A cold atom Sagnac interferometer and its use method

Abstract

The present application discloses a cold atom Sagnac interferometer and a method for using the same, which solves the problems of poor symmetry of the magnetic ring trap and rough magnetic ring cavity in the prior art, which affect the measurement accuracy. The cold atom Sagnac interferometer comprises a magnetic ring cavity generation module. The magnetic ring cavity generation module comprises an upper chip, a lower chip, an upper conductive coil group and a lower conductive coil group. The upper chip and the lower chip are facing each other. The upper conductive coil group and the lower conductive coil group both comprise concentric conductive coils with opposite current directions. The currents of all conductive coils are equal. The upper conductive coil group and the lower conductive coil group are respectively located on the lower surface of the upper chip and the upper surface of the lower chip. The currents of the conductive coils facing each other in the upper and lower conductive coil groups are in opposite directions. The annular magnetic potential well constructed in the present application has good symmetry and stability, which can effectively solve the problem of weak local binding ability of the magnetic potential well, improve the smoothness of the magnetic ring guide, and thus effectively improve the measurement accuracy of the system.

Description

Technical Field

[0001] The present application relates to the field of quantum sensing technology, and in particular to a cold atom Sagnac interferometer and a method of using the same. Background Art

[0002] The Sagnac effect was first used in fiber optic gyroscopes. In recent years, with the rapid development of laser cooling technology, cold atom Sagnac interferometers have gradually become a research hotspot. Cold atom Sagnac interferometers can be divided into two types: free-space type and guided type according to the different propagation modes of matter wave packets. Among them, the guided type can effectively avoid the thermal expansion problem of the atomic cloud during movement and can well control the propagation path of the atoms. Its stability is better than the space type. Among the guided types, the chip-type cold atom Sagnac interferometer has more application advantages in the field of inertial navigation due to its small size, high sensitivity, and easy small-scale integration.

[0003] Chip-based cold-atom Sagnac interferometers utilize on-chip magnetic ring guides to achieve cold-atom Sagnac interferometry. In these experiments, the symmetry of the potential well and the smoothness of the magnetic ring guide are crucial factors influencing the sensitivity of the system's rotational measurements. On the one hand, potential well asymmetry can lead to weaker binding of the atomic cluster at local locations within the well, which in turn causes localized thermal expansion of the cluster, ultimately affecting the accuracy of the measurement results. On the other hand, poor potential well symmetry can reduce the smoothness of the magnetic ring guide. A rough magnetic ring guide can cause energy loss during the rotation of the atomic cluster, reducing the accuracy of the system's rotational measurements.

[0004] Current chip-based cold-atom Sagnac interferometers are primarily based on a three-wire annular guide structure [PHYSICAL REVIEW A97, 033405(2018)]. This utilizes three concentric circular rings of current-carrying conductors on the same surface to generate a magnetic ring guide for conducting cold-atom Sagnac interferometry experiments. The magnetic potential well generated by this structure places extremely high demands on the current ratio in the current-carrying conductors. Improper adjustment of the current ratio will directly affect the symmetry and smoothness of the annular potential well, thereby reducing the measurement accuracy of the system's rotation. Furthermore, the magnetic potential well generated by the three-wire structure is located above the plane of the conductors and is therefore highly susceptible to the influence of external magnetic fields. This influence will inevitably destroy the symmetry of the potential well and increase the roughness of the magnetic ring guide, thereby reducing the stability of the system. Summary of the Invention

[0005] The embodiments of the present application provide a cold atom Sagnac interferometer and a method for using the same, which solve the problems in the prior art of poor symmetry of the magnetic ring trap and roughness of the magnetic ring cavity, which affect measurement accuracy.

[0006] An embodiment of the present application provides a cold atom Sagnac interferometer for rotation sensing, comprising a magnetic ring cavity generation module. The magnetic ring cavity generation module comprises an upper chip, a lower chip, an upper conductive coil group, and a lower conductive coil group. The upper conductive coil group comprises a first conductive coil and a second conductive coil that are concentric and have opposite current directions. The lower conductive coil group comprises a third conductive coil and a fourth conductive coil that are concentric and have opposite current directions. The currents of all conductive coils are equal. The upper conductive coil group and the lower conductive coil group are respectively located on the lower surface of the upper chip and the upper surface of the lower chip. The first conductive coil is coaxial with the third conductive coil, has the same radius, and has opposite current directions. The second conductive coil is coaxial with the fourth conductive coil, has the same radius, and has opposite current directions.

