CN111781654A - Multi-component cold atom gravity gradient measurement system and method - Google Patents
Multi-component cold atom gravity gradient measurement system and method Download PDFInfo
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Abstract
The invention discloses a multi-component cold atom gravity gradient measurement system which comprises a plurality of atom interference units, wherein each atom interference unit comprises a vacuum cavity, an alkali metal sample source, a cooling laser emitter, an anti-Helmholtz magnetic field coil pair and a photoelectric detector, the vacuum cavity comprises a cold atom preparation cavity and a projection vacuum tube which is vertically arranged and communicated with the cold atom preparation cavity, the projection vacuum tube is divided into an atom detection area and an atom interference area, the photoelectric detector is arranged on the side part of the atom detection area, and the centers of the atom interference areas of every two vacuum cavities are connected through a vacuum tube. The invention can realize the measurement of all gravity gradient components in a collinear mode, thereby obtaining higher noise common mode rejection effect.
Description
Technical Field
The invention relates to the field of quantum sensing based on an atomic interferometer technology, in particular to a multi-component cold atom gravity gradient measurement system and a multi-component cold atom gravity gradient measurement method. The method is suitable for precision survey of the gravitational field.
Technical Field
The gravity field is the inherent property of the earth, can reflect the mass distribution of the earth surface and the underground, and has distinct local characteristics. The gravity high-precision measurement technology can be used for resource exploration, environment monitoring and geophysical research in the civil field, can be used for autonomous navigation of submarines and searching and monitoring of underground and underwater military targets in the national defense field, and has very important significance for national economic development and national safety guarantee. The gravity gradient field is the second order differential of the gravity potential, has higher spatial resolution compared with the gravity field of the first order differential, and meanwhile, the gravity gradiometer can work in a differential measurement mode of a dual-dynamometer, and better environment adaptability is realized through a noise common mode rejection technology, so the gravity gradient measurement technology is an extremely important component in the gravity measurement technology. Existing gravity gradient measurement schemes include rotational accelerometer schemes, superconducting schemes, electrostatic levitation schemes, and cold atom interferometry schemes. The atomic gravity gradiometer based on the cold atomic interference scheme has the advantages of high precision, good long stability, normal temperature solid state device and the like, and is a gravity gradiometer with great application prospect.
The gravity gradient is the spatial rate of change of the gravitational acceleration g and can be mathematically expressed as a 3 x 3 matrix:
such asxyRepresents the spatial rate of change of the y-direction component of the gravitational acceleration in the x-direction. Since the gravity field is a conservative field and has a characteristic of no rotation, the following relationship needs to be satisfied among 9 components:
ij＝ji({i,j}∈{x,y,z})
xx+yy+zz＝0
there are therefore 5 independent components in the gravity gradient matrix.
Up to now, it has only been internationally realized that a single principal diagonal component in a gravity gradient matrix can be measured ((S))xx、yy、zz) (iii) atomic gravity gradiometers (e.g. the documents sensing limits of a Raman analyzer as a gradiometer, F. Sorrentino et al, Physical Review A, Vol. 89, pp. 023607, 2014, and the documents Testing scale with col-atom interferometers, G.W. Biedermann et al, Physical Review A, Vol. 91, pp. 033629, 2015), for the off-diagonal component (for a non-diagonal component: (for a non-diagonal component) ((for a non-diagonal component)xy、xz、yz) The measurement of (A) is not reported. The main reason for this is that, on the one hand, the direction of the measurement of the gravitational acceleration of the atomic gravimeter is determined by the pointing direction of the raman laser beam, and, on the other hand, the ambient vibration noise, which is the main external noise source of the instrument, is transmitted to the measurement result by the phase noise converted into raman laser. In the measurement process of the main diagonal component, the direction to be measured of the gravity acceleration is consistent with the extension direction of the base line, so that a group of Raman laser beams can penetrate through the two atomic gravimeters along a straight line to realize the synchronous measurement of the two atomic gravimeters. For off-diagonal components, the direction of gravity acceleration to be measured is not coincident with the direction of baseline extension, e.g.xzThe direction of gravitational acceleration measurement of (a) is the z-direction and the direction of baseline extension is the x-direction, so these off-diagonal components cannot be directly measured using the above-described method. Recent research groups have proposed passing raman laser light between different atomic gravimeters via reflectors to account for off-diagonal componentsThe method for measuring the Raman laser has a common-mode suppression effect only on the inherent frequency and phase noise of the Raman laser inside the instrument, the external environment vibration noise can still be converted into non-common-mode Raman laser phase noise through a reflector for transmitting the Raman laser between two atomic gravimeters, and meanwhile, the smoothness and the surface type precision of the reflector also become the limiting factors of the measuring signal-to-noise ratio, so although the method can theoretically measure the non-diagonal components in the gradient matrix, in practical situation, if no excellent measuring environment and extremely high vibration isolation level and the processing installation level of the reflector exist, the high-precision measuring result is difficult to obtain, and the method is extremely unfavorable for the instrument which is used as a target.
