The h Bar

@DanielSank That's an interesting explanation for why it's common in Europeans

Genau!

(I'm learning German, slowly)

Oh, my sympathies. Have you raged about grammatical gender yet? ;P

7:33 PM

pffft

Spanish, Greek, and Russian all have gender.

This ain't new.

Ah, then you're well-prepared :)

I'm just glad that German has only four cases, and that the genetive is way less common in German than in e.g. Russian.

It is my understanding that, in German, the dative is to the genetive his death.

Yeah, der Dativ ist dem Genitiv sein Tod is sort of a proverb

Right. I love it.

Russian has six cases and you better believe they all get used.

So what's new in physics?

Good question - I haven't really been keeping up with recent developments, to be honest

7:40 PM

Ah well.

How's the job?

Going well, haven't tired of it yet, so that's a good sign :)

How's the quantum engineering?

Quantum engineering is going along nicely.

I gave a talk to an audience of mostly computer programmers a couple days ago.

It was a guest talk in a quantum computing course (within Google!).

My goal was: give the audience some notion of how to connect physical hardware to the abstract quantum algorithms they were learning about.

It was recorded, so I listed to part of myself. I gotta say, that's a bit of a difficult experience. Noticing one's annoying verbal habits is... discouraging(?).

Did that work? I imagine that's pretty hard to do for people who likely don't have a background in quantum mechanics

I'm not sure how well it worked.

@DanielSank Heh, almost no one enjoys listening to themselves

7:44 PM

I spent ten slides talking about vibration modes (I had a guitar with me). Then I said that QM is basically when the amount of motion in the modes is quantized.

Then I talked about how an LC circuit has a vibration mode, and that's our qubit.

Not sure if it worked.

There were not many questions in the first half, which is a bad sign IMHO.

Second half had more questions.

Yeah, trying to explain enough QM in the span of one session gotta be pretty hard

Perhaps.

It's not that complicated though.

@DanielSank I think the problem is less the actual complicatedness (is that a word?) of the material but the apparent unintuitiveness of it. It's not that the audience is unable to comprehend the basis of QM, it's that it's frequenty unwilling/incredulous

Perhaps. But these folks were already two lectures into a quantum computing course.

I like this slide. Not sure if the audience did.

my parents made a recording of my thesis defense. I have not listened to it

And I am not planning to

7:55 PM

Heheh

I’d be more willing to do the talk again than listen to it tbh

hahaha

nice

Though partly that’s because giving the talk again would be an opportunity to do it better

(As long as it’s for an actual audience. I can’t practice a talk to an empty room without getting stuck in a loop)

A thing that seems tricky with QM is to find simple examples to play around with

@Semiclassical Actually, I think a vibrating string is the best example.

I think starting with a "single particle" is a mistake.

It feels easier, but it results in so much confusion later on.

One of the points of that slide above is to get rid of any opportunity for being confused about single particles vs. multiple particles.

For my part the best simple example for QM remains the Stern-Gerlach experiment

by contrast, I’m less and less fond of the double slit experiment

8:02 PM

Ok yeah, there are various aspects of QM.

Stern-Gerlach is great. The problem though is that everyone will assume there are hidden variables.

It's annoying that you have to get to Bell's theorem before you really believe QM.

Heh

Well, it’s still a good starting point since you can do a two-particle experiment with different SG devices

Though I think the issue is not just QM there, but how one formalizes the notion of a hidden variables theory

After all, you can have nonlocal hidden variables just fine

@Semiclassical Yeah we mostly ignore that though.

lol

I think most people look at Bell violation experiments and think "Well, I guess Nature has no objective reality apart from my measurement results".

I think that credits people with more philosophical thinking than they really have

I'd put the more usual reaction as just "Well, I guess Nature is pretty weird"

8:09 PM

perhaps

Beh, do y'all understand kronecker product?

@DanielSank Sure, it's just a tensor product ;)

Bah!

lol

Suppose I have two qubits.

I order my basis states as 00, 01, 10, 11.

something something...

If I have an operator $\sigma_x \otimes 1$, which qubit is the $\sigma_x$ operating on?

The left one or the right one?

the left one, I'd say

8:12 PM

hmmm

The left one. $\lvert 00\rangle$ is just a shorthand notation for $\lvert 0\rangle \otimes \lvert 0\rangle$.

Yeah I know.

What I'm not sure of is this: if I use the kronecker product on matrix representations of $\sigma_x$ and $1$, does the resulting matrix agree with what you just said?

Checking...

