Day Off

Sadly, I have a fever so I can't work on the experiment today. Hopefully I can get an update out tomorrow.

Day 12 DPF

Today we actually did some readings on the DPF (Dual Polarized Filter, more in post "Day 10"). The last time we tried this we measured an interference pattern which was unexpected. Today we found, after a close inspection, that the needle in the DPF was slightly off center allowing light to pass through with out being polarized and also allowing a single polarization of light to go around both sides of the needle. We realized we should also check that the needle is centered and covers the seam between the two polarizations.


Here in this chart you can see a comparison between the DPF (Pink) no interference, and the needle (blue) interference.

Rap on partical acceleration

Day 11 On Polarization

One of the key aspects of this experiment is polarization. We use polarization in our experiment for two things: decreasing the amount of light (also called attenuating the light), and forcing the light to take one instead of both possible paths. Today we took a break from data collection to reflect on polarization.

Polarization is the shape of the electrical fluctuation. This means if somehow you could take a picture of light as it travels towards you, the shape that you would see is the polarization. Another explanation is with a jump rope. Imagine a jump rope tied to a tree, if you twirl it you will see the circular "polarization" of the rope. To understand a polarizing filter think of a frictionless picket fence between you and the tree with the rope in between two slats. When you twirl the rope it is circularly polarized between you and the fence. Between the fence and the tree it is vertically polarized. The fence is acting as a vertical filter; it only allows vertical waves to pass through. Now lets rotate that filter to horizontal. Again, the shape of the waves in the rope from you to the fence remain circular, but this time the shape from the fence to the tree is horizontal. You can rotate the fence to any angle and make any linear polarization. In this experiment, our "fence" is a linearly polarized camera filter and our "rope" is the laser light.

Circular polarization filters are more difficult to imagine. They do the same thing as a linear filter except they only allow circular waves to pass through. Unlike linear filters, rotating a circular filter will not change the filter polarization because a circle rotated is still a circle. Even so you can get two polarizations out of a circular filter by flipping it over. This creates right hand circular on one side and left hand circular polarization on the other.



These are some representations of various polarizations.

Day 10

We have finally gotten a consistent interference pattern. After rebuilding our sensor platform we got a reliable inference pattern. Also, we managed to find even more stray light sources around the room such as a florescent glow from an overhead light even after it was turned off, and some assorted LED's.

The axes in this chart show the photon rate in Hertz vs. time in milliseconds on the x axis. This picture can be identified as interference because of the peaks and troughs. The amplitude is getting bigger because the sensor was moving towards the center of the laser. We want to reduce the photon rate to the thousands so we can make sure that the photons are not interfering with each other and not themselves.

Raw Data Files:

• Dark Count 1
  
• Basic Interference 1
• Basic Interference 2
• Basic Interference 3
• Basic Interference 4
  

We ran into some problems when we tried to use the Dual Polarization Filter which is a two sided filter with opposite (+45 and -45) sides to separate the sides there is a needle. When we conducted this experiment we saw an interference wave, we were expecting a smooth decreasing line when we looked closer we realized the last polarization before the Dual Polarization Filter was the same as one of the sides.

Day 9

Today we ran into a small problem with the speed of the platform. We thought we could see the interference with the speed we were using, but it was bunched up. We could not be sure of the interference because of noise (light from the outside). When we tried to slow the platform down, that setting didn't have enough power to push the platform. After rebuilding almost everything, we geared the motor down so it runs slowly and smoothly. Here is the new apparatus.


John Bergesen, a good friend who has seen the full light version of the experiment, had trouble posting these comments, so I'm going to post and answer some of them here:

Is the Sens-L being scanned (using the Lego train) over the plane we have seen in the past that showed the interference patterns?
Yes, the active area on the counter is very small so we need to move it to read the full interference pattern.

Are you still using the pin/polarizer configuration?
Not for the first tests, but we plan to run all the tests again in low light. Right now, we are just using a needle because then we can work on perfecting our detection and the least amount can go wrong with the setup.

Are you trying to show that a single stream of photons aimed at the pin will find its way around the pin as if it were two independent streams on either side of the pin?
Yes, that is part of it. The other part we'd like to show is the quantum side of a simple experiment, such as the two slit experiment.

If you have a hypothesis you want to show, how do you plan to prove it from your measurements?
We are looking for a sine wave in the measurements. A low photon rate would be a dark spot and a high photon rate would indicate a bright spot.

Day 8

Today we worked on two things: Measuring the output of the photon detector with a Parallax USB oscilloscope and gnu radio, and programming and testing the sensor platform. The program is fairly simple: we go slowly forward, then rewind at normal speed to test again.

This picture is the response of the detector after a photon is detected; the red is what we're looking at.


This is a photon train; you can see 11 photons.


This is a high resolution shot of a photon. I want to learn more about the part happening before the peak; notice how there is a bounce.


Finally we are ready to collect our first readings! We plan on collecting them tomorrow. So check back tomorrow for the initial results.

Day 7

Before the sensor came, we built a linear actuator from a Lego Mindstorms kit, to move the sensor across the detection field. When the sensors arrived, we realized that they would be too heavy for the light-weight actuator. We came up with some options, but were not happy with any of them. One idea was to use a conveyor belt system, which would have worked, but we didn't have the parts for it. Another idea was to have the table's smooth surface support the weight of the sensor and use the actuator to slide the sensor across the table. Finally, we came up with a plan that made sense and that we could build: a train. By combining a Lego train set with our existing actuator, we created a system able to haul the weight of the sensor smoothly, predictably, and precisely. Click on the picture to enlarge.
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Day 6

Today I am working on telling more about the history of this experiment.
The whole thing started a little over a year ago after my dad had explained some of quantum theory to me. I loved the endless possibilities and crazy but highly predictable outcomes. So my dad searched up this.
The first experiment was conducted in a hotel room in full light with paper, polarized 3-D glasses. We learned that precision was important to good outcomes. After that, we became more and more careful. Now, 3 generations later, this is our system: we select glasses with the fewest manufacturing defects, such as scratches, and then cut them out of the paper frame; next, we take a needle and place it in between 2 of the polarized filters and tape the tops and bottoms together with clear tape.


Now with the generous loan of 2 photon detectors from Sens-L, we will retest our experiment with one photon at a time to ensure that the photons are taking all paths from the source to the screen and not just bouncing off each other to create the interference.

To learn more about the experiment itself, download my power point presentation on the subject.

Day 5

Today I fixed the problem, it just was a matter of minimization and doing things in the correct order. I also worked on the dark count count and the biggest spike was at 50 photons, but mostly the count was around 10 photons.

Day 4

Today I made a light proof "shelter" for the computer. I used spray adhesive and black construction paper. While I was spraying adhesive, my laptop rebooted and then the software for the sensor wouldn't fully open. I checked everything I could think of, but still nothing changed. The window of the software would open, all except for the bottom left corner and the buttons were unresponsive. I'm going to try again tomorrow.

light proofing

We light proofed the basement today by putting cardboard and thick dark fabric over the window and putting electrical tape over all the little LED's on the appliances. Also we curtained off an area with 2 dark sheets to keep away the unwanted light from the laptop. Currently the dark count is at an average of around 10 photons per second. We also plan on conducting the experiment in a large light proof box.

Sensors are Working

These are the first readings. Today we hooked up both sensors and marveled at the accuracy of them. We also tested them with a polarizing filter and a half silvered mirror. We plan on doing more preliminary tests tomorrow.

We have our Eqipment!

Today we received the much anticipated single photon detection equipment from Sensl !
We plan to start readings next Wednesday,
Keep you posted.