difference between the two states.

[0015] In the case of rotation, both states must travel along a closed path that includes a non-zero area, and in opposite directions for |a> and |b>. Therefore, a term that depends on the Sagnac Effect, and therefore on the rotation speed, is added to the energy difference between the two states.

[0016] To achieve these trajectories, a known method is to use a microwave separator (a waveguide in which a microwave signal is applied). The microwave field generated then "dresses" the state, which has the effect of generating a force that causes it to move. This dressing removes the energy of the states |a> and |b> from E a Change to E' a And from E b Change to E' b .

[0017] The structure and operating principles of gyroscopic sensors are described in documents US 15 / 778605, US 17 / 924340, US 17 / 832615 and US 17 / 832616 and will be reviewed below. For example, document WO2017089489 describes an on-chip ultracold atomic gyroscopic inertial sensor that uses trapped matter waves describing a closed path including an area.

[0018] The measurement of rotation in this type of device is carried out by exploiting the Sagnac effect. In a reference frame rotating at an angular velocity Ω, the Sagnac-induced phase shift θ between two counter-rotating matter waves is given by:

[0019]

[0020] where A is the area enclosed by the path of the atom, m is the mass of the atom, and is the simplified Planck constant.

[0021] Ultracold atoms are defined as atoms whose temperature is below 400 nanoKelvin, and preferably below 300 nanoKelvin. For example, for rubidium atoms, the temperature of hot ultracold atoms is between 50 and 400 nanoKelvin, and preferably between 100 and 300 nanoKelvin.

[0022] The principle is to obtain the paths along which two counter-propagating clouds of magnetically trapped atoms travel. Figure 1 In the topology shown in Figure 1, the creation of magnetic traps and their movement along the path are carried out by conductive wires and microwave waveguides.

[0023] Figure 1 Schematically shown is an ultracold atom chip 1, its ultracold atoms 12 and the paths 16 of the two atomic clouds CL1 and CL2. A portion of the surface of the chip 1 forms a measurement plane 13. An axis perpendicular to the measurement plane 13 defines a measurement axis Z about which a measurement Ωz of the rotation is performed by a gyroscope.

[0024] The chip 1 comprises a unit suitable for generating a first ultracold atom trap T1 and a second ultracold atom trap T2, the traps allowing a cloud of ultracold atoms 12 to be fixed at a predetermined distance h from the measurement plane 13 in a different internal state than the other trap. For example, the trap T1 comprises atoms in an electronic energy level or state |a> (cloud CL1), and the trap T2 comprises atoms in a state |b> (cloud CL2). The energy levels |a> and |b> are fixed at a frequency ω 0 / 2π separation. For example, in the case of rubidium 87, it is the two hyperfine levels |F=1,m that are separated by about 6.8 GHz. -F =-1> and |F=2,m -F =1>.

[0025] For example, Figure 1 As shown, these means also allow the cloud to move along a path 16 lying in a plane parallel to the measurement plane 13 and at a height h from this plane. These means consist of waveguides and conducting wires, for example as described below.

[0026] The device comprises a device adapted to operate at an angular frequency ω b and ω aA first waveguide CPW1 and a second waveguide CPW2 propagating microwaves. The waveguides are arranged symmetrically with respect to the Y axis of the measurement plane, preferably in parallel. The two waveguides CPW1 and CPW2 are connected to at least one generator for generating a voltage or current at microwave frequencies. For example, each of the waveguides is manufactured by depositing three conductive lines in parallel to form a coplanar waveguide. In other embodiments, other types of waveguides may be used, in particular waveguides whose manufacture is compatible with microfabrication techniques using deposition or etching. It is possible, for example, to manufacture microstrip lines.

[0027] The device also includes conductive lines integrated into the chip 1 and capable of being traversed by a DC current. The conductive lines are divided into conductive lines WIz along a symmetry axis Y perpendicular to X and contained in the measurement plane 13, and a plurality of conductive lines Wldi parallel to each other and to the X axis, the index number i varying from 1 to n, n being at least equal to 2. Figure 1 In the example of , n=3, that is, there are three conductive wires WId1, WId2, and WId3. The conductive wires are arranged to define n intersections Ci (intersections between WIz and Wldi) located on the Y axis, and here are three intersections C1, C2, C3.

[0028] Each conductive line is connected to one or more current and / or voltage generators, which themselves are connected to a processing unit comprising at least one microprocessor. The voltage and / or current generators allow driving both DC current and AC current through the wire. Specifically, a DC current is driven to flow through the conductive line.

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

[0030] Atom dispensers, such as those implemented by heated filaments that generate rubidium vapor;

[0031] Primary (optical and / or magnetic) atom traps allow a cloud of ultracold atoms to be pre-cooled and placed near the chip with the purpose of loading the atoms into the magnetic traps T1 and T2 described below.

[0032] The sensor also comprises a magnetic field source external to the chip 1. It allows generating a uniform and static magnetic field Bc over a thickness of at least the order of height h above the measurement plane 13. Advantageously, the direction of the uniform magnetic field is parallel to the measurement plane.

[0033] exist Figure 1In FIG. 1 , the dashed path 16 shows the path of the cloud of ultracold atoms 12. This closed path defines an area denoted A. The plane of the path 16 is separated from the measurement plane 13 of the chip by a distance h. Preferably, h is between 500 nm and 1 mm, and preferably, between 5 μm and 500 μm.

[0034] Figure 2 The waveguides and wires of the atom chip and the geometry of the traps T1 and T2 are shown.

[0035] The specific arrangement of the conductive wires and waveguides together with the uniform magnetic field source make it possible to easily obtain two traps T1 and T2 (e.g. Figure 2 As shown in part a) of ). Each trap T1 and T2 has the same non-zero minimum value V0 and the same curvature, which is a necessary condition for the operation of the sensor. Specifically, as explained below, when a DC current is applied to at least two conductive lines at an intersection, the minimum value of the potential is located perpendicular to this intersection. When microwave power is subsequently sent through the waveguide, the central minimum value is converted into two minima located on either side of the initial minimum value in the direction of the waveguide. If the initial minimum value is not strictly located at an equal distance from the two waveguides, the two potential minima generated will not have strictly the same minimum value V0 and the same curvature.

[0036] Figure 2 Part c) of FIG. 5 shows the layout of the conductive lines and the layout of the waveguide (seen from above) defining the initial crossing point C1. Figure 2 Part b) describes the corresponding layout of the conductive lines and waveguides printed on the chip as seen in the cross-sectional profile, the section passing through the conductive line WId1 intersecting the conductive line WIz along the symmetry axis Y. The waveguides CPW1 and CPW2 are coplanar waveguides located on the first level N1. The isolation layer 18 advantageously allows the measurement plane to be flattened. The material of the electrical isolation layer can be, for example, silicon dioxide, silicon nitride or benzocyclobutene. A conductive material (for example gold) is used to make the conductive lines and is deposited on the substrate 15 to form the second level N2. The substrate can be made of silicon, aluminum nitride or silicon carbide, for example.

[0037] Part a) shows the symmetrical separation of the ultracold atoms, which is specific to their internal state and more precisely to the variation in the potential as a function of the position on the X-axis of the chip 1 .

