Cold atom gravity measurement method and device based on entangled state enhancement

Abstract

The invention provides a cold atom gravity measurement method and device based on entangled state enhancement, and belongs to the technical field of cold atom gravity measurement, and the method comprises the steps: carrying out the excitation of a nonlinear crystal, obtaining an entangled photon pair, and enabling the entangled photon pair to comprise a first photon and a second photon in an entangled state; laser parameters of an area where a cold atomic group is located are controlled, the first photons are coupled into the cold atomic group, and a plurality of cold atoms in an entangled state are obtained; and placing the plurality of cold atoms in the entangled state in a gravity field, measuring the phase difference of the cold atoms under the action of the gravity field, and determining a gravity measurement result based on the phase difference. According to the invention, entangled photons are introduced to be coupled with cold atoms, so that the measurement limit is improved to the Heisenberg limit, and higher-precision gravity measurement is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of cold atom gravity measurement, and in particular to a cold atom gravity measurement method and device based on entangled state enhancement. Background Art

[0002] Cold atom gravimeters are widely used in the field of precision gravity measurement. The measurement principle is to cool atoms to an ultra-low temperature close to absolute zero and then use the influence of the gravitational field on their interference pattern to achieve measurement.

[0003] However, the measurement accuracy of cold atom gravimeters is mainly limited by the standard quantum limit (SQL). For geophysical exploration, geological exploration and basic physics experiments, this accuracy still cannot meet the requirements in many cases. ,in n This means that increasing the number of atoms is necessary to increase the measurement accuracy, but too many atoms will increase the cooling difficulty and system complexity.

[0004] Therefore, there is an urgent need to provide a cold atom gravity measurement method and device based on entanglement state enhancement, so as to improve the measurement accuracy without increasing the number of atoms, so as to take into account both measurement accuracy and system simplicity. Summary of the invention

[0005] In view of this, it is necessary to provide a cold atom gravity measurement method and device based on entanglement state enhancement to solve the technical problem in the prior art of improving measurement accuracy by increasing the number of atoms, resulting in higher cooling difficulty and system complexity.

[0006] On the one hand, in order to solve the above technical problems, the present invention provides a cold atom gravity measurement method based on entangled state enhancement, comprising: Exciting the nonlinear crystal to obtain a pair of entangled photon pairs, wherein the entangled photon pair includes a first photon and a second photon in an entangled state; Controlling laser parameters in the region where the cold atom cluster is located, coupling the first photon into the cold atom cluster, and obtaining a plurality of cold atoms in an entangled state; The plurality of cold atoms in an entangled state are placed in a gravitational field, the phase difference of the cold atoms under the action of the gravitational field is measured, and the gravitational measurement result is determined based on the phase difference.

[0007] In a possible implementation, a nonlinear crystal is excited to obtain an entangled photon pair, including: Acquiring target parameters of a tunable laser source, and adjusting the pump light based on the target parameters to obtain target pump light; The nonlinear crystal is excited based on the target pump light to obtain the entangled photon pair.

[0008] In a possible implementation manner, after exciting the nonlinear crystal based on the target pump light to obtain the entangled photon pair, the method further includes: adjusting a phase shift between the first photon and the second photon to obtain an enhanced entangled photon pair; The enhanced entangled photon pair is processed based on the phase-locked amplification technology to obtain a stable entangled photon pair.

[0009] In a possible implementation manner, before coupling the first photon into the cold atom group to obtain a plurality of cold atoms in an entangled state, the method further includes: Acquire the wavelength and polarization state of the first photon and the target wavelength and coupling characteristics of the cold atom; The wavelength and the polarization state are adjusted based on the target wavelength and the coupling characteristic.

[0010] In a possible implementation, controlling laser parameters in a region where the cold atom cluster is located, coupling the first photon into the cold atom cluster, and obtaining a plurality of cold atoms in an entangled state includes: Controlling laser parameters in the area where the cold atom cluster is located to construct an entangled response between each of the cold atoms in the cold atom cluster and the first photon; Based on the interaction between the plurality of cold atoms and the entangled response, the plurality of cold atoms in an entangled state are obtained.

