Atomic gravity gradient sensor based on funnel-shaped reflector

Abstract

The present invention discloses an atomic gravity gradient sensor based on a funnel-shaped reflector, and relates to the field of measuring gravity gradient using atomic interference technology. The sensor is: the first vacuum container is coaxially installed in the vertical direction directly above the second vacuum container to form a long cylindrical structure; from top to bottom, the first laser emitter, the first cooling laser beam, the first three-dimensional magneto-optical trap, the upper part of the trapped magnetic field coil pair, the first cold atomic sample, the first funnel-shaped reflector, the lower part of the trapped magnetic field coil pair, and the upper and lower parts of the bias magnetic field coil pair are connected in sequence; then the second three-dimensional magneto-optical trap, the second funnel-shaped reflector, the second cold atomic sample, the second atomic interference zone, the second cooling laser beam and the second laser emitter are connected in sequence. The present invention realizes the measurement of atomic gravity gradient of a single-beam double-trap scheme through two funnel-shaped reflectors, and at the same time solves the problem that the atoms in the two atomic samples feel different effects of the same beam of modulated Raman laser π or π / 2 pulse.

Description

Technical Field

[0001] The invention relates to the field of measuring gravity gradient by using atomic interference technology, and in particular to an atomic gravity gradient sensor based on a funnel-shaped reflector. Background Art

[0002] High-precision measurement of gravity gradient has important applications in resource exploration, geological survey, inertial navigation and basic research. Among the gravity gradiometers using macroscopic test masses, superconducting gravity gradiometers have the highest accuracy, but they are large in size, require a low-temperature environment, are relative measurements, and are difficult to maintain. The atomic gravity gradiometer using cold atoms as test mass not only has high measurement accuracy and high repetition rate, but also belongs to absolute measurement, is easy to maintain, and has attracted people's attention.

[0003] The cold atom gravity gradiometer uses atomic interference in two cold atom samples that are synchronized in time but separated in space to measure the gravity gradient. Different configurations of the relative spatial positions of the two cold atom samples can form gravity gradiometers that measure different gravity gradient components. The most commonly used are horizontal atom gravity gradiometers and vertical atom gravity gradiometers, which are used to measure the horizontal and vertical components of the gravity gradient, respectively. A typical high-precision cold atom gravity gradiometer requires two three-dimensional magneto-optical traps to prepare two cold atom samples. Each magneto-optical trap requires six cooling laser beams, so the entire system is large and complex and is often used in basic research, such as measuring the gravitational constant. At present, the miniaturization of cold atom gravity gradiometers is being carried out in an orderly manner, and different designs of miniaturized atomic gravity gradiometers have been proposed. The MAKaservich team used a fully microcrystalline glass (Zerodur) vacuum cavity instead of the commonly used titanium metal vacuum cavity, which greatly reduced the volume and weight of the atomic gravity gradiometer, but the two three-dimensional magneto-optical traps that capture and cool atoms still require six cooling laser beams each, and a total of 12 beams for the two, so the optical and control systems are still complex. The P.Bouyer team used a pyramidal hollow reflector to realize a single-beam three-dimensional magneto-optical trap (Pub.NO.: US2011 / 0073753A1), which miniaturized the atomic gravimeter. Similar designs have also been used to miniaturize atomic gravity gradients. The French company Moquis used a small pyramid and a large pyramid to reflect the center and edge of the same cooling beam to realize two spatially separated three-dimensional magneto-optical traps (Publication No. CN105026960A). However, since the cooling light of the two magneto-optical traps comes from different parts of the same beam, the optical parameters of the two magneto-optical traps are different, resulting in different sizes, shapes and atomic numbers of the two cold atom samples, which ultimately affects the common-mode suppression effect of the gradient meter. In addition, in this type of scheme, the cold atom interference zone and the three-dimensional magneto-optical trap are in different areas of the same vacuum cavity, and no vacuum isolation measures are taken between them, so the two areas have the same vacuum degree. To ensure that the three-dimensional magneto-optical trap can quickly capture and cool a sufficient number of atoms from the background gas, its vacuum degree cannot be too high. If the vacuum degree of the cold atom interference zone is not high, the detection signal will have a large background noise and the signal-to-noise ratio will decrease. The present invention proposes an atomic gravity gradient scheme based on a funnel-shaped reflector to solve the above problems, which will help promote the miniaturization of atomic gravity gradient instruments and their application on mobile platforms. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings and deficiencies of the prior art and to provide an atomic gravity gradient sensor based on a funnel-shaped reflector, so as to simplify the vacuum and optical systems of the atomic gravity gradiometer at the same time, which will help promote the miniaturization of the atomic gravity gradiometer and its application on mobile platforms.