[0038] Curve "a" shows a potential well corresponding to a uniform magnetic field and the association of the field generated by two tangential conductive wires (wire WIz through which current IZ passes, and wire WId1 through which current Id1 passes). A local potential well is generated that forms a three-dimensional atomic trap T. An ultracold atomic cloud can be trapped therein and cooled.

[0039] Curve "b" schematically shows the frequency ω of the waveguide CPW1. b The electric potential generated by the transmission of microwaves. Microwaves travel at a frequency of ω b The field emitted when passing allows to change the energy of the ultracold atoms and to move the atoms of the internal state |b>. Curve "e" shows the potential seen by the internal state |b> due to the contribution of the potentials shown by curves "a" and "b". Curve "e" has a local potential minimum, allowing the cloud of ultracold atoms of the internal state |b> to be locally trapped.

[0040] Similarly, curve "d" schematically shows the flow of current through waveguide CPW2 at a frequency ω a The electric potential generated by the transmission of microwaves. Microwaves travel at a frequency of ω a The field emitted during the passage allows to change the energy of the ultracold atoms and to move the atoms of the internal state |a>. Curve "c" shows the potential seen by the atoms of the internal state |a> due to the contribution of the potentials shown by curves "a" and curve "d". Curve "c" has a local energy minimum, allowing the cloud of ultracold atoms of the internal state |a> to be locally trapped.

[0041] The association of a DC magnetic trap (generated by a DC current in a wire and a uniform field Bc) and a microwave field creates a so-called "decorated" trap. The term "decorated" is understood to mean a trap generated at least in part by a microwave, radiofrequency or optical oscillating field. Changes in the microwave field (power, frequency and the waveguide in which they propagate) make it possible to move the decorated trap and, therefore, the atoms. The DC magnetic trap is Figure 2 In the figure, it is represented by curve a. a The microwave field at Figure 2 In the figure, the curve d represents the b The microwave field at Figure 2 The decorated trap T1 of state |a> (the association of curves a and d) is represented by curve c, and the decorated trap T2 of state |b> (the association of curves a and b) is represented by curve e.

[0042] By simultaneously making the frequency ω a The wave propagates through CPW2 and the frequency ω b The waves propagate through CPW1 and the ultracold atomic clouds of the internal states |a> and |b> can be separated and trapped symmetrically with respect to the symmetry axis Y. In order to obtain two traps whose minima are of the same value V0 and whose curvatures are of the same value, it is important to place the intersection point C1 at an equal distance from CPW1 and CPW2 on the symmetry axis Y.

[0043] Figure 3 The principle of generation of the path 16 is shown. Figure 3 Part a) schematically shows the characteristics of each ultracold atomic cloud at a characteristic time t1 to 9 Part b) shows in a complementary manner the sequence of the respective currents applied to the conductive line, the sequence of the powers applied to the waveguide, and the sequence of the frequencies applied to the waveguide at times corresponding to those of part a).

[0044] exist Figure 3 In the sequence shown, the current I flowing through WIz z (not shown) is static and of constant value. In part b), the values ​​of current, power and frequency are arbitrary values. The y-axis labeled delta frequency corresponds to the frequency change relative to the average frequency value expressed in arbitrary units. In the case of using rubidium atoms, the current through the conductive wire can be between 100 μA and 10 A, and the angular frequency injected into the waveguide can be between 6.6 GHz and 7 GHz.

[0045] In step A0, there is a phase of preparing atoms. A cloud of ultracold atoms 12 is generated, which comprises a phase of distributing said atoms, a phase of cooling said atoms, a phase of initializing said atoms to at least one internal state |a>, and a phase of trapping said cloud of ultracold atoms in a local potential minimum at a distance h from the measurement plane (trap T, Figure 2 Curve "a" of part a)). Since the uniform magnetic field Bc is non-zero, the height h is not equal to 0. The trapping is achieved by passing a DC current through the wire WIz and through one of the wires WIdi, the intersection of these two wires defining the starting point (here C1 with WId1). At the same time, a bias magnetic field Bc is applied parallel to the plane of the atomic chip, which is superimposed on the magnetic field generated by the first two wires. The atomic cloud is then trapped perpendicularly relative to C1 (the intersection of the conductive wires Wlz and Wld1).

[0046] In step B0, the internal state is initialized by coherently superposing the ultracold atoms between the states |a> and |b> via a first π / 2 pulse. This pulse can be generated by a laser, a microwave transmitter or more generally using a method of emitting waves at an appropriate transition frequency. The current I Z and I d1 are applied to the conductive lines WIz and WId1, respectively. The two internal states |a> and |b> are coherently and spatially superimposed perpendicularly to the intersection C1.

[0047] Then the wave function is:

[0048]

[0049] In step C0, the cloud of atoms of the internal state |a> in one trap T1 is spatially separated from the cloud of atoms of the internal state |b> in the other trap T2, and the traps are moved in opposite directions along a closed path 16 contained in a plane perpendicular to the measurement axis Z. The cloud of atoms of the internal state |a> has been represented by circles of light texture, and the cloud of atoms of the internal state |b> has been represented by circles of darker texture. This step starts from t 1 Continue to t 9 .

[0050] In t 1 With t 2 The microwave power injected into waveguides CPW1 and CPW2 gradually changes from 0 to its maximum value. b sent to the waveguide CPW1, and the angular frequency ω a sent to the waveguide CPW2, which allows two clouds of different internal states to be on either side of the symmetry axis Y with respect to t 2 The schematically shown positions are separated by a distance d. Therefore, the above 1 The ultracold atom trap T at is converted into two ultracold atom traps T1 and T2, each of which allows an ultracold atom cloud with an internal state different from that of the other trap to be fixed (in this case, the internal state |a> in one of the traps (e.g., T1), and the internal state |b> in the other trap T2, as Figure 2 as described in part a) of this document).

[0051] The intersection point Ci corresponds to the intersection of the wire WIz and the wire WIdi.

[0052] In t 2 With t 3 Between, the current I d1 Gradually cut off, and I d2 Gradually reaches its maximum value (t 2 With t 3 The time interval separating them is typically of the order of 10 ms and may be between 0.1 ms and 100 ms): The two traps T1 and T2 move rightward to the time interval corresponding to t 3 Location shown schematically.

[0053] In t 3 With t 4 Between, the current I d2 Gradually cut off, and I d3 Gradually reaching its maximum value: the two traps move to the right for t 4 Location shown schematically.

[0054] In t 4 With t 5 The microwave power is gradually cut off:5 As shown schematically, the two traps are brought back to the same position on the chip.

[0055] In t 5 At the point, the angular frequencies of the two microwave waveguides are changed: angular frequency ω a is applied to CPW1, and the angular frequency ω b is applied to CPW2.

[0056] In t 5 With t 6 The power in the two waveguides gradually changes from 0 to its maximum value: as shown in the figure for t 6 As shown schematically, the traps are separated in the vertical direction.

[0057] In t 6 With t 7 Between, the current I d3 Gradually cut off, and I d2 Gradually reaching its maximum value: the two traps T1 and T2 move to the left to target t 7 Location shown schematically.

