马赫-泽德干涉仪的搭建技巧
EDU-QE1
EDU-QE1/M
Quantum Eraser
User Guide
Quantum Eraser
Table of Contents
Chapter 1Warning Symbol Definitions (2)
Chapter 2Safety (3)
Chapter 3Product Description (4)
Chapter 4Setup (6)
https://www.wendangku.net/doc/3b8529202.html,ponents and Parts List (6)
https://www.wendangku.net/doc/3b8529202.html,ponent Assembly (8)
4.3.Setup and Adjustment (10)
https://www.wendangku.net/doc/3b8529202.html,ser Setup (10)
4.3.2.Mirrors and Beamsplitters (11)
4.3.3.Screens and Alignment (12)
Chapter 5Experiment (16)
5.1.Experiment 1: Path Information in Quantum Physics (16)
5.2.Experiment 2: Quantum Eraser (18)
5.3.Experiment 3: Thought Experiment (19)
Chapter 6Didactic Tips (21)
Chapter 7Troubleshooting (23)
Chapter 8Regulatory (24)
8.1.Waste Treatment is Your Own Responsibility (24)
8.2.Ecological Background (24)
Chapter 9Thorlabs Worldwide Contacts (25)
Page 1MTN002250-D02 Rev B, January 22, 2014
Quantum Eraser Chapter 1: Warning Symbol Definitions Page 2
Chapter 1 Warning Symbol Definitions
Below is a list of warning symbols you may encounter in this manual or on your device.
Symbol
Description Direct Current Alternating Current Both Direct and Alternating Current Earth Ground Terminal Protective Conductor Terminal
Frame or Chassis Terminal Equipotentiality
On (Supply)
Off (Supply)
In Position of a Bi-Stable Push Control
Out Position of a Bi-Stable Push Control
Caution: Risk of Electric Shock
Caution: Hot Surface
Caution: Risk of Danger
Warning: Laser Radiation
Quantum Eraser
Chapter 2 Safety
Page 3MTN002250-D02 Rev B, January 22, 2014
Quantum Eraser Chapter 3: Product Description
Chapter 3 Product Description
In a Mach-Zehnder interferometer, a beam of light is split into one of two optical paths by a beamsplitter. Due to a difference in optical path lengths between the two paths, complementary interference patterns are observed when the light is recombined by a second beamsplitter. These interference patterns are observed on two viewing screens, as the second Beamsplitter produces two combined beams.
A Mach-Zehnder interferometer is very useful in order to demonstrate the quantum mechanical properties of complementarity and the erasure of path information. If a polarizer is placed in each arm of the interferometer and their polarization planes are turned 90° to one another, the interference pattern disappears. This can be completely explained through classical electrodynamics. However, a quantum-mechanical description can also be applied if the beam of light in the interferometer reduced to individual photons (or to only an individual photon). By inserting the crossed polarizers into the setup, the two possible light paths are made distinguishable by obtaining path information. The interference pattern (wave property) and path information (particle property) cannot be measured simultaneously, since measuring the path information destroys the interference pattern.
If one adds a third polarizer between the second beamsplitter and the screen, with the polarization axis at 45° to the other polarizers, all of the photons that reach the screen once again have the same polarization. This polarizer “erases” the path information and an interference pattern is once more visible on the screen.
Rather than using single photons, as in the original quantum eraser experiment, this kit uses a green continuous-wave (CW) laser light source that emits a beam that is visible to the eye. While the outcome of the experiment can be explained using classical physics, using a quantum-mechanical description provides a perfect analogy to the single-photon quantum eraser experiment.
