The h Bar

HDE 226868

20:00

@dmckee Leavitt wasn't the only one, AFAIK. There were a substantial number of female scientists around the same time involved in observational stellar astronomy. Annie Jump Cannon was fairly impressive.

DanielSank

@dmckee Didn't something similar happen with Watson/Crick?

heather

@dmckee, oh, I've read about that!

@DanielSank, yeah, I've read about this.

DanielSank

Also Lise Meitner was instrumental in discovering fission... but that one's more widely known nowadays.

GPhys

That reminds me I need to sign up for two of my department's Responsible Conduct of Research ("RCR") training sessions

which is an NSF thing, I guess

DanielSank

@JohnRennie Found a very lucid description of "bollocks".

HDE 226868

20:02

@DanielSank Rosalind Franklin, although she worked independently, I believe. One of her colleagues still won the Nobel, though.

heather

@DanielSank, they basically stole some "images" Rosalind took that confirmed the structure they came up with. She died at 30-ish, though, of cancer, before she realized what had happened.

dmckee

A good book on the topic (of underappreciated female scientists) is Headstrong: 52 women who changed Science—and the world by Rachel Swaby.

Bunch of short bios.

DanielSank

@JohnRennie It boggles the mind that people in Britain can understand one another. Exhibit A.

Secret

I think before all this awareness in this(?) century, the only recognised women scientists and mathematicians are Emmy Noether and Marie Curie

Shing

I am confused, I have often read question if something is real or really exist.

user116211

20:07

Hey @0celo7, did you follow any books on analytical geometry? I need a good book to read.

Shing

what exactly do we mean when we say something exists/ real in physics?

dmckee

@Shing It often means whatever the asker wants it to mean.

DanielSank

@Shing Those questions are often not so great.

At least, they're not questions admitting of a single obviously correct answer.

dmckee

People can be specific about what they mean, but that leads to facing up to the fact that there are shades of "realness", rather than the kind of all or nothing property to beloved of philosophers.

DanielSank

You know, I wonder: is admitting an obviously correct answer a prerequisite for questions on our site or not?

dmckee

20:10

@DanielSank Enter "Good subjective, bad subjective" where ever that is. Answer from on high: "Sorta."

Secret

For me, existence in physics is whether you can infer it from some experimental observations, and the ability to manipulate it to do stuff for you

user116211

@0celo7, I'm seeing Adrian Albert's book, a Dover reprint; have to check...

user116211

Aha!!

user116211

It's Bourbaki style except that it has some good examples.

Shing

@DanielSank you mean those questions are usually not well-posed?

DanielSank

20:19

@Shing I mean exactly what I said: they don't admit one obviously correct answer.

Shing

@DanielSank obviously correct = main stream?

DanielSank

Here's an example of a question without an obviously correct answer:

"What is the meaning of the wave function?"

(I don't understand the "mainstream" criterion. That's not what I'm talking about.)

Shing

I suppose it is okay, if "meaning" = "physics interpretation"

heather

@Shing, one of the close reasons is too opinion based. Your question is basically the poster child for that.

DanielSank

@Shing I would disagree. Go talk to ten physicists about their interpretation of the wave function. You'll get ten different answers.

@heather What question? Link?

heather

20:23

@DanielSank, this one:

15 mins ago, by Shing

what exactly do we mean when we say something exists/ real in physics?

Shing

@DanielSank So you mean it is too opinion-based for this website?

DanielSank

@Shing No. An opinion is a question like "What's the best ice cream flavor?"

Everyone has their own opinion.

The wave function has probably some finite number of reasonable interpretations.

heather

@DanielSank, well, wouldn't you say that the opinion-based close reason could be used on that question? Because it is someone's opinion which interpretation is best.

DanielSank

You could write an answer explaining all of them, but that would be a very large answer which would have to get into the role of mathematics and theory within the natural sciences.

@heather I suppose.

Shing

I see, I understand the mechanism of stack exchange is bad for discussion.

DanielSank

20:25

Let me say this another way.