In conclusion, high-precision gravity gradient measurement has very important significance for national economy and national safety, and a gravity gradient measurement scheme based on an atomic interferometer has wide application prospect, but is limited by a common mode rejection mechanism for environmental vibration noise, so that only the measurement of the main diagonal component of a gradient matrix is internationally realized at present, and a measurement scheme which can realize a higher noise common mode rejection level for the non-diagonal component in the gradient matrix is not very good.
Disclosure of Invention
The invention provides a multi-component cold atom gravity gradient measurement system and a multi-component cold atom gravity gradient measurement method, aiming at the problem that the non-diagonal components of a gravity gradient matrix are difficult to directly measure with a higher noise common mode rejection effect in the prior art. The cold atom gravity gradient measurement system consisting of four atom interference units can measure all tensor components of the gravity gradient field.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a multi-component cold atom gravity gradient measurement system comprises atom interference units, wherein each atom interference unit comprises an atom interference area, the connecting line of the centers of the atom interference areas of every two atom interference units is a measuring line, the extending points of the two ends of each measuring line are respectively provided with a Raman laser emission device and a Raman laser reflection device, the centers of the atom interference areas of the atom interference units are respectively positioned at the top points of a distribution triangle,
each atomic interference unit also comprises a vacuum cavity, an anti-Helmholtz coil pair and three pairs of cooling laser transmitters,
the vacuum cavity comprises a cold atom preparation cavity and a casting vacuum tube which is vertically arranged and communicated with the cold atom preparation cavity,
the three pairs of cooling laser emitters are distributed around the cold atom preparation cavity, the emitting directions of the three pairs of cooling laser emitters all point to the center of the cold atom preparation cavity, and the anti-Helmholtz coil pairs are symmetrically distributed on two sides of the cold atom preparation cavity by taking the emitting directions of one pair of cooling laser emitters as axes.
The atom interference unit also comprises a fourth atom interference unit, the fourth atom interference unit comprises an atom interference area, the center of the atom interference area of the fourth atom interference unit is positioned above the center of the distribution triangle,
the connecting lines of the centers of the atomic interference regions of the fourth atomic interference unit and the centers of the atomic interference regions of the first atomic interference unit, the second atomic interference unit and the third atomic interference unit are measuring lines respectively, a Raman laser emitting device and a Raman laser reflecting device are respectively arranged at the extending positions of two ends of the measuring line where the center of the atomic interference region of the fourth atomic interference unit is positioned,
the fourth atomic interference unit also comprises a vacuum cavity, an anti-Helmholtz coil pair and three pairs of cooling laser transmitters,
in the fourth atomic interference unit: the vacuum cavity comprises a cold atom preparation cavity and a vertically arranged projection vacuum tube communicated with the cold atom preparation cavity, three pairs of cooling laser emitters are distributed around the cold atom preparation cavity, the emitting directions of the three pairs of cooling laser emitters all point to the center of the cold atom preparation cavity, and the anti-Helmholtz coil pairs are symmetrically distributed on two sides of the cold atom preparation cavity by taking the emitting directions of one pair of cooling laser emitters as axes.
The centers of the atomic interference regions of the respective atomic interference units as described above are connected by a vacuum pipe.
Preferably, the atom detection area and the atom interference area are arranged in the projectile vacuum tube, the atom detection area is positioned above the cold atom preparation cavity, the atom interference area is positioned above the atom detection area, and the photoelectric detector is arranged on the side part of the atom detection area.
Preferably, the atom detection region and the atom interference region are arranged in the projectile vacuum tube, the atom interference region is positioned below the cold atom preparation cavity, the atom detection region is positioned below the atom interference region, and the side part of the atom detection region is provided with the photoelectric detector.
Preferably, the atom interference zone is arranged in the cast vacuum tube, the atom interference zone is positioned above the cold atom preparation cavity, and the side part of the cold atom preparation cavity is provided with the photoelectric detector.
A multi-component cold atom gravity gradient measurement method comprises the following steps:
and 6, taking the gravity gradient components of the directions of all measuring lines, and according to a projection relation:
wherein, thetaiIs a measuring line LiI ∈ { 1-3 };
is a measuring line LiA gravity gradient component of;xx,yy,xyall gravity gradients in a right-hand rectangular coordinate system;
and performing joint calculation on the gravity gradient components in the direction of each measurement line to obtain component values of the gravity gradient in the triangular configuration in a right-hand rectangular coordinate system.
A multi-component cold atom gravity gradient measurement method comprises the following steps:
and 6, taking the gravity gradient component of the direction of the five measuring lines, and according to the projection relation:
wherein, thetaiAnd
are respectively a measuring line LiI ∈ { 1-6 };
is a measuring line LiA gravity gradient component of;xx,yy,xyare the gravity gradients in a right-handed rectangular coordinate system,
the gravity gradient components in the direction of each measuring line are jointly calculated to obtain the component value of the gravity gradient in a right-hand rectangular coordinate system,
and 7, repeating the step 6, and averaging component values of the gravity gradient under all the five measurement line combinations in the right-hand rectangular coordinate system.
