All Questions
Tagged with quantum-computing or quantum-computer
904 questions
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Grover's algorithm & using wave interference for computing
Grover's quantum search algorithm contends that it is possible to search for a specific item in an N-sized unsorted database in only $\sqrt N$ attempts. Classically, it takes N/2 attempts on average ...
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If a qubit can be a 1 or 0, and will return both - how can we rely on it?
In essence, a qubit may 'present itself' (upon observation) as a 1 or a 0. My understanding (as inaccurate as it may be) is that the observation of one particular qubit may result in different outputs....
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2
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474
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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 ...
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Why does nobody try to calculate the possibility to implement quantum computer with math and physics principle? [closed]
UPDATED: Classic computer can be easily implemented in many ways just in different computing velocities, But we have not found any easy way to construct quantum computer scalable by using quantum ...
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Outer Product Other form [closed]
The outer product of a ket $|\psi\rangle$ with a bra $\langle\phi|$ according to the textbook Quantum Computing Explained by D. McMahon, behaves likes an operator. He illustrates this by applying an ...
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Trace of an operator matrix (Quantum computation and quantum information)
I'm reading the book Quantum computation and quantum information by Mike & Ike and I'm stuck at 2.60/2.61. There, the author says that, given the operator $A|ψ⟩⟨ψ|$, its trace is:
$${\rm tr}(A|\...
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1
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959
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What is the connection between quantum thermal relaxation and phase and amplitude damping?
I have read that amplitude and phase damping of a quantum system describe the energy and quantum information loss of a quantum system due to the interaction with its environment. This is related to ...
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Counterfactual Quantum Computation is Really Weird
In this video https://www.youtube.com/watch?v=dQIfSrRBEgw a high level 'popular' introduction to Counterfactual Quantum Computation is provided.
The only part that seemed to 'come out of the blue' was ...
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Assumptions in the proofs for the optimality of Grover's Search Algorithm
I was trying to understand this paper in which it is proved that Grover's search algorithm is optimal.
On page 4, beginning of section 2 of the paper the author says the following
In the proof I ...
- 2,666
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267
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How to find the second quantized form of Hamiltonian for particle in a box?
A single particle Hamiltonian can be written in the second quantized form as follows:
$$F_{1}= \sum f_i(r_i,p_i)$$
$$F_1=\sum(l|f_i|l')a_{l}^{\dagger}a_l$$
When we use this for the hamiltonian of a ...
- 41k
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Simulate a quantum computer on a normal one
Would it be possible to simulate a quantum computer on a normal computer. I was thinking something like have a bunch of GPU's running a set of entangled quantum particles and then produce the results. ...
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2
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Can Quantum Computers test modified quantum mechanics?
I wonder if with the raise of the quantum computing era, we could test somehow non-linear quantum mechanics failures up to certain scales. That is, how could quantum computers test key assumptions of ...
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Why do we need different models of thermal relaxation noise for $T2>T1$ and $T2<T1$?
Noisy quantum channels are in generally described by the operator-sum representation with kraus operators (see eg. in Nielsen,Chuang). But for the thermal relaxation error different modeling used for ...
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How is a state of $|0\rangle$ created experimentally?
In the context of quantum computing, many times in textbooks and online courses, they say "we generate a state of $|0\rangle$", and then proceed to apply quantum (logic) gates.
My question ...
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2 qubit entanglement in a QC
To my knowledge, in a Quantum Computer it is possible to obtain any Bell state by applying a Hadamard gate onto a qubit state $|x\rangle$ followed by a CNOT gate onto some target qubit state $|y\...
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What textbooks would you recommend to learn quantum systems engineering?
I am a first-year undergraduate doing a BA in Physics. I have studied quantum mechanics at the rudimentary level, and as far as my mathematical background is concerned: I know linear algebra and ...
- 213k
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Hamiltonian for 2-qubit system
What is the general form of a Hamiltonian for a 2 qubit system?
The Hamiltonian for D-Wave system is:
$H = K_1\sigma_x^1 + K_2\sigma_x^2 + H_1\sigma_z^1 + H_2\sigma_z^2 + J_{12}\sigma_z^1\sigma_z^2 $
...
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What is a difference between solitons and anyons?
In the article Creation and annihilation of mobile fractional solitons in atomic chains the authors claim that they prepared 1D solitons which can be used in topological quantum computing. Based on ...
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What is the difference between "cluster states" and "graph states"?
I wonder about the difference between the cluster state and the graph state.
I guess the only difference is the graph of the cluster state is limited to a two-dimensional square lattice
The concept of ...
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38
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How to numerically simulate random quantum circuit?
Recent years, measurement induced phase transition has been widely studied with random quantum circuit model https://journals.aps.org/prx/abstract/10.1103/PhysRevX.7.031016 . I know little about ...
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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 ...
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Does increasing numbers of qubit come with increasing decoherence?
Does increasing numbers of qubit come with increasing decoherence? I assume it does for superconducting, but what about photonic or ion trap?
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Compute the Schmidt Decomposition of a two-qubit state
I'm trying to compute the schmidt composition of $$ |A\rangle = \frac{1}{2 \sqrt{2}}(|00\rangle + \sqrt{3}|01\rangle + \sqrt3 |10\rangle + |11\rangle) $$
I've calculated the eigenvalues to be $$ 1+\...
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Quantum Computing is not Analog Computing. Really?
Let's review first these two computation processes to see if in their core fundamental nature are actually different:
1) Quantum Computing
One of the properties of quantum mechanics that is exploited ...