[0007] Furthermore, the system also includes an atomic system cooling module, a first pulse generation module, a second pulse generation module, and an atomic interference fringe detection module. The atomic system cooling module is used to cool the atomic cloud to be measured to the ground state and place it in the magnetic ring cavity module. The magnetic ring cavity generation module is used to receive the atomic cloud and cause it to rotate. The first and second pulse generation modules are used to generate π / 2 Raman laser pulses that are injected into the magnetic ring cavity generation module. The atomic interference fringe detection module is used to detect the interference fringes produced after the cold atomic cloud is coherently combined.

[0008] Furthermore, the system further comprises a detection signal output module, which is used to output the interference fringe signal detected by the atomic interference fringe detection module.

[0009] Preferably, the atomic system cooling module uses a laser beam and a static magnetic field to build a magneto-optical trap.

[0010] Preferably, the detection signal output module adopts a photoelectric conversion signal output device.

[0011] Further preferably, the atomic cloud selects Rb-87 atoms.

[0012] Further preferably, the magneto-optical trap is located in the annular cavity in a partially overlapping state.

[0013] The present application also provides a method for using a cold atom Sagnac interferometer, using the cold atom Sagnac interferometer described in any one of the above embodiments, the method comprising the following steps:

[0014] The atomic cloud is cooled to the ground state through the atomic system cooling module, and the cold atomic cloud is transferred to the magnetic ring cavity.

[0015] A π / 2 Raman pulse is injected into the atomic cloud in the magnetic ring cavity, causing the cold atomic cloud to split into two atomic clouds with opposite internal spins, which rotate towards each other along the magnetic ring cavity.

[0016] When the two atomic clouds meet again, a second π / 2 Raman pulse is injected, causing the two atomic clouds to interfere and obtain interference fringes.

[0017] The interference fringes are measured using an atomic interference fringes detection module, and the detection signal output module is used to output the detection signal.

[0018] Furthermore, when the magneto-optical trap is located in the annular cavity between the two conductive coil assemblies, the step of cooling the atomic cloud to the ground state by the atomic system cooling module and transferring the cold atomic cloud to the magnetic annular cavity further comprises the following steps:

[0019] The coil assembly switch is in the open state, and the magneto-optical trap cools the atomic cloud.

[0020] After the atomic cloud cools to the ground state, the laser beam and static magnetic field of the magneto-optical trap are removed, and the switch of the conductive coil group is closed to confine the cooled atomic cloud in the magnetic ring trap.

[0021] Furthermore, the method further comprises the steps of:

[0022] The Sagnac phase and rotational angular velocity information of the inertial rotating system are inferred based on the output detection signal.

[0023] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0024] This application utilizes a cold atom interferometer to achieve high-precision measurement of the angular velocity of a rotating system. The constructed annular magnetic potential well exhibits excellent symmetry and stability, effectively addressing the problem of weak localized confinement within the potential well and improving the smoothness of the magnetic ring, thereby significantly enhancing the measurement accuracy of the system. Furthermore, this cold atom interferometer is a chip-based device, offering advantages such as small size and ease of integration and packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0026] Figure 1 This is a structural diagram of an embodiment of a magnetic ring cavity generation module for a cold atom Sagnac interferometer of this application;

[0027] Figure 2 This is a schematic diagram of an embodiment of the current direction of the magnetic ring cavity generating module of the present application;

[0028] Figure 3 This is a structural diagram of the overall embodiment of the cold atom Sagnac interferometer of this application;

[0029] Figure 4This is a flow chart of an embodiment of a method for using the cold atom Sagnac interferometer of this application;

[0030] Figure 5 This is a schematic diagram of an embodiment of the first pulse generating module and the second pulse module injecting pulses in the present application;

[0031] Figure 6 This is a flow chart of another embodiment of the method for using the cold atom Sagnac interferometer of the present application;

[0032] Figure 7 This is a flow chart of an embodiment of a method for obtaining data using a cold atom Sagnac interferometer in this application. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the specific embodiments of this application and the corresponding drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0034] The following describes in detail the technical solutions provided by various embodiments of the present application in conjunction with the accompanying drawings.