[0058] In t 7 With t 8 Between, the current I d2 Gradually cut off, and I d1 Gradually reaching its maximum value: Both traps move leftwards to target t 8 This operation can be repeated multiple times with other first conductive lines to increase the area enclosed by the path 16 .

[0059] In t 8 With t 9 The microwave power in the waveguide is gradually cut off. The two traps T1 and T2 move until they merge into a single trap located at t 1 A single trap at the starting point is shown schematically.

[0060] Thus, DC currents are applied to the two conductors corresponding to the initial intersection C1, and as time passes, these currents are successively applied to the respective intersections Ci located on the axis of symmetry while microwave power is simultaneously applied to the waveguide.

[0061] During step C0, the DC current applied to each conductor WIdi varies between 0 and the maximum value Idimax ( Figure 3 The two traps T1 and T2 are kept at a height h throughout the sequence A0, B0 and C0.

[0062] The two traps T1 and T2 move in the direction of the "on" of the intersections: from intersection C1 to intersection Cn. The return trip is achieved by reversing the microwave frequency and successively switching on a DC current in the wires corresponding to each intersection, passing through the wire from Cn to C1.

[0063] The trap is thus caused to travel along a closed path 16 .

[0064] The closed path 16 of the atom then has area A, and hence the atomic wave function is:

[0065]

[0066] in:

[0067]

[0068] In step D0, the internal states |a> and |b> are recombined by applying a second π / 2 pulse to the ultracold atoms, which transfers the phase difference to the populations of the two atomic energy levels:

[0069]

[0070]

[0071] where ω is the angular frequency of the π / 2 pulse.

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

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

[0074] Next, in step E0, the atomic density in at least one internal state selected from at least |a> and |b> is measured. This measurement can be performed, for example, by using laser absorption to detect the resonance between the angular frequency specific to the internal state and the angular frequency of the laser. The Sagnac phase shift of the ultracold atoms is then determined, and the rotation speed of the sensor about the Z axis is calculated.

[0075] The measurement of at least one populated atom in one of the states |a> or |b> allows, for example, the determination of the Sagnac phase shift for the internal state |a> using equation (1) and then the determination of the rotation speed Ω using equation (6) z .

[0076] The trap can be made to travel along this path N times before measuring the Sagnac phase shift, and thus a phase shift that will likely be N times higher can be measured.

[0077] To implement the above method, it is allowed to measure the rotation speed Ω zUltracold atomic sensors include:

[0078] The atomic chip 1 as described above has a waveguide and a conductive line,

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

[0080] a generator for generating a uniform magnetic field Bc,

[0081] at least one DC current or voltage generator suitable for controlling the current in the conductive wire and at least one microwave current or voltage generator connected to the waveguide,

[0082] The detection system, which is typically used to detect light intensity, is suitable for measuring at least one population of ultracold atoms in an internal state, which measurement allows determining the Sagnac phase shift and the rotation speed Ωz.

[0083] The gyroscopic sensor also includes at least one processor that controls the operation and implementation of the sensor, such as in a predetermined sequence (e.g. Figure 3 The sequence in part b) drives the signals applied to the wires and microwave waveguides.

[0084] like Figure 4 As shown, because the two clouds follow straight outward and return paths, they use the same Figure 3 The same logic and form, so the accelerometer sensor exhibits a "simplified" operation compared to the gyroscope. Here a single wire WId is required to define the intersection C.

[0085] Figure 4 Part a) schematically shows each ultracold atomic cloud at a characteristic time t 1 to 3 Part b) shows the sequence of the respective currents applied to the conductive wire, the sequence of the powers applied to the waveguide, and the sequence of the frequencies applied to the waveguide at times corresponding to those of part a). Figure 4 In the presented sequence, the current I flowing through WIz z (not shown) is static and of constant value. The current applied to WId is also constant throughout the sequence.

[0086] Initially in t 1 At , no power is applied to the waveguide and the cloud is trapped above point C.

[0087] In t 1 With t' 1 The microwave power injected into waveguides CPW1 and CPW2 gradually increases from 0 to its maximum value, and then this value is t' passing through T2. 1and t' 2 The maximum value is maintained between and remains constant. a sent to the waveguide CPW2, and the angular frequency ω b sent to the waveguide CPW1, which allows two clouds of different internal states to be on either side of the symmetry axis Y with respect to t 2 The schematically shown positions are separated, which can be very small for the entire duration t' 2 -t' 1 The inside remains unchanged.

[0088] In t' 2 With t 3 The microwave power in the waveguide is gradually switched off. The two traps T1 and T2 move until they merge into a single trap located at the starting point schematically shown for t1.

[0089] For both types of sensors, and in general for any inertial sensor, considering Equations 3, 4, and 5, it can be seen that the phase has an effect on the two “decoration” energy levels E′ b -E' a The energy difference between the two atomic energy levels is sensitive, which is expressed as a -E b The function of the energy difference between:

[0090] For the state |a>, the energy changes from E a Change to E' a ,in:

[0091]

[0092] For the state |b>, the energy changes from Eb to E' b ,in:

[0093]

[0094] Among them, Ω a (Respectively, Ω b ) is the Rabi frequency associated with the decoration of the state |a> (respectively, |b>). To simplify notation, all coupling factors are classified in terms of the Rabi frequency, which is a function of the square root of the microwave power (amplitude of the microwave field) applied to the waveguide.

[0095] Δ a (Respectively, Δ b ) is the frequency ω of the microwave field decorating the state |a> (respectively, the state |b>) a (Respectively, ω b ) and the transition frequency ω of the considered decorated state |a> (respectively, |b>) 0a(Respectively, ω b0 ) between the frequency ω 0a and ω 0b is the frequency of the atomic transitions used to implement the interferometer.

[0096] The following results are obtained:

[0097] Δ a =ω a -ω 0a (9)

[0098] Δ b =ω b -ω 0b (10)

[0099] ω hfs represents the hyperfine frequency of the transition used.

[0100] An example of a transition used is the σ transition between two hyperfine levels F=1 and F=2 in rubidium 87, as Figure 5 As shown, each energy level has Zeeman sublevels separated by the same amplitude αB, where, for rubidium 87, α = 700kHz / G, and B is the DC magnetic field to which the atom is subjected. The following results are obtained:

[0101] ω 0a =ω hfs -αB (11)

[0102] ω 0b =ω hfs +αB (12)

[0103] The energy difference between |a> and |b>, to which the Ramsey interferometer is sensitive, is then expressed as:

[0104]

[0105] in:

[0106]

[0107] The term ΔE is related to the population oscillation given above (Equations 5 and 6), and therefore to the phase, and is a source of interferometer noise.

