The tag has no usage guidance.

learn more… | top users | synonyms (2)

0
votes
1answer
39 views

Relationship between Toffoli gate and Deutsch gate

I am reading a book called "Quantum Computing for computer scientists" and stuck at this exercise for a day. Bellow is the description of Deutsch gate: And here is the description of Toffoli ...
-4
votes
2answers
67 views

Quantum computers for string theory? [closed]

I read something about that locating our space in the multitude of multidimensional spaces of M-theory (and so identifying particular particles which we can measure with particular strings) is a too ...
1
vote
1answer
39 views

Controlled Phase Gates

The Quantum Fourier Transform consists of 2 gates. Controlled Phase Gates, and Hadamard gates. I'm assuming the Controlled Phase Gate is a combination of a Control Gate, and a Phase Gate. But what ...
1
vote
0answers
27 views

How is this circuit equivalent to a Bell measurement?

The circuit elements are : CNOT gate, first qubit is the control bit Hadamard gate (H) The dials represent measurements made in the computational basis Therefore, the circuit (without the ...
0
votes
0answers
25 views

How to find a single coefficient of quantum Fourier transform reliably

Quantum Fourier transform transform $X \in \mathbb{C}^{2^n}$ to $Y \in \mathbb{C}^{2^n}$. Suppose one wishes to find $y_0$, the first coefficient of "vector" $Y$. However, as this is quantum process, ...
0
votes
1answer
34 views

Can a classical 50/50 probability be distinguished from a quantum superposition with a single measurement?

$\renewcommand{\ket}[1]{|#1\rangle}$ A "false" (equally superimposed qubit) is created by mechanically firing with 50/50 probability a resonance photon at a Hydrogen atom qubit in the ground state. ...
0
votes
2answers
57 views

Is a universal quantum computer expected to be able to shed any light on the measurement problem? - Part B [closed]

Following up on Part A. Suppose we build a universal quantum computer and it functions as we currently expect it to. Is there any reason to suggest that, beyond its uses for things like ...
2
votes
0answers
74 views

Is a universal quantum computer expected to be able to shed any light on the measurement problem? - Part A [closed]

Suppose we build a universal quantum computer and it functions as we currently expect it to. Is there any reason to suggest that, beyond its uses for things like cryptography and quantum system ...
4
votes
1answer
129 views

How is classical information put into and retrieved from a quantum computer?

How, if you had to find the factors of say a 256 digit number, would you go about inputting the data and how do the proper answers "drop out" of a quantum computer. Other than terms such as qubits, ...
0
votes
1answer
64 views

Classical Computation without NOT [closed]

Is it possible to do universal classical computation using bits and 2-bit gates when you cannot perform a NOT operation on a single bit (hence cant do CNOT and so on). If yes, what are the possible ...
0
votes
0answers
23 views

Generallized Controlled-$U$ gates

Let $U$ be a quantum gate that acts on $n$ qubits represented by the $2^n \times 2^n$ matrix: $$U = [u_{ij}] \qquad \text{where} \qquad i,j \in \{ 1,2,3,\dots, 2^n \}$$ Can I state that the ...
20
votes
7answers
6k views

Could quantum computers break any cipher? [closed]

I've been told that physicists and computer scientists are working on computers that could use quantum physics to increase significantly computation capabilities and break any cipher so cryptography ...
0
votes
1answer
65 views

What are typical error rates of quantum computers?

I read in an article that in order to perform error correction on a quantum computer there can only be one error per 10.000 calculations (=unitary transformations). This sounds pretty high but how ...
0
votes
1answer
38 views

Why does a measurement on one qubit force another one into a given state in Simon's algorithm?

This comes from trying to understand the "Simon's algorithm". So we have a set of $2^n$ kets $|x_i >$ one each for $i \in \{0,1\}^n$. Each $x_j \in \{0,1\}^n$. And we have the further constraint ...
0
votes
3answers
88 views

The $n$-th root of the NOT gate

I simply can not find material containing facts about the $n$-th root of the NOT gate and it's realization in Q.M. and also in C.M.. Does anyone have material? A comparison of the $n$-th root NOT ...
1
vote
1answer
63 views

What causes continuous errors in a qubit?

I read that due to decoherence a qubit in a superpositon gets destroyed or put into one definite eigenstate. This kind of error seems to occur due to interactions with other stuff like the environment ...
1
vote
1answer
63 views

Quantum computing can be done via measurement alone, why is this significant?