[0011] In a possible implementation, the method further includes: synchronously acquiring first phase data of the cold atom and second phase data of the first photon; determining a coupling strength of the entangled response based on the first phase data and the second phase data; When the coupling strength does not meet the requirement, the laser parameters are adjusted so that the coupling strength of the entangled response meets the requirement.

[0012] In a possible implementation manner, the laser parameters include a laser field frequency and a laser field phase.

[0013] In a possible implementation manner, the method further includes: before determining the gravity measurement result based on the phase difference, further including: The phase difference is subjected to noise filtering.

[0014] In a possible implementation manner, after performing noise filtering on the phase difference, the method further includes: The noise-filtered phase difference is compensated based on the quantum noise compensation algorithm.

[0015] On the other hand, the present invention also provides a cold atom gravity measurement device based on entangled state enhancement, comprising: An entangled photon pair generation module is used to excite the nonlinear crystal to obtain a pair of entangled photon pairs, wherein the entangled photon pair includes a first photon and a second photon in an entangled state; A photon-cold atom coupling module, used to control laser parameters in the area where the cold atom cluster is located, and couple the first photon into the cold atom cluster to obtain a plurality of cold atoms in an entangled state; The gravity measurement module is used to place the multiple cold atoms in the entangled state in a gravity field, measure the phase difference of the cold atoms under the action of the gravity field, and determine the gravity measurement result based on the phase difference.

[0016] The beneficial effects of the present invention are as follows: the cold atom gravity measurement method based on entangled state enhancement provided by the present invention, after exciting the nonlinear crystal to obtain an entangled photon pair, couples the first photon of the entangled photon pair to the cold atom group to obtain multiple cold atoms in an entangled state, provides additional quantum resources for cold atom gravity measurement, utilizes the quantum entanglement effect to reduce phase uncertainty, and increases the measurement accuracy from the standard quantum limit ( ) to the Heisenberg limit (1 / n), that is, the measurement accuracy of cold atom gravity measurements is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 A schematic flow chart of an embodiment of a cold atom gravity measurement method based on entanglement state enhancement provided by the present invention; Figure 2 For the present invention Figure 1 A schematic flow chart of an embodiment of S101; Figure 3 A schematic diagram of a flow chart of an embodiment of adjusting the wavelength and polarization state of a first photon provided by the present invention; Figure 4 For the present invention Figure 1 A schematic flow chart of an embodiment of S102; Figure 5 A schematic diagram of a flow chart of an embodiment of adjusting the entanglement response provided by the present invention; Figure 6A schematic structural diagram of an embodiment of a cold atom gravity measurement device based on entanglement state enhancement provided by the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0020] It should be understood that the schematic drawings are not drawn to scale. The flowchart used in the present invention shows the operations implemented according to some embodiments of the present invention. It should be understood that the operations of the flowchart can be implemented out of order, and the steps without logical context can be reversed in order or implemented simultaneously. In addition, those skilled in the art, under the guidance of the content of the present invention, can add one or more other operations to the flowchart, and can also remove one or more operations from the flowchart. Some of the block diagrams shown in the accompanying drawings are functional entities, which do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor systems and / or microcontroller systems.

[0021] Reference to an "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0022] The present invention provides a cold atom gravity measurement method and device based on entanglement state enhancement, which are described below respectively.

[0023] Figure 1 A schematic flow chart of an embodiment of the cold atom gravity measurement method based on entanglement state enhancement provided by the present invention is shown in FIG. Figure 1 As shown, the cold atom gravity measurement method based on entangled state enhancement includes: S101, exciting a nonlinear crystal to obtain a pair of entangled photon pairs, where the entangled photon pair includes a first photon and a second photon in an entangled state; S102, controlling laser parameters in the region where the cold atom cluster is located, coupling the first photon into the cold atom cluster, and obtaining a plurality of cold atoms in an entangled state; S103, placing a plurality of cold atoms in an entangled state in a gravitational field, measuring the phase difference of the cold atoms under the action of the gravitational field, and determining the gravity measurement result based on the phase difference.

