Updates

6/9/08

· Updated LabView vi’s to use our new FPGA-based CCU.

6/7/08

· Updated Coincidence Counting Unit page to reflect our new FPGA-based CCU.

12/20/07

· Added course lecture notes and updated lab manual.

8/21/07

· Updated Labview vi’s.

8/1/07

· The coincidence circuit is ready: email beckmk at whitman.edu (replace "at" with @) to get the details.

7/9/07

· Updated the LabView vi’s. Now there are versions for LV 7 and LV 8.2.

· Added an updated parts list to the main page.

· The coincidence circuit should be ready for general release by the end of the month.

9/9/06

· We’ve tried the Power Technology 185mw laser. WOW! LOTS of coincidences! However, the jury is still out on the achievable level of entanglement you can generate with this laser. In tests of Bell’s Inequality we are able to get larger S values with the 50mW laser than the 185mW laser (although the error is less with the 185mW laser, because we get more counts and thus better statistics). We’re not sure if this is just because it’s a new laser to us, and we haven’t spent much time working on the alignment, or if it’s something more fundamental with the laser itself. This 185mW laser does have multiple spatial modes, and the beam is larger and more elliptical than our circularized 50mw laser.

· Our coincidence circuit is coming along. We’ve done two prototypes which work quite well. We’re currently working on a version with improved time resolution.

· I’ve added some new presentations on the entry page.

· I’ve updated the LabView vi’s.

· I’ve made available a copy of the Lab Manual for the lab portion of our QM course. This lab is being taught for the first time in the fall of 2006.

2/15/06

· We’re working on a circuit that makes coincidence counting cheaper, and hope to have more to say about this in the next few months.

1/23/06

· Power Technology http://www.powertechnology.com/ now has 185mw, 405 nm laser diode modules available!

· The Bell inequality and Hardy test experiments require making measurements at several different waveplate settings. While it’s not necessary to use a motorized rotation stage for this, it does make things nicer. Newport has recently released a relatively low-cost motorized rotation stage, the NSR1. It uses the same Newstep controller that we use for the linear stepper motor in the single-photon interference experiment. Total cost to automate the waveplate movement for these experiments would be about $2,600. I should note that I have never used these stages, so I can’t personally vouch for them. They only have a resolution of 1^o, but that’s probably sufficient for these experiments.

· I’ve just released updated LabView vi’s for these experiments. Included is a vi that allows one to mimic the behavior of a multichannel analyzer using an A/D board.

1/21/05

• We are currently using one of the 4-channel SPCM's mentioned in our AJP article (Perkin-Elmer APCM-AQ4C, $9k, available from Pacer).  It needs 3 external power supplies (2, 5, and 30 V), and the user manual is a bit short on details about how to wire it up. Putting it together is much easier if you purchase the adapter card [SPCM-AQ4C-IO, $265].   However, you’ll still need to know how to connect the power supplies to the board (not in the user manual), and a circuit diagram to help you do that is here. Another important thing to note is that the unit is gated ON when the gates are either grounded or floating. To gate the unit OFF you need to apply 5V to the gate. When we built a box to hold ours, we added a 5V pullup to the gate so that on powerup the counters are gated OFF. Some pictures of the unit in its box can be found on our pictures page.

• In the spring of 2004 we purchased a 50mW blue laser diode module from Power Technology http://www.powertechnology.com/ .  We got the circularized output option [Model IQ1C (LD1539) G2X23, $7k]  We’re using it in the Bell inequality and Quantum Eraser experiments and it works quite well.  They probably have modules with even higher powers now.

• In the experiments involving polarization entangled photons using two crystals mounted back-to-back (as in the article by Dehlinger and Mitchell), the company who sells the crystals has changed its name to Photop Technologies http://www.photoptech.com/.  We are using two 0.5mm thick crystals rather than the 0.1 mm thick crystals used by Dehlinger and Mitchell.  We get higher count rates with the thicker crystals, which makes things easier. The thicker crystals don't appear to hurt the quality of the Bell Measurement (I'd hesitate to go much thicker though.)

• We have found green LED lightbulbs that are great for illuminating the lab because their wavelength is well blocked by the RG780 filters in front of our detectors. The background singles count rates increase slightly with these LED’s on, but they contribute nothing to the coincidence rates. These bulbs screw directly into a standard incandescent lightbulb socket. Model PAR20-66-0AG-120AN , $108, from http://www.ledtronics.com/. It’s great to be able to do photon counting with the lights on!

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webpage updated 6/9/08

beckmk at whitman.edu (replace "at" with @)