Magnetic field system for atomic chip

Abstract

A magnetic field system of an atomic chip comprises a U-shaped wire on a copper base, three pairs of bias coils, a pair of quadrupole magnetic field coils, three pairs of compensation coils, an atomic chip and a glass absorption cell with ultra-high vacuum. The U-shaped wire and the three pairs of bias coils generate a three-dimensional magnetic optical trap magnetic field, the midpoint of the symmetry axis of the pair of quadrupole magnetic field coils coincides with the zero point of the three-dimensional magnetic optical trap magnetic field generated above, and a quadrupole magnetic field is generated for trapping cold atoms; the compensation coils offset the external interference magnetic field after adding the magnetic field above. The combination of the coils for generating the magnetic field required by the three-dimensional magnetic optical trap and the bias coils and the coils for generating the quadrupole magnetic field not only meets the requirements of the chip mirror surface magnetic optical trap for the magnetic field, but also can further evaporate and cool in the mixed potential well composed of the quadrupole magnetic field and the optical dipole potential field, which can effectively reduce the influence of the copper base heating caused by the wire energization on the chip, and create favorable conditions for the super-cooled atomic experiment on the chip.

Description

Technical Field

[0001] This invention relates to atomic chips, and more particularly to a magnetic field system for an atomic chip in an atomic chip interferometer. Background Technology

[0002] Atomic chips, developed since the beginning of this century, are integrated experimental devices for preparing ultracold atoms and are widely used in research on atomic interference, low-dimensional quantum gases, quantum dynamics, and quantum thermodynamics [Mark Keil, Omer Amit, Shuyu Zhou, David Groswasser, Yonathan Japha and Ron Folman, J. Modern Optics 63, 1840 (2016)]. In atomic chip experiments, different types of magnetic fields are needed depending on the purpose, making magnetic field design a crucial part of the experiment. In previous designs of atomic chip magnetic field systems, both domestically and internationally, three schemes were used to generate the quadrupole magnetic field required for a three-dimensional mirror magneto-optical trap:

[0003] Scheme 1 employs a pair of anti-Helmholtz coils perpendicular to the chip normal, using a conventional three-dimensional magneto-optical trap optical path, without utilizing the chip to construct a mirror magneto-optical trap [Chen Yushui, Zhang Haichao, Xu Xinping, Wang Yuzhu, Chinese Patent No. CN103985497]. In this scheme, the distance from the center of the magneto-optical trap to the chip surface is typically greater than 1 cm, requiring additional transfer coils to transfer cold atoms from the magneto-optical trap to a magnetic trap near the chip surface. These additional coils severely obstruct the light transmission path.

[0004] Option 2 uses a pair of anti-Helmholtz coils with their axes tilted at 45 degrees relative to the chip normal, which can generate the quadrupole magnetic field required for the mirror magneto-optical trap in an atomic chip system. The drawback of this option is that this pair of tilted anti-Helmholtz coils, placed outside the ultra-high vacuum cavity, occupies a large space, restricts the installation of other coils, and blocks the optical path.

[0005] Option 3 involves placing a U-shaped copper wire close to the back of the chip. When current is passed through it, a bias magnetic field can be used to create the quadrupole magnetic field required for a mirror magneto-optical trap [Ron Folman, Peter Krüger, Jörg Schmiedmayer, Johannes Denschlag, and Carsten Henkel, Adv. in At. Mol. Opt. Physics 48, 263(2002)]. The main problem with this option is that the U-shaped copper wire heats up when current is passed through it. If the U-shaped copper wire and the chip are placed together inside the ultra-high vacuum cavity, the copper wire is difficult to cool effectively. The heating of the copper wire leads to a deterioration of the vacuum, and the thermal expansion of the copper wire can cause the magnetic trap to shift and the chip to deform, even damaging the chip in severe cases. If the U-shaped copper wire and the base are outside the ultra-high vacuum cavity, effective cooling can theoretically be achieved. Previous designs involved bonding the U-shaped copper wires and base to the chip and vacuum chamber. While water cooling provided a significant cooling effect, the unavoidable air bubbles or turbulence in the water caused mechanical vibrations, severely impacting cold atom physics experiments performed on the chip. Examples of these failures exist.

