The Quantum Information

The Quantum Information

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Stitched surface codes: two logical qubits from four patches and a GHZ corridor
Google Quantum AI concatenates four surface-code patches with the [[4,2,2]] code on a planar chip, decodes it with plain matching, and tests it on…
 • Doraking
The classical cost of simulating a qudit: finite expected bits, infinite expected alphabet
Castellano, Sekatski and Brunner give an exact one-way classical simulation of any qudit experiment with O(d log d) expected bits, and prove that for d…
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The Rényi Area-Law Conjecture Fails Below α = 1 in Two and Higher Dimensions
Tomotaka Kuwahara builds uniformly gapped lattice Hamiltonians whose ground states obey a von Neumann area law but a volume law for every Rényi entropy…
 • Doraking
Classical feedback cannot boost energy-limited bosonic dephasing channels
Arqand and Smith prove that, at any finite photon budget, the quantum and private capacities of bosonic dephasing channels are unchanged by two-way…
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Weak noise can make the quantum Markov length infinite
Newsom and Levin show that arbitrarily weak local noise can make a product state's Markov length jump from zero to infinity, challenging recent…
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Escaping Magic: Single-Shot CCZ Factories for Quantum LDPC Codes
Menon, Mehta et al. make CCZ magic transversally in 3D tricycle codes and teleport it into single-shot 4D quadcycle codes, reporting 10–40× lower…
 • Doraking
Fully addressable lattice surgery has a quadratic price
A short counting argument shows that sparse surgery ancillas able to measure any logical subset need about k² qubits.
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The Rains Bound Is Not the PPT Distillation Rate
Ludovico Lami certifies that a two-qutrit Werner state distils at most 0.62107 ebits per copy under PPT operations, below the regularised Rains bound of…
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A Concrete Counterexample to Tsirelson’s Problem, Checked in Lean
Gao, Yu and Zhi write down a 1.4-million-equation parity game that commuting-operator players win perfectly, while finite-dimensional quantum strategies…
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Black-hole radiation decoding is exponentially hard in the Haar random oracle model
Recovering one qubit from the radiation needs queries proportional to the remaining black hole's dimension, a tight unconditional bound that also yields…
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Universal logic from depth-one layers on a single error-correcting code
Dua, Holmes, Gullans and Albert build 110 qubit CSS codes whose universal gate sets need only few-qubit depth-one layers and error correction…
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Hamiltonian simulation at square-root sparsity cost, without the hidden overhead
Berry, Rawat, Simon and Low give sparse-access algorithms for simulation, linear ODEs and linear systems whose cost scales with √s, with nearly matching…
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