Method for improving optical lattice clock frequency measurement precision in microgravity environment

Abstract

The invention particularly relates to a method for improving the frequency measurement accuracy of an optical lattice clock in a microgravity environment, which comprises the following steps of: splitting two beams of lattice light through a lattice light laser, respectively splitting two beams of lattice light from each beam of lattice light, and forming two one-dimensional horizontal optical lattices by four beams of lattice light; wherein a certain distance exists between the beam waist positions of the two one-dimensional horizontal optical lattices in the vertical direction, the midpoint position of the two one-dimensional horizontal optical lattices is the position of a magnetic field zero point in the magneto-optical trap, the projections of the axial directions of the two horizontal optical lattices in the vertical plane are parallel to each other, and the projections of the axial directions of the two horizontal optical lattices in the horizontal plane are perpendicular to each other; an acousto-optic modulator with identical parameters is loaded on a light path of each beam of lattice light and is used for linear frequency shift and modulation of lattice light frequency; two beams of clock laser are split by a clock laser light source to respectively excite different atomic groups in two one-dimensional horizontal optical lattices. Differential comparison of transition frequencies of different atomic group clocks is realized by synchronously detecting transition spectrum lines of different atomic group clocks, so that common-mode noise in an optical clock system is suppressed. According to the method, the optical lattice clock with ultra-high frequency measurement precision in a microgravity environment can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of atomic optical lattice clock, and particularly relates to a method for improving the frequency measurement precision of an optical lattice clock in a microgravity environment. BACKGROUND

[0002] In recent years, the optical lattice clock based on neutral atoms has been widely used in time frequency metrology, quantum precision measurement, quantum sensing, quantum simulation and other fields due to its ultra-high frequency measurement precision, stability and accuracy. In the development of optical clock, the improvement of precision is undoubtedly the primary goal pursued by optical clock development teams all over the world. Since the advent of optical lattice clock in 2005, the technology of neutral atom optical lattice clock has been continuously developing, and various optical clock development teams around the world have proposed numerous schemes to improve the frequency measurement precision of optical clock. From one-dimensional optical lattice clock to three-dimensional optical lattice clock, optical tweezer clock, Wannier-Stark clock and differential optical lattice clock based on shallow optical lattice, the frequency measurement precision of optical clock has been improved from E-18 to E-21 or even higher. The last two clocks are the optical lattice clocks with the highest reported frequency measurement precision, and both of them are based on shallow optical lattice. The advantage of shallow optical lattice is that it can reduce the scattering rate and atomic heating rate in the optical lattice, thereby prolonging the decoherence time of atoms in the lattice and providing a more stable place for the detection of clock transition spectrum. In July 2024, the Joint Institute for Laboratory Astrophysics (JILA) reported their latest strontium optical clock NEW JILA SrClock, with a system frequency uncertainty of 8.1×10 -19 This is the most accurate neutral atom optical clock so far, and it is realized based on shallow optical lattice. This also shows that the shallow optical lattice technology plays a very important role in improving the frequency measurement precision and accuracy of neutral atom optical clock. However, shallow optical lattice will have tunneling effect, which will cause the broadening and splitting of clock transition spectrum. Both Wannier-Stark clock and differential optical lattice clock use vertical optical lattice and utilize gravity potential to introduce gradient potential field between different lattice sites, thereby suppressing tunneling. However, this method will not work in a microgravity environment. Therefore, if we want to improve the frequency measurement precision of space optical clock or star-borne optical clock operating in a microgravity environment, we need to suppress the tunneling phenomenon in shallow optical lattice through non-gravitational means to improve the precision of optical lattice clock operating in a microgravity environment. It should be noted that the information disclosed in the above background section is only used to strengthen the understanding of the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0003] The application provides a method for improving the frequency measurement precision of an optical lattice clock in a microgravity environment, which can improve the frequency measurement precision of a neutral atom optical lattice clock in a microgravity environment, and can overcome the defects in the prior art to some extent.

[0004] Other characteristics and advantages of the application will become apparent from the detailed description, or will be learned by practice of the application.

[0005] According to a first aspect of the application, a method for improving the frequency measurement precision of an optical lattice clock in a microgravity environment is provided, and the method comprises: Two beams of lattice light are divided from one lattice light laser, and each beam of lattice light is further divided into two beams of lattice light, and four beams of lattice light form two one-dimensional horizontal optical lattices; wherein the waist positions of the two one-dimensional horizontal optical lattices have a certain interval in the vertical direction, and the midpoint position is the position of the magnetic field zero point in the magneto-optical trap, and the axial directions of the two horizontal optical lattices are parallel to each other in the projection in the vertical plane, and are perpendicular to each other in the projection in the horizontal plane; Two beams of clock light are divided from one clock laser source to excite different groups of atoms in the two one-dimensional horizontal optical lattices; An acousto-optic modulator with the same parameters is loaded on the light path of each beam of lattice light for linear frequency shift and modulation of the lattice light frequency, wherein the acousto-optic modulator loaded on the light path of the two beams of lattice light for generating one one-dimensional horizontal optical lattice is connected to an arbitrary function generator, and the acousto-optic modulator loaded on the light path of the two beams of lattice light for generating another one-dimensional horizontal optical lattice is connected to another arbitrary function generator; An acousto-optic modulator is also loaded before the clock light is divided for scanning the clock light frequency, and the acousto-optic modulator on the clock light is connected to a third arbitrary function generator; The three arbitrary function generators are all traced back to the same hydrogen clock as a frequency reference source.

[0006] In some example embodiments, the two beams of lattice light are divided from one lattice light laser, and each beam of lattice light is further divided into two beams of lattice light, and four beams of lattice light form two one-dimensional horizontal optical lattices, specifically: The lattice light output by the lattice light laser is divided into two beams by a polarization beam splitter, and each beam of lattice light is further divided into two beams of lattice light by a polarization beam splitter, and the four beams of lattice light are first lattice light, second lattice light, third lattice light and fourth lattice light; wherein the initial optical powers of the first lattice light and the second lattice light are set to be the same, and the initial optical powers of the third lattice light and the fourth lattice light are set to be the same; the initial optical powers of the first lattice light and the second lattice light are greater than the initial optical powers of the third lattice light and the fourth lattice light; The first lattice light and the second lattice light are incident on the atomic group captured by the magneto-optical trap at a 90° angle, the third lattice light and the fourth lattice light are incident on the atomic group captured by the magneto-optical trap at a 90° angle, and the third lattice light is opposite to one of the first lattice light and the second lattice light, and the fourth lattice light is opposite to the other of the first lattice light and the second lattice light, thereby forming two one-dimensional horizontal optical lattices.