It certainly should! Otherwise your formula for the Kronecker product is wrong :P

a property of the Kronecker product per Wikipedia: $(A\otimes B)(C\otimes D)=(AC)\otimes (BD)$

lol

Ok, so IMO, "kronecker product" is for matrix representations of the tensor product.

8:15 PM

where the matrices A,B,C,D have appropriate dimensions for the matrix multiplication should make sense

@DanielSank Yep, agreed

Calling $\otimes$ a "kronecker product" is a little confusing to me.

Anyway, lemme check a simple case.

Ok, if $\sigma_x \otimes 1$ has the $\sigma_x$ acting on the left qubit in our ket notation, then we have this:

00 -> 10
01 -> 11
10 -> 00
11 -> 01

If the states are ordered 00, 01, 10, 11, then the matrix is

$$\left( \begin{array}{cccc} 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 1 \\1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \end{array} \right)$$

Is that the right ordering?

In short, we have stuffed an identity matrix into each element of a $\sigma_x$ matrix. The question is now: does that match with what the Kronecker product would tell us to do?

obv the first and last are right. but I'm not sure about 01 vs. 10

8:19 PM

@Semiclassical "Right" in the sense of what the Kronecker product wants? I'm not sure. Let's look it up...

yeah, I'm forgetting if that's obvious

Kronecker product

In mathematics, the Kronecker product, denoted by ⊗, is an operation on two matrices of arbitrary size resulting in a block matrix. It is a generalization of the outer product (which is denoted by the same symbol) from vectors to matrices, and gives the matrix of the tensor product with respect to a standard choice of basis. The Kronecker product should not be confused with the usual matrix multiplication, which is an entirely different operation. The Kronecker product is named after Leopold Kronecker, even though there is little evidence that he was the first to define and use it. Indeed, in the...

would we have $|0\rangle =\binom{1}{0}$ here?

According to the article $A \otimes B$ is represented by tiling $B$ around, each time multiplied by the components of $A$.

That does in fact match the matrix we wrote above.

@Semiclassical Not sure what you mean.

Well, if $|0\rangle = \binom{1}{0}$ and $1\rangle = \binom{0}{1}$, then $$|01\rangle = \binom{1}{0} \otimes \binom{0}{1} = \begin{pmatrix} 1\binom{0}{1} \\ 0 \binom{1}{0}\end{pmatrix} = \begin{pmatrix} 0 \\ 1 \\ 0 \\ 0 \end{pmatrix}$$

8:25 PM

Hm, the Wikipedia article needs an edit.

@Semiclassical Correct.

so that'd support the ordering being 00, 01, 10, 11

As I said, the ordering I assumed was 00, 01, 10 11.

@Semiclassical yes

just wanted to make sure everything was consistent

Yes of course. This is exactly what needs to be understood.

Right.

In which case it should all work out.

8:26 PM

The Wiki article doesn't specify the basis state order though. It should.

Editing math in Wikipedia is such a PITA

yeah

I think the main point is that, for a given basis, the Kronecker product is a tensor product

but you could have of course picked a different basis. you'd still have the same tensor product (operators would send kets to kets in the same way) but the matrices would look different

The kronecker product gives you matrix representing tensor products of operators.

right

@Semiclassical Right.

nbcnews.com/mach/science/…

8:29 PM

But there is one definition of the kronecker product, so to not get confused, it's important to order the basis states right.

@vzn ^ latest wave of string theory bashing :p

'"I can't believe what this once-venerable profession has become," she writes. "Theoretical physicists used to explain what was observed. Now they try to explain why they can't explain what was not observed. And they're not even good at that."'

@DanielSank The Wiki article is indeed confusing. I'm not sure why we need the "Kronecker product" as a notion separate from "the tensor product in a specific basis", anyway :P

@ACuriousMind Hmmmmmm

IMHO, it's good to separate operator thingies from matrix thingies.

in the realm of physics news, I saw some discussion of the sterile neutrino anomaly in the transcript

not sure what to make of it

I like having a clear distinction between when I'm doing operator algebra without reference to a basis, and when I'm manipulating representations of those operators.

In another way of thinking about it: a Kronecker product is a thing I can call in my numerical code.

...but my numerical code doesn't know what a "linear operator" is.

¯\_(ツ)_/¯

8:35 PM

code knows how to perform matrix multiplication. it doesn't know what a linear transformation is. (usually)

and that's all it needs to know, really

I think it's just an old name for tensor products of matrices, from the wiki, 'the Kronecker product ... is a generalization of the outer product ... and gives the matrix of the tensor product with respect to a standard choice of basis', but yeah it bugs me a bit too

Yo any of you mammajammas want to give a talk at my lab?