If someone asks "Is X real in physics?", they probably need a discussion about the role of math and theory in natural science in general.

heather

@Shing, yes, stack exchange is not designed for discussion. There are places like chat where you can invite discussion, but the main site doesn't want discussion.

DanielSank

@heather I agree with that.

That's well said.

heather

@DanielSank, okay, just wanted to make sure I had that right =)

@Shing, and to understand why discussion isn't really good anywhere but chat, it is so things are neater, the answers are well defined, and everyone can tell what is going on. It's hard to have the definitive answer to a question when really there's a bunch of discussion over it.

0celo7

ok @heather I am now with the republic

heather

@0celo7, is the republic democratic?

Sanya

20:28

@0celo7 bad choice :)

0celo7

@heather nope

@Sanya why

dmckee

To give a concrete reference to what Daniel is saying about math consider this answer of mine in which I argue that the "only in the math" virtual particles are real enough to design experiments around.

DanielSank

@heather Well, whether I agree or disagree with you doesn't make something right or wrong :)

heather

@0celo7, then what is it?

Sanya

@0celo7 everything will fall to pieces :o

0celo7

20:29

@Sanya people hate the legion

heather

@DanielSank, yeah, good point =)

DanielSank

@dmckee I'm not following that answer.

Maybe I need to know more about particles to follow it.

@heather I voice my opinions with conviction, some times too much.

I do that mostly because I'm used to a style of learning wherein everyone says what they think with as much support as possible, and then everyone subjects the opinions to various tests of logic until a better whole comes out of the mess.

It's effective in some cases, but actually I've learned from people here that it's also effective to think very carefully and make more gentle, qualified statements.

ACM is extremely good at that, IMHO.

dmckee

@DanielSank Both of those reaction depend on the existence of anti-quarks in the nucleus (or nucleon) that has a valence content entirely made of normal-matter quarks.

DanielSank

@dmckee I understand almost none of that, lol.

Don't even know what "valence content" means.

heather

@dmckee, I understood about half of the words in your sentence but had no idea what they meant together. =)

dmckee

20:37

The anti quarks come from the "sea", so we have an experimental process that only happens because there are anti-quarks in there when we know that the "real" make-up of the nucleons is all quarks.

Shing

Me neither. I don't understand the answers as well as the question.

dmckee

So dismissing the math that shows all those temporary $q\bar{q}$ pairs and glouns as "just math" is overlooking something.

DanielSank

@dmckee I don't think anyone says you should dismiss the math.

I think the statement would be more that virtual particles aren't "real".

Which, IMHO, should be spelled "detectable".

dmckee

@DanielSank But does it count if I hammer them with a beam particle to put them on-shell (i.e. they aren't "virtual" when detected, but they must have been originally)?

The point is that the terms of the series are 'just' terms of the series but it is also possible to build an experiment that relies on their existence.

DanielSank

@dmckee If you put an external drive (beam) then you get real particles.

You see that in the math, of course.

"Virtual particles" just means "intermediate states in a Dyson series", roughly. They're not intermediate if you detect them :)

@dmckee This is a semantic argument.

I don't have to say that the experiment "relies" on them.

The experiment relies on Nature.

Your math relies on them :)

dmckee

20:43

Exactly. The whole question "Is $X$ real?" turns on the sematics of reality which is a philosophical question.

The pion production reaction is particularly interesting in this case because my 'real' beam and target are leptons and particles with a 'real' content only consisting of (normal-type )quarks, but the produced particle includes an anti-quark in it's 'real' content. So, where did that come from?

DanielSank

@dmckee Yep.

Er, wait... uh... philosophical?

Merrrrghhh I dunno.

heather

@DanielSank, where would be a good place to learn about how quantum computers are constructed? I know some general things, but I can't seem to find any specifics.

DanielSank

@heather There are several aspects of that question.

Are you interested in the physical realization of qubits, how qubits are thought to be connected up to form a useful system, or about the whole system including the classical computer algorithms needed for error correction?

heather

21:00

@DanielSank, well, probably all of that. I understand that qubits can be realized as electrons, or photons, or other elementary particles, using spin. But I don't know much else about it.

