Large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman

Abstract

The invention discloses a large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman, which comprises a vacuum system, a cold atomic group arranged in the vacuum system comprises atomic groups of two components, a first Raman laser, a second Raman laser and a third Raman laser which are incident to the vacuum system form Raman light of a first component, and a second Raman laser and a third Raman laser which are incident to the vacuum system form Raman light of a second component. The first Raman laser, the second Raman laser and the fourth Raman laser form Raman light of a second component; and the frequency of the third Raman laser and the frequency of the fourth Raman laser are changed to compensate Doppler frequency shift caused by the recoil speed difference in the atomic large momentum transfer process of the two components. The characteristic that the two-component atom interferometer is insensitive to the third frequency of Raman laser is utilized, and the frequency of non-shared laser of the two-component atom interferometer is independently adjusted, so that large momentum transfer of the two-component atom interferometer of which the number of recoil photons is not limited by Doppler frequency shift difference is realized while common-mode suppression of two-component atom phase noise is guaranteed, and the large momentum transfer of the two-component atom interferometer is realized. And the differential measurement precision is improved.

Description

Technical Field

[0001] The present invention relates to the fields of cold atom physics and quantum precision measurement, and in particular to a large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman. Background Art

[0002] With the development of cold atom manipulation technology and atomic interferometry technology, atom interferometers have become powerful tools for conducting basic physics (such as equivalence principle tests) and precision inertial sensing (such as gravity, gravity gradient measurement, and inertial navigation). Increasing the amount of momentum transferred during the interaction between light and atoms (Large Momentum Transfer, LMT) is an effective method to improve the measurement accuracy of atom interferometers (Peter Asenbaum et al., Physical Review Letters, Vol. 125, No. 191101, 2020). At present, large momentum transfer experiments in single-component atom interferometers (using the same type of atoms) have made great progress, with the maximum transferred momentum reaching 408 ( is the reduced Planck constant, represents the wave vector), and for the two-component atom interferometer (using two different atoms) used in experiments such as equivalence principle testing and gravity gradient measurement, the maximum transfer momentum reported so far is only 12 How to improve the measurement accuracy of a two-component atom interferometer by transferring more photon momentum is a hot topic in current atom interferometer research.

[0003] The main approaches currently under research include expanding single-diffraction Raman pulse trains, Bragg diffraction, Bloch oscillation schemes, and their hybrids. These techniques, applied to two-component atom interferometers to achieve greater momentum transfer, all have limitations, primarily in the following areas: In the extended single-diffraction Raman pulse sequence scheme, uneven light intensity can lead to uneven distribution of Rabi frequencies and decoherence caused by spontaneous radiation, which will reduce the contrast and signal-to-noise ratio of the interference fringes. In addition, in the interference loop, the internal states of atoms are different, and the electromagnetic field noise of the environment will have a significant impact. When applied to a two-component atom interferometer, it is constrained by compatibility issues caused by differences in the physical properties of atoms.

[0004] In Bragg diffraction schemes, the required laser power increases almost exponentially with increasing Bragg diffraction orders. A typical 10th-order Bragg diffraction requires over 3 W of optical power, and the fringe contrast is severely degraded. The greatest challenge in a two-component atom interferometer is the difficulty in simultaneously transferring large momentum of the two atoms through high-order Bragg diffraction due to the mass differences between the atoms.

[0005] While Bloch oscillation schemes can achieve high photon transfer momentum in single-component atom interferometers, for two-component atom interferometers, the mass differences between the atoms prevent the same set of laser pulses from transferring large momentum for both atoms. Furthermore, this scheme is severely limited by lattice beam wavefront distortion and laser phase noise.

[0006] In summary, while existing large momentum transfer schemes have been successful in single-component atom interferometers, their application to two-component atom interferometers is generally constrained by compatibility issues caused by differences in the physical properties of the atoms. Specifically, when the two-component atoms do not share a common laser, this scheme allows both interferometers to achieve large momentum transfer. However, the phase noise of the different lasers will have a serious impact, limiting the accuracy of differential measurements. For non-isotopic atoms, the common-mode effect will be even worse due to the greater difference in wave vectors. When the two-component atoms share a common laser, this scheme can effectively suppress laser phase noise. However, due to the mass difference between the two-component atoms, as the photon momentum transfer increases, it will be difficult to resonate with both atoms simultaneously using the same laser pulse. For differential measurements in two-component atom interferometers, the shared laser can better utilize its common-mode characteristics. Therefore, how to effectively address the problem of limited recoil photons during large momentum transfer in two-component atom interferometers while achieving common-mode noise suppression is a core issue in current large momentum transfer technology for two-component atom interferometers. Summary of the Invention

[0007] In order to solve the problem that in the existing two-component atom interferometer, when achieving large momentum transfer, the difference in the mass of the two atoms leads to a difference in the Doppler frequency shift caused by the different recoil momentum. This difference limits the number of photon recoils in the two-component atom interferometer for large momentum transfer, thereby affecting the measurement sensitivity, the present invention proposes a two-component atom interferometer for large momentum transfer based on four-wave double-diffraction Raman.