[0005] The specific problems solved are:

[0006] 1) In the prior art, the cooling lights of the two three-dimensional magneto-optical traps come from different parts (the central part and the edge part) of the same cooling light beam, which makes the optical parameters of the two magneto-optical traps different, resulting in different sizes, shapes and atomic numbers of the cold atomic samples prepared by the two magneto-optical traps, which ultimately affects the common-mode suppression effect of the atomic gravity gradiometer.

[0007] 2) The three-dimensional magneto-optical trap and the atomic interference zone in the prior art share the same vacuum container, and no vacuum isolation measures are taken in between, so that the vacuum degree of the atomic interference zone is not high, resulting in large background noise of the detection signal, reduced signal-to-noise ratio, and affecting the measurement accuracy of the gravity gradient.

[0008] 3) In the prior art, the distance between the trapping centers of the two three-dimensional magneto-optical traps (i.e., the two cold atom samples) is not equal to an integer multiple of the half-wavelength of the microwave corresponding to the splitting of the ground state energy level of the D2 line of the selected working atom. When the atoms in the two cold atom samples are operated to produce interference using the same beam of modulated Raman light π / 2-π-π / 2 pulse sequence, the atoms in the two samples respectively feel different effects of the π / 2 and π pulses, so that the two atomic interference signals cannot reach the optimum at the same time, thereby affecting the accuracy of gravity gradient measurement.

[0009] The object of the present invention is achieved in that:

[0010] The sensor comprises a first vacuum container, a second vacuum container, a first funnel-shaped reflector, a second funnel-shaped reflector, a pair of trapped magnetic field coils, a pair of bias magnetic field coils, a detector, a first laser emitter, a second laser emitter, a first cold atomic sample, a second cold atomic sample, a first cooling laser beam and a second cooling laser beam;

[0011] The first vacuum container includes a first three-dimensional magneto-optical trap and a first atomic interference region;

[0012] The second vacuum container includes a second three-dimensional magneto-optical trap and a second atomic interference region;

[0013] Its location and connectivity are:

[0014] The first vacuum container is coaxially installed directly above the second vacuum container in the vertical direction to form a long cylindrical structure;

[0015] The distance L between the first three-dimensional magneto-optical trap and the second three-dimensional magneto-optical trap is equal to an integral multiple of a half wavelength of microwaves corresponding to the splitting of the upper and lower energy levels of the D2 line ground state of the trapped alkali metal atoms;

[0016] The distance L between the first cold atom sample and the second cold atom sample is equal to an integral multiple of the half wavelength of microwaves corresponding to the splitting of the upper and lower energy levels of the D2 line ground state of the trapped alkali metal atoms;

[0017] From top to bottom, the first laser emitter, the first cooling laser beam, the first three-dimensional magneto-optical trap, the upper part of the trapped magnetic field coil pair, the first cold atomic sample, the first funnel-shaped reflector, the lower part of the trapped magnetic field coil pair, and the upper and lower parts of the bias magnetic field coil pair are connected in sequence;

[0018] Then the second three-dimensional magneto-optical trap, the second funnel-shaped reflector, the second cold atomic sample, the second atomic interference region, the second cooling laser beam and the second laser emitter are connected in sequence;

[0019] Detectors are respectively arranged at the bottom of the first atomic interference region and the bottom of the second atomic interference region.

[0020] The present invention has the following advantages and positive effects:

[0021] 1) The same part of a single cooling laser beam is reflected twice by two first and second funnel-shaped reflectors with exactly the same structure and shape, forming two three-dimensional magneto-optical traps with the same optical parameters. The size, shape, distribution and number of atoms of the two cold source samples prepared in the two three-dimensional magneto-optical traps are the same.

[0022] 2) The three-dimensional magneto-optical trap and the atomic interference zone are isolated by a differential hole, and the vacuum degree between the two differs by about one order of magnitude, which is beneficial to improving the speed and number of atoms in preparing cold atomic samples by the three-dimensional magneto-optical trap, while reducing background atomic noise and improving the signal-to-noise ratio of the detection signal.

