Throughout my physics career including PhD, analog electronics was the most difficult but probably also the most rewarding class to me. I fondly remember staying until 2am in broida at ucsb trying to get a filter to work, getting a few hours sleep, then being back in the lab before sunrise. Of course, this was mostly the result of procrastination, but damn were those good times.
One thing that really bothered me then was the idea of a current source. I was perfectly happy with a voltage source, perhaps naively(1). But a current source seemed magical. I was asking Martinis about this and he seemed dumbfounded that I didn't understand. Of course, the answer is feedback. And, of course, good voltage sources also require feedback. But he was so familiar with feedback control he didn't even consider saying that's whats happening, while I never even heard of controls.
Long story short, sometime later I asked to join his lab as an undergrad researcher. He said no, and to this day I think it's because I didn't understand current sources. Or maybe I was too late, or maybe the A- (see the aforementioned procrastination). That led me to asking a biophysicist, and therefore I became a biophysicist instead of condensed matter/QI/QC. In hindsight, I think this was fortunate. I would've never considered biophysics, which has been one of the loves of my life since then. Who knows, maybe I would've been just as happy with quantum stuff. I'm working through Mike and ike now and find it fascinating.
Funny enough, after my PhD, I co-founded a startup in industrial control & automation. Now I understand feedback quite while, and thus current sources, albeit many years too late.
(1) Of course, good voltage sources vary their resistance just like good current sources vary their voltage. My best guess as to the reason I was more bothered by the current sources is that I was so familiar with voltage sources with confidently claimed constant voltages (batteries). Not a very good reason, I should've questioned it more. In practice, it's much easier to make a near ideal voltage source (very high resistance) than a near ideal current source (0 resistance).
Did you mean to say "good voltage sources vary their current just like good current sources vary their voltage"?
(I know nobody really cares, and I promise I'll seek help for whatever neurological condition I seem to have.)
Or that might have just been a mistake.
Edit- I just looked up switching power supplies and remembered that I did actually know about those!
For a design without feedback, and in an energetically inefficient way, maybe this can work too:
1. Determine what will be the maximum resistance of the "current consumer" part of your circuit throughout its operation.
2. Prepare a resistor several magnitudes larger than the resistance above.
3. Connect to the resistor above a (huge) voltage source so that the resulting current is the one you target for your current source
4. Put the "current consumer" part of your circuit in series with the large resistor.
On the other hand that circuit is very easy to understand and build and test.
Both Devoret and Martinis are also highly involved in pushing quantum engineering to new levels - Devoret at Google Quantum AI and Martinis (formerly at Google) with his company, Qolab.
Coincidentally, I have a close friend doing his PhD with Devoret and know someone working with Martinis. I am curious to see if they will ever see their respective supervisors again, given that the Nobel Prize attention will likely garner them countless invitations for talks and keynotes...
The prize rules stipulate that they need to hold one lecture related to their winning topic with the institution that picked the winner within 6 months.
Iirc the 2024 physics prize lecture (on the roots of neural networks) was held in the days just before the prize giving ceremony and can be watched on the Swedish broadcasters "education" channel as well as youtube.
https://urplay.se/program/239905-nobelforelasningar-2024-geo...
"We know that the ball will bounce back every time it is thrown at a wall. A single particle, however, will sometimes pass straight through an equivalent barrier in its microscopic world and appear on the other side. This quantum mechanical phenomenon is called tunnelling."
Is the particle just failing to collide with the wall since objects are mostly empty space? Or is something more spooky or interesting happening?
The idea that a particle could pass through a wall by luckily avoiding collisions is a classical way of thinking. In that view, a particle is a tiny solid ball and a wall is just a collection of other tiny balls with space between them.
Quantum tunneling is based on a completely different concept. In quantum mechanics, the "wall" is not a physical object but a high energy barrier. Classically, a particle cannot be in a region if it doesn't have enough energy to overcome that barrier (this is why people often use the idea of a high wall and a ball that cannot make it over the wall). However, quantum mechanics treats particles as having wave-like properties. This wave is related to the probability of finding the particle at any given location. While the probability of finding the particle inside the high-energy barrier is very low, it is not zero. The wave's amplitude shrinks inside the barrier, but a small portion of it extends to the other side. This means there is a small but finite probability that if you measure the particle's position, you will find it on the other side. When that happens, we say the particle has "tunneled" through.
The surprising success of the experiments that led to the Nobel Prize today is that it wasn’t just a single particle (like an electron) that they measured tunneling through a barrier, it was a macroscopic group of particles. These particles were able to tunnel through the barrier because they were kept in a coherent state that allowed them to have a wave function that coherently extended through the barrier. This meant that they had a reasonable finite amplitude on the other side of the barrier so that a measurement could show that they tunneled through the barrier.
And, if so, is there then actually a practical difference between the classical and quantum interpretations? (i.e. could it simply be said that, the denser wall just has more chances to collide with the particle and stop it from passing through, thus explaining why the probability of finding it on the other side is lower?)
Have you heard of Schrodinger's cat, which is hypothetically dead and alive at the same time? Schrodinger described this thought experiment to argue that quantum mechanics led to absurdities if you took it too far. Ironically, many physicists now believe that such an experiment is possible in principle, though it would be extremely difficult.
But you should not really think of a physical wall in this case. The experiments that have proven the macroscopic tunneling behave according to the same exact math, but nothing is really tunneling through macroscopic walls. The cooper pair electrons are, but that’s a different Nobel prize (Josephson, 1973).
The real limit is not based on the size or number of particles, but on the coherence of the group of particles. Using the word coherence is probably not helpful without context, so let me give a quick explanation of what that means.