[0008] The above-mentioned purpose of the present invention is achieved through the following technical solutions: Large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman, including vacuum system, A magnetic shielding system is disposed outside the upper portion of the vacuum system, and the top of the magnetic shielding system is open; the lower region within the vacuum system is an ejection region and a detection region, the detection region is located above the ejection region, the initial position of the cold atomic cluster is located in the ejection region, the cold atomic cluster includes atomic clusters of two components, and a fluorescence collection system and an imaging CCD are sequentially disposed outside the vacuum system and at positions corresponding to the detection region; a cooling laser is disposed outside the vacuum system and at positions corresponding to the ejection region, the first branch beam of the third Raman laser, the first branch beam of the fourth Raman laser, the detection laser, and the first Raman laser are incident upon the vacuum system from the top, the second branch beam of the third Raman laser, the second branch beam of the fourth Raman laser, and the second Raman laser are reflected by a compensating reflector disposed below the bottom of the vacuum system, and then are incident upon the vacuum system from the bottom of the vacuum system and propagate toward the top of the vacuum system; The first Raman laser, the second Raman laser and the third Raman laser constitute a first component of Raman light, and the first Raman laser, the second Raman laser and the fourth Raman laser constitute a second component of Raman light; The frequencies of the third Raman laser and the fourth Raman laser are changed to compensate for the Doppler shift caused by the difference in recoil velocity during the large momentum transfer process of the atoms of the two components.

[0009] The gravity differential measurement method comprises the following steps: Step 1: Build a large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman, and set the initial frequencies and intensities of the first Raman laser, the second Raman laser, the third Raman laser, and the fourth Raman laser; Step 2: Use cooling laser to cool and emit the cold atomic clusters; Step 3: Implementing an extended Mach-Zehnder interferometer sequence using the first Raman laser, the second Raman laser, the third Raman laser, and the fourth Raman laser. The extended Mach-Zehnder interferometer sequence includes: First π / pulse, first π pulse group, first free evolution time T, second π pulse group, π pulse, the third π pulse group, the second free evolution time T, the fourth π pulse group, the second π / pulse; The first π pulse group, the second π pulse group, the third π pulse group and the fourth π pulse group all include A series of π pulses; Each pulse is a simultaneous action of all Raman lasers, and the pulse includes π / Pulse, π pulse and π pulse, all Raman lasers include the first Raman laser, the second Raman laser, the two branched beams of the third Raman laser, and the two branched beams of the fourth Raman laser; Step 4: Use quenching light and detection laser to excite the cold atomic clusters in sequence, and use the imaging CCD to capture the shearing interference fringe image of the first component and the shearing interference fringe image of the second component; Step 5: Extract the corresponding interferometer fringes from the sheared interference fringe images of each component through the principal component analysis method, extract the corresponding interference phase from the interferometer fringes of each component, and obtain the differential phase from the difference in the interference phases of the two components.

[0010] As mentioned above, the two components of the cold atomic group are Atoms and atoms, the initial frequencies of the first Raman laser, the second Raman laser, the third Raman laser, and the fourth Raman laser satisfy the following conditions: , , , in, are the initial frequencies of the first Raman laser and the initial frequency of the fourth Raman laser; and They are Atomic energy level Linear The energy difference between the two ground states and Atomic energy level Linear The energy level difference between the two ground states; It is the preset frequency difference limit value.

[0011] As described above, the initial frequencies of the first Raman laser, the second Raman laser, the third Raman laser, and the fourth Raman laser satisfy the following conditions: , , , in, is the frequency reference zero point, equal to atomic The transition frequency of the line |F=3>-|F'=4>.

[0012] As described above, the light intensities of the first Raman laser, the second Raman laser, the third Raman laser, and the fourth Raman laser satisfy the following conditions: , in, is the intensity of the first Raman laser Fourth, the intensity of the Raman laser.

[0013] As described above, the two branched beams in the third Raman laser, the two branched beams in the fourth Raman laser, the first Raman laser, and the second Raman laser are all chirped, and the chirp rates of the fourth Raman laser and the first Raman laser are , the chirp rates of the second Raman laser and the third Raman laser are , the chirp rate value , is the effective wave vector, is the acceleration due to gravity.

