A continuous cold atomic optical clock based on optical cohesion

Abstract

This application provides a continuous cold atom optical clock based on optical clusters, relating to the fields of cold atom technology and atomic clocks. It includes a first laser, a second laser, a first acousto-optic modulator, a second acousto-optic modulator, a third acousto-optic modulator, a first polarizer, a first polarizing beam splitter, a vacuum chamber, an electro-optic modulator, a detector, and a servo feedback circuit. By combining cold atom optical cluster technology with an atomic clock, a cold atom optical clock based on cold atom optical clusters is constructed. By maintaining the continuous action of the probe light, while the atoms are continuously cooled, the probe light can continuously act on the cold atom optical clusters, thereby obtaining continuous and stable clock transition spectra, realizing a continuous optical clock based on cold atom optical clusters, and obtaining continuous atomic clock transition signals. Furthermore, the probe light used to detect the atomic clock transition spectra and the re-pump light used to cool the atoms are provided by the same laser, which simplifies the optical clock structure.

Description

Technical Field

[0001] This application relates to the field of cold atom technology and atomic clocks, and in particular to a continuous cold atom optical clock based on optical clusters. Background Technology

[0002] With the advancement of science and technology and humanity's increasing pursuit of time precision, since the establishment of quantum theory, the reference for time has shifted from the oscillation frequency of quartz crystals in the macroscopic world to the atomic transition frequency in the microscopic world. This led to the emergence of quantum frequency standards that use cold atoms (or atomic ensembles) as references, such as microwave atomic clocks. Furthermore, the invention and development of laser cooling technology have enabled microwave atomic clocks based on cold atoms to be widely applied and developed. On this basis, the frequency stability of cold atom optical clocks has been improved by several orders of magnitude compared to microwave atomic clocks.

[0003] Among them, strontium atomic optical clocks, ytterbium atomic optical clocks, and aluminum ion optical clocks are all cold atom optical clocks with relatively high frequency stability. However, these cold atom optical clocks are difficult to obtain continuous atomic clock transition signals, and therefore cannot be used for continuous timekeeping, which limits their application in fields such as satellite navigation and aerospace. Summary of the Invention

[0004] This application provides a continuous cold atom optical clock based on optical clusters to solve the problem that existing cold atom optical clocks cannot obtain continuous atomic clock transition signals and therefore cannot be used for continuous timekeeping.

[0005] In a first aspect, this application provides a continuous cold atom optical clock based on optical clusters, comprising: a first laser, a second laser, a first acousto-optic modulator, a second acousto-optic modulator, a third acousto-optic modulator, a first polarizer, a first polarizing beam splitter, a vacuum chamber, an electro-optic modulator, a detector, and a servo feedback circuit.

[0006] The first laser is used to emit the first laser beam. After the first laser beam is detuned by the first acousto-optic modulator, the cooled light is obtained.

[0007] A second laser emits a second laser beam. After being detuned by a second acousto-optic modulator, the second laser beam passes through a first polarizer and a first polarizing beam splitter to obtain a re-pump beam and a probe beam. The re-pump beam is coupled with a cooling beam and then acts on a vacuum chamber. After cooling in the vacuum chamber, cold atom optical clusters are obtained. The intensity and spot size of the cooling beam and the re-pump beam are matched to enhance the cooling effect. The vacuum chamber includes a single-stage vacuum chamber and a two-stage vacuum chamber, both used to obtain continuous cold atom optical clusters. The probe beam is detuned by a third acousto-optic modulator and then transmitted to an electro-optic modulator. After modulation by the electro-optic modulator, it acts on the cold atom optical clusters to obtain the corresponding clock transition spectral lines. The electro-optic modulator is used to perform high-speed modulation of the received laser beam, with a modulation rate on the order of hundreds of kilohertz to hundreds of megahertz.

[0008] The detector is used to detect clock transition spectral lines and transmit the detected clock transition spectral lines to the servo feedback circuit.

[0009] A servo feedback circuit is used to modulate and demodulate the clock transition spectrum to obtain the frequency discrimination signal corresponding to the clock transition spectrum. The frequency discrimination signal is fed back to the third acousto-optic modulator and the second laser through the servo feedback circuit, so that the second laser can stabilize its frequency and lock the probe light based on the clock transition spectrum. This allows the probe light, after being detuned by the third acousto-optic modulator, to continuously act on the cold atom optical clusters to obtain continuous clock transition spectrums, thus realizing a cold atom optical clock based on cold atom optical clusters. The feedback rate of the servo feedback circuit is at least one order of magnitude larger than the feedback rate of the laser linewidth.

[0010] In one possible implementation, the continuous cold atom optical clock based on optical clusters may further include a second polarizer, a third polarizer, and a second polarizing beam splitter. The two-stage vacuum chamber may include a two-dimensional vacuum chamber and a three-dimensional vacuum chamber. The second polarizer and the second polarizing beam splitter are used to split the cooling light into a first cooling light and a second cooling light, and to split the re-pump light into a first re-pump light and a second re-pump light after passing through the third polarizer and the second polarizing beam splitter. The first re-pump light is coupled with the first cooling light and acts on the two-dimensional vacuum chamber to form a two-dimensional magneto-optical trap, which is used to pre-cool the atoms. The second re-pump light is coupled with the second cooling light and acts on the three-dimensional vacuum chamber to form a three-dimensional magneto-optical trap, which is used to cool the pre-cooled atoms to obtain cold atom optical clusters.