[0006] Physics experiments performed on atomic-chip devices typically require quantum degenerate gases (such as Bose-Einstein condensates). Therefore, the cold atoms trapped in a three-dimensional magneto-optical trap need to be loaded into a static magnetic trap for evaporation and cooling to obtain a quantum degenerate gas. Previously, the static magnetic traps used in atomic chips were created using microwires etched on the chip or Z-shaped or cross-shaped current-carrying copper wires on the back of the chip; the limited trap volume restricted the number of atoms that could be loaded to 102. 7 This limits the number of atoms in the resulting quantum degenerate gas (e.g., Bose-Einstein condensate) to no more than 10. 5 Using a pair of macroscopic anti-Helmholtz coils can generate a quadrupole magnetic trap with a much larger trap volume. Combined with an optical dipole trap, this can yield a quantum degenerate gas containing an order of magnitude more atoms than before. This approach was not used in previous atomic chip devices, mainly for the following reasons: the structures of the aforementioned magneto-optical trap coil schemes 1 and 2 make it extremely difficult to add such quadrupole magnetic field coils; scheme 3 typically involves bonding the chip to the top of a vacuum absorption cell or embedding the chip system within a vacuum cavity, where the vacuum level can usually only achieve... Therefore, rapid evaporation is required in the micro magnetic trap formed by the chip structure, rather than in the macroscopic mixed potential trap.

[0007] In existing patent CN103985497B, the inventive point lies in improving the traditional circular coil into a rectangular coil and solving its installation problem. However, it does not mention the U-shaped coil and its installation scheme. This invention employs a separate installation method for the U-shaped coil and the chip, solving the thermal impact caused by coil heating. The purpose of the rectangular coil in patent CN103985497B is to load atoms to achieve atomic transfer. In this invention, three pairs of rectangular bias coils generate a quadrupole magnetic field through the cooperation of the U-shaped wire, and the bias magnetic field is adjusted to achieve geometric matching with the beam and other parameters. Summary of the Invention

[0008] This invention addresses the aforementioned problems by providing a magnetic field system for an atomic chip. This compact magnetic field system, located outside a vacuum cavity, prevents direct contact between the chip and the copper substrate, thus avoiding thermal deformation and damage to the chip caused by direct contact with the copper substrate. Furthermore, it enables evaporative cooling within a hybrid potential well formed by a quadrupole magnetic trap and an optical dipole potential. This invention primarily achieves three functions: a three-dimensional magneto-optical trap magnetic field is generated by a U-shaped wire and three pairs of bias coils; a static magnetic field is generated by a quadrupole magnetic field coil for magnetically confining cold atoms; and a compensation coil is added to counteract surrounding interfering magnetic fields.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A magnetic field system for an atomic chip includes: a copper base, three pairs of bias coils, a pair of quadrupole magnetic field coils mounted on the base plate, three pairs of bias coils, a copper rod, the atomic chip, and an ultra-high vacuum glass absorption cell; characterized in that the pair of quadrupole magnetic field coils are two coils of the same size and number of turns, coaxially arranged, and by adjusting their spacing and passing currents in opposite directions, a magnetic field with zero center point and a magnetic field gradient greater than [value missing] on the coil axis is generated. The magnetic field is used to trap atoms in the three-dimensional magneto-optical trap for the next step of evaporation and cooling.

[0011] The three pairs of bias coils consist of a horizontally parallel pair of upper and lower bias coils, a vertically parallel pair of front and rear bias coils, and a vertically parallel pair of left and right bias coils. The atomic chip is centered and aligned with the center of the magnetic field of each coil. The three pairs of compensation coils intersect in pairs to cancel out the interference magnetic fields in the three directions. Each pair of bias coils consists of two coils of the same size and number of turns, arranged coaxially.

[0012] The copper base is a rectangular copper metal block with a square cross-section. The metal block has a groove for installing U-shaped wires. The bottom of the copper base has a threaded connection hole for connecting one end of a copper rod. The copper rod is inserted into a metal support and fixed to fix the relative position of the copper base.