[0023] 3) The distance L between the trapping centers of the two three-dimensional magneto-optical traps (two cold atomic samples) satisfies: L = Nλ / 2, which solves the problem that when a modulated Raman laser π or π / 2 pulse acts on two atomic samples with a distance of L in space, the atoms in the two atomic samples feel exactly the same effect of the π or π / 2 pulse, with no difference.

[0024] In summary, the present invention realizes the measurement of atomic gravity gradient in a single-beam double-well scheme through two funnel-shaped reflectors, and solves the problem that atoms in two atomic samples feel different effects of the same beam of modulated Raman laser π or π / 2 pulse, which will promote the miniaturization of atomic gravity gradient sensors and their application on mobile platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the structure of the sensor;

[0026] Figure 2 It is a structural schematic diagram of a funnel-shaped reflector;

[0027] Figure 3 Schematic diagram of forming a double MOT for a single cooling beam.

[0028] in:

[0029] 1—1st vacuum container,

[0030] 1.1—the first three-dimensional magneto-optical trap, 1.2—the first atomic interference zone;

[0031] 2—Second vacuum container,

[0032] 2.1—the second three-dimensional magneto-optical trap, 2.2—the second atomic interference zone;

[0033] 3a—1st funnel-shaped reflector;

[0034] 3b—second funnel-shaped reflector;

[0035] 4—trapping magnetic field coil pair;

[0036] 5—Bias magnetic field coil pair;

[0037] 6—Detector;

[0038] 7a—1st laser transmitter;

[0039] 7b—second laser transmitter;

[0040] a—the first cold atomic sample;

[0041] b—the second cold atomic sample;

[0042] c1—the first cooling laser beam;

[0043] c2—second cooling laser beam;

[0044] L—the distance between the first and second three-dimensional magneto-optical traps or the first and second cold atomic samples. DETAILED DESCRIPTION

[0045] The following is a detailed description with reference to the accompanying drawings and embodiments:

[0046] I. Overall

[0047] like Figure 1 As shown, the sensor includes two atomic measuring devices (A, B) of identical structure and the first and second laser emitters 7a, 7b; each atomic measuring device A (or B) is composed of the first (or second) vacuum container 1 (or 2), a trapped magnetic field coil pair 4, a bias magnetic field coil pair 5, a photodetector 6, an alkali metal sample cell and a vacuum pump (not shown in the figure).

[0048] The first (or second) vacuum container is divided into a three-dimensional magneto-optical trap 1.1 and an atomic interference zone 1.2 by the first (or second) funnel-shaped reflector 3a (or 3b). An alkali metal sample pool is installed in the three-dimensional magneto-optical trap zone, and a vacuum pump is installed at the bottom of the atomic interference zone. The two vacuum zones are connected through the differential hole at the top of the first (or second) funnel-shaped reflector. The vacuum degree of the atomic interference zone is about one order of magnitude higher than that of the three-dimensional magneto-optical trap.

[0049] The first and second funnel-shaped reflectors 3a and 3b are reflectors with the same structure, each having an opening at the top and an inner surface in the shape of a cone or a regular 2n pyramid. Figure 2 As shown, n is an integer greater than 1. The inner surface of the first funnel-shaped reflector 3a is coated with a semi-reflective and semi-transmissive film (reflection and transmission each account for about 50%), and the inner surface of the second funnel-shaped reflector 3b is coated with a total reflection film.

[0050] The first vacuum container 1 is coaxially installed vertically above the second vacuum container 2. The first and second funnel-shaped reflectors 3a, 3b and their respective trapping magnetic field coil pairs 4 form two three-dimensional magneto-optical traps with the same parameters. The distance L between the trapping centers of the two magneto-optical traps satisfies: L = Nλ / 2, where N is a positive integer and λ is the microwave wavelength corresponding to the splitting of the ground state energy level of the selected working atom D2 line. The first laser beam emitter 7a is located above the first vacuum container 1, and the second laser beam emitter 7b is located below the second vacuum container 2.

