Quantum Journal

The noise cost of reservoir locality in broadband quantum amplifier chains

Directional quantum amplifiers enable weak-signal readout while protecting the source, but reservoir noise limits sensitivity. Finite-band suppression must reconcile frequency-dependent responses with fixed local couplings and finite rates. We construct adjacent-site loss channels attaining the known single-frequency minimum under local compatibility conditions, as an uncapped benchmark. For specified uniform and dimerized chains, we compare fix...

Mechanical trisqueezing in circuit quantum acoustodynamics with SNAIL devices

Continuous-variable quantum information processing with mechanical oscillators requires a uni- versal gate set, including a genuine non-Gaussian evolution. While circuit quantum acoustodynamics (cQAD) experiments have realized bilinear and quartic (four-wave mixing) operations by coupling mechanical modes to transmon qubits, the intrinsic Kerr nonlinearity of these devices precludes access to odd-order effective Hamiltonians such as trisqueezing...

Quantum Partial Information Decompositions, an Operational Order on Ensembles, and Direct Quantifications of Objective Information

The partial information decomposition (PID) framework is an extension of classical information theory that enables a systematic analysis of the structure of information in multipartite systems. We advance a simple extension of this framework enabling the construction of multipartite quantum PIDs (QPIDs); generalizing recent, exclusively bipartite, extensions. We construct two QPIDs of the Holevo quantity. First a naive QPID based on the classica...