[0013] Outside the copper base are the pair of quadrupole magnetic field coils, and outside the quadrupole magnetic field coils are the three pairs of compensation coils.

[0014] The atomic chip is adhered to the lower end of the glass absorption cell and does not contact the copper base.

[0015] The glass absorption cell is connected to the ultra-high vacuum system via an ultra-high vacuum tube and a flange.

[0016] When current is passed through the U-shaped wire installed on the copper base, a quadrupole magnetic field is generated after the magnetic field of the pair of bias coils in the vertical direction. The three pairs of bias coils are combined to form a uniform magnetic field that can be adjusted in the X, Y and Z directions.

[0017] The U-shaped conductor and three pairs of bias coils can adjust the angle of the quadrupole magnetic field required for the generated three-dimensional magneto-optical trap in three directions, which are orthogonal to each other.

[0018] The metal support is made of copper, a metal with a high thermal conductivity, and is used to carry away the heat generated when the U-shaped wire is energized.

[0019] The H-shaped line is used to generate the cigar-shaped magnetic field required for the subsequent transfer of atoms.

[0020] Its magnetic field strength varies with the size of the quadrupole magnetic field coil, the number of copper wire turns, and the magnitude of the current. To achieve high-efficiency loading, the initial position of the magneto-optical trap atom cluster and the offset of the zero-point position of the quadrupole magnetic field coil should not exceed [a certain value]. To achieve this goal, we need to determine the initial position of the magneto-optical trap atomic cluster at the beginning, and then adjust the zero point position of the quadrupole magnetic field by fine-tuning the three pairs of bias magnetic fields in different directions so that it can be well aligned with the center of the magneto-optical trap, thus achieving mode matching between the quadrupole magnetic field and the magneto-optical trap.

[0021] The compensation coil consists of three pairs of coils surrounding the quadrupole magnetic field coil and the bias coil. These three pairs of coils are parallel and coaxial, with large size and small number of turns. Their function is to cancel out all interfering magnetic fields, including the Earth's magnetic field and the ion pump magnetic field.

[0022] The copper base has shallow grooves on its surface for mounting coils. The front of the copper base has threaded connection holes for connecting a copper rod. The copper rod serves two purposes: first, it connects the copper base to the platform support, fixing their relative positions; second, it conducts the heat generated by the metal wires to the connecting rod on the base. The connecting rod then directly transfers the heat into the air via convection, and through its direct connection with the support, the heat is conducted to the support and finally dissipated throughout the entire magnetic field system.

[0023] The chip is directly bonded to the top of the glass absorption cell using ultra-high vacuum epoxy resin (EPO-TEK 353ND). Unlike traditional chip magnetic field systems, the chip in this invention does not directly contact the copper substrate surface; instead, a gap greater than [missing information] exists between them. and less than The gap between the copper base and the magnetic field system ensures that heat generated on the copper base can only affect the chip through thermal radiation and convection. However, the primary heat transfer path is conduction, with the vast majority of heat being discharged through the metal connecting rod that securely mounts the copper base. This mounting method significantly reduces the impact of heat generated by the copper base on the chip.

[0024] Technical effects of the present invention;

[0025] The present invention features a compact magnetic field system located outside a vacuum cavity, where the chip and copper substrate do not directly contact each other. This prevents thermal deformation and damage to the chip caused by direct contact with the copper substrate, and allows for evaporative cooling within a hybrid potential well composed of a quadrupole magnetic trap and an optical dipole potential. The invention primarily achieves three functions: a three-dimensional magneto-optical trap magnetic field is generated by a U-shaped wire and three pairs of bias coils; a static magnetic field is generated by a quadrupole magnetic field coil for magnetically trapping cold atoms; and a compensation coil is added to counteract surrounding interfering magnetic fields.

[0026] The magnetic field system has a compact structure, which aims to reduce the system's size and power consumption, and expands the system's optical channels, which is beneficial for further experiments. Attached Figure Description

[0027] Figure 1 This is a three-dimensional schematic diagram of the atomic chip magnetic field system of the present invention.