[0051] Specifically, the sensor includes a first vacuum container 1, a second vacuum container 2, a first funnel-shaped reflector 3a, a second funnel-shaped reflector 3b, a pair of trapped magnetic field coils 4, a pair of bias magnetic field coils 5, a detector 6, a first laser emitter 7a, a second laser emitter 7b, a first cold atomic sample a, a second cold atomic sample b, a first cooling laser beam c1, and a second cooling laser beam c2;

[0052] The first vacuum container 1 comprises a first three-dimensional magneto-optical trap 1.1 and a first atomic interference region 1.2;

[0053] The second vacuum container 2 includes a second three-dimensional magneto-optical trap 2.1 and a second atomic interference region 2.2;

[0054] Its location and connectivity are:

[0055] The first vacuum container 1 is coaxially installed directly above the second vacuum container 2 in the vertical direction to form a long cylindrical structure;

[0056] The distance L between the first three-dimensional magneto-optical trap 1.1 and the second three-dimensional magneto-optical trap 2.1 is equal to an integral multiple of a half wavelength of microwaves corresponding to the splitting of the upper and lower energy levels of the D2 line ground state of the trapped alkali metal atoms;

[0057] The distance L between the first cold atom sample a and the second cold atom sample b is equal to an integral multiple of the half wavelength of microwaves corresponding to the splitting of the upper and lower energy levels of the D2 line ground state of the trapped alkali metal atoms;

[0058] From top to bottom, the first laser emitter 7a, the first cooling laser beam c1, the first three-dimensional magneto-optical trap 1.1, the upper part of the trapped magnetic field coil pair 4, the first cold atomic sample a, the first funnel-shaped reflector 3a, the lower part of the trapped magnetic field coil pair 4, and the upper and lower parts of the bias magnetic field coil pair 5 are connected in sequence;

[0059] Then the second three-dimensional magneto-optical trap 2.1, the second funnel-shaped reflector 3b, the second cold atomic sample b, the second atomic interference region 2.2, the second cooling laser beam c2 and the second laser emitter 7b are connected in sequence;

[0060] Detectors 6 are respectively arranged at the bottom of the first atomic interference region 1.2 and the bottom of the second atomic interference region 2.2.

[0061] Working mechanism:

[0062] The sensor comprises a first vacuum container 1, a second vacuum container 2, a first funnel-shaped reflector 3a, a second funnel-shaped reflector 3b, a pair of trapped magnetic field coils 4, a pair of bias magnetic field coils 5, a detector 6, a first laser emitter 7a, a second laser emitter 7b, a first cold atomic sample a, a second cold atomic sample b, a first cooling laser beam c1 and a second cooling laser beam c2;

[0063] 1) The first laser emitter 7a emits a cooling beam along the vertical axis direction of the first vacuum container 1 and the second vacuum container 2. After the beam enters the first funnel-shaped reflector 3a, it is cut into a reflected beam, a transmitted beam and a central beam, as shown in FIG. Figure 3 As shown. The reflected light beam forms a counter-incident horizontal cooling light; the transmitted light beam is totally reflected after entering the second funnel-shaped reflector, forming a counter-incident horizontal cooling light; the central light beam directly passes through the top small holes of the first funnel-shaped reflector 3a and the second funnel-shaped reflector 3b, and is reflected back along the original path after entering the second laser beam reflector 7b, forming a cooling laser pair that is vertically opposite to the incident central light beam, and the cooling laser pair and the above-mentioned two groups of horizontally opposite cooling lights intersect vertically at the central zero point of the quadrupole magnetic field generated by their respective pairs of trapped magnetic field coils, forming two three-dimensional magneto-optical traps with the same structure and parameters, which are used to prepare cold atomic samples.

[0064] The effect is:

[0065] By using the first funnel-shaped reflector 3a and the second funnel-shaped reflector 3b with the same structure, the same part of the single cooling laser beam is reflected twice, forming two three-dimensional magneto-optical traps with the same spatial structure, shape and distribution. The size, shape, distribution and number of atoms of the two cold source samples prepared in the two three-dimensional magneto-optical traps are the same, which is conducive to suppressing common mode noise.

[0066] 2) The three-dimensional magneto-optical trap region and the atomic interference region are connected by a differential hole. The size of the differential hole can adjust the vacuum ratio between the atomic interference region and the three-dimensional magneto-optical trap to meet the different requirements of the two vacuum regions for the vacuum degree: the vacuum degree of the atomic interference region is about one order of magnitude higher than that of the three-dimensional magneto-optical trap region.