DanielSank

@heather Are you aware that qubits can be realized by things other than elementary particles?

heather

@DanielSank, can they be represented by atoms? (Short answer to your question being no.)

user218912

is quantum field theory used in the field of ultracold condensed matter?

DanielSank

@bl00 Yes.

@heather Yeah you can make qubits out of atoms.

Did you know you can also make qubits out of much, much bigger things?

user218912

@DanielSank how much field theory is used in quantum computing?

DanielSank

21:04

@bl00 In my experience, only a little. We use basic QFT when we have distributed elements like coaxial line resonators.

user218912

okay, thanks.

heather

@DanielSank, can you make a qubit out of any object that exhibits quantum effects?

DanielSank

@heather In principle, yes.

In reality, you need those objects to:

1) Maintain quantum coherence long enough to do useful stuff.

2) Couple to each other strongly enough to actually do logic.

3) Be measurable.

4) Be controllable.

That's a pretty tall order.

@heather Here's something you might find very interesting.

Consider a normal computer.

Do you know how the data in that computer is physically realized?

heather

@DanielSank, well, I know that data in the computer is represented as bits, and that bits can be represented as differences in voltage or magnetic field (I'm pretty sure the magnetic field is used in memory, which just might be why it's bad to have a phone and a magnet in the same pocket).

DanielSank

@heather Yeah, good. Each bit is a single physical system with two possible states. Those can be voltage states, charge states, magnetic dipole orientation...

Of course, note that you can use an abacus to do computations too. In that case, the physical information is the position of beads on a wire.

The point is that information is physical.

okay, so you know that in a computer you have data stored in bits.

Call that the "memory".

heather

21:14

Right

DanielSank

Now suppose you want the computer to do something.

What happens to the data in that memory?

heather

Well, it's manipulated, by passing through gates, right? Like the AND and OR and all the gates that can be built from those two.

DanielSank

@heather Yeah.

Here's an example of a transistor NAND gate

heather

So it would be transferred, maybe converted from a mangetic dipole orientation to a voltage state because it is leaving the memory (how would that work?) and then passed through a gate, where the charge is changed somehow (how would that work?) and then passed back to the memory where it is converted back again.

DanielSank

^ Excellent

You've identified all the important physical steps in information processing!

Let's focus on the part where you say "...where the charge is changed somehow...".

heather

21:17

Yeah, that's a tad vague.

DanielSank

It's fine!

heather

Okay, I've got a guess:

DanielSank

Inside the logic gate itself, the voltages of the two bits have to interact in some way, such that the output voltage is produced as desired.

Ok, give your guess.

heather

Actually, okay, I tried to write it and realized it made no sense. So nevermind. =)

DanielSank

Well, let's not get into too much detail. The point is that somehow we need a physical system in which the two voltages interact in a way that manifests a NAND gate.

Like, you have to actually build a physical system where the voltage at one point is the NAND of the voltages at two other points.

Right?

(transistors are good for that, by the way)

heather

21:21

@DanielSank, okay, yeah, that makes sense.

And that would explain why when I've done a few simple circuits controlling various things, I've used transistors.

DanielSank

Yeah ok, now here's the thing...

it's the same story in quantum computation.

You have to build a physical system which is quantum mechanical and in which you can get the state of the qubits to transform based on your desired logic.

heather

Yeah, that makes sense.

DanielSank

You have to build a quantum system wherein the qubits physically interact in the right way to perform logic operations.

heather

Okay, that sounded hard enough when you have macroscopic objects...

DanielSank

So here's the deal: you need qubits that are coherent and qubits that interact.

The problem is that coherence and interaction are fundamentally against each other.

heather

21:23

Coherent: what exactly does that mean?

DanielSank

I'm about to tell you.

heather

Oh, okay. =)

DanielSank

"Coherent" essentially means "stays quantum", and in the end that really means "doesn't interact with the environment against my will".

If a quantum system interacts with random stuff that you don't know about, the quantum state "leaks" into the surrounding degrees of freedom and your qubit is no longer in a nice quantum state.

heather

Oh! Because measuring a qubit means it "collapses".

DanielSank

Yes, it's a similar idea.

heather

21:25

So you have to isolate the qubit from the world.