Compared with the prior art, the invention has the following beneficial effects:
the n atom interference units in the multi-component cold atom gravity gradient measurement system are connected pairwise through Raman laser beams generated by a Raman laser emitting device and a Raman laser reflecting device on a reverse extension line of a connecting line, projection synthetic values of components of a gradient matrix along the connecting line direction are obtained through measurement in a straight line penetrating mode, original values of the components in the gradient matrix are solved through a mathematical equation, and measurement of the components in each gravity gradient direction in a three-dimensional space can be achieved through an enhanced noise common mode inhibition effect.
The atom interference units are connected by adopting a vacuum pipeline, so that the Raman laser beams penetrating through any two atom interference units are transmitted in vacuum between the two atom interference units, and the relative phase noise of the Raman laser introduced by air disturbance can be eliminated.
When the atom interference unit works in the upper polishing mode, the positive effect of reducing the size of the vacuum cavity is achieved.
When the atom interference unit works in a free release mode, the atom interference unit has the positive effect of reducing the complexity of the system.
Drawings
FIG. 1 is a schematic structural diagram of a multicomponent cold atom gravity gradient measurement system of the present invention;
FIG. 2a is a schematic diagram of a single atomic interference unit with a photo-detector mounted on one side of the intermediate region between the atomic interference region and the cold atomic preparation chamber in an embodiment of the present invention;
FIG. 2b is a schematic diagram of a single atomic interference unit with a photodetector mounted on one side of a cold atomic preparation chamber according to an embodiment of the present invention;
FIG. 2c is a schematic diagram of a falling structure of a single atomic interference unit in an embodiment of the present invention;
FIG. 3 is a schematic diagram of the position relationship and the collinear measurement direction in a right-handed rectangular coordinate system according to an embodiment of the present invention;
fig. 4 is a conversion diagram of a rectangular coordinate system and a spherical coordinate system.
Detailed Description
The present invention will be described in further detail with reference to examples for the purpose of facilitating understanding and practice of the invention by those of ordinary skill in the art, and it is to be understood that the present invention has been described in the illustrative embodiments and is not to be construed as limited thereto.
Aiming at the defect that the off-diagonal component of a gravity gradient matrix is difficult to be directly measured with a higher noise common mode rejection effect in the prior art, the embodiment of the invention discloses an implementation scheme of a multi-component cold atom gravity gradient measurement system based on a non-orthogonal collinear measurement scheme.
The number of atomic interference units is 3:
the atomic interference units comprise a first atomic interference unit, a second atomic interference unit and a third atomic interference unit, each atomic interference unit comprises an atomic interference area 2-2, a connecting line of the centers of the atomic interference areas 2-2 of every two atomic interference units is a measuring line, a Raman laser emitting device 1-1 and a Raman laser reflecting device 1-2 are respectively installed at the extending positions of two ends of each measuring line, and the centers of the atomic interference areas 2-2 of the atomic interference units are respectively located at the vertexes of a distribution triangle to form a triangular structure.
The first atom interference unit G1, the second atom interference unit G2, and the third atom interference unit G3 have the same structure.
Case where the number of atomic interference units is 4:
that is, the atomic interference unit includes a first atomic interference unit G1, a second atomic interference unit G2, a third atomic interference unit G3, and a fourth atomic interference unit G4. Each atom interference unit comprises an atom interference area 2-2, the connecting line of the centers of the atom interference areas 2-2 of every two atom interference units is a measuring line, a Raman laser emitting device 1-1 and a Raman laser reflecting device 1-2 are respectively installed at the extending positions of two ends of each measuring line, and the centers of the atom interference areas 2-2 of the first atom interference unit G1, the second atom interference unit G2 and the third atom interference unit G3 are respectively located at the top points of the distribution triangle. The center of the atom interference region 2-2 of the fourth atom interference unit is positioned above the center of the distribution triangle to form a tetrahedral structure.
The first atomic interference unit G1, the second atomic interference unit G2, the third atomic interference unit G3, and the fourth atomic interference unit G4 have the same structure.