[0067] The effect is:

[0068] The vacuum degree of the three-dimensional magneto-optical trap is about 10 -6 Pa is conducive to the three-dimensional magneto-optical trap to quickly capture and imprison a sufficient number of cold atomic samples from the alkali metal rarefied gas. The vacuum degree of the atomic interference zone is about one order of magnitude higher than that of the three-dimensional magneto-optical trap zone, which is conducive to reducing the background atomic noise of the detection signal and improving the signal-to-noise ratio, thereby improving the measurement accuracy of the gravity gradient.

[0069] 3) The distance L between the trapping centers of the two three-dimensional magneto-optical traps formed by the reflection of the single light beam satisfies: L=Nλ / 2, where N is a positive integer and λ is the microwave wavelength corresponding to the splitting of the ground state energy level of the D2 line of the selected working atom.

[0070] The effect is:

[0071] The distance between the first and second cold atomic samples trapped in the two three-dimensional magneto-optical traps is equal to L. When the same π / 2-π-π / 2 pulse sequence of modulated Raman light is used to operate the atoms in the two cold atomic samples to produce interference, the effects of the π / 2 and π pulses felt by the atoms in the two samples are exactly the same, with no difference, so that the two interference signals are synchronized to the best, thereby improving the measurement accuracy of the atomic gravity gradiometer.

[0072] 2. Functional Components

[0073] 1. No. 1 and 2 vacuum containers 1 and 2

[0074] like Figure 1 The first and second vacuum containers 1 and 2 are long containers made of titanium metal, transparent resin or all-glass, with a window on the top connected to the alkali metal sample pool (not shown), and a window on the bottom connected to the vacuum pump (not shown); the upper and lower ends are sealed with glass windows; the first and second vacuum containers 1 and 2 are separated by the first and second funnel-shaped reflectors 3a and 3b with holes on the top into the first and second three-dimensional magneto-optical traps 1.1 and 2.1 and the first and second atomic interference zones 1.2 and 2.2 with a vacuum degree difference of about one order of magnitude.

[0075] 2. The first and second funnel-shaped reflectors 3a and 3b

[0076] like Figure 2 As shown, the first and second funnel-shaped reflectors 3a and 3b are reflectors with the same structure, with two openings at the top and inner surfaces in the shape of cones or 2n pyramids, where n is an integer greater than 1. The inner surface of the first funnel-shaped reflector 3a is plated with a semi-reflective and semi-transmissive film (reflection and transmission each account for about 50%), and the inner surface of the second funnel-shaped reflector 3b is plated with a total reflection film, which is usually made of a transparent medium such as glass or resin.

[0077] 3. Trapping magnetic field coil pair 4

[0078] The pair of trapped magnetic field coils 4 is a common coil made of wound metal wires or printed on a film.

[0079] 4. Bias magnetic field coil 5

[0080] The bias magnetic field coil 5 is a general coil formed by winding a metal wire or printing on a film.

[0081] 5. Photodetector 6

[0082] The photodetector 6 is a universal device for measuring fluorescence signals, and may be a semiconductor photodiode or a fluorescence imaging device.

[0083] 6. First and second laser emitters 7a and 7b

[0084] The first laser emitter 7a is a transmitting terminal composed of a laser parameter adjustment system composed of a semiconductor laser and a universal optical element and a universal propagation device, and the end can be a fiber collimating lens group or a reflector system; the second laser emitter 7b is a laser reflection terminal composed of a quarter glass slide and a reflector.

[0085] 3. Working Principle

[0086] This sensor is composed of two atomic measuring devices with the same structure. Each atomic measuring device can use atomic interference technology to measure the local gravity where the device is located. The two local gravity signals can extract the gravity gradient signal through the ellipse fitting method. Since the two atomic measuring devices share the first and second laser emitters 7a and 7b, that is, they share the same optical path to emit cooling beams, detection beams and Raman beams in different stages, the two atomic measuring devices can be synchronized at different stages of atomic interference to achieve the purpose of suppressing common mode noise, thereby improving the measurement accuracy and stability of the gravity gradient of the sensor. The following is a brief description of the working principle of this sensor divided into several different working stages.