As I mentioned in my answer above, particles can exhibit wave-like properties. A group of particles will each have their own wave packet. In our everyday lives, two particles, even those right next to each other, are jiggling around randomly due to temperature and experiencing slightly different environments. You can think of each of these separate random jiggles as a measurement that collapses the wave function of that particle. Then, after the particle's wave function collapses, it begins to evolve again until the next measurement. As a side note, saying a measurement collapses the wave function is quantum mechanics talk for the observed reality that when we measure where a particle is, we do not find a wave, we find a particle. So, the shorthand for this view of quantum mechanics is that a measurement collapses the wave function.
Ok, so now we have a bunch of particles, like a chair. Why won't a chair tunnel through a wall? Well, all the particles that make up the chair are not just physically separated, but they are jiggling due to their temperature and their slightly different environments. So, all of these particles that make up the chair keep having their wave function collapsed randomly. The chance of one particle tunneling through the wall is small. The chance of all 10^27 particles in the chair independently tunneling through the barrier at once is not going to happen before the universe ends.
Back to coherence. All of these particles of the chair are independently jiggling around, and each one has its own wave function collapsed very quickly. For this reason, you can treat each particle as an independent particle. We would say the wave functions of these particles are not coherent with each other.
Now, imagine that we have two particles right next to each other. At room temperature, they are constantly jiggling and having their wave functions collapsed. If we cool them down to reduce the jiggling, and they are close enough to each other, their respective wave functions can start to overlap. When the jiggling of the particles is small enough and their wave functions overlap sufficiently, they begin to behave as a single quantum entity. This is a coherent state. In a suitably constructed experiment, these coherent particles can then exhibit quantum behaviors such as tunneling together.
Back to your question: is there some maximum size for a group of particles that could be forced to maintain the correct state to pass through the wall? Since the group of particles must be in a coherent quantum state to tunnel, the real question is how big of a group can be put into such a state. You have to cool them to slow the jiggling, isolate them from anything in the environment that might collapse their wave functions, and get them close enough together for their wave functions to overlap. There is likely a theoretical limit that could be calculated, but as a practical matter, extraordinary engineering efforts are required to get even a very small group of particles into a coherent quantum state. The direct answer to your question is that while there may be a theoretical maximum possible size of a coherent state for our universe, the real limit is set by the immense practical challenges of creating and maintaining a coherent state. This is what makes the work of this year’s Nobel Prize winners so impressive.
It so happens that when you solve for this problem, a ball bouncing against a wall, in this wave function paradigm then you end up with a non-zero probability that the ball appears on the other side of the wall.
I'm not sure if there is a deeper explanation at play here but that's how I understand it.
The Paris-Sud University was a new name to me. Apparently, this will be the 4th Nobel laureate associated with the university.
So it's hard to have a good grasp.
I'm pretty sure this is true in the US, too. Maybe we're just a little more delusional about it here.
Amazing professors, great students to prof ratio, professors were in their offices all the time and happy to see students. The night before final labs were due profs would be up helping students debug problems.
Only 2 courses I took there even had TAs. Work was typically hand graded by professors as soon as you passed the first intro to course, and quite a few of the intro courses were fully taught by professors as well.
Does my school have any good research coming out of it? Not really. Not the point. It has a bunch of professors who are there because they want to teach, and it has a bunch of students who are getting to benefit from those professors.
https://pmc.ncbi.nlm.nih.gov/articles/PMC431568/
>Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems [2007]
https://www.nature.com/articles/nature05678
>Explaining the Efficiency of Photosynthesis: Quantum Uncertainty or Classical Vibrations? [2022]
https://pubs.acs.org/doi/10.1021/acs.jpclett.2c00538
>Reassessing the role and lifetime of Qx in the energy transfer dynamics of chlorophyll a [2025]
https://pubs.rsc.org/en/content/articlelanding/2025/sc/d4sc0...
>Full microscopic simulations uncover persistent quantum effects in primary photosynthesis [2025]
Can't help you with "a weird paper on the unexpected efficiency of photosynthesis", try asking a biologist at your local university, or possibly an organic chemist.
Tip: this page links to further reading of older stuff.
hints galore.
Devoret was my co-authors phd advisor (and who is also my advisor now on some of my work).
We sorely need more open quantum systems built/designed with open source tooling. The IBM's, Ionq's, Quantinuum's and Googles, will be happy if we all remain serfs to their multimillion dollar machines and hardware direction.
(Still better than last year's award which wasn't really physics at all!)
https://www.tkm.kit.edu/downloads/TKM1_2011_more_is_differen...
He also won a Nobel by the way.
Many great discoveries follow from new instrumentation leading to better and novel data, and less often some conceptual leap. This is why the genius of Einstein is all the more remarkable in coming up with relativity. Interestingly, he got his Nobel for something else :)
This is a practical implementation of something that was only theoretically possible or observed on very small scale.
There's a tradition of Nobel Prizes awarded for clever experiments, even if they do not uncover new fundamental laws.
Sounds like there was some politics shenanigans between them where Martinis was moved into a useless role and took the hint at the height of covid lockdown.
He kept working on the problem. The question now looking back over 6 years is did Google make a mistake. I've seen this at IBM and other large research divisions where people who did something significant 20 or 30 years in fields like AI become stagnant burning tens and hundreds of millions. There was a political battle and Martinis got pushed out. The question I have is did the people who pushed him out know the path forward in quantum computing or did they just know how to play office politics licking the correct behinds.
[0] https://www.forbes.com/sites/moorinsights/2020/04/30/googles...