The structural composition of the atomic interference unit is described in detail by taking the above-described structure (fig. 2a) with the photodetector 6 installed on the side of the atomic detection region between the atomic interference region 2-2 and the cold atom preparation chamber 2-1 as an example:
the atomic interference unit comprises a vacuum cavity 2, an alkali metal sample source 3, a cooling laser emitter 4, an anti-Helmholtz magnetic field coil pair 5 and a photoelectric detector 6, wherein the vacuum cavity 2 comprises a cold atom preparation cavity 2-1 and a projection vacuum tube 7 which is vertically arranged and communicated with the cold atom preparation cavity 2-1, the projection vacuum tube 7 is divided into an atom detection area 2-3 and an atom interference area 2-2 along the longitudinal direction, and the photoelectric detector 6 is arranged on the side part of the atom detection area 2-3. The centers of the atomic interference regions 2-2 of every two vacuum cavities 2 are connected through a vacuum tube, the line connecting the centers of the atomic interference regions 2-2 of every two vacuum cavities 2 is a measuring line, the extended positions of the two ends of each measuring line are respectively provided with a Raman laser emitting device 1-1 and a Raman laser reflecting device 1-2, Raman laser beams continuously penetrating through the centers of the atomic interference regions 2-2 of the two atomic interference units along the measuring line can be generated, and therefore the difference measurement of gravity gradient components in the direction of the line connecting can be realized in a collinear measurement mode. The alkali metal sample source 3 is arranged in a cold atom preparation cavity 2-1 of the vacuum cavity 2, three pairs of cooling laser emitters 4 are spatially symmetrically and uniformly distributed around the cold atom preparation cavity 2-1, the emitting directions of the three pairs of cooling laser emitters all point to the center of the cold atom preparation cavity 2-1, and the anti-Helmholtz coil pairs 5 are symmetrically distributed on two sides of the cold atom preparation cavity 2-1 by taking the emitting directions of one pair of cooling laser emitters 4 as axes.
The photodetector 6 is installed at the side of the atom detection region 2-3. So that the atomic groups are detected in the atomic detection region 2-3 between the atomic interference region 2-2 and the cold atom preparation chamber 2-1 after the atomic interference region 2-2 is reciprocated when the atomic interference unit is operated in the upward-throwing mode.
For ease of understanding, a right-hand rectangular coordinate system (fig. 3) and a spherical coordinate system (fig. 4) were constructed:
the number of atomic interference units is 3:
establishing a right-hand rectangular coordinate system (figure 3) and a spherical coordinate system (figure 4) with the center of the atomic interference region 2-2 of the first atomic interference unit G1 as an origin in the triangular structure, wherein the plane where the centers of the atomic interference regions 2-2 of the first atomic interference unit G1, the second atomic interference unit G2 and the third atomic interference unit G3 are located in the right-hand rectangular coordinate system is set as an x-y plane, the direction where the central connecting lines of the atomic interference regions 2-2 of the first atomic interference unit G1 and the third atomic interference unit G3 are located is set as a y axis, and the direction where the center of the atomic interference region 2-2 of the first atomic interference unit G1 is perpendicular to the y axis is set as an x axis; the corresponding relation between the spherical coordinate system parameters (R, theta) and the right-hand rectangular coordinate system parameters (x, y) is as follows:
x＝Rcosθ,
y＝Rsinθ。
the centers of the atomic interference regions 2-2 of the first atomic interference unit G1, the second atomic interference unit G2 and the third atomic interference unit G3 are positioned at three vertex positions of a regular triangle, and the side length of the regular triangle is Lm; the included angle between the direction in which the center of the atomic interference region 2-2 of the first atomic interference unit G1 is connected with the center of the atomic interference region 2-2 of the second atomic interference unit G2 and the x-axis is
In the triangular structure of the embodiment of the invention, three atom interference units (G1, G2 and G3) operate simultaneously to form a group of measuring lines in pairs, which are sequentially numbered as L1, L2 and L3,
the line connecting the center of the atomic interference region 2-2 of the first atomic interference unit G1 and the center of the atomic interference region 2-2 of the second atomic interference unit G2 is a measuring line L1;
the line connecting the center of the atomic interference region 2-2 of the second atomic interference unit G2 and the center of the atomic interference region 2-2 of the third atomic interference unit G3 is a measuring line L2;
the line connecting the center of the atomic interference region 2-2 of the third atomic interference unit G3 and the center of the atomic interference region 2-2 of the first atomic interference unit G1 is a measuring line L3;
as shown in fig. 3; the atoms in the first to third atom interference units G1-G3 can simultaneously obtain the result of one measuring line (measuring line L1 or measuring line L2 or measuring line L3) after each upward-throwing and falling process, and gravity gradient components in the directions of three measuring lines in the x-y plane can be measured through three different combinations.
Due to the collinear measurement, the gravity gradient component measured in this experimental example is the gravity gradient component in the direction of the three measuring lines (L1, L2, L3), and the gravity gradient component of the three measuring lines (L1, L2, L3) can be expressed as:
the measurement of the one-time up-throwing falling process is described in detail below by taking the collinear measurement of the L1 measuring line as an example:
cold radicals are prepared simultaneously in three atomic interference units (G1, G2, G3) and in exactly the same steps, the required steps consisting of: the atomic groups enter cold atom preparation cavities 2-1 of the first atomic interference unit G1-the third atomic interference unit G3 from an alkali metal source 3, and are cooled and confined by cooling light emitted by a cooling laser transmitter 4 and a magnetic field formed by an anti-Helmholtz coil 5. After enough atoms are cooled and trapped, the frequency of cooling light emitted by the cooling laser emitter 4 is adjusted, so that the atomic group is accelerated by the action force of the upper unbalance and the lower unbalance to form the upward throwing. The radicals leave the atomic preparation region 2-1 by an upward throwing motion into the atomic interference region 2-2. As shown in FIG. 2a, the atomic interference region 2-2 is located above the cold atom preparation chamber 2-1.