[0011] In one possible implementation, the two-dimensional vacuum chamber and the three-dimensional vacuum chamber are connected by a differential pipe.

[0012] In one possible implementation, the continuous cold atom optical clock based on optical clusters further includes at least one of the following: a first mirror for reflecting the light after the second re-pump light and the second cooling light are coupled to a three-dimensional vacuum chamber.

[0013] In one possible implementation, the first polarizer, the second polarizer, and the third polarizer are all half-wave plates.

[0014] In one possible implementation, the servo feedback circuit can be specifically used to provide a reference signal and use the reference signal to modulate the clock transition spectrum detected by the detector to obtain a mixed signal. Then, the mixed signal is demodulated to obtain the frequency discrimination signal corresponding to the clock transition spectrum.

[0015] In one possible implementation, the continuous cold atom optical clock based on optical clusters further includes: a signal generator connected to the first acousto-optic modulator, the second acousto-optic modulator, and the third acousto-optic modulator, respectively. The signal generator is used to provide corresponding frequency modulation signals to the first acousto-optic modulator, the second acousto-optic modulator, and the third acousto-optic modulator, and the frequency modulation signals are used to modulate the laser frequency.

[0016] In one possible implementation, the continuous cold atom optical clock based on optical clusters further includes a signal amplifier, the input of which is connected to the output of a signal generator for amplifying the frequency modulation signal.

[0017] In one possible implementation, the continuous cold atom optical clock based on optical clusters may further include at least one of the following:

[0018] The second reflector is used to reflect the probe light to the third acousto-optic modulator;

[0019] The third mirror is used to reflect the re-pumped light to the third polarizer;

[0020] The fourth reflector is used to reflect the probe light, which has been detuned by the third acousto-optic modulator, to the electro-optic modulator.

[0021] In one possible implementation, both the first laser and the second laser are narrow-linewidth external cavity semiconductor lasers.

[0022] This application provides a continuous cold atom optical clock based on optical clusters. It constructs a cold atom optical clock by combining cold atom optical cluster technology with an atomic clock. The detected clock transition spectrum is then fed back to a third acousto-optic modulator and a second laser via a servo feedback circuit, achieving laser frequency stabilization and maintaining the continuous action of the probe light. While the atoms are continuously cooled, the probe light can continuously act on the cold atom optical clusters, thus obtaining a continuous and stable clock transition spectrum, realizing a continuous optical clock based on cold atom optical clusters, and obtaining continuous atomic clock transition signals. This can be applied in aerospace, satellite navigation, and other fields. Furthermore, the probe light used to detect the atomic clock transition spectrum and the re-pump light used to cool the atoms are provided by the same laser, which simplifies the optical clock structure. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0024] Figure 1 This is a schematic diagram illustrating an application scenario of the cold atom optical clock provided in one embodiment of this application;

[0025] Figure 2 This is a schematic diagram of the structure of a continuous cold atom optical clock based on optical clusters provided in an embodiment of this application;

[0026] Figure 3 This is a schematic diagram of the structure of a rubidium atom optical clock based on rubidium atom optical clusters provided in one embodiment of this application;

[0027] Figure 4 This is a schematic diagram of the structure of a continuous cold atom optical clock based on optical agglomerates provided in another embodiment of this application.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1: First laser;

[0030] 2: Second laser;

[0031] 3: First audio-visual modulator;

[0032] 4: Second acousto-optic modulator;

[0033] 5: First polarizer;

[0034] 6: First polarizing beam splitter;

[0035] 7: Third audio-visual modulator;

[0036] 8: Vacuum chamber;

[0037] 9: Electro-optic modulator;

[0038] 10: Detector;

[0039] 11: Servo feedback circuit;

[0040] 12: Second polarizer;

[0041] 13: Third polarizer;

[0042] 14: Second polarizing beam splitter;

[0043] 15: 2D vacuum chamber;

[0044] 16: 3D vacuum chamber;

[0045] 17: First reflecting mirror;

[0046] 18: Second reflecting mirror;

[0047] 19: Third reflecting mirror;

[0048] 20: Fourth reflecting mirror.

[0049] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0050] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0051] The terms “first,” “second,” etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, products, or apparatus.

[0052] First, some of the technical terms used in this application will be explained:

[0053] Vacuum degree: refers to the degree of rarefaction of gas in a vacuum state. A high vacuum degree means a "good" vacuum degree, while a low vacuum degree means a "poor" vacuum degree.

[0054] Electro-optic modulator, or EOM for short, is a modulator based on the electro-optic effect. That is, when a certain crystal is subjected to an external electric field, its refractive index changes, and when light waves pass through this crystal medium, their transmission characteristics are affected and changed.

[0055] Servo feedback circuits can also be called servo feedback control circuits, servo circuit systems, or frequency stabilization systems.

[0056] Currently, alkali metal atom gases are important media that humans can experiment with and utilize. Cold atom optical aggregates, used as quantum references, have advantages such as simple structure, mature cooling technology, high atom utilization, high spectral signal-to-noise ratio, and easy continuous operation. They can be used to realize high-performance time-keeping clocks that are continuously operated and portable.

[0057] In related technologies, existing cold atom optical clocks, such as strontium atomic optical clocks, ytterbium atomic optical clocks, and aluminum ion optical clocks, cannot be used for continuous timekeeping because the cooling process is complex and it is difficult to obtain continuous atomic clock transition signals.