[0014] As mentioned above, the first π / pulse, π pulse, second π / The frequency of the third Raman laser corresponding to the pulse is the initial frequency of the third Raman laser ; First π / pulse, π pulse, second π / The frequency of the fourth Raman laser corresponding to the pulse is the initial frequency of the fourth Raman laser ; The first pulse in the odd-numbered π pulse group The frequencies of the third Raman laser and the fourth Raman laser corresponding to the π pulses are: , , in, The π pulse groups with odd serial numbers are the first π pulse group and the third π pulse group; Indicates the number of the π pulse group with an odd sequence number. The frequency of the third Raman laser in the π pulse; Indicates the number of the π pulse group with an odd sequence number. The frequency of the fourth Raman laser in the π pulse; Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the third Raman laser; Indicates the number of the π pulse group with an odd sequence number. The frequency change of the fourth Raman laser corresponding to a π pulse is: , , The sequence number of a π pulse in an odd-numbered π pulse group , is the total number of π pulses in a π pulse group; Indicates rounding up; yes Atomic Doppler shift; yes Atomic Doppler shift; The first pulse in the π pulse group with an even number The frequencies of the third Raman laser and the fourth Raman laser in a π pulse are: , , in, The π pulse groups with even serial numbers are the second π pulse group and the fourth π pulse group; Indicates the number of the π pulse group with an even sequence number. The frequency of the third Raman laser in the π pulse; Indicates the number of the π pulse group with an even sequence number. The frequency of the fourth Raman laser in the π pulse; Indicates the number of the π pulse group with an even sequence number. Each π pulse corresponds to the frequency change of the third Raman laser; Indicates the number of the π pulse group with an even sequence number. The frequency change of the fourth Raman laser corresponding to a π pulse is: , , The sequence number of a π pulse in an even-numbered π pulse group , Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the third Raman laser; Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the fourth Raman laser.

[0015] The above-mentioned step 2 specifically includes the following steps: Using cooling laser and three-dimensional magneto-optical trap (3D-MOT) Atoms and The atoms are cooled and loaded synchronously, and the cooling laser forms an atomic fountain with a (0,0,1) configuration; the loaded cold atomic cluster is subjected to free fall or vertical downward throwing, and then vertically upward throwing.

[0016] Compared with the prior art, the present invention has the following beneficial effects: Realize dual-component synchronous large momentum transfer: By combining the four-wave double-diffraction Raman light configuration and expanding the pulse sequence to use the four-wave double-diffraction 4WDR scheme to adjust the frequency of the third Raman laser and the fourth Raman laser, independent compensation of the recoil Doppler frequency shift in the large momentum transfer of the dual-component system is achieved, enabling two different atoms to simultaneously obtain large momentum transfer far exceeding the existing level.

[0017] Enhanced measurement sensitivity: The large momentum transfer achieved directly amplifies the phase response of the atom interferometer to inertial effects. times, of which is the total number of π pulses in a π pulse group (similar to π / - π-π / Compared with the pulse sequence, it significantly improves the measurement sensitivity and lays the foundation for higher-precision basic physics inspection and inertial sensing applications.

[0018] The present invention utilizes the characteristic that the two-component atom interferometer is insensitive to the third frequency of the Raman laser, and independently adjusts the frequency of the non-shared laser of the two-component atom instrument to offset the Doppler frequency shift difference of the two-component atoms caused by the large momentum transfer process, thereby solving the problem faced by the traditional large momentum transfer scheme of the two-component atom interferometer, that is, the number of photon recoil momentum of the two-component atom interferometer is limited due to the mass difference of the two atoms. At the same time, the present invention maintains the common mode suppression characteristics of the four-wave double diffraction scheme while experimentally performing large momentum transfer of the two-component atom interferometer, thereby improving the measurement sensitivity and accuracy of the two-component interferometer. The present invention overcomes the technical bottleneck that the traditional technical means of the two-component atom interferometer are incompatible with the large momentum transfer of two atoms, and lays the foundation for future basic research such as the equivalence principle test with higher precision and applications such as inertial measurement.

[0019] Maintaining common-mode noise suppression: The dual-diffraction scheme and shared Raman optical path design maintains intrinsic common-mode laser phase noise suppression. Through precise control, the differential wave vector effect that may be introduced during large momentum transfer is minimized, effectively suppressing the impact of common-mode noise such as environmental vibration on differential measurements, ensuring measurement stability and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the structure of a large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman according to the present invention; Among them, 101-cold atomic group, 102-vacuum system, 103-magnetic shielding system, 104-cooling laser, 105-detection laser, 106-first Raman laser, 107-second Raman laser, 108-third Raman laser, 109-fourth Raman laser, 110-fluorescence collection system, 111-imaging CCD, 112-compensation mirror; Figure 2 Schematic diagram of the frequency configuration of each Raman laser beam; F represents the total angular momentum quantum number of the ground state, and F' represents the total angular momentum quantum number of the excited state; are the initial frequencies of the first Raman laser and the initial frequency of the fourth Raman laser; are the intensity of the first Raman laser Fourth, the intensity of the Raman laser; Figure 3 To expand the space-time diagram of the double-diffraction Raman pulse sequence atom interferometer; π / 、 π and π respectively represent π / pulse, π pulse and π pulse; is the total number of π pulses in a π pulse group; T is the free evolution time; Figure 4 Extraction of fringe phase shifts for interferometer fringe EMCCD imaging and principal component analysis; (a) is a two-component two-dimensional interference image captured by the EMCCD camera, (b) is a two-component one-dimensional interference image, and (c) is a two-component interference fringe. Figure 5 The figure is a flow chart of the dual-component large momentum transfer atom interferometer based on four-wave double-diffraction Raman of the present invention. DETAILED DESCRIPTION

