Quantum Information
Decoherence as the Origin of Classical-Quantum Dynamics
This paper demonstrates that classical-quantum dynamics, often used to describe gravity where quantum matter interacts with a classical mediator, can emerge as an effective description from fully quantum systems undergoing decoherence. This finding offers a bridge between fully quantum and classical…
Superlinear Amplitude Amplification in Quantum Search
This paper introduces a novel quantum search algorithm that achieves superlinear (specifically, quadratic) amplitude amplification, contrasting with the linear amplification of standard algorithms. While this offers a theoretical advantage in the rate of success probability increase, the practical a…
Adaptive Protocols Boost Entanglement Purification Yields Across Fidelities
Leung and Shor introduce a family of entanglement purification protocols generalizing four prior methods (recurrence, modified recurrence, Maneva-Smolin, Leung-Shor) using two-way classical communication. These protocols achieve higher yields than predecessors over a broad range of initial fidelitie…
Concatenated Cat Codes Beat Quantum Hashing Bound for Highly Noisy Depolarizing Channels
DiVincenzo, Shor, and Smolin introduce additive quantum error-correcting codes using cat code concatenation within random hashing that achieve positive capacity for depolarizing channels at fidelity f > 0.80944, surpassing the quantum random coding threshold of f > 0.81071. A block size-5 cat code p…
Oblivious Remote State Preparation Matches Teleportation's Communication Cost
For pure states whose projectors form a basis, oblivious remote state preparation protocols—using only forward communication, entanglement, deterministic exact preparation without leaking extra information—can be modified to require just one copy of the state from the sender. This modification prese…
Unextendible Product Bases Generate Bound Entangled States with Purely Multipartite Entanglement
Unextendible product bases (UPBs) are incomplete orthogonal product bases in multipartite quantum systems whose complementary subspace contains no product states. The uniform mixed state over this complementary subspace is a bound entangled state, undetectable by distillation. A specific 2x2x2 tripa…
Nonadditivity of Bipartite Distillable Entanglement Proven via Bound Entangled Werner States Conjecture
Assuming a conjecture that certain Werner states are undistillable, Shor, Smolin, and Terhal demonstrate that the tensor product of two bipartite states—each with zero distillable entanglement—possesses nonzero distillable entanglement. Their example combines a bound entangled state from an unextend…
Quantum Walks Reveal Exponential Speedups for Hierarchical Graphs
This work explores quantum walk algorithms on a class of hierarchical graphs, demonstrating potential for super-polynomial or even exponential speedups over classical algorithms. The key insight lies in how quantum walks leverage the graph's symmetry, effectively navigating a lower-dimensional subsp…
Kavli Symposium to Feature "The Road to Quantum Advantage" Discussion
John Preskill will present on "The Road to Quantum Advantage" at the Kavli Symposium during the APS Global Physics Summit. This topic is closely related to a previous presentation by Jens Eisert titled "Mind the gaps," which together form the complete title of their collaborative article, "Mind the …
Limited Entanglement Assistance Induces Superadditivity in Additive Classical Quantum Channels
Researchers construct a quantum channel with additive unassisted classical capacity, yet its classical capacity with limited entanglement assistance exhibits superadditivity. This occurs because full entanglement assistance yields an additive capacity, but restricting entanglement across channel use…
First Bounds on CHSH_q Game Link Quantum Protocols to Szemerédi-Trotter Incidence Geometry
The paper establishes the first asymptotic and explicit bounds on both classical and entangled values for the CHSH_q game, a finite-field generalization of the CHSH inequality where players output elements in F_q to satisfy a + b = xy. It reveals a novel connection between this quantum game and geom…