Table of Contents
Single Photon Interference Development Project
The overall goal of the experiment is to perform a series of experiments probing the concept of wave-particle duality. The results of which can be explained quantum mechanically but not from a classical physics perspective.
Quantum mechanics allows for both wave and particle like behavior in nature, meaning what we ordinarily think of as a particle, such as a single electron or photon, can also behave like a wave under some circumstances. Classically the concepts of waves and particles are mutually exclusive.
- Particles exist at a specific point in space at a given time, a particle cannot be found simultaneously at multiple places at the same time for example. A classical wave on the other hand can extend through out all of space.
- Multiple waves can also occupy the same physical space at the same time (superposition) and can interfere with each other, particles do not superimpose nor do they exhibit interference effects in a purely classical interpretation.
In this lab you will conduct experiments with individual photons of light, with the goal of testing whether or not individual photons are able to exhibit both particle and wave like behavior. In the process of doing this, you will gain experience working with quantum optics, single photon detectors and coincidence measurement techniques.
The lab is broken down into two parts, particle studies and wave studies. Beginning with the particle studies you will learn how correlated pairs of vertically polarized photons are produced via Spontaneous Parametric Down Conversion (SPDC) in a BBO crystal. You will gain hands on experience placing and aligning basic quantum optical components to detect the Down Converted (DC) photons and perform measurements of their behavior when interacting with polarizers and beam splitters. You will make use of coincidence counting techniques to determine if a single photon can be observed in more than one location at one time.
In the wave part of the experiment you will work with a Mach-Zhender interferometer to test whether or not individual photons of light can behave like waves. The optical setup for this part of the experiment requires a high degree of precision in the positioning and alignment of the optical components, this alignment has already been done for you and in this part all you have to focus on is what measurements need to be made.
Part I
Setup
Radius of curvature of guide = 84cm.
LASER Current = 70.7mA LASER Temp = 10.31°C
Alignment and detection
Down Conversion Studies
Part 2 : Wave Nature
Your goal is to show a clear contradiction between your experimental results with the expectations of a purely classical interpretation of light. Keep in mind the following assumptions which we went over at the start of the lab.
- We are assuming knowledge of the photo-electric effect experiment which showed that light is always observed in discrete quanta which we refer to as photons.
- Our experiments are being conducted on single photons, meaning that the effects we observe are the result of one and only one photon at a time interacting with the apparatus.
- The classical definition of a particle is that particles always have a discrete location in space at a given time, and that multiple particles do not occupy the same location in space at the same time.
- The classical definition of a wave is that waves extend throughout space and therefor can be detected in multiple locations at the same time. Multiple waves can be present in the same space at the same time, and in doing so they will superimpose and can exhibit interference effects.
The apparatus, which is described in more detail here allows you to do the following things:
- Measure the singles counts from all three detectors.
- Measure coincidences between two pairs of the three detectors.
- Modulate the path length of one arm of the interferometer. The displacement of the mirror attached to the Piezo crystal is 61±15nm/V.
- Independently set the polarization state of light passing through each arm of the interferometer.
In Part 1 of the lab you should have gained insight into and collected data that establishes the particle nature of light when viewed on the individual photon level. Now you want to take measurements which you can use to make the argument that single photons passing through the interferometer show behavior which is consistent with having waves passing through both arms. To do this you need to think about what characteristics define superposition and interference effects, and what measurements can you make that would test for these characteristics.
Analysis
For your analysis simply make a bullet point list of what you think are the individual logic points for your argument and then do any calculations, plots, fits, etc. needed to support each point.