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How can one compute the quantum motion of an ion in a trapped ion quantum computer?
I am trying to get a conceptual idea of a trapped ion quantum computer.
For simplicity, I am looking at a single ion in a Paul ion trap.
It is easy enough to define the potential of the ion trap and ...
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173
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What exactly is meant by the quality of a qubit?
When looking at a quantum annealer, we can see that D-Wave solutions have produced an annealer with over 5000 qubits whilst other companies that take a quantum gate approach have only managed 127 (IBM)...
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How much classical information is transmitted in continuous variable teleportation?
In order to do quantum teleportation of $n$ qubits, you need to send $2n$ bits of classical information, in order to ensure that you get the original state and not a relative phase change of the ...
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Can a quantum field theory be completely simulated by a quantum computer? [closed]
I heard a talk on quantum computing and black hole. In this talk Leonard susskind raised a question: can QFT be completely simulated by using a quantum computer? But he said he was not going to answer ...
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Hamiltonian reduction having constant of the motion [closed]
I have this $2^n*2^n$ matrix that represent the evolution of a system of $n$ spin.
I know that I can have only one excited spin in my configuration a time.
(eg: 0110 nor 0101 ar not permitted, but ...
CommunityBot
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Unitary transform using displacement operator to get time-independent Hamiltonian?
I am considering a driven cavity field with Hamiltonian
$$H = \hbar\omega a^{\dagger}a + f(t)(a + a^{\dagger})$$
where $f(t) = \epsilon e^{-i\omega_{d}t} + \epsilon^* e^{i\omega_{d}t}$ is a classical ...
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471
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Can quantum computing solve the curse of dimensionality?
The curse of dimensionality is ubiquitous in machine learning (ML) modeling, stochastic control and reinforcement learning, arising in a probabilistic sense, with strong connections to quantum ...
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Quantum and classical physics are reversible, yet quantum gates have to be reversible, whereas classical gates need not. Why?
I've read in many books and articles that because Schrödinger's equation is reversible, quantum gates have to be reversible. OK. But, classical physics is reversible, yet classical gates in classical ...
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Is quantum computation possible in a superdeterministic universe?
I've seen many renowned scientists arguing that the universe is superdeterministic, but superdeterminism is a "hidden variable" theory. Is this compatible with the concept of quantum ...
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Are qubits just analog, continuous classical bits?
Topologically, classical bits (cbits) are essentially special cases of qubits restricted to the poles of the Bloch sphere. However, this restriction doesn't seem to be classical per se, but is simply ...
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Is the Hilbert-space description of quantum many-body physics misleading and unphysical?
It is well known that any quantum time-evolution of local, time-dependent Hamiltonians can be described using a poly-depth (in number of qubits) quantum circuit (DOI:10.1103/PhysRevLett.106.170501; ...
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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 computer harder and harder to keep working (...
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Are there any physical realizations of a rebit (a qubit with real coefficients for probability amplitudes of a two-state system)?
While being introduced to the world of quantum computation and qubits, I’ve come across the term rebit, which I understand to mean a two-state quantum system that may be expressed as a real linear ...
CommunityBot
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Quantum computer vs. classical probabilistic computer
Is it possible to make a quantum computer from a perfect random number generator. I'm wondering if anybody that's studied it could make one from that type of random number generator.
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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?
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Deutsch-Jozsa algorithm
Quantum queries
We just apply the boolean function to the computational basis labels.
X is an n-bit string representing an n-qubit state, then we can try $|x\rangle$ to $f(x)$. but if $f(x)$ is ...
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Why do quantum gates have to be reversible?
One possible reason I have come up with is that we are modeling quantum gates by unitary matrices. And since unitary operations are reversible we have to be able reverse the operation in the physical ...
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Could we have a quantum algorithm that have the quantum speed-up, but don’t need universal gates?
When it comes to building a quantum computer, it's like we need to consider how to perform universal gates fault-tolerantly, which is an unsolvable problem so far. While Clifford gates may be easier ...
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What errors can be detected in QEC (Quantum Error Correction)?
In the introduction of Eastin and Knill's paper on the no-go Theorem for universal and transversal quantum gate sets, they assert that an error E can only be detected if PEP∝P, where P is the ...
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What is the idea behind quantum speed limits?
Could someone please explain to me how the very basic idea behind existence of a quantum speed limit arises?
I think I understand (if it's correct) how it arises naturally between two pure states ...
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How does non-commutativity of observables lead to quantum speedup in solving algorithms in quantum computing?
The question might be misleading, but I'd like to understand a thing. By reading this really interesting question, one realises that the relevant thing in quantum mechanics and not reproducible in ...
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Filling factors and implementation for non-Abelian models
Currently reading through Pachos' Introduction to Topological Quantum Computation, and perusing other related articles and papers online. Have seen in many places that the 5/2 filling factor for ...
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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 ...
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Why doesn't the no-cloning theorem make lasers impossible?
As I understand lasers, you start off with a few photons that are in an identical state, and other photons that are created later tend to have the same quantum numbers due to Einstein-Bose statistics. ...
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Is every Quantum Computer working with entangled particles? [closed]
Is every Quantum Computer working with entangled particles?
I ask this question, because entangled particles are not allways local.
I read that a Quantum Gate can be used to concatenate quantum ...
- 213k
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Wavelength-dependence of optical elements in integrated photonic circuits
I am interested in integrated photonic circuits or silicon photonic circuits. In the long run, I would like to analyze these circuits using a rigorous and analytical mathematical approach, taking the ...
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