Mach-Zehnder interferometers and beam splitters

MIT 8.04 Quantum Physics I, Spring 2016
Instructor: Barton Zwiebach

License: Creative Commons BY-NC-SA

[MuhammedAhmed]

your videos used to reach me after I search for something in Quantum Mechanics. Now, they are always in the recommended videos and I watch some of them just for fun. Very clear explanations. Thanks a lot, Professor.

[fjs]

Professor Zwiebach is awesome, then again would expect nothing less for MIT

[isatousarr]

The Mach-Zehnder interferometer is a pivotal device in the field of optics and quantum mechanics, showcasing the principles of wave interference and superposition. It consists of two beam splitters and two mirrors arranged in such a way that light entering the interferometer can take two distinct paths, recombining later to produce interference patterns. Beam splitters serve as crucial components in this setup, allowing incoming light to be divided into two separate beams. These splitters can operate in various ways, reflecting and transmitting light depending on their design—often characterized by a 50/50 splitting ratio for balanced interference. By varying path lengths or introducing phase shifts in one of the arms, the Mach-Zehnder can produce constructive or destructive interference at the output, revealing important information about the phase relationships of the light waves. This interplay between beam splitters and interferometers has profound implications in applications ranging from optical metrology to quantum computing and information processing, demonstrating the fundamental principles that underpin the behavior of light in both classical and quantum realms. The Mach-Zehnder interferometer not only serves as a tool for precise measurements but also as a platform for exploring the counterintuitive nature of quantum superposition and entanglement.

[Jehannum]

This is great stuff because you can play around with the maths yourself and learn more by doing so.

[romankostal]

At 14:34 he cleans the blackboard and later starts coughing because he breathed in all the chalk dust. Please use also water to clean the BB. It is unpleasant to watch you damaging your lungs.

[Whateverbro]

6:19 did a physicist just say ask an engineer?! Lol

[iwonakozlowska]

BS is a mirror matrix (det=-1), but the rotation matrix (det=1) could also work.

[nan]

Who is the one disliking this?
This Beam splitters matrix is mad.

[CricSahil]

I'm from India Your video is so good 👍👍

[ramonbarrio]

If somebody could help me:
at 11:41 he is justifying the choices on the matrix's elements and says that, because his first try (all = 1/2^(0.5)) resulted in a non normalized state, his proposed matrix for the action of the beam splitter couldn't be right. It just so happens that early in the video (or in a previous video) he states that the physics of measuring a particle in a certain state doesn't change at all by multiplying it by a factor, so why can't he just say this his previous (1 1)' is actually ('/2^(0.5))*(1 1)'? Going by his previous statement, this matrix could be validated... is it clear?

[virtusdude]

on 8:41, why does a times zero state and beta times 1 state, where does s, t and v, w come from? arent these values from the last example, this one being an arbitrary one?

[tavinderthind]

Photon structure imagine in three phases
Circular - scalar
Longitudinal - vector
Junction - give rise to 3 and 4
And further
In
First rotation around a notional centre held by a veirtual centre
Creating
5 and 6
7 and 8
Back to 9
Then a repeat
Above some what spell out THEORY OF CREATION OF THE DIMENSIONS

[benmansourmahdi]

this is very interesting but what if u share some exercices corrections and harder stuff

[zhyfn]

If I use the [1, 1;1, -1] for a BS, how is the phase of scattered state of [1;0] be different than [0;1] in the way that one acquires a negative one in the case of [0;1] but both are positive in the case of [1;1]?

[edwardlavelle]

Wouldn't the light passing into D0 have twice the amplitude due to the constructive interference, making the output light brighter than the light from the source? This is the part that kills me.

[ENGRAINING]

the investors say "when shall we see a return on our investment?"

i would say: "maybe, we have to work on better interferometry."

[cafe-tomate]

So the BS is not considered as a measurement ? Since the incoming photon doesn't have to choose between two states.

[Blazo]

sir,
what is the physical interpretation of having a negative number in the Beam Splitter Matrix.

[cafe-tomate]

The BS matrix turns out to be the matrix of the reflexion with respect to the axis that makes an angle π/8 with the (Ox) axis. What does this π/8 represents?

[DiskMail-lv]

this is like philosophy. tapping in the dark