[0021] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below with reference to the embodiments. The embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0022] Example 1 Large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman, such as Figure 1 As shown, it includes a cold atomic group 101 (the cold atomic group 101 includes two components of atomic groups. In this embodiment, the first component is atoms, the second group is atoms), vacuum system 102, magnetic shielding system 103, cooling laser 104, detection laser 105, first Raman laser 106, second Raman laser 107, third Raman laser 108 and fourth Raman laser 109, fluorescence collection system 110, imaging CCD 111, angle with the ground The compensating reflector 112 is placed, wherein the third Raman laser 108 and the fourth Raman laser 109 each include two branched beams. The specific structure is as follows: The upper outer shell of the vacuum system 102 is provided with a magnetic shielding system 103, and the top of the magnetic shielding system 103 is open; the lower area inside the vacuum system 102 is the ejection area and the detection area, the cold atomic group 101 is initially located in the ejection area, and the detection area is located above the ejection area. A fluorescence collection system 110 and an imaging CCD 111 are sequentially arranged outside the vacuum system 102 and at positions corresponding to the detection area; cooling lasers 104 are arranged outside the vacuum system 102 and at positions corresponding to the ejection area (three pairs of cooling lasers 104 are arranged, and each pair is perpendicular to each other, Figure 1 Only two pairs of horizontally propagating cooling lasers 104 are drawn in the figure. The two beams of light in the other pair of cooling lasers 104 propagate relative to each other along the extension direction of the vacuum system 102). The first branched beam of the third Raman laser 108, the first branched beam of the fourth Raman laser 109, the detection laser 105, and the first Raman laser 106 are incident on the vacuum system 102 from the top. A compensating reflector 112 is provided below the bottom of the vacuum system 102. After being reflected by the compensating reflector 112, the second branched beam of the third Raman laser 108, the second branched beam of the fourth Raman laser 109, and the second Raman laser 107 are incident on the vacuum system 102 from the bottom, and then propagate upward in a direction parallel to the central axis of the vacuum system 102. By rotating the compensating mirror 112, the second branched beam of the third Raman laser 108, the second branched beam of the fourth Raman laser 109, and the second Raman laser 107 are directed in the positive direction of the z-axis, that is, from the bottom of the vacuum system 102 to the top of the vacuum system 102, as shown in FIG. Figure 1 As shown, the first branch beam in the third Raman laser 108, the first branch beam in the fourth Raman laser 109, and the first Raman laser 106 point to the negative direction of the z-axis.

[0023] The imaging CCD 111 used in this embodiment is an EMCCD camera.

[0024] The first Raman laser 106, the second Raman laser 107 and the third Raman laser 108 constitute a first component (in this embodiment atoms), the first Raman laser 106, the second Raman laser 107 and the fourth Raman laser 109 constitute the second component (in this embodiment atoms) of Raman light.

[0025] The present invention will Atoms and The first Raman laser 106 and the second Raman laser 107 shared by the atoms are used as chirped lasers to compensate for the Doppler frequency shift caused by gravity during the movement of atoms in the cold atomic cluster 101. The frequencies of the third Raman laser 108 and the fourth Raman laser 109 are adjusted to compensate for the Doppler frequency shift caused by the difference in recoil velocity during the large momentum transfer of atoms of the two components. The specific process is shown in Example 2.

[0026] Example 2 The gravity differential measurement method utilizes the large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman described in Example 1. The first Raman laser 106 and the second Raman laser 107 are used as chirped lasers to compensate for the Doppler frequency shift caused by gravity during atomic motion. The frequencies of the third Raman laser 108 and the fourth Raman laser 109 are adjusted to compensate for the Doppler frequency shift caused by the difference in recoil velocity during the large momentum transfer of the two atoms. The momentum of the transferred photons is gradually increased by increasing the Raman laser pulse sequence to realize a large momentum transfer two-component atom interferometer. Finally, high-precision gravity differential measurement is achieved through a specific optical structure and operation method. Figure 5 The specific steps are as follows: Step 1: Build a large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman, and set the initial frequencies and intensities of the first Raman laser 106 , the second Raman laser 107 , the third Raman laser 108 and the fourth Raman laser 109 .

