Quadrupole Coil Assembly User Manual ColdQuanta, Inc. 1600 Range St., Ste. 103 Boulder, CO 80301 USA (303) 440-1284 www.coldquanta.com Document revision 1.0 October 2013
Table of Contents 1. Overview... 3 2. Layout and Physical Orientation... 3 3. Driving the Coils... 4 4. Electrical Connections... 5 5. Limited Warranty... 6 6. Technical Drawings... 7 RuBECi is a registered trademark of ColdQuanta Inc. Boulder, CO USA This document 2013, ColdQuanta Inc. Boulder, CO USA 2
1. Overview ColdQuanta s quadrupole coil assembly serves two essential purposes for the production and utilization of ultracold atoms and quantum degenerate gases: (1) Providing the magnetic bias and quadrupole fields for creating magnetooptical traps (MOTs) and Ioffe-Pritchard traps, optical pumping, and nulling of stray magnetic fields, and (2) Vertically transporting cold atoms from the center of a RuBECi s 3D MOT cell to the atom chip at the top of the cell. Together, these two purposes combine the basic functionalities of ColdQuanta s 3D MOT coil assembly and Z-coil assembly. However, the quadrupole coil assembly achieves this without the need to mount coils above the RuBECi, freeing up space for other components that must be mounted above the top-side of the atom chip (optics, RF antennae, etc.). 2. Layout and Physical Orientation Figure 1 shows the layout of the assembly, along with the coordinate system used for the coil naming convention. Eight rectangular coils, arranged in four pairs, are affixed onto an anodized aluminum frame that slides along the four stainless steel rails that come mounted around the RuBECi s 3D MOT cell. The assembly is affixed to the rails using eight #6-32 set screws. Figure 1: Diagram of the quadrupole coil assembly. For reference, the front of the assembly is the side with the connector. Coils X2, Y2, and Z2 are not labeled. 3
The two coils oriented along the x-axis (labeled X1 and X2) and the two oriented along the y- axis (Y1 and Y2) can be driven individually. When driven with electrical currents in the proper configuration, either gradients (anti-helmholtz configuration) or bias fields (Helmholtz configuration) can be produced along these two directions. The two coils oriented along the z- axis (Z1 and Z2) are connected in series in a Helmholtz configuration for producing a vertical bias field. To enable vertical transport of cold atoms, a pair of transfer coils (T1 and T2) is oriented along the x-axis. These coils are connected in series in an anti-helmholtz configuration, and can therefore only produce a gradient. Compared to coils X1 and X2, the axis of the transfer coils is shifted upward by 15 mm. The assembly should be positioned such that the axis of the transfer coils lies on the horizontal plane of the atom chip. At this position, coils X1 and X2 will then be centered on the 3D MOT. For defining a coordinate system for the atom chip and the rest of the RuBECi, we recommend orienting the coil assembly so that the side with the micro-d connector (i.e. the front of the assembly) is closest to the RuBECi s ion pump (see the photograph on the cover). The following table lists the properties of each coil. Values for resistance and inductance are typical; actual measured values are reported on the test datasheet shipped with each unit. Position Resistance (Ω) Inductance (mh) Front (X1) 1.8 2.0 Back (X2) 1.8 2.0 Right (Y1) 2.0 1.0 Left (Y2) 2.0 1.0 Bottom (Z1) + Top (Z2) 4.1 1.4 Transfer Coils 3.6 3.6 3. Driving the Coils To create gradients and bias fields, current must flow through both coils oriented along a given direction. For bias fields, current must flow in the same direction through the coil-pair oriented along a given direction. By flipping the sign of the current passing through one of these coils, a magnetic gradient is created instead. The table below quantifies these bias fields and gradients: 4