[0058] To address the aforementioned problems, this application proposes a continuous-type cold atom optical clock based on optical clusters. This clock utilizes a polarizer and a polarizing beam splitter to separate a probe beam from the re-pump light emitted by a laser used to cool atoms and obtain cold atom optical clusters. This probe beam is then used to detect atoms, thereby obtaining the clock transition spectra of alkali metal atoms, such as rubidium atoms. 87 Rb or 85 The clock transition spectral lines of Rb are obtained; at the same time, during the process of capturing atoms to obtain cold atom optical aggregates (or cold atom aggregates), the probe light is kept continuously applied. While the atoms are continuously cooled, the probe light can continuously act on the cold atom optical aggregates to continuously detect the clock transition spectral lines of the atoms, thereby obtaining continuous and stable clock transition spectral lines, realizing a continuous optical clock based on cold atom optical aggregates, and obtaining continuous atomic clock transition signals.

[0059] Furthermore, the probe light and the re-pump light used to cool atoms in this cold atom optical clock are provided by the same laser, which simplifies the structure of the cold atom optical clock.

[0060] Clocks, as an indispensable tool in human society, have a wide range of applications. From pendulum clocks to mechanical clocks, and then to quartz crystal clocks, the accuracy of timekeeping has continuously improved. With the development of modern science and technology, scientists have utilized the highly stable transition frequencies of the hyperfine structure of atoms—the clock transition lines—to develop atomic clocks with even higher precision than quartz crystal clocks. Optical clocks, currently the most promising type of atomic clock, utilize laser-cooled atom technology to create cold atom optical clocks, further improving the accuracy of time measurement and holding promise for applications in aerospace, satellite navigation, and other fields.

[0061] Figure 1 This is a schematic diagram illustrating an application scenario of the cold atom optical clock provided in one embodiment of this application. For example... Figure 1 As shown, when the cold atom optical clock is applied to satellite navigation, the application scenario includes a client 101 and a satellite navigation system 102. There can be at least one client 101. The satellite navigation system 102 is equipped with a cold atom optical clock. The client 101 can receive time synchronization from the cold atom optical clock in the satellite navigation system, resulting in more accurate and stable timing.

[0062] It should be noted that the satellite navigation system 102 can also be replaced by other systems that can use cold atom optical clocks. The client 101 can be a mobile phone, computer, laptop, or personal digital assistant (PDA), etc.

[0063] The following combination Figure 1 Application scenarios, refer to Figure 2 This application describes a cold atom optical clock according to exemplary embodiments thereof. It should be noted that the above application scenarios are shown only to facilitate understanding of the spirit and principles of this application, and the embodiments of this application are not limited to those described herein. Figure 1 The limitations of the application scenarios shown.

[0064] Figure 2 This is a schematic diagram of the structure of a continuous cold atom optical clock based on optical clusters according to an embodiment of this application. Figure 2 As shown, the continuous cold atom optical clock based on optical agglomerates in this embodiment includes: a first laser 1, a second laser 2, a first acousto-optic modulator 3, a second acousto-optic modulator 4, a first polarizer 5, a first polarizing beam splitter 6, a third acousto-optic modulator 7, a vacuum chamber 8, an electro-optic modulator 9, a detector 10, and a servo feedback circuit 11. Wherein:

[0065] The first laser 1 is used to emit the first laser. After the first laser is detuned by the first acousto-optic modulator 3, the first laser is cooled to obtain the cooling light.

[0066] The second laser 2 is used to emit a second laser. After the second laser is detuned by the second acousto-optic modulator 4, it passes through the first polarizer 5 and the first polarizing beam splitter 6 to obtain a repump beam and a probe beam. The repump beam is coupled with a cooling beam and then acts on a vacuum chamber 8. After being cooled by the vacuum chamber 8, cold atom optical clusters are obtained. The intensity and spot size of the cooling beam and the repump beam are matched to improve the cooling effect. The vacuum chamber includes a single-stage vacuum chamber and a two-stage vacuum chamber, both used to obtain continuous cold atom optical clusters. The probe beam is detuned by the third acousto-optic modulator 7 and then transmitted to the electro-optic modulator 9. After being modulated by the electro-optic modulator 9, it acts on the cold atom optical clusters to obtain the clock transition spectrum corresponding to the cold atom optical clusters. The electro-optic modulator 9 is used to perform high-speed modulation of the received laser, with a modulation rate on the order of hundreds of kilohertz to hundreds of megahertz.

[0067] Detector 10 is used to detect clock transition spectral lines and transmit the detected clock transition spectral lines to the servo feedback circuit.

[0068] The servo feedback circuit 11 is used to modulate and demodulate the clock transition spectrum to obtain the frequency discrimination signal corresponding to the clock transition spectrum. The frequency discrimination signal is fed back to the third acousto-optic modulator 7 and the second laser 2 through the servo feedback circuit, so that the second laser 2 can stabilize the frequency and lock the probe light based on the clock transition spectrum. It also allows the probe light, after being detuned by the third acousto-optic modulator 7, to continuously act on the cold atom optical clusters to obtain continuous clock transition spectrums, thereby realizing a cold atom optical clock based on cold atom optical clusters. The feedback rate of the servo feedback circuit is at least one order of magnitude larger than the feedback rate of the laser linewidth.

[0069] For example, since both the probe light and the repump light are obtained from a second laser, in one possible implementation, it is not necessary to separate the probe light; the repump light can simultaneously maintain the functions of atomic repumping and detection.

