Questions concerning computations performed on a quantum-computer. DO NOT USE THIS TAG just because the question concerns a computation of a quantum-system!
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74 views
Is Photonics going to be the next phase in Electronics? Considering the recent Nobel Prize 2012 award for Physics [closed]
Photonics seems to be a rather closed field involving only specialists and experts working on it. Will there be a period which is going to define the power of Photonics in which Electronics is ...
3
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2answers
227 views
Mathematically challenging areas in Quantum information theory and quantum cryptography
I am a physics undergrad and thinking of exploring quantum information theory. I had a look at some books in my college library. What area in QIT, is the most mathematically challenging and rigorous? ...
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1answer
149 views
Will quantum computers ever work? [duplicate]
Possible Duplicate:
Why do some physicists believe that scalable quantum computing is possible?
The idea of a quantum computer is that a quantum system can be in a Quantum Superposition of ...
2
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1answer
91 views
Quantum computers and algorithm performance
I have a question. Gradually quantum computers will emerge someday. So, nowadays making algorithm efficient is important; I mean, making it optimal to run as fast as possible. But once quantum PC ...
4
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2answers
186 views
What is the most natural classical polynomial complexity class that includes all of BQP and NP?
Since we know that there are some oracle problems which can be solved on a quantum computer, but not on an NP machine with the same oracle, the idea of nondeterministic (i.e. infinitely parallel) ...
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3answers
143 views
How can quantum (Internet) network be possible?
According to the knowledge I have, there are routers, switches etc. Therefore, packets would have to be "measured" before continuing on. (If not, how will anyone know the damn IP address?)
But this ...
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1answer
441 views
Does Heisenberg's energy-time uncertainty principle imply that quantum computing is no more efficient than classical computing?
See http://arxiv.org/abs/quant-ph/0006080v1 "On Non Efficiency of Quantum Computer", by Robert Alicki. In this paper, the author argues using Heisenberg's energy-time uncertainty principle, that ...
5
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1answer
281 views
If quantum mechanics is ultimately deterministic, would Shor's factorization algorithm still work for large integers?
Victor Stenger argues that the apparent randomness in quantum mechanics is a result of the randomness in the macroscopic detectors (similar to the randomness in the laws of thermodynamics) and is not ...
3
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1answer
67 views
Does quantum fingerprinting really argue for the exponential size of wavefunctions?
Does quantum fingerprinting really argue for the exponential size of wavefunctions? Quantum fingerprinting is the idea that an exponentially long classical string can be encoded in a linear number of ...
4
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1answer
107 views
Fast algorithm for maximizing the quantum fidelity
Consider the following optimization problem: Given a quantum state $\sigma$, a constant $b$ and a Hermitian operator $A$, find
$\underset{\rho} \max F(\rho,\sigma)$
subject to $\text{Tr}(\rho ...
4
votes
5answers
589 views
Why do some physicists believe that scalable quantum computing is possible?
If you drop a glass cup on the ground, it will break and shatter into pieces. This happens all the time and is consistent with quantum mechanics. But it never happens that a shattered glass cup ...
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3answers
273 views
what breakthrough Physics needs to make quantum computers work?
I read some posts on this forum and some articles which repeatedly state that it is not impossible to build q-comps but to make it successful, physics needs a great breakthrough.
I tried finding but ...
4
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2answers
319 views
Shor's algorithm and Bohmian Mechanics
Do quantum computer's tell us anything about the foundations of quantum theory? In particular Shor argued in the famous thread by 't Hooft
Why do people categorically dismiss some simple quantum ...
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0answers
50 views
Efficiently distinguishing mixed quantum states?
Assume we know two different mixed states, p and q, and an efficient (quantum) algorithm for creating such two. Does it follow that there exists a computationally efficient method/measurement for ...
7
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3answers
2k views
Can a parallel computer simulate a quantum computer? Is BQP inside NP?
If you have an infinite memory infinite processor number classical computer, and you can fork arbitrarily many threads to solve a problem, you have what is called a "nondeterministic" machine. This ...
6
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2answers
319 views
What nonstandard theory forbids quantum computers?
What would a nonstandard model which reproduces all experimental quantum data so far but still cause quantum computers to fail when implementing Shor's algorithm look like? Would it have to be very ...
