Spins 1.0

Thomas Moore--September 2007

(Based on a Mac Classic program by Dan Schroeder)

This program allows one to create a laboratory of simulated Stern-Gerlach devices and run experiments. The program is meant to be used with chapters Q5 and Q6 in the unit Q text for my Six Ideas That Shaped Physics series of introductory texts (2nd edition, McGraw-Hill, 2003). 

Creating Laboratory Devices 

To set up a simulated laboratory, click and hold on the gun's nozzle and drag the mouse to the right. You should see a line appear connecting the nozzle to the mouse position. When you release the mouse button, a menu will appear that allows you to choose a device. When you select an item from the menu, the device will appear connected to the gun. Click and drag from one of this device's outputs to create a new device, and so on. The lines connecting the devices represent quanton beams. Quantons emerging from any device output that is not connected to to a subsequent device will be lost, as if there was a barrier at that output.   

Deleting and Moving Laboratory Devices 

If you click on a device you have created, a selection rectangle will appear. If you press the Delete key, the selected device and all subsequent devices connected to its outputs will disappear. You can also move a selected device around by dragging it to a new position, or (one pixel at a time) by using the arrow keys. (There is no provision at present for changing a device to another kind of device without deleting it and creating the new device.)

About SG-Theta Devices 

An SG-Theta device is a Stern-Gerlach device that measures the projection of the quanton's spin on an axis in the yz plane that makes an angle theta with the z axis. The default angle is 0 degrees, making the device the same as an SGz device. To change the angle, click on the number, type a new number in the edit box that appears, then hit return or enter or click outside the device to enter the number. You cannot run an experiment until the number has been entered.   

About Recombiners

A recombiner takes two quanton beams and recombines them in such a way that it is impossible to determine which of the original beams the quanton came from. When you create a recombiner using the technique describe above, both of its inputs will be automatically connected to the output of the previous device. You can only connect a recombiner to the top channel of a Stern-Gerlach device, and only when the device's other channel is not yet connected.   

The Quanton's Initial State 

The quanton's emerge from the gun with a well-defined quantum state defined by the Source menu. The default is the state corresponding to spin in the +z direction (equivalent to electrons emerging from the + channel of an SGz device). The other selections set the electron state to one of three different specific states. The state vectors corresponding to these states can be determined by appropriate experiments.   

Doing a Run 

When your setup is complete, press one of the Do buttons to fire a certain number of quantons from the gun. Each quanton is either registered by a counter that you have set up or emerges uncounted from one of the unconnected device outputs in your setup. The bar associated with each counter displays the fraction of quantons registered by each counter compared to the total number fired (which appears in the lower left corner of the window). The Reset button resets the counters to zero. 

Printing the Display 

You can print the current display window at any time by selecting Print from the File menu. The drawing is automatically scaled to fit the width of a normal sheet of paper.  

Concluding Comments 

I have tried to make this program as transparent and as easy-to-use as possible. Please send any bug reports or feature requests to me at tmoore@pomona.edu. This program is a first version and does not yet have all the features of Dan Schroeder's original Spins program for the Mac Classic environment: such features will be added as soon as I am able. This program was written using REALBasic, a superb development environment for Macintosh, Windows, and Linux platforms. For more information, visit www.realbasic.com. This program is freeware, and may be freely distributed, used, and/or modified, subject to the terms of the GNU Public License, version 2 or higher (http://www.opensource.org/licenses/gpl-license.php).