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Quantum Eraser Page 5 MTN002250-D02 Rev B, January 22, 2014
Figure 1 Mach-Zehnder Interferometer Setup and Diagram, Including (1) Laser, (2) Lens, (3)
Beamsplitters, (4) Polarizers, (5) Mirrors, and (6) Viewing Screens
Quantum Eraser Chapter 4: Setup Page 6
Chapter 4 Setup
4.1. Components and Parts List
In cases where the metric and imperial kits contain parts with different item numbers, metric part numbers and measurements are indicated by parentheses unless otherwise noted. 1 x CPS532-C21
532 nm Laser Diode
Module
1 x LDS5(-EC)
5 VDC Laser Power
Supply 1 x
KM100V(/M)
Kinematic Laser Mount 1 x LB1901
?1" Lens, f = 75 mm
1 x LMR1(/M)
?1" Lens Mount 2 x EBS2 ?2" 50:50 Beamsplitter
2 x KM200T
?2" Beamsplitter Mount 1 x LPVISE2X2 (Stamped into 3 ?1" Circles)
Linear Polarizer 3 x RSP1C(/M) ?1" Rotating Polarizer
Mounts
1 The CPS532-C
2 is a low power, Class 2 version of our Class
3 CPS532 laser diode module.
Quantum Eraser
Page 7 MTN002250-D02 Rev B, January 22, 2014
2 x ME1-G01
?1" Aluminum Mirror
2 x
KM100T
?1" Mirror Mount 2 x EDU-VS1(/M)
Viewing Screen
9 x TR3 (TR75/M)
?1/2" (?12.7 mm)
Mounting Post, 3"
(75 mm) Long 9 x PH3 (PH75/M) ?1/2" (?12.7 mm) Post Holder, 3" (75 mm) Long 2 x TR2 (TR50/M) ?1/2" (?12.7 mm) Mounting Post,
2" (50 mm) Long, for
Viewing Screen
2 x PH2 (PH50/M)
?1/2" (?12.7 mm) Post
Holder, 2" (50 mm) Long,
for Viewing Screen 9 x BA1(/M) Mounting Base, 1" x 3" x 3/8" (25 mm x 58 mm x10 mm)
2 x BA2(/M) Mounting Base, 2" x 3" x 3/8" (50 mm x 75 mm x 10 mm) 1 x MB1824 (MB4560/M)
Aluminum Breadboard,
18" x 24" (45 cm x 60 cm) 1 x RDF1 4 Rubber Breadboard Feet 3 x SM1RR SM1-Threaded Retaining Ring
Quantum Eraser Chapter 4: Setup
Page 8 4 x F25SSK1-GOLD
Gold Adjuster Knob
Imperial Kit
Type
Quantity Type Quantity 1/4"-20 x 1/2" Cap Screw
11 1/4" Nut 4 1/4"-20 x 5/8" Cap Screw
11 1/4" Washer 11
1/4"-20 x 3/4" Cap Screw 4 1 x BD-3/16L Balldriver for 1/4”-20 Screws 8-32 Screws Included with Mounts
1 x Hex Key for 8-3
2 Screws (1/8″)
0.035", 5/64" and 0.050" Hex Keys contained in RSP1C
Metric Kit
Type
Quantity Type Quantity M6 x 12 mm Cap Screw
11 M6 Nut 4 M6 x 16 mm Cap Screw
11 M6 Washer
11
M6 x 20 mm Cap Screw 4 1 x BD-5ML Balldriver for M6 Screws
M4 Screws Included with Mounts
1 x Hex Key for M4 Screws (3mm)
0.9 mm, 1.3 mm and 2.0 mm Hex Keys
contained in RSP1C/M
4.2. Component Assembly
1. First, assemble the individual optical components and mounts. Use the 1/2" (12
mm) long 1/4"-20 (M6) screws to connect the PH3 (PH75/M) and PH2 (PH50/M) post holders to the BA1(/M) and BA2(/M) bases, respectively. Throughout the assembly, use the 5/8" (16 mm) long 1/4"-20 (M6) screws to mount the components to the breadboard.