4
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1answer
228 views
Entanglement of qubits circuit- Bell states
I know that the quantum circuit $\text{CNOT}\; (H \otimes I)$, where $\text{CNOT}$ is the controlled-not gate and $H$ the Hadamard gate, takes the computational basis of two qubits ...
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3answers
371 views
Can I study Quantum Computing or Quantum Mechanics with an Engineering background?
Sir,
I am studying Electrical & Elctronics Engg. now. I wish to pursue Quantum Mechanics or Quantum Computing as my research subject. Is it possible for me to do my M.Tech. & then pursue ...
4
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1answer
252 views
Areas of computer science required for quantum computing
What knowledge of computer science should I have, to be able to pursue research in quantum computing. I am a Physics undergrad and would take three core courses in QM, before the completion of my ...
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1answer
208 views
Existence of quantum computer
At time there are talks about quantum computers and lot of talks and discussion on its exponential speed. But studying in some more details it makes reference to "Heisenberg uncertainty principle", ...
6
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1answer
196 views
Ground state degeneracy of a variation of Toric Code model
We know that the ground state degeneracy of Toric Code model is 4. An easy way of seeing this is the following:
Consider a 2D spin model where all the spins live on the links. The Hamiltonian is ...
5
votes
2answers
485 views
What is “code” in “toric code”?
When I first heard people talking about using Kitaev's toric code to do topological quantum computation, I was thinking how many lines does the toric code have. Then I was told that
the "code" really ...
3
votes
1answer
119 views
How can you distinguish between projections of quantum states?
Consider this problem in quantum cryptography:
We have two pure states $\phi_1,\phi_2$ as input and constants $0 \leq \alpha <\beta \leq 1 $, where "Yes instances" are those for which ...
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0answers
142 views
Quantum Compting or DNA computing [closed]
My friend and me are working on DNA computing and on some improvements to it.
Of course, we are working on computing aspects of this branch. So, we have insufficient knowledge about physics and ...
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0answers
45 views
Commutating Annihilators with a beamsplitter
I am reading Nielsen and Chuang on P. 291, for anyone interested in the origin of my question.
Given an annihilator a and its corresponding creator a_adj such that [a,a_adj] = 1 and another ...
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1answer
52 views
Building some measurement appratus that distinguish between two mixtures
We have a measurement $M$ that distinguishs between $\rho_1$ and $\rho_0$, if it has three possible answers 1,2,3 and whenever it answers something different than 3 it's correct.
$M$ succeeds with ...
6
votes
1answer
159 views
partial trace with sparse matrices
Let $\rho_{ABCD}$ be a sparse matrix of 4 systems each in a $d$-dimensional Hilbert space.
For $d<7$ in a reasonable time (few seconds) I able to perform the partial trace $\rho_{AD}$ using the ...
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0answers
46 views
Looking for description of Helstrom's measurement
I hope someone can help me find the page or chapter where Helstrom discusses his famous measurement for distinguishing between two mixtures in the textbook Quantum Detection and Estimation Theory.
...
2
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1answer
129 views
Shor's Algorithm: Why throw away the f(x)?
I'm having a little trouble understanding Shor's algorithm - namely, why do we throw away the result f(x) that we get after applying the F gate? Isn't that the answer we need?
My notation:
...
1
vote
1answer
141 views
Quantum Coin Flipping Protocol
$\newcommand{\ket}[1]{\left|#1\right>}$
I have the next protocol:
$A$ tosses a fair coin $a\in \{0,1\}$, if $a=0$, $A$ sends to $B$ $\ket{\psi_0}=\ket0$, if $a=1$ $A$ sends to $B$, ...
4
votes
1answer
139 views
Transpose Map Positive, But Not Completely Positive?
I am reading Introduction to Quantum Computing by Kaye, Laflamme, and Mosca. Here is a question I am struggling with:
Exercise 3.5.6: Prove that the transpose map, which maps $\rho \mapsto ...
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0answers
19 views
Is the universe a quantum computer - is light speed barrier a computational constraint [duplicate]
Possible Duplicate:
Is the universe a quantum computer - is light speed barrier a computational constraint
Cross-posting this question, since physics.stackexchange has not provided any ...
