Ultra-cold atom control device and method based on quadrupole trap magnetic field gradient compensation method

Abstract

The invention discloses an ultra-cold atom control device and method based on a quadrupole trap magnetic field gradient compensation method, and belongs to the field of ultra-cold atom and angular velocity precision measurement. The device comprises a vacuum cavity, a cooling light source, a light trap light source, a Bragg pulse light source and a quadrupole trap coil. The vacuum cavity is used for providing an ultrahigh vacuum environment; the cooling light source is used for preliminarily cooling atoms; the light trap light source forms an orthogonal light trap and is used for evaporating and cooling atoms; the quadrupole trap coil adopts a reverse Helmholtz configuration to form a quadrupole trap; the Bragg pulse light source is used for generating a Bragg pulse laser light source; and the center of the quadrupole trap is positioned right above the center of the light trap. The mixed trap formed by combining the optical trap and the quadrupole trap is adopted, a quadrupole trap magnetic field gradient compensation method is adopted to replace a time orbital trap, suspension of ultra-cold atoms in the quadrupole trap can be achieved, cold atoms are trapped by the atoms in the horizontal plane, and then the Sagnac effect can be achieved. The method has the advantages that current control is simple, equipment complexity is reduced, and the method is suitable for the outside of a metal cavity.

Description

Technical Field

[0001] The invention relates to an ultracold atom manipulation device and method based on a quadrupole trap magnetic field gradient compensation method, and belongs to the field of ultracold atoms and angular velocity precision measurement. Background Art

[0002] Existing ultracold atoms are often bound at the bottom of a potential well without a magnetic field zero point. Common ones include optical traps composed of lasers, QUICs with compensated magnetic field zero points, and time-orbit averaged potential wells. After preparation, ultracold atoms often stay at the bottom of the potential well and are in a steady state. Ultracold atoms can rotate in the potential well to achieve the Sagnac effect, and the angular velocity of the system can be inferred by the interference phase. The time-orbit potential well is often used for the suspension of ultracold atoms, and then the atoms are driven to circle in the potential well by Bragg pulses to achieve the Sagnac effect. The time-orbit potential requires three pairs of coils to be placed orthogonally and an alternating current to be applied, thereby achieving an alternating three-dimensional magnetic field and trapping atoms. Since the alternating magnetic field cannot penetrate the metal cavity, a metal scientific cavity cannot be used. A glass cavity is required, or the coil is built into the scientific cavity. Therefore, the time-orbit trap method requires three pairs of orthogonal magnetic field coils, a complex vacuum structure, and precise AC magnetic field control. These characteristics are not conducive to the development of experiments. Summary of the invention

[0003] In order to simplify the requirements of complex magnetic field coils, high-precision current control and complex vacuum devices of the time orbit trap device in the ultracold atom gyroscope, the purpose of the present invention is to provide an ultracold atom manipulation device and method based on the quadrupole trap magnetic field gradient compensation method, which adopts a hybrid trap combining an optical trap and a quadrupole trap, and can realize the suspension of ultracold atoms in the quadrupole trap, and realize the Sagnac effect of atoms in the horizontal, thereby achieving the effect of trapping cold atoms. The present invention has the advantages of simple current control, being conducive to reducing the complexity of the equipment, and being suitable for the outside of the metal cavity.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] The invention discloses an ultracold atom manipulation device based on a quadrupole trap magnetic field gradient compensation method, comprising a vacuum cavity, a cooling light source, a light trap light source, a Bragg pulse light source, and a quadrupole trap coil.

[0006] The vacuum cavity is used to provide an ultra-high vacuum environment; the cooling light source is used to preliminarily cool atoms; the light trap light source constitutes an orthogonal light trap for evaporative cooling of atoms; the quadrupole trap coil adopts an anti-Helmholtz configuration to form a quadrupole trap; the Bragg pulse light source is used to generate a Bragg pulse laser light source; and the center of the quadrupole trap potential field is located directly above the center of the light trap.

[0007] The present invention also discloses an ultracold atom manipulation method based on a quadrupole trap magnetic field gradient compensation method, and an ultracold atom manipulation device based on a quadrupole trap magnetic field gradient compensation method. The ultracold atom manipulation method based on a quadrupole trap magnetic field gradient compensation method uses a cooling laser light source to achieve Doppler cooling and polarization gradient cooling to obtain cold atoms; the light trap is turned on, and the cold atoms are transferred into the light trap. The cold atoms are evaporated and cooled in the light trap to obtain a Bose-Einstein condensate, i.e., an ultracold atom. The quadrupole trap magnetic field is linearly turned on at the end of the evaporative cooling, and the ultracold atoms are adiabatically transferred to the quadrupole trap. Due to the characteristics of the non-harmonic potential field of the quadrupole trap, after the action of the Bragg pulse, the ultracold atoms in the quadrupole trap cannot be restricted to move only in the XY plane, so that the super-atom will not be able to form a closed interference loop. However, after the action of the Bragg pulse, the magnetic field gradient compensation method is used to compensate for the movement of the ultracold atoms, so that the ultracold atoms can move in the XY plane.