[0007] In some example embodiments, the two beams of clock laser respectively excite different atomic groups in the two one-dimensional horizontal optical lattices, and the specific process is as follows: The clock laser output by the clock laser is split into two beams by a polarization beam splitter, which are the first clock laser and the second clock laser, the first clock laser is combined with one of the third lattice light and the fourth lattice light through a dichroic mirror, and the second clock laser is combined with the other of the third lattice light and the fourth lattice light through a dichroic mirror.

[0008] In some example embodiments, a half-wave plate, a linear polarizer and a convex lens are sequentially connected at the end of the optical path of each lattice light, wherein: The half-wave plate and the linear polarizer are used to adjust the polarization direction of each beam of lattice light, so that the polarization direction remains vertical polarization; The convex lens is used to fix the waist position of the lattice light at the center of the atomic group in the magneto-optical trap.

[0009] In some example embodiments, the polarization direction is adjusted by adding a half-wave plate to each of the two beams of clock laser, so that the polarization direction of the clock laser is consistent with the polarization direction of the lattice light; then a convex lens is combined with the convex lens in the lattice light beam, so as to adjust the waist size and position of the clock laser.

[0010] In some example embodiments, a microwave switch, a voltage-controlled attenuator and a timing control system are provided between the acousto-optic modulator and the arbitrary function generator; A series of TTL digital pulse signals generated by the timing control system are transmitted to the microwave switch, and then the microwave switch turns on or off the radio frequency signal output by the arbitrary function generator according to the instructions of the timing system, thereby realizing the switching of the lattice laser and the control of the linear frequency shift signal and the frequency modulation signal in the action time; The timing control system transmits a time-varying analog voltage waveform to the voltage-controlled attenuator, thereby realizing variable attenuation of the radio frequency signal intensity.

[0011] In some example embodiments, the method further comprises selecting modulation parameters suitable for the depth of a specific optical lattice by Floquet design technology, and the specific process is as follows: Two identical modulated radio frequency signals are output from an arbitrary function generator. Both signals are sinusoidal modulations with identical carrier frequencies and modulation parameters. These two signals are then synchronously loaded onto the acousto-optic modulators of the first and second lattice lights. The start and duration of the signals are controlled by a timing control system and a microwave switch. The parameters of the sinusoidal modulation signals are selected by the tunneling rate modulation function, which is determined by the modulation depth corresponding to the zero of the first type of Bessel function. The parameters of the frequency modulation functions loaded on the two one-dimensional horizontal optical lattices must be completely identical.

[0012] In some exemplary embodiments, the method further includes accelerating and moving the optical lattice by changing the frequency difference between two opposing lattice beams in two one-dimensional horizontal optical lattices to prepare multiple atomic samples required for a differential optical clock. The specific process is as follows: Two radio frequency (RF) signals with identical carrier frequencies but no modulation to those output by the arbitrary function generator described in claim 7 are initially output by another arbitrary function generator. These two signals are then synchronously loaded onto the acousto-optic modulators of the third and fourth lattice lights. Simultaneously, the start time and duration of the signal are controlled by a timing control system in conjunction with the microwave switch and the acousto-optic modulators. By cooperating with the timing control system, the arbitrary function generator, and the acousto-optic modulators, the output frequency of the unmodulated RF signal is changed within a given duration, introducing a frequency difference between the RF signal carrier frequency loaded onto the acousto-optic modulators of the first and second lattice lights. This accelerates the optical lattice, causing the atomic clusters within the optical lattice to split. The split atomic clusters are then moved as a whole to a position symmetrical about the zero point of the magnetic field in the magneto-optical trap, in order to prepare multiple atomic cluster samples required for the differential optical clock.

[0013] In some exemplary embodiments, the excitation process uses two time-intervals. The frequency scanning function of the clock laser is achieved through a pulse, using a timing control system, an acousto-optic modulator on the clock laser optical path, and a third arbitrary function generator connected to it. This allows for the detection of the complete Ramsey spectral lines within a given frequency band. Simultaneously, the timing control system, in conjunction with a microwave switch and the acousto-optic modulator, controls two pulses during the excitation process. The duration of the laser pulse and the interval between two pulses are controlled; and the timing control system, voltage-controlled attenuator, and acousto-optic modulator work together to adjust the corresponding excitation times. The required clock laser power for the pulse is used to achieve synchronous detection of the Ramsey spectral lines of the clock transition and closed-loop locking of the clock transition frequency. The clock transition frequencies obtained from multiple atomic samples are compared pairwise, and then the elliptic fitting correction bias method is used to eliminate the influence of common-mode noise on the clock transition frequency shift.

[0014] The method for improving the frequency measurement accuracy of the optical lattice clock in the microgravity environment provided by the embodiment of the application combines the Floquet engineering technology with the differential optical lattice clock technology, realizes the synchronous differential optical lattice clock of multiple quantum samples by constructing 8 atomic group samples in two horizontal optical lattices, and suppresses the tunneling phenomenon in the shallow optical lattice through the Floquet engineering technology, so as to realize the optical lattice clock with ultra-high frequency measurement accuracy in the microgravity environment, which is of great significance to the establishment of the time frequency reference source in the space environment and the basic physical research based on the optical lattice clock. The specific embodiments are as follows: The Floquet engineering technology is introduced, that is, the optical lattice potential field is constructed by modulating the optical lattice frequency, the modulation of the tunneling rate in the optical lattice potential is realized, and the tunneling effect in the shallow optical lattice is suppressed, so as to overcome the problem that the optical lattice step potential field cannot be introduced by the gravitational potential in the microgravity environment to suppress the tunneling effect in the shallow optical lattice. The double one-dimensional horizontal multi-division multiplexing differential optical lattice device is used to eliminate the clock transition frequency shift caused by various common-mode noise such as clock laser noise and environmental fluctuation changes such as blackbody radiation, magnetic field gradient and electric field gradient, so as to improve the frequency measurement accuracy of the optical clock, especially the frequency measurement accuracy of the optical clock in the microgravity environment. It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the application. BRIEF DESCRIPTION OF DRAWINGS

[0015] The drawings incorporated into the specification and constituting a part of the specification show embodiments consistent with the application and, together with the specification, serve to explain the principles of the application. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained from these drawings without creative labor for those skilled in the art.