2. Mount the ME1-G01 mirrors into the KM100T mounts, the EBS2 beamsplitters
into the KM200T mounts, and the LB1901 lens into the LMR1(/M) mount using the threaded retaining rings that are already placed in the mounts. Replace the
Quantum Eraser Page 9 MTN002250-D02 Rev B, January 22, 2014
lower knobs on the KM100T and KM200T mounts with the gold-colored F25SSK1-GOLD knobs by placing a hex key inside the knob and unfastening the black knob. An instructional video can be found on the web page for the KM100T on https://www.wendangku.net/doc/3b8529202.html,.
Figure 2 Component Assembly Procedure
3. Mount the KM100V(/M), KM100T, KM200T, LMR1(/M), and RSP1C(/M) mounts
to TR3 (TR75/M) posts using the included 8-32 (M4) cap screws or setscrews, and insert them into PH3 (PH75/M) Post Holders. Attach the viewing screens to the TR2 (TR50/M) posts using the included setscrews and insert them into the PH2 (PH50/M) post holders.
Figure 3
Mounting the KM100V(/M), KM100T and KM200T on a Post
Quantum Eraser Chapter 4: Setup
4. After removing the protective films, place the LPVISE2X2
polarizer films into the RSP1C(/M) mounts and secure them
using the included retaining rings. The orientation of the
polarizer is indicated by its form, as shown in the image on the
right. Instructions on how to ensure that the polarizers are
mounted and aligned properly are given in steps 6 through 8.
5. Mount the CPS532-C2 laser onto the KM100V(/M) V-mount, connect it to the
LDS5(-EC) power supply, switch it on, and place the polarizer in front of it.
6. Turn the polarizer mount (and thereby the polarization film) so that the laser
beam transmitted through the polarizer is attenuated as much as possible.
7. Loosen the two silver screws on the front of the polarizer mount and turn the
movable scale to 90°. Then, re-tighten the screws.
8. Now, turn the polarizer mount and film back to 0°, and repeat the described
procedure for the two remaining polarizers.
4.3. Setup and Adjustment
4.3.1. Laser Setup
1. Attach the laser assembly to the end of the optical breadboard.
2. Check that the laser is polarized at 45° by placing a polarizer set to -45° in front
of the laser and rotating the laser in the bracket until effectively no light passes
through the polarizer. Then, remove the polarizer from the setup again.
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Figure 4 Laser Setup
4.3.2. Mirrors and Beamsplitters
1. Bolt the base of the mounted mirror at the other end of the board so that the
laser is reflected by it at a 90° angle. Ideally, you should align the laser beam with the rows of holes in the breadboard, as shown in Figure 4. Match the height of both components so that the beam hits the center of the mirror and also runs parallel to the surface of the plate as much as possible.
2. Insert one of the beamsplitters between the laser and the first mirror (labeled as
path 1 in Figure 5, below), so that the beam is divided into two perpendicular partial beams.
3. The beam which forms path 2 should be reflected by the second mirror so that
the reflected beam runs parallel to the beam in path 1, as shown
in
Figure 5 below. Ensure that the distances are about the same in both paths.
Quantum Eraser Chapter 4: Setup
Page 12
Figure 5 Mirror and Beamsplitter Setup
4. Once again, ensure that the beam runs parallel to the row of holes and adjust
the heights of the components.
5. Insert the second beamsplitter at the intersection of the two partial beams in the
setup, as shown in Figure 6.
4.3.3. Screens and Alignment
6. Set up one of the EDU-VS1(/M) observation screens relatively close behind the
beamsplitter (labeled as screen 1 in Figure 6, below), the other at a distance of about 2 - 3 meters (or ideally an even greater distance). The goal is to overlap and co-propagate both partial beams so that they can
interfere
with one another.
Quantum Eraser Page 13 MTN002250-D02 Rev B, January 22, 2014
Figure 6 Screens and Alignment
7. Initially, you will probably see two laser spots on the screens. Position the spots
on top of one another with the aid of the fine adjustment screws on the mirror and beamsplitter mounts.
Note: When you adjust the screws on the mirrors, the laser spot will move on both screens in the same direction. If you only want to move one spot on one screen, you must tilt the beamsplitter by using the screws on the respective mount.