[0070] Optionally, the servo feedback circuit 11 can be specifically used to: provide a reference signal and use the reference signal to modulate the clock transition spectrum detected by the detector to obtain a mixed signal; then demodulate the mixed signal to obtain the frequency discrimination signal corresponding to the clock transition spectrum. In practical applications, the laser is not frequency-stabilized, that is, the laser frequency emitted by the laser fluctuates. However, after interacting with atoms, some points with stable frequencies can be detected. After locking onto these points, a stable laser frequency can be obtained. Therefore, in this application, after the probe light (i.e., laser) interacts with cold atom optical aggregates (atoms), a stable clock transition spectrum can be detected by the detector, and the frequency discrimination signal corresponding to the clock transition spectrum can be obtained through the servo feedback circuit. The frequency discrimination signal is then fed back to the third acousto-optic modulator and the second laser after passing through the locking module in the servo feedback circuit, thereby stabilizing the frequency of the second laser and locking the laser frequency.

[0071] For example, the first acousto-optic modulator 3, the second acousto-optic modulator 4, and the third acousto-optic modulator 7 are all acousto-optic modulators (AOMs) based on the acousto-optic effect, where the acousto-optic effect refers to the phenomenon of light waves being diffracted or scattered by an ultrasonic wave field when propagating in a medium. An acousto-optic modulator includes an acousto-optic medium, an electro-acoustic transducer, a sound-absorbing (or reflecting) device, and a driving power supply, etc.

[0072] In some embodiments, detector 10 can be a high-speed photodetector used to convert optical signals into electrical signals.

[0073] Optionally, the first polarizer, the second polarizer, and the third polarizer are all half-wave plates.

[0074] Specifically, the intensity and spot size of the cooling light and the re-pump light used to cool the atoms need to be adjusted to match in order to improve the cooling effect of rubidium atoms. For example, the spot diameter can be selected between 10-30 millimeters (mm), and the light power can be selected as 120 milliwatts (mW). Light can be directed at the atoms from six directions, 20mW in each direction, where the light intensity is equal to the light power per unit area.

[0075] For example, the cooling light can be selected with a spot size of 25 mm and an optical power of 120 mW, and the cooling light is directed at the atom from six directions, with 20 mW in each direction; the pump light can be selected with a spot size of 25 mm and an optical power of 2-3 mW in each direction; the probe light can be selected with a spot size of 1 mm and an optical power of 0.1-1 mW.

[0076] Currently, alkali metal atoms include lithium (Li) atoms, sodium (Na) atoms, potassium (K) atoms, rubidium (Rb) atoms, cesium (Cs) atoms, and francium (Fr) atoms. The continuous-type cold atom optical clock based on optical aggregates provided in this application can use any of the alkali metal atoms to prepare cold atom optical aggregates, such as using rubidium atoms to prepare... 87 Rb cold atom optical aggregates. Furthermore, different alkali metal atoms correspond to different atomic transition energy levels, thus requiring the use of lasers of different wavelengths. For example, when preparing cold atom optical aggregates using rubidium atoms, a 780 nm laser (also known as the D2 line) and a 795 nm laser (also known as the D1 line) are used. In specific applications, different D1 and D2 lines can be used depending on the alkali metal atom, and each D1 and D2 line will correspond to a different wavelength (nm).

[0077] Based on practical experience, the transition rates of the D1 and D2 lines of alkali metal atoms are typically on the order of MHz. Therefore, the number of atom detections per unit time can be increased by six orders of magnitude compared to optical clocks based on narrow linewidth transitions, effectively further increasing the number of atoms and the spectral signal-to-noise ratio. It is estimated that the continuous cold atom optical clock based on optical aggregates provided in this application, using a relatively simple atomic system, such as a rubidium atom system, can achieve short-term stability comparable to the highest precision optical clocks currently available.

[0078] In practical applications, the number of atoms is key to improving the signal-to-noise ratio of the reference signal of a cold atom optical clock. As the number of captured cold atoms increases, the signal-to-noise ratio of the cold atom optical clock reference signal will increase, thereby improving the frequency stability of the cold atom optical clock.

[0079] Specifically, taking rubidium atoms as an example, this application can achieve a number of atoms of up to 10. 9 The continuous optical aggregates of rubidium atoms yielded a stable quantum reference. 87 Rb cold atom optical clusters serve as quantum references, significantly reducing the Doppler effect and frequency shift caused by atomic collisions; simultaneously, the number of captured cold atoms (i.e., rubidium atoms) reaches 10-10. 9 This can also significantly improve the signal-to-noise ratio of the cold atom optical clock reference signal, thereby improving the frequency stability of the cold atom optical clock. The frequency stability of the rubidium atom optical clock obtained by this application based on rubidium atom optical clusters is theoretically comparable to the best existing cold atom optical clocks.

[0080] The continuous cold atom optical clock based on optical clusters provided in this application combines cold atom optical cluster technology with an atomic clock to construct a cold atom optical clock based on cold atom optical clusters. The detected clock transition spectrum is then fed back to a third acousto-optic modulator and a second laser through a servo feedback circuit to achieve laser frequency stabilization and maintain the continuous action of the probe light. While the atoms are continuously cooled, the probe light can continuously act on the cold atom optical clusters, thereby obtaining a continuous and stable clock transition spectrum, realizing a continuous optical clock based on cold atom optical clusters, and obtaining continuous atomic clock transition signals. It can be applied in aerospace, satellite navigation and other fields.