[0016] Figure 1 The theoretical principle diagram for suppressing tunneling by Floquet engineering for the embodiment of the application; Figure 2 The optical path schematic diagram of the one-dimensional horizontal double optical lattice device provided by the embodiment of the application; Figure 3 The radio frequency signal link diagram in the one-dimensional horizontal double optical lattice device provided by the embodiment of the application; Figure 4 The differential optical lattice clock timing control schematic diagram based on the Floquet engineering provided by the embodiment of the application; Figure 5 The one-dimensional horizontal double optical lattice atomic group provided by the embodiment of the application; (a) the distribution of the atomic sample without optical lattice acceleration and movement; (b) the distribution of the atomic sample after optical lattice acceleration and movement. DETAILED DESCRIPTION

[0017] Example implementations will now be described more fully with reference to the accompanying drawings. Example implementations can be implemented in any

[0018] Moreover, the drawings represent a simplified diagram of the invention and are not necessarily to scale. Like reference numerals in different drawings denote the same or similar parts, and so repeated description thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities that do not necessarily have to correspond to physically or logically independent entities. These functional entities can be implemented in software, or in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0019] At present, there are many techniques for improving the frequency measurement precision of optical lattice clocks, such as the existing shallow optical lattice technique and the differential optical lattice clock technique. By combining the two techniques, the frequency measurement precision of E-21 or even higher order can be achieved by using only a clock laser with a linewidth of the order of hertz. However, to achieve such high frequency measurement precision for a single quantum sample of a conventional shallow optical lattice clock without a differential structure, a clock laser local oscillator with a linewidth of the order of millihertz is required. However, the optical lattice device for realizing the differential shallow optical lattice clock is a one-dimensional vertical multiplexing optical lattice device, and the suppression of the tunneling phenomenon in the shallow optical lattice mainly depends on the gravitational potential. In a microgravity environment, the tunneling phenomenon in the shallow optical lattice cannot be effectively suppressed, resulting in broadening of the clock transition spectrum of the optical lattice clock and causing deterioration of the frequency stability and uncertainty of the optical clock. Therefore, the frequency measurement precision of the optical clock cannot be improved by using the shallow optical lattice differential optical lattice clock device.

[0020] In a microgravity environment, if a shallow optical lattice is used to realize an optical lattice clock with higher frequency measurement precision, the tunneling phenomenon in the shallow optical lattice cannot be suppressed by the gravitational potential field. In order to solve the problems of the prior art, the present application proposes to construct an optical lattice potential field by Floquet design technology to modulate the tunneling rate in the optical lattice potential, thereby suppressing the tunneling phenomenon in the shallow optical lattice in a microgravity environment. The present application proposes to combine a one-dimensional horizontal shallow optical lattice based on Floquet design with differential optical lattice clock technology to further improve the frequency measurement precision of the optical lattice clock in a microgravity environment. This can reduce the research and development cost of the ultra-stable clock laser system in a space environment, while improving the precision of the optical clock.

[0021] This invention upgrades the optical path and electronic control system of an optical lattice device based on an existing conventional strontium optical clock system in the laboratory. By adding lattice light frequency modulation and scanning functions, tunneling suppression and atomic group movement processes in shallow optical lattices are achieved through non-gravity means. A differential optical lattice clock function is realized through a dual-level one-dimensional optical lattice structure.

[0022] Specifically, by modulating the lattice light frequency, the potential field function of the optical lattice is designed to modulate the tunneling rate to near zero, thus avoiding spectral broadening and splitting of clock transition lines due to tunneling. Under sinusoidal modulation, the effective tunneling rate of the driving optical lattice satisfies the same condition as the unmodulated tunneling rate. ,in It is a Bessel function of the first kind of order 0. For the modulation coefficients, for each different order in the expansion term have Because the tunneling rate includes and The terms can be expanded into a Fourier series, and the resulting expansion coefficients are the Bessel functions of the first kind. . Figure 1 Demonstrates the modulation of sinusoidal functions = 0th, 1st, and 2nd order Bessel functions and the modulation depth coefficients corresponding to the first zeros of each order Bessel function. In this invention, sinusoidal functions are also used as the frequency modulation function of lattice light. By setting the modulation parameters in the experimental system at the zero point of the Bessel function in the figure, the tunneling effect can be almost completely suppressed, thus eliminating the need to introduce a stepped potential field by gravity to suppress tunneling between lattice points.

[0023] Specifically, by changing the center frequency difference between the two beams of light forming the optical potential trap, the spatial distribution of atomic clusters within the optical lattice is altered. When two laser beams from the same laser source are directed at each other to form a standing wave field, since the two beams originate from the same source, without any external frequency shifting device, the center position of the atomic clusters within the optical lattice will be located at the waist of the laser beam. However, when a frequency shifting device is used to create a frequency difference between the two laser beams... At that time, some atomic clusters in the optical lattice will be dragged a certain distance by such a moving optical lattice. If the frequency difference between two lattice laser beams does not change with time, then it is fixed. Then the velocity at which the atoms move with the lattice is If the frequency difference varies with time, then the acceleration of the lattice movement can be written as: Therefore, by changing the frequency difference between the two beams of lattice laser forming the optical lattice and its action time and rate, the movement and splitting of the atomic group in the optical lattice can be realized. By controlling the acceleration of the lattice movement to ensure that the kinetic energy of the high-energy state atom is close to the potential energy of the optical lattice potential well, then non-adiabatically changing the frequency difference of the two counter-propagating lattice lasers quickly, while also keeping the 689 nm magneto-optical trap corresponding to the process of atomic secondary narrow-band cooling open, part of the atoms in the low-energy state are tightly bound by the optical lattice potential well and move with the optical lattice, while the remaining high-energy state atoms are thrown out of the lattice or tunneling and captured by the magneto-optical trap, thereby staying at the original center position, so that a group of atomic samples is divided into two groups of atomic samples in space. By using this atomic group splitting technology multiple times, a small differential optical clock network can be formed to perform various quantum precision measurements. The optical lattice device in the application is composed of a standing wave field formed by two beams of laser light divided from a lattice laser, and an acousto-optic modulator with the same parameters is loaded on each of the two beams of divided laser light to realize independent control of the center frequency and frequency modulation function of the two beams of lattice light.