[0027] Set the initial frequency: The four-wave double diffraction (4WDR) scheme is used according to Atoms and The energy level structure of the atom is shown in Figure 1. The first Raman laser 106, the second Raman laser 107, the third Raman laser 108 and the fourth Raman laser 109 (the wave vectors are denoted as , the initial frequencies are recorded as ) After frequency, intensity, and polarization control, it is injected into the interference zone in the vacuum system 102 through the optical fiber. The interference zone is located above the detection zone. The relative frequency relationship of each Raman laser is: , , , in, are the initial frequencies of the first Raman laser to the fourth Raman laser respectively; and They are Atomic energy level Linear The energy difference between the two ground states and Atomic energy level Linear The energy level difference between the two ground states; , ; It is the preset frequency difference limit value, used to limit the use and near, and near, and near.

[0028] In this embodiment, the absolute frequencies of the six Raman laser beams are set as follows: Figure 2 As shown, specifically: set up atomic The transition frequency of line |F=3>-|F'=4> is the frequency reference zero point , ; ; ; Set the light intensities of the first Raman laser 106, the second Raman laser 107, the third Raman laser 108, and the fourth Raman laser 109: The ratio of the intensity of each Raman laser beam is: , is the intensity of the first Raman laser Fourth, the intensity of the Raman laser.

[0029] Furthermore, in order to compensate for the Doppler shift of the vertical upward motion of the atoms, the six Raman laser beams (the two branch beams in the third Raman laser 108, the two branch beams in the fourth Raman laser 109, the first Raman laser 106, and the second Raman laser 107) are all chirped. The chirp rate of the fourth Raman laser 109 (including the two branch beams in the fourth Raman laser 109) and the first Raman laser 106 is The chirp rates of the second Raman laser 107 and the third Raman laser 108 (including the two branched beams in the third Raman laser 108) are , the chirp rate value , ,in is the effective wave vector, is the acceleration due to gravity, is the average value of the initial wave vector, which is equal to the average value of the initial wave vectors of the first Raman laser 106 to the fourth Raman laser 109.

[0030] Step 2: Atom preparation and launch.

[0031] In step 2, the cold atomic group 101 is cooled and emitted by the cooling laser 104. In this embodiment, the specific process is as follows: Using cooling laser 104 and three-dimensional magneto-optical trap 3D-MOT Atoms and The atoms are cooled and loaded synchronously. Four cooling laser beams 104 are placed horizontally, and the other two beams propagate along the positive and negative directions of the z-axis, forming an atomic fountain with a (0,0,1) configuration. The experimental setup is shown in Figure 1. For the cooling laser 104, the laser power is stabilized to ensure the light intensity balance of each cooling laser beam 104, further suppressing the fluctuation of the center position of the cold atomic cluster 101. Atoms and The cold atomic cluster 101 corresponding to the atom is subjected to free fall or vertical throwing downward, and then vertical throwing upward, so that the cold atomic cluster 101 prolongs the interaction time with the cooling laser 104 at the intersection center of the cooling laser 104 and is fully accelerated. Here, the cold atomic cluster 101 first moves downward for a very short distance (without hitting the bottom of the vacuum system 102), the purpose of which is to fully contact the cooling laser 104 and perform secondary polarization gradient cooling (PGC) during the moving optical adhesive, so that the temperature of the cold atomic cluster 101 is further reduced, thereby increasing the intensity of the falling atom signal.

[0032] Step 3: Large momentum transfer in a two-component atom interferometer.

[0033] The double-diffraction large momentum pulse sequence is expanded to construct an expanded Mach-Zehnder interferometer sequence. The expanded Mach-Zehnder interferometer sequence is implemented using the first Raman laser 106, the second Raman laser 107, the third Raman laser 108, and the fourth Raman laser 109. The expanded Mach-Zehnder interferometer sequence includes: First π / pulse, first π pulse group, first free evolution time T, second π pulse group, π pulse, the third π pulse group, the second free evolution time T, the fourth π pulse group, the second π / pulse; Among them, all π pulse groups (i.e., the first π pulse group, the second π pulse group, the third π pulse group, and the fourth π pulse group) include A series of π pulses; each pulse (ie, π / Pulse, π pulse and π pulses) are all Raman lasers (i.e., the two branched beams in the third Raman laser 108, the two branched beams in the fourth Raman laser 109, the first Raman laser 106, and the second Raman laser 107) acting simultaneously, but The atoms resonate only with the first Raman laser 106, the second Raman laser 107 and the third Raman laser 108. The atoms resonate only with the first Raman laser 106, the second Raman laser 107, and the fourth Raman laser 109), and both atoms are measured simultaneously; is a positive integer, the total momentum transferred is .