DanielSank

Yes, basically.

heather

But then you need the qubit to interact with other qubits for the gates...

DanielSank

Consider an electron: that thing is super duper small and has a tiny electric field. Therefore, it doesn't interact strongly with stuff.

@heather Yes!

heather

Wow, how do you pull that off?

DanielSank

...but that also means the electron doesn't interact with other electrons very strongly either.

@heather It's hard. That's why we're all working our butts off!

heather

21:26

Huh, okay - does that mean you are sacrificing interact-ness for coherence (with the electron)?

DanielSank

You have to build something where the qubits interact with each other exactly the way you want, but not with anything else.

@heather Yes.

Basically yes.

heather

But then with bigger objects I'm guessing you have more interact-ness but less coherence.

DanielSank

There are always these articles coming out about some latest and greatest qubit with amazing coherence, but in so many cases, those qubits aren't so great because they don't interact well.

@heather Yep.

heather

Okay, that makes sense. So then how do you build something where they interact exactly the way you want?

DanielSank

Our qubits are several hundred microns in size. That's about a million times larger than an atom.

@heather There are various strategies.

The original one was to use atoms (actually ions) as qubits. They are trapped in space using laser light, and you move the atoms around.

You also use the laser to manipulate the quantum state.

heather

21:29

Oh, I read about this! The laser excites the atom to a higher state (more to a 1) right?

DanielSank

It actually works! The approach there is essentially to start with something very, very coherent (the atoms) and force them to interact using insanely strong electromagnetic fields (the laser) and very close distances.

@heather Yeah.

heather

What is wrong with doing that? Or is it just that there is a better way?

DanielSank

That approach works pretty ok, but they're sort of stuck because they can't get 2D arrays of ions to work.

They've only done 1D chains of ions and that limits the performance of the "computer" severely.

The Nobel was given to Dave Wineland a couple years ago (or last year?). He's a big figure in trapped ions.

heather

2D arrays of ions? Does that mean the ions can only be in a line instead of a grid?

And if so, why is that true? Is it because of the electromagnetic fields?

DanielSank

@heather Yes.

@heather Yeah, more or less.

The engineering challenge of getting ions trapped in a 2D grid is very hard.

So hard that the field of trapped ions is sort of stuck.

heather

21:32

That makes sense.

But how does the 1D thing limit the performance of the computer?

DanielSank

This is an important note: much of real life experimental physics is decided by engineering capabilities.

What can and cannot be built in the lab by the people in that lab is very important. It's important for physicists, both theorists and experimentalists, to understand what can be built, and for experimentalists to train hard in good building skills.

@heather Well, consider a normal computer. Suppose your computer program says this:

x = 4
y = 1
z = x + y

Suppose x and y happen to be stored in parts of memory that are physically very far away.

heather

Sure.

DanielSank

In a normal computer, we just run wires to ship the data around.

In a 1D chain of qubits, that's not so easy :)

So now you can't do certain logic operations easily.

You have to do all kinds of intermediate steps to do what would otherwise be a simple operation.

It turns out that this is a very big problem when it comes to error correction.

You see, no quantum system remains coherent forever. There's always a limit.

We don't hope to get that limit high enough that all the qubits are coherent for the duration of an algorithm.

Instead, it turns out that you can do error correction on quantum systems, so we need to get the coherence high enough to make error correction work.

heather

And the coherence can be lower for error correction?

DanielSank

In 1D, the operations needed for error correction are too slow to work. In 2D the requirements are vastly easier to satisfy.

heather

21:37

Oh, that makes sense.

DanielSank

@heather Yeah. You can do a round of error correction way faster than you can do an entire computational algorithm.

heather

But how exactly does error correction work? Does it "recognize" decoherence and get the calculation back on track?

DanielSank

@heather Yes.

heather

How in the universe...? Okay, that's cool.

DanielSank

The details require a bit of mathematics that you probably don't know yet (and you have to know quantum mechanics), but that's the basic idea.

heather

21:38

Okay.

DanielSank

@heather Yes it is. It's actually totally amazing that quantum error correction is even possible.