[0024] The traditional optical lattice clock system usually detects the clock transition spectrum of a quantum sample composed of an atomic group, and evaluates the stability and uncertainty of the optical clock by the time-sharing self-comparison method. Generally, the fractional frequency stability of a standard quantum limit optical clock is determined by quantum projection noise (QPN), which can be expressed as: (1) wherein, is the mass factor (the ratio of transition frequency to linewidth) of the atomic clock transition energy level transition spectrum, is the number of atoms being detected, is a period of clock closed loop operation, is the average time, is the number of photons detected by each atom, characterizes the measurement fluctuation introduced by the detection technology, and the fluctuation is the change of the normalized atomic fraction excitation rate. As can be seen, the number of atoms in the quantum sample of the neutral atom optical clock is much larger than that in the single ion optical clock, so this is why the neutral atom optical clock can reach the same stability faster than the single ion optical clock in the same average time. Although the quantum projection noise limit calculated by the typical parameter values of the neutral atom optical lattice clock can reach 1x10 -17 / However, in the traditional optical clock spectrum detection of single-atom quantum samples, the atomic detection noise is usually masked by the noise from the optical phase-locked loop. In the process of quantum state preparation and reading, the optical phase-locked loop does not act on the clock laser, so that frequency fluctuation aliasing occurs, and this aliasing noise is called Dick noise. During the laser tuning process, it will be compensated for errors, thereby affecting the stability of the optical clock. At this time, the stability of the optical clock is mainly determined by the optical phase-locked loop, not the atomic system, so if you want to improve the stability of the optical clock, you need to use a higher-performance optical phase-locked loop through iteration. Sometimes this phase-locked loop is more complex in the experiment than the atomic system it detects, which is a challenge for the application of optical clocks in scenarios outside the laboratory.

[0025] If the detection method of the clock transition spectrum of the optical clock is Ramsey spectrum, the fractional frequency uncertainty of the comparison of two optical clocks with the same performance under the QPN limit is: (2) Where, is the transition frequency of the clock transition energy level, is the coherence time of the clock laser and the atom, is the quantum state preparation time during the operation of each clock ring, also known as the dead time, and the sum of the two is a clock ring operation period . is the contrast of the Ramsey fringe, and the factor is assumed that the two optical clock pairs have equal contributions to the uncertainty. As can be seen from equation (2), increasing the number of atoms and the coherence time of the atom and the laser can improve the stability of the optical clock, but the frequency noise of the clock laser will reduce the coherence time of the atom and the laser, and due to the existence of Dick effect, it will hinder the stability of the optical clock to reach the QPN limit. At this time, Dick noise is the main factor that limits the highest level of optical clock stability.

[0026] So, there are generally two methods to reduce Dick noise, one is to further reduce the frequency noise of the clock laser, and the clock laser based on the strontium atomic optical lattice clock in the ground laboratory can achieve a laser linewidth of 8 mHz. By interacting with atoms through such ultra-stable clock laser, a high-stability optical clock can be realized. The advantage is that the noise of the laser itself is lower, so the noise mixed into the optical clock is also lower, which is suitable for various structures of optical clock system, but the disadvantage is that the technical challenge is great, the cost is high, and the Dick effect cannot be completely eliminated. The other method is to eliminate the influence of clock laser noise on optical clock frequency uncertainty through differential optical clock, that is, to use two or more cold atomic systems with the same structure in parallel, and to use a clock laser to perform Ramsey synchronous detection on different atomic samples to realize noise suppression such as detector electronic noise and short-term frequency drift of the laser. The advantage of this method is that the stability requirement of the clock laser itself is not very high. The disadvantage is that through this differential structure, two or more atomic quantum sample systems need to be prepared respectively, and the structure will become complex. If these differential quantum samples are not generated by the same physical system, some new environmental noise may be introduced. But if the differential quantum samples are generated in the same physical system, even if they are divided into several parts by the same atomic group, the common-mode noise caused by environmental fluctuations, such as blackbody radiation frequency shift, AC Stark shift introduced by lattice light and clock laser, will be significantly reduced. At the same time, the complexity of the device structure is much simpler than that of the separately prepared atomic quantum sample system.

[0027] Therefore, the differential optical clock scheme in the same physical system is more suitable for realizing high-precision space optical clock and high-performance movable optical clock in microgravity environment.

[0028] Based on the above principle analysis, a method for improving the frequency measurement accuracy of optical lattice clock in microgravity environment is provided in the example embodiment, including the following three aspects: On the one hand, the lattice light output by the lattice laser is divided into four beams through a plurality of polarization beam splitters, and the initial optical power of two beams is P 1 set to 600 mW, and the initial optical power of the other two beams of lattice light is P2. The power is set to 200 mW. An identical acousto-optic modulator is added to each of the four lattice beams to achieve linear frequency shifting and modulation of the lattice beam frequency. Two higher-power lattice beams are horizontally incident on the atomic clusters trapped in the magneto-optical trap at a 90° angle in the horizontal plane. The beam waists of the two beams are at the same horizontal position, with a vertical spacing of 200 μm and a consistent beam waist diameter of approximately 100 μm. The polarization direction of each lattice beam is adjusted by adding a linear polarizer and a half-wave plate to each of the four lattice beams to maintain vertical polarization. Simultaneously, the two weaker lattice beams are incident on the two stronger lattice beams to form a one-dimensional horizontal two-beam lattice structure. Meanwhile, a clock laser passes through a dichroic mirror from the weaker beams... P The two clock laser beams are combined with the lattice beam at both ends. Both beams originate from the same laser source and are of the same origin. A waveplate is used to adjust the polarization direction, ensuring that the clock laser's polarization direction aligns with that of the lattice beam. A convex lens is then used in combination with a lens in the lattice beam to adjust the beam waist size and position of the clock laser, making it as planar as possible within the optical lattice region to guarantee the uniformity of energy level transitions within excited atoms. Furthermore, the radio frequency drive signal and modulation signal acting on the acousto-optic modulator are both generated by an arbitrary function generator, with the two beams having a power of [missing information]. P Both acousto-optic modulators in the lattice light path of beam 1 are connected to the same arbitrary function generator to achieve frequency modulation of the lattice light; the two beams have power of P The two acousto-optic modulators on the lattice laser path are both connected to another arbitrary function generator to achieve frequency shifting of the lattice laser; while the acousto-optic modulator on the clock laser path is connected to a third arbitrary function generator to achieve frequency sweeping of the clock laser. Furthermore, all three arbitrary function generators are traced back to the same hydrogen clock as a frequency reference source. To perform timing control of the lattice laser, a microwave switch is connected between the arbitrary function generator and the voltage-controlled attenuator. This microwave switch transmits a series of TTL digital pulse signals generated by the timing control system to the microwave switch, which then turns the radio frequency signal output from the arbitrary function generator on or off according to the instructions of the timing system. This enables the switching of the lattice laser and the manipulation of the linear frequency shift signal and frequency modulation signal in terms of their duration. In order to adjust and control the power and power change rate of the lattice laser incident on the atomic group, a voltage-controlled attenuator needs to be connected between the microwave switch and the acousto-optic modulator. Then, an analog voltage waveform that changes with time is transmitted to the voltage-controlled attenuator through a timing control system, so as to realize the variable attenuation of the radio frequency signal strength.

