The h Bar

DanielSank

19:21

Hi, everybody.

ACuriousMind

Hello, Dr Sank

DanielSank

I can see from here that you have too much blood!

ACuriousMind

Oh, no, will you have to cover me in leeches?

DanielSank

Yes. Yes I will.

ACuriousMind

Thank you!

DanielSank

19:25

You know about hemocromatosis?

ACuriousMind

Interesting segue, but yes, I do

Leeches are good for that, I guess.

DanielSank

They are!

Also, hemocromatosis makes you more resilient to the black plague!

There's some possibility that the plague selected for hemocromatosis, and that leeching people during the middle ages was actually a good idea because it may have been treating the hemocromatosis.

Isn't that interesting?

ACuriousMind

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

DanielSank

Genau!

(I'm learning German, slowly)

ACuriousMind

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

DanielSank

19:33

pffft

Spanish, Greek, and Russian all have gender.

This ain't new.

ACuriousMind

Ah, then you're well-prepared :)

DanielSank

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.

ACuriousMind

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

DanielSank

Right. I love it.

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

So what's new in physics?

ACuriousMind

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

DanielSank

19:40

Ah well.

How's the job?

ACuriousMind

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

How's the quantum engineering?

DanielSank

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(?).

ACuriousMind

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

DanielSank

I'm not sure how well it worked.

ACuriousMind

@DanielSank Heh, almost no one enjoys listening to themselves

DanielSank

19:44

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.

ACuriousMind

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

DanielSank

Perhaps.

It's not that complicated though.

ACuriousMind

@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

DanielSank

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

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

Semiclassical

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

And I am not planning to

DanielSank

19:55

Heheh

Semiclassical

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

DanielSank

hahaha

nice

Semiclassical

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

DanielSank

@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.

Semiclassical

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

DanielSank

20:02

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.

Semiclassical

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

DanielSank

@Semiclassical Yeah we mostly ignore that though.

Semiclassical

lol

DanielSank

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

Semiclassical

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"

DanielSank

20:09

perhaps

Beh, do y'all understand kronecker product?

ACuriousMind

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

DanielSank

Bah!

Semiclassical

lol

DanielSank

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?

Semiclassical

the left one, I'd say

DanielSank

20:12

hmmm

ACuriousMind

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

DanielSank

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...

ACuriousMind

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

Semiclassical

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

DanielSank

lol

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

Semiclassical

20:15

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

ACuriousMind

@DanielSank Yep, agreed

DanielSank

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

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

Semiclassical

Is that the right ordering?

DanielSank

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?

Semiclassical

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

DanielSank

20:19

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

Semiclassical

yeah, I'm forgetting if that's obvious

DanielSank

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...

Semiclassical

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

DanielSank

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.

Semiclassical

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

DanielSank

20:25

Hm, the Wikipedia article needs an edit.

@Semiclassical Correct.

Semiclassical

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

DanielSank

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

@Semiclassical yes

Semiclassical

just wanted to make sure everything was consistent

DanielSank

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

Semiclassical

Right.

In which case it should all work out.

DanielSank

20:26

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

Editing math in Wikipedia is such a PITA

Semiclassical

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

DanielSank

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

Semiclassical

right

DanielSank

@Semiclassical Right.

bolbteppa

nbcnews.com/mach/science/…

DanielSank

20:29

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

bolbteppa

@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."'

ACuriousMind

@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

DanielSank

@ACuriousMind Hmmmmmm

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

Semiclassical

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

DanielSank

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)_/¯

Semiclassical

20:35

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

bolbteppa

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

DanielSank

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

We're trying to bring in more guest speakers.

Semiclassical

Where is your lab?

DanielSank

Santa Barbara, California.

Semiclassical

neat

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

dmckee

20:50

@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.

Semiclassical

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.

Semiclassical

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

ACuriousMind

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

Semiclassical

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

DanielSank

20:53

@ACuriousMind But it should be.

dmckee

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

DanielSank

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

ACuriousMind

@DanielSank I don't disagree

bolbteppa

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

DanielSank

21:42

@EmilioPisanty Our masterpiece.

Emilio Pisanty

22:16

@DanielSank nicely written up

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

Danu

22:31

huuullo

DanielSank

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

ACuriousMind

hiya @Danu

Danu

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

DanielSank

hahaha

Danu

@ACuriousMind how's life?

DanielSank

22:36

do it

ACuriousMind

@Danu life's very good :)

Danu

@ACuriousMind Anything particular? :)

ACuriousMind

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

Danu

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

ACuriousMind

@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

Danu

22:39

Yo the weather over here doe

it's been SO good

Northern Germany is the new California

ACuriousMind

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

Danu

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.

ACuriousMind

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

Danu

yupyup

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

Balarka Sen

!!

@Danu How are you

Danu

22:48

A wild Balarka appeared!

See above @Balarka ;)

Balarka Sen

scrolls up

scrolls down

@Danu Nice!

Danu

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

ACuriousMind

@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)

Balarka Sen

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.

Danu

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

Balarka Sen

22:51

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.

Danu

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

Balarka Sen

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

Danu

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

Balarka Sen

lmao

"Oppenheimer had a sore throat" - Danu 2018

Danu

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

Balarka Sen

22:53

Yep.

Danu

:)

My closest collaborator is also from India

Balarka Sen

Oh, nice. May I know the name?

Danu

Arpan Saha

He's also a student of my supervisor

Balarka Sen

Ah gotcha.

Danu

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

Balarka Sen

22:55

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

Cool beans

Danu

:)

ACuriousMind

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

Balarka Sen

Top 10 anime crossovers

Danu

lmao

bolbteppa

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

Danu

22:57

^and then forget about it :D

Balarka Sen

lol

Danu

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

bolbteppa

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

Danu

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

ACuriousMind

@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

bolbteppa

22:59

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

Balarka Sen

@ACuriousMind Oh no what a terrible resolution of the dilemma

Danu

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.

Mithrandir24601

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

Danu

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

ACuriousMind

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

Danu

23:02

Good delivery of that line in the Wire:

The Wire 3x09 - Lester Freamon, a wise man

►

ACuriousMind

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

Mithrandir24601

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

Danu

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

bolbteppa

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

ACuriousMind

@Danu NO REGRETS

Danu

23:09

@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.

Mithrandir24601

@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')

bolbteppa

@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?

bolbteppa

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

ACuriousMind

"engineering math" is a rather vague concept :P

Balarka Sen

23:21

All you need to know is multivariable calculus.

So with greater likelihood the answer is "yes"

Lozansky

Thanks!

bolbteppa

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

Sheer insanity contained in there

Mithrandir24601

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

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

bolbteppa

@Mithrandir24601 there are about 10 courses on it?

Mithrandir24601

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

bolbteppa

23:28

Oh

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

Mithrandir24601

@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? :/

bolbteppa

Subject needs to prove itself worthy of that (runs)

Mithrandir24601

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

Danu

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

bolbteppa

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

Mithrandir24601

23:39

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

Danu

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.

Avantgarde

@BalarkaSen How's TIFR?

Balarka Sen

Not bad

Avantgarde

not a very .. excited reply

Balarka Sen

23:55

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

Avantgarde

You prefer working alone and not discussing much?

Balarka Sen

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.

Avantgarde

haha

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