In the measurement line L1, the raman laser transmitter 1-1 and the raman laser reflector 1-2 located at both ends of the extension line of the measurement line L1 generate raman light, the raman light acts on the atomic interference region 2-2 of the first atomic interference unit G1 and the atomic interference region 2-2 of the second atomic interference unit G2, and the atoms thrown up to the atomic interference region 2-2 are split, reflected, combined, and the like, and finally, interference is completed. Interference phases obtained by interference processes are respectively obtained by the photoelectric detectors 6 at the sides of the atom measuring areas of the first atom interference unit G1 and the second atom interference unit G2, and further gravity acceleration component information containing the direction of the measuring line L1 is respectively obtained
Obtaining the gravity gradient component of the direction of the measuring line L1 according to the gravity acceleration component information of the direction of the measuring line L1L1。
The gravity gradient component can be derived directly from the gravitational acceleration information:
where L is1-2That is, the length of the upper line L1, is the length of the two atomic interference unitsThe position of (G1, G2) is determined and is a known amount.
Two collinear measurements were continued and the gravity gradient components in the direction of the remaining three lines (L2 and L3) were obtained:
because there is corresponding relation in spherical coordinate system and right hand rectangular coordinate system, and have:
wherein, thetaiIs a measuring line LiAzimuth angle of (i ∈ { 1-3 }), thetaiIs a measuring line LiI ∈ { 1-3 };
is a measuring line LiA gravity gradient component of;xx,yy,xyboth are gravity gradients in the right-hand rectangular coordinate system.
In the present embodiment, the gravity gradient components in the directions of three measuring lines (L1, L2, L3) are taken
Through coordinate system transformation, the gravity gradient components of the three measuring lines are subjected to angle decomposition to obtain the gravity gradient in a right-hand rectangular coordinate system in an x-y planexx,yy,xyComprises the following steps:
case where the number of atomic interference units is 4:
establishing a right-hand rectangular coordinate system (figure 3) and a spherical coordinate system (figure 4) in a tetrahedral structure, wherein the right-hand rectangular coordinate system takes the center of the atomic interference region 2-2 of the first atomic interference unit G1 as an origin, the plane in which the centers of the atomic interference regions 2-2 of the first atomic interference unit G1, the second atomic interference unit G2 and the third atomic interference unit G3 are located in the right-hand rectangular coordinate system is set as an x-y plane, the direction in which the central connecting lines of the atomic interference regions 2-2 of the first atomic interference unit G1 and the third atomic interference unit G3 are located is set as a y axis, the direction in which the center of the atomic interference region 2-2 of the first atomic interference unit G1 and the direction perpendicular to the y axis are set as an x axis, and the vertical direction is a z axis; spherical coordinate system parameter
The corresponding relation with the right-hand rectangular coordinate system parameters (x, y, z) is as follows:
the centers of the atomic interference regions 2-2 of the first atomic interference unit G1, the second atomic interference unit G2 and the third atomic interference unit G3 are located at the three vertex positions of a regular triangle, the side length of the regular triangle is Lm, the center of the atomic interference region 2-2 of the fourth atomic interference unit G4 is located above the regular triangle, and the point of the projection of the center of the atomic interference region 2-2 of the fourth atomic interference unit G4 in the x-y plane is located at the center of the regular triangle; the directions in which the centers of the atomic interference regions 2-2 of the first atomic interference unit G1 and the center of the atomic interference region 2-2 of the fourth atomic interference unit G4 are connected are represented by spherical coordinates
Center of atomic interference region 2-2 of fourth atomic interference unit G4 to firstDistances of the centers of the atomic interference regions 2-2 of the atomic interference unit G1, the second atomic interference unit G2, and the third atomic interference unit G3 are denoted as Ln.