[0035] Figure 1 This is a structural diagram of an embodiment of a magnetic ring cavity generation module for a cold atom Sagnac interferometer of this application.

[0036] An embodiment of the present application provides a cold atom Sagnac interferometer for rotation sensing, including a magnetic ring cavity generation module 31.

[0037] The magnetic ring cavity generation module includes an upper chip 11 , a lower chip 12 , an upper conductive coil assembly 13 and a lower conductive coil assembly 14 .

[0038] The upper chip and the lower chip are facing each other.

[0039] The upper conductive coil assembly includes a first conductive coil 131 and a second conductive coil 132 that are concentric and have currents in opposite directions.

[0040] The lower conductive coil assembly includes a third conductive coil 141 and a fourth conductive coil 142 that are concentric and have currents in opposite directions.

[0041] The current in all the coils is equal.

[0042] The upper conductive coil assembly and the lower conductive coil assembly are respectively located on the lower surface of the upper chip and the upper surface of the lower chip.

[0043] The first conductive coil and the third conductive coil are coaxial, have the same radius, and have currents in opposite directions. The second conductive coil and the fourth conductive coil are coaxial, have the same radius, and have currents in opposite directions.

[0044] Figure 2 This is a schematic diagram of an embodiment of the current direction of the magnetic ring cavity generating module of this application.

[0045] For example, between two layers of chips are two coaxial and symmetrical layers of current-carrying conductors, one on top and one on the bottom. Each layer of current-carrying conductors consists of two concentric circular rings of conductors (i.e., a first conductor coil and a second conductor coil). The currents in the four coils are equal, but the currents in the two concentric coils flow in opposite directions. The two first coils and the two second coils facing each other on the upper and lower layers flow in opposite directions. The magnetic potential well generated by this structure is an annular structure, extending along the direction of the conductors to form a ring-shaped cavity, referred to herein as a "magnetic ring cavity" or "magnetic ring well." The plane of the ring cavity lies midway between the planes of the upper and lower layers of current-carrying conductors.

[0046] The existing three-wire atomic Sagnac interferometer [PHYSICAL REVIEW A 97,033405(2018)] produces a magnetic ring trap with poor symmetry and a rough magnetic ring cavity, which seriously affects the accuracy of the system's rotational angular velocity measurement. The ring cavity produced by the four-wire structure proposed in this invention effectively avoids these problems. Between the two layers of chips is a coaxial double-layer concentric conductor coil, and the upper and lower concentric conductor coils are symmetrical. The current in the wires is the same, and the current direction is opposite in the conductor coils facing each other.

[0047] The magnetic ring generated by the ring cavity device is located in the middle of the plane where the two-layer conductive coil group structure is located, forming a sandwich-like shape, which can effectively avoid the interference of the external magnetic field on the ring magnetic potential well.

[0048] The four-wire ring guide structure has a chip layer above and below the double-layer wire, making the interferometer easier to integrate and package.

[0049] Figure 3 This is a structural diagram of the overall embodiment of the cold atom Sagnac interferometer of this application.

[0050] The cold atom Sagnac interferometer further includes a magnetic ring cavity generation module 31, that is, the four-wire ring guide structure described in the above embodiment, and also includes an atomic system cooling module 32, a first pulse generation module 33, a second pulse generation module 34 and an atomic interference fringe detection module 35.

[0051] The atomic system cooling module is used to cool the atomic cloud to be measured to the ground state and place it in the magnetic ring cavity module.

[0052] For example, the atomic system cooling module uses a laser beam and a static magnetic field to build a magneto-optical trap to cool atoms to the ground state and obtain a cold atomic cloud.

[0053] Laser cooling is used, that is, a magneto-optical trap is constructed by combining a laser beam with a static magnetic field.