[0024] Specifically, the nonlinear crystal in step S101 is a lithium niobate crystal.

[0025] Among them, the first photon and the second photon in the entangled state have the same or similar frequencies and are separated in space, but maintain a quantum entanglement relationship, so that the state of one of the photons can be transferred to couple to the cold atomic cluster.

[0026] It should be understood that a cold atom cluster refers to a collection of multiple cold atoms.

[0027] Among them, cold atoms refer to: placing rubidium or cesium atoms in optical tweezers for cooling, cooling them to an ultra-low temperature state close to absolute zero (a few nanokelvins), and then configuring mutually perpendicular laser cooling axes to capture and cool the atoms through lasers, so that their speed gradually decreases to approach a static state. At this time, the atoms reach a superfluid state or a Bose-Einstein condensate state.

[0028] The superfluid state or Bose-Einstein condensate can ensure that cold atoms have high coherence and long coherence time. Cold atomic clusters in ultra-low temperature state can realize collective coherent motion in the quantum state, thereby stably maintaining the quantum interference pattern in the gravitational field, greatly improving the accuracy of gravity measurement and reducing the interference of thermal noise on the measurement.

[0029] It should be noted that the purpose of coupling the first photon into the cold atomic cluster in step S102 is to enable the atom to capture and maintain the phase information provided by the first photon.

[0030] It should also be noted that: the specific method of measuring the phase difference of cold atoms under the action of the gravitational field in step S103 is: the wave function of the cold atomic cluster is divided into two parts by a beam splitter to obtain two beams of light. The two beams of light evolve freely under the action of the gravitational field, and a small phase difference occurs in the process. The direction of the split light beam is controlled based on a reflector. When the two light beams are re-merged, the interference fringes after the interference of the two light beams are recorded based on the detector, and the phase difference is obtained based on the interference fringes.

[0031] Since the gravity measurement results rely on the phase difference, in order to improve the measurement accuracy of the phase difference and thus improve the measurement accuracy of the gravity measurement results, in some embodiments of the present invention, the phase difference can be detected in real time based on a high-sensitivity quantum state detection system to ensure that the measurement accuracy of the quantum state reaches the single-photon level.

[0032] At the same time, it can also be equipped with fast-response photodetectors and time-resolved detectors to accurately detect and feedback the phase difference of cold atoms in a short time, thereby improving the real-time response capability of gravity measurement.

[0033] Compared with the prior art, the cold atom gravity measurement method based on entangled state enhancement provided by the embodiment of the present invention obtains entangled photon pairs by exciting nonlinear crystals, and then couples the first photon of the entangled photon pairs to cold atom groups to obtain multiple cold atoms in an entangled state, thereby providing additional quantum resources for cold atom gravity measurement, and utilizing the quantum entanglement effect to reduce phase uncertainty, thereby increasing the measurement accuracy from the standard quantum limit ( ) to the Heisenberg limit (1 / n), that is, the measurement accuracy of cold atom gravity measurements is improved.

[0034] In some embodiments of the present invention, Figure 2 As shown, step S101 includes: S201, acquiring target parameters of a tunable laser source, and adjusting pump light based on the target parameters to obtain target pump light; S202. Excite the nonlinear crystal based on the target pump light to obtain entangled photon pairs.

[0035] Among them, the purpose of the target parameters is to make the generated entangled photon pairs have strong quantum entanglement properties to ensure the accuracy of subsequent gravity measurements.

[0036] Specifically, the target parameter may be the wavelength of the tunable laser source.

[0037] Furthermore, the target parameters of the tunable laser source may also be parameters related to the generation rate of entangled photon pairs and the purity of the entangled state, which will not be described in detail here.

[0038] It should be noted that: in some embodiments of the present invention, the quantum entanglement characteristics of the generated entangled photon pairs can also be ensured by adjusting the nonlinear coefficient of the nonlinear crystal through the spontaneous parametric down-conversion (SPDC) effect of the nonlinear crystal.