[0108] In practice, to ensure the interferometer works (to ensure symmetry), it is necessary to choose and Δ a =-Δ b(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 cancelling the previous term and thus eliminating its influence. However, in practice, the cancellation of this term ΔE is not perfect and there are difficulties. From an experimental point of view, this is even more problematic:

[0109] and and The proportional powers of the two microwave fields exhibit noise, and the equalization of the two Rabi frequencies is never perfect;

[0110] Two mismatch terms Δ a and Δ b involves the value of the DC magnetic field that traps the atom, which also contains noise (see equations 9 to 12):

[0111] Δ a =ω a -ω hfs -αB (15)

[0112] Δ b =ω b -ω hfs +αB (16)

[0113] As can be seen from the above equation, the interferometer noise originates from the DC magnetic field B, including the uniform magnetic field Bc applied to the atoms and the DC magnetic field from the conductive wire (term Δ), on the one hand, and from the microwave field (term Ω) on the other hand.

[0114] The current solution to reduce the noise on the DC magnetic field is to use a current source that is as stable as possible.The current solution for reducing the noise on the amplitude of the microwave field is to create a feedback loop of the amplitude of the microwave field in order to stabilize it as much as possible.

[0115] Both of these solutions are unsatisfactory because, although they reduce the noise level, the noise still remains within the sensor's error budget.

[0116] An object of the present invention is to remedy the above mentioned drawbacks by proposing an ultracold atom inertial sensor with an attenuated noise level. Summary of the invention

[0117] A subject of the present invention is an ultracold atomic sensor comprising:

[0118] The atom chip, which is placed in a vacuum chamber, includes an XY plane, called a measurement plane, perpendicular to the Z axis and includes:

[0119] a first waveguide and a second waveguide adapted to propagate microwaves and a DC current, at least a first conductive line and a second conductive line, respective projections of which are tangent at a point defining a first intersection,

[0120] an atom generating device configured to generate an ultracold atom cloud near the XY plane of the atom chip,

[0121] a generator for generating a uniform magnetic field,

[0122] A power supply device, the power supply device comprising at least one microwave generator and at least one DC current generator, the power supply device being configured to:

[0123] applying a microwave signal and a DC current referred to as a CMW current to the first and second waveguides,

[0124] applying a DC current called CWI current to the conductive wire,

[0125] The waveguide, the conductive wire and the power supply device are configured to spatially separate a first ultracold atom cloud in a first internal state from a second ultracold atom cloud in a second internal state by changing the energy of the ultracold atoms, thereby forming a first ultracold atom trap and a second ultracold atom trap, respectively, when implementing the sensor, and move the traps along a linear or closed path contained in a plane perpendicular to Z,

[0126] the power supply device being configured to apply the microwave signal to the first waveguide and the second waveguide and spatially separate the two traps, thereby initiating the spatial separation, and then apply the CMW current instead of the microwave signal, thereby maintaining the spatial separation,

[0127] The sensor further comprises a detection system adapted to measure at least one population of said ultracold atoms in said internal state.

[0128] According to one embodiment, the sensor is an accelerometer and the path followed by the two traps is linear.

[0129] According to another embodiment, the sensor is a gyroscope comprising a plurality of second conductive lines defining a plurality of intersection points, the path along which the two traps follow is closed, and the first trap and the second trap travel along the path in opposite directions.

[0130] According to one embodiment, each waveguide comprises three lines: two outer ground lines and one inner signal line, into which the CMW current is injected.

[0131] According to one embodiment, the power supply device further comprises at least one three-port bias tee connected to the at least one microwave generator and the at least one DC current generator and configured to apply the microwave signal and the CMW current to the waveguide.

[0132] According to another aspect, the invention relates to a method for measuring inertial parameters using an ultracold atomic sensor, the ultracold atomic sensor comprising an atomic chip placed in a vacuum chamber, the atomic chip comprising an XY plane perpendicular to the Z axis, referred to as the measurement plane, the atomic chip comprising:

[0133] a first waveguide and a second waveguide, the first waveguide and the second waveguide being suitable for propagating microwaves and DC current,

[0134] at least a first conductive line (W1) and a second conductive line, respective projections of the first conductive line (W1) and the second conductive line being tangent at a point defining a first intersection point,

[0135] The method comprises the following steps:

[0136] A. generating an ultracold atomic cloud in the vicinity of the XY plane of the atom chip, comprising: a phase of distributing the atoms, a phase of cooling the atoms, a phase of initializing the atoms to at least a first internal state, and a phase of trapping the ultracold atomic cloud in a local potential minimum at a controlled height from the XY plane, the trapping being performed by passing a DC current through a first conductive wire and a second conductive wire,

[0137] B. initializing the first internal state and the second internal state of the ultracold atom by coherently superimposing the ultracold atom between the first internal state and the second internal state in a π / 2 pulse manner,

[0138] C spatially separating a first ultracold atomic cloud in a first internal state from a second ultracold atomic cloud in a second internal state by varying the energy of the ultracold atoms, thereby forming a first ultracold atom trap and a second ultracold atom trap, respectively, and moving the traps along a linear or closed path contained in a plane perpendicular to Z and initialized at a first intersection point,

[0139] The steps of separating and moving the ultracold atoms are performed by applying a uniform magnetic field to the ultracold atoms, applying a DC current called CWI current to the conductive wire, and applying a microwave signal (I MW ) and a DC current called CMW current,

[0140] The separation step includes: an initialization sub-step, the initialization sub-step includes: applying the microwave signal to the waveguide; and a maintenance sub-step, the maintenance sub-step includes: applying the CMW current instead of the microwave signal,

[0141] D. recombining the first internal state and the second internal state by applying a second π / 2 pulse to the ultracold atoms, and E. measuring the ultracold atoms in at least one population of at least one of the internal states.

[0142] According to one embodiment, the separation step includes a transient sub-step between the initialization sub-step and the maintenance sub-step, the transient sub-step including: turning off the microwave signal and turning on the CMW current.

[0143] According to a first embodiment, during the transient sub-step, the switching off of the microwave signal occurs simultaneously with the switching on of the CMW current. According to one embodiment, the transient sub-step has a duration of less than 100 μs.

[0144] According to a second embodiment, during the transient sub-step, said switching off of the microwave signal occurs before or after said switching on of the CMW current.

[0145] According to one embodiment, during the moving step, the two clouds are spatially recombined by gradually switching off the CMW current.

[0146] According to one embodiment, during the moving step, the two clouds are spatially recombined by switching off the CMW current and by simultaneously switching the microwave signal back on, and then by gradually switching off the microwave signal.

[0147] The following description presents several exemplary embodiments of the device of the invention: these examples do not limit the scope of the invention. These exemplary embodiments contain not only the features essential to the invention but also additional features associated with the embodiment in question.

[0148] The invention will be better understood, and other features, objects and advantages thereof will become apparent from the following detailed description given with reference to the accompanying drawings, which are given by way of non-limiting examples, and in which:

[0149] Already cited Figure 1 An example of the topology of an atom chip including conductive wires and microwave waveguides for moving a magnetic trap along a closed path is shown.

[0150] Already cited Figure 2 The waveguides and wires of the atom chip and the geometry of the traps T1 and T2 are shown.

[0151] Already cited Figure 3 In its lower part an example is shown in which, in the case of a gyroscopic sensor, various signals are applied to wires and waveguides according to the prior art to cause two traps T1 and T2 (and therefore, two clouds of trapped atoms) to travel along a closed path, and in its upper part the positions of the two clouds corresponding to selected times are shown.