[0081] In addition, the probe light used to detect the transition lines of the atomic clock and the re-pump light used to cool the atoms are provided by the same laser, which simplifies the optical clock structure.

[0082] In some embodiments, the vacuum chamber 8 can be a single-stage vacuum chamber or a two-stage vacuum chamber, both used to obtain continuous cold atom optical clusters. Specifically, ultra-high vacuum technology can be used to maintain the vacuum levels of the two-stage vacuum chambers, namely the two-dimensional (2D) vacuum chamber and the three-dimensional (3D) vacuum chamber, at 10⁻⁶. -7 Pascal (Pa) and 10-9 Pa provides a high-vacuum environment for cooling atoms. Among them, the 3D vacuum chamber has an even higher vacuum level, which can reduce the loss of other atoms due to collisions and maintain the lifetime of atoms. In addition, the use of a two-stage vacuum chamber is to obtain a greater number of continuous cold atom optical clusters, such as rubidium atom optical clusters, and to maintain the lifetime of cold atoms in the millisecond (ms) range, laying the foundation for obtaining continuous cold atom clock transition spectra.

[0083] In addition, if vacuum chamber 8 is a primary vacuum chamber, then the primary vacuum chamber can be a two-dimensional vacuum chamber or a three-dimensional vacuum chamber, which can be set according to specific needs, and there are no restrictions here.

[0084] If vacuum chamber 8 is a multi-stage vacuum chamber, then the multi-stage vacuum chambers are interconnected. For example, a two-dimensional vacuum chamber and a three-dimensional vacuum chamber can be connected through a differential pipe. The differential pipe can be used to maintain the pressure of the two vacuum chambers and prevent gas flow from causing the pressure of the two vacuum chambers to become the same.

[0085] Based on the above embodiments, the continuous cold atom optical clock based on optical clusters may further include a second polarizer, a third polarizer, and a second polarizing beam splitter. The two-stage vacuum chamber may include a two-dimensional vacuum chamber and a three-dimensional vacuum chamber. The second polarizer and the second polarizing beam splitter are used to split the cooling light into a first cooling light and a second cooling light, and to split the re-pump light into a first re-pump light and a second re-pump light after passing through the third polarizer and the second polarizing beam splitter. The first re-pump light, after coupling with the first cooling light, acts on the two-dimensional vacuum chamber, forming a two-dimensional magneto-optical trap within the two-dimensional vacuum chamber. The two-dimensional magneto-optical trap is used for pre-cooling the atoms. The second re-pump light, after coupling with the second cooling light, acts on the three-dimensional vacuum chamber, forming a three-dimensional magneto-optical trap within the three-dimensional vacuum chamber. The three-dimensional magneto-optical trap is used for cooling the pre-cooled atoms, resulting in cold atom optical clusters. Among them, the magneto-optical trap (MOT) is an effective means of trapping neutral atoms. It can effectively capture atoms, such as rubidium atoms, and then cool the captured atoms in a 2D vacuum chamber and / or a 3D vacuum chamber using cold atom optical clustering technology to obtain cold atom optical clusters.

[0086] As an example, a rubidium atom optical clock based on optically bonded continuous-type cold atom optical clocks is used to illustrate this. For example... Figure 3As shown, the rubidium atomic optical clock may include: a first laser 1, a second laser 2, a first acousto-optic modulator 3, a second acousto-optic modulator 4, a first polarizer 5, a first polarizing beam splitter 6, a third acousto-optic modulator 7, an electro-optic modulator 9, a detector 10, a servo feedback circuit 11, a second polarizer 12, a third polarizer 13, a second polarizing beam splitter 14, a 2D vacuum chamber 15, and a 3D vacuum chamber 16.

[0087] In the rubidium atomic optical clock, the first laser 1 can be a 780nm laser, and the second laser 2 can be a 795nm laser. Specifically, using... 87 Rb's 780nm laser emits 780nm light as cooling light in the process of cooling atoms. 87 The 795nm laser emitted by Rb's 795nm laser is used as re-pumping light in cold atom processes and as detection light for clock transition spectral lines.

[0088] The 780nm laser emitted by the 780nm laser is detuned by the first acousto-optic modulator 3 (i.e., frequency shifting), then passes through the second polarizer 12 and the second polarizing beam splitter 14, splitting into two cooling beams: a first cooling beam and a second cooling beam, which are used as cooling beams for the 2D vacuum chamber 15 and the 3D vacuum chamber 16, respectively. The 795nm laser emitted by the 795nm laser is detuned by the second acousto-optic modulator 4, then passes through the first polarizer 5 and the first polarizing beam splitter 6, splitting into a re-pump beam used for atomic cooling and a probe beam for detecting clock transition lines. The repumped light can be split into a first repumped light and a second repumped light after passing through the third polarizer 13 and the second polarizing beam splitter 14. The first repumped light is coupled with the first cooling light of 780nm and then acts on the 2D vacuum chamber 15. The second repumped light is coupled with the second cooling light of 780nm and then acts on the 3D vacuum chamber 16.