8. Make sure that the two beams overlap well on the beamsplitter. It is not enough
to have overlapping spots on the screens! If the beams do not overlap sufficiently on the beamsplitter, change the mirror position accordingly. An interference pattern will only appear when the beams overlap well on the beamsplitter and the screens.
9. There are two possible ways to proceed in adjusting the interferometer. There is
no ideal way to do it—please choose your favoritemethod:
a. Position the spots according to step 8 such that they overlap. Next,
expand the beam to obtain the interference ring pattern by installing
the LB1901 lens between the laser and the first beamsplitter. If the
interference pattern does not show, slowly tilt
and rotate
one of the
Quantum Eraser Chapter 4: Setup
Page 14
mirrors. If the interference pattern still doesn’t show, the previous
adjustment steps need to be repeated.
b. Position the spots according to step 8 until you see a flickering in the
laser spots. Next, expand the beam to obtain the interference ring
pattern by installing the diverging lens between the laser and the first
beamsplitter. If the interference pattern does not show, slowly tilt and
rotate one of the mirrors. If the interference pattern still doesn’t show,
the previous adjustment steps need to be repeated.
10. Once you have obtained an interference pattern (see Figure 9, below), place a
polarizer in each path. With parallel polarization planes, interference is observed, but with perpendicular planes, it disappears (see Chapter 5). The third polarizer ("eraser") can now be placed directly in front of one of the screens.
Note: When light is reflected by the mirrors or beamsplitters, the polarization isrotated. Position the polarizers as shown in Figure 7 with one placed immediately after the beamsplitter in path 1 and the other placed after the mirror in path 2. This configuration has been shown to yield optimal results.
Figure 7 Interferometer Final Setup
Quantum Eraser Page 15 MTN002250-D02 Rev B, January 22, 2014
Additional note:
As stated above, the most distinct interference pattern is obtained when both arms of the interferometer are of equal length. In the case where one arm is much longer than the other, an interference pattern can be observed, but it is much smaller than with an optimal adjustment. Here, we discuss briefly why that is the case and why we see a circular pattern.
When the interferometer arms are not of equal length (which is always the case since it’s practically impossible to adjust the interferometer with nanometer precision) then there exist two (virtual) light sources as seen by the screen which correspond to the different light paths through the interferometer. If the path is stretched out in one dimension, one source is behind the other due to the different lengths of the interferometer arms.
As with all interference patterns (such as, e.g., for the double slit) one can now determine the difference in the paths length between the path from light source A to point X and from light source B to point X which then translates to, e.g., constructive or destructive interference, see Figure 8.
Figure 8 Explanation of a Circular Interference Pattern If the arms of the interferometer have very different lengths, the two virtual light sources are far apart. In this case, a small position change on the screen corresponds to a large change in the path length difference, which again translates into a smaller spacing between the fringes. This explains why the interference pattern gets smaller when the interferometer arms have very different lengths.
This line of argument is the same for all points on the screen. Since the lens diverges the beam symmetrically around the optical axis, the interference pattern needs to be symmetric, i.e., concentric, as well.
Quantum Eraser Chapter 5: Experiment
Chapter 5 Experiment
First, it should be pointed out once again that this experiment represents an analogy experiment to the true single-photon “quantum eraser", as it can also be explained in purely classical terms. In the original single-photon experiment, classical physics ultimately fails. In spite of this, the experiment can be described with quantum mechanics principles and terminology.
The quantum eraser serves to illustrate several basic quantum mechanics principles and "mysteries", such as complementarity or the quantum mechanics measuring process in conjunction with interference phenomena.
The two possible paths in the interferometer represent two possibilities for one photon to move. The two polarizers are used to mark the paths, which makes them distinguishable.
5.1. Experiment 1: Path Information in Quantum Physics
Place a polarizer in each arm of the interferometer and adjust the polarization of both to the same orientation.