[0087] 1) Preparation of cold atomic samples

[0088] The switch of the trapped magnetic field coil pair 4 of the three-dimensional magneto-optical trap is turned on to establish a quadrupole magnetic field in the three-dimensional magneto-optical trap. Then, the first and second laser emitters 7a and 7b emit cooling beams mixed with return pump light, and two three-dimensional magneto-optical traps with the same parameters are formed at the optical centers of the first and second funnel-shaped reflectors 3a and 3b, respectively. Figure 3 As shown, it is used to prepare the first cold atom sample a and the second cold atom sample b. The distance L between the two cold atom samples is equal to an integer multiple of the half wavelength of the microwave corresponding to the splitting of the upper and lower energy levels of the ground state of the trapped alkali metal atom D2 line. The effect is that when the atoms in the two cold atom samples are operated to interfere with each other using the same π / 2-π-π / 2 pulse sequence of modulated Raman light, the effects of the π / 2 and π pulses felt by the atoms in the two samples are exactly the same, without any difference, so that the synchronization of the two interference signals is optimal, thereby improving the measurement accuracy of the atomic gravity gradiometer. The preparation time of the cold atom sample ranges from a few milliseconds to tens of milliseconds, which is specifically related to the parameters of the magneto-optical trap.

[0089] 2) Atoms in free fall

[0090] After the cold atom sample is prepared, it enters the free fall stage. In this stage, the magnetic fields of the two magneto-optical traps are turned off first, and then the cooling laser beam is turned off. The two cold atom samples begin to fall freely at the same time under the action of gravity. During the fall, the distance L between the two cold atom groups is equal to the integer multiple of the half-wavelength of the microwave corresponding to the splitting of the upper and lower energy levels of the D2 line ground state of the trapped alkali metal atoms, and remains unchanged.

[0091] 3) Atomic initial state preparation

[0092] In the free fall process, the atom is at the energy level of each magnetic sub-level of the ground state, and the initial state of the atom used for atomic interference is prepared at the energy level m in the ground state. F = 0, which is insensitive to magnetic fields. Therefore, the initial state must be prepared. Before the atoms fall into the atomic interference region, the first and second laser emitters 7a and 7b emit Raman light π pulses to convert the ground state energy level m F = 0 atomic state preparation in the ground state energy level m F = 0, blow away the atoms in the upper energy level of the ground state, and the remaining atoms are in the lower energy level of the ground state. F =0, the initial state preparation is completed.

[0093] 4) Atomic interference

[0094] After the atoms fall into the atomic interference zone, atomic coherence operations are performed. The first and second laser emitters 7a and 7b emit a sequence of π / 2-π-π / 2 Raman light pulses to irradiate the atoms, so that the atomic wave packets are split, reflected and combined to form an interference loop. Interference fringes can be obtained by measuring at the loop exit, where the time interval between two adjacent Raman pulses is T.

[0095] 5) Final state detection

[0096] In the final state detection stage, the first and second laser emitters 7a and 7b emit detection light to simultaneously illuminate the first cold atom sample a and the second cold atom sample b, and use fluorescence detection technology to respectively detect the number of atoms N in the first cold atom sample a and the second cold atom sample b at the ground state energy level. a1 、N b1 and the number of atoms in the lower energy level N a2 and N b2 , the probability of the atoms in the first cold atom sample a and the second cold atom sample b being in the ground state energy level is calculated to be P a =N a1 / (N a1 +N a2 ) and P b =N b1 / (N b1 +N b2 ). By scanning the phase of the last π / 2 Raman pulse, two interference fringes can be synchronously output on the two photodetectors 6.

[0097] 6) Ellipse fitting

[0098] Since the parameters of the two three-dimensional magneto-optical traps are basically the same, the size, shape and number of atoms of the trapped atomic samples are the same, and the same Raman light and detection light are used in the atomic interference and detection stages, the phase difference of the atomic interference fringes output by the upper and lower atomic measurement devices mainly comes from the difference in local gravitational acceleration. The phase difference Δφ of the two atomic interference fringes can be extracted by ellipse fitting. According to the atomic interference theory, the gravity gradient Δg=Δφ / (k eff T 2 L), where k eff , T, and L are the effective wave vector of the Raman laser, the time of free evolution of atoms, and the distance between the two atomic samples, respectively. All of them are known quantities, and the gravity gradient measurement is now completed.