We're trying to bring in more guest speakers.

Where is your lab?

Santa Barbara, California.

neat

a pity i'm up in MN (and am entirely unqualified)

dmckee

8:50 PM

@bolbteppa Meh. The author—who should know better—makes the same mistake as typical readers of pop-sci: he mistakes high-energy particle physics, cosmology, and general relativity for all of physics.

yeah

dmckee

Enormous amounts of real physics are going on at intermediate scales—in condensed matter, in soft matter, in materials.

In non-linear optics, too.

even in GR, I imagine there's a lot of good astrophysics going on

@dmckee "Physicists make incremental increase in medium-sized non-weird physics" is simply not a good story :/

and in particle physics, the fact that sterile neutrinos are currently in the news suggest that the field is not as experimentally sterile as one might think

8:53 PM

@ACuriousMind But it should be.

dmckee

@ACuriousMind No, but it is hugely good for the physical conditions of human civilization.

I'm sure good articles could be written. Focus on the humans, maybe.

@DanielSank I don't disagree

From the science section of a news site, written by a non-scientist science journalist, basing it off the new book by a LQG researcher bashing theory, copying the standard technique of only 'the big ideas'

An article on the 3-D Ising model is hardly going to entice a writer un-prepared in the topic to talk about advances, this is why the Michio Kaku's and Tyson's of the world are so important despite the condescending attitudes :p

A weekly pop-sci-style write up of arxiv submissions would be a useful thing for non-science writers to skim and then write articles on, probably be really hard to find people to do this

9:42 PM

@EmilioPisanty Our masterpiece.

Emilio Pisanty

10:16 PM

@DanielSank nicely written up

@DanielSank if you'll fly me from the east coast I might be able to

10:31 PM

huuullo

@EmilioPisanty We cover travel. If you can give a talk on something quantum computery, we'd be happy to have you.

hiya @Danu

@DanielSank I'm gonna have a deep think about how moduli spaces of string theories can be related to quantum computing ;D

hahaha

@ACuriousMind how's life?

10:36 PM

do it

@Danu life's very good :)

@ACuriousMind Anything particular? :)

@Danu I'm sure there's something to be said about TQFTs, braids and quantum computing, actually...

Yeah, for sure. But I don't work on those kind of things :P

@Danu Not really, I'm just pretty content with the current state of affairs. Busy - but not too busy - at work, nice weather, good friends - it's all good

10:39 PM

Yo the weather over here doe

it's been SO good

Northern Germany is the new California

I'm sure happy I don't live in Wuppertal anymore after it's been basically flooded last week, though

ghehe

Life's been really nice here too---besides the good weather, I'm finally starting to make some friends in Hamburg. Also my work is progressing a bit, which helps to make me more excited about it.

Good to hear :) Stereotypically, people in the north can take some time warming up to

yupyup

as usual, it was mostly an issue of finding the first 1-2 people; now it gets easier

!!

@Danu How are you

10:48 PM

A wild Balarka appeared!

See above @Balarka ;)

scrolls up

scrolls down

@Danu Nice!

And you? I saw in one of the chat transcripts that you finished high school exams?

@Danu Yeah, I'm pretty happy I stayed in Heidelberg since it appears plenty of people I like are staying here, too. I find less and less time to play my beloved video games as my spare time gets eaten up by miscellaneous social things (not that that's a bad thing :P)

Yeah that's a thing - I'm a high school graduate now (finally). I also apparently got through the admission exams for one of the universities I applied for.

@ACuriousMind Yeah, not playing video games is a good indicator for me that I'm doing well :P

10:51 PM

On the flip side I have a terrible sore throat, for which I took an anti-allergic, and after about 12 hours of sleep I woke up feeling like death.

@BalarkaSen Oh, great news! Are you happy with that uni? Will you be enrolling there?

Yeah I'm pretty happy with it. I still have the interview.

@BalarkaSen Now you know what Oppenheimer meant when he said "Now I am become death.." (jk)

lmao

"Oppenheimer had a sore throat" - Danu 2018

So you'll be staying in India, I assume?

10:53 PM

Yep.

:)

My closest collaborator is also from India

Oh, nice. May I know the name?

Arpan Saha

He's also a student of my supervisor

Ah gotcha.

grk1670.math.uni-hamburg.de/researchers/saha

10:55 PM

Huh, he's a former visiting student of TIFR apparently. I am at TIFR right now.

