Why do we only need to correct for diagonal Pauli errors (X, Z)?
Why do we only need to account for Pauli X and Z errors for full QEC?The basis of quantum error correction is that we only need to correct for X and Z errors. We can choose Paulis as a basis set for...
View ArticleIs Extropic's "thermodynamic computing" just a classical stochastic computer...
I was looking at this new company Extropic and their claims (Video, Paper).They claim they are using thermodynamics to keep a bit in a "superposition" of 0 and 1, but then explicitly state it is not...
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Semi-Auto Magic State
I'm currently reading this paper. The figure shown below performs bit-wise addition and then uncomputes the result. Specifically, it computes $s_{k} = ((a_{k-1} \oplus s_{k-1}) \cdot (b_{k-1} \oplus...
View ArticleCan we know if two subsystems are entangled by only looking at one of them?
Today I bring a question similar to other posted before(i.e. How to know if any two arbitrary qubits are entangled?, How do I show that a two-qubit state is an entangled state?) but not exactly...
View ArticleDrop‑in replacement for Monte Carlo using Quantum Amplitude Estimation...
I’m an independent enthusiast exploring quantum algorithms. I want to share a personal idea/hypothesis and get honest feedback. I’m not claiming I’ve found “the truth”— I’m trying to understand...
View ArticleMeasurement-induced dephasing rate: factor of 2 discrepancy in two published...
I am studying measurement-induced dephasing in the dispersive regime of circuit QED.In the paper Yan et al., Nat. Commun. 7, 12964 (2016), equation (5), they use the expression$$\Gamma_\phi = \bar{n}...
View ArticleCan Schmidt decomposition geometry predict quantum computational advantage?
The ProblemPredicting which quantum systems will achieve computational advantage remains unsolved. Traditional metrics (gate fidelity, coherence times, quantum volume) achieve only 57-74%...
View Articlestim: understanding DEM probability calculations
I'm trying to understand how the probabilities in a stim DEM are calculated.I tried three simple cases; I understand the first, but can't seem to go beyond that :case 1: I understand the probabilities...
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What is AIRouting doing step by step?
I am trying to understand how AIRouting tool from qiskit is optimal for routing. Therefore I am trying to understand its choice of swap/ie the sequence of action applied. I feed a random cnot gates...
View ArticleConverting qubit eigenstate to pyscf eigenstate
I use PySCF for molecular chemistry calculations and want to convert the resulting PySCF wavefunction representation in terms of CIstrings to a representation of a qubit state with Jordan-Wigner...
View ArticleIs there a way to know the propagated errors at a certain place of a circuit...
What I want to realize in Stim is:Given a circuit, errors are sampled. Then, at a certain place of a circuit (e.g., qubit 6 after a certain CNOT gate), I want to know the errors there if we propagate...
View ArticleHelp debugging flat dissociation curve from IBM Quantum Runtime Batch
I've been working on a VQE implementation to calculate the dissociation curve of the H₂ molecule using Qiskit. The simulated curve (using Aer) looks great and behaves as expected. However, when I...
View ArticleAsymptotic scaling of surface codes, why p and not 2p/3?
In Fowler's paper, "Surface codes: Towards practical large-scale quantum computation" (link), a rudimentary probabilistic model for logical errors is described. My only issue with this is the...
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Stabilizer flow details when using detslice figures
I only have a rough idea that this is a back propagations of the pauli flow. But some details really confuse me.What's the difference between the filled and hollow circles. For example, tick 96 we a...
View ArticleMethods for generating Random Tensor Network and trace diagrams
I’m looking for effective ways to draw Random Tensor Networks and trace diagrams that show tensor contractions and Haar averages clearly. The goal is to generate clean, editable visuals where tensors...
View ArticleConfirm $f \otimes g$ is a linear map
In the textbook, "Dancing with Qubits," it states:"Let $V, W, X,$ and $Y$ be finite dimensional vector spaces over $\mathbb{F}$. If $f: V \rightarrow X$ and $g: W \rightarrow Y$ are linear maps, then...
View ArticleIs operator entanglement entropy related to a Choi state?
$\newcommand{\kket}[1]{|#1\rangle\!\rangle}\newcommand{\bbra}[1]{\langle\!\langle #1|}\newcommand{\hilbert}{\mathcal{H}}\newcommand{\ket}[1]{|#1\rangle}$I'm interested in an intrinsic notation for...
View ArticleIn Google Stim, is there a separate algorithm for handling measurement errors...
Based on the paper “Sparse Blossom: Correcting a Million Errors per Core Second with Minimum-Weight Matching,” my understanding is that the MWPM decoder performs minimum-weight matching between the...
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Minimal ancilla-free CCCNOT (C³X) decomposition using controlled-S conjugation
While experimenting in Quirk, I found a very compact and fully functional decomposition of the three-controlled NOT gate (also known as CCCNOT or C³X).This construction requires no ancilla qubits and...
View ArticleUnderstanding theorem 6 of postBQP=PP paper
In this paper, $\mathsf{BQP}_p$ is defined to be similar to $\mathsf{BQP}$ in all aspects except that the Born's measurement rule is changed. For a normalised state$$|{\psi}\rangle =\sum_x \alpha_x...
View ArticleHow to show used qubits in a transpiled circuit in Qiskit?
If a QuantumCircuit is created in Qiskit and then compiled using transpile the returned circuit has num_qubits with the total qubits from the backend, as opposed as only the qubits used in the...
View ArticleWhat is the biggest pain point for quantum developers?
I'm working on building an AI platform to streamline/automate the workflow for quantum developers. I was curious to learn from those who are actively involved in the field (building circuits, writing...
View ArticleDefinition of lg in IBM quantum learning resources
In its discussion of Shor's algorithm IBM's quantum learning platform uses the definition$$n = \lg(N-1) = \lfloor{\log(N-1)}\rfloor+1$$to describe the number of bits needed to encode the value...
View ArticleWhy have my Qiskit VQE results changed, even though I haven’t changed anything?
I am computing the 1-RDM of the H₂ molecule (STO-3G, 0.735 Å) using VQE in Qiskit + Qiskit Nature. A few months ago, when I ran the exact same code on the same laptop, the spin-summed 1-RDM always had...
View ArticleUsing restarts to prove QMA in PP
I am going through Ryan O'Donnell's quantum computing class homeworks, and on problem 6 of this assignment you are asked to prove $QMA$ in $PP$ using the fact that $RestartingPP = PP$, where...
View ArticleDo identical reduced system trajectories ρₛ(t) guarantee identical...
In a small open quantum system with a system qubit $S$ and an environment split into an accessible fragment $F$ and an inaccessible remainder $R$, consider the following situation.Two global evolutions...
View ArticleDrawbacks of writing a compiler in Smalltalk
Sorry for the vague title, what I’m really asking is: when writing a compiler for a quantum DSL, many languages have chosen an imperative or functional host language. Few, if any, have chosen a purely...
View Articlestim : confusion about the use of observables
The role of adding observables is not clear to me. Here are some points of confusion :(1)From the circuit I generate a detector error model using dem from which I generate twomatrices (pcm and lcm) as...
View ArticleQFT of two superposed states
Given a N qubits quantum register, in state $1/\sqrt{2}(|a\rangle+|b\rangle)$, my goal is to find sum of a and b (a+b) or subtraction (b-a).Taking classical example, let [7, 13], the discret FT will...
View ArticleHow to construct a block-diagonal embedded Fourier matrix?
We know the quantum circuit representation of Fourier operator. Now, I want the quantum circuit for the following unitary matrix using single and two qubit gates:$$U =\begin{pmatrix}F_3 & 0 \\0...
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