[0099] This sensor uses two identical funnel-shaped reflectors and only a single laser beam to realize two three-dimensional magneto-optical traps with the same parameters. It also solves the problem that the atoms in the two atomic samples feel different effects of the modulated Raman laser π or π / 2 pulse. It not only miniaturizes the atomic gravity gradient sensor, but also improves the measurement accuracy of the atomic gravity gradiometer, which will help promote the miniaturization of the atomic gravity gradiometer and its application on mobile platforms.

Claims

1. An atomic gravity gradient sensor based on a funnel-shaped reflector, Features: The invention comprises a first vacuum container (1), a second vacuum container (2), a first funnel-shaped reflector (3a), a second funnel-shaped reflector (3b), a pair of trapped magnetic field coils (4), a pair of bias magnetic field coils (5), a detector (6), a first laser emitter (7a), a second laser emitter (7b), a first cold atomic sample (a), a second cold atomic sample (b), a first cooling laser beam (c1) and a second cooling laser beam (c2); The first vacuum container (1) comprises a first three-dimensional magneto-optical trap (1.1) and a first atomic interference region (1.2); The second vacuum container (2) comprises a second three-dimensional magneto-optical trap (2.1) and a second atomic interference region (2.2); Its location and connectivity are: The first vacuum container (1) is coaxially installed in the vertical direction directly above the second vacuum container (2) to form a long cylindrical structure; The distance L between the first three-dimensional magneto-optical trap (1.1) and the second three-dimensional magneto-optical trap (2.1) is equal to an integral multiple of a half wavelength of microwaves corresponding to the splitting of the upper and lower energy levels of the D2 line ground state of the trapped alkali metal atoms; The distance L between the first cold atom sample (a) and the second cold atom sample (b) is equal to an integer multiple of the half wavelength of microwaves corresponding to the splitting of the upper and lower energy levels of the D2 line ground state of the trapped alkali metal atoms; From top to bottom, the first laser emitter (7a), the first cooling laser beam (c1), the first three-dimensional magneto-optical trap (1.1), the upper part of the trapped magnetic field coil pair (4), the first cold atomic sample (a), the first funnel-shaped reflector (3a), the lower part of the trapped magnetic field coil pair (4), and the upper and lower parts of the bias magnetic field coil pair 5 are connected in sequence; Then the second three-dimensional magneto-optical trap 2.1, the second funnel-shaped reflector 3b, the second cold atomic sample b, the second atomic interference region 2.2, the second cooling laser beam c2 and the second laser emitter 7b are connected in sequence; Detectors (6) are respectively arranged at the bottom of the first atomic interference region (1.2) and the bottom of the second atomic interference region (2.2); The first and second funnel-shaped reflectors (3a, 3b) are reflectors of the same structure with an opening at the top and an inner surface in the shape of a cone or a 2n pyramid, wherein n is an integer greater than 1; the inner surface of the first funnel-shaped reflector (3a) is coated with a semi-reflective and semi-transmissive film, with reflection and transmission each accounting for 50%; the inner surface of the second funnel-shaped reflector (3b) is coated with a total reflection film.

2. The atomic gravity gradient sensor according to claim 1, Features: The first and second vacuum containers (1, 2) are long containers made of titanium metal, transparent resin or all-glass, with a window on the top connected to the alkali metal sample pool and a window on the bottom connected to the vacuum pump; the upper and lower ends are sealed with glass windows; the first and second vacuum containers (1, 2) are separated by first and second funnel-shaped reflectors (3a, 3b) with holes on the top into first and second three-dimensional magneto-optical traps (1.1, 2.1) and first and second atomic interference regions (1.2, 2.2) with vacuum degrees differing by one order of magnitude.

3. The atomic gravity gradient sensor according to claim 1, Features: The first and second funnel-shaped reflectors (3a, 3b) are made of transparent media such as glass or resin.

4. The atomic gravity gradient sensor according to claim 1, Features: The first laser transmitter (7a) is a transmitting terminal formed by connecting a semiconductor laser, a laser parameter adjustment system composed of a universal optical element, and a universal propagation device, and the end may be a fiber collimating lens group or a reflector system; The second laser emitter (7b) is a laser reflection terminal composed of a quarter glass slide and a reflection mirror.

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