[0152] Already cited Figure 4 In its lower part an example is shown in which, in the case of an accelerometer sensor, various signals are applied to a wire and a waveguide according to the prior art to cause two traps T1 and T2 (and therefore, two clouds of trapped atoms) to travel along a linear path, and in its upper part the positions of the two clouds corresponding to a selected time are shown.

[0153] Already cited Figure 5 The σ transition between two hyperfine levels F=1 and F=2 of rubidium 87 used in cold atom inertial sensors is shown along with the individual frequencies of interest.

[0154] Figure 6 shows the DC magnetic potential V generated by applying a DC current to the waveguide DC-MW .

[0155] Figure 7 An ultracold atomic sensor 10 according to the present invention is shown.

[0156] Figure 8 A block diagram of an embodiment of a sensor according to the present invention is shown, in which a three-port bias device is used to superimpose a microwave current and a DC current in a signal line of a waveguide.

[0157] Fig. 9 An embodiment is shown in which an additional three-port biasing device TPol add It has been integrated at the output of the waveguide and before the terminal TMW.

[0158] Fig.10 In its left-hand part a timing diagram of the application of various signals when implementing an accelerometer sensor according to a first spatial recombination variant is shown, and in its right-hand part the movement of two clouds at selected times is shown.

[0159] Fig.11 In its left-hand part a timing diagram of the application of various signals when implementing an accelerometer sensor according to the second spatial recombination variant is shown, and in its right-hand part the movement of two clouds at selected times is shown.

[0160] Fig.12A timing diagram for implementing the application of various signals of a gyroscope sensor according to a first spatial recombination variation is shown.

[0161] Fig.13 shows the relationship between the two clouds Fig.12 The movement at the selected time associated with the signal in .

[0162] Fig.14 A timing diagram for implementing the application of various signals of a gyro sensor according to a second spatial recombination variation is shown.

[0163] Fig.15 shows the relationship between the two clouds Fig.14 The movement at the selected time associated with the signal in . DETAILED DESCRIPTION

[0164] Ramsey Time T R Is divided into two times: time T R off , during which no microwave signal is applied to the waveguide; and time T R on , during which a microwave signal is applied to the waveguide:

[0165]

[0166] The noise N accumulated on the phase of the interferometer is given by:

[0167]

[0168] Among them, σ MW The interferometer is composed of microwave signals (only at T on The noise generated during the period is integrated into the phase noise, and σ DC is the noise caused only by the DC magnetic field (present in the entire sequence).

[0169] σ MW and σ DC The unit is Hz.

[0170] Starting from Equation 14, assume that there is an error or noise δB on the DC magnetic field and that Ω a and Ω b There is error or noise δΩ a and δΩ b , the difference of the two shifts ΔE can be rewritten as follows:

[0171]

[0172] Noise or error to ω a and ω bThe effects of have been neglected because their influence is negligible in the experiment.

[0173] Term σ MW ,in:

[0174]

[0175] Then to form noise on the phase of the interferometer, it is necessary to add the noise to the other terms contained in the phase of the interferometer, that is to say to the energy difference E b -E a In. For simplicity, collision displacement, detection noise, Dicke Effect, etc. are ignored, and only the term corresponding to the energy difference in the presence of a DC magnetic field is retained. The noise on this term (microwave field off) only involves the noise on the DC magnetic field δB and has the form (for example, see the publication "Magnetically trapped atoms for compact atomic clocks" P.Rosenbusch, Appl.Phys.B (2009), 95, p 227-235):

[0176] σ DC =2b(BB m )δB (19)

[0177] To give the order of magnitude of various noises, the example of Rubidium 87 gives:

[0178] b=431Hz / G 2 ,

[0179] The DC magnetic field is close to B m =3,23G.

[0180] Δ a =-Δ b =200kHz

[0181] Ω a =50kHz and Ω b =50kHz

[0182] δB=1mG

[0183] BB m =100mG

[0184] δΩ a / Ω a =δΩ b / Ω b =10 -3

[0185] This gives:

[0186]

[0187] as well as

[0188] 2b(BB m )δB≈100mHz

[0189] It can be seen that the presence of two microwave fields significantly increases the noise level. This is the first factor that must be reduced.

[0190] The idea of ​​the invention is to reduce the noise level by replacing the microwave field (after the two states have been separated) with a DC current to create two magnetic traps, each containing one state.

[0191] Therefore, during the entire phase in which the two states |a> and |b> remain separated, the two microwave fields used for decoration are switched off. During this phase of the interferometer, the phase is no longer controlled by the noise term σ MW For DC magnetic field δB or microwave field δΩ a and δΩ b The amplitude of the noise is sensitive, but the term σ DC It is still sensitive to δB.

[0192] like Figure 3 and Figure 4 As shown in the figure from t1 to t2, a microwave signal (typically, a microwave current I MW ) to separate the two clouds (initializing the spatial separation). This step of gradually switching on the waveguides is similar to that already described in the prior art.

[0193] Next, according to the present invention, the current I MW is cut off, and the DC current I DC-MW are applied alternately to the microwave waveguides CPW1 and CPW2. Before and during the change of the type of current applied to the waveguides, a DC current is applied to the conductive wires.

[0194] The initial separation of the two states |a> and |b> of the interferometer using microwave current is very important because microwave current makes it possible to create a selective trap of the internal state, unlike DC current. It is very important to create a selective trap of the internal state at the beginning of the separation, otherwise the two states will remain mixed after the separation.

[0195] exist Figure 6 The DC current I DC-MW applied to the waveguide to generate a DC magnetic potential V DC-MW .like Figure 2 As shown in curves c and e in a), the magnetic potential V DC-MW replaced by the microwave current I MWThe DC magnetic potential generated by the microwave field. DC-MW This allows the cold atoms to continue to be trapped and the two clouds to be kept as spatially separated as possible during the remainder of the Ramsey sequence. Figure 2 Curve a) in FIG. 5 shows the DC magnetic potential generated by applying a DC current in two conducting wires (beginning of the sequence, before the cloud separates and therefore before the microwave current is switched on).

[0196] Figure 7 An ultracold atomic sensor 10 according to the present invention is shown. The sensor 10 includes an atomic chip ACh placed in a vacuum chamber, which has an XY plane called a measurement plane perpendicular to the Z axis. The chip ACh has a first waveguide CPW1 and a second waveguide CPWX2 suitable for propagating microwaves and DC currents, and at least a first conductive wire WIz and a second conductive wire WId, and the corresponding projections of the first conductive wire WIz and the second conductive wire WId are tangent at a point defining a first intersection C1. The two waveguides are arranged symmetrically with respect to the Y axis; typically, but not limited to: they are parallel to each other. The sensor also includes: an atom generation device ACG, the atom generation device ACG is configured to generate an ultracold atomic cloud CL near the XY plane of the atomic chip; and a generator GB, the generator GB is used to generate a uniform magnetic field Bc.

[0197] The sensor 10 according to the invention also comprises a power supply device PSD comprising at least one microwave generator GMW and at least one DC current generator GDC. There can be one microwave generator per waveguide, or one generator for two waveguides. Similarly, there can be a single common generator GDC for all conductors and waveguides, or a plurality of generators.