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3answers
932 views
Is the universe a quantum computer - is light speed barrier a computational constraint
There is currently a debate ongoing on leading maths blog Gödel’s Lost Letter, between Gil Kalai and Aram Harrow, with the former arguing that building a quantum computer may not be possible due to ...
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1answer
155 views
Quantum Cryptography
First question was a little bit ambiguous.
Photons are passed through a linear polarizer that is oriented $\theta$ degrees again the photon passes through another linear polarizer that also have a ...
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2answers
821 views
Quantum memories: What are they?
Searching the literature for the term "quantum memory" seems to bring up results from two different communities.
On the one hand there are quantum opticians, who see a quantum memory as something ...
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3answers
37 views
Depolarizing threshold for CSS codes
Many years ago, when CSS codes were first invented, the error threshold of p=0.11 was found when bit and phase flips are independent. Has a threshold yet been found for the case of depolarizing noise?
...
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9answers
553 views
Examples of number theory showing up in physics
My question is very simple: Are there any interesting examples of number theory showing up unexpectedly in physics?
This probably sounds like rather strange question, or rather like one of the ...
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2answers
452 views
Quantum Computing, Qubit Creation/Entanglement
I am currently a high school student researching quantum computing. I was referred to this site by Google and a friend. Currently I am researching the qubit part of quantum computing. My question is ...
12
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4answers
208 views
direct sum of anyons?
In the topological phase of a fractional quantum Hall fluid, the excitations of the ground state (quasiparticles) are anyons, at least conjecturally.
There is then supposed to be a braided fusion ...
11
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1answer
49 views
Principle behind fidelity balance in quantum cloning
If we do optimal state estimation on an unknown qubit, we can recreate a state with fidelity $F_c=2/3$ with respect to the original. Let us define the "quantum information content" $I_q=1-2/3=1/3$ as ...
14
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2answers
51 views
Counting complete sets of mutually unbiased bases composed of stabilizer states
Consider $N$ qubits. There are many complete sets of $2^N+1$ mutually unbiased bases formed exclusively of stabilizer states. How many?
Each complete set can be constructed as follows: partition the ...
11
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1answer
51 views
Stabilizer formalism for symmetric spin-states?
This question developed out of conversation between myself and Joe Fitzsimons. Is there a succinct stabilizer representation for symmetric states, on systems of n spin-1/2 or (more generally) n higher ...
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3answers
3k views
Quantum entanglement faster than speed of light?
recently i was watching a video on quantum computing where the narrators describes that quantum entanglement information travels faster than light!
Is it really possible for anything to move faster ...
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3answers
318 views
What is the use of a Universal-NOT gate?
The universal-NOT gate in quantum computing is an operation which maps every point on the Bloch sphere to its antipodal point (see Buzek et al, Phys. Rev. A 60, R2626–R2629). In general, a single ...
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3answers
124 views
Question about orthonormal decompositions over unitary operators
I'm teaching myself quantum information theory using Nielson and Chuang's "Quantum Computation and Quantum Information" and I'm at a point in the book where the formalism is starting to make my eyes ...
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3answers
148 views
Quantum computing and quantum control
In 2009, Bernard Chazelle published a famous algorithms paper, "Natural Algorithms," in which he applied computational complexity techniques to a control theory model of bird flocking. Control theory ...
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0answers
87 views
What can quantum adiabatic computation provably accomplish?
Let's say I have a quantum adiabatic computer in a black-box that works perfectly, doesn't suffer from decoherence/noise problems, etc. Are there any proven bounds for an adiabatic algorithm that ...
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1answer
507 views
How Does a Quantum Computer Work?
I've read Wikipedia, I've read How Stuff Works, I've read The Singularity is Near, but I still just don't get it. How does a Quantum Computer work? It sounds very intriguing, but I just can't wrap my ...
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1answer
484 views
Can quantum annealing be used for factorization?
It is known that there is a famous quantum factorization algorithm by Peter Shor. The algorithm is thought to be suitable only for quantum gate computer.
But can a an adiabatic quantum computer ...
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1answer
1k views
What is quantum discord?
What is quantum discord? I stumbled upon this term on Quantum Computing: The power of discord, but have never heard of it before. Can you give a bit more mathematical explanation of the term here?