You should still see interference rings on both screens. Now imagine that only a single photon passes through the setup at a time. One often uses the expression that the photon interferes "with itself". From a quantum mechanics point of view, this means that the state of the photon is a superposition of the two states: "photon in path 1" and "photon in path 2". The probability of each of the two possibilities is 50%. The intensity pattern, which one can observe on the screen after many individual photons have passed through the setup, meaning the probability distribution of these photons, emerges as an interference pattern (see Figure 9). We do not know which path the photon took, as both paths are indistinguishable.
However, as a photon is indivisible, it can ultimately only "land" on one screen. This illustrates the complementarity of the pattern – where a maximum occurs on one screen, there is a minimum on the other (this can be seen particularly well in the center of the pattern).
Now, turn one of the polarizers by 90°. The different paths in the interferometer are now “marked” by polarization, and so we obtain information regarding the path that the photon took. This results in the disappearance of the interference pattern, as the two paths are now distinguishable. A smooth intensity distribution appears on the screen without an interference pattern (see Figure 10).
If the interference pattern does not fully vanish when the polarizers are set to 0° and 90°, it is most likely caused by non-perpendicular polarizers. You may need to make sure again that the film polarizers have the correct orientation in their mount (c.f. chapter 4.2 component assembly).
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Quantum Eraser Page 17 MTN002250-D02 Rev B, January 22, 2014
Figure 9 Interference Patterns
Figure 10 Disappearance of the Interference Pattern
Quantum Eraser Chapter 5: Experiment
Trick question:
Above, we’ve argued that the presence of a 0° polarizer in one arm and a 90° polarizer in the other arm of the interferometer results in a defined path and no interference pattern. We argued that the photon will have either 0° or 90° polarization on the screen/detector and that we could thereby tell which way it went. Does the same line of argument work when a 0° and an 80° polarizer are used?
Answer:
One might be inclined to say “yes” since one might make the mistake of thinking that a photon that has an 80°polarization at the screen must follow the path with the 80°polarizer. However, there is a certain probability that a photon polarized at 0°will be absorbed on the screen with 80°polarization, even though the probability is small. Therefore, the path information is undefined. In other words: the two possible paths (or possible states) superimpose, and we find a low contrast interference pattern.
5.2. Experiment 2: Quantum Eraser
In this experiment, the two polarizers in the setup should first be turned 90° in relation to one another, as described above, so that no interference is observable due to the path information. Then, the third polarizer, the "eraser", is installed between the last beamsplitter and a screen. The eraser is oriented 45°from the other two polarizers. What can be observed on the screen?
As one can see in Figure 11, an interference pattern appears again. Figure 11 shows the screen with the eraser in front of it on the left hand side and the screen without eraser on the right hand side. Therefore, an interference pattern is observable on the left screen whereas no pattern is observable on the right screen.
These observations can be explained as follows: the eraser restores the interference pattern again, as the path information of the photons is now no longer present. All photons, which hit the screen, have a 45°polarization. The photons, which reach the other screen without the "eraser", still carry this path information – one can determine whether they passed through path 1 (0°polarization) or path 2 (90°polarization). Therefore, no interference pattern is observable on the right screen.
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Quantum Eraser Page 19 MTN002250-D02 Rev B, January 22, 2014
Figure 11 R ight Screen: No Interference Pattern. Left Screen: Interference Pattern Behind the
Eraser
5.3. Experiment 3: Thought Experiment
The physicist John Wheeler came up with the following thought experiment: Imagine that the second beamsplitter is inserted into the setup after the photon (according to classical thinking) must have already “chosen” one of the two possible paths in the interferometer. What result is expected—interference or not?
First of all, we sketch the interferometer, with and without the second beamsplitter: (a) 4
4
1
2
2 (b) 123442
Figure 12 (a) Sketch of the Setup without the Second Beamsplitter, (b) Setup with Second
Beamsplitter, (1) First Beamsplitter, (2) Mirror, (3) Second Beamsplitter, (4) Screens.
When a photon is sent into the setup depicted in Figure 12(a), the path information is defined.
As
a result, no interference pattern is visible. As we’ve discussed above, the