I read in the Afterword section of Nielsen and Chuang's book Quantum Computation and Quantum Information that A second area of progress has been in understanding of what physical resources are ...
3
votes
1answer
132 views

Approximating a target operator

I was wondering if anyone knew how the author got to equation 12 on page four of this paper, I will attempt to explain the situation below. Given $C$, a target operator, we wish to create an ...
0
votes
1answer
41 views

Why do Transformations on Qubits for Quantum Computation have to be Unitary?

In the quantum circuit model we prepare some inital state $|\psi\rangle$ and throw our algorithm in form of some unitary transformation(s) $U$ on it to get our result $|\Psi\rangle$: ...
0
votes
1answer
62 views

How to apply Controlled-NOT gate?

look at the figure below it is about an example to multiply two qubits by 3 Controlled gate to get the SWAP operation .. I'm trying to follow this step-by-step but I couldn't know how this is ...
1
vote
0answers
15 views

Creating an arbitrary state of the quantum simple harmonic oscillator [duplicate]

Suppose $\mathcal{B}=\{\lvert 0\rangle, \lvert 1\rangle, \lvert 2\rangle, ... \}$ is the energy eigen-basis of a quantum simple harmonic oscillator. I want to create the state \begin{equation} ...
1
vote
2answers
49 views

Do we have algorithms that are polynomial on a Q-Computer but not poly. on a classical Computer?

I am currently reading “Introduction to Topological Quantum Computation” by J.K. Pachos. In the book the author mentions that Shor’s factoring algorithm is polynomial (with regard to the complexity ...
0
votes
0answers
67 views

Limitations of Quantum Simulations on a Classical Computer

My question is on the simulation of a quantum computer on a classical machine. I understand that a classical computer to simulate any quantum algorithm--the problem is that the quantum computer does ...
0
votes
0answers
62 views

Proof that Quantum Computation cannot be simulated on classical computers

I have read , for example , in chapter 3, Computer-aided-design Methods for Emerging Quantum Computing Technologies By David Dov Yehuda Feinstein this statement several times, but I am not able to ...
2
votes
1answer
80 views

How powerful would a quantum computer need to be to break RSA encrytion codes?

First off, just to reassure everybody, I have no motive other than pure curiosity for asking this question. I don't want my bank account hacked any more than you want the same done to yours. My ...
3
votes
0answers
74 views

Anyonic Braiding and Conformal Field Theory

I am looking for resources (both pedagogical and newer research articles) on the connection between topological quantum computation and conformal field theory. In particular, a CFT description of ...
1
vote
0answers
25 views

Is the first excited state of a superconducting qubit a stationary state?

A superconducting qubit is essentially an anharmonic oscillator with uneven spacings of the eigenstates. These states are eigenstates of the overall hamiltonian, which should mean that it is an energy ...
1
vote
0answers
75 views

How useful is the study of entanglement entropy to quantum computing? [closed]

My question is somewhat conceptual: how, exactly, can we get closer to building a quantum computer by studying entanglement entropy? I've been reading all about the AdS/CFT correspondence and watching ...
0
votes
1answer
31 views

How does one measure the state probabilities of a 2 level Hydrogen atom qubit?

I have been struggling with trying to understand how one could measure the probabilities of a superimposed Hydrogen atom's two energy states. Say the atom is in a superimposed state: Psi = a|0> + ...
3
votes
1answer
83 views

Rigorous definition of superselection sector/quasiparticle type in anyon systems

The systems I have in mind are for example Kitaev's toric code model (arXiv:quant-ph/9707021) and Kitaev's honeycomb model (arXiv:cond-mat/0506438). What I'm looking for is a mathematically rigorous ...
2
votes
2answers
120 views

Why is a transmon a charge qubit?

The classic charge qubit is the cooper pair box which is a capacitor in series with a Josephson junction. In my understanding, by changing the gate voltage at the capacitor, one can create a ...
3
votes
1answer
97 views

which are the non-abelian anyons for universal quantum computation

I am trying to get a list of non-abelian anyons that can be used for universal quantum computation by implementing gates via braiding. I found that Majorana fermions and para-fermions (not sure about ...
1
vote
1answer
100 views

Topological Quantum Computing beyond Anyonic Braiding

In materials such as those that exhibit fractional quantum hall states, the ground-state topological degeneracy is known to be robust against external perturbations. This ultimately tells us that we ...
1
vote
1answer
65 views

are there known fundamental limits of quantum computer scaling?