[0034] First π / pulse, π pulse, second π / The frequency of the third Raman laser 108 corresponding to the pulse is the initial frequency of the third Raman laser ; First π / pulse, π pulse, second π / The frequency of the fourth Raman laser 109 corresponding to the pulse is the initial frequency of the fourth Raman laser ; The π pulse groups with odd serial numbers (the π pulse groups with odd serial numbers are the first π pulse group and the third π pulse group) The frequencies of the third Raman laser 108 and the fourth Raman laser 109 corresponding to the π pulses are: , , in, Indicates the number of the π pulse group with an odd sequence number. The frequency of the third Raman laser in the π pulse; Indicates the number of the π pulse group with an odd sequence number. The frequency of the fourth Raman laser in the π pulse; Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the third Raman laser; Indicates the number of the π pulse group with an odd sequence number. The frequency change of the fourth Raman laser corresponding to a π pulse is: , , The sequence number of a π pulse in an odd-numbered π pulse group , is the total number of π pulses in a π pulse group; Indicates rounding up; yes Atomic Doppler shift, kilohertz; yes Atomic Doppler shift, kilohertz; The π pulse groups with even numbers (the π pulse groups with even numbers are the second π pulse group and the fourth π pulse group) The frequencies of the third Raman laser 108 and the fourth Raman laser 109 in the π pulses are: , , in, Indicates the number of the π pulse group with an even sequence number. The frequency of the third Raman laser in the π pulse; Indicates the number of the π pulse group with an even sequence number. The frequency of the fourth Raman laser in the π pulse; Indicates the number of the π pulse group with an even sequence number. The frequency change of the third Raman laser corresponding to a π pulse is: Indicates the number of the π pulse group with an even sequence number. The frequency change of the fourth Raman laser corresponding to a π pulse is: , , The sequence number of a π pulse in an even-numbered π pulse group , Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the third Raman laser; Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the fourth Raman laser.

[0035] This embodiment uses Taking the change of the third Raman laser 108 during the large momentum of the atom as an example, the total number of π pulses in a π pulse group is 3. The initial momentum of the atom is Move in the positive direction of the z axis, Initial first π / After the pulse, the cold atom cluster 101 splits the beam and the upper interferometer arm The momentum of the atomic absorption two-photon (corresponding to the first Raman laser 106 and the third Raman laser 108) becomes ( Reduced Planck constant, for The initial motion of the atom corresponds to the wave vector of the de Broglie wave), the upper interference arm The Doppler shift corresponding to the atom is (in, represents the speed of light, express mass of the atom); lower interferometer arm The momentum of the atomic absorption two-photon (the second Raman laser 107 and the third Raman laser 108) becomes , lower interference arm Atomic correspondence The atomic Doppler shift changes to ; Upper and lower interference arms Atomic momentum splitting ; The frequency of the third Raman laser 108 corresponding to the first π pulse in the first π pulse group increases (Right now , ), due to the Doppler shift, the upper interferometer arm The atoms resonate only with the first Raman laser 106 and the third Raman laser 108. The atomic momentum becomes , the same as the lower interferometer arm The atoms resonate only with the second Raman laser 107 and the third Raman laser 108. The atomic momentum becomes , upper and lower interference arms The atomic momentum is split into ; The frequency of the third Raman laser 108 corresponding to the second π pulse in the first π pulse group increases (Right now , ), upper interference arm The atomic momentum becomes , lower interference arm The atomic momentum becomes , upper and lower interference arms The atomic momentum splitting becomes ; The frequency of the third Raman laser 108 corresponding to the third π pulse in the first π pulse group increases (Right now , ), upper interference arm The atomic momentum becomes , lower interference arm The atomic momentum becomes , upper and lower interference arms The atomic momentum is split into , the atom interferometer obtains The large momentum splitting corresponds to Figure 3 The absolute value of the slope of the middle curve is the largest; Atoms every time After the pulse interaction, the internal state of the atom will flip ( atom The line ground state hyperfine level has two states); After the free evolution time T, The frequencies of the respective π pulses in the second π pulse group (the frequencies of the third Raman laser 108 are 、 、 ) Move the upper and lower interference arms in sequence The atomic momentum splitting is reduced to ; middle π pulse is a four-photon process (at this time The frequency of the third Raman laser 108 in the π pulse is restored to the initial frequency of the third Raman laser ), the upper and lower interference arms Atomic momentum splitting is caused by becomes , but the internal state of the atom does not change; The frequencies of the respective π pulses in the third π pulse group (the frequencies of the third Raman laser 108 are , , ) Move the upper and lower interference arms The atomic momentum splitting changes to , after a free evolution time T, Each π pulse in the fourth π pulse group (the frequency of the third Raman laser 108 is 、 、 ) Move the upper and lower interference arms The atomic momentum splitting changes in sequence - , thus not introducing additional phase shift, and finally applying the second π / Upper and lower interferometer arms after pulse The atomic momentum is the same, realizing the recombination of atomic wave packets.