[0039] It can be seen from the above description that the entangled state of multiple cold atoms is crucial to the gravity measurement result. Therefore, in some embodiments of the present invention, after step S202, the cold atom gravity measurement method based on entangled state enhancement further includes: adjusting the phase shift between the first photon and the second photon to obtain an enhanced entangled photon pair; The enhanced entangled photon pairs are processed based on the phase-locked amplification technology to obtain stable entangled photon pairs.

[0040] Then the first photon and the second photon in step S101 are two photons in a stable entangled photon pair.

[0041] The embodiment of the present invention enhances the coherence of the cold atom entangled state formation process by adjusting the phase offset of the first photon and the second photon, and processes the enhanced entangled photon pairs based on the phase-locked amplification technology to ensure that the generated stable entangled photon pairs have a stable phase relationship, thereby ensuring the phase control accuracy during subsequent gravity measurement.

[0042] In order to maximize the transmission efficiency of the phase information of the first photon in the cold atomic group, in some embodiments of the present invention, Figure 3 As shown, before step S102, it also includes: S301, obtaining the wavelength and polarization state of the first photon and the target wavelength and coupling characteristics of the cold atom; S302: Adjust the wavelength and polarization state based on the target wavelength and coupling characteristics.

[0043] The adjustment of wavelength and polarization state can be achieved through wave plates and polarization beam splitters.

[0044] The embodiment of the present invention adjusts the wavelength and polarization state of the first photon based on the target wavelength and coupling characteristics of the cold atom, so that the first photon adapts to the wavelength and coupling characteristics of the cold atom, and then matches the transition frequency of the first photon with that of the cold atom, thereby maximizing the transmission efficiency of the phase information of the first photon in the cold atom cluster.

[0045] In some embodiments of the present invention, Figure 4 As shown, step S102 includes: S401, controlling laser parameters in the area where the cold atom cluster is located, and constructing an entangled response between each cold atom in the cold atom cluster and the first photon; S402. Based on the interaction and entanglement response between the multiple cold atoms, multiple cold atoms in an entangled state are obtained.

[0046] It should be noted that the entangled response of each cold atom in the cold atom cluster and the first photon is independent. Therefore, the laser parameters for controlling the area where the cold atom cluster is located in step S401 should be the laser parameters for controlling the position of each cold atom to ensure that an entangled response is constructed for each cold atom and the first photon.

[0047] The principle of obtaining multiple cold atoms in an entangled state in step S402 is: the first photon transmits phase information to the multiple cold atoms through its coherence, and the multiple cold atoms influence each other through the group effect to obtain multiple cold atoms in an entangled state.

[0048] In a specific embodiment of the present invention, the laser parameters include laser field frequency and laser field phase.

[0049] Since the entangled response between the first photon and the cold atom may collapse or decay under the influence of the external environment or other disturbances, resulting in the inability to accurately measure gravity, in order to avoid this problem, in some embodiments of the present invention, such as Figure 5 As shown, the cold atom gravity measurement method based on entangled state enhancement also includes: S501, synchronously acquiring first phase data of cold atoms and second phase data of first photons; S502, determining the coupling strength of the entanglement response based on the first phase data and the second phase data; S503. When the coupling strength does not meet the requirement, adjust the laser parameters so that the coupling strength of the entanglement response meets the requirement.

[0050] The embodiment of the present invention ensures the coupling strength of the entanglement response under any circumstances by synchronously detecting the first phase data of the cold atom and the second phase data of the first photon, and adjusting the laser parameters based on the coupling strength obtained by the detection. That is, it can quickly make adjustments when the entanglement response is unstable under the influence of external environment or disturbance, thereby ensuring the reliability and stability of the entanglement response, and further ensuring that the coherent information can be effectively transmitted to the cold atom, thereby improving the accuracy of subsequent gravity measurements.

[0051] Furthermore, the embodiment of the present invention synchronously acquires the first phase data and the second phase data, thereby avoiding the adverse effect of different acquisition times on the determination of coupling strength, thereby ensuring the accuracy of gravity measurement.