[0029] For example, such as Figure 2As shown, the one-dimensional horizontal double optical lattice device optical path schematic diagram provided by the embodiment of the present application, first, a 813 nm laser output a beam of lattice light, through a wave plate and a polarizing beam splitter into two power equal lattice laser, the two beams of lattice light through a wave plate and a polarizing beam splitter, two beams of laser into four beams of laser, respectively, the first lattice light, the second lattice light, the third lattice light and the fourth lattice light, wherein the first lattice light and the second lattice light two beams of power are strong, are set to P 1= 600 mW, the third lattice light and the fourth lattice light two beams of power are weak, are set to P 2= 200 mW. The four beams of lattice light through the necessary 813 nm waveband high reflector light guide, and four beams of light through a acousto-optic modulator, a half wave plate, a linear polarizer and a convex lens in turn, so as to realize the linear frequency shift or frequency modulation function of each lattice light through these optical elements, and ensure that it is vertical linearly polarized light, and through a convex lens, the waist position is fixed at the center of the atomic group in the magnetic optical trap. At the same time, a beam of power higher lattice light and a beam of power lower lattice light form a one-dimensional horizontal optical lattice, while the remaining one beam of power higher lattice light and another beam of power lower lattice light form a second one-dimensional horizontal optical lattice, the projection of the optical axis of the two one-dimensional horizontal optical lattices in the horizontal plane is two vertical straight lines, while the projection of the two optical axes in the vertical plane is two parallel straight lines, and the optical axes of the two one-dimensional horizontal optical lattices are out of plane and perpendicular, and the interval is 200 μm. The two beams of lattice light with power P 1 are respectively incident on the atomic group captured by the magnetic optical trap at positive 45° and negative 45° horizontally; the two beams of lattice light with power P 2 are respectively incident on the atomic group captured by the magnetic optical trap at positive 135° and negative 135° horizontally. In addition, the clock laser first passes through an acousto-optic modulator to realize the scanning of the clock laser frequency and the functions of light switching and power adjustment, and then passes through a half wave plate and a polarizing beam splitter to divide the clock laser into two, and then the two beams of clock laser pass through a half wave plate to adjust the polarization direction to vertical polarization, which is consistent with the polarization direction of the lattice light, and then pass through a convex lens to cooperate with the convex lens before the lattice light is incident on the atomic group to adjust the waist position and spot size of the clock laser, so as to ensure that the spot size of the clock laser incident on the atomic group in the optical lattice hardly changes, and the power density in the area of the optical lattice is uniform, thereby realizing the uniform excitation of the atoms in the detection of the clock transition spectrum. Finally, the two beams of clock laser pass through a dichroic mirror which has high reflectivity for 813 nm wavelength light and high transmittance for 698 nm wavelength light, and is combined with the lattice light with weak power.

[0030] On the other hand, the timing control involved in the one-dimensional horizontal dual-light lattice device in the optical clock is modified, and then the power and frequency of the lattice light and clock laser are changed and modulated through optoelectronic components such as acousto-optic modulators, voltage-controlled attenuators, and microwave switches, so as to realize the Flokai-designed differential optical lattice clock that can be used to improve the frequency measurement accuracy of optical clocks under microgravity environments. Among them, Figure 2 The radio frequency signal transmission links involved in each acousto-optic modulator are as follows: Figure 3 As shown in the figure, the timing control system controls the timing of the radio frequency drive signal applied to the acousto-optic modulator by connecting a microwave switch and a voltage-controlled attenuator. The specific timing control diagram for implementing the Floch design differential optical lattice clock is shown below. Figure 4 As shown. First, after primary atomic cooling via a 461 nm magneto-optical trap and secondary broadband cooling via a 689 nm magneto-optical trap, during the secondary narrowband cooling process, cold atomic clusters in the 689 nm magneto-optical trap are loaded using a deep-light lattice. At this point, under the influence of two relatively high-power lattice lights... P At the incident end 1, the same lattice light modulation signal is applied by acousto-optic modulators 1 and 3 respectively. At the two weaker lattice light incident ends, the same lattice light frequency shift signal is applied by acousto-optic modulators 2 and 4 respectively, thereby realizing the movement of atomic clusters within the optical lattice. Figure 4 The process within the black dashed box enables the spatial splitting and movement of atomic clusters. Figure 5 This demonstrates the change in the spatial distribution of atomic clusters within the optical lattice during this process. When the frequency difference between the incident and reflected light is... At that time, the optical lattice will move at a speed To move, therefore, the frequency difference is first set to... Then the optical lattice moves at a speed The atom cluster moves forward, then stops at the predetermined position, and the frequency difference is reduced to 0, causing the atom cluster to stop moving. The duration is... t 1. Then set the frequency difference to... Since no particularly large acceleration is needed to separate the atomic clusters during the later stages of moving the optical lattice, but only a short period of time is required to move them to the designated positions, the two frequency differences are usually set to... Then the optical lattice moves at a speed Move backward. During this process, The choice is also crucial, if If the atoms are too small, they are more likely to follow adiabatically, and the splitting is not obvious. If the frequency difference is too large, many atoms will be ejected from the lattice or tunneled and then captured by the magneto-optical trap, resulting in a loss of atoms in the moving lattice and a decrease in splitting efficiency. This invention selects a frequency difference on the order of hundreds of kHz or even lower. It is more appropriate to realize obvious atomic group splitting, and the adjustment needs to be made according to the potential well depth of the optical lattice and the temperature distribution of the atoms. The maintenance time of each frequency difference t 2and t 4can be preliminarily calculated through the specific values of the speed, acceleration, action time and separation distance of the optical lattice, and then fine-tuned in combination with the experimental conditions. In the process of realizing atomic group splitting, the 689 nm magneto-optical trap narrow-band cooling needs to be kept on until the atomic splitting is completed, and then the magneto-optical trap is turned off, and then the smaller lattice light frequency difference is used to move the split atomic groups to the position symmetrically centered on the zero point of the magnetic field in the magneto-optical trap, and keep the spatial position distance unchanged. This is because in the process of realizing atomic group splitting by accelerating through the optical lattice, part of the atoms have too high temperature or too wide momentum distribution, and if there is no assistance of the magneto-optical trap, the atoms are likely to escape from the lattice potential well, resulting in loss of the number of atoms and reducing the atomic splitting efficiency. After realizing the atomic sample distribution in Figure 5 , in order to further reduce the atomic temperature, the power of the lattice light is first adiabatically reduced to reduce the well depth of the optical lattice potential well, the power of the lattice light is adjusted by adjusting the acousto-optic modulator on the weaker P 2end of the lattice light, so as to reduce the well depth of the optical lattice, and the atoms with higher temperature in the high-order Bloch sideband of the optical lattice are thrown out of the optical lattice, and then the well depth is adiabatically increased to the original deep well depth. Then, the strong π pulse of the clock laser with the frequency at the red sideband is used to quickly pump the atoms to the lower-order Bloch sideband, i.e. the transition experienced by the atoms is . Then, the strong π pulse of the clock laser with the carrier frequency is used to pump the atoms to the ground state, i.e. . If necessary, this process can be repeated 2-3 times to ensure that most of the atoms are as much as possible in the ground state. Thus, the preparation of atomic motion state and the reduction of well depth are realized.

