ALPhA’s Single Photon Detector Initiative

Breaking News (October, 2016):
ALPhA’s seventh batch order of educationally priced single-photon detectors for instructional labs has sold out. Andy Dawes, who has taken over the project from Gabe Spalding, is arranging for an eighth batch of 60 single-photon detectors.

Questions? Potential interest? Contact Gabe at or Andy at

Ordering Information

Individuals interested in purchasing the set of four single-photon detectors, one of which is shown in the photo at left, should contact Prof. Gabe Spalding, the coordinator of this initiative; his address and contact information are below. Please note that ALPhA is only an intermediary for the purchase and assumes no liability or responsibilities with respect to these detectors; the manufacture, service, and warranty are provided by and the responsibility of Excelitas Corporation.

Dr. Gabriel Spalding, Professor of Physics, Illinois Wesleyan University, Department of Physics, P.O. Box 2900, Bloomington, IL 61702-2900. Email: Telephone: 309-556-3004

Photo of the Single Photon Detector produced for ALPhA

Photo of the one of the four single photon detectors manufactured by Excelitas to ALPhA's specifications.

ALPhA, in its role as advocate for instructional advanced physics laboratories, has arranged for the production and sale of single photon detectors at a cost significantly lower than for comparable research-quality detectors. This came about after it was determined that the high cost of the single photon detectors was the single largest expense incurred in setting up the single photon detection experiments that are emerging as a most exciting class of undergraduate advanced physics lab experiments. These detectors are being made available through ALPhA as a joint project between ALPhA, the AAPT, and Excelitas Corporation (formerly part of Perkin-Elmer). The detectors have specifications more than sufficient for the performance of the undergraduate laboratory experiments for which they are aimed, albiet slightly reduced compared with the industry standard detectors.

There is a very important, emerging class of instructional laboratory experiments aimed at demonstrating quantum mechanics in the undergraduate curriculum (e.g., demonstrating the existence of photons, single-photon interference, indistinguishability and the quantum eraser, entanglement and tests of Bell’s inequalities, etc.).1-9 Many students have a difficult time grasping quantum mechanical models and this new generation of instructional experiments is deemed to provide the absolutely critical visualization and tangible proof that are needed to convince students of key elements of quantum theory.

The NSF has, through a number of grants, actively supported development of these specific instructional labs through its old CCLI (“Course, Curriculum, and Laboratory”) program and the new TUES (“Transforming Undergraduate Education in Science, Technology, Engineering and Mathematics”) program. These labs have been featured highlights of the 2009 Advanced Lab Topical Conference in Ann Arbor and of the 2010 Gordon Conference on Physics Research and Education, and have been incorporated into the highly successful “ALPhA Immersion Program,” which provides hands-on training for lab instructors, and led ALPhA to establish a group focused on furthering efforts to make these sorts of labs more affordable.

The cost of the required lasers has dropped precipitously (to less than $40), now leaving detector cost as the key remaining bottleneck to widespread adoption of these experiments. Up to now, it has cost about $10K for the Excelitas Model SPCM-AQ4C, which contains 4 detectors (sold as a unit) and is the module that has been purchased for these instructional labs by early adopters. In order to address this issue, ALPhA gathered together a number of laboratory instructors who are currently using the Excelitas module, with the goal of convincing the manufacturer to make something more affordable available to the educational market. After extended discussions, ALPhA approached the manufacturer with a set of relaxed specifications appropriate to the educational market, and has successfully lobbied the newly spun-off manufacturer, Excelitas, to create a special product category. These efforts by ALPhA have cut the primary cost for this sort of instructional lab by almost half, so that a set of four single-photon detectors can be purchased at a significant cost saving special price instead of the $10,000 price that has served as a barrier to adoption at so many institutions. We believe our efforts will have a huge impact on the number of students who will have access to this key, new generation of instructional labs.

The manufacturer, Excelitas, has put forth two conditions: (1) To ensure that these units are sold for instructional labs, each purchaser must be a member of ALPhA. The detectors carry labels specifying that these units belong in the undergraduate instructional labs and not in research labs. These educational detectors have reduced specs, notably a higher background dark count rate, compared to other models from the company. (2) Secondly, the manufacturer will not accept individual orders. ALPhA is to collect the accept individual orders, and coordinate these into single group orders (15 institutions each ordering a set of four detectors).

Faculty-Staff Training Opportunities:
This summer’s ALPhA Immersion Program includes two opportunities to work with single-photon quantum mechanics experiments, at Colgate University and the University of Rochester. Registration is available online at

Those unable to attend one of the ALPhA Immersions should note that Mark Beck of Whitman College maintains a website that includes a great deal of useful information for DIY electronics set-ups that can be easily and (relatively) cheaply assembled. Tom Colton of Berkeley has posted a list of resources he has found on his wiki page. Kiko Galvez writes “I note that Newlight Photonics, a company in Canada has been making BBO crystals for making entangled sources (the two type-I, or one type-II), and they know the technical details of crystal cuts so that all you need specify is the wavelength of your pump laser. They deliver a nicely mounted crystal(s) for very a competitive price (much cheaper than most crystal manufacturers - e.g. Cleveland). Set-up is relatively easy (once you know what to do, of course).” Mark Beck writes “I can currently buy a 50+ mW surplus diode for $17.43 at I've used these lasers, and they work fine for what we need.”

These single-photon instructional labs will also be a centerpiece of the 2012 Conference on Laboratory Instruction Beyond the First Year (the BFY Conference, pronounced as “The Buffy Conference”), to be held in Philadelphia over the 2.5 days leading into the AAPT Summer Meeting. It will accommodate 150 participants and is expected to sell out, as did the 2009 Topical Conference on Advanced Labs. The ALPhA group will lead a panel discussion at the BFY Conference, highlighting these new instructional opportunities, followed by a second panel discussion on the evolution of available tools for assessing the impact of labs upon student understanding of quantum mechanics. We will also have a hands-on workshop for small groups dealing with this equipment, offered in 12 round-robin rounds.

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