quant-ph

Random Access Codes: Explicit Constructions, Optimality, and Classical-Quantum Gaps

This paper presents a constructive framework for designing optimal classical random access codes (RACs) under both average and worst-case criteria, deriving explicit solutions for general parameters and closed-form optimal encoders for the $(L, L-1)$ case that also achieve conjectured bounds for their quantum counterparts, while revealing a potential significant performance gap between classical and quantum codes in the worst-case nonasymptotic regime.

Third Quantization for Order Parameter (I): BCS-BEC crossover with macroscopically coherent state

This paper proposes that "third quantization," where the order parameter's phase and particle number obey macroscopic commutation relations emerging naturally from second quantization, provides a unified framework to interpret both BEC and BCS states as macroscopic bosonic coherent states, thereby redefining the BCS-BEC crossover as a process where inter-segment tunneling locks phases to establish global coherence.

Observation of quantum multi-Mpemba effect in a trapped-ion system

This paper experimentally observes a novel quantum multi-Mpemba effect in a trapped-ion system where initial states with larger overlaps with the slowest decay mode relax faster due to dominant fastest decay modes, leading to multiple trajectory crossings that challenge the conventional long-time limit explanation.

Sufficient support size of measurements for quantum estimation

This paper establishes that for both locally unbiased and Bayesian quantum estimation, optimal measurements can be restricted to rank-one POVMs with a finite number of outcomes bounded by a specific function of the Hilbert space dimension and parameter count, thereby significantly reducing the search space for optimal estimators.

pygridsynth: A fast numerical tool for ancilla-free Clifford+T synthesis

Scalable surface ion trap design for magnetic quantum sensing and gradiometry

This study presents a novel, scalable surface Paul trap design featuring multiple trapping regions that enables trapped ions to function as ultra-sensitive magnetic sensors capable of detecting fields from DC to hundreds of MHz with sub-millimeter spatial resolution for precise gradiometry.

Ghost Degrees of Freedom Without Quantum Runaway: Exact Moment Bounds from an Operator Conservation Law

This paper proves that a harmonic oscillator coupled to a ghost degree of freedom remains quantum-stable with bounded second moments for all time, provided the interaction is bounded and vanishes at large separations, thereby demonstrating that ghost-induced instabilities are not inevitable consequences of wrong-sign kinetic terms but depend critically on the interaction structure.

Vertical Shuttling Protocols for Trapped Ions in Multi-Rail, Multi-Zone Surface Ion Trap Architectures

This paper presents optimized vertical ion-shuttling protocols for multi-rail surface ion traps that minimize motional energy gain, demonstrating that adiabatic transport within 0.5 ms can restrict excitation to fewer than eight quanta, thereby meeting the fidelity requirements for high-performance quantum sensing and information processing.

Time-Uniform Error Bound for Temporal Coarse Graining in Markovian Open Quantum Systems

This paper resolves the limitations of existing approximation methods for deriving GKSL generators from the Born-Markov master equation by establishing a unified, time-uniform error bound for the general class of temporal coarse graining techniques, thereby guaranteeing their accuracy over arbitrarily long timescales.

The Geometry Underlying the Quantum Harmonic Oscillator

This paper demonstrates that the eigenfunctions of the two-dimensional quantum harmonic oscillator correspond to specific geometric structures in a reduced phase space, revealing a deep correspondence between classical and quantum states that also extends to the Kepler/hydrogen atom problem.