[0031] For example, as shown in Figure 3 , a radio frequency signal link diagram in a one-dimensional horizontal double optical lattice device provided by an embodiment of the application is shown. Figure 2In order to realize the arbitrary change of the lattice light and clock laser frequency with time and the switching of the light, the TTL digital pulse signal and the variable analog voltage signal need to be transmitted to the microwave switch and the voltage-controlled attenuator through the timing control system first, so as to realize the timing control of the radio frequency signal output by the arbitrary function generator, and then the radio frequency signal controlled by timing is connected to the acousto-optic modulator, so as to realize the regulation and switching of the frequency and power of the lattice light and clock laser. The radio frequency driving signal acting on the acousto-optic modulator is provided by three arbitrary function generators, two of which are used to generate the radio frequency driving signal of the acousto-optic modulator in the lattice light path, and the other one is used to generate the radio frequency driving signal of the acousto-optic modulator in the clock laser path, and the three arbitrary function generators are all traced back to the same hydrogen clock, and the 1PPS pulse output by the hydrogen clock is used for external triggering of the arbitrary function generator, so as to realize effective and synchronous high-precision timing control.

[0032] As shown in Figure 4 Fig. 1 is a schematic diagram of the timing control of the differential optical lattice clock based on the Floquet design provided by the embodiment of the present application. First, in the magnetic optical trap of the captured 87 The operation is divided into two stages. In the first stage, the magnetic optical trap operates on the strong dipole transition at 461 nm to reduce the atom temperature to the order of mK. This stage is also called primary cooling. In our experiment, this process usually takes about 500 ms. In the second stage, broadband and narrowband cooling are performed by the magnetic optical trap at 689 nm to cool the atoms to the order of μK. This stage is also called secondary cooling. The broadband cooling in the secondary cooling takes about 100 ms, and the narrowband cooling in the non-differential optical lattice clock takes about 50 ms. Since the initial power of the lattice laser in the present application is smaller than that of the lattice light laser in the prior art, the corresponding trap depth is also smaller, and therefore the lattice moving acceleration for separating a plurality of samples from the atomic group is also lower. Therefore, more sufficient time is reserved between the movement and acceleration of the optical lattice to allow the system to stabilize. The total time of the secondary narrowband cooling and the separation of a plurality of atomic samples after loading is set to 100 ms. During this process, the center frequency of the 813 nm lattice laser P at the 2 end is increased to the offset of the center frequency of the 1 end within P 1 time t 1 time , a part of the atoms is dragged, and then the frequency difference is kept constant within t 2 time t1linearly varied back to zero, the distance between the two separated atomic groups is fixed, and this process is repeated three times, so that the original large atomic group is divided into four smaller atomic groups, and then the narrow-band magneto-optical trap at 689 nm is turned off, so that the four separated atomic group samples are moved back to the spatial position symmetrically centered on the zero point of the magnetic field in the magneto-optical trap. The frequency change of the two one-dimensional horizontal optical lattice devices is synchronous change, which ensures the consistency of the two horizontal optical lattices as much as possible, thereby forming a differential optical clock structure with eight separate atomic groups. In space, the center positions of the two optical lattices have a spatial distance of 200 μm in the vertical direction, so as to avoid the overlap of the two one-dimensional optical lattices to form a two-dimensional optical lattice, which causes difficulty in atomic group separation, and the midpoint of this spacing also coincides with the zero point of the magnetic field. This design is more effective for eliminating the frequency shift caused by the magnetic field gradient in the vertical or horizontal direction. Figure 5 The atomic sample distribution before and after the atomic group splitting is realized by acceleration and movement through the optical lattice is shown. Figure 5 (a) is the atomic sample distribution diagram of one-dimensional horizontal double optical lattice atomic group without optical lattice acceleration and movement. The left graph shows the projection sample distribution of the atomic group in the horizontal plane before splitting, and the right graph shows the projection sample distribution in the vertical plane. Figure 5 (b) is the atomic sample distribution diagram of one-dimensional horizontal double optical lattice atomic group after optical lattice acceleration and movement. Similarly, the left graph shows the projection sample distribution of the atomic group in the horizontal plane after splitting, and the right graph shows the projection sample distribution in the vertical plane. Among them, Figure 5 (g in (a) and 5(b) is the direction of gravity, and if it is in a microgravity environment, it represents the direction perpendicular to the xoy plane.

[0033] In another aspect, by using the Ramsey clock transition spectrum synchronous detection method, all differential atomic groups are synchronously excited by a clock laser to realize multiplexing of one-dimensional optical lattice differential optical clock comparison, thereby suppressing some common mode noise. First, a clock laser pulse is used to excite the atoms, so that the distribution of the atoms in the internal state ground state and the excited state is 1:1; then the free evolution is carried out in the Ramsey detection dark time without the action of the clock laser; finally, another pulse is used to read the phase difference generated by the two atomic states after free evolution, and through pairwise comparison, the clock transition frequency difference between different atomic groups is determined. By using the absorption imaging normalization detection method, the fluorescence intensity of the atoms in the ground state and the excited state at different spatial positions is measured by using an electron multiplication charge coupled device combined with a photomultiplier tube, so as to obtain the fractional excitation rate of the clock laser at the excitation frequency. In the standard Ramsey spectrum detection process, the free evolution time between the two The system accumulates a phase: (4) where is the eigenfrequency of the atomic clock transition, is the frequency of the clock laser. For the clock transition frequency comparison of two atomic samples, one can record their fractional excitation rates and , with the phase fluctuation of the clock laser between each clock running period, one can get a series of points , . When the two atomic samples have the same frequency, then = 0, the points , , fall on a diagonal line, and when they have a fixed frequency difference, their phase difference is fixed, i.e. is a constant, then the trajectory of these scattered points is an ellipse. Thus, one can obtain the phase difference by fitting the ellipse formed by the fractional excitation rates of the two atomic samples, and then deduce the clock transition frequency difference between the two atomic samples: (5) Without knowing the frequency variation of the clock laser itself. For the differential optical clock of multiple atomic samples, the fractional excitation rate in the Ramsey spectrum measurement of a single sample is: (6) where is the contrast, which is a constant between 0 and 1. is the phase difference between the frequency of the clock laser and the eigenfrequency of the transition of the th atomic sample . Model the frequency drift of the clock laser as a common mode term: , the eigenfrequency of the atomic clock transition , the accumulated phase in the Ramsey spectrum of the two atomic samples is and , and the phase difference between the two samples is . When , the fractional excitation rates of the two atomic samples are completely consistent, and the ellipse degenerates into a diagonal line, while when At this point, the fractional ratio of the excitation rate cosine values ​​of the two atomic samples shows the largest misalignment, resulting in the flattest ellipse. This method, also known as ellipse fitting bias correction, fails when the phase difference is 0 or π. It is only effective within the open interval (0, π) by using the frequency difference between different atomic sample pairs to correct the clock transition frequency of the differential optical clock system. This eliminates the influence of frequency shift caused by some common-mode noise within the system. Compared to systems without bias correction, it can significantly improve the frequency uncertainty of clock closed-loop operation, thereby reducing the system's requirements for clock laser noise limits.

