1. Visible Light Photon Counter Integrator Group 48: Katie Nguyen, Austin Jin ECE445 Spring 2016 May 1, 2016

2. Motivation  Optical Quantum Information [1] –Quantization of detected photons –Quantum communication: Using properties of photons to securely store and transmit information

3. Introduction  Proposed project by Professor Kwiat  Current method: threshold method  Proposed method: integration method

4. Example of Photon Pulse in MATLAB  Pulse height ~-150mV * n for n incident photons Figure 1: One photon per pulse Figure 2: Two photons per pulse

5. Example of Photon Pulse in MATLAB  Worst case example Figure 3: Two photons overlapping Figure 4: Three photons overlapping

6. Objectives  More precise method of calculating number of photons per pulse –Distinguish between 1 – 5 photons per pulse –Synchronized Integrator with External Trigger  Make integral accessible through device for further processing.  Add Features for Readability –Graphical User Interface –Logging capabilities

7. Diagram of Design Figure 5: Block diagram

8. Integrator Circuit Figure 6: Integrator circuit diagram

9. Integrator Output Calculations

10. Integrator Simulation Results  Simulated voltage is measured at 10 ns R (Ω)Calc (mV)Sim (mV)% diff 50150144.743.507 1007573.521.973 20037.537.051.2 5001514.890.733 1K7.57.4580.56 5K1.51.4930.467 10K0.750.74680.427 Figure 7: Integrator simulation Table 1: Integrator simulation result

11. Integrator Simulation Results  Unstable when capacitance is larger than 100 pF Figure 8: Integrator simulation at 1nF Figure 9: Single integrator simulation at 1nF

12. Power Supply Circuit  Input: 120V AC wall outlet –Stepped down to 12V AC via center-tapped transformer –Full-wave rectified –Linear regulators on PCB  Provide a set of stable voltages –+/- 2.5V to the integrator circuit –3V to the ADC

13. Power Supply Circuit Transformer Regulators  The constant current load assumed Rectifier/Smoothing caps Figure 10: Power supply circuit

14. Power Supply Simulations Figure 11: Power supply simulation  Voltage level at +/- 2.5V, 3V  Negligible ripples  Stable level achieved by 1ms

15. Power Supply Setup Figure 12: Transformer top-view (top) and front-view (bottom) Figure 13: Power supply PCB

16. Power Supply Results  Possible explanation for 2.5V –PCB burned during testing, due to narrow traces  Should not matter if within the amplifier operational range Designed Output (V)Actual Output (V)% Difference -2.5-2.4880.48 2.52.2689.28 32.9860.56 Table 2: Power supply results

17. ADC for Post-Processing  Considerations for Design –Fast enough to accurately sample within a narrow window –High Speed ADCs are Expensive Minimum Speed To Sample Minimum Resolution

18. ADC for Post-Processing  Decision for Design –ADC08200-200Msps will allow us to sample for a 5ns duration frequency = 1/time = 1/5E-9s = 2E8s = 200Msps –ADC08200 –8 bit ADC IC will accept a voltage range of 0-3.3V Voltage Resolution = (3.3V - 0V) / 256 bits = 12.94 mV/bit –This tells us that an 8 bit ADC will give us enough resolution to discriminate one photon from another. Figure 14 : TI ADC08200

19. Proposed Post-Processing Setup  Simulate Laser Source for 0- 10 Photons Per Pulse in Matlab  Integrate Pulses in Matlab  Feed Integrated Pulses using a Function Generator into ADC Figure 15 : Flowchart of Experimental Setup

20. Example of Integral in MATLAB  Each photon generates a fixed amount of charge. Figure 16 : Integral of One Photon Figure 17: Integral of Two Photons

21. Post-Processing (Software)  Use WiringPi to Allow Communication with BCM2835 on Raspberry Pi (8 bit data lines)  Enable Serial Peripheral Interface (SPI) bus for SCLK access  QT Framework for Graphical User Interface Figure 18 : Flow Chart of Post Processing

22. Post-Processing Results Figure 19 : VLPC GUI Figure 20 : VLPC Log File

23. Post-Processing Results Figure 21 : No photonsFigure 22 : One photons Figure 22 : Two photons

24. Challenges  Precisely Synchronize Sampling with Trigger –Missing Photon Pulse  Account for Large Quantity of Noise –Mindful of Width of PCB Traces –Impedance matching

25. Conclusion  Extensive research on a working design  Delivered on proposed features –Graphical user interface –Log file  Future work : integrator circuit hardware– in progress

26. Figure 23 : DC2266A Schematic (LTC6409 demo board) LTC640 9

27. Special Thanks  Ankit (TA)  Dr. Sahoo and Dr. Hanumolu  Professor Kwiat  Fumihiro Keneda (Post-Doc)

28. Questions?

29. References  [1] "New nanodevice shifts light's color at single- photon level", Phys.org, 2016. [Online]. Available: http://phys.org/news/2016-04-nanodevice-shifts-single- photon.html. [Accessed: 30- Apr- 2016].