Configuration X Bias ( X1 X2) X Grad ( X1 X2) Y Bias ( Y1 Y2) Y Grad ( Y1 Y2) Z Bias ( Z1 Z2) Transfer Gradient ( T1 T2) Value 19.9 G/A x 9.0 G/(cm A) 22.6 G/A ŷ 15.5 G/(cm A) 7.6 G/A z 13.3 G/(cm A) For gradients and bias fields, the coils can be connected in series and driven with a single power supply. To create a gradient whose center does not coincide with the center of the cell, the pair of coils should be driven with unequal currents. In this scenario, each coil in a pair must be powered by its own driver. 4. Electrical Connections Electrical connections are made to the coils through a pigtailed cable group that is located on the lower front of the assembly. The cable comes with raw wire ends so the user can choose what connector best fits their system requirements. A pin diagram for the cable bundle is shown in the figure below. For each coil, a positive current (i.e. one flowing from the positive terminal to the negative terminal) will produce a magnetic field pointing in the positive direction of the coil s axis. For example, a positive current flowing through coils X1 and X2 will produce a positive bias field along the x direction. The coils Y1 (Z1) and Y2 (Z2) are connected in a Helmholtz configuration inside the assembly. All other coil-pairs can be connected in Helmholtz or anti- Helmholtz configurations. The Y and Z coils are rated for continuous operation at 3 A. The X and Transfer coils are rated for 3A at continuous operation, and for peak currents up to 12 A (for durations less than 100 ms). The coils will get warm during normal operation, but must not be allowed to exceed 80 C. 1 Y1+ 7 X2-2 T1-8 T2+ 3 X1-9 Z1+ 4 Z2-10 X1+ 5 T2-11 T1+ 6 X2+ 12 Y2-5
5. Limited Warranty 1. Definitions a) Delivery means standard ColdQuanta shipping to and arrival at the receiving area at the Ship To address specified in Customer s Order. b) Exhibits means attachments that describe or otherwise apply to the sale of Products. c) Products means hardware, documentation, accessories, supplies, parts and upgrades that are determined by ColdQuanta to be available from ColdQuanta upon receipt of Customer s Order. Custom Products means Products modified, designed or manufactured to meet Customer requirements. d) Specifications means specific technical information about ColdQuanta Products that has been delivered by ColdQuanta to the Customer with Customer s Order. e) Support means hardware maintenance and repair; training; and other standard support services provided by ColdQuanta. Custom Support means any agreed nonstandard support, including consulting and custom project services. 2. Limited Warranty a) ColdQuanta warrants ColdQuanta hardware Products against defects in materials and workmanship for a period of one year from the delivery date. b) ColdQuanta does not warrant that the operation of Products will be uninterrupted or error free. c) If ColdQuanta receives notice of defects, ColdQuanta will, at its option, repair or replace the affected Products. If ColdQuanta is unable, within a reasonable time, to repair, replace or correct a defect or non-conformance in a Product to a condition as warranted, Customer will be entitled to a prorated refund of the purchase price upon prompt return of the Product to ColdQuanta. Such refunded amount will be prorated based on a four-year straight line depreciation schedule. Customer will pay expenses for return of such Products to ColdQuanta. ColdQuanta will pay expenses for shipment of repaired or replacement Products. d) ColdQuanta warrants that ColdQuanta Support will be provided in a professional and workmanlike manner. Some newly manufactured ColdQuanta Products may contain and ColdQuanta Support may use remanufactured parts that are equivalent to new in performance. e) The above warranties do not apply to defects resulting from: (i) improper or inadequate maintenance by Customer; (ii) customer or third party supplies; (iii) unauthorized modification; (iv) improper use or operation outside of the Specifications for the Product; (v) excessive rubidium loading of the ion pump; (vi) abuse, negligence, accident, loss or damage in transit; (vii) improper site preparation; or (viii) unauthorized maintenance or repair. f) THE ABOVE WARRANTIES ARE EXCLUSIVE AND NO OTHER WARRANTY, WHETHER WRITTEN OR ORAL, IS EXPRESSED OR IMPLIED. TO THE EXTENT PERMITTED BY LAW, COLDQUANTA SPECIFICALLY DISCLAIMS THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, TITLE, AND NONINFRINGEMENT. 6
6. Technical Drawings 7