[0034] For example, after separating and moving multiple atomic cluster samples, the next step is to further cool and reduce the optical lattice potential well for the detection of clock transition spectral lines. This process mainly involves... P The laser power at the two ends of the lattice is slowly reduced and then maintained at a well depth of approximately 15-20. E r ( E r A certain value in the recoil energy of the optical lattice is kept constant, and this process lasts for approximately 200 ms. Then, according to the atomic state requirements for clock transition Ramsey spectroscopy, atomic state preparation is performed, which takes approximately 100 ms. Finally, clock transition Ramsey spectroscopy is performed, using two time intervals... T 2 698 nm clock laser The pulses excite the atoms and detect the phase difference between their atomic states; the duration of the two pulses is... T 1. The specific implementation process involves setting the required parameters in the timing control system. T 1 and T The time is 2 seconds, and the corresponding TTL digital pulse signal is output to the microwave switch to control the switching time of the clock laser. The RF drive signal output by the arbitrary function generator to the acousto-optic modulator is controlled to achieve timing control of the clock laser during excitation. The timing control system works in conjunction with the voltage-controlled attenuator to change the intensity of the RF drive signal acting on the acousto-optic modulator, thereby adjusting the corresponding excitation time. The clock laser power required for the pulse. Because... 87 The excited state lifetimes of Sr atomic clock transitions exceed 100 seconds. Electrons in the excited state rarely return to the ground state through spontaneous emission in a short time. Moreover, even if they do return, the 698 nm fluorescence is extremely weak and cannot be directly observed using a photomultiplier tube. Therefore, we need to indirectly measure the number of particles in the ground state using the more easily observable strong dipole transition at 461 nm. First, the number of particles in the ground state can be directly excited using a 461 nm probe light, and the fluorescence intensity at this point is recorded. This fluorescence intensity corresponds to the number of particles in the ground state. N gMeanwhile, the excitation of the probe light also makes the atoms escape from the optical lattice potential, which actually plays a role in emptying the ground state population. Then the excited state population is pumped back to the ground state by the 679, 707 nm repump light 1 On S0, the excited state population is measured by the same method N e The corresponding fluorescence intensity is calculated by normalizing the two recorded fluorescence intensities to obtain the atomic transition probability P e = N e / ( N g + N e ), P e It is also called fractional excitation rate, and this method of collecting the strontium atomic clock transition spectrum is called normalized electron shelving detection. Using this method to detect the clock transition spectrum has another advantage, that is, after normalization, the influence introduced by the fluctuation of the number of atoms in each cycle of the optical clock can be reduced, thereby improving the signal-to-noise ratio of the collected spectrum. Figure 4 The three 461 nm probe light pulses in the middle blue dashed box are usually set to a fixed value of 2-5 ms, the first pulse is used to detect the number of atoms in the ground state, the second pulse is used to detect the number of atoms in the excited state, and the last pulse is used to detect the noise of the light. The fluorescence intensities detected by the first two pulses are respectively subtracted by the fluorescence intensity detected by the last pulse, and the normalized atomic spectrum excitation rate is obtained. The 679, 707 nm repump light pulse time is set to about 10 ms. In this process, the frequency modulation of the lattice light is always in the open state, and the modulation parameter is the best modulation parameter corresponding to the suppression of tunneling at a specific well depth. In this way, a complete clock cycle is realized. After one cycle, the excitation rate of the clock transition Ramsey spectrum at a certain clock laser frequency is obtained. To detect a clock transition Ramsey spectrum, multiple such cycle cycles need to be run, and the frequency of the clock laser does not change in each cycle, but the frequency of the clock laser needs to be scanned by the acousto-optic modulator 5 in each cycle. The step size of each frequency change is the same. This frequency sweeping function is realized by the timing control system and the acousto-optic modulator 5 in the clock laser light path and the arbitrary function generator 3 connected thereto. In this way, a clock transition Ramsey spectrum in a frequency range is obtained. By comparing the clock transition frequencies obtained by detecting the Ramsey spectra of different atomic groups, the frequency difference between different atomic groups is obtained, and the elliptical fitting bias correction method is used to eliminate the influence of common mode noise in the system on the clock transition frequency shift.

[0035] Moreover, the above-described figures are only a schematic representation of the processes comprised in the method according to the exemplary embodiments of the present application, and are not intended to limit purposes. It is readily understood that the processes shown in the above-described figures do not indicate or limit the chronological order of these processes. In addition, it is readily understood that these processes can be executed, for example, synchronously or asynchronously in a plurality of modules.

[0036] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0037] It is to be understood that the application is not limited to the precise details of design and construction set forth above and illustrated in the drawings, but that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application is indicated by the appended claims, rather than by the foregoing description.