[0028] Figure 2 yes Figure 1 Top view of an atomic chip magnetic field system

[0029] Figure 3 This is a schematic diagram of the quadrupole magnetic field coil frame of the present invention.

[0030] Figure 4 This is a schematic diagram of the three pairs of bias coil frames of the present invention.

[0031] Figure 5 This is a schematic diagram of the copper base for placing the U-shaped wire according to the present invention, where a is the copper base, b is a top view of the copper base (U-shaped wire installation area), and c is a top view of the copper base (H-shaped wire installation area).

[0032] Figure 6 This is a schematic diagram of each vertex during the calculation of the U-shaped line in this invention.

[0033] Figure 7 This is a pseudo-color image obtained from magnetic field calculations when x=x0.

[0034] Figure 8 This is a pseudo-color image obtained from magnetic field calculations when y=y0.

[0035] Figure 9 This is a pseudo-color image obtained from magnetic field calculations at z=z0.

[0036] Figure 10 This is a schematic diagram of the magnetic field calculation result z=z(y). Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this does not imply any limitation on the scope of protection of the present invention.

[0038] Please see Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 , Figure 1 This is a three-dimensional schematic diagram of the atomic chip magnetic field system of the present invention. Figure 2 yes Figure 1 Top view of an atomic chip magnetic field system. Figure 3 This is a schematic diagram of the quadrupole magnetic field coil frame of the present invention. Figure 4 This is a schematic diagram of the three pairs of bias coil frames of the present invention. Figure 5 This is a schematic diagram of the U-shaped copper base of the present invention. As shown in the figure, the magnetic field system of the atomic chip of the present invention includes: a copper base 9, three pairs of bias coils 1-6, one pair of quadrupole magnetic field coils 7-8, three pairs of compensation coils 10, an atomic chip 14, and an ultra-high vacuum glass absorption cell 15.

[0039] The copper base 9 is a rectangular copper metal block with a square cross-section. There is a groove on the metal block for installing U-shaped wires. The bottom of the copper base 9 has a threaded connection hole for connecting one end of the copper rod 16. One end of the copper rod 16 is inserted into the metal support 11 and fixed to fix the relative position of the copper base 9.

[0040] Outside the copper base 9 are the pair of quadrupole magnetic field coils 7 and 8. The two coil frames of these quadrupole magnetic field coils 7 and 8 are mounted on the bottom base plate 12, facing each other in the left-right direction. The pair of quadrupole magnetic field coils 7 and 8 are two coils of the same size and number of turns arranged coaxially with their spacing adjusted. When currents are applied in opposite directions, a magnetic field with zero center point and a gradient greater than [value missing] on the coil axis is generated. The magnetic field is used to trap atoms in the three-dimensional magneto-optical trap for the next step of evaporation and cooling.

[0041] Outside the quadrupole magnetic field coils 7 and 8 are the three pairs of bias coils. These three pairs of bias coils include bias coils 1 and 2 in the vertical direction, bias coils 3 and 4 in the front-back direction, and bias coils 5 and 6 in the left-right direction. The bias coils 1 and 2 in the vertical direction, the bias coils 3 and 4 in the front-back direction, and the bias coils 5 and 6 in the left-right direction are all made by coaxially arranging two coils of the same size and number of turns. Combining the three pairs of bias coils together forms an adjustable uniform magnetic field in the X, Y, and Z directions. When installing the bias coils 1-6, attention should be paid to the position of the atomic chip 14. The atomic chip 14 needs to be centered and aligned with the center of the magnetic field of each coil.

[0042] The atomic chip 14 is directly bonded to the lower end of the high vacuum glass absorption cell 15 with ultra-high vacuum epoxy resin, but does not directly contact the copper base 9 with U-shaped wires installed. The glass absorption cell 15 is connected to an ultra-high vacuum tube (not shown in the figure), which is connected to an ultra-high vacuum system through a CF35 flange. Therefore, the glass absorption cell 15 has an ultra-high vacuum degree.