[0054] In order to ensure that the cold atomic cloud transfer process does not affect the atomic cloud state, an adiabatic transfer method is adopted. Figure 2 As shown, the annular magnetic conductivity generating device and the atomic system cooling module are both placed in a magneto-optical trap vacuum device. The magneto-optical trap is located in a partially overlapping state in the annular cavity, that is, the magneto-optical trap is located in the annular cavity between the two conductive coil groups, and the center of the magneto-optical trap (i.e., the position where the atoms are cooled to the ground state) is located in the annular cavity.

[0055] The cooled atomic cloud is transferred to the magnetic ring cavity by an adiabatic transfer method, which successfully avoids the impact of the transfer operation on the state of the atomic cloud.

[0056] The atomic cloud is selected from Rb-87 atoms, and the Rb-87 atoms are cooled to a ground state to obtain an Rb-87 cold atomic cloud.

[0057] The magnetic ring cavity generating module is used to receive the atomic cloud and make it rotate.

[0058] The first pulse generating module and the second pulse generating module are used to generate π / 2 Raman laser pulses that are injected into the magnetic ring cavity generating module.

[0059] For example, the π / 2 Raman laser pulse generated by the first pulse generating module is injected into the magnetic ring cavity to act on the cold atomic cloud in the ground state, thereby achieving coherent beam splitting of the cold atomic cloud.

[0060] The second pulse generating module generates a π / 2 Raman laser pulse which enters the magnetic ring cavity when the split cold atomic clouds meet, causing the two cold atomic clouds rotating in opposite directions to coherently combine to obtain a final state and generate interference fringes.

[0061] The first pulse generating module hits the magnetic ring cavity module when the atomic cloud is in the ground state, causing the atomic cloud to split; the second pulse generating module hits the magnetic ring cavity module when two atomic clouds meet, causing the two atomic clouds to interfere and produce interference fringes.

[0062] The atomic interference fringe detection module is used to detect the interference fringes generated after the cold atomic cloud is coherently combined.

[0063] When the split cold atomic clouds meet, they are hit by a π / 2 Raman laser pulse, causing coherent beam combination to produce interference fringes.

[0064] Furthermore, the system further includes a detection signal output module 36. The detection signal output module is configured to output the interference fringe signal detected by the atomic interference fringe detection module. Preferably, the detection signal output module employs a photoelectric conversion signal output device. The rotational angular velocity of the system in which the magnetic ring cavity is located can be inferred based on the output interference fringe information.

[0065] Figure 4 This is a flow chart of an embodiment of the method for using the cold atom Sagnac interferometer of this application.

[0066] The present application also provides a method for using a cold atom Sagnac interferometer, which uses the cold atom Sagnac interferometer described in any one of the above embodiments, comprising the steps of:

[0067] Step 101: Cool the atomic cloud to the ground state through the atomic system cooling module, and transfer the cold atomic cloud to the magnetic ring cavity generation module.

[0068] For example, the magneto-optical trap and the annular cavity are partially overlapped, and the atomic cloud reaches the position where the magneto-optical trap and the annular cavity overlap and is cooled to the ground state, becoming a cold atomic cloud.

[0069] Step 102: inject a π / 2 Raman pulse into the atomic cloud in the magnetic ring cavity, so that the cold atomic cloud is split into two atomic clouds with opposite internal spins, and the two atomic clouds rotate in opposite directions along the magnetic ring trap.

[0070] The π / 2 Raman pulse is injected into the atomic cloud in the magnetic ring cavity generation module, causing the cold atomic cloud to change from the ground state to a coherent superposition state with opposite internal spins. This quantum state is the initial state for the rotation measurement of the inertial system.

[0071] Step 103: When the two atomic clouds meet again, a second π / 2 Raman pulse is injected to cause interference between the two atomic clouds to obtain interference fringes.

[0072] After free evolution, two atomic clouds with opposite internal spin directions meet again and obtain the Sagnac phase.