Claims

1. A method for improving the frequency measurement accuracy of an optical lattice clock in a microgravity environment, characterized in that, The method comprises: two beams of lattice light are divided from one lattice light laser, each of the two beams of lattice light is further divided into two beams of lattice light, and four beams of lattice light form two one-dimensional horizontal optical lattices; wherein the waist positions of the two one-dimensional horizontal optical lattices exist a certain interval in the vertical direction, and the midpoint position is the position of the magnetic field zero point in the magneto-optical trap, and the projections of the axial directions of the two horizontal optical lattices in the vertical plane are parallel to each other, and the projections in the horizontal plane are perpendicular to each other; two beams of clock laser are divided from one clock laser source to excite different atomic groups in the two one-dimensional horizontal optical lattices; an acousto-optic modulator with the same parameters is loaded on the light path of each beam of lattice light for linear frequency shift and modulation of the lattice light frequency, wherein the acousto-optic modulator loaded on the light path of the two beams of lattice light for generating one one-dimensional horizontal optical lattice is connected to an arbitrary function generator, the acousto-optic modulator loaded on the light path of the two beams of lattice light for generating another one-dimensional horizontal optical lattice is connected to another arbitrary function generator; an acousto-optic modulator is also loaded before the clock laser beam splitting for scanning the clock laser frequency, and the acousto-optic modulator on the clock laser is connected to a third arbitrary function generator; the three arbitrary function generators are all traced back to the same hydrogen clock as the frequency reference source.

2. The method of claim 1, wherein, The two beams of lattice light are divided from one lattice light laser, each of the two beams of lattice light is further divided into two beams of lattice light, and four beams of lattice light form two one-dimensional horizontal optical lattices, which are specifically: the lattice light output by the lattice light laser is divided into two beams by a polarization beam splitter, each beam of lattice light is further divided into two beams of lattice light by a polarization beam splitter, and the four beams of lattice light are first lattice light, second lattice light, third lattice light and fourth lattice light; wherein the initial optical powers of the first lattice light and the second lattice light are set to be the same, the initial optical powers of the third lattice light and the fourth lattice light are set to be the same; the initial optical powers of the first lattice light and the second lattice light are greater than the initial optical powers of the third lattice light and the fourth lattice light; the first lattice light and the second lattice light are incident on the atomic group captured by the magneto-optical trap at a 90° angle, the third lattice light and the fourth lattice light are incident on the atomic group captured by the magneto-optical trap at a 90° angle, and the third lattice light is opposite to one of the first lattice light and the second lattice light, and the fourth lattice light is opposite to the other of the first lattice light and the second lattice light, thereby forming two one-dimensional horizontal optical lattices.

3. The method of claim 1, wherein, The two beams of clock laser are divided from one clock laser source to excite different atomic groups in the two one-dimensional horizontal optical lattices, which are specifically: the clock laser output by the clock laser is divided into two beams by a polarization beam splitter, which are first clock laser and second clock laser, the first clock laser is combined with one of the third lattice light and the fourth lattice light through a dichroic mirror, and the second clock laser is combined with the other of the third lattice light and the fourth lattice light through a dichroic mirror.

4. The method of claim 2, wherein, A half-wave plate, a linear polarizer and a convex lens are connected in sequence at the end of the light path of each beam of lattice light, wherein: the half-wave plate and the linear polarizer are used to adjust the polarization direction of each beam of lattice light to keep it vertically polarized; the convex lens is used to fix the waist position of the lattice light at the center of the atomic group in the magneto-optical trap.

5. The method of claim 3, wherein, The polarization direction of the clock laser is adjusted by adding a half wave plate to each of the two clock lasers, so that the polarization direction of the clock laser is consistent with the polarization direction of the lattice light; then a convex lens is combined with the convex lens in the lattice light beam, so that the waist size and position of the clock laser are adjusted.

6. The method of claim 1, wherein, A microwave switch, a voltage-controlled attenuator and a time sequence control system are arranged between the acousto-optic modulator and the arbitrary function generator. The time sequence control system generates a series of TTL digital pulse signals, which are transmitted to the microwave switch, and then the microwave switch turns on or off the output radio frequency signal of the arbitrary function generator according to the instruction of the time sequence system, so as to realize the switching of the lattice laser and the control of the action time of the linear frequency shift signal and the frequency modulation signal. The time sequence control system transmits a time-varying analog voltage waveform to the voltage-controlled attenuator, so as to realize variable attenuation of the radio frequency signal strength.

7. The method of claim 6, wherein, The modulation parameters suitable for the specific optical lattice well depth are selected by Floquet design technology, and the specific process is as follows: Two identical modulation radio frequency signals are output by an arbitrary function generator, both of which are sine modulation, and the carrier frequency and modulation parameters are completely consistent, then the two signals are loaded on the acousto-optic modulators of the first and second lattice lights, and the start time and action time of the signals are controlled by the time sequence control system and the microwave switch; the parameters of the sine modulation signal are selected by the tunneling rate modulation function, that is, the modulation depth corresponding to the zero point of the first Bessel function; wherein the parameters of the frequency modulation function loaded on the two one-dimensional horizontal optical lattices must be completely consistent.

8. The method of claim 7, wherein, The acceleration and movement of the optical lattice are realized by changing the frequency difference of the two counter-propagating lattice lights in the two one-dimensional horizontal optical lattices, so as to prepare multiple atomic samples required by the differential optical clock, and the specific process is as follows: Two radio frequency signals without modulation are output by another arbitrary function generator, which have the same carrier frequency as the radio frequency signal output by the arbitrary function generator in claim 7, then the two signals are loaded on the acousto-optic modulators of the third and fourth lattice lights, and the start time and action time of the signals are controlled by the time sequence control system, the microwave switch and the acousto-optic modulator; the output frequency of the unmodulated radio frequency signal is changed within a given action time period by the time sequence control system, the arbitrary function generator and the acousto-optic modulator, so as to introduce a frequency difference with the carrier frequency of the radio frequency signal loaded on the acousto-optic modulators of the first and second lattice lights, thereby accelerating the optical lattice, splitting the atomic group in the optical lattice, and moving the split atomic group as a whole to the position symmetric to the zero point of the magnetic field in the magnetic optical trap, so as to prepare multiple atomic group samples required by the differential optical clock.

9. The method of claim 1, wherein, The excitation process involves using two time intervals. The frequency scanning function of the clock laser is achieved through a pulse, using a timing control system, an acousto-optic modulator on the clock laser optical path, and a third arbitrary function generator connected to it. This allows for the detection of the complete Ramsey spectral lines within a given frequency band. Simultaneously, the timing control system, in conjunction with a microwave switch and the acousto-optic modulator, controls two pulses during the excitation process. The duration of the laser pulse and the interval between two pulses are controlled; and the timing control system, voltage-controlled attenuator, and acousto-optic modulator work together to adjust the corresponding excitation times. The required clock laser power for the pulse is used to achieve synchronous detection of the Ramsey spectral lines of the clock transition and closed-loop locking of the clock transition frequency. The clock transition frequencies obtained from multiple atomic samples are compared pairwise, and then the elliptic fitting correction bias method is used to eliminate the influence of common-mode noise on the clock transition frequency shift.

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