[0043] When current is passed through the U-shaped wire installed on the copper base 9, and the magnetic field of the pair of bias coils 1 and 2 in the vertical direction is added, a quadrupole magnetic field will be generated.

[0044] The outermost part of the device consists of three pairs of compensation coils 10. Each pair of compensation coils 10 consists of two coils of the same size and number of turns arranged coaxially and their spacing adjusted. After the three pairs of compensation coils are combined, they intersect in pairs to cancel out the interference magnetic fields in three directions.

[0045] The U-shaped conductor and three pairs of bias coils can adjust the angle of the quadrupole magnetic field required for the generated three-dimensional magneto-optical trap in three directions, which are orthogonal to each other.

[0046] The high-vacuum glass absorption cell 15 includes a glass cell cavity, a glass-to-metal transfer tube, and a metal flange (not shown in the figure).

[0047] The bottom of the copper base 9 on which the U-shaped wire is installed needs to have a threaded hole for installing the metal copper rod 16; the metal support is threadedly connected to the copper base 9, and in order to carry away the heat generated after the U-shaped wire is energized, the metal copper rod 16 is made of copper, a metal material with a high thermal conductivity.

[0048] The copper base 9 with the U-shaped wire is also equipped with an H-shaped wire, which can generate the cigar-shaped magnetic field required for subsequent atomic transfer.

[0049] Example

[0050] The device for generating a uniform magnetic field consists of a pair of quadrupole magnetic field coils, a U-shaped coil on a copper base, three pairs of mutually orthogonal bias coils, and three pairs of compensation coils.

[0051] The quadrupole magnetic field coils 7 and 8 are a pair of circular coils of the same size and number of turns. In this embodiment, the inner diameter of the coils is... The outer diameter is The diameter of the coil wire is Each coil has 11 layers, totaling 200 turns. Passing currents in opposite directions through coils 7 and 8 generates a uniform gradient magnetic field in the middle of the coil. The strength of this magnetic field varies with the coil size, number of turns, and current magnitude. The four-pole magnetic field coil frame structure is as follows: Figure 3 As shown, two coil frames are mounted on the bottom base plate 12 with their directions opposite each other.

[0052] Figure 4 This is a schematic diagram of the three pairs of bias coils of the present invention. Each pair of bias coils (1, 2; 3, 4; 5, 6) is coaxially arranged and has the same size. In the embodiment, the smallest rectangular coil size of coils 1 and 2 is... The minimum rectangular coil size for coils 3 and 4 is The minimum rectangular coil size for coils 5 and 6 is The diameter of the three sets of coil wires is All coils have 60 turns. ,thickness It is made of aluminum alloy U-shaped grooves. The connection method between the coils is shown in the figure. The two coils are connected and fixed by metal blocks with grooves on both sides. To ensure a stable connection and to make the design more compact and reduce interference between coils, the metal blocks are only fixed at the diagonal points of the coils that need to be connected, such as... Figure 4 As shown.

[0053] When installing the bias coil, pay attention to the chip's position; the chip needs to be centered and aligned with the center of the magnetic field of each coil. When installing the copper base 9 with the U-shaped wire into the system, ensure the center point of the U-shaped wire's magnetic field matches the center points of other magnetic fields. If the distance between the U-shaped wire and the chip is too close, use fine-tuning to reduce the distance between them.

[0054] Figure 1 The chip 14 is directly attached to the ultra-high vacuum glass absorption cell 15. The glass absorption cell 15 achieves this ultra-high vacuum because it is connected to an ultra-high vacuum tube, which is connected to an ultra-high vacuum system (containing an ion pump and a sublimation pump) via a CF35 flange, thus enabling the entire vacuum system to reach a pressure of [pressure value missing]. The degree of vacuum.

