Quantum Computing Stack Exchange
Quantum Computing Stack Exchange

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Are ladder operators ever extensively used in any model of quantum computation?

Computer scientists and others who are interested in learning more about quantum computation might be exposed, or re-exposed, to various concepts and classes of matrices from linear algebra. For example because of familiarity with truth-tables,…
Mark Spinelli
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Which codes have transversal $T$ gate?

A previous post transversal P (phase) gate shows that codes where all stabilizer elements have weights that are multiple of 4 will have a transversal $P$ gate. "Transversal" seems to have multiple definitions; here a gate $G$ is transversal for the…
unknown
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When you act on a multi-qubit system with a 2-qubit gate, what happens to the third qubit?

I am learning to manipulate Qbits and recently I saw the teleportation algorithm. I read about it in two places: Wikipedia and Lecture Notes from Ronald de Wolf (Page 7, 1.5 Example: Quantum Teleportation). I'd like to understand how to operate with…
Marcelo Fornet
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Why is the fidelity, rather than the trace distance, the standard choice to compare quantum states?

I don't think it's particularly controversial to say that the "standard" way people use to compare quantum states is via the fidelity. Yes, sometimes the trace distance is used as well, but it seems to me that the "canonical choice", the first one…
glS
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How are IBM's 127 qubits more potent than the 5760 qubits D-Wave - Advantage_system6.1?

Hi I'm a newbie in quantum computing recently I had a look at the AWS braket and I've seen they had a machine called D-Wave - Advantage_system6.1 that has 5760 qubits but when I googled the highest qubits quantum computer so far it showed me IBM's…
Zakaria Halloumi
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Rotation resolutions in operations for qubits in commercial implementations

I have found information about Honeywell provider supporting operations with high-resolution rotations (i.e. around $\pi/500$) here. What are typical maximal rotation resolution values supported by existing implementations and what is their…
Mariusz
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Given a non-Clifford quantum circuit $U$, is it possible to construct a commuting Clifford circuit $C$?

Let a non-Clifford circuit $U$, say $$U = \prod_{i=1}^k e^{i \theta_i P_i} $$ for $P_i \in \{ I,X,Y,Z\}^{\otimes n} $ with $\theta_i \in \mathbb{R}$ be given. Is it possible to construct a non-trivial Clifford circuit $C$ with commutes with $U$?
KAJ226
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Has anyone analyzed multi-round nonlocal games?

The traditional definition of a nonlocal game is restricted to having two players and one round (e.g., here), but it is natural to consider a more general class of games that may have more than two players and more than one round of questions. While…
Evan Jenkins
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Can separable states have quantum mutual information larger than one?

Consider bipartite (qubit) systems. The classical mutual information between a pair of binary registers, $$I(X:Y)\equiv H(X)+H(Y)-H(X,Y),$$ is always lesser than $1$ (and non-negative). On the other hand, the quantum mutual information of a…
glS
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Is the Clifford group a semidirect product?

This is from Is the Clifford group finite? "Define the Clifford group $ \mathrm{Cl}_n(p) $ of n qudits of prime dimension p as the unitary normaliser of the generalised Pauli group. Define the projective group…
Ian Gershon Teixeira
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How do you send an array of qubits to an operation in Q#?

I have the following operation in my .qs files: operation myOp(qubits: Qubit[]) : () { // uses elements from the qubit array } How do I send an array of qubits to this in the driver file? The following did not work: Qubit[] qubits =…
Mahathi Vempati
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From Q# measurements to Bloch sphere

I would like to represent the state of a qubit on a Bloch sphere from the measurements made with Q#. According the documentation, it is possible to measure a qubit in the different Pauli bases (PauliX, PauliY, PauliZ). This returns Zero if the +1…
JRial95
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One-qubit gate results in QISKit

I found it odd that the result of the action of identity gate (namely a $2\times2$ identity matrix) on a pure state $|0\rangle$ (namely the vector corresponding to the $2\times1$ matrix $\begin{bmatrix} 1\\0 \end{bmatrix}$) becomes a $2\times2$…
Mathist
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What are examples of the correspondence between channels and their Stinespring dilations?

In this post I read that "quantum measurements are special cases of quantum channels (CPTP maps). Stinespring's dilation states that any quantum channel is realized by partial tracing a unitary operator acting on a possibly bigger Hilbert space." Is…
Naima
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How can I show that $\mathsf{QMA}\subseteq \mathsf{PSPACE}$

Lately I have seen the claim that $\mathsf{QMA}\subseteq \mathsf{PSPACE}$, and I wonder how can it be proved. Thanks
omerna
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