[0198] The power supply device PSD is configured to apply a microwave signal (typically, a current I MW ) and the DC current I called CMW current DC-MW , and applies a DC current I called CWI current to the conductor wire DC-WI .

[0199] The waveguide, the conductive wire and the power supply device are configured such that, when the sensor is implemented, i) a first ultracold atomic cloud CL1 in a first internal state |a> is spatially separated from a second ultracold atomic cloud CL2 in a second internal state |b> by changing the energy of the atoms, thereby forming a first ultracold atomic trap T1 and a second trap T2, respectively, and ii) and the traps (T1, T2) are moved along a linear or closed path contained in a plane perpendicular to Z.

[0200] According to the present invention, the power supply device PSD is configured to apply a microwave signal I to the first waveguide and the second waveguide.MW To spatially separate the two traps, spatial separation is initiated, and then a CMW current I is applied DC-MW Instead of microwave (current) signal I MW To maintain spatial separation,

[0201] Finally, the sensor 10 according to the invention comprises a detection system SDET suitable for measuring at least one population of said ultracold atoms in said internal state.

[0202] The cold atom sensor has the same structure as that described in the prior art, except that a waveguide is capable of propagating a DC current and a power supply device makes it possible to apply a DC current to the waveguide.

[0203] By applying a DC current to the waveguide during most of the Ramsey sequence instead of applying a microwave signal, the The noise component (Formula 17) caused by This is significantly reduced by the reduction in . Therefore, this reduces the amount of noise accumulated on the phase of the interferometer. It has been shown above that this noise component is a factor limiting the measurement, and any gain on this noise component directly translates into a gain in measurement sensitivity.

[0204] like Figure 4 As shown in a), the first type of sensor according to the invention is an accelerometer and the path followed by the two traps is linear. Two wires IWz and Iwd are required to be tangent at C1 to define the start / end point of the path and the movement here is consistent with the spatial separation.

[0205] The second type of sensor is the gyroscope. Then, as Figure 1 As shown, the atomic chip includes a plurality of second conductive wires WIdi (Wld1, Wld2, Wld3) defining a plurality of intersections Ci (C1, C2, C3), and the path along which the two traps are located is closed, and the two traps travel along the path in opposite directions (e.g. Figure 3 as described in a) above.

[0206] As described in the above-mentioned documents US 15 / 778605, US 17 / 924340, US 17 / 832615 and US 17 / 832616, the gyroscope according to the invention is compatible with any atomic chip geometry comprising two microwave waveguides and an electrically conductive line.

[0207] When implementing the sensor according to the invention, the two clouds are separated by the microwave signal and once the clouds have been separated the separation is maintained by the CMW DC current applied to the waveguide.The microwave field can be switched off and replaced by two DC currents in three different ways.

[0208] In a first variant, the power supply device PSD is configured so that the switching off of the microwave signal occurs simultaneously with the switching on of the DC current. This mode allows the microwave current to be switched off quickly and therefore makes it possible to reduce (see Eq. (17)), and thus reduce the MW The accumulation of noise caused by

[0209] According to the first embodiment, the time t at which the switch-off and switch-on occur simultaneously trans Very fast, meaning that the rising or falling edge is very fast compared to the frequency of the magnetic trap. Typically, t trans Must be less than or equal to 100μs.

[0210] According to a second embodiment, the simultaneous switching off and on occurs with two slow ramps (a slowly falling RF ramp and a simultaneously rising DC ramp), which means that the ramps must be slow compared to the frequency of the magnetic trap. Typically, t trans Must be at least 10ms.

[0211] According to the third embodiment, at t trans Between these two values ​​of , the ramp has a complex shape in order to form an adiabatic shortcut.

[0212] In a second variant, the power supply device PSD is configured so that the switching off of the microwave signal occurs before the switching on of the CMW current. This mode allows switching off the microwave current even faster than the first mode, but makes the use of the microwave current I MW The pitfalls of using a DC current I DC-MW The time during which nothing is applied is called t int This time should be less than the frequency of the trap ω p The frequency of the trap indicates its "rigidity". The shape of the magnetic potential forming the trap is approximately parabolic near the minimum. Let r be the minimum value of the potential V 0 distance, and the electric potential can be written as:

[0213]

[0214] It is therefore necessary to:

[0215]

[0216] In a third variant, the power supply device PSD is configured so that the microwave signal is switched off after the CMW current is switched on. This mode simplifies the use of the microwave current I MW The pitfalls of using a DC current I DC-MW transmission between traps.

[0217] According to one embodiment, each waveguide comprises three lines: two external ground lines and one internal signal line, and a DC current CMW is injected into the signal line (coplanar waveguide). However, the sensor 10 according to the invention may integrate any type of microwave waveguide compatible with the application of DC current, such as a microstrip.

[0218] According to one embodiment, the superposition of the microwave current and the DC current in the signal line of the waveguide is performed by a three-port bias device. Figure 8 As shown in the block diagram of FIG. 1 , the power supply device PSD further comprises at least one three-port bias device TPol, which is connected to the microwave generator and the DC current generator and is configured to apply a microwave signal (microwave current I MW ) and CMW current (DC current I DC-MW ). A three-port bias device is a component including two inputs and one output, one input for DC current, another input for oscillating current, and one output for superimposing DC current and oscillating current. The output can also be used as an input for superimposing DC current and oscillating current, and two inputs are two outputs, one giving DC current and the other giving oscillating current. Figure 8 As shown, in order to avoid unnecessary reflection of the microwave signal that has passed through the microwave waveguide, a microwave terminal TMW is integrated at the output of the atom chip.

[0219] Preferably, if Fig. 9 As shown in the block diagram, in order to ensure good separation between the DC current and the microwave signal at the output of the microwave waveguide, an additional three-port biasing device T-Pol is integrated at the output of the waveguide and before the terminal TMW. add .

[0220] According to another aspect, the present invention relates to a method for measuring inertial parameters using the ultracold atom sensor according to the present invention as described above. The method comprises a first step A: generating an ultracold atom cloud CL near the XY plane of the atom chip, comprising: a phase of allocating atoms, a phase of cooling atoms, a phase of initializing atoms to at least a first internal state, and a phase of trapping the ultracold atom cloud in a local potential minimum at a controlled height from the measurement XY plane, the trapping being performed by passing a DC current through a first conductive wire and a second conductive wire. This step is similar to step A0 described in the prior art.

[0221] In step B, the first internal state |a> and the second internal state |a> of the ultracold atoms are initialized by coherently superimposing the ultracold atoms between the first internal state and the second internal state in a π / 2 pulse. This step is similar to step B0 described in the prior art.

[0222] In step C, a first ultracold atomic cloud in a first internal state is spatially separated from a second ultracold atomic cloud in a second internal state, thereby forming a first ultracold atom trap T1 and a second ultracold atom trap T2, respectively. The separation is performed by changing the energy of the ultracold atoms. The traps (T1, T2) are then moved along a linear path (accelerometer) or a closed path (gyroscope) contained in a plane perpendicular to Z and activated at the first intersection.