In the embodiment of the invention, four atom interference units (G1, G2, G3 and G4) in the tetrahedron operate simultaneously to form a group of measuring lines in pairs, which are sequentially numbered as L1, L2, L3, L4, L5 and L6,
the line connecting the center of the atomic interference region 2-2 of the first atomic interference unit G1 and the center of the atomic interference region 2-2 of the second atomic interference unit G2 is a measuring line L1;
the line connecting the center of the atomic interference region 2-2 of the second atomic interference unit G2 and the center of the atomic interference region 2-2 of the third atomic interference unit G3 is a measuring line L2;
the line connecting the center of the atomic interference region 2-2 of the third atomic interference unit G3 and the center of the atomic interference region 2-2 of the first atomic interference unit G1 is a measuring line L3;
the line connecting the center of the atomic interference region 2-2 of the third atomic interference unit G3 and the center of the atomic interference region 2-2 of the fourth atomic interference unit G4 is a measuring line L4;
the line connecting the center of the atomic interference region 2-2 of the first atomic interference unit G1 and the center of the atomic interference region 2-2 of the fourth atomic interference unit G4 is a measuring line L5;
the line connecting the center of the atomic interference region 2-2 of the second atomic interference unit G2 and the center of the atomic interference region 2-2 of the fourth atomic interference unit G4 is a measuring line L6;
as shown in fig. 3; when the atoms in the first to fourth atom interference units G1-G4 finish the up-throwing and down-dropping process once, the results of two measuring lines (measuring lines L1 and L4 or measuring lines L2 and L5 or measuring lines L3 and L6) can be obtained at the same time, and the gravity gradient components in the directions of six measuring lines can be measured through three different combinations of every two.
Because of the collinear measurement, the gravity gradient component measured in this experimental example is the gravity gradient component in the direction of the six measuring lines (L1, L2, L3, L4, L5, L6), and the gravity gradient component of the six measuring lines (L1, L2, L3, L4, L5, L6) can be expressed as:
the measurement of the one-time upward-throwing falling process is described in detail below by taking the simultaneous collinear measurement of two measuring lines L1 and L4 as an example:
cold radicals are prepared simultaneously in four atomic interference units (G1, G2, G3, G4) and in exactly the same steps, the required steps comprising: the atomic group enters the cold atom preparation cavities 2-1 of the first atomic interference unit G1 to the fourth atomic interference unit G4 from the alkali metal source 3, and is cooled and confined by cooling light emitted by the cooling laser emitter 4 and a magnetic field formed by the anti-Helmholtz coil 5. After enough atoms are cooled and trapped, the frequency of cooling light emitted by the cooling laser emitter 4 is adjusted, so that the atomic group is accelerated by the action force of the upper unbalance and the lower unbalance to form the upward throwing. The radicals leave the atomic preparation region 2-1 by an upward throwing motion into the atomic interference region 2-2. As shown in FIG. 2a, the atomic interference region 2-2 is located above the cold atom preparation chamber 2-1.
In the measurement line L1, the raman laser transmitter 1-1 and the raman laser reflector 1-2 located at both ends of the extension line of the measurement line L1 generate raman light, the raman light acts on the atomic interference region 2-2 of the first atomic interference unit G1 and the atomic interference region 2-2 of the second atomic interference unit G2, and the atoms thrown up to the atomic interference region 2-2 are split, reflected, combined, and the like, and finally, interference is completed. Interference phases obtained by interference processes are respectively obtained by the photoelectric detectors 6 at the sides of the atom measuring areas of the first atom interference unit G1 and the second atom interference unit G2, and further gravity acceleration component information containing the direction of the measuring line L1 is respectively obtained
In the measurement line L4, the raman laser transmitter 1-1 and the raman laser reflector 1-2 located at both ends of the extension line of the measurement line L4 generate raman light, the raman light acts on the atomic interference region 2-2 of the third atomic interference unit G3 and the atomic interference region 2-2 of the fourth atomic interference unit G4, and the atoms thrown up to the atomic interference region 2-2 are split, reflected, combined, and the like, and finally, interference is completed. By a third atomic interference unit G3 and the photoelectric detector 6 at the side of the atom measurement area of the fourth atom interference unit G4 respectively obtain interference phases obtained in the interference process, and further respectively obtain gravity acceleration component information containing the direction of the measuring line L4
According to the gravity acceleration component information of the direction in which the measuring line L1 and the measuring line L4 are located, the gravity gradient component of the direction in which the measuring line L1 and the measuring line L4 are located is obtained
The gravity gradient component can be derived directly from the gravitational acceleration information:
where L is1-2The length of the upper line L1 is determined by the position where two atomic interference units (G1, G2) are located and is a known quantity.
Continuing the two collinear measurements, the gravity gradient components in the direction of the remaining four lines (L2, L5 and L3, L6) can be obtained:
because there is corresponding relation in spherical coordinate system and right hand rectangular coordinate system, and have:
xx+yy+zz＝0，
wherein, thetaiAnd
are respectively a measuring line LiI ∈ { 1-6 };
is a measuring line LiA gravity gradient component of;xx,yy,xyboth are gravity gradients in the right-hand rectangular coordinate system.