[0073] Let the prepared system initial state |ψ> in Free evolution begins within the magnetic ring cavity. Specifically, two clouds of cold atoms with opposite internal spins begin rotating toward each other within the ring magnetic guide at time t = 0. After a rotational evolution of τ, the two potential wells meet and acquire a relative phase, the Sagnac phase. At this point, the initial state undergoes free evolution, resulting in |ψ(τ)>=U(Ω, τ)|ψ> in .

[0074] At time t=τ, the second π / 2 Raman pulse is injected, and the two atomic clouds interfere to obtain interference fringes.

[0075] Step 104: Measure the interference fringes using the atomic interference fringes detection module, and output the detection signal using the detection signal output module.

[0076] An atomic interference fringe detection module is used to measure the interference fringes of the final state of the atomic cloud, and a photoelectric conversion device is used as a detection signal output module to output the detection signal.

[0077] Figure 5 This is a schematic diagram of an embodiment of the first pulse generating module and the second pulse module injecting pulses in the present application.

[0078] For example, alkaline metal atoms, Rb-87, were used as a matter-wave source in the detection experiment. First, the Rb-87 atomic cloud was cooled to its ground state using the Atomic System Cooling Module. This module uses a laser beam and a static magnetic field to create a magneto-optical trap within a vacuum glass cavity to cool the atomic cloud, generating a cold Rb-87 atomic cloud. The cooled atomic cloud was then adiabatically transferred to the constructed magnetic ring cavity generation module.

[0079] The π / 2 Raman pulse generated by the first pulse generation module is injected into the pre-built magnetic ring cavity generation module and acts on the Rb-87 cold atomic cloud. The cold atomic cloud is coherently split by the Raman pulse, turning it into two cold atomic clouds with opposite spins: that is, the cold atomic cloud changes from the ground state to a coherent superposition state with opposite internal spins. This quantum state is the initial state for the rotation measurement of the inertial system.

[0080] Prepare the initial state |ψ> in After that, this initial state begins to evolve freely in the magnetic ring cavity, as shown in the attached figure. Figure 5 As shown in the figure, two cold atomic clouds with opposite internal spins start from time t=0 and move in the annular magnetic guide at angular velocity ω. p +Ω and ω p -Ω rotates in opposite directions, where Ω is the rotational angular velocity of the system where the annular magnetic guide is located. ω p +Ω means that the atomic cloud rotates in the same direction as the annular magnetic permeance, ω p -Ω indicates the opposite direction of rotation. After the rotation evolution of τ time, the two potential wells meet and obtain the relative phase, that is, the Sagnac phase φ. At this time, the initial state undergoes free evolution and obtains |ψ(τ)>=U(Ω, τ)|ψ> in .

[0081] The π / 2 Raman pulse is injected again to cause interference between the two atomic groups and obtain the final interference fringes, which is the detectable quantum state.

[0082] Finally, the detection device is used to measure the interference fringe information of the final state of the atomic cloud, and the photoelectric conversion device is used to output the interference fringe signal. Based on the output information, the rotational angular velocity of the rotating system where the atomic cloud is located is inferred.

[0083] The four-wire magnetic ring trap constructed by the present invention has good symmetry and stability. At the same time, the rotational angular velocity of the system is measured using the GHZ state as the initial state, which can effectively improve the measurement accuracy.

[0084] Figure 6 A flow chart of another embodiment of the method for using the cold atom Sagnac interferometer of this application.

[0085] Furthermore, when the magneto-optical trap is located in the annular cavity between the two conductive coil assemblies, step 101 further includes the following steps:

[0086] Step 105: The coil assembly switch is turned on, and the magneto-optical trap cools the atomic cloud.

[0087] Step 106: After the atomic cloud cools to the ground state, the laser beam and static magnetic field of the magneto-optical trap are removed, and the switch of the conductive coil assembly is closed to confine the cooled atomic cloud in the magnetic ring trap.

[0088] The coil switches are in the open state. Once the MOT cools the atomic cloud, the current switches in the four coils are immediately closed, creating a circular magnetic potential trap that traps the cooled atomic cloud. Thus, the cold atomic cloud is transferred from the MOT to the magnetic ring cavity without any displacement.

[0089] Figure 7 This is a flow chart of an embodiment of a method for obtaining data using a cold atom Sagnac interferometer in this application.