[0223] Step C of separating and moving the ultracold atoms is performed by applying the following in a predetermined sequence:

[0224] Apply a uniform magnetic field Bc to the ultracold atoms.

[0225] A DC current called CWI current is applied to the guide wire.

[0226] Apply a microwave signal (typically, a microwave current I MW ) and DC current which is called CMW current.

[0227] In the method according to the invention, the separation step comprises an initialization sub-step Cinit comprising applying a microwave signal to the waveguide and a maintenance sub-step Cmaint comprising applying a CMW current instead of a microwave signal. The originality of the method according to the invention lies in the separation and movement step C, and in particular in the step Cmaint.

[0228] In step D, by applying a second π / 2 pulse to the ultracold atoms, the first internal state and the second internal state are recombined (once the travel along the path has been completed, the two clouds are then spatially merged again), thus completing the Ramsey sequence initialized with the first π / 2 pulse. This step is similar to step D0 described in the prior art.

[0229] Finally, in step E, at least one population of ultracold atoms in at least one of said internal states is measured, from which the value of the inertial parameter (acceleration, velocity and / or rotation angle relative to a given axis) can be derived. This step is similar to step E0 described in the prior art.

[0230] In the method according to the invention, the usual sequence for separating and recombining the two states |a> and |b> is altered.

[0231] The usual sequence includes:

[0232] gradually switching on two microwave fields, each located in a waveguide (CPW1 and CPW2) of the chip, making it possible to separate the two states |a> and |b>;

[0233] Maintaining two microwave fields in the waveguides CPW1 and CPW2, thereby maintaining two separate states |a> and |b> (with this separation of microwave fields in Figure 2 As shown in a) in FIG.

[0234] The two microwave fields are gradually switched off in order to spatially recombine the two states |a> and |b>. This spatial recombination is different from the recombination in step D. The spatial recombination occurs only once before step D for the accelerometer ( Figure 4 The time t in a) 3 ), and twice when traveling along a closed path for the gyroscope ( Figure 3 The time t in a) 5 and t 9 ).

[0235] The sequence according to the present invention is described below by taking the example of a three-line coplanar waveguide.

[0236] gradually switching on two microwave fields, each located in a waveguide of the chip, thus making it possible to separate the two states |a> and |b>;

[0237] Once the states have been separated, the two microwave fields are preferably switched off quickly and the DC currents in the two signal lines of the two microwave waveguides are preferably switched on simultaneously and quickly. This makes it possible to create two separate DC magnetic traps, each containing one of the two internal states |a> and |b> (the two traps are in Figure 6 )

[0238] According to two variants, the two states are spatially recombined in a move step:

[0239] According to a first variant, by gradually switching off the two DC currents flowing through the two signal lines of the two microwave waveguides;

[0240] According to a second variant, the two states |a> and |b> are recombined by preferably rapidly switching off the two DC currents of the two signal lines through the two microwave waveguides and preferably simultaneously by rapidly switching the two microwave fields back on and then by gradually switching off the two microwave fields.

[0241] Preferably, the separation step of the method according to the present invention comprises: a transient sub-step Ctrans located between the initialization sub-step Cinit and the maintenance sub-step Cmaint, the transient sub-step Ctrans comprising: switching off the microwave signal and switching on the CMW current.

[0242] According to the three variants described above, the microwave field can be switched off and replaced with two DC currents:

[0243] First variant: During the transient sub-step, the switching off of the microwave signal occurs simultaneously with the switching on of the CMW current. Preferably, the transient sub-step has a duration of less than 100 μs.

[0244] Second variant: During the transient sub-step, the switching off of the microwave signal occurs before the switching on of the CMW current.

[0245] Third variation: During the transient sub-step, the MW signal is switched off after the CMW current is switched on.

[0246] The method according to the invention will now be explained using the example of a timing diagram.

[0247] The following symbols are used:

[0248] P1 MW and P2 MW denote the power of microwave signals applied to waveguides CPW1 and CPW2, respectively,

[0249] ω a represents the angular frequency sent to the waveguide CPW2, and ω b represents the angular frequency sent to the waveguide CPW1,

[0250] Iz represents the intensity of the DC current applied to the first conductive wire WIz,

[0251] Id, Id 1 、Id 2 、Id 3 represents the intensity of a DC current called CWI current applied to the second conductive wire or wires,

[0252] I1 DC-MW and I2 DC-MW denotes the intensity of a DC current referred to as a CMW current applied to the waveguides CPW1 and CPW2, respectively.

[0253] Fig.10 a) and Fig.11 a) shows a timing diagram of the application of various signals when, during a separation / movement step C, the accelerometer sensor according to the first spatial recombination variant and the second spatial recombination variant, respectively, is implemented. Fig.10 b) and Fig.11 b) in Figure 2 shows the movement of two clouds at selected times. These figures also show a first variant of the switch-off / switch-on sequencing, that is, switching off the MW power while switching on the CMW current.

[0254] Throughout the sequence, the angular frequency ω a is applied to CPW2, and the angular frequency ω b is applied to CPW1 (same as above, Figure 4 a)).

[0255] exist Fig.10 In t 1 With t 2 Microwave power is applied to the waveguide. 2 At t, the two clouds CL1 and CL2 are separated. Next, at t 2 With t 3 The MW signal is gradually turned off, and the DC current I1 DC-MW and I2 DC-MW At the same time. 3 With t 4 These currents are maintained for measurement. 4 With t 5 Between, current I1 DC-MW and I2 DC-MW Gradually decreases, thereby spatially recombining the two clouds (the first spatial recombination variant). 5 At this point, the two clouds recombine in space.

[0256] According to the first embodiment, the currents Id and Iz are kept constant. Fig.10 In the second embodiment shown in a) in FIG. 1 , when the current I1 is applied DC-MW and I2 DC-MW , the current Iz decreases slightly in order to increase the potential barrier between the two states ( Figure 6 ). When these currents are no longer applied, Iz increases slightly again. According to this second embodiment, Id preferably varies like Iz.

[0257] exist Fig.11 until time t 4 So far, the beginning of the sequence is the same. 4 With t 5 ', the microwave signal is turned back on while the DC current is turned off, and the clouds remain separated. 5 'With t 6 ', spatial recombination is performed by gradually turning off the MW signal (second spatial recombination variant). 6 ', the two clouds recombine in space.

[0258] Fig.12 and Fig.14 A timing diagram is shown for implementing the application of various signals of the gyroscopic sensor during the separation / movement step C according to a first spatial recombination variant and a second spatial recombination variant, respectively. Fig.13 and Fig.15The movement of two clouds at selected times is shown. These figures also show a first variant of the switch-off / switch-on sequencing, that is to say switching off the MW power while switching on the CMW current.

