Quantum Computing Stack Exchange
Quantum Computing Stack Exchange is a specialized, community‑driven Q&A outlet dedicated to the theory, practice, and implementation of quantum computing.
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Modeling CHSH Degradation (S = 2.404) on Rigetti Cepheus-1-108Q: Environmental Thermal Noise vs. Pure Quantum Decoherence (opens the original)
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I am analyzing experimental CHSH benchmark data obtained directly from runs on Rigetti Cepheus-1-108Q hardware via Open Quantum. The run yielded an empirical value of $S = 2.404$ (with single correlations $E_1 = +0.556$, $E_2 = -0.672$, $E_3 = +0.592$, $E_4 = +0.584$), clearly violating the classical bound ($S \le 2.0$) but falling short of the maximum Tsirelson bound ($2\sqr
Is entanglement a property of a state rather than of the spaces, and how should "irreducible to its parts" be stated precisely? (opens the original)
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I'm not a mathematician and I'm trying to make sure I understand this correctly. My understanding is: (1) Hilbert spaces with ⊗ form a symmetric monoidal category, and the product is non-cartesian; (2) entanglement is a property of a state in H_A ⊗ H_B, namely one not in the image of the map from pairs of states; (3) decoherence disperses correlations into the environment, so the pair alone looks mixed while the joint state stays pure. Is this right? And is there a standard way to say a construc
Question about the non-cloning theorem (opens the original)
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The standard proof to the non-cloning theorem shows that no sequence of unitary quantum gates/base states measurements could be used to duplicate the state of some unknown qubit while preserving its state. But may it be possible to clone a qubit with some physical mechanism other than quantum gates or measurement? The proof ignores the possibility of other physical ways to extract information from the quantum system. So may it be possible to clone the full quantum state of a qubit by other means
Has there been a recent breakthrough in experimental quantum computing that makes commercial applications possible within 10 years? (opens the original)
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I'm struggling to reconcile the current experimental status of quantum error correction with the confidence expressed in recent quantum computing roadmaps. My understanding is that we are still establishing the basic ingredients of scalable logical computation. For example, Google’s Quantum error correction below the surface code threshold demonstrates improving a logical memory by increasing code distance. This is a significant result, but there is a substantial gap between the demonstration an
Model of logical errors in circuit from logical errors of individual operations (opens the original)
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Can I infer logical error rates of circuits from logical error rates of single operations? For this, I want to distinguish between two scenarios of different levels of simplification. Scenario 1: Let's say I have a certain QEC code and decoder. I experimentally implemented the state preparation of the logical 0- and +-states and determined the probability of success p(init,0). I also implemented the state preparation + logical operation for a universal set of logical operations, each with 0-stat
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