Category Archives: Events

Notes on “The Limits of Knowledge…”

I went to a talk at The Simons Center for Geometry at Stonybrook today, given by Michael H. Freedman from Station Q, Microsoft Research.

The talk was titled: The Limits of Knowledge: The Philosophical & Practical aspects of Building a Quantum Computer”. It was quite an ambitious topic, and right away it took off in an unexpected direction, with the speaker announcing he intended to interweave Philosophy and Math/Physics using an unexpected analogy between Catholicism & Math/Physics. Everyone raised an eyebrow at this, but the analogy made sense: both are long term institutions and deal with difficult idea’s on the long timescale. He focused on the  difficult ideas aspect and narrowed the analogy down to four ideas:

Omniscience >> P/NP
Original Sin >> Universality
Redemption >> Quantum Mechanics
Unicity >> Free Will

From those four ideas he moved on to idea’s about scaling. Like universality, things viewed from 10 feet away and 10 nanometers away, often look like the same thing. His slide photos showed the Mandlebrot set, which reminded me of Mandlebrot’s book, where the coast of England and the contours of a pebble from the coast of England are compared with each other. (They look the same)

Quantum Computing is between Physics, Computer Science and Math. and there are some problems we are trying to solve, and some problems we can solve. They go in order of difficulty: Pspace >>>> Q >> NP >> P ,right now we can solve P and in a short amount of time. NP we can solve but it takes quite a lot of time (work?). Q we hope to be able to solve using Quantum Computing technology, which obeys different scaling laws.

Now, for a brief bit on the history of computers. Classical computers are all Turing machines, they can handle P and sometimes NP.  At the most, all we will ever know (compute) is in the Q region of problems. (unless possibly in a different universe where NP-complete could be solved efficiently…)

So, what is the special thing about QC which lets us move into the Q region of problems? Here the speaker was quite dramatic, and said he could tell us why in one word. “Superposition”. But he then went on to note, that this doesn’t really mean much unless you understand the idea of superposition.

Nature likes square roots of probabilities (Like the double slit experiment)
We observe | a + b | but we expected to see |a|^2 + |b|^2 Why is this? Shor’s algorithm is like the double slit experiment, where useless paths cancel out. There is a classical aspect and quantum aspect to Shor’s algorithm. The quantum mechanical aspect allows for a Fourier Transformation to k space, making it much easier to find the period. (Which is used in factoring)

Some of the things a Quantum Computer could do: Physics! Things like: Strongly correlated electron systems, High temperature superconductors, 2 dimension electron gasses (2 DEG), Exotic magnets (condensed matter), Sample google large linear equation sets, Drug design and AI.

How are we going to get these computers? (An excellent question was asked after the talk too, If we do get them and have no classical means of solving the problem, how will we know the QM computer is actually solving it?) One of the ways to get it is by using Topology, which has to do with the math of strings and braids (ironic, that the only math class I’ve taken on this was at FIT, because supposedly art students love topology…) The topological approach avoids using the physically provided degrees of freedom, and instead works to touch all the degrees at once, (Need 2DEG for this) the eventual goal is to get some Majorana Fermions (MJ’s?) localized in “vortices”. I’m not too sure what MJ’s are exactly, or if that is the actual goal..

MJ’s allow for huge, but still finite blackboards of Hilbert space. I think the Fractional Quantum Hall Effect has something to do here too… Maybe MJ’s are Quantum Hall States?

Fractional Quantum Hall Effect is topological, meaning distance plays a limited role in them.

There was a picture of four dots, and how when you connect two at a time over time, it forms a braid like pattern. I drew it in my notebook.

And near the end was a slide of man’s toolbox it went:
Fire > Number > Machine > Decimal > Computer > Nuclear > Biology > Quantum Computer

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Modes – LTC Visit

  Today I stopped by the LTC and Dr Noe was explaining to me how a laser works by reflecting light back and forth between two mirrors, one which is 1% transparent which is where the visible laser beam emerges from.

This lead to a plot showing the gain vs the frequency, and Dr Noe was talking about the modes of the laser. I had not heard of modes before, and wanted to know more about them. So the length of the gas filled tube between the two mirrors is equal to the number of Nodes times the wavelength divided by two.

Inside the Gain vs Frequency plot, the frequencies are really only amplified at a few specific frequencies (which are somewhat distributed (fuzzy?) because of the Doppler shift). Those amplified frequencies are the modes of the Laser. I think the change in frequency between each mode was this Very Important Formula: Delta f = c/2L

We also looked at an open cavity laser (Neon Hydrogen! it’s spectrum was huge), so I could see how the light bounced back and forth from the gas between the two mirrors. We looked at the Temporal (Length / Longitudal) and the Spatial Mode (HG Mode).

Modes are a set of numbered solution functions.