Quantum computers provide exponential speedup relative to classical computers. However, it is empirical fact that increasing of number of qubits makes the the computer harder and harder to keep ...
0
votes
2answers
70 views

Why can't a classical bit behave like a qubit?

For example i have a 2 qubits which can have 4 possibilities i.e. 00, 01, 10, 11 so this shows that the 2 qubits can contain four bits of information as they are superpositioned but i think 2 ...
2
votes
1answer
72 views

How does quantum superposition make calculation faster?

In every description of a quantum computer I've seen (that isn't extremely technical), they've been described as computers that use qubits, that use a superposition of 1 and 0 to make processing ...
0
votes
1answer
75 views

Dilemma: Fusion space from a direct sum of anyons or NOT

In Preskill's note, 9.1.2 in page 44, concerning the fusion space, it states that: The fusion rules of the model specify the possible values of the total charge $c$ when the constituents have ...
5
votes
0answers
58 views

Why do flux qubits have to be micrometer-sized?

Flux qubits are made using micrometer sized Josephson junctions. They exploit superconducting properties to create and interfere with the magnetic flux between them. My question is that I've seen ...
1
vote
1answer
54 views

Quantum Computer Implementation

Hey I recently finished my bachelor in nanotechnology and am rather interested in quantum computation. I've already looked at the recommendation threads for this topic but they tend to be about ...
0
votes
0answers
54 views

Difference between apply quantum gate and measure a qubit?

When you apply a quantum gate, why does the superposition state not collapse? Does this in any way intervene with the qubit as in the measurement?
1
vote
2answers
86 views

Anyonic braiding statistics from density matrix renormalization group (DMRG) simulations

How does the ground state energy of the system change when we braid two anyons? Can the braiding of anyons be simulated with a computational method such as the density matrix renormalization group, ...
1
vote
1answer
56 views

CNOT gate application to separated qubits

In the case 1 in the picture, it is easy to perform matrix calculations concerning the circuit to obtain a final state. In case 2 however, I am wondering what is a general procedure to calculate it ...
0
votes
2answers
81 views

What type of Quantum Gate is this

I'm trying to work out if this is a certain type of 'known' Quantum Gate $|1\rangle|1\rangle $ goes to $|1\rangle|1\rangle $ $|1\rangle|0\rangle $ goes to $|1\rangle|0\rangle $ $|0\rangle|1\rangle ...
0
votes
1answer
72 views

Hadamard Gate application help

I need to prove that if you apply Hadamard gates on the input/output before and after a CNOT gate that you get the same answer as flipping the target and control qbits of a CNOT. So for example I'm ...
2
votes
1answer
59 views

Continued Fraction Algorithm in Shor's Algorithm

I am just trying to make the final link of Shor's algorithm clear. Here $r$ is the order of $x$ modulo $N$. We have a number $\psi$, which for a rational number $\dfrac{s}{r}$ satisfies ...
1
vote
0answers
48 views

In Grover and Shor Algorithms 2 registers of qubits are handled at books, but it's really just one seen as 2?

I found in the literature that we require at least two quantum registers for arithmetics operation. Example: The function $f(x)=x^2$ is then a unitary evolution of the two registers, in this ...
1
vote
1answer
62 views

Quantum computer simulators [closed]

What are good, free, open source, GUI-based quantum computer simulators? I remember there used to be a Java-based one that was very good, but it doesn't seem to be online anymore, or it's relocated.
0
votes
1answer
29 views

Condition for quantum error correction based on encoded states

I am trying to understand the properties of quantum error correcting codes. Consider a quantum code on a lattice, with the property that a given region $R$ is correctable (for any error localized to ...
5
votes
0answers
202 views

Quantum Error Correction: Surface code vs. color code

Recently, two groups working on quantum computers published results on quantum error correction. The first was Rainer Blatt's group, who used trapped ions to perform a topologically encoded qubit ...
1
vote
0answers
44 views

Have there been any experiments that have demonstrated a quantum error correcting code?

Has quantum error correction been demonstrated? I know that classical error correction has been demonstrated by [1], they correct a single bit flip error, but has anyone been able to detect and ...