[0036] This embodiment is based on the four-wave double diffraction (4WDR) scheme. Atom fourth Raman laser 109, Taking advantage of the insensitivity of the third Raman laser 108, the frequencies of the third Raman laser 108 and the fourth Raman laser 109 are adjusted respectively to compensate for the difference in Raman light k-wave loss caused by the difference in atomic masses during the large momentum transfer of the two-component atom interferometer, so that the two groups of interferometers can obtain large momentum transfer at the same time and ensure the common mode characteristics of the synchronous two-component atom interferometer.

[0037] Step 4: Atom detection and signal extraction.

[0038] After the cold atomic cluster 101 has been flying freely for a period of time, the cold atomic cluster 101 is excited by the quenching light and the detection laser 105 in sequence, as shown in FIG. Figure 4 As shown in (a) and (b), the imaging CCD 111 takes the first component (i.e. atoms) and the shear interference fringe image of the second component (i.e. atoms), thereby obtaining the shear interference fringe images of the two atoms in two output states (in this embodiment, namely atom The upper ground state and atom The atomic number distribution of the ground state on the line.

[0039] Step 5: Differential phase measurement and analysis.

[0040] Long-term measurements of tens of hours, such as Figure 4 As shown in (c), the corresponding interferometer fringes are extracted from the sheared interference fringe images of each component by the principal component analysis method, and the corresponding interference phase is extracted from the interferometer fringes of each component respectively. The differential phase is obtained from the difference in the interference phases of the two components.

[0041] In this embodiment, Atomic shearing interference fringe image extraction The interferometer fringes of atoms and Atomic shearing interference fringe image extraction Interferometer fringes of atoms; extracted from The interferometer fringes of atoms and The interference fringes of atoms are extracted separately Atomic interference phase and Atomic interference phase ; Calculate differential phase The differential phase It is not sensitive to common mode noise (such as laser phase noise, platform vibration), but is sensitive to effects that depend on atomic species (such as equivalence principle violation signals, gravity gradients). A series of differential phases obtained by multiple measurements through Allan variance data processing , and obtain the confidence interval of gravity differential measurement data. Due to the large momentum transfer, the scale factor is increased and the sensitivity is improved.

[0042] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman, characterized by: including a vacuum system (102), A magnetic shielding system (103) is disposed outside the upper portion of the vacuum system (102), and the top of the magnetic shielding system (103) is open. The lower region within the vacuum system (102) is an ejection region and a detection region, wherein the detection region is located above the ejection region. The initial position of the cold atomic group (101) is located in the ejection region. The cold atomic group (101) includes two components of atomic groups. A fluorescence collection system (110) and an imaging CCD are sequentially disposed outside the vacuum system (102) and at positions corresponding to the detection region. (111); A cooling laser (104) is provided at a position corresponding to the ejection zone outside the vacuum system (102); the first branched beam in the third Raman laser (108), the first branched beam in the fourth Raman laser (109), the detection laser (105) and the first Raman laser (106) are incident from the top of the vacuum system (102) into the vacuum system (102); the second branched beam in the third Raman laser (108), the second branched beam in the fourth Raman laser (109) and the second Raman laser (107) are reflected by a compensation reflector (112) provided below the bottom of the vacuum system (102), and then are incident from the bottom of the vacuum system (102) into the vacuum system (102) and propagate toward the top of the vacuum system (102); The first Raman laser (106), the second Raman laser (107), and the third Raman laser (108) constitute a first component of Raman light, and the first Raman laser (106), the second Raman laser (107), and the fourth Raman laser (109) constitute a second component of Raman light; The frequencies of the third Raman laser (108) and the fourth Raman laser (109) are varied to compensate for the Doppler shift caused by the difference in recoil velocity during the large momentum transfer process of the atoms of the two components.

2. A gravity differential measurement method using the large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman according to claim 1, characterized in that: The steps include: Step 1: constructing a large momentum transfer two-component atom interferometer based on four-wave double-diffraction Raman, and setting the initial frequencies and light intensities of the first Raman laser (106), the second Raman laser (107), the third Raman laser (108) and the fourth Raman laser (109); Step 2: Cooling and emitting the cold atomic cluster (101) using a cooling laser (104); Step 3: Implementing an extended Mach-Zehnder interferometer sequence using the first Raman laser (106), the second Raman laser (107), the third Raman laser (108), and the fourth Raman laser (109). The extended Mach-Zehnder interferometer sequence includes: First π / pulse, first π pulse group, first free evolution time T, second π pulse group, π pulse, the third π pulse group, the second free evolution time T, the fourth π pulse group, the second π / pulse; The first π pulse group, the second π pulse group, the third π pulse group and the fourth π pulse group all include A series of π pulses; Each pulse is a simultaneous action of all Raman lasers, and the pulse includes π / Pulse, π pulse and π pulses, all Raman lasers include the first Raman laser (106), the second Raman laser (107), two branched beams in the third Raman laser (108), and two branched beams in the fourth Raman laser (109); Step 4: sequentially exciting the cold atomic group (101) with the quenching light and the detection laser (105), and imaging the CCD (111) to capture the shearing interference fringe image of the first component and the shearing interference fringe image of the second component; Step 5: Extract the corresponding interferometer fringes from the sheared interference fringe images of each component through the principal component analysis method, extract the corresponding interference phase from the interferometer fringes of each component, and obtain the differential phase from the difference in the interference phases of the two components.

