QUANTUM OPTICS AND QUANTUM INFORMATION TEACHING LABORATORY at

QUANTUM OPTICS AND QUANTUM INFORMATION TEACHING LABORATORY at the Institute of Optics, University of Rochester Svetlana Lukishova and Carlos Stroud, Jr, sluk@lle. rochester. edu AAPT Summer Meeting, 21 July 2008, Edmonton, Alberta, CA

This course introduces undergraduate students to the basic concepts and tools of quantum optics and quantum information using modern photon counting instrumentation Areas of applications of photon counting instrumentation (prepared by organizers of second international workshop “Single Photon: Sources, Detectors, Applications and Measurements Methods” (Teddington, UK, 24 -26 October 2005)).

New teaching laboratory 4 -credit-hour-course consists of four experiments 1. Lab. 1: Entanglement and Bell inequalities (~ 5 weeks); 2. Lab. 2: Single-photon interference: Young’s double slit experiment and Mach-Zehnder interferometer ( ~ 1 week); 3. Lab. 3: Confocal microscope imaging of single-emitter fluorescence (~ 5 weeks); 4. Lab. 4: Hanbury Brown and Twiss setup. Fluorescence antibunching and fluorescence lifetime measurement (~ 1 week). • 6 students (3 groups) worked twice per week (total 6 hours per week); • 26 freshmen and more than 15 visitors (including students of Colgate University) participated in demonstration of four quantum optics experiments.

Lab. 1. Entanglement and Bell inequalities Particles are called entangled if their state cannot be factored into single-particle states. Any measurements performed on first particle would change the state of second particle, no matter how far apart they may be. This is the standard Copenhagen interpretation of quantum measurements which suggests nonlocality of the measuring process. The idea of entanglement was introduced into physics by Einstein, Podolsky, Rosen (Phys. Rev. , 47, 777 (1935)). In the mid-sixties it was realized that the nonlocality of nature was a testable hypothesis (J. Bell (Physics, 1, 195 (1964)), and subsequent experiments confirmed the quantum predictions. 1966: Bell Inequalities – John Bell proposed a mathematical theorem containing certain inequalities. An experimental violation of his inequalities would suggest the quantum theory is correct.

Lab. 1. Entanglement and Bell inequalities Creation of Polarization Entangled Photons: Spontaneous Parametric Down Conversion in two type I BBO crystals

Lab. 1. Entanglement and Bell inequalities 1. 2. D. Dehlinger and M. W. Mitchell, “Entangled Photon Apparatus for the Undergraduate Laboratory, ” Am. J. Phys, 70, 898 (2002). D. Dehlinger and M. W. Mitchell, “ Entangled Photons, Nonlocality, and Bell Inequalities in the Undergraduate Laboratory”, Am. J. Phys, 70, 903 (2002).

Photograph of experimental setup built by the Institute of Optics’ students on entanglement and Bell’s inequalities using spontaneous parametric down conversion process. The cross-sections of the cones of downconverted photons with 2λinc at the output of both type I (left) and type II (right) BBO crystals. Cooled EM-CCD-camera i. Xon of Andor Technologies and a new UV argon ion laser Beam. Lok (donated to the course by the Spectra -Physics division of Newport corporation) were used in these experiments. Photograph of experimental setup is shown in a bottom figure.

Dependence of coincidence counts on polarization angle The probability P of coincidence detection for the case of 45 o incident polarization and phase compensated by a quartz plate, depends only on the relative angle β-α: P(α, β) = 1/2 cos 2 (β-α).

Calculation of Bell’s Inequality We used Bell’s inequality in the form of Clauser, Horne, Shimony and Holt, Phys. Rev. Lett. , 23, 880 (1969) Bell’s inequalities define the sum S. A violation of Bell’s inequalities means that |S|>2. , where: The above calculation of S requires a total of sixteen coincidence measurements (N), at polarization angles α and β: After collecting data at the appropriate angles, we calculated: S=2. 652, a clear violation of Bell’s inequalities!

