All Questions
Tagged with quantum-computing or quantum-computer
904 questions
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Replace $\vert1\rangle$ with identity operator
I am learning quantum computing recently and found an exercise on the Internet. I have been thinking about how to solve it but still confused. The following is the question
Consider a single qubit ...
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How to find stabilizer generators of a subsystem from a known set of generators?
$\newcommand{\ket}[1]{\left|#1\right>}$
I am working on a problem and would appreciate some help. I'm working with a multi-qubit state defined by a set of stabilizer generators, ie $\ket{\psi} \in ...
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Google, IBM, Rigetti, and IQM all manufacture superconducting quantum computers, what are the main differences of their chips? [migrated]
Google, IBM, Rigetti, and IQM all manufacture superconducting quantum computers. What are the main reasons for the differences in the accuracy of their chips?
IBM has recently released its latest ...
- 213k
17
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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 ...
- 3,142
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3
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822
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Role of entanglement in quantum computing
I'm not a physicist and thus, I'm looking for a simple explanation on the role of entanglement in making quantum computers fast. I got a good analogy of a qubit: a coin tossed in the air can be ...
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Go a step further and get the both results of $f(x)$ in Deutsch algorithm
The Deutsch-Josza algorithm gives the result in one operation of the type of a $(0,1) \mapsto (0,1)$ function $f(x)$, i.e. if $f(x)$, is constant or balanced. With the parallel computing power of a ...
Buzz♦
- 17.1k
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Can a quantum computer simulate a classical field theory efficiently?
I know there’s a large speed-up in simulating quantum field theories, but was wondering if quantum computers are able to simulate a classical field theory as efficiently as they can simulate a quantum ...
- 213k
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Should one learn the math of quantum computing from a "pure" perspective, or is quantum computing texts "good enough"? [closed]
Math for quantum computing includes advanced linear algebra, functional analysis, group and representation theory, probability theory, and more.
There are plenty of pure math books out there for those,...
- 60.3k
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How to experimentally perform a POVM measurement?
Reading through Nielsen and Chuang, I came across the following example.
Consider a POVM containing three elements,
$$
E_1 \equiv \frac{\sqrt{2}}{1 + \sqrt{2}} |1⟩⟨1|,\\
E_2 \equiv \frac{\sqrt{2}}...
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Relationship between coupling Strength in Cross-Resonance Gates and Coefficients in Hamiltonian Tomography
In the effective Hamiltonian for the cross-resonance (CR) gate, the interaction term is written as:
$$
\tilde{H}_{\rm eff}^{\rm CR} = - \frac{\Delta_{12}}{2}\sigma_1^z
+ \frac{\Omega(t)}{2} \left(\...
- 21
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Can a universe-sized computer predict the universe? [duplicate]
I'm not asking about a simulation and so I don't see this as a duplicate, and I'm not a physicist or anything like that, I have some physics-related questions though.
Current models suggest local ...
2
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422
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Universe simulation
Is it theoretically possible to simulate the universe? I know that some philosophical theories say that our universe is a computer simulation, but is this feasible? Would it ever be possible for a ...
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How to transform collapse operators in rotating frame?
I want to simulate the evolution of a transmon qubit driven by a classical voltage using qutip. The problem is that the qubit (and the drive) have a frequency of around 5GHz and I typically run ...
- 213k
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473
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What is the decoherence time scale for the most promising quantum computing implementations?
I'm searching for some data about decoherence time scales for qubits in modern quantum computing implementations. By "data", I mean time scales.
The only reference I have is a table in ...
CommunityBot
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Are there quantum computing algorithms specialized for machine learning applications?
I've heard that some companies are attempting to utilize quantum computing algorithms for machine learning tasks (ex:protein folding and drug discovery). As far as I know, quantum computing has been ...
- 213k
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Is useful Shor factorization really practically feasible?
INTRO TO THE ISSUE. After studying this beautiful math concept many years ago, I recently revisited Shor's algorithm for factoring integers and its implications for RSA encryption. This time, I needed ...
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How does Quantum Gate Teleportation Actually Work?