[0052] Among them, the adjustment of laser parameters can be carried out in real time through phase modulators and frequency modulators to ensure that the entangled response between the first photon and the cold atom remains stable during the entire measurement process.

[0053] Since quantum systems are easily affected by the surrounding environment (light, temperature, etc.), any interaction with the environment may lead to information leakage, causing the entangled state to gradually decay, a process called "decoherence". Decoherence is one of the main obstacles that need to be overcome in quantum computing and quantum communication. To avoid this technical problem, in some embodiments of the present invention, before determining the gravity measurement result based on the phase difference in step S103, it also includes: Perform noise filtering on the phase difference.

[0054] The specific means of performing noise filtering on the phase difference is: measuring the phase difference noise based on a spectrum analyzer, and setting filtering parameters of the noise filter based on the phase difference noise, thereby achieving noise filtering.

[0055] The embodiment of the present invention eliminates noise interference caused by the surrounding environment such as ambient light and temperature changes by performing noise filtering on the phase difference, thereby minimizing the error of the gravity measurement result.

[0056] To further improve the accuracy of the gravity measurement result, in some embodiments of the present invention, after the phase difference is subjected to noise filtering, the method further includes: The noise-filtered phase difference is compensated based on the quantum noise compensation algorithm.

[0057] The embodiment of the present invention can dynamically compensate for the measurement error caused by quantum noise by setting a quantum noise compensation algorithm, thereby further improving the accuracy of gravity measurement.

[0058] The quantum noise compensation algorithm may be any noise compensation algorithm in the prior art adapted to the embodiment of the present invention, which will not be described in detail herein.

[0059] In summary, the cold atom gravity measurement method based on entanglement state enhancement proposed in the embodiment of the present invention couples the first photon of the entangled photon pair to the cold atom group to obtain multiple cold atoms in an entangled state, which provides additional quantum resources for cold atom gravity measurement, reduces phase uncertainty by using the quantum entanglement effect, and significantly reduces the phase noise of cold atom gravity measurement, making the measurement accuracy from the standard quantum limit ( ) to the Heisenberg limit (1 / n), that is, the measurement accuracy of cold atom gravity measurement is improved, the measurement accuracy breaks through the standard quantum limit, and high-precision measurement of gravity signals is achieved.

[0060] In order to better implement the cold atom gravity measurement method based on entangled state enhancement in the embodiment of the present invention, on the basis of the cold atom gravity measurement method based on entangled state enhancement, the embodiment of the present invention also provides a cold atom gravity measurement device based on entangled state enhancement, such as Figure 6 As shown, the cold atom gravity measurement device 600 based on entangled state enhancement includes: An entangled photon pair generation module 601 is used to excite the nonlinear crystal to obtain a pair of entangled photon pairs, where the entangled photon pair includes a first photon and a second photon in an entangled state; The photon-cold atom coupling module 602 is used to control the laser parameters in the area where the cold atom cluster is located, couple the first photon into the cold atom cluster, and obtain a plurality of cold atoms in an entangled state; The gravity measurement module 603 is used to place a plurality of cold atoms in an entangled state in a gravity field, measure the phase difference of the cold atoms under the action of the gravity field, and determine the gravity measurement result based on the phase difference.

[0061] The cold atom gravity measurement device 600 based on entangled state enhancement provided in the above embodiment can implement the technical solution described in the above embodiment of the cold atom gravity measurement method based on entangled state enhancement. The specific implementation principles of the above modules or units can refer to the corresponding contents in the above embodiment of the cold atom gravity measurement method based on entangled state enhancement, which will not be repeated here.

[0062] Those skilled in the art will appreciate that all or part of the processes of the above-mentioned embodiments can be implemented by instructing related hardware (such as a processor, a controller, etc.) through a computer program, and the computer program can be stored in a computer-readable storage medium, wherein the computer-readable storage medium is a disk, an optical disk, a read-only storage memory, or a random access memory, etc.