It's a relatively new discovery, actually.

heather

A lot of quantum computing is amazing. =) I bet the person who discovered quantum error correction got the Nobel prize!

Shing

This question may be a bit dumb, but what exactly is the problem with a path-dependent potential? I am not quite sure about this one, I think besides it will be a mutlivalued function, maybe things are just too complicated if you are dealing with a path dependent potential.

DanielSank

@heather I don't think so.

I think the first quantum error correction code might have been from Peter Shor. Lemme check.

heather

Wikipedia seems to suggest it was Shor.

DanielSank

21:41

@heather I see the article, but where does it give the chronology?

heather

@DanielSank, at the bottom it says Models, and it lists Shor's first, and the rest improve on his (for example, the second one uses 7 qubits instead of 9) which suggests that his was first. Of course, I'm not sure.

DanielSank

ah

Secret

Well I guess for starters is that such potential will be defined by an integral
$$\Phi(\mathcal{C})=\int_{\mathcal{C}}\textrm{blahblahblah} d\mu$$ thus doing calculus on it will automatically be functional calculus stuff, which is a lot less straightforward than the usual calculus as the whole path have to be taken account of in order to define the potential

DanielSank

@Secret What does a path dependent potential mean?

I guess I'm asking: how do you define "potential"?

@heather any idea when you'll be in CA?

heather

@DanielSank, unfortunately not yet.

Shing

21:44

@DanielSank it can mean any normal electric potential under a changing electric field.

heather

My parents were trying to figure that out the other night.

Secret

It basically will mean that the value of $\Phi$ will be determined by the set of points in a path in some kind of state space. I think Feymann path integrals has a similar logic

Shing

which depends on path

or a magnetic scalar potential

heather

@DanielSank, I'll keep reading about quantum error correction. So lasers/trapped ions don't work currently. What are the other options?

DanielSank

So you're defining potential as the integral, along a curve, of the electric field?

@heather Well, what do you mean by "work"?

Nobody has built a fully functioning quantum computer in any physical system.

user218912

21:46

idk if I want to be a theorist because there is just too much to learn...

DanielSank

(Caveat: I'm only talking about gate-based quantum computing, i.e. not quantum annealers)

heather

@DanielSank, perhaps by that I mean it is hard to improve upon the current system to get to a fully functioning computer.

DanielSank

@bl00 There's a lot to learn in experiment too, bro.

2

user218912

@DanielSank xD

DanielSank

@heather Yeah, it's hard, but note that folks are working on it.

Secret

21:47

NB googling "path dependent potentials" found a bunch of interesting papers related to feymann integral stuff. I am guessing such potential is the norm in QFT

DanielSank

The "big players" are:
1) Trapped ions
2) Electron spins in silicon crystals
3) Superconducting circuits (my lab)
4) photons

heather

@DanielSank, okay. So currently it is an engineering problem, but it still could be solved such that 2D arrays are possible?

DanielSank

@heather yeah, it's really hard but I'm not ready to say they'll never get it to work.

heather

@DanielSank, okay. Sounds like I have a lot of reading to do about all the different methods. =)

Secret

Anyway, I need to sleep now cause its 8:48 am in my place. Really hate Aust timezones so out of alignment with the northern hemisphere

DanielSank

21:50

@heather I wouldn't even know what to say you should read.

heather

The google will help me. =)

DanielSank

If you find good stuff, please let me know.

Oh actually, you know what you could try? Chapter 1 of my thesis.

web.physics.ucsb.edu/~martinisgroup/theses/Sank2014.pdf

A few non-scientists told me they found the first chapter good at explaining the basics.

heather

@DanielSank, okay! One last question: the photon implementation of quantum computing - is that what this is talking about?

Or is that something different?

DanielSank

yeah, basically

That approach is really, really, really hard.

They have super awesome coherence but doing logic is dang near impossible.

heather

Doing computations with light doesn't exactly sound simple.

DanielSank

21:54

@heather It's not. Photons really don't like to interact with one another.

heather

@DanielSank, how exactly do these four approaches compare in terms of success? I mean, what is, for example, the largest number of qubits set up using each method?