I am trying to understand how quantum GATE teleportation works. Abstractly, I understand it as the ability to do a 2-qubit operation between two qubits that are not located in proximity.
From ...
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Why the parameters of quantum convolutional neural network (QCNN) is $O(\log N)$ for a $N$-qubits input?
I am currently reading the paper arXiv:1810.03787. The authors claim that QCNN uses only $O(\log N)$ variational parameters, where $N$ is the number of qubits. However, I am having difficulty ...
- 213k
33
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2
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Basic questions in Majorana fermions
Why any fermion can be written as a combination of two Majorana fermions? Is there any physical meaning in it? Why Majorana fermion can be used for topological quantum computation?
- 3,270
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A variant of Campbell (1897) identity (related to BCH formula)
Campbell's identity (see in https://en.wikipedia.org/wiki/Baker%E2%80%93Campbell%E2%80%93Hausdorff_formula) takes the form:
$$ e^XYe^{-X}\equiv ad_{e^X}Y=e^{ad_X}Y\equiv \sum_{n=0}^\infty\frac{[(X)^n,...
- 213k
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1
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How to Construct Arbitrary Rotations from Discrete Rational Rotations?
One of the most commonly used universal quantum gates sets is the Clifford + T set, containing {CNOT, H, S, T}. However, as S is a $\pi / 2$ rotation about the Z axis of the bloch sphere and as T is a ...
2
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Edge Modes and SPT Order
I am trying to understand the notion of edge modes in the context of symmetry protected topological order (SPTO) and its relation (if there is any) with the virtual quantum register that sits at the ...
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Using classical $g^{(1)}$ to calculate quantum $g^{(1)}$
Imagine a free space optical switch with several inputs and outputs. My question is: can we use the first order cross correlation between the complex amplitudes of two classical beams of light at the ...
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Scrambling Time in Black Holes
Peter Shor argues that the scrambling time for a black hole—defined as the time it takes for information to be thoroughly mixed across the event horizon—scales as $\mathcal{O}(M^2)$, where M is the ...
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How to calculate quantum cost of a reversible logic circuit?
I am trying to develop new reversible logic synthesis algorithm. But I need a good quantum cost measure for a synthesized circuit to compare my results with existing ones.
For now I'm using RCViewer+ ...
0
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1
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100
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Conjugacy of $x$ and $p$ for simulation of Schrodinger's equation
In Nielsen-Chuang, page 207, there is this box:
I have some strong doubts about the last passage. The logic they follow is that since $H_0$ is diagonal in momentum basis but not in position basis, ...
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469
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What is a quantum random walk?
I am an undergraduate doing research on QC/QI. My current topic to learn is continuous-time quantum walks, but first I must learn the random quantum walk. That being said, I was wondering if someone ...
CommunityBot
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3
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312
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Why isn't spin-statistics applied in quantum computing?
Why isn't spin-statistics taken into account in quantum computing?
By spin statistics I mean the fact that fermion and boson states must by respectively totally anti-symmetric and symmetric. I say it'...
- 28.6k
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Questions on Matrix Product States (Tensor Networks)
I just have a few questions on Matrix Product States. I have learnt them from the point of view of performing cuts via Schmidt Decompositions, as seen in Chubb and Bridgeman 2017.
Is the bond ...
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How can a quantum gate be constructed to evaluate a blackbox function (as in the Deutsch's algorithm)?
The standard Deutsch's algorithm uses a control-U gate, which takes the control qubit state $x$ as input to get the output from a black-box function $f(x)$. And the output modifies the quantum state ...
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Understanding the Relationship Between Stochastic Reconfiguration and Natural Gradient in Variational Monte Carlo
I've been delving into variational Monte Carlo methods, particularly in the context of ground state energy minimization for quantum wave function ansatzes. In my studies, I've come across multiple ...
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What is a stoquastic Hamiltonian?
Recently, I've often read about the term 'stoquastic Hamiltonian'. But I couldn't find a precise definition anywhere. I found that the Ising-Hamiltonian is a stoquastic Hamiltonian, but that does not ...