[0063] The above is a detailed introduction to the cold atom gravity measurement method and device based on entanglement state enhancement provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for technical personnel in this field, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A cold atom gravity measurement method based on entangled state enhancement, characterized in that: include: Exciting the nonlinear crystal to obtain a pair of entangled photon pairs, wherein the entangled photon pair includes a first photon and a second photon in an entangled state; Controlling laser parameters in the region where the cold atom cluster is located, coupling the first photon into the cold atom cluster, and obtaining a plurality of cold atoms in an entangled state; The plurality of cold atoms in an entangled state are placed in a gravitational field, the phase difference of the cold atoms under the action of the gravitational field is measured, and the gravitational measurement result is determined based on the phase difference.

2. The cold atom gravity measurement method based on entangled state enhancement according to claim 1 is characterized in that: Excite the nonlinear crystal to obtain a pair of entangled photons, including: Acquiring target parameters of a tunable laser source, and adjusting the pump light based on the target parameters to obtain target pump light; The nonlinear crystal is excited based on the target pump light to obtain the entangled photon pair.

3. The cold atom gravity measurement method based on entangled state enhancement according to claim 2 is characterized in that: After exciting the nonlinear crystal based on the target pump light to obtain the entangled photon pair, the method further includes: adjusting a phase shift between the first photon and the second photon to obtain an enhanced entangled photon pair; The enhanced entangled photon pair is processed based on the phase-locked amplification technology to obtain a stable entangled photon pair.

4. The cold atom gravity measurement method based on entangled state enhancement according to claim 1 is characterized in that: Before coupling the first photon into the cold atom group to obtain a plurality of cold atoms in an entangled state, the method further includes: Acquire the wavelength and polarization state of the first photon and the target wavelength and coupling characteristics of the cold atom; The wavelength and the polarization state are adjusted based on the target wavelength and the coupling characteristic.

5. The cold atom gravity measurement method based on entangled state enhancement according to claim 1, characterized in that: Controlling laser parameters in the area where the cold atom cluster is located, coupling the first photon into the cold atom cluster, and obtaining a plurality of cold atoms in an entangled state, comprising: Controlling laser parameters in the area where the cold atom cluster is located to construct an entangled response between each of the cold atoms in the cold atom cluster and the first photon; Based on the interaction between the plurality of cold atoms and the entangled response, the plurality of cold atoms in an entangled state are obtained.

6. The cold atom gravity measurement method based on entangled state enhancement according to claim 5 is characterized in that: The method further comprises: synchronously acquiring first phase data of the cold atom and second phase data of the first photon; determining a coupling strength of the entangled response based on the first phase data and the second phase data; When the coupling strength does not meet the requirement, the laser parameters are adjusted so that the coupling strength of the entangled response meets the requirement.

7. The cold atom gravity measurement method based on entangled state enhancement according to any one of claims 1 to 6, characterized in that: The laser parameters include laser field frequency and laser field phase.

8. The cold atom gravity measurement method based on entangled state enhancement according to claim 1, characterized in that: The method further includes, before determining the gravity measurement result based on the phase difference, further including: The phase difference is subjected to noise filtering.

9. The cold atom gravity measurement method based on entangled state enhancement according to claim 1, characterized in that: After performing noise filtering on the phase difference, the method further comprises: The noise-filtered phase difference is compensated based on the quantum noise compensation algorithm.

10. A cold atom gravity measurement device based on entangled state enhancement, characterized in that: include: An entangled photon pair generation module is used to excite the nonlinear crystal to obtain a pair of entangled photon pairs, wherein the entangled photon pair includes a first photon and a second photon in an entangled state; A photon-cold atom coupling module, used to control laser parameters in the area where the cold atom cluster is located, and couple the first photon into the cold atom cluster to obtain a plurality of cold atoms in an entangled state; The gravity measurement module is used to place the multiple cold atoms in the entangled state in a gravity field, measure the phase difference of the cold atoms under the action of the gravity field, and determine the gravity measurement result based on the phase difference.

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