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Quantum Interferometric Sensors – talk by Prof Jonathan Dowling

The talk began with a diagram, of three overlapping circles, Quantum Information, Quantum Computing and Quantum Imaging. Sitting in the overlapping point of the three circles was where we were going to be for this talk, and the whole diagram made up a large outer circle Quantum Metrology. (I thought that is the science of predicting the weather?)

At first the speaker was talking about funding for Quantum computing and how it has started to decrease as the focus narrows, meaning at first there were all sorts of ideas but now that there is a better idea of what works, the focus and funding has narrowed. He talked about the idea’s which have seen a decrease, and one of them what Single photon circuits, which was quite startling to me. He also said they (DARPA?) are aiming for 2020 hardware for quantum computing.

Then a bit about a quantum internet, and how Quantum repeaters would be needed to see this happen…

In general though the point seemed to be that by using ideas fro Quantum computing and Quantum Imaging it is possible to build better measuring devices, which do not suffer from as much loss. There is quite a lot to understand. Things to read about:

– Parity measurement (Is this Modulo?)
– exp ( ) Notation
– an exponent that looks like a small cross
– Optical Tables
– Post Selection
– Kerr Material
– "Projective measurements yields effective Kerr"
– Ancillas
– Vortex
– OAM Beam (did I hear this right?)

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Non-Equilibrium Statistical Mechanics talk

Today I attended a seminar on a Variational approach to Non-Equilibrium Statistical mechanics. (Maximum Caliber) It was quite a popular presentation. The speaker was talking about his new method for calculating small number problems, which are like when you are trying to find an average, so you look at the first case, and see it is one answer. So for that first case all you know is that the first case is one answer.

He briefly gave an example of a single cell about to evolve and choose the left path or the right path. It’s only a little length of the path, but the decision to go left or right makes a very big deal.

It touched on Risk Analysis for stocks too, just like the Barra system I’ve been using at work. If you think of your stocks as a horse race, at first all of the horses are in the gate, then the gate opens and the horses take off running. Some are a little behind and some are a little ahead.

It reminded me of the book I read about Evolution (well really it was on economics, but it was on the evolution of economic systems… I need to find the book again)

There was also talk of Maxwell’s Demon’s.

I was pondering why I seem to be writing more handwritten notes and why the difference between learning by hand and by machine. I tend to not need to think the speech in my head but as I write by hand but by keyboard the words are clearly visible. This same feature exists for writing in code and for writing by hand. But at times when writing by code on keyboards the thought are no longer in English. This is why when I write code by hand it is hard and sometimes when I write physics by computer it is harder. Because for code it goes to pure code when I am translating through a keyboard and for physics it goes to pure symbol when writing by hand.  And as always with any type of writing eventually it is no longer speech and I can transition to pure symbolic calculations. That’s when I’ve learned to do things “In my head”.

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Quark gluon plasma and gauge/gravity duality

The talk started out on viscosity of fluids, like when a plate is sliding across a fluid spread across a stationary plate. There was a graphic showing how the fluid formed a ‘gradient’ as the top layer of fluid had to move faster to keep up with the top plate, while the bottom fluid did not really want to move, but eventually the top fluid managed to drag it along.

Then this moved into the viscosity of gases, and eventually arrived at Maxwell’s formula for viscosity of dilute gas and how pressure of the gas does not matter. There was a quick aside as the speaker mentioned how Robert Boyle might have conducted an experiment along the same lines, using a pendulum suspended inside of a vacuum, where despite changes in pressure no visible difference in the swing of the pendulum could be detected. Robert Boyle also thought to do other things, like stick a butterfly into the vacuum jar and see what happened…


The reason for the viscosity of dilute gas not being affected by pressure had to do with “mass density” (I think). So even though the gas is more spread out the speeds it is bouncing around at increase. (I think).

This was just the introduction. Then discussion moved onto Quantum Cromo Dynamics, lots of phase diagrams and energy density / c2. And c in this case is something like mass density in the general description of viscosity.

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Holographic Superfluidity and Superconductivity

I went to a talk today in the Physics department. It is interesting in that I did not understand most of it, but at the same time I felt like I will be able to understand it eventually. Also, someone asked: “What dimension are we in?” Answer: Just 3 + 1

So, here are the interesting terms I heard today. I’ll need to investigate these further. Perhaps they will make good train reading.

  • QCP – Quantum Critical Point
  • QPT – Quantum Phase Transition
  • Ads/CFT
  • Nerst effect
  • dyonic black hole
  • cyclotron resonance
  • Lorenzen (sp?) z=1
  • phenomenological – Need a dictionary for this
  • quiver: L263 (Included a neat picture)
  • gluino field
  • Holographic Phase Transition
  • charged scalar field
  • abelion gauge field
  • tachyonic
  • BPS bound
  • modulus

I better take a few chemistry classes too or at least read a few textbooks.

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