[0008] The magnetic field gradient compensation method is as follows: The quadrupole well potential field U felt by the known atom is

[0009]

[0010] The magnetic moment is μ = g F m F μ B , g F is the Lande factor, m F is the magnetic quantum number, μ B is the Bohr magneton, B grad is the magnetic field gradient generated by the quadrupole trap, B0 is the magnetic field bias, and (x, y, z) are the spatial coordinates of the atom. The acceleration felt by the ultracold atom in the direction of gravity, i.e., the Z direction, is a=F z / mg, where F z is the force exerted by the quadrupole trap on the atom in the z direction, m is the mass of the ultracold atom, and g is the gravitational acceleration. In order to make the acceleration in the z direction zero, the ultracold atom moves in the XY plane. Then the acceleration of the ultracold atom in the z direction is a z Expressed as

[0011]

[0012] Where z0 is the coordinate of the initial position of the atom, which is generally below the zero point of the magnetic field; the polar coordinate position of the atom is ρ = x 2 +y 2 After the Bragg pulse, in order to maintain a z =0, the magnetic field gradient B needs to be changed according to the above formula grad , achieving the effect of restricting the movement of cold atoms in the XY plane.

[0013] Beneficial effects:

[0014] 1. Compared with the time-orbit trap method, the ultracold atom manipulation device and method based on the quadrupole trap magnetic field gradient compensation method disclosed in the present invention adopts a hybrid trap combining an optical trap and a quadrupole trap, which can realize the suspension of ultracold atoms in the quadrupole trap, thereby achieving the effect of trapping.

[0015] 2. The ultracold atom manipulation device and method based on the quadrupole trap magnetic field gradient compensation method disclosed in the present invention use ultracold atoms, which have lower temperature and longer interference operation time, and help to form a higher interference area, thereby improving the accuracy of measuring angular velocity.

[0016] 3. The ultracold atom manipulation device and method based on the quadrupole trap magnetic field gradient compensation method disclosed in the present invention adopts the quadrupole trap magnetic field gradient compensation method to compensate for the movement of ultracold atoms, which can realize the movement of ultracold atoms in the XY plane and can be used to realize an ultracold atom interferometer gyroscope.

[0017] 4. The ultracold atom manipulation device and method based on the quadrupole trap magnetic field gradient compensation method disclosed in the present invention adopts the quadrupole trap magnetic field gradient compensation method to replace the time orbit trap, which can avoid the complex multi-coil and high-noise AC current control of the time orbit trap. The current control is simple, which is conducive to reducing the complexity of the equipment.

[0018] 5. The ultracold atom manipulation device and method based on the quadrupole trap magnetic field gradient compensation method disclosed in the present invention utilizes the quadrupole trap to simplify the magnetic trap structure, has the characteristics of simple structure and convenient DC control, and is conducive to the application in ultracold atom gyroscopes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of a quadrupole trap-light trap structure;

[0020] Figure 2 This is the overall flow chart of the ultracold atom manipulation method based on the quadrupole trap magnetic field gradient compensation method;

[0021] Figure 3 Theoretical calculation results of magnetic field gradient compensation method

[0022] In the figure: 1—quadrupole well magnetic field coil, 2—quadrupole well potential field, 3—orthogonal optical trap, 4—ultracold atoms. DETAILED DESCRIPTION

[0023] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0024] Embodiment 1:

[0025] The ultracold atom manipulation device based on the quadrupole trap magnetic field gradient compensation method disclosed in this embodiment is mainly composed of a vacuum cavity, a quadrupole trap magnetic field coil 1, a quadrupole trap potential field 2, an orthogonal optical trap 3, and ultracold atoms 4.

[0026] The schematic diagram of the quadrupole trap-light trap structure in the vacuum cavity is shown in Figure 1 As shown, the center of the orthogonal light trap 3 composed of far-detuned lasers is 150um below the center of the quadrupole well potential field 2. The atoms are loaded into the cross light trap after cooling light Doppler cooling and polarization gradient cooling, and evaporative cooling is performed in the orthogonal light trap 3 to obtain ultracold atoms 4 with a temperature below 100nK.

[0027] like Figure 2 The figure shows the overall experimental flow chart. First, a cooling laser light source is used to achieve Doppler cooling and polarization gradient cooling to obtain cold atoms; then the orthogonal light trap 3 is turned on to transfer the cold atoms into the orthogonal light trap 3. The cold atoms are evaporated and cooled in the orthogonal light trap 3 to obtain a Bose-Einstein condensate, i.e., an ultracold atom 4. Then, at the end of the evaporative cooling, the quadrupole trap magnetic field coil 1 is linearly turned on to transfer the ultracold atoms adiabatically to the quadrupole trap potential field 2. Finally, the atoms are manipulated by a Bragg pulse laser, and the magnetic field gradient compensation of the quadrupole trap is turned on by the quadrupole trap magnetic field coil 1 to achieve manipulation of the ultracold atom 4 in the XY plane.

