6,004 reputation
1641
bio website jfitzsimons.org
location Singapore, Singapore
age 32
visits member for 3 years, 5 months
seen Dec 6 '13 at 16:11

I have just moved to the Center for Quantum Technologies in Singapore, after spending the last 3 years as a Merton College JRF in Theoretical Physics and a Senior Research Fellow in Oxford University Department of Materials. My research focuses largely on theoretical aspects of quantum information processing. In particular I am interested in spin networks, measurement based computation, cryptography and computational complexity.


Nov
18
comment Home experiments to derive the speed of light?
@Frédéric: I'm not sure you can simply take the difference of two times in traceroute. It neglects the processing overhead which may be substantially different at each node.
Nov
18
comment Home experiments to derive the speed of light?
@Frédéric: Yes, I guessed it wouldn't be much. I just can't figure out where he got the numbers from.
Nov
18
comment Home experiments to derive the speed of light?
@sigoldberg1: The speed of light is approximately $3\times 10^8 m s^{-1}$. Thus it takes only $10^{-7} s$ to travel through 30m, unless the speed is orders of magnitude lower in the fiber. This is 100 nanoseconds, not 10 microseconds. For a 10 microsecond delay you need 3km.
Nov
12
comment Home experiments to derive the speed of light?
Well, I don't know about you, but I don't have 30000 km of optical fiber in my kitchen cabinets.
Nov
12
comment Home experiments to derive the speed of light?
Even if you used the retroreflector left on the moon (which is never more than 406000 km from us, the time delay between sending and recieving a reflected signal is only a little over a second. For a signal bounced off the ISS (assuming you could even achieve this) the time delay would be roughly 1ms. It would be extremely hard to measure this accurately using 'common household tools', not to mention the difficulty of actually distinguishing the signal from the background noise.
Nov
12
comment Home experiments to derive the speed of light?
Yes. Fortunately it is usually written on them.
Nov
11
comment Physics and Computer Science
I'm not so sure about this. It is not particularly hard to learn the background for an undergrad course, even if it is not particularly in your area, provided you have a sufficiently numerate background.
Nov
9
comment The Many Body problem
@Noldorin: Thanks. I only know this stuff because I have spent quite a while working in this exact field. By the way,ground states are to some extent less relevant because the systems for which is is computationally hard to calculate the ground state of (at least on a QC) don't cool efficiently either.
Nov
8
comment Home experiments to derive the speed of light?
Damn, beat me to it! I must have been typing my answer when you posted this.
Nov
8
comment Physics and Computer Science
Physicists usually use mathematical equations to model the world, not algorithms. This is not the same thing as algorithms, and indeed the existence of an algorithm to solve these systems of equations is not a prerequisite.
Nov
8
comment The Many Body problem
@Tobias: Simulation of either is at least BQP-complete, so it makes little difference which you use.
Nov
8
comment Velocity of Object from electromagnetic field
I believe the fastest rail gun speed achieved is about 10 km/s. I don't, however, understand why you have given a magnetic field strength as an EMF. The units simply don't make sense. Even if they did, this is simply not enough information. Is the projectile charged, magnetic, etc? The maximum velocity will be limited by conservation of energy as already pointed out, but without knowing how the system you have in mind works, we have no way to calculate the initial potential energy and any driving force etc.
Nov
8
comment Physics and Computer Science
So, why are people voting to close without leaving a comment?
Nov
8
comment Physics and Computer Science
Actually, the courses you end up teaching are often not entirely dependent on your expertise. More often it is a case of what courses need teaching when you join the department.
Nov
7
comment Why can't the outcome of a QM measurement be calculated a-priori?
There have been a lot of papers written on this, but they are philosophy not physics. The practical answer is that there are multiple possibilities, and by the pigeon hole principle you must get one of them. For the probabilities, etc., see Everett's thesis or more recent review papers.
Nov
7
comment Why can't the outcome of a QM measurement be calculated a-priori?
@Sklivvz Well, this all depends on interpretations, but sticking with the Everett interpretation it is that we perceive both in different branches of the wave function but each branch is unaware of the other.
Nov
5
comment The Many Body problem
Yes, that is true. Calculating ground states seems to be beyond their reach though.
Nov
5
comment The Many Body problem
It definitely can only make things harder as you can encode a discrete system in the CV but not necessarily the other way around.
Nov
5
comment The Many Body problem
By which I mean the problem with simulating the system, not a problem with your answer.
Nov
5
comment The Many Body problem
The problem here, of course, is that the field modes are continuous variables.