[0089] Corresponding to the above embodiments, refer to Figure 3For a rubidium atom optical clock, the first repump light is coupled with the first cooling light to form a 2D magneto-optical trap (2D MOT) in a 2D vacuum chamber 15. After pre-cooling the rubidium atoms, a near-resonant light beam can be used to transfer the rubidium atoms from the 2D vacuum chamber 15 to a 3D vacuum chamber 16. In the 3D vacuum chamber 16, the second repump light is coupled with the second cooling light to form a 3D magneto-optical trap (3D MOT). After the rubidium atoms are trapped and cooled again in the 3D magneto-optical trap, optical agglomeration technology is used to further cool the rubidium atoms to obtain rubidium atom optical agglomerates. The near-resonant light beam can be 780nm light or light near 780nm, which is equivalent to applying an external force to the pre-cooled rubidium atoms in the 2D vacuum chamber 15 to realize the transfer of rubidium atoms from the 2D vacuum chamber 15 to the 3D vacuum chamber 16.

[0090] Based on the above embodiments, after cooling the rubidium atoms, a 795nm probe light can be applied to the cold atom optical clusters, i.e., the rubidium atom optical clusters. Specifically, the detuning of the probe light is scanned by scanning the driving frequency of the third acousto-optic modulator 7, and the detuned probe light is modulated (i.e., laser frequency shifting) before reaching the electro-optic modulator 9. The electro-optic modulator 9 can perform high-speed modulation of the received laser, with a modulation rate on the order of hundreds of kilohertz (kHz) to hundreds of megahertz (MHz), and the modulated probe light is applied to the rubidium atom optical clusters in the 3D vacuum chamber 16. Then, the detector 10 is used to detect the laser after interacting with the rubidium atom optical clusters, or to detect the fluorescence signal emitted by the rubidium atom optical clusters, thereby obtaining the clock transition spectrum of the 795nm rubidium atom optical clock.

[0091] Based on the obtained clock transition spectral lines, after demodulation by the servo feedback circuit 11, the signals are fed back to the third acousto-optic modulator 7 and the second laser 2, i.e., the 795nm laser. The feedback rate of the servo feedback circuit 11 is more than an order of magnitude larger than the feedback rate of the laser linewidth, achieving frequency stabilization of the 795nm laser and thereby locking the 795nm probe light onto the [optical path]. 87 By utilizing the clock transition lines of Rb atoms, a rubidium atom optical clock based on rubidium atom optical clusters can be realized.

[0092] Furthermore, after the 795nm laser achieves frequency stabilization, the emitted 795nm laser light is also split into a re-pump beam and a probe beam after passing through the first polarizer 5 and the first polarizing beam splitter 6. The probe beam passes through the third acousto-optic modulator 7, then the electro-optic modulator 9, and finally passes through the vacuum chamber 16 containing rubidium atom optical clusters before being detected by the detector 10. Throughout the entire rubidium atom cooling process, the probe beam can be kept on continuously for cooling and detecting the rubidium atoms. When the probe beam continuously acts on the rubidium atom optical clusters, the clock transition spectrum of the continuous rubidium atom optical clock can be obtained.

[0093] After obtaining the clock transition spectrum of the continuous rubidium atom optical clock, the stable clock transition spectrum (or detection signal) detected by the detector can be connected to the servo feedback circuit 11. This signal is mixed with a reference signal provided by a standard signal source in the servo feedback circuit 11 to obtain a mixed signal. The mixed signal is then identified by other electrical components in the servo feedback circuit 11, thus completing the modulation and demodulation process of the clock transition spectrum and obtaining a frequency discrimination signal based on this clock transition spectrum. The frequency discrimination signal is then fed back to the third acousto-optic modulator 7 and the 795nm laser after passing through the servo feedback circuit 11, thereby completing the locking of the rubidium atom clock transition spectrum based on the 795nm laser. Throughout the process, because the probe light continuously acts on the rubidium atom optical aggregates, the clock transition spectrum (or clock transition reference signal) of the continuous rubidium atom optical clock can be obtained, thus realizing a continuous optical clock based on rubidium atom optical aggregates, i.e., completing the continuous detection of the clock transition spectrum.

[0094] In another embodiment, since both the probe light and the repump light are obtained from the second laser, the additional probe light can be eliminated. Instead, the repump light can be used to perform the detection function of the probe light, thus achieving dual-purpose use of a single light source and ensuring the simplicity of the continuous cold atom optical clock based on optical clusters. For example, such as Figure 4 As shown, the continuous cold atom optical clock based on optical clusters may also include: a first laser 1, a second laser 2, a first acousto-optic modulator 3, a second acousto-optic modulator 4, a third acousto-optic modulator 7, a second polarizer 12, a third polarizer 13, a second polarizing beam splitter 14, a 2D vacuum chamber 15, a 3D vacuum chamber 16, an electro-optic modulator 9, a detector 10, and a servo feedback circuit 11.

[0095] In this process, the first laser emitted by the first laser 1 is detuned by the first acousto-optic modulator 3, and then passes through the second polarizer 12 and the second polarizing beam splitter 14 to obtain the first cooling light and the second cooling light. The second laser emitted by the second laser 2 is detuned by the second acousto-optic modulator 4, and then passes through the third polarizer 13 and the second polarizing beam splitter 14 to obtain the first repumped light and the second repumped light.