[0090] Based on steps 101 to 104 of the embodiment, the method further includes the following steps:

[0091] Step 107: Determine the Sagnac phase and rotational angular velocity information of the inertial rotating system based on the output detection signal.

[0092] The Sagnac phase and rotational angular velocity information of the inertial rotating system are inferred based on the output information.

[0093] The foregoing is merely an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A cold atom Sagnac interferometer for rotation sensing, characterized in that: Contains a magnetic ring cavity generation module; The magnetic ring cavity generation module comprises an upper chip, a lower chip, an upper conductive coil assembly and a lower conductive coil assembly; The upper conductive coil assembly and the lower conductive coil assembly are respectively located on the lower surface of the upper chip and the upper surface of the lower chip; The upper conductive coil assembly comprises a first conductive coil and a second conductive coil that are concentric and have currents in opposite directions; The lower conductive coil assembly comprises a third conductive coil and a fourth conductive coil which are concentric and have currents in opposite directions; The current in all the coils is equal; The first conductive coil and the third conductive coil are coaxial, have the same radius and current directions are opposite; The second conductive coil and the fourth conductive coil are coaxial, have the same radius and current directions are opposite; The magneto-optical trap is located in the annular cavity between the two conductive coil assemblies.

2. The cold atom Sagnac interferometer according to claim 1, characterized in that: It also includes an atomic system cooling module, a first pulse generating module, a second pulse generating module and an atomic interference fringe detection module; The atomic system cooling module is used to cool the atomic cloud to be measured to the ground state and place it in the magnetic ring cavity module; The magnetic ring cavity generation module is used to receive the atomic cloud and make it rotate; The first pulse generating module and the second pulse generating module are used to generate pulses that are driven into the magnetic ring cavity generating module. Raman laser pulses; The atomic interference fringe detection module is used to detect the interference fringes generated after the cold atomic cloud is coherently combined.

3. The cold atom Sagnac interferometer according to claim 1, characterized in that: It also includes a detection signal output module; The detection signal output module is used to output the interference fringe signal detected by the atomic interference fringe detection module.

4. The cold atom Sagnac interferometer according to claim 2, characterized in that: The atomic system cooling module uses a laser beam and a static magnetic field to build a magneto-optical trap.

5. The cold atom Sagnac interferometer according to claim 3, characterized in that: The detection signal output module adopts a photoelectric conversion signal output device.

6. The cold atom Sagnac interferometer according to claim 2, characterized in that: The atomic cloud selected Rb-87 atoms.

7. The cold atom Sagnac interferometer according to claim 4, characterized in that: The magneto-optical trap is located in the annular cavity in a partially overlapping state.

8. A method for using a cold atom Sagnac interferometer, using the cold atom Sagnac interferometer according to any one of claims 1 to 7, characterized in that: Contains steps: The atomic cloud is cooled to the ground state through the atomic system cooling module, and the cold atomic cloud is transferred to the magnetic ring cavity generation module; Will The Raman pulse hits the atomic cloud in the magnetic ring cavity, splitting the cold atomic cloud into two atomic clouds with opposite internal spins, which rotate in opposite directions along the magnetic ring cavity. When the two atomic clouds meet again, a second beam is injected Raman pulses cause interference between two atomic clouds to produce interference fringes; The interference fringes are measured using an atomic interference fringes detection module, and the detection signal output module is used to output the detection signal.

9. The method for using the cold atom Sagnac interferometer according to claim 8, characterized in that: When the magneto-optical trap is located in the annular cavity between the two conductive coil assemblies, the method comprises the following steps: The switch of the coil assembly is in the open state, and the magneto-optical trap cools the atomic cloud; After the atomic cloud cools to the ground state, the laser beam and static magnetic field of the magneto-optical trap are removed, and the switch of the conductive coil group is closed to confine the cooled atomic cloud in the magnetic ring trap.

10. The method for using the cold atom Sagnac interferometer according to claim 8, characterized in that: Also includes the steps: The Sagnac phase and rotational angular velocity information of the inertial rotating system are inferred based on the output detection signal.

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