# Unanswered Questions

98 questions with no upvoted or accepted answers
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### Explicit Lieb-Robinson Velocity Bounds

Lieb-Robinson bounds describe how effects are propagated through a system due to a local Hamiltonian. They are often described in the form $$\left|[A,B(t)]\right|\leq Ce^{vt-l},$$ where $A$ and $B$ ...
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I'm interested in the conversion between different sets of universal gates. For example, it is known that each of the following sets is universal for quantum computation: $\{T,H,\textrm{cNOT}\}$ $\{H,... 0answers 210 views ### Quantum simulation of environment-assisted quantum walks in photosynthetic energy transfer This question is related to Can the theory of quantum computation assist in the miniaturization of transistors? and Is Quantum Biocomputing ahead of us? About 10 years ago, several papers discussed ... 0answers 125 views ### Quantum walk with binary tree I’m trying to grok quantum walks, and would like to create an example that walks a perfect binary tree to find the one and only marked leaf node. Is this possible? If so, suppose the depth of the tree ... 0answers 71 views ### Quantum machine learning after Ewin Tang Recently, a series of research papers have been released (this, this and this, also this) that provide classical algorithms with the same runtime as quantum machine learning algorithms for the same ... 0answers 128 views ### Quantum Walk: Why the need of adding “tail” nodes to the root? As stated in the question, I have found in several papers (e.g. 1, 2) that in order to perform a quantum walk on a given tree it is necessary to add some nodes to the root$r$, say$r^{'}$and$r^{"}$.... 0answers 99 views ### Devising “structured initial guesses” for random parametrized quantum circuits to avoid getting stuck in a flat plateau The recent McClean et al. paper Barren plateaus in quantum neural network training landscapes shows that for a wide class of reasonable parameterized quantum circuits, the probability that the ... 0answers 30 views ### Reference that explains how to read 3d topological diagrams for surface code computations I like making diagrams to describe computations. For the surface code, an excellent tool is 3d topological diagrams. Here is an example diagram (made by me in SketchUp): The basic idea is that white ... 0answers 90 views ### Estimate/determine Bures separability probabilities making use of corresponding Hilbert-Schmidt probabilities For two-qubit states, represented by a$4\times 4$density matrix, the generic state is described by 15 real parameters. For ease of calculation, it can help to consider restricted families of states, ... 0answers 52 views ### Active improving of nanodiamond surfaces for NV centers? This question is related (and complementary) to "Passive improving of nanodiamond surfaces for NV centers?". Nitrogen-Vacancy centers (NVs) have astonishing quantum properties, which make them ... 0answers 129 views ### Entanglement transfer of spin-entangled triplet-pair states between flying qubits and stationary qubits The context: We are in the solid state. After a photon absortion by a system with a singlet ground state, the system undergoes the spin-conserving fission of one spin singlet exciton into two spin ... 0answers 93 views ### Does the Curry-Howard correspondence have a quantum-specific type system? In Wikipedia we can read that the Curry–Howard correspondence is a correspondence between formal proof calculi and type systems for models of computation. In particular, it splits into two ... 0answers 128 views ### What is the difference between quantum control and quantum optimal control? In the context of quantum control theory, it is common to see references to both quantum control and quantum optimal control (e.g. 0910.2350 or the guide on qutip quantrum control functions). ... 0answers 66 views ### How is Bell’s Inequality converted to the CHSH inequality? Bell’s inequality is $$S = P(a,b)-P(a,d)+P(c,b)+P(c,d) \leq 2,$$ which is calculated as $$S = ab – ad + cb + cd \leq 2.$$ The CHSH version is:$$E = \frac{N_{11} + N_{00} - N_{10} -N_{01}} {N_{11} + ... 0answers 70 views ### Building Intuition for Relative Von Neumann Entropy This is how I think about classical relative entropy: There is a variable that has distribution P, that is outcome$i$has probability$p_i\$ of occuring, but someone mistakes it to be of a ...

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