[0028] Figure 3 is the theoretical calculation result of the magnetic field gradient compensation method. It is known that the quadrupole well potential field 2 felt by the atom is

[0029]

[0030] The magnetic moment is μ = g F m F μ B , g F is the Lande factor, m F is the magnetic quantum number, μ B is the Bohr magneton, B grad is the magnetic field gradient generated by the quadrupole trap magnetic field coil 1, B0 is the magnetic field bias, and (x, y, z) is the spatial coordinate of the atom. The motion acceleration felt by the ultracold atom 4 in the direction of gravity (Z direction) is a=F z / mg, where F z is the force exerted by the quadrupole trap on the atom in the z direction, m is the mass of the ultracold atom, and g is the gravitational acceleration. In order to make the acceleration in the z direction zero, the ultracold atom 4 moves in the XY plane. The acceleration a of the ultracold atom 4 in the z direction is z Expressed as

[0031]

[0032] Where z0 is the coordinate of the initial position of the atom, which is generally below the zero point of the magnetic field; the polar coordinate position of the atom is ρ = x 2 +y 2 After the Bragg pulse, in order to maintain a z =0, the magnetic field gradient B needs to be changed according to the above formula grad , in order to achieve the effect of limiting the movement of ultracold atoms 4 in the XY plane. The relevant magnetic field gradient compensation relationship is as follows Figure 3 shown. Figure 3 In order to keep the acceleration in the direction of gravity zero under different bias magnetic fields B0, the parameter magnetic field gradient B grad The relationship between the ultracold atom 4 and the polar coordinate ρ. Under a given bias magnetic field B0, the ultracold atom 4 moves in the XY plane, and ρ also increases. In order to keep the acceleration zero, the magnetic field gradient B grad Therefore, in order to achieve the effect of cold atom suspension in the experiment, the magnetic field gradient B grad Will press Figure 3 The function changes in the operation are performed.

[0033] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Ultracold atom manipulation device based on quadrupole trap magnetic field gradient compensation method, characterized by: It includes a vacuum chamber, a cooling light source, a light trap light source, a Bragg pulse light source, and a quadrupole trap coil; The vacuum cavity is used to provide an ultra-high vacuum environment; the cooling light source is used to preliminarily cool atoms; the light trap light source constitutes an orthogonal light trap for evaporative cooling of atoms; the quadrupole trap coil adopts an anti-Helmholtz configuration to form a quadrupole trap; the Bragg pulse light source is used to generate a Bragg pulse laser light source; and the center of the quadrupole trap potential field is located directly above the center of the light trap.

2. The ultracold atom manipulation method based on the quadrupole trap magnetic field gradient compensation method is implemented based on the ultracold atom manipulation device based on the quadrupole trap magnetic field gradient compensation method as claimed in claim 1, characterized in that: Doppler cooling and polarization gradient cooling are achieved by using a cooling laser light source to obtain cold atoms; the light trap is turned on and the cold atoms are transferred into the light trap; the cold atoms are evaporated and cooled in the light trap to obtain a Bose-Einstein condensate, i.e., an ultracold atom; at the end of the evaporative cooling, the quadrupole trap magnetic field is linearly turned on to adiabatically transfer the ultracold atoms to the quadrupole trap; due to the characteristics of the non-harmonic potential field of the quadrupole trap, after the action of the Bragg pulse, the ultracold atoms in the quadrupole trap cannot be restricted to move only in the XY plane, so that the super-atoms will not be able to form a closed interference loop; but after the action of the Bragg pulse, the magnetic field gradient compensation method is used to compensate for the movement of the ultracold atoms, so that the ultracold atoms are restricted to move in the XY plane.

3. The ultracold atom manipulation method based on the quadrupole trap magnetic field gradient compensation method according to claim 2, characterized in that: The magnetic field gradient compensation method is as follows: The quadrupole well potential field U felt by the known atom is The magnetic moment is μ = g F m F μ B , g F is the Lande factor, m F is the magnetic quantum number, μ B is the Bohr magneton, B grad is the magnetic field gradient generated by the quadrupole trap, B0 is the magnetic field bias, and (x, y, z) are the spatial coordinates of the atom; The acceleration felt by the ultracold atom in the direction of gravity, i.e., the Z direction, is a = F z / mg, where F z is the force exerted by the quadrupole trap on the atom in the z direction, m is the mass of the ultracold atom, and g is the gravitational acceleration; in order to make the acceleration in the z direction zero, and at the same time the ultracold atom moves in the XY plane; then the acceleration of the ultracold atom in the z direction is a z Expressed as Where z0 is the coordinate of the initial position of the atom; the polar coordinate position of the atom is ρ = x 2 +y 2 ; After the Bragg pulse, in order to maintain a z =0, the magnetic field gradient B needs to be changed according to the above formula grad , achieving the effect of restricting the movement of cold atoms in the XY plane.

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