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1500 questions
6
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Is the complexity of a quantum circuit constant in the depth of the circuit?
Take a quantum circuit on $n$ qubits, you have some sequence of gates.
You can represent these gates as hermitian matrices, and then with some padding, you could take the product of these matrices, by closure would be a hermitian matrix, a quantum…
abrahimladha
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6
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Does Grover's algorithm always give the correct answer with 100% certainty for two-qubit states?
In the Qiskit tutorial on Grover's algorithm it is stated that with a 2 qubit algorithm the chance of measuring the "right" state is already 100%.
But I thought that the algorithm would amplify the 'right' amplitude around 9 times and respectively…
eli44
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6
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What algorithm does Qiskit use to decompose arbitrary n-qubit unitaries on Rotations + CNOT?
I found that Qiskit uses Unroll3qOrMore in the transpiler class function to decompose an arbitrary $n > 2$ unitary and represent it as a directed acyclic graph (DAG). But I can't find an algorithm (or paper for it). Could you help?
Игорь Токарев
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Does the circuit with qubit-wise CZ gates compute the inner product of two states? If not, is there another circuit that does?
I've been searching for a quantum algorithm to compute the the inner product between two $n$-qubit quantum states, namely $\langle\phi|\psi\rangle$, which is in general a complex number.
One can get $|\langle\phi|\psi\rangle|^2$ through thte SWAP…
cwhsing
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6
votes
1 answer
What are the current solutions to generate entangled qubits in the solid state?
Pairs of entangled qubits (or Bell pairs, or EPR pairs) are a fundamental resource for quantum computing, in the sense that any computational platform that cannot generate entanglement will also be unable to provide a computational advantage.[1] In…
agaitaarino
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6
votes
1 answer
What is the relation between single photon qubits and squeezed light qubits?
In my constant thrill to know more about Quantum Computing I wanna know what is this relation. Additionally: Can one use squeezed light to effect multi-qubit operations on single photon qubits, or are these completely independent approaches?
Daniel Tordera
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Optical quantum computers VS Superconducting quantum computers VS Electron-spin quantum computers
One of the main problems of superconducting quantum computers is that it is necessary to maintain a very low temperature (near absolute zero).
Such cooling is very expensive and complex.
Why, then, are Intel, IBM, and many other corporations…
alexhak
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6
votes
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Quantum capacity for serial composition of quantum channels
Recently, I have been working with quantum channel capacity for quantum-quantum channels and I was wondering if there exist some results for channel compositions.
Specifically, I have been looking for results on what happens to quantum channel…
Josu Etxezarreta Martinez
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2 answers
Why is the time ordering omitted in the trotterised version of the time-dependent evolution operator?
The unitary evolution of a time-dependent hamiltonian is given by the time-ordered matrix exponential
$$\begin{aligned}
U(t)&=\mathcal T\exp\left[-i\int_0^tH(\tau)d\tau\right]\\
&=I-i\int_0^td\tau\,H(\tau)-\frac12\int_0^td\tau\int_0^t…
Dyon J Don Kiwi van Vreumingen
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6
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1 answer
Finding the norm of a Hamiltonian
I am experimenting with https://journals.aps.org/prx/pdf/10.1103/PhysRevX.8.041015 and in equation 36 I find that they use the norm of the Hamiltonian.
Is there a clean way to compute it, or an upper bound lower than $\lambda = \sum_j |w_j|$ for the…
Pablo
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6
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3 answers
Do the 'fundamental circuit elements' have a correspondence in quantum technologies?
Capacitors, Inductors and Resistors are well-known circuit components. Since the proposal of Leon Chua in 1971, the Memristor joined them as a fundamental component.
I am wondering whether these elements would be somehow imitated by the means of…
SalvaCardona
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6
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2 answers
How can one check whether a given quantum state is a graph state?
We can build a quantum state from a graph, which is a mathematical concept.
But, vice versa, how can one check whether or not a given quantum state is a graph state?
narip
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6
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1 answer
What is the physical unit of the energy calculated using VQE on Qiskit?
Suppose there is any arbitrary ansatz producing variational energy for any arbitrary Hamiltonian. What is the physical unit corresponding to the energy? Since numerical algorithms only output a numeric value, the unit is missing. I know for quantum…
quantum
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5 answers
How do I get the Unitary matrix of a circuit without using the 'unitary_simulator'?
I am using jupyter notebook and qiskit. I have a simple quantum circuit and I want to know how to get the unitary matrix of the circuit without using 'get_unitary' from the Aer unitary_simulator. i.e.:By just using matrix manipulation, how do I get…
Jared
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6
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Is a "kernel" just the quantum equivalent of classical SVMs?
I'm confused about the relationship between kernel methods and SVM methods used in quantum machine learning. Sometimes the two seem to be used interchangeably, but often I'll see them both in the same sentence. I understand what an SVM is in the…
Jay Muntz
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