In the present embodiment, the gravity gradient component in the direction of five measuring lines (L1, L2, L3, L4, L6) is taken
Through coordinate system transformation, the gravity gradient components of the five measuring lines are subjected to angle decomposition, and the gravity gradient in a right-hand rectangular coordinate system is obtainedxx,yy,xy,xz,yzComprises the following steps:
in addition, in the invention, the atomic interference unit can be formed by changing the installation position of the photoelectric detector 6 except the structure (figure 2a) of the upper-throwing type and the photoelectric detector 6 is arranged at one side of the detection region between the atomic interference region 2-2 and the cold atom preparation cavity 2-1, and the structure (figure 2b) of the photoelectric detector 6 arranged at one side of the cold atom preparation cavity 2-1 is formed; namely, the atom interference zone 2-2 is arranged in the cast vacuum tube 7, the atom interference zone 2-2 is positioned above the cold atom preparation cavity 2-1, and the photoelectric detector 6 is arranged on the side part of the cold atom preparation cavity 2-1.
Alternatively, the atomic emission pattern is changed to form a falling structure as shown in FIG. 2 c. Namely, an atom detection area 2-3 and an atom interference area 2-2 are arranged in a projectile vacuum tube 7, the atom interference area 2-2 is positioned below a cold atom preparation cavity 2-1, the atom detection area 2-3 is positioned below the atom interference area 2-2, and a photoelectric detector 6 is arranged on the side part of the atom detection area 2-3.
The invention discloses a multi-component cold atom gravity gradient measurement system based on a non-orthogonal collinear measurement scheme, which has the advantages and positive effects that:
the multi-component cold atom gravity gradient measurement system disclosed by the embodiment of the invention comprises 4 atom interference units, Raman laser beams generated by a Raman laser emitting device 1-1 and a Raman laser reflecting device 1-2 on a reverse extension line of a connecting line are connected pairwise, projection synthetic values of components of a gradient matrix along the connecting line direction are obtained by measuring in a straight line penetrating mode, original values of the components in the gradient matrix are solved by a mathematical equation, and measurement of the components in each gravity gradient direction in a three-dimensional space can be realized by an enhanced noise common mode inhibition effect.
The atom interference units are connected by adopting a vacuum pipeline, so that the Raman laser beams penetrating through any two atom interference units are transmitted in vacuum between the two atom interference units, and the relative phase noise of the Raman laser introduced by air disturbance can be eliminated.
The atom interference unit works in an upper polishing mode, and has the positive effect of reducing the size of the vacuum cavity.
When the atom interference unit works in a free release mode, the atom interference unit has the positive effect of reducing the complexity of the system.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (8)
1. A multi-component cold atom gravity gradient measurement system comprises an atom interference unit, and is characterized in that: the atom interference unit comprises a first atom interference unit, a second atom interference unit and a third atom interference unit, each atom interference unit comprises an atom interference area (2-2), the connecting line of the centers of the atom interference areas (2-2) of every two atom interference units is a measuring line, the extended positions of the two ends of each measuring line are respectively provided with a Raman laser emitting device (1-1) and a Raman laser reflecting device (1-2), the centers of the atom interference areas (2-2) of each atom interference unit are respectively positioned at the top points of a distribution triangle,
each atomic interference unit also comprises a vacuum cavity (2), an anti-Helmholtz coil pair (5) and three pairs of cooling laser transmitters (4),
the vacuum cavity (2) comprises a cold atom preparation cavity (2-1) and a casting vacuum tube (7) which is vertically arranged and communicated with the cold atom preparation cavity (2-1),
the three pairs of cooling laser emitters (4) are distributed around the cold atom preparation cavity (2-1), the emitting directions of the three pairs of cooling laser emitters all point to the center of the cold atom preparation cavity (2-1), and the anti-Helmholtz coil pairs (5) are symmetrically distributed on two sides of the cold atom preparation cavity (2-1) by taking the emitting directions of one pair of cooling laser emitters (4) as axes.
2. A multicomponent cold atom gravity gradient measurement system according to claim 1, wherein the atom interference unit further comprises a fourth atom interference unit comprising an atom interference zone (2-2), the center of the atom interference zone (2-2) of the fourth atom interference unit being located above the center of the distribution triangle,
the connecting line of the center of the atom interference region (2-2) of the fourth atom interference unit and the centers of the atom interference regions (2-2) of the first atom interference unit, the second atom interference unit and the third atom interference unit is a measuring line, the extending positions of two ends of the measuring line where the center of the atom interference region (2-2) of the fourth atom interference unit is positioned are respectively provided with a Raman laser emitting device (1-1) and a Raman laser reflecting device (1-2),
the fourth atomic interference unit also comprises a vacuum cavity (2), an anti-Helmholtz coil pair (5) and three pairs of cooling laser transmitters (4),
in the fourth atomic interference unit: the vacuum cavity (2) comprises a cold atom preparation cavity (2-1) and a casting vacuum tube (7) which is vertically arranged and communicated with the cold atom preparation cavity (2-1), three pairs of cooling laser emitters (4) are distributed around the cold atom preparation cavity (2-1), the emitting directions of the three pairs of cooling laser emitters all point to the center of the cold atom preparation cavity (2-1), and the anti-Helmholtz coil pair (5) is symmetrically distributed on two sides of the cold atom preparation cavity (2-1) by taking the emitting direction of one pair of cooling laser emitters (4) as an axis.