[0055] Figure 1 The three pairs of compensation coils 10 are installed on the outermost periphery of the magnetic field system. Each pair of coils is coaxially arranged and has the same size. Figure 1 The bias coil 10 is composed of three pairs of coils. In this embodiment, the minimum rectangular coil size of the front and rear coils is... The minimum rectangular coil size of the upper and lower coils is The minimum rectangular coil size for the left and right coils is The diameter of the three pairs of coil wires is All coils have 20 turns. The function of compensation coil 10 is to ensure that the magnetic field system is not disturbed by external magnetic fields, including the Earth's magnetic field, static magnetic field, pump magnetic field, etc. After applying the compensation coil, the residual magnetic fields in the x, y, and z directions are all less than [value missing]. .

[0056] Figure 5 This is a schematic diagram of the copper base 9 for mounting the U-shaped wire in this invention. In this embodiment, the top surface dimension of the copper base is... The copper base has shallow grooves on its surface for U-shaped traces and M8 threaded holes at the bottom for connecting to the copper support pillars. Besides fixing the relative position of the copper base, the copper support pillars also efficiently conduct heat generated by the wires on the copper base to the magnetic field system, thereby reducing the impact of heat on the chip. In this embodiment, the U-shaped traces on the copper base have 6 turns.

[0057] Calculation of the U-shaped magnetic field on the copper base in the embodiment:

[0058] First, establish a coordinate system, such as Figure 5 As shown, determine the coordinates of the U-shaped conductor. The magnetic field generated by each side of the U-shaped conductor is calculated separately. The formula for calculating the magnetic field of a fixed-length straight conductor is as follows:

[0059]

[0060] The magnitude of the magnetic field generated by each segment of the conductor is calculated based on the coordinates of the conductor below, and then the results are superimposed. All coordinates below (X0, Y0, Z0=0) are in mm. Assume AB, BC, and CD are three straight conductor segments. Figure 6 As shown:

[0061] The vertex coordinates of each U-shaped coil turn are given below.

[0062]

[0063] Current Vertical bias magnetic field Front and rear bias magnetic fields The magnetic field region we are interested in is based on Centered on, positive and negative The distribution of the magnetic field within a square three-dimensional region.

[0064] Magnetic field calculation pseudo-color image as follows Figure 7 , 8 As shown in Figures 9 and 1, the three pseudo-color images depict the changes in the magnetic field along the three axes. The units for the horizontal and vertical axes are all... The unit of the color bar on the right is .

[0065] The magnetic field calculation results are as follows Figure 10 As shown, the calculated magnetic field strength and location both meet the requirements for subsequent experiments.

[0066] Heat conduction calculation of the U-shaped copper base in the embodiment:

[0067] To avoid coil overheating, chip 14 and copper base 9 are mounted in a non-direct contact manner, with a surface distance between them greater than 0 mm and less than 1 mm, minimizing the thermal impact on the chip. The heat generated by the copper base 9 affects chip 14 from two sources: air convection and surface radiation. The primary way the copper base 9 outputs heat is through metal conduction.

[0068] Natural convection heat coefficient of air Values Surface area of ​​square copper base 9 Substitute into the convection calculation formula. ,in The local temperature after the copper base wire is heated is defined here as: . The surface temperature of our chip is... After calculation .

[0069] Radiant energy emitted from the surface of a gray body The surface emissivity of smooth-surfaced metallic copper , The general approximation is Substituting into the formula, the radiant energy of the copper base 9 to the chip 14 is calculated. .

[0070] The square copper base is directly connected to a copper support rod and an aluminum base at its bottom, maintaining the temperature of the copper base facing the chip at room temperature. Heat is dissipated through the connected copper rod and the aluminum base that holds the rod in place. Copper has a low thermal conductivity. The thermally conductive copper rod area ,length If the temperature difference is The heat transferred out through thermal conduction is .

[0071] The calculations above show that a large amount of heat is directly conducted away from the system by the metal base, and the heat generated by the copper base has a negligible impact on the chip. The mounting method in this embodiment is sufficient to maintain heat dissipation during continuous operation of the U-shaped cable.

[0072] Temperature difference limit is The basis for this is to keep the low-temperature end temperature above the dew point. For a room temperature of 22 degrees Celsius and a relative humidity of 60%, the dew point is below 14 degrees Celsius, so a low-temperature end temperature of 15 degrees Celsius meets the requirement.