[0096] In this process, the first re-pump light, coupled with the first cooling light, acts on the 2D vacuum chamber 15; the second re-pump light, coupled with the second cooling light, acts on the 3D vacuum chamber 16. When the first re-pump light acts on the 2D vacuum chamber 15, the atoms are not yet fully cooled, so there is no need to detect the cold atom optical clusters; therefore, the first re-pump light does not need to perform a detection function. However, when the second re-pump light acts on the 3D vacuum chamber 16, the atoms are fully cooled, so the second re-pump light can be used instead of the detection light to detect the fully cooled cold atom optical clusters in the 3D vacuum chamber 16. Specifically, after the second re-pump light is used as the detection light, it is modulated by the third acousto-optic modulator 7 and the electro-optic modulator 9 before acting on the cold atom optical clusters in the 3D vacuum chamber 16, obtaining the clock transition spectral lines corresponding to the cold atom optical clusters. Furthermore, this is equivalent to combining the probe light with the second repump light into one beam, which can simplify the structure of the continuous cold atom optical clock based on optical clusters.

[0097] In addition, the functions of the electro-optic modulator 9, detector 10, and servo feedback circuit 11 are the same as those in the above embodiment, and will not be repeated here.

[0098] In some embodiments, the continuous cold atom optical clock based on optical clusters may further include at least one of the following: a first mirror for reflecting the light coupled from the second repumped light and the second cooled light into a three-dimensional vacuum chamber. For example Figure 3 The first reflector 17 shown in the diagram allows the second-path re-pump light and the second-path cooling light, after being coupled together, to pass through the first reflector 17 before acting on the 3D vacuum chamber 16. It can be understood that the first reflector can alter the light transmission path to achieve the aforementioned effect.

[0099] Furthermore, the continuous cold atom optical clock based on optical clusters may also include: a signal generator (not shown), connected to the first acousto-optic modulator, the second acousto-optic modulator, and the third acousto-optic modulator, respectively. The signal generator is used to provide corresponding frequency modulation signals to the first acousto-optic modulator, the second acousto-optic modulator, and the third acousto-optic modulator, and the frequency modulation signals are used to modulate the laser frequency. The signal generator may be a radio frequency signal source.

[0100] Accordingly, the continuous-type cold atom optical clock based on optical clusters may further include: a signal amplifier (not shown), the input of which is connected to the output of a signal generator for amplifying the frequency-modulated signal. The signal amplifier may be a radio frequency amplifier.

[0101] For example, the first, second, and third acousto-optic modulators are all driven by an RF signal source amplified by an RF amplifier. The required laser detuning can be adjusted by regulating the driving frequency of the RF signal source. For instance, to change the laser frequency, such as by shifting it by 50MHz, an external signal from the RF signal source is needed. Specifically, an RF signal source emits a signal, which is then amplified by an RF amplifier and driven to the acousto-optic modulator. Simultaneously, it must be ensured that the amplified signal can achieve a 50MHz laser frequency shift.

[0102] In some embodiments, the continuous-type cold atom optical clock based on optical clusters may further include at least one of the following: a second mirror for reflecting probe light to a third acousto-optic modulator; a third mirror for reflecting repump light to a third polarizer; and a fourth mirror for reflecting light detuned by the third acousto-optic modulator to an electro-optic modulator. Referring again... Figure 3 For the second reflector 18, the probe light can be reflected to the third acousto-optic modulator 7; for the third reflector 19, the repump light can pass through the third reflector 19 and the third polarizer 13 in sequence, and then pass through the second polarizing beam splitter 14 to split into the first repump light and the second repump light; for the fourth reflector 20, after the detuned probe light is modulated (i.e., laser frequency shifted), it is reflected to the electro-optic modulator 9 through the fourth reflector 20.

[0103] In practical applications, both the first and second lasers can be narrow-linewidth external cavity semiconductor lasers, or other types of lasers; no restrictions are placed here.

[0104] In this application, the continuous stability of cold atom optical aggregates is one of the key points for realizing continuous cold atom optical clocks based on optical aggregates. For example, if the process of preparing rubidium atom optical aggregates is continuous, a stable and continuous clock transition spectrum can be obtained. Alternatively, a new rubidium atom cooling process can be quickly started before the end of the previous rubidium atom optical aggregate lifetime, i.e., the cooling period is less than the rubidium atom optical aggregate lifetime, thereby realizing the preparation of continuous rubidium atom optical aggregates.

[0105] Those skilled in the art will understand that Figure 2 , Figure 3 and Figure 4 The schematic diagram shown does not constitute a limitation on the continuous cold atom optical clock based on optical clusters, and may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0106] In summary, this application has at least the following advantages:

[0107] 1. Compared with traditional microwave clocks, the stability of continuous cold atom optical clocks based on optical agglomerates, such as rubidium atomic optical clocks, is improved by at least two orders of magnitude.

[0108] 2. By combining cold atom optical cluster technology with atomic clocks, a continuous cold atom optical clock based on cold atom optical clusters can be constructed. For example, the frequency stability of the rubidium atomic optical clock based on rubidium atomic optical clusters can theoretically be comparable to the best existing cold atom optical clocks.

[0109] 3. By using the re-pumping light from the atomic cooling process to split off a path as the detection light for detecting the transition lines of the atomic clock, there is no need to use an additional laser, providing a new approach for the miniaturization of the cold atom optical clock optical path system.

[0110] 4. By continuously applying probe light to cold atom optical clusters, such as rubidium atom optical clusters, the clock transition spectrum (or clock transition reference signal) of a continuous rubidium atom optical clock can be obtained, thus laying the foundation for realizing a continuous optical clock based on rubidium atom optical clusters. Furthermore, it provides the possibility for continuous timekeeping of cold atom optical clocks based on rubidium atom optical clusters, which may be applied in aerospace, satellite navigation and other fields in the future.