3. A multicomponent cold atom gravity gradient measurement system according to any one of claims 1 or 2, wherein the centers of the atomic interference zones (2-2) of the atomic interference units are connected by a vacuum pipe.
4. A multicomponent cold atom gravity gradient measurement system according to any one of claims 1 or 2, wherein an atom detection region (2-3) and an atom interference region (2-2) are provided in the ejector vacuum tube (7), the atom detection region (2-3) is located above the cold atom preparation chamber (2-1), the atom interference region (2-2) is located above the atom detection region (2-3), and a photodetector (6) is provided at the side of the atom detection region (2-3).
5. A multicomponent cold atom gravity gradient measurement system according to any one of claims 1 or 2, wherein an atom detection region (2-3) and an atom interference region (2-2) are provided in the ejector vacuum tube (7), the atom interference region (2-2) is located below the cold atom preparation chamber (2-1), the atom detection region (2-3) is located below the atom interference region (2-2), and a photodetector (6) is provided at the side of the atom detection region (2-3).
6. A multicomponent cold atom gravity gradient measurement system according to any one of claims 1 or 2, wherein the atomic interference region (2-2) is arranged in the projectile vacuum tube (7), the atomic interference region (2-2) is located above the cold atom preparation chamber (2-1), and the photodetector (6) is arranged at the side of the cold atom preparation chamber (2-1).
7. A multi-component cold atom gravity gradient measurement method using any one of the multi-component cold atom gravity gradient measurement systems of claim 1, comprising the steps of:
step 1, preparing cold atomic groups in each atomic interference unit simultaneously and throwing or dropping along a throwing vacuum tube (7);
step 2, selecting a measuring line;
step 3, Raman laser emitting devices (1-1) and Raman laser reflecting devices (1-2) positioned at two ends of an extension line of the selected measuring line generate Raman light, the Raman light acts on atom interference regions (2-2) of atom interference units at two ends of the measuring line to interfere atoms of the atom interference regions (2-2), photoelectric detectors (6) on the sides of atom measurement regions of the atom interference units at two ends of the measuring line respectively obtain interference phases obtained in the interference process, and then the atom interference units at two ends of the measuring line respectively obtain gravity acceleration component information in the direction of the measuring line;
step 4, obtaining a gravity gradient component in the direction of the measuring line according to the gravity acceleration component information in the direction of the measuring line obtained by the atom interference units at the two ends of the measuring line;
step 5, repeating the steps 3-4 to obtain all measuring lines (L)1～L3) A gravity gradient component in the direction;
and 6, taking the gravity gradient components of the directions of all measuring lines, and according to a projection relation:
wherein, thetaiIs a measuring line LiI ∈ { 1-3 };
is a measuring line LiA gravity gradient component of;xx，yy，xyall gravity gradients in a right-hand rectangular coordinate system;
and performing joint calculation on the gravity gradient components in the direction of each measurement line to obtain component values of the gravity gradient in the triangular configuration in a right-hand rectangular coordinate system.
8. A multi-component cold atom gravity gradient measurement method using any one of the multi-component cold atom gravity gradient measurement systems of claim 2, comprising the steps of:
step 1, preparing cold atomic groups in each atomic interference unit simultaneously and throwing or dropping along a throwing vacuum tube (7);
step 2, selecting a measuring line;
step 3, Raman laser emitting devices (1-1) and Raman laser reflecting devices (1-2) positioned at two ends of an extension line of the selected measuring line generate Raman light, the Raman light acts on atom interference regions (2-2) of atom interference units at two ends of the measuring line to interfere atoms of the atom interference regions (2-2), photoelectric detectors (6) on the sides of atom measurement regions of the atom interference units at two ends of the measuring line respectively obtain interference phases obtained in the interference process, and then the atom interference units at two ends of the measuring line respectively obtain gravity acceleration component information in the direction of the measuring line;
step 4, obtaining a gravity gradient component in the direction of the measuring line according to the gravity acceleration component information in the direction of the measuring line obtained by the atom interference units at the two ends of the measuring line;
step 5, repeating the steps 3-4 to obtain all measuring lines (L)1～L6) A gravity gradient component in the direction;
and 6, taking the gravity gradient component of the direction of the five measuring lines, and according to the projection relation:
wherein, thetaiAnd
are respectively a measuring line LiI ∈ { 1-6 };
is a measuring line LiA gravity gradient component of;xx，yy，xyare the gravity gradients in a right-handed rectangular coordinate system,
the gravity gradient components in the direction of each measuring line are jointly calculated to obtain the component value of the gravity gradient in a right-hand rectangular coordinate system,
and 7, repeating the step 6, and averaging component values of the gravity gradient under all the five measurement line combinations in the right-hand rectangular coordinate system.
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