[0073] For semiconductor cooling chips, a cooling capacity of tens of watts is very easy to achieve.

[0074] The calculations above show that the magnetic field strength of this invention meets the requirements, and the heat generated by the wires has a negligible impact on the chip. This prepares the chip for subsequent implementation.

[0075] Experiments show that by aligning the midpoint of the symmetry axis of a pair of quadrupole magnetic field coils with the zero point of the three-dimensional magneto-optical trap magnetic field generated above, a quadrupole magnetic field can be generated to trap cold atoms. After the bias coils are subjected to this magnetic field, they can effectively cancel out external interfering magnetic fields. The atom chip is directly bonded to the glass absorption cell, without direct contact with the copper substrate, and the distance between the chip and the surface of the copper substrate is less than [amount missing]. Effective heat insulation. The combination of the wires and bias coils that generate the magnetic field required for the three-dimensional magneto-optical trap, and the coils that generate the quadrupole magnetic field, not only meets the magnetic field requirements of the chip mirror magneto-optical trap, but also allows for evaporative cooling in the mixed potential trap formed by the quadrupole magnetic field and the optical dipole potential field. This effectively reduces the impact of the heating of the copper base on the chip after the wires are energized, creating favorable conditions for ultracold atom experiments on the chip.

Claims

1. A magnetic field system for an atomic chip, comprising: The copper base (9), three pairs of bias coils, a pair of quadrupole magnetic field coils (7, 8) mounted on the base plate, three pairs of compensation coils, a metal support (11), an atomic chip (14), and an ultra-high vacuum glass absorption cell (15); characterized in that, The aforementioned pair of quadrupole magnetic field coils (7, 8) are two coils of the same size and number of turns, arranged coaxially. By adjusting their spacing and passing currents in opposite directions, a magnetic field with zero center point and a gradient greater than 1 / 3 on the coil axis is generated. The magnetic field is used to trap atoms in the three-dimensional magneto-optical trap for the next step of evaporation and cooling. The three pairs of bias coils consist of a horizontally parallel pair of upper and lower bias coils (1, 2), a vertically parallel pair of front and rear bias coils (3, 4), and a vertically parallel pair of left and right bias coils (5, 6). The atomic chip (14) is centered and aligned with the center of the magnetic field of each coil. The three pairs of compensation coils intersect each other to cancel out the interference magnetic fields in the three directions. Each pair of bias coils consists of two coils of the same size and number of turns, arranged coaxially. The copper base (9) is a rectangular copper metal block with a square cross-section. The metal block has a groove for installing U-shaped wires. The bottom of the copper base (9) has a threaded connection hole for connecting one end of a copper metal rod (16). The copper metal rod (16) is inserted into the metal support (11) and fixed to fix the relative position of the copper base (9). Outside the copper base (9) are the pair of quadrupole magnetic field coils (7, 8), and outside the quadrupole magnetic field coils (7, 8) are the three pairs of compensation coils. The atomic chip (14) is attached to the lower end of the glass absorption cell (15) and does not contact the copper base (9); The glass absorption cell (15) is connected to the ultra-high vacuum system via an ultra-high vacuum tube and a flange.

2. The magnetic field system of the atomic chip according to claim 1, characterized in that, A current is passed through the U-shaped wire installed on the copper base (9), and together with the magnetic field generated by the pair of bias coils (1, 2) in the up and down directions, a quadrupole magnetic field is formed.

3. The magnetic field system of the atomic chip according to claim 1 or 2, characterized in that, The U-shaped conductor and three pairs of bias coils can adjust the angle of the quadrupole magnetic field required for the generated three-dimensional magneto-optical trap in three directions, which are orthogonal to each other.

4. The magnetic field system of the atomic chip according to claim 1, characterized in that... The metal support (11) is made of copper, a metal material with a high thermal conductivity, and is used to carry away the heat generated by the U-shaped wire after it is energized.

5. The magnetic field system of the atomic chip according to claim 1, characterized in that, The copper base (9) is also provided with H-shaped lines to generate the cigar-shaped magnetic field required for the subsequent transfer of atoms.

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