DanielSank

Largest number of qubits in gate model quantum computing is probably trapped ions.

If you include quantum annealing, it's superconducting circuits by a huge margin.

heather

Okay, I don't quite understand: what is quantum annealing and how does it differ from quantum computing?

DanielSank

It's a version of quantum computing.

1) Quantum computing = processing information using quantum systems.

2) Gate model quantum computing = doing #1 by making the qubits do logic gates.

3) Quantum annealing = doing #1 by letting a quantum system fall into the ground state, measuring that state, and taking the result as the answer to a minimization problem.

heather

Oh, so 1 is the overarching thing and then 2 and 3 are ways to do that thing. 2 is what uses things like Hadamard gates and CNOT gates, and what we've been talking about.

DanielSank

22:04

Yes.

heather

For quantum annealing, then, would the structure of the information processing be different? Because you don't have a gate changing the bit/qubit state?

DanielSank

@heather Yeah, it's very different.

heather

@DanielSank, oh. Does your lab do both?

DanielSank

@heather Yeah.

heather

Cool!

Huh, I think I'll have to read about quantum annealing - I'm not sure I understand how it works.

DanielSank

22:07

@heather Well, I can explain the basic idea.

Suppose I want to find the values of the variables that minimize this expression:

$$x^2 - 4y - z + 3 xz + 2xy - 3 yz$$

And suppose each of the variables can only be $\pm 1$.

That's an example of a minimization problem.

Many problems can be expressed as minimization problems.

heather

Okay, so it is reducing an expression where the variables can only be $\pm$ a number?

Or is it more general than that?

DanielSank

Not sure what you mean.

We're asking to find the values of the variables that makes the value of the expression as small as possible.

So, you could just try all the possible values of the variables, but that's slow.

heather

But then can't you pick $- \infty$ for each of the variables? Or do you say that the variables can only be $\pm$ a number you pick?

DanielSank

Each variable can only be $\pm 1$.

heather

Oh, okay.

That makes sense.

DanielSank

22:12

Another approach would be to literally build a physical system with three degrees of freedom, $x$, $y$, and $z$, whose energy is given by our expression.

heather

Oh...huh, okay.

DanielSank

Then you'd just let the system fall to its low energy state and measure the values of the parameters.

Done.

However, this doesn't actually work because there can be local minima: arrangements of the system that have lower energy than other nearby arrangements, but which are not actually the lowest overall energy arrangement.

The system can get stuck in those arrangements.

heather

Oh, okay, that makes sense. How do you fix that?

DanielSank

So, "annealing" is where you start the system off in some random arrangement, but at a high temperature. The thermal motion causes the system to bounce around. The idea is that if the system gets stuck in a local minimum, the thermal motion should un-stuck it.

Then you slowly lower the temperature and eventually when the temperature is low enough you should be in the ground state.

heather

Huh, that's cool!

DanielSank

22:15

This has problems too though because thermally escaping a local minimum can be slow.

etc. etc.

Now, "quantum annealing" is actually a misnomer. I'm not going to go into the exact details, but we don't actually change the temperature... we change something else.

Don't worry about it.

heather

Okay. So, what's an example of a problem that can be represented as a minimization problem? Would, say, the traveling salesman problem be a minimization problem?

DanielSank

Anyway, the point of quantum annealing is that quantum tunneling should help your system escape local minima without having to go over the energy barriers.

The system goes through them instead!

heather

Oh, that's so cool!

DanielSank

That's the goal.

There's a company called DWave that is already selling quantum annealers.

However, it remains to be seen whether they actually work better than anything else.

heather

I've read about that. People seem to have rather strong feelings on the subject.

DanielSank

22:17

They're initial idea was that maybe coherence doesn't matter much for quantum annealing, so they built a system with lots and lots of qubits, but they're all very not coherent.

dmckee

It may be worth mentioning that the annealing concept can be added to many (most? nearly all?) MCMC type simulations.

DanielSank

@dmckee Yes, although note that MCMC may not be known to our young participant here.

Shing

@DanielSank yes, in that case

DanielSank

@heather Indeed they do.