[0259] exist Fig.12 and Fig.13 In the two waveguides (t 1 With t 2 MW power is applied between the two clouds to separate them. For this purpose, 073701CN CJO / VBO

[0260] DC currents Id1 and Idz are applied to WIz and WId1, respectively. Next, at t 2 With t 3 The MW signal uses a DC current I1 DC-MW and I2 DC-MW Replace. 3 With t 4 By turning off the current Id1 and turning on the current Id2 in WId2, the two clouds move from the first intersection C1 to the second intersection C2 along Y. 4 With t 5 By turning off the current Id2 and turning on the current Id3 in WId3, the two clouds move from the second intersection C2 to the third intersection C3 along Y. Next, at t 5 With t 6 By shutting off the DC current I1 DC-MW and I2 DC-MW (First spatial recombination variant), at C3 (halfway through the travel along the closed path) a first spatial recombination of the two clouds is performed. 6 At t, the frequency applied to the waveguide is reversed and the second half stroke begins, passing through t 6 With t 7 Applying a MW field to the waveguide separates the two clouds again.

[0261] Here, too, according to Fig.12 In one embodiment shown, when current I1 is applied DC-MW and I2 DC-MW During this period, the current Iz decreases slightly and increases again when they are turned off, and the currents Id1 and Id3 follow the change of Iz. According to another embodiment, the currents Iz and Id1, Id2 and Id3 do not have two plateaus (see, for example Figure 3 changes in Idi).

[0262] exist Fig.14 and Fig.15 until t 5 So far, the sequence is the same. 5 With t6 ', the DC current is turned off at the same time as the microwave signal is turned back on, and the cloud remains separated. 6 'With t 7 ', spatial recombination is performed by gradually turning off the MW signal (second spatial recombination variant). 11 'With t 12 ', where the DC current is turned off and the microwave signal is turned on at the same time, and then at t 12 'With t 13 ', spatial recombination is performed by gradually switching off the MW signal.

Claims

1. An ultracold atomic sensor (10), comprising: Atom chip (ACh), which is placed in a vacuum chamber, includes an XY plane called a measurement plane perpendicular to the Z axis, and includes: a first waveguide (CPWX1) and a second waveguide (CPWX2), wherein the first waveguide (CPWX1) and the second waveguide (CPWX2) are suitable for propagating microwaves and DC currents, at least a first conductive line (WIz) and a second conductive line (WId, WId1), respective projections of said first conductive line (WIz) and said second conductive line (WId, WId1) being tangent at a point defining a first intersection point (C1), an atom generator (ACG), the atom generator (ACG) being configured to generate an ultracold atom cloud near the XY plane of the atom chip, a generator (GB) for generating a uniform magnetic field (Bc), A power supply device (PSD), the power supply device (PSD) comprising at least one microwave generator (GMW) and at least one DC current generator (GDC), the power supply device being configured to: Applying a microwave signal to the first waveguide and the second waveguide (I MW ) and the DC current known as CMW current (I DC-MW ), applying a DC current called CWI current to the conductive wire, The waveguide, the conductive line and the power supply device are configured to: when the sensor is implemented, a first ultracold atom cloud (CL1) in a first internal state is spatially separated from a second ultracold atom cloud (CL2) in a second internal state by changing the energy of the ultracold atoms, thereby forming a first ultracold atom trap (T1) and a second ultracold atom trap (T2), respectively, and the traps (T1, T2) are moved along a linear or closed path contained in a plane perpendicular to Z, the power supply device being configured to apply the microwave signal to the first waveguide and the second waveguide and spatially separate the two traps, thereby initiating the spatial separation, and then apply the CMW current instead of the microwave signal, thereby maintaining the spatial separation, The sensor further comprises a detection system (SDET) adapted to measure at least one population of the ultracold atoms in the internal state.

2. The sensor according to one of the preceding claims, the sensor being an accelerometer, the path along which the two traps follow being linear.

3. A sensor according to any one of the preceding claims, the sensor being a gyroscope comprising a plurality of second conductive lines (WIdi) defining a plurality of intersection points (Ci), the path along which the two traps follow being closed, and the first trap and the second trap travelling along the path in opposite directions.

4. The sensor according to one of the preceding claims, wherein Each waveguide comprises three lines: two outer ground lines and one inner signal line into which the CMW current is injected.

5. The sensor according to one of the preceding claims, wherein The power supply device further includes at least one three-port bias device connected to the at least one microwave generator and the at least one DC current generator and configured to apply the microwave signal and the CMW current to the waveguide.

6. A method for measuring inertial parameters using an ultracold atomic sensor, the ultracold atomic sensor comprising an atom chip (ACh) placed in a vacuum chamber, the atom chip (ACh) comprising an XY plane perpendicular to the Z axis, referred to as a measurement plane, the atom chip comprising: a first waveguide (CPWX1) and a second waveguide (CPWX2), wherein the first waveguide (CPWX1) and the second waveguide (CPWX2) are suitable for propagating microwaves and DC currents, at least a first conductive line (W1) and a second conductive line (W2), respective projections of the first conductive line (W1) and the second conductive line (W2) being tangent at a point defining a first intersection (O), The method comprises the following steps: A. generating an ultracold atomic cloud in the vicinity of the XY plane of the atom chip, comprising: a phase of distributing the atoms, a phase of cooling the atoms, a phase of initializing the atoms to at least a first internal state, and a phase of trapping the ultracold atomic cloud in a local potential minimum at a controlled height from the XY plane, the trapping being performed by passing a DC current through the first conductive wire and the second conductive wire, B. initializing the first internal state and the second internal state of the ultracold atom by coherently superimposing the ultracold atom between the first internal state and the second internal state in a π / 2 pulse manner, C spatially separates a first ultracold atomic cloud in the first internal state from a second ultracold atomic cloud in the second internal state by changing the energy of the ultracold atoms, thereby forming a first ultracold atom trap (T1) and a second ultracold atom trap (T2), respectively, and moves the traps (T1, T2) along a linear or closed path contained in a plane perpendicular to Z and initialized at the first intersection, The steps of separating and moving the ultracold atoms are performed by applying a uniform magnetic field (Bc) to the ultracold atoms, applying a DC current called CWI current to the conductive wire, and applying a microwave signal (I) to the waveguide in a predetermined sequence. MW ) and a DC current called CMW current, The separation step includes: an initialization sub-step, the initialization sub-step includes: applying the microwave signal to the waveguide; and a maintenance sub-step, the maintenance sub-step includes: applying the CMW current instead of the microwave signal, D. recombining the first internal state and the second internal state by applying a second π / 2 pulse to the ultracold atom, E measuring at least one population of said ultracold atoms in at least one of said internal states.

7. A method according to the preceding claim, wherein: The separation step includes: a transient sub-step located between the initialization sub-step and the maintenance sub-step, and the transient sub-step includes: turning off the microwave signal and turning on the CMW current.

8. A method according to the preceding claim, wherein: During said transient sub-step, said switching off of said microwave signal occurs simultaneously with said switching on of said CMW current.

9. The method according to the preceding claim, wherein: The instantaneous sub-step has a duration of less than 100 μs.

10. The method according to claim 6, wherein: During the transient sub-step, the switching off of the microwave signal occurs before or after the switching on of the CMW current.

11. The method according to one of claims 6 to 10, wherein: During the moving step, the two clouds are spatially recombined by gradually switching off the CMW current.

12. The method according to claim 6, wherein: During the moving step, the two clouds are spatially recombined by switching off the CMW current and by simultaneously switching the microwave signal back on, and then by gradually switching off the microwave signal.

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