3. The gravity differential measurement method according to claim 2, characterized in that: The cold atomic group (101) includes two components: Atoms and atoms, the initial frequencies of the first Raman laser (106), the second Raman laser (107), the third Raman laser (108) and the fourth Raman laser (109) satisfy the following conditions: ， ， ， in, are the initial frequencies of the first Raman laser and the initial frequency of the fourth Raman laser; and They are Atomic energy level Linear The energy difference between the two ground states and Atomic energy level Linear The energy level difference between the two ground states; It is the preset frequency difference limit value.

4. The gravity differential measurement method according to claim 3, characterized in that: The initial frequencies of the first Raman laser (106), the second Raman laser (107), the third Raman laser (108), and the fourth Raman laser (109) satisfy the following conditions: ， ， ， in, is the frequency reference zero point, equal to atomic The transition frequency of the line |F=3>-|F'=4>.

5. The gravity differential measurement method according to claim 2, characterized in that: The light intensities of the first Raman laser (106), the second Raman laser (107), the third Raman laser (108), and the fourth Raman laser (109) satisfy the following conditions: ， in, is the intensity of the first Raman laser Fourth, the intensity of the Raman laser.

6. The gravity differential measurement method according to claim 2, characterized in that: The two branched beams in the third Raman laser (108), the two branched beams in the fourth Raman laser (109), the first Raman laser (106), and the second Raman laser (107) are all chirped, and the chirp rates of the fourth Raman laser (109) and the first Raman laser (106) are , the chirp rates of the second Raman laser (107) and the third Raman laser (108) are , the chirp rate value , is the effective wave vector, is the acceleration due to gravity.

7. The gravity differential measurement method according to claim 3 or 4, characterized in that: The first π / pulse, π pulse, second π / The frequency of the third Raman laser (108) corresponding to the pulse is the initial frequency of the third Raman laser ; First π / pulse, π pulse, second π / The frequency of the fourth Raman laser (109) corresponding to the pulse is the initial frequency of the fourth Raman laser ; The first pulse in the odd-numbered π pulse group The frequencies of the third Raman laser (108) and the fourth Raman laser (109) corresponding to the π pulses are: ， ， in, The π pulse groups with odd serial numbers are the first π pulse group and the third π pulse group; Indicates the number of the π pulse group with an odd sequence number. The frequency of the third Raman laser in the π pulse; Indicates the number of the π pulse group with an odd sequence number. The frequency of the fourth Raman laser in the π pulse; Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the third Raman laser; Indicates the number of the π pulse group with an odd sequence number. The frequency change of the fourth Raman laser corresponding to a π pulse is: ， ， The sequence number of a π pulse in an odd-numbered π pulse group , is the total number of π pulses in a π pulse group; Indicates rounding up; yes Atomic Doppler shift; yes Atomic Doppler shift; The first pulse in the π pulse group with an even number The frequencies of the third Raman laser (108) and the fourth Raman laser (109) in the π pulses are respectively: ， ， in, The π pulse groups with even serial numbers are the second π pulse group and the fourth π pulse group; Indicates the number of the π pulse group with an even sequence number. The frequency of the third Raman laser in the π pulse; Indicates the number of the π pulse group with an even sequence number. The frequency of the fourth Raman laser in the π pulse; Indicates the number of the π pulse group with an even sequence number. Each π pulse corresponds to the frequency change of the third Raman laser; Indicates the number of the π pulse group with an even sequence number. The frequency change of the fourth Raman laser corresponding to a π pulse is: ， ， The sequence number of a π pulse in an even-numbered π pulse group , Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the third Raman laser; Indicates the number of the π pulse group with an odd sequence number. Each π pulse corresponds to the frequency change of the fourth Raman laser.

8. The gravity differential measurement method according to claim 2, characterized in that: The step 2 specifically includes the following steps: Using cooling laser (104) and three-dimensional magneto-optical trap (3D-MOT) Atoms and The atoms are cooled and loaded synchronously, and the cooling laser (104) forms an atomic fountain with a (0,0,1) configuration; the loaded cold atomic cluster (101) is subjected to free fall or vertical downward throwing, and then vertical upward throwing.

Images