Cool beans

:)

Calling it now: A few years from now Danu's gonna be advising Balarka

Top 10 anime crossovers

lmao

@BalarkaSen Well done, keep Cambridge Part III in the back of your mind

10:57 PM

^and then forget about it :D

lol

I am not too impressed with the 1-year degrees that are typically offered in the UK

Part III is the best course in the world, 2 year MSc's are a waste :p (argument ensues)

Honestly, I find that the people I know that came from those places were usually very smart and capable, but had a narrow range of knowledge.

In comparison with students from e.g. my degree, they are really lacking basic knowledge in many areas.

Which is not a huge deal

but I think that, during the student years, it is much preferable to take some extra time to broaden your academic horizons

@Danu A friend of mine went for one of these and came back very confused about what he wanted to do. I think he's in some sort of biophysics now :P

10:59 PM

A lot of European MSc's, the 2nd year is like the first year of a phd (without the actual phd) + insane courses and for a 3 + 2 instead of 4 + 1 mentality so it all kind of balances out

@ACuriousMind Oh no what a terrible resolution of the dilemma

Perhaps it'd be best to say that students doing a MSc. in the UK might have some ground to make up if they come to mainland Europe for a PhD.

@bolbteppa Considering that Part II seems to be comparable to an MSc (from experience, in physics)...

I, for one, am really happy with the many, many courses I got to take during my master's.

@BalarkaSen Life is what happens while you were making other plans :P

The Wire 3x09 - Lester Freamon, a wise man

11:02 PM

Good delivery of that line in the Wire:

►

@Danu Yeah, I'll never use most of it but I loved many of my master's courses

@Danu Heh. It ends in tears, with everyone approaching mental breakdown :P

@ACuriousMind Yeah man, so worth it. I took like 22 courses and I don't regret it at all

I have never ever heard of European MSc's being better than UK MScs or UK ones preparing one less

@Danu NO REGRETS

11:09 PM

@bolbteppa Like I said above, I don't think the students from the UK are weaker. But in my experience they all have a lot less base knowledge compared to people that took my degree.

@Danu Yeah, I agree, never once have I regretted that first year of CS. A few times it's been in some way helpful, whereas to catch up in that extra bit of physics that could have been done in that time wouldn't be anywhere near as hard as learning that at-least-occasionally-useful CS mindset

@Danu Depends a lot on the Uni - some places are very focused on something very specific while others are very broad (e.g. NatSci, which is designed to give people a lot of 'base knowledge')

@Danu I think you just want to see it that way :p

Lozansky

Is do Carmo's "Differential Geometry of Curves and Surfaces" accessible for someone with only engineering math as a background?

@Lozansky it's supposed to be, videos on youtube ICTP follow it

"engineering math" is a rather vague concept :P

11:21 PM

All you need to know is multivariable calculus.

So with greater likelihood the answer is "yes"

Lozansky

Thanks!

maths.cam.ac.uk/system/files/partiii_guide2017.pdf

Sheer insanity contained in there

@bolbteppa Still a distinct lack of quantum info, despite the researchers that have came from there :/

(OK, 1 course, but... Not a lot)

@Mithrandir24601 there are about 10 courses on it?

@bolbteppa 1 course on 'Quantum Computation, Information and Foundations'

11:28 PM

Oh

Is the subject advanced enough to deserve more than 1 course?

@bolbteppa The physics department also has a course on quantum computation

(where the Maths Part III course is only quantum info)

And the quantum computation people that have came from DAMTP are really good

Also, "This is an introductory course on QIT", so why don't they have a more advanced course as well? :/

Subject needs to prove itself worthy of that (runs)

@bolbteppa I'm very tempted to abuse my mod-edit privileges here... :P

Meh, a grand total of 6 courses covering “Geometry and Topolgy” don’t impress me too much.

My sense is that field is new enough that one course would be enough prep to begin a phd with comp sci background?

11:39 PM

@bolbteppa A course on quantum computation as well as one on quantum info. would, but quantum info by itself? I'm not so sure

And 8 courses for all of QFT and strings co,bined, also rather little.

Anyways, I am speaking from my experiences with students that came here to do a PhD. You’re welcome to consider my assessment invalid, of course.

@BalarkaSen How's TIFR?

Not bad

not a very .. excited reply

11:55 PM

Eh, it's the same thing I do at home. Reading books, thinking about what I am reading, proving things. I just have some people to talk math with now, and some upcoming talks to attend, etc.

I guess "Same thing I do, but tenfold more social" is the right description

But I also have never really been a people person anyway

You prefer working alone and not discussing much?

I don't have to pay for food and internet, though, so that's a plus.

@Avantgarde Heh, I write things in this stupid chat when I have to pass around an idea to see if it works.