Lab. 2. Single-photon interference Mach-Zehnder interferometer mirror Polarizer A |V> Polarizer C NPBS Polarizer D screen Path 2 Path 1 laser Spatial filter PBS |H> mirror Polarizer B Polarizer D, absent Polarizer D at 45 No Fringes M. B. Schneider and I. A. La. Puma, Am. J. Phys. , 70, 266 (2002).

Young’s Double Slit Experiment with cooled, Electron Multiplying CCD i. Xon Camera of Andor Technologies 0. 5 s 1 s 2 s 3 s 4 s 5 s 10 s 20 s

Labs 3 -4: Single-photon Source Based on Single-emitter Fluorescence Lab. 3. Confocal microscope imaging of single emitter fluorescence Lab. 4. Hanbury Brown and Twiss setup. Fluorescence antibunching and fluorescence lifetime measurements

The main elements of our setup • Confocal fluorescence microscope • Pulsed 532 -nm, 6 ps, 76 MHz rep. rate laser • Hanbury Brown and Twiss unit with two avalanche photodiode SPCM • Single-photon counting, cooled EM-CCD camera • Time-Harp 200 computer card and software to build antibunching histogram APD Start Stop APD LASER EM-CCD CAMERA 13

Confocal microscope raster scan images of single colloidal quantum dot fluorescence Histogram showing fluorescence antibunching (second order correlation function g(2)(0) ~ 0). Antibunching is a proof of a singlephoton nature of a light source.

EVALUATION OF STUDENTS’ KNOWLEDGE AND LABORATORY COURSE SUCCESS We used both formative and summative evaluation techniques which tell us (1) whether students like these labs and what needs to be improved; (2) whether students mastered particular concepts. Formative evaluation was carried out by six students enrolled in the laboratory course. These evaluations took place both in oral (after each lab) and in written (after the whole course) forms. All students evaluated the course very positive that indicates the success of the course. The main improvements of the course should be in more intensive homework tasks. Some students wanted to build experimental set-ups from scratch. Summative evaluation was accomplished by two ways: (1) using different questionnaires (without grading) and (2) using the grades for each lab. Two teaching assistants helped in summative evaluation. For instance, using questionnaire with 36 questions on photon quantum mechanics showed that one half students answered correctly more than 75% of questions, 70% of students answered correctly more than 70% of questions and all students answered correctly more than 60% of questions. It shows the success in students’ learning. Students’ mastery in photon-counting instrumentation showed that 50% of students received total scores of “A” and the rest of students received total scores of “A-“. The grades were based on students’ capability of carrying out the experiments, writing the reports, and delivering oral presentations. To recognize and analyze alternative explanations and models students were asked to write the essays on alternative technologies to single-photon sources based on single colloidal quantum dots. For communication skills development students were divided into groups (two or three students in each group depending on particular lab). Each group of students presented a single report written by all group members although students within each group can received different grades for the lab. The grade also depended on students’ activity and knowledge during the whole lab. Before each lab students were asked and were able to ask their instructor any questions.

Future plans for new teaching experiments • Using a new UV argon ion laser with a much higher power than the power of a diode laser, we are planning to make some new experiments on entangled photon generation in a spontaneous parametric down conversion process with development of imaging of the cones of down converted light by a cooled, EMCCD camera. • Development of the experiments on spectroscopy and fluorescence lifetime measurements of colloidal quantum dots in microcavities for single-photon source applications. Acknowledgements The authors acknowledge the support by the National Science Foundation Awards ECS-0420888, DUE-0633621, the University of Rochester Kauffman Foundation Initiative, and the Spectra-Physics division of Newport Corporation. The authors thank L. Novotny, A. Lieb, J. Howell, T. Brown, R. Boyd, P. Adamson, W. Knox for advice and help, and students A. Jha, C. White, L. Bissell and B. Zimmerman for assistance.