I have to go do some house work, @heather. This was fun. I'm always happy to chat.

heather

@DanielSank, thanks so much for all your help! This conversation was quite enlightening.

dmckee

22:19

@DanielSank I'm trying to figure how to explain it in a few words. I mean "step-wise random exploration of the configuration space" is accurate but perhaps not very clear.

DanielSank

@dmckee Sounds clear to me :P

I joke.

heather

@dmckee, google tells me that MCMC is the Markov Chain Monte Carlo. Is that right?

dmckee

Yeah. That.

The Metropolis-Hastings algorithm is very common in nuclear and particle applications.

heather

Oh geesh. I've clicked through three times (Markov chain, stochastic process, markov property) and I still have no idea what in the universe it is talking about.

DanielSank

Hey @heather, where are you in math?

dmckee

22:21

You sample the system at under some configuration then use random numbers to pick a new place "near by" to sample again.

heather

@DanielSank, I've taken Algebra I, I'm in the middle of geometry, and I have taught myself some basic linear algebra.

And I'm starting to teach myself trigonometry.

dmckee

Deciding how to choose the steps and when to take or reject the steps is where all the fun happens.

heather

@dmckee, so it is sort of like having a function, and then picking a random x, and seeing what the y is, and then picking another random x to get another random y?

Or do I misunderstand the "under some configuration" part?

dmckee

@heather Exactly. And you are trying to find the ;largest value of the function in some range.

DanielSank

or smallest.

dmckee

22:24

Only the function is too complicated to just use calculus and the range is too big to just try "all" possible options.

DanielSank

Doesn't matter, obviously, because you can just put a minus sign in front of the function.

heather

@dmckee, so it is like the opposite of the minimization problem (unless you use the minus sign in front of the function).

dmckee

@heather Well, Metropolis is usually conceived in terms of maximization, but the process doesn't care what kind of extreme you are looking for.

heather

Huh, that's really cool. So it can be used to solve problems as well? How is it run on a computer?

dmckee

In the real problem the function depends on many variable $f = f(x,y,z,w,u,v,s,t,p,r,q,...)$ and may take quite a lot of (classical) processing to evaluate.

heather

22:27

And I assume this is where quantum annealing comes in?

dmckee

Traditionally these problems have been hand coded, but there are frameworks to make that faster and easier than writing it from scratch.

@heather Well, it is where any kind of simulated annealing comes in. The quantum bit is expected (hoped?) to make it faster.

heather

@dmckee, oh! I didn't realize you could do it on classical computers as well.

How do you favorite a conversation?

dmckee

@heather Don't know if you can. You can get a link for any single message from the pop-up menu on the far left. Then save that somewhere, I guess.

heather

@dmckee, oh, okay. I thought I read somewhere you can favorite conversations.

dmckee

You can star messages, but the star-board on the right is transient. Thew value of stars fades over time.

Shing

22:51

I can't believe I got 3 downvoters (I think) in my answer:
http://physics.stackexchange.com/questions/286616/is-there-a-ball-that-bounces-higher-past-the-point-that-it-is-dropped/286620#286620

Some ppl don't have childhood with playing balls, I guess.

dmckee

@Shing It's much more fun with at least three balls. I've seen it down with a basketball, volleyball and tennis ball and the last one dinged off the 28 ft ceiling of the lecture hall and nearly beaned a student in the front row.

Good times, that.

Shing

@dmckee wow

never tried that

I am going to try it, thanks for telling me

dmckee

It takes some practice to keep them stacked and let them go just so, but the result is worth it.

DanielSank

@heather You can bookmark conversations!

The interface for doing it is confusing though.

@dmckee @heather I bookmarked our conversation. Here's the link.

To create a bookmark, go here, and click on "view transcript". You can navigate the chat log by day and time. There's a button on the right for making bookmarks.

Here are all of hbar's bookmarked conversations

Shing

23:08

h bar is a great place for discussion. I learned a lot of things here

dmckee

@DanielSank Shows you what I know.

Sheesh!

DanielSank

@dmckee I learned about this very recently.

I mean... who looks at the transcript page?!

heather

@DanielSank, oh, thanks!

Good to know.

Transcript for