[0111] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0112] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A continuous-type cold atom optical clock based on optical clusters, characterized in that, include: The system comprises a first laser, a second laser, a first acousto-optic modulator, a second acousto-optic modulator, a third acousto-optic modulator, a first polarizer, a first polarizing beam splitter, a vacuum chamber, an electro-optic modulator, a detector, and a servo feedback circuit. The first laser is used to emit a first laser beam, and after the first laser beam is detuned by the first acousto-optic modulator, a cooled light beam is obtained. The second laser emits a second laser beam. After being detuned by the second acousto-optic modulator, the second laser beam passes through the first polarizer and the first polarizing beam splitter to obtain a re-pump beam and a probe beam. The re-pump beam is coupled with the cooling beam and then acts on the vacuum chamber. After being cooled by the vacuum chamber, cold atom optical clusters are obtained. The intensity and spot size of the cooling beam and the re-pump beam are matched to improve the cooling effect. The vacuum chamber includes a single-stage vacuum chamber and a two-stage vacuum chamber, both used to obtain continuous cold atom optical clusters. The probe beam is detuned by the third acousto-optic modulator and then transmitted to the electro-optic modulator. After being modulated by the electro-optic modulator, it acts on the cold atom optical clusters to obtain the clock transition spectral lines corresponding to the cold atom optical clusters. The electro-optic modulator is used to perform high-speed modulation of the received laser beam, with a modulation rate on the order of hundreds of kilohertz to hundreds of megahertz. The detector is used to detect the clock transition spectral line and transmit the detected clock transition spectral line to the servo feedback circuit. The servo feedback circuit is used to modulate and demodulate the clock transition spectrum to obtain the frequency discrimination signal corresponding to the clock transition spectrum. The frequency discrimination signal is fed back to the third acousto-optic modulator and the second laser through the servo feedback circuit, so that the second laser can stabilize its frequency and lock the probe light based on the clock transition spectrum. The probe light, after being detuned by the third acousto-optic modulator, continuously acts on the cold atom optical clusters to obtain continuous clock transition spectrums, thereby realizing a cold atom optical clock based on cold atom optical clusters. The feedback rate of the servo feedback circuit is at least one order of magnitude larger than the feedback rate of the laser linewidth.

2. The continuous-type cold atom optical clock based on optical clusters according to claim 1, characterized in that, It also includes a second polarizer, a third polarizer, and a second polarizing beam splitter. The two-stage vacuum chamber includes a two-dimensional vacuum chamber and a three-dimensional vacuum chamber. The second polarizer and the second polarizing beam splitter are used to split the cooling light into a first cooling light and a second cooling light, and to split the repumped light into a first repumped light and a second repumped light after passing through the third polarizer and the second polarizing beam splitter. In this process, the first repumping light is coupled with the first cooling light and acts on the two-dimensional vacuum chamber to form a two-dimensional magneto-optical trap, which is used to pre-cool the atoms; the second repumping light is coupled with the second cooling light and acts on the three-dimensional vacuum chamber to form a three-dimensional magneto-optical trap, which is used to cool the pre-cooled atoms to obtain the cold atom optical cluster.

3. The continuous cold atom optical clock based on optical clusters according to claim 2, characterized in that, The two-dimensional vacuum chamber and the three-dimensional vacuum chamber are connected by a differential pipe.

4. The continuous cold atom optical clock based on optical clusters according to claim 2, characterized in that, It also includes at least one of the following: a first reflector for reflecting the light after the second re-pump light and the second cooling light are coupled to the three-dimensional vacuum chamber.

5. The continuous-type cold atom optical clock based on optical clusters according to any one of claims 2 to 4, characterized in that, The first polarizer, the second polarizer, and the third polarizer are all half-wave plates.

6. The continuous-type cold atom optical clock based on optical clusters according to any one of claims 1 to 4, characterized in that, The servo feedback circuit is specifically used for: A reference signal is provided, and the clock transition spectral line detected by the detector is modulated using the reference signal to obtain a mixed signal; The mixed signal is demodulated to obtain the frequency discrimination signal corresponding to the clock transition spectrum line.

7. The continuous cold atom optical clock based on optical clusters according to any one of claims 1 to 4, characterized in that, Also includes: A signal generator is connected to the first acousto-optic modulator, the second acousto-optic modulator, and the third acousto-optic modulator, respectively. The signal generator is used to provide corresponding frequency modulation signals to the first acousto-optic modulator, the second acousto-optic modulator, and the third acousto-optic modulator. The frequency modulation signals are used to frequency modulate the laser.

8. The continuous cold atom optical clock based on optical clusters according to claim 7, characterized in that, Also includes: A signal amplifier, the input of which is connected to the output of the signal generator, is used to amplify the frequency modulation signal.

9. The continuous-type cold atom optical clock based on optical clusters according to any one of claims 2 to 4, characterized in that, It also includes at least one of the following: The second reflector is used to reflect the probe light to the third acousto-optic modulator; The third reflecting mirror is used to reflect the re-pumped light to the third polarizer; The fourth reflector is used to reflect the light, after it has been detuned by the third acousto-optic modulator, back to the electro-optic modulator.

10. The continuous cold atom optical clock based on optical clusters according to any one of claims 1 to 4, characterized in that, Both the first laser and the second laser are narrow-linewidth external cavity semiconductor lasers.

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