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Failed attempt to escape from the quantum pigeon conundrum

A recent criticism by Kunstatter et al. [Phys. Lett. A 384, 126686 (2020)] of a quantum setup violating the pigeon counting principle [Aharonov et al. PNAS 113, 532 (2016)] is refuted. The quantum nature of the violation of the pigeonhole principle …

Always-On Quantum Error Tracking with Continuous Parity Measurements

We investigate quantum error correction using continuous parity measurements to correct bit-flip errors with the three-qubit code. Continuous monitoring of errors brings the benefit of a continuous stream of information, which facilitates passive …

Acoustic versus electromagnetic field theory: scalar, vector, spinor representations and the emergence of acoustic spin

We construct a novel Lagrangian representation of acoustic field theory that describes the local vector properties of longitudinal (curl-free) acoustic fields. In particular, this approach accounts for the recently-discovered nonzero spin angular …

Footprints of quantum pigeons

We show that in the mathematical framework of the quantum theory the classical pigeonhole principle can be violated more directly than previously suggested, i.e., in a setting closer to the traditional statement of the principle. We describe how the …

Optimizing measurement strengths for qubit quasiprobabilities behind out-of-time-ordered correlators

Out-of-time-ordered correlators (OTOCs) have been proposed as a tool to witness quantum information scrambling in many-body system dynamics. These correlators can be understood as averages over nonclassical multi-time quasi-probability distributions …

Benchmarks of nonclassicality for qubit arrays

We present a set of practical benchmarks for N-qubit arrays that economically test the fidelity of achieving multi-qubit nonclassicality. The benchmarks are measurable correlators similar to 2-qubit Bell correlators, and are derived from a particular …

Out-of-Time-Ordered-Correlator Quasiprobabilities Robustly Witness Scrambling

Out-of-time-ordered correlators (OTOCs) have received considerable recent attention as qualitative witnesses of information scrambling in many-body quantum systems. Theoretical discussions of OTOCs typically focus on closed systems, raising the …

Weak values from strong interactions in neutron interferometry

In their original framework weak values must be measured by weak measurements that are minimally disturbing, meaning that the coupling between an investigated quantum system and a measurement device has no influence on the evolution of the system. …

Strengthening weak measurements of qubit out-of-time-order correlators

For systems of controllable qubits, we provide a method for experimentally obtaining a useful class of multitime correlators using sequential generalized measurements of arbitrary strength. Specifically, if a correlator can be expressed as an average …

Quasiprobability behind the out-of-time-ordered correlator

Two topics, evolving rapidly in separate fields, were combined recently: the out-of-time-ordered correlator (OTOC) signals quantum-information scrambling in many-body systems. The Kirkwood-Dirac (KD) quasiprobability represents operators in quantum …