> On 22 Aug 2018, at 05:05, Bruce Kellett <[email protected]> wrote: > > From: Jason Resch <[email protected] <mailto:[email protected]>> >> >> On Tue, Aug 21, 2018 at 7:43 PM Brent Meeker <[email protected] >> <mailto:[email protected]>> wrote: >> >> >> On 8/21/2018 3:37 PM, Jason Resch wrote: >>> >>> >>> On Tue, Aug 21, 2018 at 5:00 PM Brent Meeker <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> >>> On 8/21/2018 2:40 PM, [email protected] >>> <mailto:[email protected]> wrote: >>>> >>>> If I start a 200 qubit quantum computer at time = 0, and 100 microseconds >>>> later it has produced a result that required going through 2^200 = 1.6 x >>>> 10^60 = states (more states than is possible for 200 things to go through >>>> in 100 microseconds even if they changed their state every Plank time >>>> (5.39121 x 10^-44 seconds), then physically speaking it *must* have been >>>> simultaneous. I don't see any other way to explain this result. How can >>>> 200 things explore 10^60 states in 10^-4 seconds, when a Plank time is >>>> 5.39 x 10^-44 seconds? >>> >>> It's no more impressive numerically than an electron wave function picking >>> out one of 10^30 silver halide molecules on a photographic plate to >>> interact with (which is also non-local, aka simultaneous). >>> >>> >>> Well consider the 1000 qubit quantum computer. This is a 1 followed by 301 >>> zeros. >> >> What is "this". It's the number possible phase relations between the 1000 >> qubits. If we send a 1000 electrons toward our photographic plate through a >> 1000 holes the Schrodinger wave function approaching the photographic plate >> then also has 1e301 different phase relations. The difference is only that >> we don't control them so as to cancel out "wrong answers". >> >> >> >> The reason I think the quantum computer example is important to consider is >> because when we control them to produce a useful result, it becomes that >> much harder to deny the reality and significance of the intermediate states. >> For instance, we can verify the result of a Shor calculation for the >> factorization of a large prime. > > Someone else is interested in factorizing primes?
The hackers and the military. All bank account are crypto encoded using (big) prime multiplication. Bt I think that today we have just been able to factor 15 (= 3 x 5) using Shortchanged quantum algorithm. The still requires 2^16 “parallel worlds”. > >> We can't so easily verify the statistics of the 1e301 phase relations are >> what they should be. >> >>> This is not only over a googol^2 times the number of silver halide >>> molecules in your plate, but more than a googol times the 10^80 atoms in >>> the observable universe. >>> >>> What is it, in your mind, that is able to track and consistently compute >>> over these 10^301 states, in this system composed of only 1000 atoms? >>> >> >> >> Are you aware of anything other than many-worlds view that can account for >> this? > > Yes. > >>> Also note that you can only read off 200bits of information (c.f. Holevo's >>> theorem). >>> >>> >>> True, but that is irrelevant to the number of intermediate states necessary >>> for the computation that is performed to arrive at the final and correct >>> answer. >> >> But you have to put in 2^200 complex numbers to initiate your qubits. So >> you're putting in a lot more information than you're getting out. >> >> You just initialize each of the 200 qubits to be in a superposition. >> >> Those "intermediate states" are just interference patterns in the computer, >> not some inter-dimensional information flow. >> >> What is interference, but information flow between different parts of the >> wave function: other "branches" of the superposition making their presence >> known to us by causing different outcomes to manifest in our own branch. > > The superposition exists in our branch. ? > >> Also, many quantum algorithms only give you an answer that is probably >> correct. So you have to run it multiple times to have confidence in the >> result. >> >> I would say it depends on the algorithm and the precision of the measurement >> and construction of the computer. If your algorithm computes the square of >> a randomly initialized set of qubits, then the only answer you should get >> (assuming perfect construction of the quantum computer) after measurement >> will be a perfect square. >> >> >> Quantum computers will certainly impact cryptography where there's heavy >> reliance on factoring primes and discrete logarithms. They should be able >> to solve protein folding and similar problems that are out of reach of >> classical computers. But they're not a magic bullet. Most problems will >> still be solved faster by conventional von Neumann computers or by >> specialized neural nets. One reason is that even though a quantum algorithm >> is faster in the limit of large problem size, it may still be slower for the >> problem size of interest. It's the same problem that shows up in classical >> algorithms; for example the Coppersmith-Winograd algorithm for matrix >> multiplication takes O(n^2.375) compared to the Strassen O(n^2.807) but it >> is never used because it is only faster for matrices too large to be >> processed in existing computers. >> >> So where do you stand concerning the reality of the immense number of >> intermediate states the qubits are in before measured? > > Brent can answer for himself. But from my point of view the idea that the > quantum computer works by doing a large number of classical computations in > parallel in different "universes" is overly naĩve. Shor's algortithm centres > on a fast Fourier transform implemented by interference; it certainly doesn't > simply calculate all classical possibilities directly in parallel. We can doubt this because some Fourier transforms will need the result of the interference of different computations in each “branch”. Bruno > > Bruce > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] > <mailto:[email protected]>. > To post to this group, send email to [email protected] > <mailto:[email protected]>. > Visit this group at https://groups.google.com/group/everything-list > <https://groups.google.com/group/everything-list>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