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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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705
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What is the purpose of the Quantum Fourier Transform or what does it operation achieve?
As far as I understand it aids with period finding which can help factor large numbers (i.e why it is used in Shor's algorithm).
What I want to know is if I have a quantum system and I apply the ...
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Is two degree quantum entanglement possible? And by two degree of entanglement I mean one in space and other in time? [closed]
Whenever we try to entangle two particles, the entanglement lasts for a very short period. If we observe our present universe we can see that all the matters present in our universe are finely ...
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256
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Is there an efficient way to execute a quantum channel using its Choi state?
Consider you are given a Choi state
$$
\sigma = (\mathcal{E} \otimes I) | \omega \rangle \langle \omega| \qquad {\rm with } \quad |\omega \rangle = \frac{1}{\sqrt{d}}\sum_{i} |ii \rangle \quad \textrm{...
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1
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What does the "quantum mutual information" quantify?
I'm having some difficulty understanding the physical meaning of the mutual information that two subsystems share with each other. For example, if $\rho_{AB}$ defines the matrix of a bipartite state, ...
- 15.1k
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Photonic classical and quantum computing
How different is the hardware used for classical and quantum photonic computers? Are there any proposals on hybrid platforms? I'm curious why I never heard of both within the same context, except for ...
- 3,013
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3
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Can quantum entanglement travel faster than the speed of light? [duplicate]
Recently I was watching a video on quantum computing where the narrators describe that quantum entanglement information travels faster than light!
Is it really possible for anything to move faster ...
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3
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1
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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 ...
CommunityBot
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Why the unit of quantum information for anyons systems should be the qubit?
I'm starting to learn more about anyons systems. I took a read on this article which is an introduction to topological quantum computing, and also took a look in other places like forums and some ...
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Is this an alternative realization of Deutsch's algorithm? [closed]
The standard Deutsch's algorithm uses two qubits and a control-$U_f$ gate, which transforms the two qubits,
$|x\rangle |-\rangle \rightarrow (-1)^{f(x)}\, |x\rangle |-\rangle $. To realize the ...
- 5,781
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Why can photons be used as qubits?
I've been studying quantum computers and while it's apparent to me how electrons are used as qubits, through their spin number, it's not as clear what makes a photon a viable candidate to be used as a ...
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1
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Can 2D graph state be represented by branching MERA?
A 2D graph state is a highly entangled state to support general measurement based quantum computation. But its state complexity is relative low. Branching MERA represents also a set of low complexity ...
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About 2D graph state and branching MERA
In my former post I asked if a 2D graph state on a 2D lattice can be represented by branching MERA. I got an answer that it seems this is true.
Then I have to following deductions
(1) 2D graph state ...
- 21.4k
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1
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Appling a Hadamard gate to a qubit in density matrix form
If a Hadamard gate is applied to a qubit that is in the state $|0\rangle$, then it becomes the state $$|+\rangle = \frac{1}{\sqrt{2}}\left(|0\rangle+|1\rangle\right)$$ In density matrix form, this ...
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When applying the adiabatic theorem, why doesn't the gap become doubly exponentially small generically?
Suppose we have a parameterised family of Hamiltonians $H(s)$, $s\in [0,1]$, acting on $n$ spins/qubits. When applying the adiabatic theorem, it is well known that if we wish to remain in the ground ...
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Why does the SWAP operator equal a particular integral over the unitary group?
Let $\mathcal{U}(d)$ be the group of $d$-dimensional unitary matrices and $P_{21}$ be the swap operator ($P_{21}$ operators on a tensor product of Hilbert spaces $\mathcal{H}_A$ and $\mathcal{H}_B$ ...
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Parallel State Machines as an Analog To Quantum Computing
I recently got into Michael Sipser's Introduction to the Theory of Computation. I've only done software a couple years professionally, but in that time have spent a lot of time thinking about state ...
4
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1
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What is three-photon interference?
Whilst reading this paper on a quantum processor that performs a type of matrix computation, I came across the concept of 'three-photon interference'. A quick Google search shows that this process is ...
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